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Ing. Michal Janošek, Ph.D.

Všechny publikace

Identification of geomagnetic pulsations in SQUID data for Space Weather research

  • DOI: 10.1109/TASC.2024.3350597
  • Odkaz: https://doi.org/10.1109/TASC.2024.3350597
  • Pracoviště: Katedra měření
  • Anotace:
    The SQUID records small geomagnetic variations such as pulsations, which are short period fluctuations of the geomagnetic field at ULF frequencies. To distinguish pulsations from uncorrelated noise, the SQUID data is correlated with fluxgate data from the two closest INTERMAGNET observatories. Man-made noise and SQUID oscillations should give low coherence. Coherence higher than 0.9 was found when pulsations were present in the data and the algorithm has also proven effective on data contaminated with the thermal SQUID oscillations.

An Improved Composition of CoFeSiB Alloy for Orthogonal Fluxgates

  • DOI: 10.3390/s22062162
  • Odkaz: https://doi.org/10.3390/s22062162
  • Pracoviště: Katedra měření
  • Anotace:
    We show that the wires with vanishing magnetostriction in their as-cast form exhibit positive magnetostriction after long-time annealing (more than 30 min), which increases the noise of the sensor. After researching the effect of the magnetostriction after annealing on the noise, we propose an alloy with a reduced amount of iron.

Offset drift in orthogonal fluxgate and importance of closed-loop operation

  • DOI: 10.1016/j.sna.2022.113583
  • Odkaz: https://doi.org/10.1016/j.sna.2022.113583
  • Pracoviště: Katedra měření
  • Anotace:
    In this paper we show an up-to-now unexplained source of offset drift affecting the fundamental mode orthogonal fluxgate. After a sudden change or removal of the magnetic field, we observe an offset transient which lasts units to hundreds of seconds. We exclude the thermal origin of such transient as well as the electric origin in the pick- up coil resonance circuit or sensing amplifiers. We prove that this transient has magnetic origin, since it depends on both the amplitude and the duration of the pulse of magnetic field applied to the sensor which can be expressed as magnetic energy. We conclude that operating the fundamental mode orthogonal fluxgate in a closed feedback-loop is useful by suppressing this transient behavior by keeping the core in a (almost) zero field, however when switching the magnetometer sensor on/off, this transient has to be taken into account.

Low frequency noise investigation of pT-level magnetic sensors by cross-spectral method

  • DOI: 10.1109/SENSORS47087.2021.9639875
  • Odkaz: https://doi.org/10.1109/SENSORS47087.2021.9639875
  • Pracoviště: Katedra měření
  • Anotace:
    We present a simple method to estimate the noise of magnetic sensors running in the Earth’s field range by establishing the cross-power spectrum density during ambient field operation and performing spectral subtraction. This method has advantages to the usual subtraction of two sensors outputs, mainly in requirements for synchronization of the sample rate and gain calibration. With this method, verified in simulation and measurements with AMR magnetometers, we could use a fluxgate as a second sensor in order to estimate the low-frequency noise of an HTS SQUID in the ambient field.

Orthogonal fluxgate sensor noise depends on annealing-induced magnetostriction of the core

  • DOI: 10.1109/SENSORS47087.2021.9639470
  • Odkaz: https://doi.org/10.1109/SENSORS47087.2021.9639470
  • Pracoviště: Katedra měření
  • Anotace:
    For long time amorphous microwires with (Co 94 Fe 6 ) 72.5 Si 12.5 B 15 composition have been extensively used for magnetic sensors, such as fluxgates but also magnetoimpedance, due to their vanishing magnetostriction. In fluxgate sensors we want to minimize the magnetostriction because it couples any mechanical stress (for instance due to thermal expansion) to the magnetic characteristic of the wire making the noise of the fluxgate sensor rise. In this paper we compared two magnetic wires, one with slightly negative and one with slightly positive magnetostriction in their as cast state and we anneal them measuring then how the magnetostriction and the noise evolves as we increase the annealing time.

Reduction of magnetic noise limits of orthogonal fluxgate sensor

  • DOI: 10.1063/9.0000231
  • Odkaz: https://doi.org/10.1063/9.0000231
  • Pracoviště: Katedra měření
  • Anotace:
    We have further lowered the white noise of an orthogonal fluxgate to about 0.3 pT/√Hz @ 8 Hz. So far, this is the lowest noise reported for a fluxgate magnetometer. The noise reduction was achieved by introducing a JFET input stage, embedded directly to the sensor head, allowing for high common-mode rejection and negligible loading of the resonant circuit. The origin of the noise was investigated by correlation measurements and we concluded that, at least in the white noise region, we observe the magnetic noise of the sensor, with about 0.1 pT/√Hz white noise contribution by the electronics. We were finally able to obtain sensor noise floor below 1 pT/√Hz @ 1 Hz also in a feedback-compensated closed-loop. Closed-loop operation allows for higher magnetometer stability and operation in Earth’s magnetic field without deteriorating its noise performance.

