Triaxial Fluxgate Magnetometer Research Articles

Application of Magneto‐Impedance (MI) Sensor to Geomagnetic Field Measurements

AbstractThe magneto‐impedance (MI) effect was discovered about 30 years ago and a microsize magnetic sensor utilizing this effect has become commercially available. We make some modifications to the commercially available MI sensors to cover the dynamic range of the geomagnetic field. The total cost of three MI sensors for the two horizontal components and one vertical component including the modification is approximately one‐third of the standard price of triaxial fluxgate magnetometer sensors. For the period of 30 March to 27 April 2018, we conducted experimental observations of geomagnetic field variations with the MI sensor magnetometer (MIM) at the Mineyama observatory, which is located about 100 km northwest of Kyoto, Japan. Data obtained with the MIM are compared with those from the fluxgate magnetometer (FGM) that has been working at the observatory. Results show that the MIM can record geomagnetic field variations such as geomagnetic storm, solar quiet variations, low‐latitude positive bays, storm sudden commencement, and long‐period geomagnetic pulsations with a peak‐to‐peak amplitude of ≤1 nT that is also detected with the FGM. Power spectra of the geomagnetic field variations measured with the MIM and FGM are almost the same. It is found that the MIM has a larger temperature drift than the FGM. The present study reveals that the MIM is comparable to the FGM in measuring the geomagnetic field variations in a period from a few tens of seconds to a few hours and is useful for researches in upper atmospheric physics or space physics.

Magnetic Fields of Devices during Electric Vehicle Charging: A Slovak Case Study

The aim of this contribution is to identify and quantify the magnetic field parameter (MP) devices for charging electric vehicles (EVs). An EV is a mobile device. The EV remains a mobile device even when it is charging in a fixed charging stand. ICNIRP and SBM standards apply to stable devices. A magnetic field (MF) creates local gradient fields that change cyclically over time near the charging stations. The rotating vector MF is a specific parameter. An MF is evaluated by its strength and spatial changes. The triaxial fluxgate magnetometer VEMA-041 was used for the measurements. The MF was observed in the frequency range of 0–250 Hz, and the magnetic induction density was from T 2 × 10−9 T to 2 × 10−5 T, with a sensitivity of 1.7 nT. The MF analysis was performed within the time and frequency range. The rotating vector MF was identified at the measurement points. Measurements were realized for the charge under the following parameters: cables, 600 A; transformer, 250 kVA (22 kV/400 V); a cab-fixed charging stand, and an AC/DC charger in the EV. EV charging was performed with 6.6 kW of power and 43-kW fast charging. The measured results were satisfactory, according to the ICNIRP and SBM 2015 standard. The values measured at a distance of 1 m from the wall of the transformer were BRMS < 2 µT. BRMS values < 3 µT were measured in the space of the cable’s entry into the distribution box. EV values should not be assessed under this regulation. However, an EV is a mobile device. In the selected EV sample (a first-generation Nissan Leaf), a frequency of 10 Hz and its multiples were detected during charging. The frequencies were generated in an AC/DC charger in the EV. These frequencies reached BRMS < 0.2 µT in the driver’s footwell. The maximum value of the MF rotating vector was Btotal < 0.3 µT and was directed to the crew area of the EV. The AC/DC charger generated BRMS = 0.95 µTin the driver’s footwell. It is necessary to look for new tools for evaluating MFs for EVs, such as the standards used for stable sources today. These standards should be based on dosimetric principles.

Signal and Noise Separation From Satellite Magnetic Field Data Through Independent Component Analysis: Prospect of Magnetic Measurements Without Boom and Noise Source Information

AbstractWe propose an application of the independent component analysis (ICA) to separate satellite‐induced time‐varying stray fields from magnetic field data obtained using onboard multiple magnetometers. The ICA is a method for estimating source signals at multiple sites so that the estimated source signals can become statistically independent of each other. Since stray field variations are statistically independent of external natural field variations, the ICA method is expected to separate the natural variations from stray fields. Thus, we applied the ICA to magnetic field data from the first Quasi‐Zenith Satellite, which has two triaxial fluxgate magnetometers, without using an extendable boom. First, we removed the long‐period trend from the original data to create detrended data. Then, we applied the FastICA algorithm to the detrended data and obtained six independent components (ICs). The stray fields were successfully separated into three ICs (noise ICs), and the natural signals were represented by the other three ICs (signal ICs). Finally, we restored the observed signals from the signal ICs, and confirmed that the natural phenomena variations were not altered by the processing step. We also proposed a selection method of the noise ICs using the C coefficient, which is the coefficient of the variance of the mixing vectors. There was a large difference in C between the ICs whose C coefficients are the largest third and fourth ones. Overall, these results demonstrate the possibility that the ICA method can support for boom‐less magnetic observations in future satellite missions.

