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prof. Ing. Pavel Ripka, CSc.

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A linear variable differential transducer for position measurement with an external armature

  • DOI: 10.1016/j.measurement.2024.115978
  • Link: https://doi.org/10.1016/j.measurement.2024.115978
  • Department: Department of Measurement
  • Annotation:
    This paper presents a novel structure for linear position sensors with external armature. The coils are designed to have a nonoverlapping structure to increase the coils’ design optimization flexibility. The 3D finite element method is utilized for design optimization to extend the linearity range of the position sensor. The excitation and pickup coils are segmented to facilitate and improve the winding process. The number of turns in each pickup coil is optimized using the 3D finite element method to minimize the nonlinearity error and enhance the linearity range of the position sensor. The simulation results are compared with experiments to validate the optimization process of the position sensor.

An axial flux eddy current sensor with perpendicular coils for speed measurement

  • DOI: 10.1016/j.sna.2023.114917
  • Link: https://doi.org/10.1016/j.sna.2023.114917
  • Department: Department of Measurement
  • Annotation:
    This paper presents an axial flux eddy current sensor with a compact and simple structure for measuring the rotating speed of iron shafts. The sensor structure is optimized for high sensitivity with a novel configuration of the coils positioned perpendicularly to each other. The sensor comprises two D-shaped excitation coils and two D-shaped pick-up coils in a double-layer structure. A disc-shaped magnetic shield or core shields the coils. Two iron shafts with different material properties are considered. A new cup-shaped configuration of nonmagnetic copper and aluminum caps mounted on iron shafts improves sensitivity and suppresses susceptibility to shaft material properties and airgap variation. 2D and 3D finite element methods are utilized for the performance analysis of the sensor. The measurements are performed at speeds up to ± 3000 rpm and different excitation frequencies from 400 Hz to 4 kHz. The eddy current speed sensor has excellent linearity characteristics with a nonlinearity error of 0.15%. The geometry of the coils is further optimized and improved for maximum sensitivity and compactness. The fault-tolerant capability of the sensor is also evaluated.

C-Shape Busbar With Frequency Invariant Points for Wideband Current Measurement

  • Authors: George, N., prof. Ing. Pavel Ripka, CSc., Grim, V.
  • Publication: IEEE Transactions on Industrial Electronics. 2024, 71(6), 6446-6456. ISSN 0278-0046.
  • Year: 2024
  • DOI: 10.1109/TIE.2023.3299010
  • Link: https://doi.org/10.1109/TIE.2023.3299010
  • Department: Department of Measurement
  • Annotation:
    A yokeless busbar current transducer with frequency-invariant points is presented for the first time in this article. Existing rectangular busbar current transducers suffer from the frequency dependency issue due to the eddy currents in the massive busbar. The proposed transducer has a novel C-shaped structure for the sensing area of the busbar. It is observed for the first time that this structure provides sets of frequency-invariant points on both sides of the C- shaped busbar. In the proposed scheme, two integrated fluxgate sensors in differential form are used to measure the magnetic flux densities at those invariant points. A finite-element method (FEM)-based three-dimensional analysis performed using the Ansys Maxwell eddy current solver provided the exact locations of the frequency-invariant points. A prototype was made, and functionality tests of the C-shape busbar transducer have been carried out in the laboratory using DRV-425 integrated fluxgate sensors from Texas Instruments. In the experiment, fluxgate sensors placed at frequency-invariant points measured the flux densities at multiple frequencies varying from 50 to 4000 Hz. The results obtained from the tests showed that the error due to frequency dependency has been reduced from 14% to -0.85% using the proposed C-shape busbar.

CMOS-based Micro-fluxgate with Racetrack Core and Solenoid Coils

  • DOI: 10.1016/j.sna.2024.115886
  • Link: https://doi.org/10.1016/j.sna.2024.115886
  • Department: Department of Measurement
  • Annotation:
    This work introduces an integrated fluxgate sensor fabricated using CMOS chip technology. The sensor uses a “racetrack” shape of the core. The material used for the core is VITROVAC 6025F, and the shape was laser-cut from 25 um thick foil. The coils are solenoids fabricated using metal layers of the chip and bonding wires. Sensing and excitation coils have 60 and 40 turns respectively. TSMC D35 technology was used for fabrication. The size of the core is 8 mm x 1.75 mm. Dimensions of the chip are 8 mm x 2.7 mm (21.6 mm2). The sensor was tested in open-loop operation using a sinewave excitation. Sensitivity increases with frequency up to 1.5 MHz, reaching 5000 V/T. This is a significantly higher value than what can be achieved using a flat pick-up coil (around 10 V/T). Fully saturating the core requires a 110 mA excitation current, leading to 300 mW power dissipation in the coil. The Core loss is 100 mW at 1 MHz excitation. The Noise at 1 Hz may be as low as 2nT/sqrt(Hz) depending on excitation signal parameters. The typical offset is below 1 uT.

Flat Magnetic X-Y Alignment sensor

  • DOI: 10.1109/LSENS.2024.3414375
  • Link: https://doi.org/10.1109/LSENS.2024.3414375
  • Department: Department of Measurement
  • Annotation:
    We propose a novel flat 2-D inductive position sensor based on stationary coils and moving armature. The geometry was optimized by FEM simulations, the predicted parameters of the final design fit well to the measured values. The position sensitivity of 100 mV/cm for 500 kHz/140 mA excitation achieved with laminated nanocrystalline armature was 5-times higher than with FeSi material. We have also shown by measurements that the influence of the liftoff variations can be effectively suppressed by ratiometric method. The total sensor thickness is only 2.5 mm. The developed sensor is suitable for position alignment in industrial applications.The present design has linear range of ±10 mm for directions up to ±30° from X and Y axes. The minimum linear range of ±5 mm is in the diagonal (45°) direction.

Material Properties Effects of Hollow Shafts on the Performance of Rotational Eddy Current Speed Sensor

  • DOI: 10.1109/IETC60657.2024.10598846
  • Link: https://doi.org/10.1109/IETC60657.2024.10598846
  • Department: Department of Measurement
  • Annotation:
    The evaluation of the material properties of hollow shafts and their effect on the performance of rotational eddy current speed sensors is presented in this paper. The eddy current sensor has two saddle excitation and pickup coils located perpendicularly. The conductivity and relative magnetic permeability of rotating shafts affect the sensor sensitivity. A 3D analytical method is used to analyze the sensor performance and for parametric calculations. The skin effect and 3D distribution of induced eddy current in the rotating hollow shaft are considered in the 3D analytical method. A measurement for the eddy current sensor is conducted at various speeds. A hollow iron shaft and a hollow aluminum shaft are considered in the modeling and the measurement to evaluate the material effects on the sensor performance. Finally, the effects of the sensor coils dimensions and the gap between coils and the rotating shaft are analyzed to further evaluate the vulnerability of the sensor against shaft material properties.

Three-Dimensional Analytical Modeling of Rotational Eddy Current Speed Sensor

  • DOI: 10.1109/JSEN.2024.3366348
  • Link: https://doi.org/10.1109/JSEN.2024.3366348
  • Department: Department of Measurement
  • Annotation:
    —The main goal of this paper is to present a novel 3D analytical method for precise and fast modeling of rotational eddy current speed sensors with cylindrical structures. An equivalent linearized model is developed using a multi-slice structure. The cylindrical structure of rotational eddy current sensors is modeled using the multi-slice linearized structure. The 3D distribution of induced eddy current in the rotating conductive rods is considered in the analytical modeling. The method of separation of variables using Fourier series is utilized for the analytical analysis of rotational eddy current speed sensors. The new calculation method is tested on the eddy current speed sensor with perpendicular coils and different rotating rods. The analytical results are compared with the calculations of 3D time harmonic and time stepping finite element methods. The measurements on the sensor prototype verified the calculations. When compared to the 3D Time Harmonic FEM, the 3D analytical method is 12-times faster.

A Comparative Study of Eddy Current Speed Sensors for Rotating Speed Measurement of Iron Shafts

  • DOI: 10.1109/ITECAsia-Pacific59272.2023.10372191
  • Link: https://doi.org/10.1109/ITECAsia-Pacific59272.2023.10372191
  • Department: Department of Measurement
  • Annotation:
    A comparative study of two rotational eddy current speed sensors is presented for sensitivity and susceptibility assessment against shaft material properties. The sensors have different coil configurations, with one excitation coil and two antiserially connected pickup coils. The performance of two sensors is compared and evaluated with two iron shafts with different materials shielded by an aluminum shell. The theoretical study of two sensors is performed using the 2D analytical method and the 3D finite element method. The eddy current sensors are measured for a speed range of ±3000 rpm and 500 Hz. The evaluation of eddy current sensors performance for higher speeds is also presented.

A Novel Structure of an Eddy Current Sensor for Speed Measurement of Rotating Shafts

  • DOI: 10.1109/TEC.2022.3195921
  • Link: https://doi.org/10.1109/TEC.2022.3195921
  • Department: Department of Measurement
  • Annotation:
    This paper presents a novel structure of an eddy current sensor for the measurement of rotational speed. The sensor has a perpendicular configuration of the excitation coil and the pick-up coil. Its maximum nonlinearity error is 0.15%. The excitation coils and the pick-up coils are divided into two identical parts with a coil span of 180 degrees. Various solid iron cylinders with different electrical and magnetic characteristics, one solid aluminum cylinder and one solid copper cylinder, were used as the rotating shafts. A novel 2D analytical method in cylindrical coordinates has been developed for fast parametric analysis of this sensor. 2D and 3D time-stepping finite-element methods that take into consideration the shaft motion are used for a performance analysis of the eddy current sensor. The measurements of the speed sensor are performed at various frequencies and speeds and are compared with the calculations for detailed analysis. The effects of the rotating shaft materials are evaluated both in the measurements and in the calculations.

An eddy current speed sensor with a novel configuration of longitudinal and transversal coils

  • DOI: 10.1016/j.sna.2023.114201
  • Link: https://doi.org/10.1016/j.sna.2023.114201
  • Department: Department of Measurement
  • Annotation:
    This paper presents a novel eddy current speed sensor for linear speed measurement of moving flat iron parts. The main goal of the paper is to present an efficient eddy current speed sensor with high sensitivity and faulttolerant capability using novel pickup coil configurations. It has one rectangular excitation coil and two sets of pickup coils for voltage measurement. The first set of pickup coils consists of eleven serially connected coils, which are perpendicularly mounted and arranged on top of the excitation coil in a transversal direction. The second set of pickup coils comprises two antiserially connected pickup coils that are in the same longitudinal direction as the excitation coil. The measurements of the sensor are performed up to +/- 17.9 m/s (64 km/h) at excitation frequencies of 1000 Hz and 4000 Hz. Analytical calculations are used for the parametric and performance analyses of the eddy current speed sensor. The calculation results are compared with the measurements. The sensor's nonlinearity error is 1%. The performance of the sensor is also assessed for a higher speed range, up to 600 km/h.

Enhancing Performance of Fluxgate Sensors Using Annealed Nanocrystalline Core

  • Authors: Hrakova, D., prof. Ing. Pavel Ripka, CSc., Kmječ, T.
  • Publication: IEEE Transactions on Magnetics. 2023, 2023(59), ISSN 0018-9464.
  • Year: 2023
  • DOI: 10.1109/TMAG.2023.3296205
  • Link: https://doi.org/10.1109/TMAG.2023.3296205
  • Department: Department of Measurement
  • Annotation:
    The magnetic core is one of the most important parts of a fluxgate sensor. This article presents a study of fluxgate sensors with a core based on nanocrystalline Fe73.5Cu1Nb3Si13.5B9 wire and compares their performance to that of sensors based on amorphous wire with a chemical composition of (Co94Fe6)75Si15B10. Both wires have a diameter of 0.12 mm and were manufactured by the Institute of Technical Physics, Iasi, Romania. The nanocrystalline as-cast (AC) FINEMET wire was annealed by the flash current method to heat up the wire to the temperature of crystallization from −590 °C to 605 °C in a few seconds, using Joule heat from 495 to 505 mA of applied current. The annealing process was carried out in a tube filled with Ar gas to prevent the surface oxidation of the annealed wire. Stress tension of 8–170 MPa was applied during the annealing. The annealing process was carried out under different conditions such as annealing duration, applied current, and applied stress to find the optimum parameters for the performance of the fluxgate sensor. The material and sensor characterization was complemented by the Mössbauer spectroscopy. The annealing results in changes in the microstructure of the AC amorphous alloy, and annealing parameters influence the amorphous-to-nanocrystalline ratio and the size of nanocrystalline grains. These controllable parameters are the keys to the improvements of the material and using the advantages of both states. The characteristics of the fluxgate sensor with the FINEMET core annealed under certain conditions—tensile stress 12 MPa, annealing current 497 mA, and duration 15 s—are comparable to the traditionally-used Cobalt (Co)-based amorphous core in terms of sensitivity and magnetic noise, around 0.8–0.9 V/mT and 20–26 pT/ $\surd $ Hz, respectively, at 8 kHz. The advantage of nanocrystalline material is that it can work at elevated temperatures as its Curie point is higher than the Curie point and crystallization temperature of Co-based amorphous alloys.

Processing of Nanocrystalline Wire for a Fluxgate Sensor Application

  • Authors: Hrakova, D., prof. Ing. Pavel Ripka, CSc.,
  • Publication: MEASUREMENT 2023 14th International Conference on Measurement. Bratislava: Slovak Academy of Sciences, Institute of Measurement Science, 2023. p. 207-208. ISBN 978-80-972629-6-9.
  • Year: 2023
  • DOI: 10.23919/MEASUREMENT59122.2023.10164535
  • Link: https://doi.org/10.23919/MEASUREMENT59122.2023.10164535
  • Department: Department of Measurement
  • Annotation:
    This work is dedicated to the study of fluxgate sensors based on the Fe73.5Cu1Nb3Si13.5B9 nanocrystalline wire as a core and comparing them to the performance of amorphous wire with chemical composition (Co94Fe6)75Si15B10 [1]. We demonstrate that proper processing of nanocrystalline alloys can bring sensors with properties comparable to the traditionally used amorphous alloys, but with better stability at elevated temperatures.

Rectangular Busbar With Circular Sensing Part for Wideband Current Measurement

  • Authors: George, N., prof. Ing. Pavel Ripka, CSc.,
  • Publication: IEEE Transactions on Instrumentation and Measurement. 2023, 72 ISSN 0018-9456.
  • Year: 2023
  • DOI: 10.1109/TIM.2023.3289559
  • Link: https://doi.org/10.1109/TIM.2023.3289559
  • Department: Department of Measurement
  • Annotation:
    A simple, reliable, and novel busbar sensing configuration for frequency-independent current measurement is presented in this article. Yokeless current transducers using arrays of magnetic sensors around a rectangular busbar are linear and lightweight, but they suffer from large frequency dependence. Several circular-array-based current transducers have been described in the literature, but their frequency characteristics have never been studied in detail. We show that the magnetic field surrounding a long circular busbar is frequency-independent, regardless of the surface effect. This feature can be used to develop an accurate circular-array-based coreless Hall current transducer for a wide range of frequencies. We propose a novel busbar configuration that has a 200-mm-long circular section in the current-sensing part of the busbar, which is compatible with the standard 10 x 60 mm rectangular busbar. A circular magnetic field sensor array is mounted in the midplane, around the circular conductor, for the current measurement. A finite-element method (FEM)-based 3-D analysis of the proposed busbar is performed with the help of an eddy current solver in the Ansys Maxwell tool. In addition, a prototype of the proposed wideband busbar was developed in the laboratory and its functionality was tested. The results that have been obtained show that the frequency dependence is reduced from -8.5% (for a rectangular busbar) to -0.45% (for the novel transducer).

Rotating speed measurement using an optimized eddy current sensor

  • DOI: 10.1016/j.measurement.2023.113547
  • Link: https://doi.org/10.1016/j.measurement.2023.113547
  • Department: Department of Measurement
  • Annotation:
    This paper presents the rotating speed measurement of solid iron hollow shafts using the optimum design of a rotational eddy current sensor. The rotating speed measurements are performed using the optimized sensor up to ±3000 rpm to evaluate sensitivity enhancement and linearity performance. The sensor is optimized for a shorter axial length and higher sensitivity with a new configuration of the coils. An aluminum shell on a solid shaft is used, which helps to improve the sensitivity and the susceptibility of the sensor to the material properties of solid iron. A 2D analytical method and a 3D time stepping finite element method are considered for the theoretical analysis of the sensor and for an assessment of the effect of this optimization on the performance. The performance of the sensor was verified by measurements. The evaluation of the speed sensor for higher speeds up to ±30,000 rpm is performed using the 2D analytical method.

A Linear Eddy Current Speed Sensor for Speed Measurement of Conductive Objects

  • DOI: 10.1109/TIA.2022.3198625
  • Link: https://doi.org/10.1109/TIA.2022.3198625
  • Department: Department of Measurement
  • Annotation:
    This paper presents the novel structure of an eddy current sensor for linear speed measurements. The sensor has one excitation coil and two pairs of antiserially connected pick-up coils, which are located inside and outside the excitation coil. The design and modeling of the sensor are considered with an air core and with a magnetic yoke (core) to compare their performances in terms of sensitivity and nonlinearity error. The experiments and the analysis are performed at different excitation frequencies and speeds. A novel 3D analytical method is developed and utilized for parametric analysis and for the design of this sensor. The simulation results are compared with measurements up to 16.7 m/s (60 km/h). The achieved nonlinearity error is as low as 0.3%

A Simplified 2D Equivalent Model for Magnetic Wire Array

  • DOI: 10.1109/TMAG.2021.3085485
  • Link: https://doi.org/10.1109/TMAG.2021.3085485
  • Department: Department of Measurement
  • Annotation:
    Demagnetization factor and corresponding apparent permeability for multiwire arrays using the 3-D finite element method (FEM) are calculated in this article. The effect of distance between magnetic wires on the demagnetization factor and apparent magnetic permeability is studied for various values of relative magnetic permeability. The simulations are compared with experimental results on arrays up to 91 wires. A novel simplified equivalent 2-D model for wire arrays is presented in this article, as a fast method for calculations. The simplified axisymmetrical model consists of a set of hollow cylinders with equivalent volume. The results of the proposed simplified 2-D model fit very well the full 3-D FEM simulations and experimental results. Two different hexagonal and square arrangements for wires are considered both for the simulations and the measurements.

An Axial Airgap Eddy Current Speed Sensor

  • DOI: 10.1109/TIE.2021.3113001
  • Link: https://doi.org/10.1109/TIE.2021.3113001
  • Department: Department of Measurement
  • Annotation:
    This paper presents a novel configuration of the eddy current speed sensor to measure the rotating speed of iron rods and shafts up to 3000 rpm. The proposed eddy current speed sensor has an axial airgap structure with one excitation coil and two antiserially connected pick up coils. The speed sensor is mounted in the end shaft part region. Different solid iron materials for rotating shaft are considered in the measurements and calculations to evaluate solid iron material effect on the eddy current speed sensor performance. 2D and 3D finite element method is utilized for the performance analysis of the speed sensor. Also, a 2D analytical method is developed for parametric analysis. A copper rod is also used to compare the speed sensor with the rotating iron shaft and copper shaft. Finally, two thin copper discs with different diameters are mounted on the solid iron shaft and their influences on the eddy current speed sensor were evaluated and measured to increase sensitivity and decrease sensor dependency on the permeability of the solid iron shaft. The achieved nonlinearity errors are about ±0.2%.

Apparent permeability of ordered magnetically soft nanowire arrays

  • DOI: 10.1063/9.0000316
  • Link: https://doi.org/10.1063/9.0000316
  • Department: Department of Measurement
  • Annotation:
    Using the equivalent 2D model for finite element method (FEM) we calculated apparent permeability μa and demagnetization factor D for permalloy nanowire and microwire arrays. The simulation results were verified by 3D FEM for arrays up to 3000 wires and experimentally for very large arrays containing up to 40 million wires. We achieved μa = 3 to 33 and coercivities Hc = 1 to 9 kA/m, which are low values for wire arrays. The μa depends mainly on the array geometry; it can be increased by increasing the distance between wires (pitch) and the wire length-to-diameter ratio L/d.

Conductivity Measurement of Nonferrous Plates using A Novel Sensor with Triangular Arrangements of Triple Coils

  • DOI: 10.1109/INTERMAG39746.2022.9827796
  • Link: https://doi.org/10.1109/INTERMAG39746.2022.9827796
  • Department: Department of Measurement
  • Annotation:
    A novel eddy current sensor is proposed in this paper for conductivity measurement of nonmagnetic metals. It has one excitation coil and two antiserially pick up coils. The three coils have rectangular forms with the equilateral triangular arrangement. The induced voltage of antiserially connected pick up coils is zero when all coils are far enough from conductive objects. However, the induced voltage is nonzero when one pick up coil is close to the conductive object due to the induced eddy currents in the conductive objects and unequal flux linkage in the pick up coils. The real and imaginary components of the induced voltage and their ratio are functions of plate conductivity. The experiments and 3D finite element method analysis of the triple coils sensor are conducted for conductivity measurement of nonferrous plates to estimate their conductivities. The accuracy of the eddy current sensor was tested and analyzed, showing that its error can be as low as 0.2%. Conductivity measurement is also presented using measured impedance change of single rectangular coil parallel to conductive plates with minimum accuracy error 0.4% and the results of conductivity estimation are compared with triple coils sensor.

Design and Modeling of An Axisymmetric Eddy Current Sensor for Speed Measurement of Nonmagnetic Rods

  • DOI: 10.1016/j.sna.2022.113728
  • Link: https://doi.org/10.1016/j.sna.2022.113728
  • Department: Department of Electromagnetic Field, Department of Measurement
  • Annotation:
    This paper presents the design and modeling of an eddy current speed sensor for nonmagnetic moving rods with an axisymmetric configuration. The sensor consists of two antiserially connected excitation coils and one pick up coil located between two excitation coils. A novel computational approach using the combined finite difference method and Fourier series is proposed for the modeling and simulations of the eddy current speed sensor. The effects of the outer diameters of moving nonmagnetic rods and their electrical conductivities on the performance of speed sensor are originally evaluated. The results of the modeling for the eddy current speed sensor are compared with the measurements at time varying speeds and various frequencies. The comparison between modeling and experimental results shows the appropriateness of the eddy current speed sensor for the speed measurement of nonmagnetic rods.

Effect of external DC field on current transformers with amorphous and nanocrystalline cores

  • DOI: 10.1016/j.jmmm.2022.170019
  • Link: https://doi.org/10.1016/j.jmmm.2022.170019
  • Department: Department of Measurement
  • Annotation:
    Nanocrystalline and amorphous stress-annealed and field annealed tapes are used for cores of DC-tolerant current transformers. We analyze the influence of external DC field of arbitrary direction on the performance of these transformers. For the realistic core shapes the demagnetization is high, which leads to effective external field suppression. However, DC tolerant transformers are tolerant to the DC component of the current and not to the external field -they can be saturated by 30 mT field from permanent magnet. This means that for the practical applications in domestic energy meters some external shielding is required.

Inkjet-printed Mn-Zn ferrite nanoparticle core for fluxgate

  • DOI: 10.1016/j.jmmm.2022.170003
  • Link: https://doi.org/10.1016/j.jmmm.2022.170003
  • Department: Department of Microelectronics, Department of Measurement
  • Annotation:
    Non-planar fluxgate sensors measuring the magnetic fields in the uT range are required for electric current, position, and torque transducers. We report the first sensor based on an inkjet-printed 17 mm diameter ring core. The sensor wide open-loop linear range of  1.5 mT allows to operate it without feedback. We describe the preparation of the very stable magnetic ink based on citrate-stabilized 13 nm diameter Mn-Zn ferrite nanoparticles that occur in superparamagnetic regime at room temperature. By printing 100 layers the total thickness of the inkjet-printed core was 2.2 µm. The achieved sensitivity was 10 mV/mT for 25 kHz excitation frequency

Magnetic position sensors

  • DOI: 10.1088/1361-6501/ac32eb
  • Link: https://doi.org/10.1088/1361-6501/ac32eb
  • Department: Department of Measurement
  • Annotation:
    Magnetic position sensors are popular in industrial and automotive applications since they are robust, resistant to dust and oil, and can be cheap. This was traditionally accompanied by low accuracy. However, new precise magnetic position sensors have been developed which can achieve 0.015% error and 10 nm resolution. The maximum achievable range is about 20 m. DC magnetic position sensors use a permanent magnet as a field source; a magnetic field sensor measures the field from that source, which is a function of distance. As a field sensor, magnetoresistors are often used instead of traditional Hall sensors. Eddy current position sensors also work with non-magnetic conduction targets. Magnetostrictive position sensors are based on the time of flight of the elastic waves excited in the magnetostrictive material. These sensors can be several meters long and their applications range from level meters to hydraulics. Magnetic trackers and long-range position sensors utilize AC field sources, which are detectable from distances up to 20 m. Compared to optical instruments, magnetic trackers do not need a direct view. Their applications include surgery, mixed reality, and underground and underwater navigation.

Multiwire Parallel Fluxgate Sensors

  • DOI: 10.1109/TMAG.2021.3093017
  • Link: https://doi.org/10.1109/TMAG.2021.3093017
  • Department: Department of Measurement
  • Annotation:
    Fluxgate sensors with straight wire or rod cores are used in NDT, portable gradiometers and sensor arrays and for the detection of small objects. We show that their sensitivity at the voltage output mode depends on the excitation parameters, properties of the core material and geometry, pick-up coil length, but only slightly on the pick-up coil diameter. This finding allows to design multiwire cores with large wire pitch, which decreases their magnetic interactions and thus reduces demagnetization and correlation of their noise. As a result, using N wires theoretically increases sensitivity N-times, which is not achievable with dense cores. We have demonstrated this tendency for N up to 8 and one type of permalloy wire.