1-pT noise fluxgate magnetometer for geomagnetic measurements and unshielded magnetocardiography

  • DOI: 10.1109/TIM.2019.2949205
  • Odkaz: https://doi.org/10.1109/TIM.2019.2949205
  • Pracoviště: Katedra měření
  • Anotace:
    We present the development of a low-noise, fundamental-mode, orthogonal fluxgate magnetometer with four amorphous, annealed ferromagnetic wires. The 1-Hz noise obtained in open-loop and closed-loop is as low as 0.75 and 1.5 pTrms/√Hz, respectively, with white noise level about 0.6 pTrms/√Hz. This is to our knowledge the lowest figure published for a fluxgate magnetometer so far. We compared the instrument performance to a low-noise observatory magnetometer when doing geomagnetic measurements and show that it is fully suitable for measurements at mHz frequencies, e.g. magnetotellurics. The magnetometer performance enables room-temperature, unshielded magnetocardiography.

Stabilized magnetic vacuum using a rotating fluxgate sensor

  • DOI: 10.1109/SENSORS47125.2020.9278793
  • Odkaz: https://doi.org/10.1109/SENSORS47125.2020.9278793
  • Pracoviště: Katedra měření
  • Anotace:
    We present an effective zero-field system utilizing a rotating, single-axis fluxgate sensor to establish and maintain a magnetic vacuum in triaxial coils. With the help of a low-noise fluxgate sensor rotating at a frequency of 1 Hz, we were able to set the magnetic zero in the horizontal plane to or below 0.5 nT, which is 10 ppm of the local magnetic field, or 100 dB suppression. With the help of an additional triaxial sensor at a 2.5-m distance, we were able to maintain the magnetic zero to about 1 nT within 30-minutes suppressing field variations and disturbances. Such a system allows for precise magnetic calibrations, paleomagnetic experiments or other tasks where magnetic vacuum is beneficial or required.

1 pT-noise fluxgate magnetometer design and its performance in geomagnetic measurements

  • DOI: 10.1109/I2MTC.2019.8826956
  • Odkaz: https://doi.org/10.1109/I2MTC.2019.8826956
  • Pracoviště: Katedra měření
  • Anotace:
    We present a design of a low-noise, fundamentalmode, orthogonal fluxgate magnetometer with amorphous wires. The noise obtained in open-loop was as low as 5, 2 and 0.8 pT/√ Hz at 0.1, 1 and 5 Hz, respectively. As the instrument is a self-contained device, powered with batteries, we were able to run a series of geomagnetic measurements and compare them to a low-noise observatory magnetometer. The geomagnetic measurements were performed at the SANSA Space Science facility in Hermanus, South Africa. The offset drift is still an issue, however we show that the instrument is fully suitable for measurements down to 10 mHz. With numeric compensation of the offset drift, sub-mHz measurements are possible. As the instrument is non-cryogenic and portable, more applications, such as magnetotellurics or an unshielded magnetocardiography with a gradiometric sensor, are foreseen.

A Digitally Compensated AMR Magnetometer

  • DOI: 10.1109/TMAG.2018.2873235
  • Odkaz: https://doi.org/10.1109/TMAG.2018.2873235
  • Pracoviště: Katedra měření
  • Anotace:
    This paper considers the possibilities of using digital feedback for precise anisotropic magneto-resistance (AMR) magnetometers using commercial off-the-shelf (COTS) components. This paper presents the full characterization of a real instrument, including its noise, linearity, stability, and power consumption.

Estimation of Angular Deviations in Precise Magnetometers

  • DOI: 10.1109/LMAG.2019.2944125
  • Odkaz: https://doi.org/10.1109/LMAG.2019.2944125
  • Pracoviště: Katedra měření
  • Anotace:
    Capabilities for calibrations of angular deviations of sensor triplets in precise magnetometers were evaluated in a 2.5-meter, triaxial Helmholtz-coil facility. The coil system is located in a magnetically quiet environment at SANSA Space Science in Hermanus, South Africa. The angular calibration results obtained from the "thin-shell" calibration procedure were compared with direct measurements on a non-magnetic tilting/rotational platform.

Magnetic Calibration System With Interference Compensation

  • DOI: 10.1109/TMAG.2018.2874169
  • Odkaz: https://doi.org/10.1109/TMAG.2018.2874169
  • Pracoviště: Katedra měření
  • Anotace:
    This paper describes a novel method for calibrating dc-precise magnetometers in the low field range (± 100 μT), which gives acceptable results even in laboratory conditions with significant magnetic interference. By introducing a closely mounted reference magnetometer and a specific calibration procedure, it is possible to compensate for the external magnetic field disturbances caused, e.g., by the local transportation operated with dc power supplies.

