Lidé

Ing. Michal Dressler

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.

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.

Characterization of a Digital AMR Magnetometer for Space Applications

  • DOI: 10.1109/TIM.2020.3043867
  • Odkaz: https://doi.org/10.1109/TIM.2020.3043867
  • Pracoviště: Katedra měření
  • Anotace:
    In this paper, we present research, development, calibration and characterization of a novel concept of a digitally compensated, low-noise magnetometer based on anisotropic magnetoresistance sensors that is suitable for space applications. The main idea of the design was to reduce the number of precise analog components while using the digital signal processing power available in a modern microcontroller. Our most recent effort targeted lowering power consumption, enhancement of radiation hardness and overall improvement of the parameters. The principle of operation is presented in detail, along with a detailed description of the instrumentation used to characterize the real instrument, including its noise, linearity, and temperature stability in the range of -20 to +70 °C. The results of total ionizing dose (TID) testing at a gamma-ray irradiation facility are discussed at the complete magnetometer and part levels. This is an extended version of a paper presented at I2MTC 2020 that contains the results of a second radiation test done with a slightly modified design. The instrument worked well throughout the entire irradiation session (TID of 1.05 kGy over 72 hours), and the stability of main parameters was very good (50 pT/Gy offset and 1 ppm/Gy sensitivity stability).

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.

AMR Magnetometer With Digital Feedback for Space Applications

  • DOI: 10.1109/I2MTC43012.2020.9129039
  • Odkaz: https://doi.org/10.1109/I2MTC43012.2020.9129039
  • Pracoviště: Katedra měření
  • Anotace:
    In this paper, we present research and development regarding a novel concept of a digitally compensated, low-noise magnetometer based on anisotropic magnetoresistance sensors that is suitable for space applications. The central idea of the design is to reduce the number of precise analog components while using the digital signal processing power available in a modern microcontroller. Our most recent effort targeted lowering power consumption and overall improvement of the parameters. Only commercial off-the-shelf components are used in the concept reported here, keeping costs manageable even for low-budget CubeSat missions. The principle of operation is presented in detail, along with a full characterization of a real instrument, including its noise, linearity, and temperature stability. The results of Total Ionizing Dose testing at a gamma-ray irradiation facility are discussed at the complete magnetometer and part levels; they suggest the instrument's good potential.

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.

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.

Za stránku zodpovídá: Ing. Mgr. Radovan Suk