Rogowski Coil with Ferromagnetic Powder Core

  • DOI: 10.1109/LMAG.2022.3143470
  • Link: https://doi.org/10.1109/LMAG.2022.3143470
  • Department: Department of Measurement
  • Annotation:
    We have used nanocrystalline powder to build a core for Rogowski coils suitable for application in energy meters. The sensor linearity error is 0.32% of full scale (FS) of its 20 A range, which is acceptable for this application. The main advantages of the new core are 15-fold increase in sensitivity, which results in lower noise, and high rejection of direct current. It operates at up to 1000 A dc with 20% change in sensitivity. Resulting accuracy of power measurement using a single-chip digital power meter is 0.22% FS.

Sensitivity and noise of parallel fluxgate sensor with amorphous wire cores

  • DOI: 10.1016/j.jmmm.2022.169981
  • Link: https://doi.org/10.1016/j.jmmm.2022.169981
  • Department: Department of Measurement
  • Annotation:
    Fluxgate sensors are vectorial magnetic field sensors suitable for the measurement of fields up to mT with maximum pT resolution. Due to their low weight, low power, and low cost, fluxgates are ideal sensors to monitor the Earth’s field and measure its spatial deviations. The sensitivity of the sensor directly depends on the material and geometry of the core, and on the geometric parameters of the coils. Fluxgate is still the most sensitive room-temperature vectorial magnetic field sensor [1]. This work is devoted to the study of parallel fluxgate with multiple wire cores. The achieved sensitivity for a 35 mm long sensor is 12 mV/µT and the minimum noise was 2350 pT/√Hz at 1 Hz for as-cast amorphous wires.

Thickness Evaluation of Hollow Nonmagnetic Cylinders Utilizing a Motional Eddy Current

  • DOI: 10.1016/j.measurement.2021.110463
  • Link: https://doi.org/10.1016/j.measurement.2021.110463
  • Department: Department of Electromagnetic Field, Department of Measurement
  • Annotation:
    This paper presents a way to calculate the shell thickness of nonmagnetic hollow cylinders for nondestructive applications. Aluminum cylinders with a solid structure and with a hollow structure are considered. The motion component of the induced eddy currents in a conductive cylinder is utilized to evaluate the shell thickness of hollow conductive cylinders at various frequencies and at variable speeds. One axisymmetric excitation coil and two axisymmetric pickup coils with antiserial connection are used. An analytical method using an axisymmetric computational model is developed for a parametric analysis of solid and hollow cylinder structures and shell thickness calculations, in which Fourier series are utilized. A 2D axisymmetric finite element method is also performed for a comparison with the results of the analytical method. The measurements at variable speeds and at various frequencies are presented with various hollow aluminum cylinders. The high linearity of the induced voltage versus the speed curve makes it possible to calculate the shell thickness of nonmagnetic hollow cylinders at different speeds.

A Linear Eddy Current Speed Sensor for Speed Measurement of Magnetic and Nonmagnetic Conductive Objects

  • DOI: 10.1109/LDIA49489.2021.9505714
  • Link: https://doi.org/10.1109/LDIA49489.2021.9505714
  • Department: Department of Measurement
  • Annotation:
    This paper presents a novel structure of contactless eddy current speed sensor for linear speed measurements of flat shape type conductive objects. The sensor consists of one excitation coil and two different antiserially connected pick up coils. The sensor is designed and analyzed with an air core and a magnetic yoke (core) to compare their drawbacks and merits at different excitation frequencies and low and high speeds. 2D and 3D finite element method and developed analytical methods are utilized for parametric analysis and design of linear eddy current speed sensor. The simulation results are compared with the measurements up to 15.5 m/s.

A Linear Eddy Current Speed Sensor With a Perpendicular Coils Configuration

  • DOI: 10.1109/TVT.2021.3065924
  • Link: https://doi.org/10.1109/TVT.2021.3065924
  • Department: Department of Measurement
  • Annotation:
    This paper presents a new linear eddy current speed sensor with rectangular-shaped coils. The excitation coil and the pick-up coil have a perpendicular configuration without a magnetic yoke. The proposed sensor is shorter than the previous designs. The sensor works for a conductive moving target; in this paper we present calculations and an experimental verification for solid iron and aluminum moving part materials. A novel 3D analytical method is presented for the description and for the design of an eddy current speed sensor that is fast and has high precision. The source fields and the reaction fields caused by induced eddy currents are separated in our 3D analytical method, which facilitates an enhanced investigation of the features of the speed sensor. Evaluations of the effects of the moving part material and of coil lift off on the performance of the speed sensor are made with the use of a 3D analytical method. Measurements are performed for an eddy current speed sensor at different speeds up to 11.65 m/s and at different frequencies with a novel analytical model in terms of the induced voltage in the pickup coil versus speed. Simplicity and high precision are the main advantages of the proposed speed sensor. The achieved linearity error is 0.47% (measured) up to 11.6 m/s, and 0.43% (calculated) up to 117 m/s (420 km/h).

A Position Sensor with Novel Configuration of Linear Variable Differential Transformer

  • DOI: 10.1109/JSEN.2021.3105879
  • Link: https://doi.org/10.1109/JSEN.2021.3105879
  • Department: Department of Measurement
  • Annotation:
    This paper presents a position sensor based on a novel configuration of linear variable differential transformer. Design and optimization of the position sensor using finite element method are presented. The measurements are also conducted to validate experimentally the sensor performance. The sensor has short air core coils and long magnetic armatures. The axis of the rectangular excitation coil and two antiserially connected rectangular pick up coils is perpendicular to the motion direction of the position sensor. The coils are located between two parallel silicon steel laminations serving as the armatures. The position sensor is optimized with compromise between minimization of nonlinearity error and maximum sensitivity. The main advantage of the proposed position sensor is the small ratio of coils dimensions to the working range. The position sensor is operated for excitation frequencies of 500 Hz, 1000 Hz, and 2000 Hz. The maximum nonlinearity error is less than 1.5% for the theoretical results and it is less than 2% for the measured results in ±90 mm position range.

Ch1 Basics in Magnetic Sensors and Magnetometers

  • Authors: prof. Ing. Pavel Ripka, CSc., Závěta, K.
  • Publication: Magnetic Sensors and Magnetometers. 2 ed. Boston: ARTECH HOUSE, 2021. p. 1-28. ISBN 9781630817428.
  • Year: 2021
  • Department: Department of Measurement
  • Annotation:
    2nd edition of a book from 2001. This chapter was completely rewritten by new authors This completely updated second edition of an Artech House classic covers industrial applications and space and biomedical applications of magnetic sensors and magnetometers. With the advancement of smart grids, renewable energy resources, and electric vehicles, the importance of electric current sensors increased, and the book has been updated to reflect these changes. Integrated fluxgate single-chip magnetometers are presented. GMR sensors in the automotive market, especially for end-of-shaft angular sensors, are included, as well as Linear TMR sensors. Vertical Hall sensors and sensors with integrated ferromagnetic concentrators are two competing technologies, which both brought 3-axial single-chip Hall ICs, are considered. Digital fluxgate magnetometers for both satellite and ground-based applications are discussed. All-optical resonant magnetometes, based on the Coherent Population Trapping effect, has reached approval in space, and is covered in this new edition of the book.

Estimation of a Magnetization Curve of a Fluxgate Wire Core Using an Inverse Technique

  • DOI: 10.1109/SENSORS47087.2021.9639484
  • Link: https://doi.org/10.1109/SENSORS47087.2021.9639484
  • Department: Department of Measurement
  • Annotation:
    We present a method for the estimation of the DC B-H curve of a straight magnetic wire which is used as a core for fluxgate sensor. An inverse technique is used as the direct precise measurement is practically impossible. 2D time stepping and 3D time harmonic finite element methods are used for numerical calculations to find a proper magnetization curve from the measurements of induced voltage into the pickup coils. Combined rational and power functions are utilized to model the magnetization curve, which is later used for numerical analysis too.

Impedance Analysis of Solid Iron Conductors

  • DOI: 10.1109/ISIE45552.2021.9576472
  • Link: https://doi.org/10.1109/ISIE45552.2021.9576472
  • Department: Department of Measurement
  • Annotation:
    Impedance analyses of a number of solid iron conductors at 400 Hz and 1000 Hz is presented in this paper. The impedance of solid nonmagnetic conductors is well documented. However, there have been fewer studies of solid magnetic conductors, because of complications caused by strong nonlinearity. Nevertheless, some industrial applications require ferromagnetic conductors, and a simple method for expressing their impedance is desirable. Solid iron conductors of various shapes are considered here. Analytical methods are developed that take into the account the eddy currents in the solid iron and its magnetic nonlinearity. Magnetization curves of solid iron conductors were measured using the yoke method and using a permeameter. The nonlinear time harmonic finite element method is used for impedance calculations of solid iron conductors. The impedance measurement results are compared with the analytical method and with finite element calculations. Hysteresis effects on resistance and inductance are also taken into consideration. The calculated results are compared with measurements at different currents and frequencies.

Magnetic Sensors and Magnetometers, 2nd edition

  • Authors: prof. Ing. Pavel Ripka, CSc., Závěta, K., Magnes, W.
  • Publication: 2 ed. Boston: ARTECH HOUSE, 2021. ISBN 9781630817428.
  • Year: 2021
  • Department: Department of Measurement
  • Annotation:
    2nd edition of a book from 2001. Some chapters were completely rewritten by new authors, some completely removed, the rest substantially updated. This completely updated second edition of an Artech House classic covers industrial applications and space and biomedical applications of magnetic sensors and magnetometers. With the advancement of smart grids, renewable energy resources, and electric vehicles, the importance of electric current sensors increased, and the book has been updated to reflect these changes. Integrated fluxgate single-chip magnetometers are presented. GMR sensors in the automotive market, especially for end-of-shaft angular sensors, are included, as well as Linear TMR sensors. Vertical Hall sensors and sensors with integrated ferromagnetic concentrators are two competing technologies, which both brought 3-axial single-chip Hall ICs, are considered. Digital fluxgate magnetometers for both satellite and ground-based applications are discussed. All-optical resonant magnetometes, based on the Coherent Population Trapping effect, has reached approval in space, and is covered in this new edition of the book.

Modeling of hysteresis loops using rational and power functions

  • DOI: 10.1016/j.jmmm.2020.167563
  • Link: https://doi.org/10.1016/j.jmmm.2020.167563
  • Department: Department of Measurement
  • Annotation:
    Simple and precise hysteresis models with a small number of parameters allowing fast calculation are required for the magnetic analysis, as the field is calculated in a very large number of points. This paper presents a new simple method for modeling the hysteresis loops of soft magnetic materials using combined rational and power functions. Three approaches are used to model the hysteresis loops analytically. In the first approach, the upper and lower curves of the hysteresis loops are estimated and are calculated separately, using combined rational and power functions. In the second approach, the hysteresis loops are calculated using the DC magnetization curve and combined rational and power functions, applying a phase shift in the magnetic field strength variations relative to the magnetic flux density. The third approach presents a novel method for modeling hysteresis loops: first, the model is fitted to the “mean curve”, which is in the middle of the measured hysteresis curve, and as a second step the phase shift is calculated as in the second approach. A solid iron sample with a rectangular cross section is used for the measurements and the hysteresis modeling. The proposed method is also applied to model the hysteresis loops of a magnetic material with high magnetic permeability and grain-oriented steel, to show the generality of the proposed methods.

Modelling and measurement of magnetically soft nanowire arrays for sensor applications,

  • DOI: 10.3390/s21010003
  • Link: https://doi.org/10.3390/s21010003
  • Department: Department of Measurement
  • Annotation:
    Soft magnetic wires and microwires are currently used for the cores of magnetic sensors. Thanks to their low demagnetization, they contribute to the high sensitivity and the high spatial resolution of fluxgates, Giant Magnetoimpedance (GMI), and inductive sensors. Arrays of nanowires can be prepared by electrodeposition into predefined pores of a nanoporous polycarbonate membrane. While high coercivity arrays with square loops are convenient for information storage and for bistable sensors such as proximity switches, low coercivity cores are needed for linear sensors. We show that coercivity can be controlled by the geometry of the array: increasing the diameter of nanowires (20 µm in length) from 30 nm to 200 nm reduced the coercivity by a factor of 10, while the corresponding decrease in the apparent permeability was only 5-fold. Finite element simulation of nanowire arrays is important for sensor development, but it is computationally demanding. While an array of 2000 wires can be still modelled in 3D, this is impossible for real arrays containing millions of wires. We have developed an equivalent 2D model, which allows to solve these large arrays with acceptable accuracy. Using this tool we have shown that as a core of magnetic sensors, nanowires are efficiently employed only together with microcoils with diameter comparable to the nanowire length.

Parallel fluxgate sensor with amorphous wire core: sensitivity study

  • Authors: Hrakova, D., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Proceedings of Student Conference on Sensors, Systems and Measurement 2021. Praha: CESKE VYSOKE UCENI TECHNICKE V PRAZE, 2021. p. 23-24. ISBN 978-80-01-06822-9.
  • Year: 2021
  • Department: Department of Measurement
  • Annotation:
    Traditional fluxgate sensors with wire core are using permalloy core material and three configurations: singe-core, Förster, and Vacquier. We recently suggested several novel multiwire design configurations with the aim to increase the sensitivity and decrease the noise. In this paper, we present the results measured on amorphous wire cores.

Rogowski Coil with Ferromagnetic Core for Precise Monitoring of Low-frequency Currents

  • DOI: 10.1109/INTERMAG42984.2021.9579562
  • Link: https://doi.org/10.1109/INTERMAG42984.2021.9579562
  • Department: Department of Measurement
  • Annotation:
    Sensitivity of precise Rogowski coils can be increased by using low-permeability magnetic core instead of air core. This allows to increase the resolution for small current values. We have studied an impact of cores with µr = 14 and 26 on linearity, frequency dependence, crosstalk from external currents and sensitivity to misplacement of the measured current. Both 3D FEM simulations and measurement were used. While we found negligible effect on crosstalk and resistance to misplacement and also on frequency characteristics, the linearity was significantly degraded. However, the linearity error in case of µr = 14, 80 mm diameter Rogowski coil with 1000 A range is still below 0.2 %, which is sufficient for energy meters.

Self-oscillating DC Current Transformer with Nanocrystalline Core

  • Authors: Grim, V., prof. Ing. Pavel Ripka, CSc.,
  • Publication: IEEE Sensors 2021 Proceedings. Sydney: IEEE, 2021. ISSN 2168-9229. ISBN 9781728195018.
  • Year: 2021
  • DOI: 10.1109/SENSORS47087.2021.9639745
  • Link: https://doi.org/10.1109/SENSORS47087.2021.9639745
  • Department: Department of Measurement
  • Annotation:
    A simple and robust circuit for contactless current measurement, based on a free-running relaxation oscillator with variable threshold values, is presented. Its performance was evaluated and compared with other methods, in particular the traditional second harmonic detection. Linearity error below 0.1% was achieved across the range of ±100A.

The apparent permeability and the amplification factor of magnetic wires and wire arrays

  • DOI: 10.1016/j.jmmm.2021.167726
  • Link: https://doi.org/10.1016/j.jmmm.2021.167726
  • Department: Department of Measurement
  • Annotation:
    We have calculated and plotted the apparent permeability and the demagnetization factor of single magnetic wires. We have also confirmed the accuracy of the analytical formula for the conversion between the apparent permeability and the demagnetization factor. We also show that, as regards wire geometry, the effective permeability calculated from the inductance does not provide a good estimate of the apparent permeability, but that it is close to the amplification factor for induction sensors. We extend the concept of apparent permeability to a wire array. This will allow us to design multiwire magnetic sensors, mainly induction sensors and fluxgates. FEM calculations have been verified on physical models with up to 91 wires. Finally, we show a simplified 2D model for studies of larger wire arrays, and we verify the accuracy of the model.

A Novel Eddy Current Speed Sensor with Ferrite E-Core

  • DOI: 10.1109/LMAG.2020.2993501
  • Link: https://doi.org/10.1109/LMAG.2020.2993501
  • Department: Department of Measurement
  • Annotation:
    This letter presents a novel speed sensor based on motion-induced eddy currents in conductive moving parts. The magnetic yoke is an E-shaped ferrite core. The excitation coil is on the center leg of the E-core, and two antiserially connected pick-up coils are on the side legs. Solid iron and aluminum materials are used for the moving part in the simulations and in the measurements. Two-dimensional and 3-D finite element methods are used for a detailed analysis and for the parametric calculations of the eddy current speed sensor. Despite its simple structure, the proposed eddy current speed sensor shows high linearity. The analysis and the measurements are performed at various speeds and excitation frequencies for an evaluation of the performance of the eddy current speed sensor. The minimum linearity error is less than 0.5%.

A Novel Position Sensor With a Conical Iron Core

  • DOI: 10.1109/TIM.2020.2999691
  • Link: https://doi.org/10.1109/TIM.2020.2999691
  • Department: Department of Measurement
  • Annotation:
    A novel position sensor for pneumatic and hydraulic cylinder applications is presented in this paper. The solid iron core conical in shape surrounded by axisymmetric coils is an essential part of the proposed position sensor. The axisymmetric coils are used for excitation and voltage measurements. The conical solid iron core is annealed to homogenize the magnetic properties and to increase the permeability of the conical solid iron core. This improves the performance of the position sensor in terms of sensitivity and linearity. Analytical and finite element analyses are utilized along with measurements in order to analyze the performance of the position sensor. The position sensor performs measurements of excitation coil inductance and pick-up coil voltages. Various frequencies are considered for the analysis and for the measurements. The measurement results show that the maximum linearity error is about 4% for the manufactured sensor, and is calculated to have a maximum value of 1% for the theoretical model. The achievable resolution of the proposed sensor is about 0.4 mm.

DC current sensor using switching-mode excited in-situ current transformer

  • DOI: 10.1016/j.jmmm.2019.166370
  • Link: https://doi.org/10.1016/j.jmmm.2019.166370
  • Department: Department of Electric Drives and Traction, Department of Measurement
  • Annotation:
    DC current component in the power grid may cause gross measurement errors and lead to overheating of power transformers. We have previously developed method how to measure DC current using fluxgate effect in existing current transformers. In this paper we show that using ferroresonance the power consumption of such device can be drastically reduced. The microprocessor can both control the H-bridge excitation unit and perform signal processing, avoiding the need of external instruments.

Design and modeling of a linear speed sensor with a flat type structure and air coils

  • DOI: 10.1016/j.jmmm.2019.165834
  • Link: https://doi.org/10.1016/j.jmmm.2019.165834
  • Department: Department of Measurement
  • Annotation:
    This paper presents the design and modeling of a linear eddy current speed sensor with a flat type structure and an air coil configuration. The theory of the eddy current speed sensor is based on utilizing the speed component of the induced currents in a solid moving conductor under stationary or alternating source fields. The stationary part comprises one rectangular excitation coil and two antiserially connected rectangular pick-up coils on the left and right sides of the excitation coil in the direction of the trajectory of the moving part. The moving part is considered firstly as a rectangular conducive ferromagnetic solid iron plate, and secondly as a rectangular aluminum plate. A 3D analytical model using Fourier series is developed to analyze the linear speed sensor in Cartesian coordinates. In addition, the 3D numerical finite element method is used for simulations of the linear speed sensor, and the results are compared with the results for analytical methods. The effects of iron permeability on the speed sensor are calculated for a rectangular ferromagnetic solid iron bar or conductor. The experimental results are presented for a linear speed sensor for a rectangular ferromagnetic solid iron plate and also for a rectangular aluminum plate, at variable speeds. The calculation and the experimental results show that the speed sensor outputs differ completely for solid iron conducive plates and for aluminum conducive plates, due to the different electrical conductivities and magnetic permeabilities.

Design and Optimization of an Eddy Current Speed Sensor for Rotating Rods

  • DOI: 10.1109/JSEN.2020.3000442
  • Link: https://doi.org/10.1109/JSEN.2020.3000442
  • Department: Department of Measurement
  • Annotation:
    This paper presents the design and optimization of a novel eddy current speed sensor for rotating rods and cylindrical shafts. The sensor consists of one excitation coil and two pick-up coils. All coils are stationary; we consider air coils, and we also use a magnetic yoke. We utilize a copper coating on an iron rod to increase the sensitivity, and we compare the performance with the performance achieved for an uncoated iron rod. 3D FEM is utilized for analyzing and for optimizing the design of the proposed sensor. The main advantages of the novel sensors are their simplicity, their low cost and their robust configuration. A linearity error of 0.5% has been achieved. The level of accuracy is limited by mechanical factors. A 1D analytical model has also been developed for rapid analysis and optimization of the sensor. An aluminum rod was also used in the measurements for a comparison with the results achieved with the iron rod.

Design of a flat-type magnetic position sensor using a finite-difference method

  • DOI: 10.1049/iet-smt.2019.0197
  • Link: https://doi.org/10.1049/iet-smt.2019.0197
  • Department: Department of Electromagnetic Field, Department of Measurement
  • Annotation:
    This study presents an analysis and the design of a new flat-type position sensor with an external armature. One excitation coil and two antiserially connected pickup coils are used in the stationary part. Solid iron segments or steel lamination segments are used for the moving armature. The proposed position sensor was modelled using linear movement. A two-dimensional finite-difference method was developed and was used for fast analysis for optimising the sensor. The induced eddy currents in the solid armature were taken into account in the finite-difference analysis. The finite-difference calculations were compared with 2D and 3D finite-element method simulations and with experimental results. The sensor has a total error of 0.23 mm root-mean-square for 36 mm range without any compensation. Unlike previous designs, the authors’ new sensor has no moving coil.

Eddy current speed sensor with magnetic shielding

  • DOI: 10.1016/j.jmmm.2020.166568
  • Link: https://doi.org/10.1016/j.jmmm.2020.166568
  • Department: Department of Measurement
  • Annotation:
    This paper presents the design and analysis of a new eddy current speed sensor with ferromagnetic shielding. Aluminum and solid iron are considered for the moving part. One excitation coil and two antiserially connected pick up coils are shielded by a thin steel lamination. 3D time stepping finite element analysis is used to analyze the sensor performance with different magnetic materials and compare with experimental results. The compactness, simplicity and excellent linearity with different magnetic materials for the moving part show uniqueness of the proposed speed sensor. The shielding increases sensitivity and reduces the influence of close ferromagnetic objects and interferences on the sensor performance.

Inductive position and speed sensors

  • DOI: 10.3390/s20010065
  • Link: https://doi.org/10.3390/s20010065
  • Department: Department of Measurement
  • Annotation:
    Magnetic position and speed sensors are rugged and durable. While DC magnetic sensors use permanent magnets as a field source and usually have only mm or cm range, inductive sensors use electromagnetic induction and they may work up to a distance of 20 m. Eddy current inductive sensors equipped with magnetoresistive sensors instead of inductive coils can operate at low frequencies, allowing detection through a conductive wall. In this paper, we make an overview of existing systems and we present new results in eddy current velocity and position measurements. We also present several types of inductive position sensors developed in our laboratories for industrial applications in pneumatic and hydraulic cylinders, underground drilling, large mining machines, and for detecting ferromagnetic objects on conveyors. While the most precise inductive position sensors have a resolution of 10 nm and linearity of 0.2%, precision requirements on the industrial sensors which we develop are less demanding, but they should have large working distance and large resistance to environmental conditions and interference.

Temperature stability of the transformer position transducer for pneumatic cylinder

  • DOI: 10.1016/j.jmmm.2020.166636
  • Link: https://doi.org/10.1016/j.jmmm.2020.166636
  • Department: Department of Measurement
  • Annotation:
    This paper presents the analysis and design of a transformer position sensor for pneumatic cylinder considering temperature stability. Two solenoid coils as excitation coil and pick up coil around cylinder are used for position transducer. The effects of temperature of aluminum cylinder and iron rod with different ferromagnetic materials on position sensor performance are analyzed and measured. We found that the effect of temperature dependence of shell resistivity is dominant, while the effect of permeability change is negligible. Based on the simulations and measurement we suggest simple method of temperature compensation.

A 3-Phase Current Transducer based on microfluxgate sensors

  • Authors: prof. Ing. Pavel Ripka, CSc., Grim, V., Chirtsov, A.
  • Publication: Measurement. 2019, 146(11), 133-138. ISSN 0263-2241.
  • Year: 2019
  • DOI: 10.1016/j.measurement.2019.06.028
  • Link: https://doi.org/10.1016/j.measurement.2019.06.028
  • Department: Department of Measurement
  • Annotation:
    Novel 3-phase DC/AC current transducer for 3-phase current lines is based on 8 integrated fluxgate sensors. Using full information from each sensor rather than gradiometric pairs, we suppress crosstalk between individual phases and external magnetic fields up to the 4th order gradients. The suppression of external currents at a distance of 1 m is 90 dB. The main advantage of the used microfluxgates is excellent temperature stability allowing operation outside the laboratory: the achieved temperature coefficient of the sensitivity is 50 ppm/K, and the offset stability is 1 mA/K. These values are 20-times better than temperature stability achievable with current transducers sensors based on Hall sensors and magnetoresistors.

Characterization of circular array current transducers

  • DOI: 10.1109/SAS.2019.8706029
  • Link: https://doi.org/10.1109/SAS.2019.8706029
  • Department: Department of Measurement
  • Annotation:
    This paper is evaluating different aspects affecting the performance of circular arrays of magnetic sensors used for contactless current transducer. Some of these error mechanisms are quantified using analytical expressions to provide designers with theoretical upper limits of achievable accuracy. Novel method of misalignment compensation using multi-axial sensors is presented. Measurements were performed with different sensor arrays to verify theoretical assumptions and determine limiting factors for real-world application of yokeless transducers.

Contactless measurement of electric current using magnetic sensors

  • DOI: 10.1515/teme-2019-0032
  • Link: https://doi.org/10.1515/teme-2019-0032
  • Department: Department of Measurement
  • Annotation:
    We review recent advances in magnetic sensors for DC/AC current transducers, especially novel AMR sensors and integrated fluxgates, and we make critical comparison of their properties. Most contactless electric current transducers use magnetic cores to concentrate the flux generated by the measured current and to shield the sensor against external magnetic fields. In order to achieve this, the magnetic core should be massive. We present coreless current transducers which are lightweight, linear and free of hysteresis and remanence. We also show how to suppress their weak point: crosstalk from external currents and magnetic fields.