Effect of amorphous wire core diameter on the noise of an orthogonal fluxgate

Effect of Amorphous Wire Core Diameter on the Noise of an Orthogonal Fluxgate

  • DOI: 10.1109/TMAG.2018.2850905
  • Odkaz: https://doi.org/10.1109/TMAG.2018.2850905
  • Pracoviště: Katedra měření
  • Anotace:
    In this paper, we investigated the effects of different diameters versus the noise of the sensor. Our purpose is to understand that if there is a room for improvement of noise by producing amorphous wires with different diameters.

Elektrická měření - Přístroje a metody

  • Pracoviště: Katedra měření
  • Anotace:
    Stejně jako původní vydání knihy Elektrická měření – přístroje a metody z roku 2003 i toto shrnuje informace týkající se oblasti elektrických a magnetických měření na úrovni absolventa inženýrského studia elektrotechnických oborů. Vzhledem k prudkému rozvoji elektroniky a číslicové techniky však byla náplň většiny kapitol značně modernizována popř. rozšířena a část věnovaná analogovým přístrojům naopak významně zredukována. V publikaci jsou vysvětleny základní principy používané v současné době pro měření elektrických popř. magnetických veličin a principy nejčastěji používaných metod pro měření ostatních fyzikálních veličin s mezipřevodem na elektrický signál. Jsou popsány též běžně používané měřicí přístroje a principy jejich činnosti, s čímž samozřejmě souvisí i jejich vlastnosti. Vzhledem k tomu, že jejich základním blokem jsou analogově-číslicové popř. číslicově-analogové převodníky, je samostatná kapitola věnována i digitalizaci signálu. Problematika určování nejistot měření je klíčovým parametrem při řízení a kontrole kvality výroby. Nejistotám měření je proto věnována nejen celá 1. kapitola, ale odhad nejistot je také zmíněn i v kapitolách věnovaným metodám měření aktivních elektrických veličina parametrů pasivních součástek.

Improving Earth’s magnetic field measurements by numerical corrections of thermal drifts and man- made disturbances

  • DOI: 10.1155/2018/1804092
  • Odkaz: https://doi.org/10.1155/2018/1804092
  • Pracoviště: Katedra měření
  • Anotace:
    This contribution deals with challenges encountered in real-world geomagnetic measurements, and is focused on improving the performance of two variometer stations of Kelčany and Polom, which have been recently established in the Czech Republic.

Orthogonal Fluxgate Gradiometer With Multiple Coil Pairs

  • DOI: 10.1109/TMAG.2017.2758680
  • Odkaz: https://doi.org/10.1109/TMAG.2017.2758680
  • Pracoviště: Katedra měření
  • Anotace:
    In this paper, we study the possibility to exploit the noise correlation in a fundamental mode orthogonal fluxgate used as a gradiometer in order to maximize the noise suppression. We study the correlation of the noise along a single core fluxgate using two short coils at a variable distance, and we derive how it drops as the distance increases. Furthermore, we observed this phenomenon with the central point of the coils located at different parts of the wire, obtaining a similar behavior. We also explain that the response of such configuration of the gradiometer to the homogeneous field is zero even if the single coils are not symmetric with the respect of the center of the core if the pairs of coils are all symmetric.

Very low frequency noise reduction in orthogonal fluxgate

  • DOI: 10.1063/1.4994208
  • Odkaz: https://doi.org/10.1063/1.4994208
  • Pracoviště: Katedra měření
  • Anotace:
    In this paper we present a simple, cheap and effective method to obtain reduction of very low frequency noise in an orthogonal fluxgate in fundamental mode. This method consists in the application of a layer of silicone over the magnetic core of the sensor filling the whole space inside the pick-up coil. In this way we avoid fast variations of temperature to affect the offset of the sensor (which is very sensitive to temperature changes).

Magnetic gradiometer with self compensation of offset drift

  • DOI: 10.1109/ICSENS.2016.7808502
  • Odkaz: https://doi.org/10.1109/ICSENS.2016.7808502
  • Pracoviště: Katedra měření
  • Anotace:
    In this paper we present a magnetic gradiometer based on a single core orthogonal fluxgate in fundamental mode. Contrarily to similar gradiometers based on detached sensor heads the use of a single core strongly reduces the offset instability of the output. The offset drift is caused by temperature variations and in a single ferromagnetic core the temperature is more uniform than in two detached cores. As a result the offset of both coils drift in a very similar way and when computing their difference to obtain the gradiometric signal the output is very stable. Moreover, we show that using a single core we have noise suppression due to correlation of the magnetic noise and this mechanism also leads to noise reduction of the gradiometric output. As a result we achieved 10 pT/m/VHz noise at 1 Hz.