Thermoelastic Response of the Juno Spacecraft's Solar Array/Magnetometer Boom and Its Applicability to Improved Magnetic Field Investigation.

Juno was inserted into a polar orbit about Jupiter on 4 July 2016. Juno's magnetic field investigation acquires vector measurements of the Jovian magnetic field using a pair of a triaxial Fluxgate Magnetometers (FGMs) colocated with four attitude‐sensing star cameras on an optical bench. The optical bench is placed on a boom at the outer extremity of one of Juno's three solar arrays. The Magnetic Field investigation (MAG) uses measurements of the optical bench inertial attitude provided by the micro‐Advanced Stellar Compass (μASC) to render accurate vector measurements of the planetary magnetic field. During periJoves, orientation of the MAG Optical Benches (MOB) is determined using the spacecraft (SC) attitude combined with transformations between SC and MOB coordinate frames. Substantial prelaunch effort was expended to maximize the thermomechanical stability of the Juno solar arrays and MAG boom. Nevertheless, the Juno flight experience demonstrates that the transformation between SC and MAG reference frames varies significantly in response to spacecraft thermal excursions associated with large attitude maneuvers and proximate encounters with Jupiter. This response is monitored by comparing attitudes provided by the MAG investigation's four Camera Head Units (CHUs) with those provided by the Stellar Reference Unit (SRU). These systematic variations in relative orientation are thought to be caused by the thermoelastic flexure of the Juno solar array in response to temperature excursions associated with maneuvers and heating during close passages of Jupiter. In this paper, we investigate these thermal effects and propose a model for compensation of the MAG boom flexure.

The Chinese Mars ROVER Fluxgate Magnetometers

The Mars Rover Magnetometers (RoMAG) will implement the first mobile magnetic field measurements on the surface of Mars. Two identical tri-axial fluxgate magnetometer sensors are mounted at the top and bottom of the mast of rover, respectively. The technology of Helmholtz compensation coil probe and digital closed-loop feedback circuit is utilized to realize high precision measurement. Each magnetometer measures the vector magnetic field with a resolution of 0.01 nT in the range of $\pm65000~\text{nT}$ . The sample rate is up to 32 Hz and the noise is $0.01~\text{nT}/\surd\text{Hz}$ @1 Hz. A rover magnetic compensation procedure was conducted to remove the most important magnetic disturbances. Mobile magnetic field measurements on the Martian surface would obtain fine-scale crust field and provide information about its remnant magnetization and any possible intrinsic magnetic field. It would help us to further understand Martian internal structure, coupling processes of solar wind-magnetosphere-ionosphere.

Flight Calibration of the Van Allen Probe Magnetometers

Abstract The twin Van Allen Probes each carry a triaxial fluxgate magnetometer. Their orbits transverse a large of range of magnetic intensity. A procedure is described that calibrates the magnetometer in the spinning-spacecraft frame and in the presence of a persistent gradient of the magnetic field. This is done by extending a model based on a constant background magnetic field to a model with a changing magnetic field during intervals used for calibration. Model parameters derived from short intervals are obtained by direct calculation, and uncertainties are propagated throughout the analysis. A daily ensemble analysis of interval-derived parameters and uncertainties is then made to correct for sensor bias and misalignment. The whole analysis is iterated to convergence in a few steps based on the estimated uncertainties associated with the model parameters.

Mars Orbiter magnetometer of China’s First Mars Mission Tianwen-1

As one of the seven scientific payloads on board the Tianwen-1 orbiter, the Mars Orbiter Magnetometer (MOMAG) will measure the magnetic fields of and surrounding Mars to study its space environment and the interaction with the solar wind. The instrument consists of two identical triaxial fluxgate magnetometer sensors, mounted on a 3.19 meter-long boom with a seperation of about 90 cm. The dual-magnetometers configuration will help eliminate the magnetic field interference generated by the spacecraft platform and payloads. The sensors are controlled by an electric box mounted inside the orbiter. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 10,000 nT per axis) with a resolution of 1.19 pT. Both magnetometers sample the ambient magnetic field at an intrinsic frequency of 128 Hz, but will operate in a model with alternating frequency between 1 and 32 Hz to meet telemetry allocations.