Eddy Current Linear Speed Sensor

  • DOI: 10.1109/TMAG.2018.2872123
  • Link: https://doi.org/10.1109/TMAG.2018.2872123
  • Department: Department of Measurement
  • Annotation:
    Novel eddy current speed sensor with axisymmetric coils and solid iron rod as moving part is presented. The analysis is performed for both dc and ac coil currents and for variable iron rod translational speed. The coil inductance and induced voltage results using the analytical method and finite-element method calculation are compared with the measured values. Two different coil configurations are used for simulations and measurement.

Magnetometric Localization and Measurement of Hidden AC Currents

  • Authors: Grim, V., Pek, J., prof. Ing. Pavel Ripka, CSc., Chirtsov, A.
  • Publication: IEEE SENSORS 2019. IEEE SENSORS Society, 2019. ISSN 1930-0395. ISBN 978-1-7281-1635-8.
  • Year: 2019
  • DOI: 10.1109/SENSORS43011.2019.8956513
  • Link: https://doi.org/10.1109/SENSORS43011.2019.8956513
  • Department: Department of Measurement
  • Annotation:
    We propose a measurement method which allows to localize and measure unknown current using a 3-axial magnetometer. By taking measurements at multiple, randomly selected points, accuracy of ±3% was achieved in an outdoor test scenario for current of 20A and 2m to 5m distance. An iterative algorithm is used for deducing magnitude and location of the unknown current from all available data points.

Magnetoresistive Sensor Development Roadmap (Non-Recording Applications)

  • Authors: Zheng, C., Zhu, K., prof. Ing. Pavel Ripka, CSc., Freitas, P., Chang, J.
  • Publication: IEEE Transactions on Magnetics. 2019, 55(4), ISSN 0018-9464.
  • Year: 2019
  • DOI: 10.1109/TMAG.2019.2896036
  • Link: https://doi.org/10.1109/TMAG.2019.2896036
  • Department: Department of Measurement
  • Annotation:
    Magnetoresistive (MR) sensors have been identified as promising candidates for the development of high-performance magnetometers due to their high sensitivity, low cost, low power consumption, and small size. The rapid advance of MR sensor technology has opened up a variety of MR sensor applications. These applications are in different areas that require MR sensors with different properties. Future MR sensor development in each of these areas requires an overview and a strategic guide. An MR sensor roadmap (non-recording applications) was therefore developed and made public by the Technical Committee of the IEEE

Rectangular Array Electric Current Transducer with Integrated Fluxgate Sensors

  • DOI: 10.3390/s19224964
  • Link: https://doi.org/10.3390/s19224964
  • Department: Department of Measurement
  • Annotation:
    Novel rectangular yokeless current transducer with the range 400 A using 16 microfluxgate sensors around the busbar conductor is presented in this paper. Compared to yokeless transducers utilizing the differential pair of magnetic sensors, our solution has much better suppression of the external currents (lower crosstalk). Compared to industrial transducers with yoke, the new transducer has 15-times lower noise, 7-times better temperature stability, and same crosstalk. The sensor design and design of the current monitoring system is presented together with the results of long-term field tests. Crosstalk error is examined in dependence on the number of operating sensors and the external current position.

Rotational Eddy Current Speed Sensor

  • DOI: 10.1109/TMAG.2019.2918163
  • Link: https://doi.org/10.1109/TMAG.2019.2918163
  • Department: Department of Measurement
  • Annotation:
    A novel eddy current speed sensor is developed to measure the rotational speed of conductive objects. The sensor consists of one excitation coil and two pick-up coils around a rotating cylinder or rod. The sensor does not use magnetic yoke. For the analysis and experimental verification, we used 30 mm diameter non-magnetic aluminum and also magnetic solid iron cylinders. The calculated and measured speed ranges are up to 1200 r/min. A 2-D analytical method is developed to calculate sensor performance. A 2-D finite element is also used for simulations to compare results with the 2-D analytical method. A 3-D finite-element analysis is required to take into account significant 3-D effects due to the air coil configuration. The experimental results are presented at different steady-state speeds. The calculation results are compared with measurements to validate theoretical models and sensor performance. The eddy current speed sensor shows high linearity even at low speeds. For ferromagnetic rods, we suggest a novel double-layer configuration: non-magnetic conductive ring or shell on top of the iron rod minimizes the influence of the permeability changes. The main advantage of the novel sensor is that it has neither mechanical nor electrical contact to the rotating rod

Three-Phase Busbar Current Transducer

  • Authors: Chirtsov, A., prof. Ing. Pavel Ripka, CSc., Grim, V.
  • Publication: IEEE Magnetics Letters. 2019, 10(1), ISSN 1949-307X.
  • Year: 2019
  • DOI: 10.1109/LMAG.2019.2957257
  • Link: https://doi.org/10.1109/LMAG.2019.2957257
  • Department: Department of Measurement
  • Annotation:
    A true three-phase 1000 A busbar current transducer is based on six micro-fluxgate sensors. Instead of using three independent single-phase current transducers, we use the full information from each sensor. Two TI DRV425 microfluxgate sensors are inserted into a hole drilled in each busbar. Our method of data processing is optimized to compensate the crosstalk between the three phases and external fields and gradients up to second order. The crosstalk error between the phases was 0.23% or smaller. The suppression of field from an external current at a distance of 10 cm is improved by a factor of 25 to 150. Our transducer has compact size, high temperature offset stability of 8.5 mA/°C, high current range up to 1000 A, low power consumption, and linearity of 0.1%. The results from a three-dimensional finite-element model and analytical computations confirm the measurements

Transformer position sensor for a pneumatic cylinder

  • DOI: 10.1016/j.sna.2019.04.046
  • Link: https://doi.org/10.1016/j.sna.2019.04.046
  • Department: Department of Measurement
  • Annotation:
    A novel transformer-based sensor for a pneumatic cylinder enables measurements of the piston position to be made through a thick conductive cylinder. Unlike existing industrial solutions, which are mainly based on a moving magnet, our sensors do not require modifications to the parts inside the cylinder.

Analysis of Material Effect on Rail Impedance

  • DOI: 10.1109/UPEC.2018.8541860
  • Link: https://doi.org/10.1109/UPEC.2018.8541860
  • Department: Department of Measurement
  • Annotation:
    In this paper, two different solid iron materials are used for two different size rails. The internal impedances, resistances and inductances of the rails are evaluated and analyzed with time harmonic and time stepping finite element methods. Two solid iron materials have different B-H curves and electrical conductivities. The analysis will be presented for different currents at different frequencies, 10 Hz - 10 kHz. The inductance analysis using finite element method is also performed under simultaneous large DC signal and small AC signal.

Analytical Functions of Magnetization Curves for High Magnetic Permeability Materials

  • DOI: 10.1109/TMAG.2018.2827932
  • Link: https://doi.org/10.1109/TMAG.2018.2827932
  • Department: Department of Measurement
  • Annotation:
    In this paper, combined rational and power functions are used to represent magnetization curves of high magnetic permeability ferromagnetic materials. The proposed functions cover much wider range of magnetic fields than functions currently used in simulation software packages. The objective is to present simple functions for approximation of magnetization curves with minimum number of unknown constants. The calculated functions are finally compared with measured magnetization curves to validate the precision in a wide field range from 10(-2) to 10(6) A/m.

Busbar current transducer with suppression of external fields and gradients

  • Authors: prof. Ing. Pavel Ripka, CSc., Chirtsov, A., Vyhnánek, J.
  • Publication: Proceedings IEEE International Magnetics Conference (INTERMAG). New Jersey: IEEE, 2018. ISBN 978-1-5386-6425-4.
  • Year: 2018
  • Department: Department of Measurement
  • Annotation:
    Yokeless busbar current transducers with circular sensor array achieve high precision when replacing Hall sensors by microfluxgate. Limited field range of fluxgate can be compensated by inverse design with sensors inside the busbar. In this paper we present novel scheme how to improve immunity of such sensor against external field and field gradient. We also examine crosstalk error for external currents close to the transducer. Using five microfluxgate sensors we designed 400 A current transducer which has suppression of 93 000 for currents in 40 cm vicinity.

Busbar Current Transducer With Suppression of External Fields and Gradients

  • DOI: 10.1109/TMAG.2018.2844254
  • Link: https://doi.org/10.1109/TMAG.2018.2844254
  • Department: Department of Measurement
  • Annotation:
    Yokeless busbar current transducers with circular sensor array achieve high precision when replacing Hall sensors by microfluxgate. Limited field range of fluxgate can be compensated by inverse design with sensors inside the busbar. In this paper, we present a novel scheme how to improve the immunity of such sensor against external field and field gradient. We also examine crosstalk error for external currents close to the transducer. Using five microfluxgate sensors, we designed a 400 A current transducer which has a suppression of 93 000 for currents in 40 cm vicinity.

DC compensated permeameter - the accuracy study

  • DOI: 10.2478/jee-2018-0063
  • Link: https://doi.org/10.2478/jee-2018-0063
  • Department: Department of Measurement
  • Annotation:
    We describe D-permeameter originally designed by Trnka and later improved by Fajt and Kaspar and we analyze its precision for the measurement of different soft magnetic materials. The device measures DC hysteresis loops using compensation method, so that H and B can be calculated from the magnetization and compensation currents. The differences from results obtained by other standard methods are below 2%.

Demagnetization Coefficient and Effective Permeability of Nanowires and Nanowire Arrays

  • Authors: prof. Ing. Pavel Ripka, CSc., Ing. Mehran Mirzaei, Ph.D., Chirtsov, A.
  • Publication: 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018). Vail, Colorado: IEEE Instrumentation and Measurement Society, 2018. ISSN 2160-0171. ISBN 978-1-5386-0974-3.
  • Year: 2018
  • DOI: 10.1109/CPEM.2018.8500785
  • Link: https://doi.org/10.1109/CPEM.2018.8500785
  • Department: Department of Measurement
  • Annotation:
    Magnetic field in the perpendicular direction cannot be sensed by thin film sensor due tolarge demagnetisation. We show that an array of nanowires has much lower demagnetization coefficient than magnetic film. This feature can be used to add third dimension to two-dimensional magnetic sensors.

Impedance of Iron Conductors with Circular and Rectangular Shapes

  • Authors: Ing. Mehran Mirzaei, Ph.D., prof. Ing. Pavel Ripka, CSc., Chirtsov, A., Vyhnánek, J.
  • Publication: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society. San Francisco: American Institute of Physics and Magnetic Society of the IEEE, 2018. p. 194-199. ISSN 1553-572X. ISBN 978-1-5090-6684-1.
  • Year: 2018
  • DOI: 10.1109/IECON.2018.8592704
  • Link: https://doi.org/10.1109/IECON.2018.8592704
  • Department: Department of Measurement
  • Annotation:
    The impedance of rectangular and circular shape solid iron conductors is studied in this paper. 2D analytical model is presented for linear iron materials with different relative magnetic permeability and the results are compared with finite element method (FEM). Experiments are performed to measure the impedances. Nonlinear time harmonic FEM results are compared with experimental results for detailed evaluations. Different solid irons are considered for measurement and simulations.

Improved 3-Phase Current Transducer

  • DOI: 10.3390/proceedings2131070
  • Link: https://doi.org/10.3390/proceedings2131070
  • Department: Department of Measurement
  • Annotation:
    We propose improved contactless DC/AC current transducer for 3-phase current lines based on 8 integrated fluxgate sensors. Using proper processing we ideally achieve a complete suppression of external homogeneous fields, and field gradients up to the 4th order. The sensitivity to external currents (crosstalk) is improved 15-times compared to [1]. The usage of micro fluxgate sensors instead of magnetoresistive sensors improves the temperature stability: the sensitivity temperature coefficient was reduced from 0.3%/K to 50 ppm/K and offset drift was reduced from 50 mA/K to 1 mA/K.

Inductance position sensor for pneumatic cylinder

  • DOI: 10.1063/1.4993559
  • Link: https://doi.org/10.1063/1.4993559
  • Department: Department of Measurement
  • Annotation:
    The position of the piston in pneumatic cylinder with aluminum wall can be measured by external inductance sensor without modifications of the aluminum piston and massive iron piston rod. For frequencies below 20 Hz the inductance is increasing with inserting rod due to the rod permeability. This mode has disadvantage of slow response to piston movement and also high temperature sensitivity. At the frequency of 45 Hz the inductance is position independent, as the permeability effect is compensated by the eddy current effect. At higher frequencies eddy current effects in the rod prevail, the inductance is decreasing with inserting rod. In this mode the sensitivity is smaller but the sensor response is fast and temperature stability is better. We show that FEM simulation of this sensor using measured material properties gives accurate results, which is important for the sensor optimization such as designing the winding geometry for the best linearity

Rectangular Array Current Transducer with Integrated microfluxgate Sensors

  • Authors: Chirtsov, A., prof. Ing. Pavel Ripka, CSc., Vyhnánek, J.
  • Publication: Proceeding - 2018 IEEE SENSORS. IEEE SENSORS, 2018. ISBN 978-1-5386-4707-3.
  • Year: 2018
  • DOI: 10.1109/ICSENS.2018.8589563
  • Link: https://doi.org/10.1109/ICSENS.2018.8589563
  • Department: Department of Measurement
  • Annotation:
    Novel rectangular yokeless current transducer with the range 400 A using 16 microfluxgate sensors around the busbar conductor is presented in this paper. Compared to yokeless transducers utilizing the differential pair of magnetic sensors, our solution has much better suppression of external currents (lower crosstalk). Compared to industrial transducers with yoke, the new transducer has to-times lower noise, to-times better temperature stability, and same crosstalk. Sensor design, different methods for calculating the current and temperature dependence are presented in this paper. Crosstalk error is examined in dependence on the number of the operating sensors and external current position.

Temperature Influence on Position Transducer for Pneumatic Cylinder

  • DOI: 10.1109/ICSENS.2018.8589788
  • Link: https://doi.org/10.1109/ICSENS.2018.8589788
  • Department: Department of Measurement
  • Annotation:
    In this paper, temperature sensitivity of inductance position transducer of a pneumatic cylinder system is presented. The magnetic solid iron rod and aluminum piston position changes the inductance of the tubular coil around the aluminum pneumatic cylinder. The measurement and finite element method are used to evaluate inductances versus piston position at different frequencies. Temperature effect on the coil inductance is analyzed. Temperature of the iron rod and the aluminum cylinder are changed for the temperature sensitivity analysis. The measured iron rod temperature dependence is in the order of 0.45 %/°C at 100 Hz and 0.27 %/°C at 200 Hz. Finally a small compensating solenoid coil is used at one side of the cylinder (entrance side for piston) to compensate temperature dependency effects

The effect of conductor permeability on electric current transducers

  • DOI: 10.1063/1.4994195
  • Link: https://doi.org/10.1063/1.4994195
  • Department: Department of Measurement
  • Annotation:
    In this paper, experimental works and theoretical analysis are presented to analyze the influence of the conductor permeability on the precision of yokeless current sensors. The results of finite-element method (FEM) fit well the measured field values around the conductor. Finally we evaluate the difference in magnetic fields distribution around non-magnetic and magnetic conductor. The calculated values show that the permeability of the ferromagnetic conductor significally affects the reading of the electric current sensors even at DC.

4-sensor yokeless electric current transducer

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: 2017 IEEE International Magnetics Conference (INTERMAG). San Francisco: American Institute of Physics and Magnetic Society of the IEEE, 2017. p. 1. ISSN 2150-4601. ISBN 978-1-5386-1086-2.
  • Year: 2017
  • DOI: 10.1109/INTMAG.2017.8007975
  • Link: https://doi.org/10.1109/INTMAG.2017.8007975
  • Department: Department of Measurement
  • Annotation:
    Contactless transducers of DC electric currents often have magnetic yoke which concentrates the flux generated by the measured current. As a result, the reading does not depend much on the conductor position inside the magnetic circuit. The yoke also shields against external magnetic fields including those caused by external currents (crosstalk error).

A Busbar Current Sensor With Frequency Compensation

  • DOI: 10.1109/TMAG.2016.2620959
  • Link: https://doi.org/10.1109/TMAG.2016.2620959
  • Department: Department of Measurement
  • Annotation:
    DC/AC yokeless galvanically insulated electric current sensors are required for applications, e.g., in automotive and aerospace engineering, where size, weight, and/or price are strictly limited. A busbar current sensor with differential fluxgate in the hole has 1000 A range and 10 mA resolution. Using an asymmetric shape, we achieved a frequency error below ±3% up to 1 kHz, while keeping high temperature stability and low sensitivity to mechanical misalignments. The 2.5 mA/°C maximum dc drift is four times better than when using an AMR sensor and 1000 times better than when using a Hall sensor. The sensor linearity error is below 0.1%.

Contactless Piston Position Transducer With Axial Excitation

  • Authors: prof. Ing. Pavel Ripka, CSc., Chirtsov, A., Grim, V.
  • Publication: IEEE Transactions on Magnetics. 2017, 11(53), 1-4. ISSN 0018-9464.
  • Year: 2017
  • DOI: 10.1109/TMAG.2017.2715073
  • Link: https://doi.org/10.1109/TMAG.2017.2715073
  • Department: Department of Measurement
  • Annotation:
    Existing piston position transducers require either drilling precise hole into the piston bar, or mounting permanent magnets or measuring device inside the pressurized cylinder. We present a new solution for aluminum pneumatic cylinders, which uses the ferromagnetic bar inside the solenoid as a marker and linear array of fluxgate sensors as a scale. Instead of relying on dc remanence we use active ac excitation; the reading is resistant against external fields, both dc and ac. Using sensor array allows to compensate for temperature effects. The linear stroke of the individual sensor is 40 mm, so that array density should be about 30 mm. 1 mm position resolution is achievable. The weak point of the new transducer is the response time: for fast moving pistons the excitation frequency should be high, which leads to weaker signal and lower resolution.

Crossfield response of industrial magnetic sensors

  • Authors: prof. Ing. Pavel Ripka, CSc., Vyhnánek, J., Chirtsov, A.
  • Publication: International Journal of Applied Electromagnetics and Mechanics. 2017, 55(S1), 39-47. ISSN 1383-5416.
  • Year: 2017
  • DOI: 10.3233/JAE-172256
  • Link: https://doi.org/10.3233/JAE-172256
  • Department: Department of Measurement
  • Annotation:
    Magnetic sensors used for non-destructive testing, metal detection and other applications are subjected to large perpendicular field. In this paper we show that the existing models describing the response of anisotropic magnetoresistors (AMR) cannot be used for fields larger than the critical value, which is 350 μT for the Honeywell HMC1001. This critical value is one order of magnitude lower than the anisotropy field and it is decreasing with increased value of the measured field. From our findings it is clear that AMR sensors cannot be safely used in applications in which fields above 250 μT can appear. Neither flipping, nor feedback compensation can compensate for this error. We show that this behaviour is caused by the fact that the single-domain state of the AMR is broken at the mentioned critical field. Compared to that, fluxgate sensors including microfluxgates are by principle immune against the crossfield. Unlike in AMR, crossfield sensitivity in fluxgate sensors is second-order effect, which can be kept under control by proper design. We show that even crossfield of 10 mT does not cause significant degradation of the sensor precision.

Experimental Comparison of the Low-Frequency Noise of Small-Size Magnetic Sensors

  • Authors: Vyhnánek, J., prof. Ing. Pavel Ripka, CSc.,
  • Publication: IEEE Transactions on Magnetics. 2017, 53(4), ISSN 0018-9464.
  • Year: 2017
  • DOI: 10.1109/TMAG.2016.2633398
  • Link: https://doi.org/10.1109/TMAG.2016.2633398
  • Department: Department of Measurement
  • Annotation:
    Small-size ac magnetic-field sensors are used for nondestructive testing (NDT), magnetic particle detection, and other applications, which require high spatial resolution. Up to now, inductive coils dominated this area, as their sensitivity at kHz frequencies, is superior to other magnetic sensors. However, some applications, such as magnetic imaging through conducting sheath, require lower working frequencies, in extreme case units of Hz. We successfully replaced inductive coils by an AMR sensor in NDT application and for distance measurement. In this paper, we compare designs of miniature ac magnetic field sensors, their achievable frequency characteristics, dynamic range, and noise parameters.

Influence of External Current on Yokeless Electric Current Transducers

  • Authors: prof. Ing. Pavel Ripka, CSc., Chirtsov, A.
  • Publication: IEEE Transactions on Magnetics. 2017, 53(11), 1-4. ISSN 0018-9464.
  • Year: 2017
  • DOI: 10.1109/TMAG.2017.2715075
  • Link: https://doi.org/10.1109/TMAG.2017.2715075
  • Department: Department of Measurement
  • Annotation:
    Yokeless electric current transducers have compact size, but they are sensitive to external magnetic fields, including those caused by electric currents in their vicinity. It is often believed that this unwanted sensitivity can be effectively suppressed by using a differential sensor. In this paper, we investigate the effect of external current with arbitrary position on busbar differential current sensor. We show the main disadvantage of the differential current sensor: increased sensitivity to currents in the transversal direction, which are not sensed by a single sensor. We analyze by finite element method simulation also the influence of real conductor size and uneven density of ac currents. The results were verified on 1000 A current transducer using a pair of microfluxgate sensors. The realistic suppression of close currents depends on the conductor angular position and in 10 cm distance it can be as low as 50, but it can be corrected if the geometry is known.

Linear Position Sensing through Conductive Wall without Permanent Magnet

  • Authors: Vyhnánek, J., prof. Ing. Pavel Ripka, CSc., Chirtsov, A.
  • Publication: Proceedings of Eurosensors 2017. Basel: MDPI AG, 2017. vol. 1. ISSN 2504-3900.
  • Year: 2017
  • DOI: 10.3390/proceedings1040390
  • Link: https://doi.org/10.3390/proceedings1040390
  • Department: Department of Measurement
  • Annotation:
    A linear position sensor for pneumatic actuators is presented. Position of the piston rod made of ferromagnetic material is detected by low frequency magnetic field which penetrates the aluminum wall of the cylinder. The sensor consists of an array of integrated fluxgate sensors and two excitation saddle coils mounted outside the actuator. The method does not need a permanent magnet attached to the piston as required by common magnetic position sensors.

Off-Center Error Correction of AMR Yokeless Current Transducer

  • DOI: 10.1155/2017/6057634
  • Link: https://doi.org/10.1155/2017/6057634
  • Department: Department of Measurement
  • Annotation:
    We present a method of calibration and error correction of the AMR yokeless current transducer consisting of a circular array of eight anisotropic magnetoresistors (AMR) with one feedback compensation loop. The main sources of errors are the nonidentical parameters of AMR sensors and off-center position of the measured current. It is well known that AMR sensors from the same batch have 2% spread of the sensitivity; we found that the variation of the factor of the internal compensation coil is the same. We developed a novel calibration process using the readings of individual residual uncompensated voltages of the AMRs. The position of the current inside the measurement hole is estimated from the individual voltages considering the influence of external DC magnetic field such as the Earth’s field. During the calibration phase, the sensor outputs are measured for several positions of the current conductor inside the measuring hole. As a result of calibration the lookup table of error corrections is calculated and stored in the memory, and then these values are used for the correction during the measurement of the unknown current. This procedure reduces the off-center error from 0.4% to 0.06%.

A Fluxgate Current Sensor With an Amphitheater Busbar

  • DOI: 10.1109/TMAG.2016.2540523
  • Link: https://doi.org/10.1109/TMAG.2016.2540523
  • Department: Department of Measurement
  • Annotation:
    Large dc and ac electric currents are often measured by open-loop sensors without a magnetic yoke. A widely used configuration uses a differential magnetic sensor inserted into a hole in a flat busbar. The use of a differential sensor offers the advantage of partial suppression of fields coming from external currents. Hall sensors and AMR sensors are currently used in this application. In this paper, we present a current sensor of this type that uses novel integrated fluxgate sensors, which offer a greater range than magnetoresistors and better stability than Hall sensors. The frequency response of this type of current sensor is limited due to the eddy currents in the solid busbar. We present a novel amphitheater geometry of the hole in the busbar of the sensor, which reduces the frequency dependence from 15% error at 1 kHz to 9%.

AMR yokeless current sensor with improved accuracy

  • DOI: 10.1016/j.proeng.2016.11.301
  • Link: https://doi.org/10.1016/j.proeng.2016.11.301
  • Department: Department of Measurement
  • Annotation:
    We analyse the influence of real parameters of KMZ51 magnetic sensors on the accuracy and characteristic of AMR current measurement sensor. The device consists of a circular array of eight magnetic field sensors. The differences in sensitivity of individual AMRs, as well as bridge resistance, the resistance of compensation coil and compensation coil factor are discussed. Finally, we present the method how to compensate the mentioned errors by reading individual sensor outputs.

DC-Compensated Current Transformer

  • Authors: prof. Ing. Pavel Ripka, CSc., Draxler, K., Styblíková, R.
  • Publication: Sensors. 2016, 16(1), 114-123. ISSN 1424-8220.
  • Year: 2016
  • DOI: 10.3390/s16010114
  • Link: https://doi.org/10.3390/s16010114
  • Department: Department of Measurement
  • Annotation:
    Instrument current transformers (CTs) measure AC currents. The DC component in the measured current can saturate the transformer and cause gross error. We use fluxgate detection and digital feedback compensation of the DC flux to suppress the overall error to 0.15%. This concept can be used not only for high-end CTs with a nanocrystalline core, but it also works for low-cost CTs with FeSi cores. The method described here allows simultaneous measurements of the DC current component.