Orthogonal fluxgate gradiometer with multiple coil pairs

  • DOI: 10.1109/INTMAG.2017.8007976
  • Odkaz: https://doi.org/10.1109/INTMAG.2017.8007976
  • Pracoviště: Katedra měření
  • Anotace:
    In this paper we present a new type of magnetic gradiometer based on orthogonal fluxgate in fundamental mode. This type of sensor can be build using two different magnetic cores, each one with its own pick-up coil, or using single core with two pick-up coils wound on it.

Low-noise magnetic observatory variometer with race-track sensors

  • Autoři: Ing. Michal Janošek, Ph.D., Ing. Vojtěch Petrucha, Ph.D., Vlk, M.
  • Publikace: Proceedings of 5th International Conference on Materials and Applications for Sensors and Transducers (IC-MAST2015). Bristol: IOP Institute of Physics, 2016. IOP Conference Series: Materials Science and Engineering. ISSN 1757-899X.
  • Rok: 2016
  • DOI: 10.1088/1757-899X/108/1/012026
  • Odkaz: https://doi.org/10.1088/1757-899X/108/1/012026
  • Pracoviště: Katedra měření
  • Anotace:
    We present a low-noise, high-stability observatory magnetometer with race-track sensors, as developed by the Czech Technical University in Prague for National Observatory of Athens. As opposed to the standard instruments, we used our novel race-track fluxgate sensors with planar oval core which were cut by state-of-the art pico-second UV-laser.

Parallel Fluxgate Magnetometers

  • Autoři: Ing. Michal Janošek, Ph.D.,
  • Publikace: High Sensitivity Magnetometers. Basel: Springer, 2016. p. 41-61. Smart Sensors, Measurement and Instrumentation. vol. 19. ISSN 2194-8402. ISBN 978-3-319-34070-8.
  • Rok: 2016
  • DOI: 10.1007/978-3-319-34070-8_2
  • Odkaz: https://doi.org/10.1007/978-3-319-34070-8_2
  • Pracoviště: Katedra měření
  • Anotace:
    This chapter gives a brief overview of parallel fluxgate development, technology and performance. Starting from theoretical background through derivation of fluxgate gating curves, the fluxgate sensor is explained on its typical examples, including sensors with rod-, ring- and race-track core. The effects of geometry, construction and magnetic material treatment on parallel fluxgate noise are discussed in detai. Basic applications of fluxgate magnetometers are given and a quick overview of commercial devices is presented, concluded with recent advances in bulk, miniature, digital and aerospace devices.

Simple estimation of dipole source z-distance with compact magnetic gradiometer

  • Autoři: Ing. Michal Janošek, Ph.D., doc. Ing. Antonín Platil, Ph.D., Vyhnánek, J.
  • Publikace: Proceedings of 5th International Conference on Materials and Applications for Sensors and Transducers (IC-MAST2015). Bristol: IOP Institute of Physics, 2016. IOP Conference Series: Materials Science and Engineering. ISSN 1757-899X.
  • Rok: 2016
  • DOI: 10.1088/1757-899X/108/1/012025
  • Odkaz: https://doi.org/10.1088/1757-899X/108/1/012025
  • Pracoviště: Katedra měření
  • Anotace:
    A compact magnetometer/gradiometer with combined homogeneous and gradient outputs facilitates precise measurement of both H and G values with good spatial and temporal coherence. By evaluating combination of both signals, it is possible to estimate distance to a dipole source with relatively small error and largely independent from precise knowledge of source strength, orientation and lateral displacement.

Compact Full-tensor Fluxgate Gradiometer

  • Pracoviště: Katedra měření
  • Anotace:
    Using full-tensor gradiometers has various advantages over simplified uniaxial gradiometers or even scalar measurements. The full-tensor information is used mainly in geophysical prospecting and in security/military applications. In our new design we combined 10 small (20-mm) fluxgate sensors operating in feedback compensated mode into one compact head in the form of 46-mm cube.

Compact magnetic gradiometer and its astatization

  • DOI: 10.1016/j.proeng.2015.08.841
  • Odkaz: https://doi.org/10.1016/j.proeng.2015.08.841
  • Pracoviště: Katedra měření
  • Anotace:
    We present a compact (10-cm head size, 3-cm base) axial magnetic gradiometer with a method of its astatization (i.e. suppression of false response to homogeneous field). For astatization, we use two integrated orthogonal sensors and a second-order polynomial correction; after astatization the gradiometer error is suppressed more than 1000×.