Arcjet Thruster Influence on Local Magnetic Field Measurements from a Geostationary Satellite

The 16th Geostationary Operational Environmental Satellite (GOES-16) is the first satellite launched from National Oceanic and Atmospheric Administration’s (NOAA’s) next-generation Geostationary Operational Environmental Satellite-R series. Observations from GOES-16 are used by the NOAA to provide terrestrial and space weather forecasts, warnings, and alerts. The magnetometer (referred to as MAG) on GOES-16, which monitors the geomagnetic field, consists of two triaxial fluxgate magnetometers mounted on an 8.5 m boom. The spacecraft uses hydrazine arcjet thrusters for station keeping; when the arcjets are fired, a large magnetic field disturbance contaminates the MAG data. Here, the characteristics of the arcjet contamination are described and possible physical mechanisms for the magnetic field disturbance are discussed. The arcjets operate for approximately every four days, and the contamination significantly impacts the utility of the MAG data for space weather operations. The arcjets create step changes in the geomagnetic field observations of up to about 20 nT ( of the nominal field strength). Two separate physical mechanisms are suggested: a large-scale diamagnetic effect caused by the dense plasma in the thruster plume, and a local current source caused by plasma pressure gradients near the thruster.

A New Calibration Method for Triaxial Fluxgate Magnetometer Based on Magnetic Shielding Room

The triaxial fluxgate magnetometers (TFMs) are widely used in space exploration, positioning and navigation, geological exploration, etc. As a high-precision vector magnetometer, the measurement accuracy will directly determine the accuracy of the obtained magnetic field data. The TFM has three kinds of own errors in measurement: zero offset error, proportional coefficient error, and nonorthogonal error. These three kinds of errors will cause the TFM to deviate from the actual magnetic field value, and the fluxgate magnetometer needs to be calibrated. At present, the accuracy of the calibration method adopted by the fluxgate magnetometer depends on the stability of the natural environment magnetic field and the triaxial turntable (there is an uncontrollable residual magnetic interference), which limits the further improvement of the calibration accuracy. And due to the wide application of electromagnetic equipment, the natural electromagnetic environment is further damaged, and the calibration accuracy is subject to deterioration. In this paper, a magnetic shielding room (MSR) is used to provide a near-zero magnetic environment, and a triaxial uniform magnetic field coil (TUMC) is installed inside the MSR to construct a controllable arbitrary vector direction magnetic field, which solves the magnetic field disturbance problem of the original method. The TUMC and TFM error models were built and the MSR magnetic ambient noise model was added. The emphasis is on the degree of distortion of the magnetic field generated by the MSR as a ferromagnetic boundary condition and the influence of the deviation of the center point of TUMC on the calibration accuracy. Then, based on the above error model and magnetic environmental conditions, the calibration accuracy of the calibration magnetic field distribution is analyzed. Finally, the calibration experiment of the TFM is carried out by using the existing MSR, which proves the feasibility and effectiveness of the calibration method, and the method can greatly improve the calibration efficiency.

Borehole magnetic surveys in weakly magnetic sediments (Chicxulub impact crater) versus strongly magnetic volcanics (Bathurst mining camp)

Borehole navigation surveys performed using a triaxial fluxgate magnetometer record the change in orientation of the magnetic vector versus depth. Variations in the orientation of the magnetic vector arise from either on- or off-hole magnetic sources. On-hole magnetic sources associated with magnetic property fluctuations in the immediate wall of the borehole (i.e., susceptibility) and (or) remanence polarity changes produce sharp-edged anomalies. Off-hole magnetic sources, caused by a magnetic body near, but not penetrated by, the borehole, produce broad smooth anomalies. Prior to the interpretation of borehole magnetic anomaly logs, data corrections must be applied. Data from each of the magnetic and tiltmeter sensors must be corrected for differential gain, base value offset, and nonorthogonality. By using a probe with two sets of triaxial fluxgates, it is possible to detect along hole magnetic field rotations, which compromise the borehole navigation calculations. After rotation into geographic coordinate space, borehole vector magnetic data from the Chicxulub impact crater in Mexico showed no evidence for any systematic change of magnetic property versus depth. What was originally interpreted as reversal stratigraphy has proved to be minor changes in borehole geometry. Borehole magnetic data from a borehole through the Stratmat deposit, located in the Bathurst mining camp, New Brunswick, show strong off-hole and on-hole anomalies associated with the pyrrhotite-rich ore bodies.