Effect of Electroplated Ni1-xFex Composition on the Field-Induced Anisotropy

  • DOI: 10.1109/TMAG.2016.2522563
  • Link: https://doi.org/10.1109/TMAG.2016.2522563
  • Department: Department of Measurement
  • Annotation:
    Field-induced anisotropy has been proposed as an effective method to produce ferromagnetic rings with radial anisotropy for fluxgate cores. Compared with stress-induced anisotropy, this method easily allows generating a radial anisotropy in electroplated rings. However, it is still not clear what the source of such anisotropy is. It has been suggested that the observed anisotropy could be the effect of the magnetocrystalline anisotropy present in the electroplated film because of the non-ideal stoichiometry of the alloy. If true, this would make impossible to electroplate films with field-induced anisotropy and, simultaneously, low magnetostriction, because this condition occurs at Ni81Fe19 composition where the magnetocrystalline anisotropy vanishes. In order to verify this hypothesis, we electroplated several rings changing the composition of the alloy, with and without radial magnetic field applied. It turned out that the field-induced anisotropy was independent on the composition of the film to a large extend, and it did not show any vanishing trend as we approach Ni81Fe19 composition. This suggests that it is, in fact, possible to obtain field-induced anisotropy and simultaneously low magnetostriction. Finally, we show how such radial field-induced anisotropy reduced the noise of the fluxgate by almost one order of magnitude.

Flugate Sensor With Pulse Feedback

  • Authors: prof. Ing. Pavel Ripka, CSc., Přibil, M., Schaeffer, V, Snoeij, M
  • Publication: IEEE Transactions on Magnetics. 2016, 52(5), ISSN 0018-9464.
  • Year: 2016
  • DOI: 10.1109/TMAG.2016.2524516
  • Link: https://doi.org/10.1109/TMAG.2016.2524516
  • Department: Department of Measurement
  • Annotation:
    Fluxgate sensors have typically only 100 μT range, which sometimes limits their applications. The main obstacle for increasing the measurement range is the power dissipated in their feedback coil. Until now, the feedback was always continuous. We suggest using pulse excitation only for the active part of the period, in which an output signal is present. In this paper, we show for the first time that if the sensor is excited by short pulses, the feedback need not be continuous, but it can be formed by the pulses slightly wider than the excitation pulses. We have shown that, in our case, the feedback current duty cycle can be only 17.25%. This means that for the same power, we can increase maximum feedback current and, thus, the range by the factor of three. We show that this can be done without compromising the sensor performance

Noise dependence on temperature in fluxgates with electroplated core

  • DOI: 10.1016/j.sna.2016.04.018
  • Link: https://doi.org/10.1016/j.sna.2016.04.018
  • Department: Department of Measurement
  • Annotation:
    Samples of electrodeposited fluxgate sensors with varying magnetostriction coefficient were manufactured and their noise was studied at various temperatures. We show that the noise of the fluxgate is, under some conditions, dependent on temperature. We studied such behaviour of the noise for samples with low and high magnetostriction and we verified that the both types of sensors presented low and high temperature dependent noise. Then we investigated as a possible source of noise the thermal cooling rate applied to the samples after electroplating and we verified that large thermal shock could induce mechanical stress and noise in the sensor.

Co-Based Amorphous Material for Giant Magneto-Impendance and Fluxgate Sensing Cores

  • Authors: Sarkar, P., Včelák, J., K Roy, R., K Panda, A., Mitra, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: IEEE Transactions on Magnetics. 2015, 51(11), ISSN 0018-9464.
  • Year: 2015
  • DOI: 10.1109/TMAG.2015.2431120
  • Link: https://doi.org/10.1109/TMAG.2015.2431120
  • Department: Department of Measurement
  • Annotation:
    Alloy composition (Co94Fe6)72.75Si12.25B13.25Cr1.75 was designed to develop nearly zero-magnetostrictive materials in the form of ribbons and wires to obtain suitable magnetic properties for use as giant magneto-impedance (GMI) and low-noise fluxgate sensor core. During the development of magnetic sensing core using amorphous wires of diameter 80 μm for GMI sensing, we observed a maximum impedance change (GMI ratio) of 430% with as-cast wires which further enhanced to 650% when annealed at 3000C for 5-minutes. The effect of temperature annealing and stress on the magnetic properties of fluxgate sensing core materials has been studied. Magnetic hysteresis loops were measured with 3 mm wide and 45 μm thickness amorphous ribbons on toroidal ring of 50 mm diameter for fluxgate sensor core. A coercivity of 10.57 A/m and saturation field of around 150 A/m was observed with as-quenched ribbon which improved to a coercivity of 2.16 A/m and saturation field about 100 A/m when annealed without stress just above its Curie temperature. An induced anisotropy transverse to excitation direction was achieved by applying temperature with stress and time (3000C/ 100 MPa/ 20-minutes) to use it for fluxgate sensor core.

Contactless Methods for Measuring Electrical Currents in Bulding Structures

  • Authors: prof. Ing. Pavel Ripka, CSc., Vyhnánek, J.
  • Publication: Sympozium Energeticky efektivní budovy 2015. Praha: Společnost pro techniku prostředí, 2015. pp. 243-247. 1. vydání. ISBN 978-80-02-02615-0.
  • Year: 2015
  • Annotation:
    Electric currents in building structures can cause electrochemical corrosion or interference in electrical systems in buildings. Currents can be introduced from the environment or may be caused by electromagnetic induction. In the paper we describe methods to measure these currents. We discuss related themes and creation and measurement of interfering magnetic fields. The article is based on experience from measurements in buildings and structures, which we conducted in cooperation with industrial partners.

Demagnetization of Current Transformers Using PWM Burden

  • DOI: 10.1109/TMAG.2014.2356574
  • Link: https://doi.org/10.1109/TMAG.2014.2356574
  • Department: Department of Electric Drives and Traction, Department of Measurement
  • Annotation:
    Current transformers (CTs) show large errors when they are magnetized by dc current. This error can be reduced after proper demagnetization. One of the methods to demagnetize the CT is to increase the core flux by increasing its burden. The burden should be adjusted according to the measured ac current. In this paper, we show that pulsewidth modulation switchable resistor can be used as variable burden for this application. This method enables to restore the nominal precision of the heavily magnetized CT from 2.5% back to 0.2% without interruption of the CT operation.

Effect of Stress Induced Anisotropy on the Noise of Ring-core Fluxgate

  • DOI: 10.1109/TMAG.2014.2358793
  • Link: https://doi.org/10.1109/TMAG.2014.2358793
  • Department: Department of Measurement
  • Annotation:
    In this paper we show how an anisotropy perpendicular to the direction of excitation is favourable to obtain low noise in fluxgate sensors. We produced ring cores by electroplating NiFe thin film (6 μm) over a bended copper substrate. After the electroplating process the sample was released and the back-stress induced anisotropy in the magnetic film due to magnetostriction of the material. As a result we obtained rings with regions showing hard behavior and orthogonal regions showing soft behavior. Then we used such rings as core for fluxgate and we measure both noise and sensitivity for different orientation of the ring in the pick-up coil. When the pick-up coil covers the area with anisotropy perpendicular to the direction of excitation the sensitivity is lower due to lower permeability but finally the noise is lower. On the other hand, rotating the core by 90 degrees the anisotropy becomes parallel to the direction of excitation and thus the sensitivity increases. Nevertheless, the noise also increases, showing that such anisotropy parallel to direction of excitation is unfavorable even if it brings higher sensitivity.

ELECTROMAGNETIC RESPONSE OF SOIL

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: XXI IMEKO WORLD CONGRESS - Full Papers. Prague: Czech Technical University in Prague, Faculty of Electrical Engineering, 2015. ISBN 978-80-01-05793-3.
  • Year: 2015
  • Department: Department of Measurement
  • Annotation:
    The possibility of measuring both timedomain and frequency-domain response on small soil samples would allow one to predict the influence of such soil on various types of mine detectors without field trial. We have measured the time-domain soil response on standard cylindrical samples. The time response to abruptly removed magnetic field is similar to 1/tx, where x is between 1.1 and 1.3. We have also measured frequency-domain response in the 400 Hz to 480 kHz band by various independent methods and compared with values calculated from the time response. This study shows that for soils with high content of nanoparticles the complete frequency characteristics should be measured instead of traditional two-point measurement

Electroplated FeNi ring cores for fluxgates with field induced radial anisotropy

  • DOI: 10.1063/1.4914874
  • Link: https://doi.org/10.1063/1.4914874
  • Department: Department of Measurement
  • Annotation:
    Being able to control the anisotropy of a magnetic core plays an important role in the development of a fluxgate sensor. Our aim is to induce anisotropy orthogonal to the direction of excitation because it generates a stable, low-noise fluxgate, as cited in the literature. In this paper, we present an original method for electroplating a ring core for a fluxgate with built-in radial anisotropy by performing the electroplating in a radial field produced by a novel yoke. The results show that the resulting anisotropy is homogeneously radial and makes the magnetization rotate, avoiding domain wall movement for low excitation fields.

Long-Range Magnetic Tracking System

  • Authors: Včelák, J., prof. Ing. Pavel Ripka, CSc., Zikmund, A.
  • Publication: IEEE Sensors Journal. 2015, 15(1), 491-496. ISSN 1530-437X.
  • Year: 2015
  • DOI: 10.1109/JSEN.2014.2345576
  • Link: https://doi.org/10.1109/JSEN.2014.2345576
  • Department: Department of Measurement
  • Annotation:
    This paper presents a new long-range full 3-D magnetic tracking system for horizontal directional drilling, and describes its performance. The system is able to determine the full 3-D mutual position of the receiver with respect to the transmitter. The system presented here belongs to the category of hybrid trackers using an active magnetic ranger, an optical gyro, and three micromachined inclinometers. The gyro is used for dead-reckoning navigation over long distances (up to 2 km), and the magnetic tracking system, consisting of a coil magnetic transmitter and a magnetometer receiver, is used when two drill heads are approaching each other beneath the surface at the assumed meeting point. The functionality of the system was verified for the maximum range of 17 m with 1,2-m rms accuracy, and with 0,34-m rms accuracy for the range below 10 m.

Magnetostriction Offset of Fluxgate Sensors

Noise dependence on temperature in fluxgates with electroplated core

  • DOI: 10.1016/j.proeng.2015.08.834
  • Link: https://doi.org/10.1016/j.proeng.2015.08.834
  • Department: Department of Measurement
  • Annotation:
    Samples of electrodeposited fluxgate sensors with varying magnetostriction coefficient were manufactured and their noise was studied at various temperatures. We show that the noise component caused by magnetostriction is, under some conditions, dependent on temperature. The conditions affecting the temperature dependence of noise are also discussed. (C) 2015 article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-ric-nd/4.0/) Peer-review under responsibility of the organizing committee of EUROSENSORS The Authors. Published by Elsevier Ltd. This is an open access

Precise Magnetic Sensors for Navigation and Prospection

  • Authors: Včelák, J., prof. Ing. Pavel Ripka, CSc., Zikmund, A.
  • Publication: The Journal of Superconductivity and Novel Magnetism. 2015, 28(3), 1077-1080. ISSN 1557-1939.
  • Year: 2015
  • DOI: 10.1007/s10948-014-2636-7
  • Link: https://doi.org/10.1007/s10948-014-2636-7
  • Department: Department of Measurement
  • Annotation:
    Navigation, position tracking, search for unexploded ammunition, and geophysical prospection of magnetic or conducting ore are key applications where very small magnetic field signatures and field increments should be detected in the presence of the Earth's magnetic field, typically 50,000 nT. The industry calls for a new generation of portable vectorial magnetic sensors with a precision better than 0.1 nT. This error requirement includes not only sensor noise but also linearity, cross-field error, hysteresis, and perming and also temperature drift of the sensitivity and mainly the offset drift. For application on moving platform, the sensors should also have fast response. We will show that these requirements can be met only by fluxgate sensors. On the other hand, mass market requires cheap, low-power, and small magnetic sensors for portable gadgets; the typical application is compass in mobile phone, with precision of several degrees, corresponding to a 100-nT precision. For these applications, anisotropic magnetoresistance (AMR) sensor is dominant, while integrated fluxgates may penetrate the high-end market.

Precise Scalar Calibration of a Tri-Axial Braunbek Coil System

  • Authors: Zikmund, A., prof. Ing. Pavel Ripka, CSc., Ketzler, R., Harcken, H., Albrecht, M.
  • Publication: IEEE Transactions on Magnetics. 2015, 51(1), ISSN 0018-9464.
  • Year: 2015
  • DOI: 10.1109/TMAG.2014.2357783
  • Link: https://doi.org/10.1109/TMAG.2014.2357783
  • Department: Department of Measurement
  • Annotation:
    A calibration of the well-defined Braunbek coil system was carried out using the scalar method. The whole measuring setup was designed to minimize the uncertainty of the scalar calibration procedure. The measurement time as well as the sampling ratio were adjusted to reduce the influence of the ambient magnetic field variation. We calibrated the coil sensitivity with the uncertainty of 30 ppm and orthogonality with the uncertainty <0.01°. The results were compared with a different technique.

ROTATIONAL SPEED MEASUREMENT AND ANGULAR POSITION REFERENCE FOR A CRYOGENIC PROPELLANT ELECTRIC PUMP

  • Department: Department of Measurement
  • Annotation:
    Hall sensors with an analog output were used as rotational speed sensors and provided an angular position reference for other diagnostics measurements during a cryogenic Propellant Electric Pump (PEP) test campaign. Frictionless foil bearing, which is a very important technology that needs to be well characterized during the tests, was tested in the PEP. Hall sensor outputs helped to process signals from eddy current radial and axial shaft displacement sensors and piezoelectric vibration sensors. The Hall sensor signal was also used as the main motor speed feedback signal for the test-bench control system.

AC/DC Current Transformer With Single Winding

  • Authors: prof. Ing. Pavel Ripka, CSc., Draxler, K., Styblíková, R.
  • Publication: IEEE Transactions on Magnetics. 2014, 50(4), 1-4. ISSN 0018-9464.
  • Year: 2014

AMR Proximity Sensor With Inherent Demodulation

  • DOI: 10.1109/JSEN.2014.2325406
  • Link: https://doi.org/10.1109/JSEN.2014.2325406
  • Department: Department of Measurement
  • Annotation:
    Our novel position sensor is based on the combination of the eddy-current and permeability effects. The primary field is excited by a coil, but instead of induction coil, the sensing part uses anisotropic magnetoresistor (AMR), which also measures dc magnetic field. As the AMR is being flipped at the excitation frequency, the sensor is self-demodulated and the output is dc. The AMR sensitivity does not depend on frequency; therefore, this sensor can be used at ultralow frequencies, where coils fail as sensors. We show the response of our sensor to ferromagnetic and nonferromagnetic metals and possibilities to distinguish between them. We also show that our sensor can measure position through the conducting sheath.

DC-compensated Current Transformer

  • Authors: prof. Ing. Pavel Ripka, CSc., Draxler, K., Styblíková, R.
  • Publication: Proceedings of Instrumentation and Measurement Technology Conference (I2MTC) 2014. Vail, Colorado: IEEE Instrumentation and Measurement Society, 2014, pp. 212-215. ISSN 1091-5281. ISBN 978-1-4673-6385-3.
  • Year: 2014
  • DOI: 10.1109/I2MTC.2014.6860737
  • Link: https://doi.org/10.1109/I2MTC.2014.6860737
  • Department: Department of Measurement
  • Annotation:
    Instrument current transformers (CTs) can be heavily influenced by DC component in the measured current. 50 A DC current in 500 A CT may cause 40% error in the current and power measurement. For small power factors the situation can be even worse due to 20 deg phase error. We use digital feedback compensation of the DC flux to suppress the overall error to 0.15%.

Electroplated Multi-ring Core Planar Fluxgate

  • DOI: 10.1016/j.proeng.2014.11.376
  • Link: https://doi.org/10.1016/j.proeng.2014.11.376
  • Department: Department of Measurement
  • Annotation:
    In this paper we studied multi-ring planar fluxgate with different number of rings. In particular we investigated the effect of the number of rings on the sensitivity and noise of the sensors. Multi-ring cores were expected to return lower noise due to mutual compensation of uncorrelated noise of every ring. Nevertheless, we observed an increase of noise for cores with higher number of rings. We believe this is due to non-uniform composition of the electroplated film, which make the inner rings magnetostrictive and therefore source of larger noise.

Fluxgate Offset Study

  • DOI: 10.1109/TMAG.2014.2329777
  • Link: https://doi.org/10.1109/TMAG.2014.2329777
  • Department: Department of Measurement
  • Annotation:
    Offset and its long-term stability is a weak point of fluxgate sensors. Even the ultrastable sensors kept at no vibrations and stable temperature at magnetic observatories show offset drift. Such drift of the fluxgate triaxial sensor can only be partly corrected by the scalar resonance magnetometer. Periodical calibration of absolute reading should be made using nonmagnetic theodolite. In this paper, we study the origin of fluxgate offset. We distinguish the real magnetic sensor offset from the offset contributions originating in the false second harmonics signal that leaks to the sensor output from the distortion in the excitation signal, or which is borne as harmonic distortion when the signal processing electronics are subjected to the large first harmonic signal leaking from the excitation. We analyze the offset dependence on the angular position of the sensor core and its response to large field shocks. The experiments give an indication that only a part of the magnetic offset stems from a remanence of magnetically hard core regions. The residual part may be caused by a magnetostrictive signal, belonging to false signal contributions, but not considered in previous studies.

Influence of Magnetostriction of NiFe Electroplated Film on the Noise of Fluxgate

  • DOI: 10.1109/TMAG.2014.2327105
  • Link: https://doi.org/10.1109/TMAG.2014.2327105
  • Department: Department of Measurement
  • Annotation:
    We electroplated NiFe thin-film over a copper layer using different current density. Magnetostriction is changed from negative to positive values, with minimum magnetostriction found at around Fe19Ni81 composition. When we used these ring cores as base for a fluxgate we observed that the noise rapidly rises as the absolute value of magnetostriction increases, while the minimum noise is achieved at lowest value of magnetostriction.

Study of Stress-Induced Anisotropy in METGLAS 2714

  • DOI: 10.1109/TMAG.2014.2329992
  • Link: https://doi.org/10.1109/TMAG.2014.2329992
  • Department: Department of Measurement
  • Annotation:
    METGLAS 2714AZ material has been stress annealed without any applied magnetic field to obtain suitable magnetic properties for use as low-noise fluxgate sensor core. During the development of magnetic cores, we observed an unusual change of the anisotropy direction on Co-based amorphous alloy of METGLAS 2714 AZ. The anisotropy direction moves from its original direction along the ribbon axis to the transverse direction as expected but for short annealing times the process is not monotonous. This occurs when annealing is performed above the Curie temperature. We explain it as a mixture of different anisotropies, which are built and released during the annealing process, since the 2714AZ ribbon has manufacturer-induced anisotropy in ribbon axis. The effect of ribbon cooling on the ribbon properties is also shown as annealing in the radiation furnace was done in different ways.

AMR Proximity Sensor with Inherent Demodulation

  • DOI: 10.1109/ICSENS.2013.6688289
  • Link: https://doi.org/10.1109/ICSENS.2013.6688289
  • Department: Department of Measurement
  • Annotation:
    The position sensor is based on the combination of the eddy-current and permeability effects. The primary field is excited by a coil, but instead of induction coil, the sensing part uses anisotropic magnetoresistor (AMR) which also measures DC magnetic field. As the AMR is being flipped by the excitation frequency, the sensor is self-demodulated and the output is DC. The AMR sensitivity does not depend on frequency; therefore this sensor can be used at ultralow frequencies, where coils fail as sensors. We show the response of our sensor to ferromagnetic and non-ferromagnetic metals and possibilities to distinguish between them. We also show that our sensor can measure position through the conducting sheath.

Calibration of the 3D Coil System's Orthogonality

  • Authors: Zikmund, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: IEEE Transactions on Magnetics. 2013, 49(1), 66-68. ISSN 0018-9464.
  • Year: 2013
  • DOI: 10.1109/TMAG.2012.2218583
  • Link: https://doi.org/10.1109/TMAG.2012.2218583
  • Department: Department of Measurement
  • Annotation:
    Two methods were tested for calibration procedures of the 3D coil system which is used as a source part of the magnetic tracker. Precise magnetometer’s positions with respect to the coil system were used for determining of the non-orthogonality of the coil system as well as for determining of the magnetic moment. The needed number of the reference positions was measured to calculate six unknown calibrated parameters. In comparison, the 3D coils system was also calibrated with a method which employs the orthogonal homogenous AC field generated in Helmholtz coils. The misalignment of up to two degrees was discovered.

Low frequency noise of anisotropic magnetoresistors in DC and AC-excited metal detectors

  • Authors: Vyhnánek, J., Ing. Michal Janošek, Ph.D., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Sensors & Their Applications XVII. Bristol: IOP Publishing Ltd, 2013, pp. 1-5. Journal of Physics Conference Series. ISSN 1742-6588. Available from: http://iopscience.iop.org/1742-6596/450/1/012031
  • Year: 2013
  • DOI: 10.1088/1742-6596/450/1/012031
  • Link: https://doi.org/10.1088/1742-6596/450/1/012031
  • Department: Department of Measurement
  • Annotation:
    AMR sensors are chosen to be evaluated in low noise measurements with combined processing of DC and AC excitation field with respect to the arrangement of processing electronics. Circuit with a commercial AMR sensor HMC1001 and AD8429 preamplifier using flipping technique exhibited 1-Hz noise as low as 125 pT/sqrtHz. Without flipping, the 1-Hz noise increased to 246 pT/sqrtHz.

Magnetic Anisotropy and Giant Magnetoimpedance in NiFe Electroplated on Cu Wires

  • DOI: 10.1166/sl.2013.2791
  • Link: https://doi.org/10.1166/sl.2013.2791
  • Department: Department of Measurement
  • Annotation:
    Magnetic anisotropy of NiFe films electrodeposited on Cu wires was studied. The influence of current density, magnetic field and strain applied during deposition on the anisotropy constant and easy axis orientation was investigated using AC hysteresis loop tracer and magneto-impedance measurements. Magnetic field applied during the electrodeposition induces weak magnetic anisotropy with the easy axis parallel to the field and features typical for atomic pair ordering mechanism.

Magnetopneumography Using Optical Position Reference

  • DOI: 10.1166/sl.2013.2805
  • Link: https://doi.org/10.1166/sl.2013.2805
  • Department: Department of Measurement
  • Annotation:
    The presented development utilizes a smart camera and retro-reflective optical markers for independent measurement of the subject body position during magnetic field scanning. This is critical in order to avoid distorting of geometrical ordering of the measured data by inadvertent movement of the subject on scanning bed in both lateral and angular way.

Measurement of DC Currents in the Power Grid by Current Transformer

  • Authors: prof. Ing. Pavel Ripka, CSc., Draxler, K., Styblíková, R.
  • Publication: IEEE Transactions on Magnetics. 2013, 49(1), 73-76. ISSN 0018-9464.
  • Year: 2013
  • DOI: 10.1109/TMAG.2012.2216862
  • Link: https://doi.org/10.1109/TMAG.2012.2216862
  • Department: Department of Measurement
  • Annotation:
    DC currents in power grids are mainly caused by geomagnetic activity especially during magnetic storms. It is desirable to monitor these currents to prevent saturation of transformers, which may cause blackout. However, adding DC current sensors to existing installations would be very costly.We suggest to convert some of the existing current transformers to fluxgate DC current sensors by injecting AC excitation current into their secondary winding. We successfully tested this concept on 500 A current transformer. The achievable accuracy is 10% for DC currents and 1.5% for AC currents, which is sufficient for protection and monitoring purposes.We analyze the DC current sensitivity dependence on the (changing) grid impedance, and we show that the sensitivity can be stabilized by controlling the secondary voltage component at the excitation frequency. Excitation current injected into the grid also depends on the grid impedance, but for realistic conditions it is below 2 A.

Metal Detector Signal Imprints of Detected Objects

  • DOI: 10.1109/TMAG.2012.2220959
  • Link: https://doi.org/10.1109/TMAG.2012.2220959
  • Department: Department of Measurement
  • Annotation:
    Humanitarian de-mining missions are activities in which an operator safety and time consumption are key issues. To increase a discrimination ability of ATMID metal detector, which we have been using, we extended the capability of the detector with mounting Inertial Measurement Unit (IMU) supplemented by two optical distance sensors on the detector head. That enabled us to perform dead reckoning based on accelerations and angular rates measured by IMU in all three axes. Optical distance sensors have been used for compensation purposes and an initial distance measurement. Our main aim was to interconnect magnetic imprint sensed by the detector with precise localization of its head, which led to imprint size estimation as well as its position. Due to low-cost MEMS (Micro-Electro-Mechanical System) based IMU implementation we have had to deal with unstable dead reckoning outcomes. For this reason we used our designed Complex Magnetic Markers (CMMs) which demarked a searched area plus provided us with precise positioning at its both edges. The main contribution of this paper is in the study and identification of CMM magnetic imprints characteristics and their differences related to various aspects of CMM usage during de-mining procedure and its conditions. The characteristics of CMMs have been studied and analyzed according to several laboratory experiments and results are presented.

Microwire Electroplated Under Torsion as Core for Coil-Less Fluxgate

  • DOI: 10.1166/sl.2013.2784
  • Link: https://doi.org/10.1166/sl.2013.2784
  • Department: Department of Measurement
  • Annotation:
    In this paper we present electroplated magnetic microwires with helical anisotropy given by torsion during electroplating. These wires have been used as core for coil-less fluxgate: linearity, noise and resolution have been measured, and they showed better performances than microwires with field induced helical anisotropy. Therefore, we conclude that electroplating under torsion is the most promising method for manufacturing microwires for coil-less fluxgates.

Security Applications of Magnetic Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Sensors & Their Applications XVII. Bristol: IOP Publishing Ltd, 2013. Journal of Physics Conference Series. ISSN 1742-6588.
  • Year: 2013
  • DOI: 10.1088/1742-6596/450/1/012001
  • Link: https://doi.org/10.1088/1742-6596/450/1/012001
  • Department: Department of Measurement
  • Annotation:
    Magnetic sensors are often used for security and military applications such as detection, discrimination and localization of ferromagnetic and conducting objects, navigation, position tracking and antitheft systems. We give only general overview, few remarks and some interesting references on these applications.