Determination of the Overhauser magnetometer uncertainty

  • Autoři: Ulvr, M., Zikmund, A., Kupec, J., Ing. Michal Janošek, Ph.D., Vlk, M., Bayer, T.
  • Publikace: Journal of Electrical Engineering. 2015, 66(7), 26-29. ISSN 1335-3632.
  • Rok: 2015
  • Pracoviště: Katedra měření
  • Anotace:
    Overhauser magnetometers are the basic instruments for scalar measurements; however, their accuracy is determined at the time of manufacture only. Because of various effects affecting the gyromagnetic ratio of the used fluid or the stability of the oscillators in the circuitry, their accuracy should be verified during the instrument lifetime. Specific methodology of data processing and determination of the Overhauser magnetometer uncertainty is described in this paper.

Electroplated FeNi ring cores for fluxgates with field induced radial anisotropy

  • DOI: 10.1063/1.4914874
  • Odkaz: https://doi.org/10.1063/1.4914874
  • Pracoviště: Katedra měření
  • Anotace:
    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.

Precise calibration method for triaxial magnetometers not requiring Earth's field compensation

  • Autoři: Zikmund, A., Ing. Michal Janošek, Ph.D., Ulvr, M., Kupec, J.
  • Publikace: IEEE Transactions on Instrumentation and Measurement. 2015, 64(5), 1250-1255. ISSN 0018-9456.
  • Rok: 2015
  • DOI: 10.1109/TIM.2015.2395531
  • Odkaz: https://doi.org/10.1109/TIM.2015.2395531
  • Pracoviště: Katedra měření
  • Anotace:
    A calibration procedure for calibrations of triaxial magnetometers is presented. The procedure uses a triaxial Helmholtz coil system and an Overhauser scalar magnetometer and is performed in the an Earth's field range. The triaxial coils are firstly calibrated with the help of the Overhauser magnetometer and subsequently a calibration of a digital triaxial magnetometer calibration is performed. As opposed to other approaches, neither Earth’s field nulling system is needed, nor are movements of the magnetometer are needed. A real calibration test was carried out and the extended uncertainty was better than 430 ppm in sensitivity and 0.06 degrees in orthogonality.

The Effect of Sensor Size on Axial Gradiometer Performance

  • DOI: 10.1109/TMAG.2014.2359960
  • Odkaz: https://doi.org/10.1109/TMAG.2014.2359960
  • Pracoviště: Katedra měření
  • Anotace:
    The case of a finite base gradiometer with ideal sensors is considered, then influence of finite-size sensing elements is modeled and finally, comparison with experimental results obtained with two ring-core fluxgates and two AMR sensors are evaluated. Some of the effects found may be counterintuitive and especially in the close proximity of dipole source, the gradient cannot be further modeled by simplified uniaxial approximation because of the sensor size. Full Biot-Savart field model was considered in those cases.

Vector Feedback Homogeneity and Inner Layout Influence on Fluxgate Sensor Parameters

  • DOI: 10.1109/TIM.2014.2362831
  • Odkaz: https://doi.org/10.1109/TIM.2014.2362831
  • Pracoviště: Katedra měření
  • Anotace:
    Vector feedback is a concept which can significantly improve linearity and stability of a magnetic field sensor. The feedback coils effectively cancel the measured magnetic field in the inner volume of the triaxial sensor. Thus, in case of fluxgates, it suppresses one possible source of nonlinearity— cross-field sensitivity error. The triaxial sensor axes orthogonality should be primarily defined by the orientation of the feedback coils, while the sensitivities are defined by feedback coil constants. The influence of the homogeneity of the feedback field and the influence of the sensor inner layout on calibration parameters of a vectorially compensated triaxial fluxgate magnetometer are presented.

AMR Proximity Sensor With Inherent Demodulation

  • DOI: 10.1109/JSEN.2014.2325406
  • Odkaz: https://doi.org/10.1109/JSEN.2014.2325406
  • Pracoviště: Katedra měření
  • Anotace:
    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.

Calibration procedure for triaxial magnetometers without a compensating system or moving parts

  • Autoři: Zikmund, A., Ing. Michal Janošek, Ph.D.,
  • Publikace: Proceedings of Instrumentation and Measurement Technology Conference (I2MTC) 2014. Vail, Colorado: IEEE Instrumentation and Measurement Society, 2014, pp. 473-476. ISSN 1091-5281. ISBN 978-1-4673-6385-3.
  • Rok: 2014
  • DOI: 10.1109/I2MTC.2014.6860790
  • Odkaz: https://doi.org/10.1109/I2MTC.2014.6860790
  • Pracoviště: Katedra měření
  • Anotace:
    A calibration procedure for calibrations of triaxial magnetometers is presented. The procedure uses triaxial Helmholtz coil system and Overhauser scalar magnetometer and is performed in the Earth's field range. The triaxial coils are first calibrated with the help of Overhauser magnetometer and subsequently the triaxial magnetometer calibration is performed. As opposed to other approaches, neither Earth's field nulling system is needed, nor are movements of the magnetometer. Calibration uncertainty better than 200 ppm in sensitivity and 0.02 degrees in orthogonality can be achieved.