InSight Auxiliary Payload Sensor Suite (APSS)

NASA’s InSight mission to Mars will measure seismic signals to determine the planet’s interior structure. These highly sensitive seismometers are susceptible to corruption of their measurements by environmental changes. Magnetic fields, atmosphere pressure changes, and local winds can all induce apparent changes in the seismic records that are not due to propagating ground motions. Thus, InSight carries a set of sensors called the Auxiliary Payload Sensor Suite (APSS) which includes a magnetometer, an atmospheric pressure sensor, and a pair of wind and air temperature sensors. In the case of the magnetometer, knowledge of the amplitude of the fluctuating magnetic field at the InSight lander will allow the separation of seismic signals from potentially interfering magnetic signals of either natural or spacecraft origin. To acquire such data, a triaxial fluxgate magnetometer was installed on the deck of the lander to obtain magnetic records at the same cadence as the seismometer. Similarly, a highly sensitive pressure sensor is carried by InSight to enable the removal of local ground-surface tilts due to advecting pressure perturbations. Finally, the local winds (speed and direction) and air temperature are estimated using a hot-film wind sensor with heritage from REMS on the Curiosity rover. When winds are too high, seismic signals can be ignored or discounted. Herein we describe the APSS sensor suite, the test programs for its components, and the possible additional science investigations it enables.

The ROVER Fluxgate Magnetometer

Martian magnetic field measurement is one of the focuses of international Mars exploration mission. China's first Mars magnetic measurement mission would carry magnetometers on the rover and the orbiter to achieve joint observation of the surface magnetic field and the spatial magnetic field. Dual tri-axial fluxgate magnetometer would be carried on the rover,which adopts Helmholtz compensation coil probe technology and all digital closed-loop feedback circuit technology to realize high precision same-point measurement of space magnetic field. Reliability, safety and space environment adaptability of the instrument are well considered in the design. According to ground calibration, the range of the ROVER fluxgate magnetometer is ±65 000 nT,the noise level is 0.01 nT/√Hz,and the resolution achieves 0.01 nT.

Design and analysis of miniature tri-axial fluxgate magnetometer

The detection technology of weak magnetic field is widely used in Earth resource survey and geomagnetic navigation. Useful magnetic field information can be obtained by processing and analyzing the measurement data from magnetic sensors. A miniature tri-axial fluxgate magnetometer is proposed in this paper. This miniature tri-axial fluxgate magnetometer with ring-core structure has a dynamic range of the Earth’s field ±[Formula: see text]65,000 nT, resolution of several nT. It has three independent parts placed in three perpendicular planes for measuring three orthogonal magnetic field components, respectively. A field-programmable gate array (FPGA) is used to generate stimulation signal, analog-to-digital (A/D) convertor control signal, and feedback digital-to-analog (D/A) control signal. Design and analysis details are given to improve the dynamic range, sensitivity, resolution, and linearity. Our prototype was measured and compared with a commercial standard Magson fluxgate magnetometer as a reference. The results show that our miniature fluxgate magnetometer can follow the Magson’s change trend well. When used as a magnetic compass, our prototype only has [Formula: see text] deviation compared with standard magnetic compass.

A component compensation method for magnetic interferential field

A new component searching with scalar restriction method (CSSRM) is proposed for magnetometer to compensate magnetic interferential field caused by ferromagnetic material of platform and improve measurement performance. In CSSRM, the objection function for parameter estimation is to minimize magnetic field (components and magnitude) difference between its measurement value and reference value. Two scalar compensation method is compared with CSSRM and the simulation results indicate that CSSRM can estimate all interferential parameters and external magnetic field vector with high accuracy. The magnetic field magnitude and components, compensated with CSSRM, coincide with true value very well. Experiment is carried out for a tri-axial fluxgate magnetometer, mounted in a measurement system with inertial sensors together. After compensation, error standard deviation of both magnetic field components and magnitude are reduced from more than thousands nT to less than 20nT. It suggests that CSSRM provides an effective way to improve performance of magnetic interferential field compensation.