Temperature Stability of AMR Sensors

  • DOI: 10.1166/sl.2013.2807
  • Link: https://doi.org/10.1166/sl.2013.2807
  • Department: Department of Measurement
  • Annotation:
    Magnetic sensors working in increased temperature range are required for many applications, such as: - down-hole orientation sensors for oil & gas exploration and production - angular position and speed measurement for turbines - engine sensors for automotive industry - electric current sensors and also for some planetary space missions (e.g. Mercury).

Temperature Stability of Sensitivity and Offset in Coil-less Fluxgate Sensors

  • Department: Department of Measurement
  • Annotation:
    Temperature stability of fluxgate sensors is very important issue, because this kind of sensors has found applications in several field where temperature is not constant. Temperature determines dilatation of the material which can result in mechanical stress to the core. In this paper we compare orthogonal fluxgates in coil-less mode, obtained with bi-phase Copper/Permalloy microwires with and without glass layer between them. We show that a glass layer between Copper and Permalloy strongly decreases the dependence of both offset and sensitivity on the temperature. We explain this by the fact that glass has lower thermal expansion coefficient than copper, therefore it compensates its dilatation which is source of mechanical stress for the Permalloy. © 2010 FEI STU.

Testing and Calibration of Magnetic Sensors

  • DOI: 10.1166/sl.2013.2806
  • Link: https://doi.org/10.1166/sl.2013.2806
  • Department: Department of Measurement
  • Annotation:
    While the measurement and testing of magnetic materials and transformers is well standardized, there is no standard for testing of magnetic sensors. This paper makes an overview of “Good Practices” how to obtain and express magnetic sensors parameters, which are reliable, comparable and reproducible. Some parameters are common to all sensors: sensitivity, offset and their temperature stability, linearity, hysteresis, noise and dynamic response. Other parameters are specific to magnetic sensors and we cover them in more detail: perming, crossfield response and angular alignment. We also describe calibration methods and devices and give typical testing and calibration results of common sensors.

A Magnetic Distance Sensor with High Precision

  • DOI: 10.1016/j.sna.2012.05.003
  • Link: https://doi.org/10.1016/j.sna.2012.05.003
  • Department: Department of Measurement
  • Annotation:
    A magnetic distance sensor working at very low frequency has been developed to measure distances up to 1 m. The principle is similar to that of the 3-D magnetic tracker, but the system is optimized to minimize the error in distance for static measurements. The system is not affected by conductive objects. The uncertainty caused by noise and interference is below 2 mm, even in a noisy environment. The measurement time of 3 min can be decreased to 1 min, depending on the amplitude of the interferences and the required accuracy. After applying corrections, systematic error of 5 mm was achieved by using a calibration model. The system is scalable up to 20 m range.

AMR Gradiometer for Mine Detection

  • DOI: 10.1016/j.sna.2012.03.007
  • Link: https://doi.org/10.1016/j.sna.2012.03.007
  • Department: Department of Measurement
  • Annotation:
    Anisotropic magnetoresistors (AMRs) are used to build an advanced mine detector. The sensing head involves a gradiometric pair of AMR sensors and a continuous-wave driven excitation coil, so the gradiometer is capable of detection of ferromagnetic materials as well as diamagnetic metals. The sensors are specially arranged to suppress the large AC-excitation field, so the mine detector senses both DC and AC field gradient responses of the object of interest. Being limited by the sensor and electronics noise of 268 pT/sqrtHz at 1 kHz, we were able to detect a 50 mm × 50 mm × 1.5 mm aluminum test object in a 20 cm depth using a 150 uT, 1-kHz excitation field.

Complex Markers for a Mine Detector

  • DOI: 10.1109/TMAG.2011.2172933
  • Link: https://doi.org/10.1109/TMAG.2011.2172933
  • Department: Department of Measurement
  • Annotation:
    This paper describes a novel type of metal markers for eddy current metal detection systems using precise positioning information. The new design for metal markers which are compounded by an ordered array of metal plates with different magnetic parameters has three fundamental advantages: 1. the markers are sensed directly by the metal detector, and no additional hardware is required; 2. the signatures are sharp; 3. not only the position but also the speed of the detector head can be evaluated. In the case of a stand-alone inertial navigation system for evaluating the position of the detector, the precision would be low due to the sensor noise and its integration. However, knowledge of the relative positions and potentially of the detector head speed over the markers can be used as auxiliary information, and so the eddy-current mapping system will be capable of determining the size of the magnetic imprint of a detected metal object and its position relative to the markers. This increases the reliability of the object discrimination during humanitarian demining, and decreases the numbers of false alarms, which nowadays constitute 99.9% of all alarms emitted by an ordinary mine detector.

Field Annealed Closed-path Fluxgate Sensors Made of Metallic-glass Ribbons

  • Authors: Butvin, P.B., Ing. Michal Janošek, Ph.D., prof. Ing. Pavel Ripka, CSc., Butvinová, B.B., Švec sr., P.Š., Kuzminski, M.K., Švec Jr., P.Š., Janičkovič, D.J., Vlasák, G.V.
  • Publication: Sensors and Actuators. 2012, 2012(184), 72-77. ISSN 0924-4247.
  • Year: 2012
  • DOI: 10.1016/j.sna.2012.07.001
  • Link: https://doi.org/10.1016/j.sna.2012.07.001
  • Department: Department of Measurement
  • Annotation:
    One-step field annealing of Co-based metallic glass was chosen to acquire low-magnetostrictive material with anisotropy required to reduce noise by favoring magnetization rotation. Despite the risk of bending stress aggravated by small -12 mm diameter, the ring cores reproducibly achieved noise 7 pT/√Hz @ 1 Hz.

Fluxgate Sensor and Real Operating-mode B-H Curve

  • Department: Department of Measurement
  • Annotation:
    The core materials are usually characterized in well-defined modes. Either static B-H loops are measured or dynamic loops are recorded with sinewave H or better sinewave B waveform as required by IEC standard. Unfortunately, neither of these represents well the real operating conditions in fluxgate core, especially when the fluxgate is tuned and excitation current peak value is optimized by appropriate capacitor. Dynamic B-H loops can be recorded by digital acquisition and signal processing in real operating conditions.

Geometrical Selectivity of Current Sensors

  • Department: Department of Measurement
  • Annotation:
    We analyze the Influence of extemal "unclamped" currents on contactless current sensors, especially the gradient sensor arrays and the current clamps. Best suppression of close currents can be achieved by using magnetic yoke with optimized shielding. DCIAC fluxgate current clamps of our design have low perming error and suppress externa' current by the factor of 20 000.

Long Range Magnetic Localization System

  • Authors: Včelák, J., Zikmund, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Journal of Electrical Engineering. 2012, 63(7), 19-22. ISSN 1335-3632.
  • Year: 2012
  • Department: Department of Measurement
  • Annotation:
    Paper presents long range magnetic position estimation system which evaluates mutual position between transmitter and receiver in applications where other methods are not available. System is designed for deep subsurface localization between transmitter and receiver. The localization is based on excitation of the coils in transmitter with the known current pattern and evaluation of this response on the receiver. The transmitter consists of a set of two specially designed coils (axial and radial coil or two axial coils). The coils are optimized to provide maximal magnetic moment from available battery source and also meet the dimension constrains. The transmitter excites the coils consecutively with predefined current pattern (number of current pulses of known l ength and amplitude). The magnetic response of the excitation is recorded and evaluated on the receiver side by two magnetometers.

Long-range Magnetic Tracking

  • Authors: prof. Ing. Pavel Ripka, CSc., Zikmund, A., Včelák, J.
  • Publication: IEEE SENSORS 2012 - Proceedings. Piscataway: IEEE Service Center, 2012. pp. 2094-2097. IEEE Catalog Number CFP12SEN-USB. ISSN 1930-0395. ISBN 978-1-4577-1765-9.
  • Year: 2012
  • DOI: 10.1109/ICSENS.2012.6411065
  • Link: https://doi.org/10.1109/ICSENS.2012.6411065
  • Department: Department of Measurement
  • Annotation:
    A long range full 3D magnetic tracking system and its performance is described in this paper. The system is able to determine full 3D position of the receiver with respect to the transmitter. The presented system belongs to hybrid trackers using active magnetic ranger, three optical gyros and three micromachined inclinometers. It has 20 m range and for distances below 5 m the position accuracy is 50 cm.

Magnetopneumography - Incorporation of Optical Position Reference

  • Department: Department of Measurement
  • Annotation:
    Magnetopneumography is a non-invasive method for estimation of amount and spatial distribution of ferromagnetic dusts deposited in lungs of metal workers. Our setup consisting of a set of fluxgate probes is sensitive enough to detect remanent fields of small amounts of previously magnetized magnetite dust. Utilization of a smart camera and retro-reflective optical markers makes the scanning independent of operator's errors and helps to scan the magnetic field independently of the actual subject body position on the bed.

Single-core fluxgate gradiometer with simultaneous gradient and homogeneous feedback operation

  • DOI: 10.1063/1.3676238
  • Link: https://doi.org/10.1063/1.3676238
  • Department: Department of Measurement
  • Annotation:
    The fluxgate gradiometer comprises of a standard pickup/feedback coil and an additional gradient pickup/feedback coil with two separate electronic blocks. The gradient coil is concentric and coaxial with the homogeneous pickup/feedback coil. The gradient coil works as a pick-up coil and it also generates the compensating field which well approximates a first order gradient field with zero spatial-mean value.

Suppression of Environmental Noise in Magnetopneumography by the use of Higher Order Gradients

  • DOI: 10.1109/TMAG.2011.2172200
  • Link: https://doi.org/10.1109/TMAG.2011.2172200
  • Department: Department of Measurement
  • Annotation:
    We use fluxgate magnetometer for measuring remanent field of contaminated volume (current experiments are mostly on phantoms). For earlier experiments we used simple 6-channel magnetometer with improvised probe holder and we used multiple 1st order gradients. However, geometrical and other instabilities forced us to upgrade both the mechanical assembly and the fluxgate electronics. The environmental noise from relatively close sources is apparent even in 1st order gradients and thus - now with more stable electronics - we evaluated 2nd order gradients in order to obtain better signal.

Uncertainty Analysis of Calibration of the 3D Coil System

  • Authors: Zikmund, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Journal of Electrical Engineering. 2012, 63 90-93. ISSN 1335-3632.
  • Year: 2012
  • Department: Department of Measurement
  • Annotation:
    The scalar calibration of the 3D coil system can be used as an efficient metrological method to identify all coil system's parame- ters. To express the method accuracy, the uncertainty of sensitivity establishing has been analytically calculated and the uncertainty of the orthogonal angles, which are numerically calculated parameters, , was evaluated with the Monte Carlo method. The method uncertainty was affected mostly by the calibration current stability and current measurements.

AMR Gradiometer for Mine Detection and Sensing

  • DOI: 10.1016/j.proeng.2011.12.089
  • Link: https://doi.org/10.1016/j.proeng.2011.12.089
  • Department: Department of Measurement
  • Annotation:
    We used anisotropic magnetoresistors (AMR's) to build an advanced mine detector. The sensing head involves a gradiometric pair of AMR sensors and a continuous-wave driven excitation coil, so the gradiometer is capable of detection ferromagnetic materials as well as diamagnetic metals. The sensors are specially arranged to suppress the large AC-excitation field, so the mine detector senses both DC and AC field gradient responses of the object of interest. Being limited by the sensor noise of 214 pTrms/sqrtHz at 1 kHz, we were able to detect an 50 mm x 50 mm x 1.5 mm aluminum test object in a 20 cm-depth using a 300uT, 1kHz excitation field.

CW Metal Detector Based on AMR Sensor Array

  • Authors: Ing. Michal Janošek, Ph.D., Vyhnánek, J., prof. Ing. Pavel Ripka, CSc.,
  • Publication: IEEE Sensors 2011 - Proceedings. Limerick: IEEE Sensors Council, 2011, pp. 1515-1517. ISSN 1930-0395. ISBN 978-1-4244-9288-6. Available from: http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=6127370
  • Year: 2011
  • DOI: 10.1109/ICSENS.2011.6127370
  • Link: https://doi.org/10.1109/ICSENS.2011.6127370
  • Department: Department of Measurement
  • Annotation:
    We developed an eddy-current metal detector with Anisotropic Magnetoresistors (AMRs) arranged in a 4x4 array. The magnetoresistive sensors in a gradiometric configuration are sensing the vertical component of a magnetic field - either originating from magnetized ferromagnetic bodies or induced by 1-kHz, alternating continuous-wave excitation. The AMRs are arranged so that the electronics can suppress the homogeneous Earth field and the large excitation field. The mine-detector was in first constructed as a standard handheld device. The presented results show that the performance is limited by the noise of the selected magnetoresistive sensor. If the size of the sensor array was increased, the system could form an advanced towed-mine-detector for quick, large-scale demining purposes.

Explosive Remnants of Wars Differentiation

  • Department: Department of Measurement
  • Annotation:
    The ability to differentiate between metal garbage and unexploded ordnance is the key point of the newest metal detectors development. This paper describes the methodology of the differentiation which would improve currently used mine detector performance. The ability relies on the metal detector output phase and amplitude evaluation.

Geometrical Selectivity of Current Sensors

  • Department: Department of Measurement
  • Annotation:
    We analyze the influence of external "unclamped" currents to contactless current sensors, especially the current clamps. Best suppression of close currents can be achieved by using magnetic yoke with optimized shielding. DC/AC fluxgate current clamps of our design have low perming error and suppress external current by the factor of 20 000.

Magnetic Tracker with High Precision

  • Authors: Zikmund, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Procedia Engineering. 2011, 25(25), 1617-1620. ISSN 1877-7058.
  • Year: 2011
  • DOI: 10.1016/j.proeng.2011.12.400
  • Link: https://doi.org/10.1016/j.proeng.2011.12.400
  • Department: Department of Measurement
  • Annotation:
    3-D magnetic tracker working at very low frequency was developed to measure distances up to 1 m. The uncertainty caused by noise and interference is below 1 mm even in the noisy environment. The measurement time of 3 minutes can be decreased to 1 s depending on the amplitude of interferences and required accuracy. Systematic errors of ±1 cm can be corrected by using calibration model.

Advances in Magnetic Field Sensors

Advances in Magnetic Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: IMEKO Symposium TC-4, TC-19 & IWADC Instrumentation for the ICT Area. Košice: Technical University of Košice, 2010. ISBN 978-1-61782-338-1.
  • Year: 2010
  • Department: Department of Measurement
  • Annotation:
    Magnetic sensors serve not only for the measurement of magnetic field, but also to measure position, speed, force, torque, electric current and other variuables.

Coil-less Fluxgate Effect in (Co0.94Fe0.06)72.5Si12.5B15 Amorphous Wires

  • Authors: Atalay, S., prof. Ing. Pavel Ripka, CSc., Bayri, N.
  • Publication: Journal of Magnetism and Magnetic Materials. 2010, 322(4), 2238-2243. ISSN 0304-8853.
  • Year: 2010

Coil-less Fluxgate Operated in Feedback Mode by means of DC Current

  • DOI: 10.1109/ICSENS.2010.5690109
  • Link: https://doi.org/10.1109/ICSENS.2010.5690109
  • Department: Department of Measurement
  • Annotation:
    We developed a novel method which allows us to operate the coil-less fluxgate in a feedback-loop without the need of any external coil. The external field is nulled by adding a compensating current to the sinusoidal excitation current with proper sign. In this way, we can extend the linear range of the coil-less fluxgate, for high measured fields.

Crossfield Effect in Commercial Fluxgate and AMR Sensors

  • Department: Department of Measurement
  • Annotation:
    Crossfield effect often seriously limits the accuracy of magnetic sensors. However, this effect is only rarely discussed by sensor. manufacturers and users. In the case of bulk fluxgates, crossfield error in the Earth's field can be suppressed by proper design below 3 nT p-p for the race-track and rod fluxgates and also for carefully designed ring-core sensors. Crossfield for miniature fluxgate can be significantly higher mainly due to imperfections in the geometry- for PCB fluxgate we measured 60 nT error.

Depth Estimation of Metal Objects

  • DOI: 10.1016/j.proeng.2010.09.102
  • Link: https://doi.org/10.1016/j.proeng.2010.09.102
  • Department: Department of Measurement
  • Annotation:
    It is very difficult to estimate depth of a metal object using signal of a traditional eddy-current metal detector which moves in constant distance from the ground. We show that the information about the object size and depth can be acquired from this signal during the detector lift-off. This could increase the discrimination ability of mine detectors which results in more efficient, safer and faster demining process.

Double Coil-less Fluxgate in Bridge Configuration

Electric Current Sensors: a Review

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Measurement Science and Technology. 2010, 21(11), 112001-112024. ISSN 0957-0233.
  • Year: 2010
  • DOI: 10.1088/0957-0233/21/11/112001
  • Link: https://doi.org/10.1088/0957-0233/21/11/112001
  • Department: Department of Measurement
  • Annotation:
    The review makes a brief overview of traditional methods of measurement of electric current and shows in more detail relatively new types of current sensors. These include Hall sensors with field concentrators, AMR current sensors, magneto-optical and superconducting current sensors. The influence of the magnetic core properties on the error of the current transformer shows why nanocrystalline materials are so advantageous for this application. Built-in CMOS current sensors are important tools for monitoring the health of integrated circuits. Of special industrial value are current clamps which can be installed without breaking the measured conductor.

Field-Programmable Gate Array-based fluxgate magnetometer with digital integration

  • DOI: 10.1063/1.3360773
  • Link: https://doi.org/10.1063/1.3360773
  • Department: Department of Measurement
  • Annotation:
    In this paper, a digital magnetometer based on printed circuit board fluxgate is presented. The fluxgate is pulse excited and the signal is extracted by gate integration. We investigate the possibility to perform integration on very narrow gates (typically 500 ns) by using digital techniques.

Magnetic Microwires for Orthogonal Fluxgates Electroplated with Pulse Current

  • DOI: 10.1016/j.proeng.2010.09.274
  • Link: https://doi.org/10.1016/j.proeng.2010.09.274
  • Department: Department of Measurement
  • Annotation:
    We fabricated microwires with pulsing current, and we studied their magnetic properties as well as their behavior when employed for orthogonal fluxgate. The noise at 1 Hz is minimum for duty cycle between 60% and 80%, whereas it increases for dc and lower duty cycles. However, wires electroplated with low duty cycle show much wider linear range than those realized with high duty cycle. Thus, we derive that high duty cycle must be preferred if the orthogonal fluxgate is used in feedback mode, whereas wires electroplated with lower duty cycle are preferred if the sensor is used in open loop.

Magnetic Microwires With Field-Induced Helical Anisotropy for Coil-Less Fluxgate

  • DOI: 10.1109/TMAG.2010.2045885
  • Link: https://doi.org/10.1109/TMAG.2010.2045885
  • Department: Department of Measurement
  • Annotation:
    We present a new method for production of magnetic microwire with helical anisotropy. Coil-less fluxgate sensors are generally composed of a bimetallic wire excited by an alternating current; in order for the wire to work in coil-less fluxgate mode, the magnetic layer of the wire needs to have helical anisotropy.

Mine Detector with Discrimination Ability

  • Department: Department of Measurement
  • Annotation:
    Metal detectors are widely used to detect Explosive Remnants of War such as landmines and Unexploded Ordnance. Almost all professional detectors are based on the eddy current principle. Currently count of false alarms rises up to 99.9% of total alarms count. Discrimination ability added to professional mine detector is therefore highly required by demining community. We show two complementary methods: using vertical signal profile and horizontal spatial maps. This is achieved by adding vertical distance sensor and inertial positioning unit to the search head. Image processing methods can be used to differentiate between metal ballast and dangerous objects. In this paper we show first steps in the development of the fully autonomous 3-D positioning unit for eddy current imaging.

PCB Fluxgate Gradiometer Measuring dBx/dy

  • Department: Department of Measurement
  • Annotation:
    We investigated a dBx/dy gradiometer formed by PCB fluxgate sensors stacked together with a gradiometric base of 20 and 10-mm, respectively. We discuss several possible arrangements of the gradiometer with the emphasis to a common compensating coil wound around the two sensors, which can be in a novel configuration also used for as a gradient pick-up coil.

Position Sensing System for Eddy-current Mine Imager

  • DOI: 10.1016/j.proeng.2010.09.101
  • Link: https://doi.org/10.1016/j.proeng.2010.09.101
  • Department: Department of Measurement
  • Annotation:
    Distinguishing of mines from scrap metal is a difficult task that provides challenge when seeking an ultimate solution. An eddy-current imaging feature added to standard handheld metal detector is an option for such discrimination. Our metal detector was enhanced by an inertial measurement unit aided by velocity information, measured by optic flow sensor. It lead to further improvement of the proposed procedure by means of position and orientation tracking. The achieved accuracy of mine signal localization is 1 cm in 1x1m scanning area.

Scalar Calibration of the 3-D Coil System

  • Authors: Zikmund, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Journal of Electrical Engineering. 2010, 61(7/s), 39-41. ISSN 1335-3632.
  • Year: 2010
  • Department: Department of Measurement
  • Annotation:
    The scalar method was used for calibration of the 3-D coil system. Set of non-linear equations was obtained using a sequence of calibration current steps into the individual coils. The coil sensitivities and angle between the magnetic coils axes were calculate by numerical method. The estimated uncertainty was 0.02 degrees for angle and 0.01% for coil constant. The developed method was tested during the calibration of a 2-meter coil system in Pruhonice.

Sensitivity and Noise of Wire-core Transverse Fluxgate

Temperature Stability of Sensitivity and Offset in Coil-Less Fluxgate Sensors

  • Department: Department of Measurement
  • Annotation:
    Temperature stability of fluxgate sensors is very important issue, because this kind of sensors find applications in several field where temperature is not constant. Temperature determines dilatation of the material which can result in mechanical stress to the core. In this paper we compare orthogonal fluxgates in coil-less mode, obtained with bi-phase Copper/Permalloy microwires with and without glass layer between them. We show that a glass layer between Copper and Permalloy strongly decreases the dependence of both offset and sensitivity on the temperature. We explain this by the fact that glass has lower thermal expansion coefficient than copper, therefore it compensates its dilatation which is source of mechanical stress for the Permalloy.

Tester for a Space Micro-accelerometer

Two Sources of Cross-field Error in Racetrack Fluxgate

Automated System for the Calibration of Magnetometers

  • DOI: 10.1063/1.3062961
  • Link: https://doi.org/10.1063/1.3062961
  • Department: Department of Measurement
  • Annotation:
    Automated non-magnetic calibration platform with three axes of freedom is presented. Main applications are scalar calibration of vector magnetometers and accelerometers and testing of their assemblies (e.g. an electronic compass).

Bi-metallic Magnetic Wire with Insulating Layer as Core for Orthogonal Fluxgate

Bi-metallic Magnetic Wire with Insulating Layer as Core for Orthogonal Fluxgate

  • Department: Department of Measurement
  • Annotation:
    Bi-metallic magnetic wire with insulating layer can be used as a core for orthogonal fluxgate.

Crossfield Effect in Magnetic Sensors

  • DOI: 10.1109/ICSENS.2009.5398405
  • Link: https://doi.org/10.1109/ICSENS.2009.5398405
  • Department: Department of Measurement
  • Annotation:
    Crossfield effect often seriously limits the accuracy of magnetic sensors. However, this effect is only rarely discussed by sensor manufacturers and users. In this paper, we present measurements on ring-core, racetrack and Vacquier type fluxgates and on one type of AMR sensor.

Crossfield Sensitivity in AMR Sensors

Current-Output of Printed Circuit Board Fluxgates

  • DOI: 10.1166/sl.2009.1064
  • Link: https://doi.org/10.1166/sl.2009.1064
  • Department: Department of Measurement
  • Annotation:
    Current-output mode of PCB fluxgate sensors is presented. As the output current is inversely proportional to the number of turns of the pickup coil, PCB fluxgates should perform well in this mode. In order to avoid serial tuning of the sensor's output, sufficiently large series capacitor must be used mainly for pickup-coils with very low impedance. The sensitivities (with sinewave excitation and 2nd harmonic detection) have been found as 86 and 32 A/T for sensor IIIA and IIB, respectively. The noise values remain the same as in voltage mode; however the linearity is slightly better.

Investigation of Crossfield Effect in AMR Sensors

Linearity of Pulse Excited Coil-less Fluxgate

Linearity of Pulse Excited Coil-less Fluxgate

  • Department: Department of Measurement
  • Annotation:
    In this paper a linearity of pulse excited coil-less fluxgate is measured and discussed.

M-H Loop Tracer Based on Digital Signal Processing for Low Frequency Characterization of Extremely Thin Magnetic Wires

Magnetic Markers Detection Using PCB fluxgate array

  • DOI: 10.1063/1.3074780
  • Link: https://doi.org/10.1063/1.3074780
  • Department: Department of Measurement
  • Annotation:
    PCB fluxgate sensors formed a sensor head for detection of ferromagnetic and paramagnetic markers. The sensors were arranged perpendicularly to the measuring plane and we measured the horizontal gradient of normal component of the measured field. When moving the sensor head, we were able to map field gradients smaller than 6 nT/mm, which was verified while measuring the magnetic markers on a dollar bill. With the help of perpendicular ac excitation at 30 Hz, we were able to detect a 0.1 ml Endorem iron-oxide superparamagnetic marker at 2 mm; volume of 0.6 ml was detectable at 10 mm.

Magnetic Sensors: Principles and Applications

  • Authors: prof. Ing. Pavel Ripka, CSc., Závěta, K.
  • Publication: Handbook of Magnetic Materials, Vol 18. Amsterdam: Elsevier, 2009. p. 347-420. ISBN 978-0-08-054814-2.
  • Year: 2009
  • Department: Department of Measurement
  • Annotation:
    The chapter gives an overview of principles and applications of magnetic sensors.