Effects of Core Dimensions and Manufacturing Procedure on Fluxgate Noise

  • Autoři: Ing. Michal Janošek, Ph.D., Vyhnánek, J., Zikmund, A., Butvin, P., Butvinová, B.
  • Publikace: Acta Physica Polonica A. 2014, 126(1), 104-105. ISSN 0587-4246.
  • Rok: 2014
  • DOI: 10.12693/APhysPolA.126.104
  • Odkaz: https://doi.org/10.12693/APhysPolA.126.104
  • Pracoviště: Katedra měření
  • Anotace:
    The effect of demagnetizing factor and manufacturing procedure on noise of the fluxgate probes, manufactured from metallic glasses, is presented. The fluxgate probes were either tape-wound, or flat, wet-etched ringcore and race-track geometries. When combining low demagnetizing factor and high enough cross-section of the probe, a minimum in the noise dependence can be found. For 50 mm ringcores, in such minimum the noise value as low as 7 pTRMS in 0.1-10 Hz frequency band was achieved, which is very low for an as-cast tape, and has not been reported before.

Electroplated Multi-ring Core Planar Fluxgate

  • DOI: 10.1016/j.proeng.2014.11.376
  • Odkaz: https://doi.org/10.1016/j.proeng.2014.11.376
  • Pracoviště: Katedra měření
  • Anotace:
    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.

Fine Smoothing of Conductive Substrate for Permalloy Layer Electroplating

  • DOI: 10.12693/APhysPolA.126.150
  • Odkaz: https://doi.org/10.12693/APhysPolA.126.150
  • Pracoviště: Katedra měření
  • Anotace:
    In this paper we study the influence of the roughness of the copper substrate on the magnetic properties of the FeNi film we electroplate onto it. The roughness and the thickness of the copper substrate are reduced by electropolishing in orthophosphoric acid: we show how to select the working point, which gives the highest smoothness, avoiding defects due to gas evolution. Finally we show how a smoother substrate contributes to reducing the coercivity of the magnetic film grown on it.

Fluxgate magnetometer vector feedback homogeneity and its influence on sensor parameters

  • Autoři: Ing. Vojtěch Petrucha, Ph.D., Ing. Michal Janošek, Ph.D., Azpurua, M. A.
  • Publikace: Proceedings of Instrumentation and Measurement Technology Conference (I2MTC) 2014. Vail, Colorado: IEEE Instrumentation and Measurement Society, 2014, pp. 460-463. ISSN 1091-5281. ISBN 978-1-4673-6385-3.
  • Rok: 2014
  • DOI: 10.1109/I2MTC.2014.6860787
  • Odkaz: https://doi.org/10.1109/I2MTC.2014.6860787
  • Pracoviště: Katedra měření
  • Anotace:
    Precise fluxgate sensors are built with a vector feedback, which eliminates the cross-field effect and improves linearity. The influence of the homogeneity of the feedback field on calibration parameters of a vectorially compensated tri-axial fluxgate magnetometer is presented.

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

  • DOI: 10.1109/TMAG.2014.2327105
  • Odkaz: https://doi.org/10.1109/TMAG.2014.2327105
  • Pracoviště: Katedra měření
  • Anotace:
    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
  • Odkaz: https://doi.org/10.1109/TMAG.2014.2329992
  • Pracoviště: Katedra měření
  • Anotace:
    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
  • Odkaz: https://doi.org/10.1109/ICSENS.2013.6688289
  • Pracoviště: Katedra měření
  • Anotace:
    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.

Dual-core fluxgate gradiometer with gradient feedback

  • DOI: 10.1109/ICSENS.2013.6688287
  • Odkaz: https://doi.org/10.1109/ICSENS.2013.6688287
  • Pracoviště: Katedra měření
  • Anotace:
    A fluxgate magnetic gradiometer with two fluxgate sensors and gradient feedback loop is presented. The two feedback coils, gradient and homogeneous, are common to both fluxgate sensors. The signal from the two sensors acts as regulating input in the two feedback loops, improving stability of the gradiometer. The presented gradiometer overcomes the problems of state-of-the art gradiometers which do not allow to decrease the sensor spacing.

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

  • Autoři: Vyhnánek, J., Ing. Michal Janošek, Ph.D., prof. Ing. Pavel Ripka, CSc.,
  • Publikace: 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
  • Rok: 2013
  • DOI: 10.1088/1742-6596/450/1/012031
  • Odkaz: https://doi.org/10.1088/1742-6596/450/1/012031
  • Pracoviště: Katedra měření
  • Anotace:
    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.