Digital Fluxgate Magnetometer for Detection of Microvibration

In engineering practice, instruments, such as accelerometer and laser interferometer, are widely used in vibration measurement of structural parts. A method for using a triaxial fluxgate magnetometer as a microvibration sensor to measure low-frequency pendulum microvibration (not translational vibration) is proposed in this paper, so as to detect vibration from low-frequency vibration sources, such as large rotating machine, large engineering structure, earthquake, and microtremor. This method provides vibration detection based on the environmental magnetic field signal to avoid increased measurement difficulty and error due to different relative positions of permanent magnet and magnetometer on the device under test (DUT) when using the original magnetic measurement method. After fixedly connecting the fluxgate probe with the DUT during the test, the angular displacement due to vibration can be deduced by measuring the geomagnetic field’s magnetic induction intensity change on the orthogonal three components during the vibration. The test shows that the microvibration sensor has angular resolution of over 0.05° and maximum measuring frequency of 64 Hz. As an exploring test aimed to detect the microvibration of earth-orbiting satellite in the in-orbit process, the simulation experiment successfully provides the real-time microvibration information for attitude and orbit control subsystem.

Attitude reconstruction of ROSETTA׳s Lander PHILAE using two-point magnetic field observations by ROMAP and RPC-MAG

As part of the European Space Agency׳s ROSETTA Mission the Lander PHILAE touched down on comet 67P/Churyumov–Gerasimenko on November 12, 2014. The magnetic field has been measured onboard the orbiter and the lander. The orbiter׳s tri-axial fluxgate magnetometer RPC-MAG is one of five sensors of the ROSETTA Plasma Consortium. The lander is also equipped with a tri-axial fluxgate magnetometer as part of the ROSETTA Lander Magnetometer and Plasma-Monitor package (ROMAP). This unique setup makes a two point measurement between the two spacecrafts in a relatively small distance of less than 50km possible. Both magnetometers were switched on during the entire descent, the initial touchdown, the bouncing between the touchdowns and after the final touchdown. We describe a method for attitude determination by correlating magnetic low-frequency waves, which was tested under different conditions and finally used to reconstruct PHILAE׳s attitude during descent and after landing. In these cases the attitude could be determined with an accuracy of better than ±5°. These results were essential not only for PHILAE operations planning but also for the analysis of the obtained scientific data, because nominal sources for this information, like solar panel currents and camera pictures could not provide sufficient information due to the unexpected landing position.

Localization of the Chelyabinsk Meteorite From Magnetic Field Survey and GPS Data

The Chelyabinsk meteorite fragment that landed in the Chebarkul lake in Russia on February 15, 2013 weighed over half a ton. We provide magnetic field maps that were obtained during underwater measurements above the fragment. The data acquisition process was multiple global position system referenced magnetic surveys 0.5–1 m above the top of the lake sediment layer at 10 m water depth. Gradiometric configuration of the survey using two triaxial fluxgate magnetometers helped to suppress local geological anomalies. The location of the ice crater and the underwater magnetic anomaly provided final meteorite landing coordinates, which were made available during meteorite recovery.

The MAVEN Magnetic Field Investigation

The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions (boomlets). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a quantization uncertainty of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05%. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers - multiple rotations about the spacecraft x and z axes - to characterize spacecraft fields and/or instrument offsets in flight.

Vector Feedback Homogeneity and Inner Layout Influence on Fluxgate Sensor Parameters

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.

Novel ST-MUSIC-based spectral analysis for detection of ULF geomagnetic signals anomalies associated with seismic events in Mexico

Recently, the analysis of ultra-low-frequency (ULF) geomagnetic signals in order to detect seismic anomalies has been reported in several works. Yet, they, although having promising results, present problems for their detection since these anomalies are generally too much weak and embedded in high noise levels. In this work, a short-time multiple signal classification (ST-MUSIC), which is a technique with high-frequency resolution and noise immunity, is proposed for the detection of seismic anomalies in the ULF geomagnetic signals. Besides, the energy (E) of geomagnetic signals processed by ST-MUSIC is also presented as a complementary parameter to measure the fluctuations between seismic activity and seismic calm period. The usefulness and effectiveness of the proposal are demonstrated through the analysis of a synthetic signal and five real signals with earthquakes. The analysed ULF geomagnetic signals have been obtained using a tri-axial fluxgate magnetometer at the Juriquilla station, which is localized in Queretaro, Mexico (geographic coordinates: longitude 100.45° E and latitude 20.70° N). The results obtained show the detection of seismic perturbations before, during, and after the main shock, making the proposal a suitable tool for detecting seismic precursors.