Model for Coilless Fluxgate

Multiple Layer Scanning in Magnetopneumography

Multiwire Core Fluxgate

  • Authors: prof. Ing. Pavel Ripka, CSc., Li, X.P., Fan, J.
  • Publication: Sensors and Actuators. 2009, 156(11), 265-268. ISSN 0924-4247.
  • Year: 2009

Origin of the Crossfield Effect in AMR Sensors

PCB Sensors in Fluxgate Magnetometer with Controlled Excitation

Study of the GMI Effect and Orthogonal Fluxgate Effect of Two-Wire Arrays of Amorphous Wires

  • Authors: Li, X., Malátek, M., Fan, J., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Intermag 2009 - Digests. Aneheim: IEEE Magnetics Society, 2009, pp. 60-61.
  • Year: 2009
  • Department: Department of Measurement
  • Annotation:
    Study of the GMI effect and orthogonal fluxgate effect of two-wire arrays of amorphous wires has shown the possibilities of such sensor.

Tester for Space Micro-Accelerometer

  • DOI: 10.1016/j.proche.2009.07.041
  • Link: https://doi.org/10.1016/j.proche.2009.07.041
  • Department: Department of Measurement
  • Annotation:
    Micro-accelerometer MAC04 has been developed in order to measure very low accelerations such as those caused to satellites by atmospheric drag and other non-gravitational forces. The instrument uses a cubic proof-mass inside a small cavity. In an open loop the change of capacitance between the cube and 12 electrodes on the inner cavity surface is a measure of the applied acceleration. It is very difficult to ground test and calibrate such a device due to gravity. The tester simulates the change of capacitances (base capacitance 13,5pF, changes in a range of +-1.5pF). Complete closed loop system is presented.

The Influence of the Tape-core Layer Number of Fluxgate Sensor to the Demagnetization Factor

  • Authors: Yulkifli, Y., Djamal, M., Khairurrijal, K., Kurniadi, D., prof. Ing. Pavel Ripka, CSc.,
  • Publication: ICICI-BME: 2009 INTERNATIONAL CONFERENCE ON INSTRUMENTATION, COMMUNICATION, INFORMATION TECHNOLOGY, AND BIOMEDICAL ENGINEERING. New York: IEEE, 2009. p. 361-365. ISBN 978-1-4244-4999-6.
  • Year: 2009
  • Department: Department of Measurement
  • Annotation:
    This paper explains the influence of the tape-core layer number to the demagnetization factor of a fluxgate sensor. The demagnetization factor was calculated based on the physical dimension, the self-inductance of coil without inserting the core (L-no_core) and by inserting the core (L-core) of the sensor. The calculated demagnetization factor to pick-up coil configurations of 2x80 are proportional, 0.51, 0.82, 1.15, and 1.40 x10(-3) whereas the one to pick-up coil configurations of 2x20 are 1.02, 1.58, 2.23, and 2.78x10(-3), each of which uses the tape-core layer number 1,2, 3, and 4 respectively.

Advances in Magnetic Sensors

  • DOI: 10.1109/ICSENS.2008.4716368
  • Link: https://doi.org/10.1109/ICSENS.2008.4716368
  • Department: Department of Measurement
  • Annotation:
    Advances in magnetic sensors are reviewed in this paper. The most important milestone in the field of magnetic sensors was that AMR sensors started to replace Hall sensors in many applications, were larger sensitivity is an advantage. GMR and SDT sensor finally found limited applications.

AMR Current Measurement Device

Characterisation of Magnetic Wires for Fluxgate Cores

Fluxgate Effect in Twisted Magnetic Wire

Improving the Accuracy of Magnetic Sensors

  • Department: Department of Measurement
  • Annotation:
    Improving the Accuracy of Magnetic Sensors is possible using various compensation and calibration techniques

Inductive Distance Sensor for Biomedical Applications

  • Authors: prof. Ing. Pavel Ripka, CSc., Humr, J.
  • Publication: IEEE SENSORS 2008 - The Seventh IEEE Conference on Sensors. Lecce: IEEE Sensors Council, 2008. p. 1230-1232. ISSN 1930-0395.
  • Year: 2008
  • Department: Department of Measurement
  • Annotation:
    Our novel inductive distance measurement system use 3 excitation and 3 sensing coils. The system was developed for monitoring the activity of the human stomach, but the miniature sensors allow to use it on rats. Multiple coil system allows corrections for the angular misalignment and lateral displacement. Inductive principle was shown to be more precise than traditionally ultrasound distance meters, which are affected by variations of sound velocity in different tissues and body liquids. Also the power consumption of our system is low enough for implantable devices. The achieved sensitivity is 4.7 μV in 10 mm distance between the transmitter and sensor capsules, each of them being 1 mm in diameter and 4 mm in length; the resolution is 20 μm.

Investigation of Crossfield Effect in AMR Sensor

  • Department: Department of Measurement
  • Annotation:
    We measured the effect of crossfield Hx on the output voltage of AMR sensor. We show that Hx can significantly affect the magnetization and cause hysteresis when it reaches hundreds of A/m. For lower field region we observe disagreement with the commonly accepted theoretical model.

Model for Coil-less Fluxgate

  • Department: Department of Measurement
  • Annotation:
    In this paper we present a model of coil-less fluxgate, which is based on simultaneous domain wall movement and magnetization rotation. Firstly we examine the case without twisting (classical orthogonal fluxgate), then we extend the derived result to the case with twisting (the final working state of our sensor).

Multiwire Core Fluxgate

  • Authors: prof. Ing. Pavel Ripka, CSc., Li, X.P., Fan, J.
  • Publication: EUROSENSORS XXII 2008. Dresden: Eurosensors, 2008, pp. 154-156. ISBN 978-3-00-025217-4.
  • Year: 2008
  • Department: Department of Measurement
  • Annotation:
    Fluxgate sensors with core made of multiple microwires are analyzed. We show that any study on sensors based on microwires should begin with detailed characterization of the magnetic properties of the wire, as they are dramatically changing within centimeters. The achieved noise level is 0.34 nT/√Hz@1Hz for doublewire core with dipolar interaction.

Origin of the Crossfield Effect in AMR Sensors

  • Department: Department of Measurement
  • Annotation:
    Crossfield sensitivity is a non-linear effect inherent to AMR sensor. It is caused by the anisotropic character of the sensor. One can reduce the effect by changing the sensor geometry, but this also reduces the sensitivity and finally increases the sensor noise. It is important to understand this effect in order to use AMR sensors correctly. The basic model is directly derived from the single-domain energy equations. It works for sensors with barber poles and including the sensors forming Wheatstone bridge. Finalyy we will show that the effect can be 1) numerically corrected, 2) suppressed using flipping or 3) almost annihilated by feedback.

Pulse Excitation of Coil-less Fluxgate

  • Department: Department of Measurement
  • Annotation:
    Coil-less fluxgate is a new kind of orthogonal fluxgate sensor. So far it has been excited by sine-wave current; 2nd harmonic extraction has been used to process the output voltage. This method was useful to prove the working mode of the sensor; however it shows serious drawbacks. In this paper we will show that the coil-less fluxgate can be excited by pulses of current, with proper height and width. The output voltage is obtained integrating a portion of the positive and negative pulse by two boxcar averagers, then summing up the resulting voltages.

Racetrack Fluxgate Sensor Core Demagnetization Factor

  • Department: Department of Measurement
  • Annotation:
    Racetrack fluxgate sensor core demagnetization factor is estimated using FEM model.

Sensors Based on Bulk Soft Magnetic Materials: Advances and Challenges

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Journal of Magnetism and Magnetic Materials. 2008, 320(20), 2466-2473. ISSN 0304-8853.
  • Year: 2008
  • DOI: 10.1016/j.jmmm.2008.04.079
  • Link: https://doi.org/10.1016/j.jmmm.2008.04.079
  • Department: Department of Measurement
  • Annotation:
    Sensors with cores, yokes or field concentrators made of bulk magnetic material are more sensitive and stable than thin-film sensors. Non-linearity and temperature dependence of sensitivity is often suppressed by a feedback.

Short-range Navigation of Minesweeping Detector

  • Department: Department of Measurement
  • Annotation:
    The current paper deals with short-range (<1m) navigation of mine detector head around suspected location. The aim is building signal strength map for pinpointing of the underground metal object position and estimation of the object type from its signature. As the low-cost MEMS inertial sensors have unacceptable drift, various compensation techniques and navigation aids must be implemented.

Temperature Offset Drift of GMI Sensors

  • Authors: Malátek, M., prof. Ing. Pavel Ripka, CSc., Kraus, L.
  • Publication: Sensors and Actuators. 2008, 147(8), 415-418. ISSN 0924-4247.
  • Year: 2008

The Precision of Gastric Motility and Volume Sensing by Implanted Magnetic Sensors

Two-Domain Model For Orthogonal Fluxgate

Algorithm for Noise Reduction in Output Signal of Race-track Core Fluxgate

  • Department: Department of Measurement
  • Annotation:
    Algorithm for Noise Reduction in Output Signal of Race-track Core Fluxgate is based on digital signal processing.

Application of Neural Networks Inversion in Magnetopneumography

  • Department: Department of Measurement
  • Annotation:
    Application of Neural Networks Inversion in Magnetopneumography gives new opportunities for solvig of the inversion

Characterisation of Magnetic Wires for Fluxgate Cores

Comparative study of the sensing perfomance of orthogonal fluxgate sensors with different amorphous sensing elements

  • Authors: Zhao, Z., Li, X., Seet, H., Qian, X., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Sensors and Actuators. 2007, 136(7), 90-94. ISSN 0924-4247.
  • Year: 2007
  • Department: Department of Measurement
  • Annotation:
    Comparative study of the sensing perfomance of orthogonal fluxgate sensors with different amorphous sensing elements has shown that soe materials are better than other materials

DC Gradiometers for Bomb Detection: Scalar Versus Vectorial

  • Department: Department of Measurement
  • Annotation:
    DC Gradiometers are used for Bomb Detection: Scalar have some advantages over Vectorial.

Fluxgate Effect in Twisted Magnetic Wires

  • Department: Department of Measurement
  • Annotation:
    Fluxgate effect in twisted magnetic wires can be used to measure magnetic fields.

Gastric Motility and Volume Sensing by Implanted Magnetic Sensors

  • DOI: 10.1166/sl.2007.002
  • Link: https://doi.org/10.1166/sl.2007.002
  • Department: Department of Measurement
  • Annotation:
    Gastric electrical stimulation has shown positive effects on weight reduction and on various gastric motility disorders. This stimulation leads to earlier satiety thus decreasing food consumption significantly. For long term effective function some control of implant activity is necessary, for which gastric volume and movements have to be sensed. For this purpose we have chosen mutual induction principle between small implantable coils. Sensors have to fulfill many requirements including biocompatibility, mechanical and chemical durability and minimum power consumption. First successful in-vivo experiments were held with simple configuration of two implantable coils and an external electronics box.

Low-power Fluxgate Signal Processing Using Gated Differential Integrator

  • DOI: 10.1166/sl.2007.046
  • Link: https://doi.org/10.1166/sl.2007.046
  • Department: Department of Measurement
  • Annotation:
    A novel technique of signal extraction method for pulse excited printed circuit board (PCB) fluxgate sensors is presented. The signal extraction electronics takes an advantage of the sensor output voltage waveform shape with bipolar consecutive pulses with polarity and amplitude corresponding to the measured field and utilizes two gated integrators active only in the presence of the sensor output pulses. The feedback loop operation has also been implemented and successfully verified for PCB fluxgate sensors. The results indicate a significant improvement in the noise of pulse-excited sensors when compared to classical 2nd harmonic detection of signal from these pulse excited sensors. The best results with PCB fluxgate sensor were noise of 20 pT/sqrt Hz @ 1 Hz, linearity error below 70 ppm (in +- 50 uT full scale range), offset stability of 3.7 nT within 3.5 hours.

Low-power Printed Circuit Board Fluxgate Sensor

  • Department: Department of Measurement
  • Annotation:
    Low-power Printed Circuit Board Fluxgate Sensor has high sensitivity and low noise.

Magnetic Sensors

  • Authors: Ripka, Š., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Modern Sensors Handbook. London: ISTE Ltd, 2007. p. 433-475. ISBN 978-1-905209-66-8.
  • Year: 2007
  • Department: Department of Measurement
  • Annotation:
    Chap. 10 - Modern Sensors Handbook (Magnetic sensors - overview and features)

Magnetic Sensors: Principles and Applications

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Encyclopedia of Materials: Science and Technology - Online Update. 2 ed. Oxford: Elsevier, 2007. p. 1-12. ISBN 0-08-043152-6.
  • Year: 2007
  • Department: Department of Measurement
  • Annotation:
    Magnetic Sensors: Principles and Applications such as electric current and position measurement

Magnetopneumography - Advances in Measurement Procedure, Modeling and Inversion Using Artificial Neural Networks

  • Department: Department of Measurement
  • Annotation:
    For more precise measurements of remnant fields of dust particles in lungs (Magnetopneumography) non-magnetic positioning device was built and new computer model of experimental sources measurements was created. The inverse problem was solved partially using various types of neural networks (NN).

Mine Detection in Magnetic Soils

  • Department: Department of Measurement
  • Annotation:
    Superparamagnetic nanoparticles in soils cause frequency dependence of susceptibility.

Sensors Based on Bulk Soft Magnetic Materials: Advances and Challenges

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Soft Magnetic Materials Conference (SMM 18) - Book of Abstracts. Cardiff, Wales: Cardiff University, Wolfson Centre for Magnetics, 2007. p. 13.
  • Year: 2007
  • Department: Department of Measurement
  • Annotation:
    Sensors based on bulk soft magnetic materials have many aplicatios. The paper reviews their advances and challenges

Application of Fluxgate Gradiometer in Magnetopneumography

Co-Rich Amorphous Material in Fluxgate and GMI Regime

  • Authors: Malátek, M., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Journal of Electrical Engineering. 2006, 57(8/S), 77-79. ISSN 1335-3632.
  • Year: 2006
  • Department: Department of Measurement
  • Annotation:
    A comparison between fluxgate and GMI sensor has been made using universal sensor structure for both regimes of operation. Temperature stability and perming effect were investigated for both. The results show that competitiveness of GMI sensors over the fluxgates is lowered mainly due to huge temperature sensitivity of the offset. Nevertheless, their easy miniaturisation allows them to be still used in vast of low cost applications, which are not demanding high accuracy.

Co-Rich Amorphous Material in Fluxgate and GMI Regime

  • Authors: Malátek, M., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Magnetic Measurements '06 - The Book of Abstracts. Bratislava: Slovak University of Technology, 2006. p. 46-47. ISBN 80-227-2452-1.
  • Year: 2006
  • Department: Department of Measurement
  • Annotation:
    A comparison between fluxgate and GMI sensor has been made using universal sensor structure for both regimes of operation. Temperature stability and perming effect were investigated for both. The results show that competitiveness of GMI sensors over the fluxgates is lowered mainly due to huge temperature sensitivity of the offset. Nevertheless, their easy miniaturisation allows them to be still used in vast of low cost applications, which are not demanding high accuracy.

Compensation of Accelerometer Drift for Improved Position Estimation

  • Department: Department of Measurement
  • Annotation:
    When direct position measurement is not possible, it may be estimated e.g. from integrated accelerations. However, the performance of most affordable devices is rather poor for this application due to unacceptable drift. With some restrictions, the drift may be compensated.

DC Gradiometers for Bomb Detection: Scalar vs. Vectorial

  • Department: Department of Measurement
  • Annotation:
    DC Gradiometers can be used for Bomb Detection. Scalar and vectorial magnetometers can be used.

Discrimination Ability of Metal Detectors

  • Authors: prof. Ing. Pavel Ripka, CSc., Lewis, A.M.
  • Publication: XX Eurosensors, 20th Anniversary. Göteborg: Eurosensors, 2006, pp. 420-421. ISBN 91-631-9280-2.
  • Year: 2006
  • Department: Department of Measurement
  • Annotation:
    Three possibilities for increasing the ability of the eddy-current metal detector are examined: time-domain methods, impedance spectroscopyand spatial distribution methods. As the existing devices are not suitable for humanitarian demining, we discuss the feasibility of an autonomous mapping system based on a low-cost inertial navigation unit. It is shown that using existing technology correction of drifts by an independent sensor would be required.

Eddy Current Metal Detectors - Pulse vs. Continuous-Wave

  • Authors: prof. Ing. Pavel Ripka, CSc., Lewis, A.
  • Publication: Magnetic Measurements '06 - The Book of Abstracts. Bratislava: Slovak University of Technology, 2006, pp. 93-94. ISBN 80-227-2452-1.
  • Year: 2006

Eddy Current Metal Detectors - Pulse vs. CW

  • Authors: prof. Ing. Pavel Ripka, CSc., Lewis, A.
  • Publication: Journal of Electrical Engineering. 2006, 57(8/S), 175-177. ISSN 1335-3632.
  • Year: 2006
  • Department: Department of Measurement
  • Annotation:
    CW metal detectors allow classification of detected object if multifrequency excitation is used. Pulse detectors are simple, low-cost and low-power. They are also immune to easy magnetic soils.

Electronic Compass with PCB Fluxgate Sensors

  • Department: Department of Measurement
  • Annotation:
    The fully digital compass with PCB fluxgate sensors and accelerometers is presented. Calibration techniques and final accuracy of the compass are discussed.

Errors of AMR Compass and Methods of their Compensation

  • Department: Department of Measurement
  • Annotation:
    The article deals with fully digital compass based on AMR sensors and accelerometers. The developed device gives information about actual azimuth, roll and pitch. The article is especially focused on errors caused by sensors misalignment, cross-axis effect and temperature offset drifts of the sensors.

Excitation Efficiency of Fluxgate Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc., Hurley, W.G.
  • Publication: Sensors and Actuators. 2006, 2006(129), 75-79. ISSN 0924-4247.
  • Year: 2006
  • Department: Department of Measurement
  • Annotation:
    Among ferromagnetic sensors, fluxgates are the most resistant to field shocks. In order to achieve low perming, the peak amplitude of the fluxgate excitation current must be high. The fluxgate excitation efficiency (Ip-p/Irms) can be increased by judicious tuning.

Low power orthogonal fluxgate sensor with electroplated Ni80Fe20/Cu wire

  • Authors: Fan, J., Li, X.P., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Journal of Applied Physics. 2006, 99(16), 08B311. ISSN 0021-8979.
  • Year: 2006
  • Department: Department of Measurement
  • Annotation:
    Low power orthogonal fluxgate sensor with electroplated Ni80Fe20/Cu wire is descridbed

Magnetometer with Pulse-excited Fluxgate Sensors

  • Authors: Janošek, M., Kubík, J., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Nové trendy rozvoja letectva - Zborník 7. medzinárodnej vedeckej konferencie. Košice: Slovenský letecký inštitút a. s., 2006, ISBN 80-8073-520-4.
  • Year: 2006
  • Department: Department of Measurement
  • Annotation:
    Magnetometer with Pulse-excited Fluxgate Sensors is described in this paper.

Magnetometer with Pulse-Excited Miniature Fluxgate Sensor

  • Department: Department of Measurement
  • Annotation:
    Magnetometer with pulse-excited miniature fluxgate sensor is described. Low power consumption allows battery power operation for several hours. The field resolution is 1 nT.

Magnetometer with Pulse-Excited Miniature Fluxgate Sensor Cores

  • Authors: Kubík, J., Janošek, M., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Magnetic Measurements '06 - The Book of Abstracts. Bratislava: Slovak University of Technology, 2006, pp. 38-39. ISBN 80-227-2452-1.
  • Year: 2006
  • Department: Department of Measurement
  • Annotation:
    Miniature fluxgate sensors have been designed using PCB technology, with amorphous race-track core. They have been used in magnetometer with pulse excitation and signal extraction using gated integrators. Sensor and magnetometer parameters are shown and discussed.

Mine Detection in Magnetic Soils

  • Authors: Lewis, A.M., prof. Ing. Pavel Ripka, CSc.,
  • Publication: EMSA '06 - 6th European Magnetic Sensors and Actuators Conference. Bilbao: University of the Basque Country, 2006. p. 59.
  • Year: 2006

Noise Spectrum of Pulse Excited Fluxgate Sensor

  • Department: Department of Measurement
  • Annotation:
    Pulse excited fluxgate sensor has low power consumprion, but higher noise.

On Cross-Axis Effect of the Anisotropic Magnetoresistive Sensors

  • Authors: Kubík, J., Včelák, J., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Sensors and Actuators. 2006, 2006(129), 15-19. ISSN 0924-4247.
  • Year: 2006
  • Department: Department of Measurement
  • Annotation:
    The article deals with fully digital compass based on AMR sensors and accelerometers. The developed device gives information about actual azimuth, roll and pitch. The article is especially focused on errors caused by sensors misalignment, cross-axis effect and temperature offset drifts of the sensors.

PCB Racetrack Fluxgate Sensor with Improved Temperature Stability

  • Authors: Kubík, J., prof. Ing. Pavel Ripka, CSc., Pavel, L.
  • Publication: Sensors and Actuators. 2006, 130(5), 184-188. ISSN 0924-4247.
  • Year: 2006
  • Department: Department of Measurement
  • Annotation:
    A low-cost flat fluxgate magnetic field sensor with amorphous racetrack core embedded in the printed circuit board (PCB) is presented.

Volume and Motility Sensing for Implantable Gastric Pacemaker

  • Department: Department of Measurement
  • Annotation:
    On-demand gastric electrical stimulation has been proposed to save energy of the pacing implant. For the purpose of control enough information about movement and size of stomach has to be measured with minimum external parts. Higher long-term efficiency of the method is expected in addition to its formerly documented positive effects in obesity treatment. Magnetic induction principle was chosen to measure the elongation of gastric wall between attached coils. In vivo a simple two coil configuration has been successfully tested and satisfactory resolution in demanded bandwidth has been proved. Especially for experimental studies directional dependence may be compensated by multi-axial sensor.

AMR Navigation Systems and Methods of their Calibration

  • Department: Department of Measurement
  • Annotation:
    The design of a navigation system with AMR and accelerometers is described in this article. The calibration methods of general triaxial sensor systems are discussed in this article and basic results are presented. The application of these calibration methods for developed navigation system is also included in this article.

Application of Fluxgate Excitation Circuit with Saturable Inductor to Magnetic Sensing

  • Authors: Duffy, M.C., Tang, S.C., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Sensors and Actuators. 2005, 2005(123/124), 430-437. ISSN 0924-4247.
  • Year: 2005
  • Department: Department of Measurement
  • Annotation:
    It is shown theoretically that if the saturable inductor is uniformly wound on a ring core, it does not introduce any second harmonic component when exposed to a uniform magnetic field. The circuit may therefore, be accurately applied in magnetic field sensing.

Current Sensor in PCB Technology

  • Authors: prof. Ing. Pavel Ripka, CSc., Kubík, J., Duffy, M., Hurley, W.G., O'Reilly, S.
  • Publication: IEEE Sensors Journal. 2005, 2005(5), 433-438. ISSN 1530-437X.
  • Year: 2005
  • Department: Department of Measurement
  • Annotation:
    New sensor for DC/AC currents is based on fluxgate principle. The sensor is manufactured in PCB technology. The core is made of electrodeposited permalloy and windings and sensor winding is formed from copper PCB layers.

Digitalization of Highly Precise Fluxgate Magnetometers

  • Authors: Cerman, A., Kuna, A., prof. Ing. Pavel Ripka, CSc., Merayo, J.M.G.
  • Publication: Sensors and Actuators. 2005, 121(2), 421-429. ISSN 0924-4247.
  • Year: 2005
  • Department: Department of Measurement
  • Annotation:
    This paper describes ways of digitalizing the fluxgate magnetometers: analogue magnetometers with digitalized output using high resolution ADC, application of the delta sigma modulation to the sensor feedback loop and fully digital signal detection.

Double-core GMI Current Sensor

  • Authors: Malátek, M., prof. Ing. Pavel Ripka, CSc., Kraus, L.
  • Publication: IEEE Transactions on Magnetics. 2005, 41(10), 3703-3705. ISSN 0018-9464.
  • Year: 2005
  • Department: Department of Measurement
  • Annotation:
    A novel design of the giant magnetoimpedance contactless current sensor is presented. A double-core structure is used in order to improve the temperature stability. The temperature coefficient of sensitivity and offset drift are reduced to one-half compared to the single-core sensor. The linearity error decreases by a factor of three. Further utilization of an ac biasing (up to 200 Hz) of the double-core sensor suppresses the temperature offset drift by a factor of 30 (down to 0.6 mA/K) and increases the open-loop linearity to 0.5 % for the 2-A range.

Double-Core GMI Current Sensor

  • Authors: Malátek, M., prof. Ing. Pavel Ripka, CSc., Kraus, L.
  • Publication: INTERMAG ASIA 2005. Piscataway: IEEE, 2005. p. 636. ISBN 0-7803-9009-1.
  • Year: 2005
  • Department: Department of Measurement
  • Annotation:
    The research is aimed at a development of a novel design of magneto-impedance current sensor, which lowers temperature influence and increase the linearity

Excitation and Temperature Stability of PCB Fluxgate Sensor

  • Authors: Tipek, A., O'Donnell, T., prof. Ing. Pavel Ripka, CSc., Kubík, J.
  • Publication: IEEE Sensors Journal. 2005, 5(6), 1264-1269. ISSN 1530-437X.
  • Year: 2005
  • Department: Department of Measurement
  • Annotation:
    Printed Circuit Board (PCB) integrated inductors have been adapted for operation as fluxgate sensors. A ring core is made from an electrodeposited permalloy thin film and is sandwiched between the layers of the PCB. The sensor excitation winding is also integrated into the PCB design. The pick-up coil is wound around the frame of the PCB core.

Fluxgate Gradiometer in Magnetopneumography

  • Department: Department of Measurement
  • Annotation:
    Magnetopneumography (MPG) serves for examination of human lungs exposition to ferromagnetic dusts and fumes (e.g. in metal-workers in industry) through measurement of remanent magnetic field after magnetization of the subject in an electromagnet. Fluxgate gradiometer is used for measurement and various methods (neural networks, etc.) are used for evaluation and estimation of the inhaled dust amount and distribution.