Magnetopneumography Using Optical Position Reference

  • DOI: 10.1166/sl.2013.2805
  • Odkaz: https://doi.org/10.1166/sl.2013.2805
  • Pracoviště: Katedra měření
  • Anotace:
    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.

AMR Gradiometer for Mine Detection

  • DOI: 10.1016/j.sna.2012.03.007
  • Odkaz: https://doi.org/10.1016/j.sna.2012.03.007
  • Pracoviště: Katedra měření
  • Anotace:
    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.

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

  • DOI: 10.1016/j.sna.2012.07.001
  • Odkaz: https://doi.org/10.1016/j.sna.2012.07.001
  • Pracoviště: Katedra měření
  • Anotace:
    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.

Magnetopneumography - Incorporation of Optical Position Reference

  • Pracoviště: Katedra měření
  • Anotace:
    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.

Magnetopneumography - Real-World Phantom Inversion

  • Pracoviště: Katedra měření
  • Anotace:
    Magnetopneumography needs inversion of weak magnetic data in order to estimate amount and spatial distribution of ferromagnetic dusts deposited in lungs of metal workers. Our continuously improved setup is sensitive enough to detect remanent fields of small amounts (<8 mg) of magnetite dust. Fluxgate probes as the best room-temperature sensors are used. Estimation of distribution of 35 unit cubes of a simplified phantom based on SVD calculated calibration inverse matrix is demonstrated here. We still cope with background noise and positioning errors that severely limit the results. Preparation of electronic calibration phantom should enable successful inversion of more complex sources.

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

  • DOI: 10.1063/1.3676238
  • Odkaz: https://doi.org/10.1063/1.3676238
  • Pracoviště: Katedra měření
  • Anotace:
    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
  • Odkaz: https://doi.org/10.1109/TMAG.2011.2172200
  • Pracoviště: Katedra měření
  • Anotace:
    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.

Temperature Dependence of Offset and Sensitivity in Orthogonal Fluxgate Operated in Fundamental Mode

  • Autoři: Butta, M., Sasada, I., Ing. Michal Janošek, Ph.D.,
  • Publikace: IEEE Transactions on Magnetics. 2012, 48(11), 4103-4106. ISSN 0018-9464.
  • Rok: 2012
  • DOI: 10.1109/TMAG.2012.2202383
  • Odkaz: https://doi.org/10.1109/TMAG.2012.2202383
  • Pracoviště: Katedra měření
  • Anotace:
    Orthogonal fluxgate in fundamental mode has low noise output but its offset is often very large. A method has been proposed to compensate the offset consisting in periodical switching of the dc bias of the excitation and subtraction of the signal obtained with positive and negative dc bias.

AMR Gradiometer for Mine Detection and Sensing

  • DOI: 10.1016/j.proeng.2011.12.089
  • Odkaz: https://doi.org/10.1016/j.proeng.2011.12.089
  • Pracoviště: Katedra měření
  • Anotace:
    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

  • Autoři: Ing. Michal Janošek, Ph.D., Vyhnánek, J., prof. Ing. Pavel Ripka, CSc.,
  • Publikace: 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
  • Rok: 2011
  • DOI: 10.1109/ICSENS.2011.6127370
  • Odkaz: https://doi.org/10.1109/ICSENS.2011.6127370
  • Pracoviště: Katedra měření
  • Anotace:
    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.

Optical Position Sensor Based on Digital Image Processing: Magnetic Field Mapping Improvement

  • Pracoviště: Katedra měření
  • Anotace:
    Optical position measurement system for an automated magnetic field mapping apparatus based on fluxgate sensors is presented. For the exact position estimation of the sensor head, a simple smart camera was developed with respect to minimal hardware configuration and real-time execution of position measurement algorithm. The camera is observing the mapped scene and evaluates position of the sensor head using an active marker. The sensor head is designed as movable, what allows keeping the scene fixed and exactly referenced to the mapped magnetic field using coordinates obtained from image. With image sensor fixed 2.5 m above the plane and range ±130 mm around the lens optical axis (image center), the total position measurement error is less than 0.5 mm. The research was realized within the scope of the task 5.6 'Optical measurement', a part of the MSM6840770015 project, GACR project GD102/09/H082.

Advances in Magnetic Field Sensors

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

  • DOI: 10.1109/ICSENS.2010.5690109
  • Odkaz: https://doi.org/10.1109/ICSENS.2010.5690109
  • Pracoviště: Katedra měření
  • Anotace:
    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

  • Pracoviště: Katedra měření
  • Anotace:
    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
  • Odkaz: https://doi.org/10.1016/j.proeng.2010.09.102
  • Pracoviště: Katedra měření
  • Anotace:
    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.