Low-power PCB Fluxgate Sensor

  • DOI: 10.1109/ICSENS.2005.1597728
  • Link: https://doi.org/10.1109/ICSENS.2005.1597728
  • Department: Department of Measurement
  • Annotation:
    New PCB (Printed Circuit Board) technology flat fluxgate sensor with integrated coils and amorphous alloy core was developed and its excitation parameters were optimized for low-power consumption. The power consumption achieved with 10 kHz, 300 mA p-p pulse excitation with duty cycle 12.5 % was only 3.9 mW, which is 3-times lower than that for sinewave flux density excitation. The sensor sensitivity reached 94 V/T.

Magnetic Field of the Lungs - Neural Network Inverse Models

  • Department: Department of Measurement
  • Annotation:
    Magnetopneumography (MPG) uses examination of remanent magnetic field for determination of amount and distribution of ferromagnetic dust respired into the lungs. Experimental physical model, fluxgate measurement setup including non-magnetic positioning bed and forward computer solver were built in order to provide data for training of neural network inverse model. Early results of the experiments are promising.

Noise Spectrum of Pulse Excited Fluxgate Sensor

  • Authors: Kubík, J., prof. Ing. Pavel Ripka, CSc.,
  • Publication: EUROSENSORS XIX - Proceedings. Barcelona: IEEE, 2005, pp. Wpb43.
  • Year: 2005
  • Department: Department of Measurement
  • Annotation:
    A low-cost flat miniature fluxgate magnetic field sensor is excited by short current pulses in order to reduce the power consumption. In this mode, the output signal contains very rich spectrum of even harmonics. Noise spectrum of individual harmonics both in untuned and tuned mode was measured. The output tuning substantially improved the noise properties of the sensor.

Noise Spectrum of Pulse Excited Fluxgate Sensor

  • Department: Department of Measurement
  • Annotation:
    A low-cost flat miniature fluxgate magnetic field sensor is excited by short current pulses in order to reduce the power consumption. In this mode, the output signal contains very rich spectrum of even harmonics. Noise spectrum of individual harmonics both in untuned and tuned mode was measured. The output tuning substantially improved the noise properties of the sensor.

Offset Stability of GMI Field Sensors

  • Authors: Malátek, M., prof. Ing. Pavel Ripka, CSc.,
  • Publication: EUROSENSORS XIX - Proceedings. Barcelona: IEEE, 2005, pp. 222-225.
  • Year: 2005
  • Department: Department of Measurement
  • Annotation:
    A single-core and a double-core GMI field sensors with permalloy PY79M material were subjected to strong magnetic shocks of both polarities (up to 40 mT). The both sensors were afterwards tested in temperature chamber and offset stabilities were achieved in temperature span from -20°C to +70°C. Moreover, single-core amorphous sensor underwent same tests. Large field shocks does not cause offset error higher than 2.7 uT and 1.2 uT, the temperature offset drift of 283 nT/K and 190 nT/K for the single- and the double-core PY sensors respectively. The perming effect 1.5 uT and temperature zero drift of -409 nT/K was achieved for the amorphous field sensor.

Offset Stability of GMI Magnetic Field Sensors

  • Department: Department of Measurement
  • Annotation:
    We show that the performance of GMI field sensors is influenced by perming effect and offset temperature drift. Magnetic field shocks in permalloy material cause offset shifts as high as 3 uT. Perming error can be reduced by increasing the measurement current. Large temperature offset drift of 283 nT/K and -409 nT/K was observed for permalloy and amorphous sensor respectively. Temperature sensitivity can be partly suppressed by double-core design.

Orthogonal Fluxgate Effect in Electroplated Wires

  • Authors: prof. Ing. Pavel Ripka, CSc., Li, X.P., Fan, J.
  • Publication: IEEE Sensors 2005 - The 4-th IEEE Conference on Sensors. Irvine, CA: IEEE Sensors, 2005. p. 69-72. ISBN 0-7803-9057-1.
  • Year: 2005
  • Department: Department of Measurement
  • Annotation:
    Orthogonal Fluxgate Effect in Electroplated Wires can serve for measerement of the magnetic field

PCB Racetrack Fluxgate Sensor with Improved Temperature Stability

  • Authors: Kubík, J., Pavel, L., prof. Ing. Pavel Ripka, CSc.,
  • Publication: EUROSENSORS XIX - Proceedings. Barcelona: IEEE, 2005. p. WC1-WC2.
  • Year: 2005
  • Department: Department of Measurement
  • Annotation:
    A low-cost flat fluxgate magnetic field sensor with amorphous racetrack core embedded in the printed circuit board (PCB) is presented. The improved design reduced internal temperature-induced stresses and thus significantly improved the temperature stability. We also show that high sensitivity at elevated excitation frequencies is paid by degradation of offset stability and noise.

PCB Racetrack Fluxgate Sensor with Improved Temperature Stability

  • Authors: Kubík, J., Pavel, L., prof. Ing. Pavel Ripka, CSc.,
  • Publication: EUROSENSORS XIX. Barcelona: Universitat de Barcelona, 2005.
  • Year: 2005
  • Department: Department of Measurement
  • Annotation:
    A low-cost flat fluxgate magnetic field sensor with amorphous racetrack core embedded in the printed circuit board (PCB) is presented. The improved design reduced internal temperature-induced stresses and thus significantly improved the temperature stability. We also show that high sensitivity at elevated excitation frequencies is paid by degradation of offset stability and noise.

Precise Vectorial Magnetic Field Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Smart Sensors and MEMS, NATO ASI Series. Dordrecht: Springer, 2005. p. 203-229. ISBN 1-4020-2927-6.
  • Year: 2005
  • Department: Department of Measurement
  • Annotation:
    Semiconductor magnetic sensors, ferromagnetic magnetoresistors, GMR, SDT, fluxgate and other precise vectorial magnetic sensors: basic principles, properties and applications, mainly in the security area.

Alternating Biasing of SDT Sensors

  • Authors: Vopálenský, M., prof. Ing. Pavel Ripka, CSc., Kubík, J., Tondra, M.
  • Publication: Sensors and Actuators. 2004, 110(1-3), 182-186. ISSN 0924-4247.
  • Year: 2004

AMR Navigation Systems and Methods of Their Calibration

  • Department: Department of Measurement
  • Annotation:
    The article deals with fully digital navigation system and method of its calibration using rotation in roll. The system calculates actial azimuth, roll and pitch from measurement of Earth's magnetic and gravitational filed vectors. Then the calculated azimuth is not influenced by actual roll or pitch.

AMR Navigation Systems and Methods of Their Calibration

  • Department: Department of Measurement
  • Annotation:
    The article deals with fully digital navigation system based on AMR sensors and MEMS accelerometers. Described are used calibration methods: scalar calibration for finding sensitivities, offsets and non-orthogonalities and rotation in roll and azimuth for finding angular deviations (misalignments) of the sensor coordinate systems.. The device calculates actual azimuth, roll and pitch from measurement of Earth's magnetic and gravitational field vectors. Then the calculated azimuth is not influenced by actual roll or pitch.

Analysis of Performance of PCB Integrated Fluxgate Sensor

  • Authors: Tipek, A., O'Donnell, T., O'Reilly, S., McCloskey, P., Kubík, J., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Magnetic Measurements 2004. Praha: Czech Technical University in Prague, 2004. p. 99. ISBN 80-01-02994-8.
  • Year: 2004

Application of Fluxgate Excitation Circuit to Magnetic Sensing

  • Authors: Duffy, M., Tang, S.C., prof. Ing. Pavel Ripka, CSc.,
  • Publication: XVIII EUROSENSORS. Roma: Pontificia Universitas Sancto Thoma Aquinate in Urbe, 2004. p. 511-512.
  • Year: 2004
  • Department: Department of Measurement
  • Annotation:
    The application of a fluxgate excitation circuit with a saturable inductor to magnetic field sensing is described. It is shown theoretically that if the saturable inductor is uniformly wound on a ring core, it does not introduce any 2nd harmonic component. Initial measurement results are presented to verify the analysis.

Application of Fluxgate Excitation Circuit to Magnetic Sensing

  • Authors: Duffy, M., Tang, S.C., prof. Ing. Pavel Ripka, CSc.,
  • Publication: XVIII EUROSENSORS. Rome: Eurosensors Steering Committee, 2004. p. P2.47-1-P2.47-2. ISBN 88-7621-282-5.
  • Year: 2004
  • Department: Department of Measurement
  • Annotation:
    The application of a fluxgate excitation circuit with a saturable inductor to magnetic field sensing is described. It is shown theoretically that if the saturable inductor is uniformly wound on a ring core, it does not introduce any 2nd harmonic component. Initial measurement results are presented to verify the analysis.

Compensated SDT for Linear Measurements

  • Authors: Vopálenský, M., Dostál, P., prof. Ing. Pavel Ripka, CSc., Tondra, M.
  • Publication: Magnetic Measurements 2004. Praha: Czech Technical University in Prague, 2004, pp. 79-80. ISBN 80-01-02994-8.
  • Year: 2004

Current Sensors Using Magnetic Materials

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS. 2004, 6(2), 587-592. ISSN 1454-4164.
  • Year: 2004

Electronics for MI Current Sensor

Electronics for MI Current Sensor

Excitation Circuit for Fluxgate Sensor using Saturable Inductor

  • Authors: Tang, S.C., Duffy, M.C., prof. Ing. Pavel Ripka, CSc., Hurley, W.G.
  • Publication: Sensors and Actuators. 2004, 2004(113), 156-165. ISSN 0924-4247.
  • Year: 2004
  • Department: Department of Measurement
  • Annotation:
    Traditional excitation circuits for fluxgate sensors consist of a lossy resistor or a bulky inductor (operated in non-saturated mode), whose function is to limit the excitation current. As a result, a high voltage source is required to provide sufficient excitation current to the sensor. For these reasons, traditional excitation circuits are unsuitable for portable battery operated devices that use fluxgate sensors. In order to reduce the circuit size and operating voltage in such applications, the use of a saturable inductor is proposed in this paper. Practical methods for choosing suitable circuit components are described to ensure that the circuit operates under optimum conditions. Experimental results illustrate a good linear relationship between the second harmonic voltage and the measured current for a fluxgate dc current sensor using the proposed excitation circuit.

Fluxgate Cores with Transverse Anisotropy

  • Authors: prof. Ing. Pavel Ripka, CSc., Závěta, K., Jurek, K.
  • Publication: IEEE Sensors 2004. Orlando, Florida: IEEE Sensors Council, 2004, pp. 314-315.
  • Year: 2004
  • Department: Department of Measurement
  • Annotation:
    Anisotropy with hard axis in magnetization direction reduces the fluxgate sensor noise. We show that such domain structure can be achieved by applying strong magnetic field in the direction normal to the sheet plane. Magnetic domains in nanocrystalline samples were observed in scanning electron microscope.

Fully Digital Fluxgate Magnetometer - First Results

  • Authors: Cerman, A., Kuna, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: 13th International Symposium on Measurements for Research and Industry Applications. Athens: IMEKO TC-4, 2004, pp. 169-172.
  • Year: 2004
  • Department: Department of Measurement
  • Annotation:
    Present paper describes design, implementation and first results of the fully digital magnetometer. The magnetometer operates in the feedback configuration and uses fully digital signal detection realized in the digital signal processor (DSP).

Fully Digital Fluxgate Magnetometer - First Results

  • Authors: Cerman, A., Kuna, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: 13th International Symposium on Measurements for Research and Industry Applications. Athens: IMEKO TC-4, 2004, pp. 169-172. ISBN 960-254-643-3.
  • Year: 2004

Fully digital fluxgate magnetometer - First results

  • Authors: Cerman, A., Kuna, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: IMEKO TC-4 Proceedings of the 13th International Symposium on Mesurements for Research and Industry Applications. Athens: IMEKO TC-4, 2004. ISBN 960-254-644-1.
  • Year: 2004
  • Department: Department of Measurement
  • Annotation:
    Presented paper describes design, implementation and first results of the fully digital fluxgate magnetometer. The magnetometer operates in feedback configuration and uses fully digital signal detection realized in the digital signal processor (DSP). The magnetometer has measuring range ±100 μT, the linearity error is less than 40 ppm of FSR, noise 1.08 nTRMS/√Hz@1Hz and the frequency range of measured magnetic field is 15 Hz.

GMI Effect in CoFeCrSiB Ribbon

  • Authors: Malátek, M., Kraus, L., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Magnetic Measurements 2004. Praha: Czech Technical University in Prague, 2004, pp. 73-74. ISBN 80-01-02994-8.
  • Year: 2004

Improved GMR Sensor Biasing Design

  • Authors: Vopálenský, M., prof. Ing. Pavel Ripka, CSc., Kubík, J., Tondra, M.
  • Publication: Sensors and Actuators. 2004, 110(1-3), 254-258. ISSN 0924-4247.
  • Year: 2004

Magnetic Field of Human Lungs: Models and Inversion

  • Authors: Tomek, J., prof. Ing. Pavel Ripka, CSc., Tipek, A.
  • Publication: Magnetic Measurements 2004. Praha: Czech Technical University in Prague, 2004. p. 71-72. ISBN 80-01-02994-8.
  • Year: 2004

Magnetic Field of Human Lungs: Models and Measurement

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: PIERS 2004 - Progress in Electromagnetics Research Symposium. Pisa: Dipartimento Sistemi Elettrici e Automazione, Universita di Pisa, 2004, pp. 815-818.
  • Year: 2004

PCB Technology Used in Fluxgate Sensor Construction

  • Authors: Tipek, A., prof. Ing. Pavel Ripka, CSc., O'Donnell, T., Kubík, J.
  • Publication: Sensors and Actuators. 2004, 115(2-3), 286-292. ISSN 0924-4247.
  • Year: 2004
  • Department: Department of Measurement
  • Annotation:
    Printed circuit board (PCB) - integrated inductors have been adapted for operation as fluxgate sensors. The ring core is made from electrodeposited permalloy sandwiched between the layers of the PCB. The sensor excitation winding is also integrated into the PCB design.

AC Characterization of Materials for Fluxgate Cores

Advances in Fluxgate Sensors

AMR Magnetometer

  • Department: Department of Measurement
  • Annotation:
    Simple anisotropic magnetoresistance magnetometer with improved parameters was developed. New flipping circuits deliver optimized current pulse with 2.8A amplitude. New type of signal processing uses switched integrator to avoid the most noisy time intervals. The achieved linearity is 0.2% in the ą200[mu]T range without feedback and 0.04% using integrated feedback coil. The magnetometer noise at 1 Hz is 2nT/Hz1/2, uncompensated temperature coefficient of sensitivity is -0.25%/K without the feedback and 0.01%/K with feedback. Temperature offset drift is typically 10nT/K.

DC/AC Current Comparator with Fully Enclosed Magnetic Shielding

DC/AC Current Comparator with Fully Enclosed Magnetic Shielding

Delta-Sigma Modulation in the Sensor Feedback Loop

  • Authors: Cerman, A., Kuna, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Eurosensors XVII. Guimaraes: University of Minho, 2003, pp. 1128-1129.
  • Year: 2003

Delta-sigma Modulation in the Sensor Feedback Loop

  • Authors: Cerman, A., Kuna, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Eurosensors XVII. Guimaraes: University of Minho, 2003, pp. 677-678. ISBN 972-98603-1-9.
  • Year: 2003

Excitation of PCB Fluxgate Sensor

  • Authors: Tipek, A., prof. Ing. Pavel Ripka, CSc., O'Donnell, T.
  • Publication: IEEE SENSORS 2003. Toronto: IEEE, 2003. p. 647-650.
  • Year: 2003

Excitation of PCB Fluxgate Sensor

  • Authors: Tipek, A., prof. Ing. Pavel Ripka, CSc., O'Donnell, T., Kubík, J.
  • Publication: IEEE Sensors 2003. Toronto: IEEE, 2003. p. 647-650. ISBN 0-7803-8134-3.
  • Year: 2003

Experiencies with Leonardo Pilot Project

  • Department: Department of Measurement
  • Annotation:
    CTU in Prague was participating in Leonardo da Vinci project CZ/PP-134026 Modular Courses on Modern Sensors. Gained experiences are shared.

Flipping Field and Stability in Anisotropic Magnetoresistive Sensors

  • Authors: Hauser, H., Fulmek, P.L., Haumer, P., Vopálenský, M., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Sensors and Actuators. 2003, 106(1-3), 121-125. ISSN 0924-4247.
  • Year: 2003

GMI - MAGNETOMETER

  • Department: Department of Measurement
  • Annotation:
    GMI effect has been observed also in crystalline materials. This paper presents design of GMI sensor made of two Mo-permalloy strips with opposite biasing to achieve bipolar response. The measuring current frequency is 100 kHz. Either DC or AC biasing can be used. The achieved parameters comprise offset stability of 0.2 uT and linearity of 3.3 % in +/- 60 uT (1.3 % with AC biasing). The noise was approximately 9.5 nT/?ă Hz @ 1Hz. The greatest problem remains the relatively large temperature coefficient.

GMI Current Sensor

Magnetic Sensors

  • Authors: Ripka, S., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Master Book on Sensors. Prague: CTU Prague a BEN, 2003. p. 10-1-10-84. ISBN 80-7300-129-2.
  • Year: 2003

Magnetometer with AMR, GMR and SDT Sensors

  • Authors: Vopálenský, M., prof. Ing. Pavel Ripka, CSc., Hauser, H.
  • Publication: Acta Avionica. 2003, V(8/S), 23-28. ISSN 1335-9479.
  • Year: 2003
  • Department: Department of Measurement
  • Annotation:
    Magnetoresistive sensors have increased their importance in the recent time. Especially the Anisotropic Magnetoresistive sensors (AMR) have went through a large development, which led to their improvements and enlargement of their possible field of application. As the magnetoresistive sensors are small, low-cost, compact and much more sensitive than the traditionally used Hall-sensors, their future expansion to the industry is imminent.This article gives an overview on the modern magnetoresistive sensors of the AMR, GMR (Giant Magnetoresistance), and SDT (Spin Dependent Tunelling) type. Suitable design of a magnetometer for these sensor types is beeing discussed.

New Technologies and Materials

  • Authors: Tipek, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Master Book on Sensors. Prague: CTU Prague a BEN, 2003. p. 11-1-11-74. ISBN 80-7300-129-2.
  • Year: 2003

PCB Technology Used in Fluxgate Sensor Construction

  • Authors: Tipek, A., prof. Ing. Pavel Ripka, CSc., O'Donnell, T.
  • Publication: Eurosensors XVII. Guimaraes: University of Minho, 2003, pp. 424-425. ISBN 972-98603-1-9.
  • Year: 2003

PCB Technology Used in Fluxgate Sensor Construction

  • Authors: Tipek, A., prof. Ing. Pavel Ripka, CSc., O'Donnell, T., Kubík, J.
  • Publication: Eurosensors XVII. Guimaraes: University of Minho, 2003. p. 717-720.
  • Year: 2003

Permalloy GMI Sensor

  • Department: Department of Measurement
  • Annotation:
    GMI effect in permalloy can be used to measure DC magnetic fields. Impedance change of 50% at a field of 0.5 mT was observed at 200 kHz frequency. Magnetometer using biased two-stripe 10-cm long sensor achieved 10% linearity in open loop and 1% hysteresis error in the +/-80 uT range.

Precise AMR Magnetometer for Compass

  • Department: Department of Measurement
  • Annotation:
    AMR sensors gain growing popularity in linear applications such as compassing [1, 2]. We discuss techniques, how to achieve precision required for 0.2 deg azimuth error in wide temperature range. While linearity of 80 ppm FS and sensitivity tempco of 20 ppm/K can be achieved by using feedback compensation, offset drift and crossfield error can be lowered to nT level by periodical flipping.

Precise AMR Magnetometer for Compass

  • DOI: 10.1109/ICSENS.2003.1278983
  • Link: https://doi.org/10.1109/ICSENS.2003.1278983
  • Department: Department of Measurement
  • Annotation:
    AMR sensors gain growing popularity in linear applications such as compassing. We discuss techniques, how to achieve precision required for 0.2 deg azimuth error in wide temperature range. While linearity of 40 ppm and sensitivity tempco of 20 ppm/K can be achieved by using feedback compensation, offset drift and crossfield error can be lowered by periodical flipping.

Precise Magnetic Sensors

  • Department: Department of Measurement
  • Annotation:
    Can magnetoresitors replace fluxgate sensors in precise applications such as navigation and detection of metal objects? AMR and GMR can reach 10 nT resolution. It is possible to improve their stability by AC techniques, but the electronics becomes complex and consumes more power. If size is not limited, fluxgate sensors are still the winners.

Precise Magnetic Sensors and Magnetometers for Military and Space Applications

Precise Vectorial Magnetic Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: SMART SENSORS and MEMS. Póvoa de Varzim: NATO OTAN Advanced Study Institute, 2003. p. 111-123. ISBN 0-9733840-0-X.
  • Year: 2003

Sampling Measurements with Digital Hysteresisgraph

  • DOI: 10.1016/S0304-8853(02)00798-9
  • Link: https://doi.org/10.1016/S0304-8853(02)00798-9
  • Department: Department of Measurement
  • Annotation:
    Digital hysteresisgraph can be used for the measurement of dynamic hysteresis loops up to 100 kHz. Digital feedback allows achievement of sinusoidal flux density by iterative modification of the excitation voltage waveform. This approach is used for the measurement of closed (toroidal) samples at higher frequencies.

Switching-Mode Fluxgate

  • Authors: prof. Ing. Pavel Ripka, CSc., Hurley, G.
  • Publication: TRANSDUCERS '03 - Digest of Technical Papers. Boston: IEEE, 2003. p. 1283-1286. ISBN 0-7803-7731-1.
  • Year: 2003

Switching-Mode Fluxgate

  • Authors: prof. Ing. Pavel Ripka, CSc., Hurley, G.
  • Publication: TRANSDUCERS '03 - Digest of Technical Papers. Boston: IEEE, 2003. p. 1283-1286. ISBN 0-7803-7732-X.
  • Year: 2003

Towards Fully Digital Magnetometer

Advances in Fluxgate Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: EMSA 2002 - Book of Abstracts. Athens: National Technical University, 2002. p. 21.
  • Year: 2002

Alternating Biasing of SDT Sensors

  • Authors: Vopálenský, M., prof. Ing. Pavel Ripka, CSc., Kubík, J., Tondra, M.
  • Publication: Eurosensors XVI - Book of Abstracts. Praha: Czech Technical University in Prague, 2002, pp. 511-512. ISBN 80-01-02576-4.
  • Year: 2002

Alternating Biasing of SDT Sensors

  • Authors: Vopálenský, M., prof. Ing. Pavel Ripka, CSc., Kubík, J., Tondra, M.
  • Publication: EUROSENSORS XVI. Proceedings. Praha: Czech Technical University in Prague, 2002, pp. 872-874.
  • Year: 2002

Calibration of Triaxial Magnetometers by Theodolite

  • Department: Department of Measurement
  • Annotation:
    Calibration and error-correction algorithms for several types of triaxial magnetometers are presented. The calibration method using theodolite is described in detail.

Current Sensor in PCB Technology

  • Authors: Duffy, M., Hurley, W.G., O'Reilly, S., Kubík, J., prof. Ing. Pavel Ripka, CSc.,
  • Publication: IEEE Sensors 2002 - Proceedings. Orlando, Florida: IEEE Sensors Council, 2002. ISBN 0-7803-7455-X.
  • Year: 2002

Current Sensor in PCB Technology

  • Authors: prof. Ing. Pavel Ripka, CSc., Duffy, M., O'Reilly, S., Hurley, W.G., Kubík, J.
  • Publication: IEEE Sensors 2002 - Proceedings. Orlando, Florida: IEEE Sensors Council, 2002. p. 779-784. ISBN 0-7803-7455-X.
  • Year: 2002

Design of Digital Fluxgate Magnetometer

  • Authors: Cerman, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: BEC 2002 - Proceedings of the 8th Biennial Baltic Electronics Conference. Tallinn: Tallinn Technical University, 2002. p. 183-186. ISBN 9985-59-292-1.
  • Year: 2002

Digitalization of Fluxgate Magnetometers

  • Authors: Cerman, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: ISIST'2002 - Proceedings. Jinan: Harbin Institute of Technology (HIT), 2002. p. 3-423.
  • Year: 2002

Excitation Circuit for Fluxgate Sensor using Saturable Inductor

  • Authors: Tang, S.C., Duffy, M.C., prof. Ing. Pavel Ripka, CSc., Hurley, W.G.
  • Publication: EUROSENSORS XVI. Proceedings. Praha: Czech Technical University in Prague, 2002, pp. 300-303.
  • Year: 2002

Excitation Circuit for Fluxgate Sensor using Saturable Inductor

  • Authors: Tang, S.C., Duffy, M.C., prof. Ing. Pavel Ripka, CSc., Hurley, W.G.
  • Publication: Eurosensors XVI - Book of Abstracts. Praha: Czech Technical University in Prague, 2002, pp. 159-160. ISBN 80-01-02576-4.
  • Year: 2002

Excitation Tuning of Fluxgate Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc., Hurley, W.G.
  • Publication: IMtc /2002. Piscataway: IEEE, 2002. p. 677-680. ISBN 0-7803-7218-2.
  • Year: 2002

Fluxgate Can Replace SQUID for Lung Diagnostics

Fluxgate Magnetometer with PWM

  • Authors: Cerman, A., Saneistr, J., prof. Ing. Pavel Ripka, CSc.,
  • Publication: EUROSENSORS XVI. Proceedings. Praha: Czech Technical University in Prague, 2002, pp. 370-371.
  • Year: 2002

Fluxgate Magnetometer with PWM

  • Authors: Cerman, A., Saneistr, J., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Eurosensors XVI - Book of Abstracts. Praha: Czech Technical University in Prague, 2002, pp. 199-200. ISBN 80-01-02576-4.
  • Year: 2002

GMI Sensor

GMI Sensor

Improved GMR Sensor Biasing Design

  • Authors: Vopálenský, M., prof. Ing. Pavel Ripka, CSc., Kubík, J., Tondra, M.
  • Publication: EUROSENSORS XVI. Proceedings. Praha: Czech Technical University in Prague, 2002, pp. 616-619.
  • Year: 2002

Improved GMR Sensor Biasing Design

  • Authors: Vopálenský, M., prof. Ing. Pavel Ripka, CSc., Kubík, J., Tondra, M.
  • Publication: Eurosensors XVI - Book of Abstracts. Praha: Czech Technical University in Prague, 2002, pp. 343-344. ISBN 80-01-02576-4.
  • Year: 2002

Improvement of AMR Magnetometer Precision

Improvement of AMR Magnetometer Precision

Industrial Applications of Programmable Hall Sensor

  • Department: Department of Measurement
  • Annotation:
    Although AMR and GMR sensors gradually penetrate many industrial applications, Hall sensors still remain the most widely used solution. However, developersof modern systems often require more added value than just plain sensor in order to satisfy specific needs in their construction.