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

  • DOI: 10.1063/1.3360773
  • Odkaz: https://doi.org/10.1063/1.3360773
  • Pracoviště: Katedra měření
  • Anotace:
    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.

PCB Fluxgate Gradiometer Measuring dBx/dy

  • Pracoviště: Katedra měření
  • Anotace:
    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.

Single-lockin Detection of AC Magnetic Fields by Fluxgate Sensor

  • Autoři: Ing. Michal Janošek, Ph.D., Ďaďo, S.
  • Publikace: Proceedings of the 12th Biennial Baltic Electronics Conference. Tallin: Tallin University of Technology, 2010, pp. 223-226. ISSN 1736-3705. ISBN 978-1-4244-7357-1. Available from: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5631591
  • Rok: 2010
  • DOI: 10.1109/BEC.2010.5631591
  • Odkaz: https://doi.org/10.1109/BEC.2010.5631591
  • Pracoviště: Katedra měření
  • Anotace:
    We present a simple narrowband method to detect the amplitude of alternating magnetic fields by a fluxgate sensor using a single lock-in amplifier, eliminating some of the drawbacks of common method of using two phase sensitive demodulators (lock-in amplifiers). We eliminated the need for two phase-sensitivite demodulators by processing the reference signals of lock-in amplifier and of the fluxgate excitation unit.

Two Sources of Cross-field Error in Racetrack Fluxgate

  • DOI: 10.1063/1.3337721
  • Odkaz: https://doi.org/10.1063/1.3337721
  • Pracoviště: Katedra měření
  • Anotace:
    Two sources of cross-field error in racetrack fluxgate are identified: geometrical imperfection of the winding and nonhomogeneity of the sensor core.

Crossfield Effect in Magnetic Sensors

  • DOI: 10.1109/ICSENS.2009.5398405
  • Odkaz: https://doi.org/10.1109/ICSENS.2009.5398405
  • Pracoviště: Katedra měření
  • Anotace:
    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
  • Odkaz: https://doi.org/10.1166/sl.2009.1064
  • Pracoviště: Katedra měření
  • Anotace:
    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.

Detection of Magnetic Markers Using Array of PCB Fluxgate Sensors

  • Autoři: Ing. Michal Janošek, Ph.D.,
  • Publikace: Workshop 09 CTU REPORTS. Praha: České vysoké učení technické v Praze, 2009, ISBN 978-80-01-04286-1.
  • Rok: 2009
  • Pracoviště: Katedra měření
  • Anotace:
    The final aim of this work was to detect superparamagnetic particles, as they are widely used in biomedicine. We used our race-track fluxgate sensors, and arranged them perpendiculary to the AC excitation field, because our sensors exhibit low sensitivity to perpendicular fields. We were able to detect a volume of of 0.6 ml Endorem marker, which is used for MRI imaging on a maximum distance of 10 mm.

Magnetic Markers Detection Using PCB fluxgate array

  • DOI: 10.1063/1.3074780
  • Odkaz: https://doi.org/10.1063/1.3074780
  • Pracoviště: Katedra měření
  • Anotace:
    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.

PCB Sensors in Fluxgate Magnetometer with Controlled Excitation

Advances in Magnetic Sensors

  • DOI: 10.1109/ICSENS.2008.4716368
  • Odkaz: https://doi.org/10.1109/ICSENS.2008.4716368
  • Pracoviště: Katedra měření
  • Anotace:
    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.

Optically Referenced 2D Magnetic Field Mapping

  • Autoři: Ing. Michal Janošek, Ph.D., Pribula, O.
  • Publikace: EUROSENSORS XXII 2008. Dresden: Eurosensors, 2008. pp. 247-249. ISBN 978-3-00-025217-4.
  • Rok: 2008
  • Pracoviště: Katedra měření
  • Anotace:
    An automated magnetic field mapping apparatus, with fluxgate sensors, is presented. The exact position in X-Y coordinates is obtained by using a smart image sensor observing the mapped scene. The sensor head is designed as movable, which allows keeping the scene fixed and exactly referenced by the image coordinates.

Short-range Navigation of Minesweeping Detector

  • Pracoviště: Katedra měření
  • Anotace:
    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.

Low-power Fluxgate Signal Processing Using Gated Differential Integrator

  • DOI: 10.1166/sl.2007.046
  • Odkaz: https://doi.org/10.1166/sl.2007.046
  • Pracoviště: Katedra měření
  • Anotace:
    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.

Magnetometer with Pulse-Excited Miniature Fluxgate Sensor

  • Pracoviště: Katedra měření
  • Anotace:
    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.

Za stránku zodpovídá: Ing. Mgr. Radovan Suk