Industrial Applications of Programmable Hall Sensor

Magnetic Sensors and their Temperature Testing

  • Department: Department of Measurement
  • Annotation:
    The construction of temperature testing system is described. The description covers temperature chamber, cooling and heating system, testing methodology and complete testing system with computer control.

Magnetometer for the MIMOSA Satellite

Magnetoresistive Sensors

Microfluxgate Versus Magnetoresistors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Magnetic Sensor Materials & Devices. Ames, Iowa: Iowa State University, 2002. pp. 19-42.
  • Year: 2002

Permalloy GMI Sensor

  • Department: Department of Measurement
  • Annotation:
    We report our work than contains investigation of attributes of permalloy GMI materials, construction of a magnetic field sensor based on GMI effect and its exploration, and design of GMI magnetometer. Achieved results of the work are presented in enclosed graphs, block diagrams and numerical results.

Permalloy GMI Sensor

Phase Error Compensation in Sampling Hysteresisgraph

Phase Error Compensation in Sampling Hysteresisgraph

  • Department: Department of Measurement
  • Annotation:
    Digital dynamic hysteresisgraph for measurement in DC to 100 kHz frequency range was developed in out department. Among the errors influencing the measurement are also the phase shifts. This contribution deals with determination and software compensation of these phase shifts.

Practical Measurements on New Types of Magnetoresistive Sensors

  • Authors: Vopálenský, M., prof. Ing. Pavel Ripka, CSc., Tondra, M., Hauser, H.
  • Publication: BEC 2002 - Proceedings of the 8th Biennial Baltic Electronics Conference. Tallinn: Tallinn Technical University, 2002. p. 215-216. ISBN 9985-59-292-1.
  • Year: 2002

Precise Magnetic Sensors

Prediction of the Flipping Fields in AMR Sensors

  • Authors: Hauser, H., Fulmek, P.L., Haumer, P., Vopálenský, M., prof. Ing. Pavel Ripka, CSc.,
  • Publication: EMSA 2002 - Book of Abstracts. Athens: National Technical University, 2002. pp. 90.
  • Year: 2002

Temperature Testing of Magnetic Sensors

Towards Fully Digital Fluxgate Magnetometer

  • Authors: prof. Ing. Pavel Ripka, CSc., Cerman, A.
  • Publication: EMSA 2002 - Book of Abstracts. Athens: National Technical University, 2002. p. 66.
  • Year: 2002

Triaxial Magnetometers and their Calibration

Adjustable Race-Track Fluxgate Sensor

  • Authors: prof. Ing. Pavel Ripka, CSc., Tipek, A.
  • Publication: Proceedings of Workshop 2001. Praha: České vysoké učení technické v Praze, 2001. pp. 382-383. ISBN 80-01-02335-4.
  • Year: 2001

AMR Magnetometer

Digital Fluxgate Magnetometers

  • Authors: Cerman, A., prof. Ing. Pavel Ripka, CSc., Kawahito, S.
  • Publication: JMW01 - 4th Joint UK Magnetics Workshop. Cardiff: The UK Magnetics Society, 2001, pp. 88.
  • Year: 2001

Fluxgate Sensors for Medical Applications

  • Authors: prof. Ing. Pavel Ripka, CSc., O'Donnell, T., O'Mathuna, S.C., Hurley, W.G.
  • Publication: Marie Curie Fellowship Association Symposium. Dublin: University College Dublin, 2001, pp. 30.
  • Year: 2001

Giant Magnetoimpedance Sensors

  • Authors: Hauser, H., Kraus, L., prof. Ing. Pavel Ripka, CSc.,
  • Publication: IEEE Transactions on Instrumentation and Measurement. 2001, 50(2), 28-32. ISSN 0018-9456.
  • Year: 2001

Laboratory of Magnetic Measurement CTU FEE Prague

Magnetic Sensors and Magnetometers

  • Authors: prof. Ing. Pavel Ripka, CSc., Hauser, H., Tondra, M., Popovic, R.S., Schott, Ch., Shibasaki, I., Didosyan, Y., Primdahl, F., Fagaly, R.L., Acuna, M.H., Sasada, I., Paperno, E., Gashelis, I.J.
  • Publication: Boston: ARTECH HOUSE, 2001. ISBN 1-58053-057-5.
  • Year: 2001

Magnetometric Examination of Lung Tissue Samples

  • Department: Department of Measurement
  • Annotation:
    In three bioptic samples and 18 samples from post mortem examination of lung tissue, the rotation magnetometer JR-4 was used for the determination of specific remanent moment (magnetism, after magnetizing by external magnetic field), which expresses the concentration of ferromagnetic substances in the sample.

Micro-Fluxgate Sensor with Closed Core

  • Authors: prof. Ing. Pavel Ripka, CSc., Choi, S.O., Kawahito, S., Tipek, A., Ishida, M.
  • Publication: Sensors and Actuators. 2001, A 91(2), 65-69. ISSN 0924-4247.
  • Year: 2001

Modern Sensors Modular Courses Education WWW System

PCB-Integrated Current Sensor

  • Authors: prof. Ing. Pavel Ripka, CSc., Duffy, M., O'Reilly, S., Hurley, W.G.
  • Publication: JMW01 - 4th Joint UK Magnetics Workshop. Cardiff: The UK Magnetics Society, 2001, pp. 89.
  • Year: 2001

Permalloy GMI Sensor

Prediction of Flipping Fields in AMR Sensors

  • Authors: Hauser, H., Fulmek, P., Haumer, P., Vopálenský, M., prof. Ing. Pavel Ripka, CSc.,
  • Publication: MMM Conference. 2001, pp. 292.
  • Year: 2001

Pulse Excitation of Micro-Fluxgate Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc., Choi, S.O., Tipek, A.
  • Publication: IEEE Transactions on Magnetics. 2001, 37(4), 1998-2000. ISSN 0018-9464.
  • Year: 2001

Pulse Excitation of the Micro-fluxgate Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: The 8th Joint MMM-Intermag Conference - Abstracts. San Antonio, Texas: Courtesy Associates, 2001. p. 506.
  • Year: 2001

Remanent Field of Human Lungs

Sampling Measurement of Dynamic Hysteresis Loops

Sampling Measurements with Digital Hysteresisgraph

Symmetrical Core Improves Micro-Fluxgate Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc., Choi, S.O., Tipek, A., Kawahito, S., Ishida, M.
  • Publication: Sensors and Actuators. 2001, 1-3(92), 30-36. ISSN 0924-4247.
  • Year: 2001

AC Magnetic Field Sensors: Fluxgate versus Induction Coil

Crossfield Effect at Fluxgate

  • Authors: prof. Ing. Pavel Ripka, CSc., Billingsley, S.W.
  • Publication: Sensors and Actuators. 2000, 81(1-3), 176-179. ISSN 0924-4247.
  • Year: 2000

Dust Detection by Magnetopneumometry

Excitation of Fluxgate Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Eurosensors XIV - Book of Abstracts. Lyngby: MIC - Mikroelektronic Centre, 2000. pp. 425-426. ISBN 87-89935-51-9.
  • Year: 2000

Factor Limiting the Accuracy of Sampling Hysteresisgraph

Induction Coils: Voltage versus Current Output

Induction Coils: Voltage versus Current Output

Magnetic Field - Problem for the Computer Monitors

Magnetic Lung Diagnostics Using Fluxgate

Magnetic Lung Diagnostics Using Fluxgate

Magnetic Shielding of Computer Monitors

Magnetometer for New Czech Satellite MIMOSA

  • Authors: Cerman, A., Tipek, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Applied Electronics 2000. Plzeň: Západočeská universita, 2000. pp. 42-46. ISBN 80-7082-650-9.
  • Year: 2000

Magnetopneumography

Magnetopneumography - Method of Examination for Determination of Dust Retention in the Lungs

Micro-Fluxgate Sensor with Double-Sided Core

  • Authors: prof. Ing. Pavel Ripka, CSc., Choi, S.O., Kawahito, S., Tipek, A., Ishida, M.
  • Publication: EMSA 2000 - 3rd European Conference on Magnetic Sensors and Actuators. Dresden: W.E.B. Universitätsverlag, 2000. p. 167-168. ISBN 3-933592-81-X.
  • Year: 2000

New Directions in Fluxgate Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Journal of Magnetism and Magnetic Materials. 2000, 215(216), 735-739. ISSN 0304-8853.
  • Year: 2000

New Types of Magnetoresistors

Precise Magnetometers

Race-Track Fluxgate with Adjustable Feedthrough

Sensor Applications of Amorphous and Nanocrystalline Materials

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: NMMSA New Materials for Multifunctional Sensor Applications - Abstract Booklet. München: Walter Schottky Institut, TU München, WE-Heraeus-Stiftung, 2000. pp. 43.
  • Year: 2000

Sensors Based on Soft Magnetic Materials

  • Authors: prof. Ing. Pavel Ripka, CSc., Vértesy, G.
  • Publication: Journal of Magnetism and Magnetic Materials. 2000, 215(216), 795-799. ISSN 0304-8853.
  • Year: 2000

Symmetrical Core Improves Micro-Fluxgate Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc., Tipek, A., Kawahito, S., Ishida, M.
  • Publication: Eurosensors XIV - Book of Abstracts. Lyngby: MIC - Mikroelektronic Centre, 2000. p. 499-500. ISBN 87-89935-51-9.
  • Year: 2000

Testing and Comparing of High-Resolution Converters ADS 1211 and AD 7714

  • Authors: Cerman, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Proceedings of Workshop 2000. Praha: České vysoké učení technické v Praze, 2000. pp. 202. ISBN 80-01-02229-3.
  • Year: 2000

Testing and Comparing of the High-Resolution Converters ADS1211 and AD7714

  • Authors: Cerman, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: BEC 2000 - Baltic Electronics Conference. Tallinn: Tallinn Technical University, 2000. pp. 315-316. ISBN 9985-59-179-8.
  • Year: 2000

Testing of Synchronous AD Converters

The AMR Magnetometer

The New Method of the Sampling in the Satellite Magnetometer

  • Authors: Tipek, A., Cerman, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Poster 2000. Praha: České vysoké učení technické v Praze, Fakulta elektrotechnická, 2000. pp. E29.
  • Year: 2000

Tuned Current-Output Fluxgate

Two-Channel ADC System for Hysteresisgraph

AC Digital Hysteresisgraph

AC-driven AMR and GMR Magnetoresistors

  • Authors: prof. Ing. Pavel Ripka, CSc., Tondra, M., Stokes, J., Beech, R.
  • Publication: Sensors and Actuators. 1999,(76), 227-232. ISSN 0924-4247.
  • Year: 1999

Accuracy of Sampling Methods in AC Magnetic Measurements

Adjustable Race-Track Fluxgate

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Eurosensors XIII. Hague: InetLingua, 1999, pp. 441-444. ISBN 90-76699-02-X.
  • Year: 1999

Calibration and Stability of the Fluxgate Gradiometer

Calibration of 3-Axis Magnetometer

Calibration of AMR Magnetic Sensors

Current Sensors

Digitising Signal of the "MIMOSA" Fluxgate Magnetometer

  • Authors: Tipek, A., Cerman, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Poster 1999. Praha: České vysoké učení technické v Praze, Fakulta elektrotechnická, 1999, pp. 66-67.
  • Year: 1999

Exposition to Industrial Aerosols

  • Authors: Švábová, K., prof. Ing. Pavel Ripka, CSc., doc. Ing. Petr Kašpar, CSc., Navrátil, P.
  • Publication: Sborník souhrnů - XXV. kongres pracovního lékařství s mezinárodní účastí. Ostrava: Česká společnost pracovního lékařství ČLS JEP, 1999. pp. 43-50.
  • Year: 1999

Fluxgate Magnetopneumography

Gradiometric Sensor

Magnetic Method of Lung Diagnostics

Magnetic Properties of the Industrial Dust

Magnetic Sensors

Magnetic Sensors for Space and Field

Magnetic Sensors for Traffic Control

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: IMEKO - XV World Congress - Vol. X - TC-17, ISMCR'99. Osaka: IMEKO, 1999, pp. 241-246. ISBN 4-907764-03-0.
  • Year: 1999

Magnetic Shielding of Computer Monitors

Magnetic Shielding of Precise DC Current Clamp

Magnetometer for the Mimosa Satellite

  • Authors: Tipek, A., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Proceedings of Workshop 99. Praha: České vysoké učení technické v Praze, 1999, pp. 200.
  • Year: 1999

Magnetopneumometric Measurements In Vivo

New Directions in Fluxgate Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Conference Abstracts "Soft Magnetic Materials 14". Budapest: Research Institute for Solid State Physics and Optics, 1999. p. 38-39.
  • Year: 1999

Processing of the Fluxgate Output Signal

  • Authors: prof. Ing. Pavel Ripka, CSc., Kawahito, S.
  • Publication: IMEKO - XV World Congress - Vol. IV - TC-4 - Measurement to Improve the Quality of Life in the 21st Century. Osaka: IMEKO, 1999, pp. 75-80. ISBN 4-907764-03-0.
  • Year: 1999

The Accuracy of Contactless Sensors of Current

  • Authors: Kejík, P., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Snímače - Senzory - Aplikace. Ostrava: Ostravská univerzita, 1999, pp. 16-22. ISBN 80-7042-785-X.
  • Year: 1999

Tuning the Current-Output Fluxgate

  • Authors: prof. Ing. Pavel Ripka, CSc., Primdahl, F.
  • Publication: Transducers'99. Tokyo: The Institute of Electrical Engineers of Japan, 1999, pp. 590-593.
  • Year: 1999

AC Digital Hysteresisgraph

AC-driven AMR and GMR Magnetoresistors

  • Authors: prof. Ing. Pavel Ripka, CSc., Tondra, M., Stokes, J., Beech, R.
  • Publication: Eurosensors XII. Bristol: Institute of Physics Publishing, 1998. p. 967-970. ISBN 0-7503-0596-7.
  • Year: 1998

Analysis of Data from 3-axis Magnetometer Calibrator

Calibration and Stability of the Fluxgate Gradiometer

Crossfield Effect at Fluxgate

  • Authors: prof. Ing. Pavel Ripka, CSc., Billingsley, S.W.
  • Publication: EMSA 98. Sheffield: University of Sheffield, 1998, pp. 62-64.
  • Year: 1998

Détermination de la poussiere ferromagnétique dans le matériel biologique

Dynamic Hysteresis Loops Measurement System

Fluxgate: Current VS Voltage Output

  • Authors: prof. Ing. Pavel Ripka, CSc., Billingsley, W.
  • Publication: The 7th Joint MMM-Intermag Conference. San Francisco: American Institute of Physics and Magnetic Society of the IEEE, 1998, pp. 329-330.
  • Year: 1998

Fluxgate: Tuned vs. Untuned Output

  • Authors: prof. Ing. Pavel Ripka, CSc., Billingsley, S.W.
  • Publication: IEEE Transactions on Magnetics. 1998, 34(4), 1303-1305. ISSN 0018-9464.
  • Year: 1998

Magnetic Properties of the Industrial Dust

Magnetic Sensors for Navigation

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: ISMCR'98 (TC17) Proceedings of the Eighth International Symposium on Measurement and Control in Robotics. Prague: Czech National Committee IMEKO/CTU Prague, 1998. p. 105-108. ISBN 80-01-01814-8.
  • Year: 1998

Magnetic Shielding of Computer Monitors

Magnetic Shielding of Precise DC Current Clamp

Portable Fluxgate Magnetometer

The Magnetometer Calibrator

Accelerometric Logger

  • Authors: prof. Ing. Pavel Ripka, CSc., Roženský, P.
  • Publication: Proceedings of the 11th European Conference on Solid-State Transducers. Warsaw University of Technology, 1997, pp. 1325-1328. ISBN 83-908335-0-6.
  • Year: 1997

Advances in Magnetic Field Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Sixteenth Annual Conference on Properties and Applications of Magnetic Materials. Chicago: Illinois Institute of Technology, 1997. pp. 1-8.
  • Year: 1997

Fluxgate Sensor for Magnetopneumometry

Fully Digital Magnetic Measuring System

How to Extend Frequency Range of Induction Coils

Magnetic Measurements on the Phantom

  • Authors: Navrátil, P., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Workshop 97. Praha: České vysoké učení technické v Praze, 1997. pp. 1087-1088.
  • Year: 1997

Magnetic Projects at the Department of Measurement of FEE-CTU Prague

Magnetopneumographic System

  • Authors: prof. Ing. Pavel Ripka, CSc., Navrátil, P.
  • Publication: XIV IMEKO WORLD CONGRESS New Measurements - Challenges and Visions. Helsinki: Finnish Society of Automation, 1997. pp. 228-231. ISBN 952-5183-00-9.
  • Year: 1997

Portable Fluxgate Magnetometer

AC - Excited Magnetoresistive Sensor

AC/DC Current Comparator with Amorphous Core

  • Authors: Kejík, P., Draxler, K., prof. Ing. Pavel Ripka, CSc., doc. Ing. Petr Kašpar, CSc.,
  • Publication: New Measurement and Calibration Methods of Electrical Quantities and Instruments. Budapest: IMEKO TC4 Technical Committee on Measurement of Electrical Quantities, 1996, pp. 141-144. ISBN 963-420-491-0.
  • Year: 1996

Alternating current-excited magnetoresistive sensor

Contactless Current Measurement

Digital Techniques in Magnetic Measurements

Fluxgate Sensor for Magnetopneumometry

  • Authors: prof. Ing. Pavel Ripka, CSc., Navrátil, P.
  • Publication: Proceedings Eurosensors X. Leuven: Katholieke Universiteit, 1996. p. 1277-1280. ISBN 90-803282-1-9.
  • Year: 1996

Magnetic Detection of Respired Dust

  • Authors: prof. Ing. Pavel Ripka, CSc., Navrátil, P.
  • Publication: Workshop 96. Praha: České vysoké učení technické v Praze, 1996, pp. 909-910.
  • Year: 1996

Magnetic Inspection of Lungs

  • Authors: prof. Ing. Pavel Ripka, CSc., Navrátil, P.
  • Publication: Analysis of Biomedical Signals and Images. Brno: VUT v Brně, 1996, pp. 276-278. ISBN 80-214-0768-9.
  • Year: 1996

Magnetic Properties of the Respired Particles

  • Authors: prof. Ing. Pavel Ripka, CSc., Navrátil, P., Žák, T., Schneeweis, O., Bláha, J., Jeřábek, J.
  • Publication: Interdisciplinary Applied Electromagnetics. Brno: Czech Society of Applied Electromagnetics, 1996, pp. 194-198.
  • Year: 1996

Measurement of Low DC and AC Magnetic Fields

Noise and Stability of Magnetic Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Journal of Magnetism and Magnetic Materials. 1996, 15(157), 424-427. ISSN 0304-8853.
  • Year: 1996

Numerical Processing in Pulse Field Measurements

Precise DC Current Sensors

Synchronous Filters in Sensor Technology

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Proceedings Eurosensors X. Leuven: Katholieke Universiteit, 1996, pp. 347-350. ISBN 90-803282-1-9.
  • Year: 1996

Technical Applications of Magnetoresistors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Program booklet ISMI 96. Anshan: Liaoning Society of Science and Technology, 1996, pp. 87. ISBN 7-81054-186-2.
  • Year: 1996

Technical problems caused by variation of magnetic field

AC - Excited Magnetoresistive Sensor

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Book of Abstracts. Philadelphia: American Institute of Physics, 1995, pp. 176-177.
  • Year: 1995

AC Magnetic Field Measurement Using the Fluxgate

DC Current Sensor

Development, Construction and Analysis of the 'Oersted' Fluxgate Magnetometer

  • Authors: Nielsen, O., Petersen, J., Primdahl, F., Brauer, P., Hernando, B., Fernandez, A., Merayo, J., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Measurement Science and Technology. 1995, 15(6), 1099-1115. ISSN 0957-0233.
  • Year: 1995

Fluxgate Magnetopneumometer

Measurement of Very Low Magnetic Fields

New Magnetic Materials for Measurement Technology

Noise and Stability of Magnetic Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: 6th European Magnetic Materials and Applications Conference. Wien: Technische Universität, 1995. p. 249.
  • Year: 1995

Precise DC Current Clamp

Virtual Complex Permeability Meter

AC Magnetic Field Measurement Using the Fluxgate

  • Authors: prof. Ing. Pavel Ripka, CSc., Primdahl, F., Nielsen, O., Petersen, J., Ranta, A.
  • Publication: Proceedings of EUROSENSORS VIII. Lausanne: Elsevier Science, 1994. p. 307-311. ISSN 0924-4247.
  • Year: 1994

AC Magnetic Field Measurement Using the Fluxgate

  • Authors: prof. Ing. Pavel Ripka, CSc., Nielsen, O., Petersen, J., Primdahl, F.
  • Publication: Eurosensors VIII Conference - Book of Abstract. Toulouse: Laboratoire d´Architecture et d'Analyse des Systémes du CNRS, 1994. p. 430.
  • Year: 1994

Amorphous & Nanocrystalline Magnetic Materials - Measurement and Technical Applications

DC Hysteresigraph

Dynamic Digital Hysteresigraph

Fluxgate Gradiometer for Magnetopneumography

  • Authors: prof. Ing. Pavel Ripka, CSc., Bláha, J., Jeřábek, J.
  • Publication: From Measurement to Innovation. Proc. of the XIII IMEKO World Congress. Torino: IMEKO, 1994, pp. 1527-1531.
  • Year: 1994

Fluxgate Magnetometers and Gradiometers

High Frequency Fluxgate Sensor Noise

  • Authors: Primdahl, F., Nielsen, O., Petersen, J., prof. Ing. Pavel Ripka, CSc.,
  • Publication: Electronics Letters. 1994, 30(6), 481-482. ISSN 0013-5194.
  • Year: 1994

Labwindows Projects at CTU Prague

Magnetic Measuring Systems

Magnetic Sensors for Industrial and Field Applications

Measurement of AC Permeability of Toroidal Samples

Measurement of DC Magnetic Pollution

Measurement of Low Frequency Noise Using a Sigma-Delta-ADC/PC Measurement System

  • Authors: Sedláček, M., prof. Ing. Pavel Ripka, CSc., Janásek, V.
  • Publication: From Measurement to Innovation. Proc. of the XIII IMEKO World Congress. Torino: IMEKO, 1994, pp. 741-746.
  • Year: 1994

Measuring System for Study of Micromagnetic Properties of Various Biological Subjects

  • Authors: Bláha, J., prof. Ing. Pavel Ripka, CSc., Podlešák, J., Jeřábek, J.
  • Publication: Abstract Book of BEMS Conference. Copenhagen: Biomagnetic Society of America, 1994, pp. 166.
  • Year: 1994

Satellite Magnetometer

  • Authors: prof. Ing. Pavel Ripka, CSc., Petersen, J., Petersen, H., Nielsen, O., Primdahl, F.
  • Publication: Journal of Electrical Engineering. 1994, 45(2), 107-109. ISSN 0013-578X.
  • Year: 1994

Software for Magnetic Measurements

Ambulatory Noise Analysis System

  • Authors: prof. Ing. Pavel Ripka, CSc., Sedláček, M., Janásek, V.
  • Publication: Intelligent Instrumentation for Remote and On-Site Measurements. Brussels: IMEKO, 1993, pp. 413-419. ISBN 90-9006205-X.
  • Year: 1993

Coherent Signal Processing in Sensor Technology

Computer-Controlled AC Magnetic Measuring System

Measurement of Noise of Fluxgate Magnetic Sensors

  • Authors: Sedláček, M., prof. Ing. Pavel Ripka, CSc.,
  • Publication: VII. Messtechnisches Symposium des AHM. Wien: Technische Universität, 1993, pp. 91-95.
  • Year: 1993

New Developments in the Fluxgate Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Workshop 93. Praha: České vysoké učení technické v Praze, 1993. pp. 151-152.
  • Year: 1993

New Tools for the Measuring Systems Programming

Race-track Fluxgate Gradiometer

Race-track Fluxgate Sensors

REVIEW OF FLUXGATE SENSORS

THE SENSITIVITY PARAMETERS OF THE SHORT-CIRCUITED FLUXGATE

Fluxgate Sensor with Increased Homogeneity

Improved Fluxgate for Compasses and Position Sensors

  • Authors: prof. Ing. Pavel Ripka, CSc.,
  • Publication: Journal of Magnetism and Magnetic Materials. 1990, 83(1-3), 543-544. ISSN 0304-8853.
  • Year: 1990
  • Department: Department of Measurement
  • Annotation:
    Fluxgate cores from etched rings of Permalloy sheet are proposed. They achieved better long-term stability and lower angle error (4' error was reached). Dynamic performance was investigated - 5 khz band-pass was obtained and 5 ms impulses were measured with an amorphous core.

Contribution to the Ring-Core Fluxgate Theory

  • Department: Department of Measurement
  • Annotation:
    Existing theories for open-core fluxgate are not fitting experimental results in the case of ring-core sensors. Simple description based on transfer functions which takes into account the interaction between two half-cores is presented. Measured inner loops and dynamical transfer functions justified this approach. Flux-evaluating fluxgate was proposed for simple instruments. Its main advantage is its insensitivity to excitation current field parameter variations, but it has a threshold level of about 100 nT in present time. Methods of calibration and noise evaluation of sensors are also mentioned.

Responsible person Ing. Mgr. Radovan Suk