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Safety in coastal areas such as beaches, ports, pontoons, etc., is a current problem with a difficult solution and on which many organizations are putting efforts in terms of technological innovation. In this work the design of a possible solution based on magnetic sensors is presented. First, a study has been made of the type of sensors that best suit the application based on parameters such as sensitivity, the allowed bandwidth of excitation, price or physical construction. Then the system of excitation of the sensors and signal measurement is presented. To justify the design, a series of simulations of magnetic field variations have been carried out in the presence of large objects of conductive material, in the vicinity of the measuring points. With these data a mathematical model has been established that allows the identification of the dimensions and position of the object through triangulation and knowing only the data of the magnetic field. It was found that although this method seems quite effective, it has a significant error, so another method based on neural networks was developed also using data from the simulations. This method seems to yield much better and more reliable results.

Fluxgate magnetometers provide sensitive and stable measurements of the static and low frequency vector magnetic field. Fluxgates form a magnetic field measurement by periodically saturating a ferromagnetic core and the intrinsic magnetic noise of this material can determine the noise floor of the instrument. We present the results of an empirical experiment to understand the physical parameters that influence the intrinsic magnetic noise of fluxgate cores. We compare two permalloy alloys – the historical standard 6 % molybdenum alloy and a new 28 % copper alloy. We examine the influence of geometry using the historical standard 1” diameter spiral wound ring-core and a new stacked washer racetrack design. We evaluate the influence of material thickness by comparing 100 µm and 50 µm foils. Finally, we investigate heat treatments in terms of temperature and ramp rate and their role in both grain size and magnetic noise. The results of these experiments suggest that thinner foils, potentially comprising the copper alloy, manufactured into continuous racetrack geometry washers may provide excellent performance in fluxgate sensors.

A concern with the isolation transformer in a dual active bridge (DAB) dc–dc converter is the dc bias in magnetization. This article proposes a fluxgate-based current sensor to measure the dc component mixed with a large, high-frequency ac current. Compared with a commercial Hall effect current sensor, the proposed sensor significantly reduces measurement error. This article presents the working principle and design considerations. A prototype is demonstrated for dc bias elimination control in a DAB converter.\ud

Detecting defects in high-permeability steel components can be challenging when using the eddy current technique. This is due to the strong magnetization signal that is simultaneously generated along with the eddy current signal. To minimize the regions of the induced eddy current and its detection, an eddy current probe based on an array of miniature fluxgate sensors (DRV425, Texas Instrument, USA) and axial inductors was proposed and fabricated in the study. The fluxgate sensors were arranged in two layers, and the sensors were sandwiched between two layers of inductors. The output signals from the fluxgate array were sampled to obtain a differential signal of the eddy current intensity and direction. A phase-sensitive detection technique was implemented to isolate the strong magnetization signal from the detected eddy current signal and utilized to characterize artificial slits with varying depths. The developed probe successfully characterized both the vertically and horizontally oriented slits with depths from 2 to 10 mm on a 12 mm thick mild steel plate. A better sensitivity was notable in the evaluation of the vertical slits where the vertical slits would increase the eddy current intensity in contrast to the horizontal slits around the slits. It was shown that the eddy current’s distribution map obtained from the developed probe could be used to reveal the physical dimension of the slit.

The closed-loop fluxgate current transducer (CFCT) is the only current sensor whose measurement accuracy can reach a level of the parts per million (ppm) at present. However, the false balance, which makes the CFCT unable to work, caused by an excessive offset current is the inherent flaw of the CFCT. The high di/dt (rate of current change) of the primary current is the main factor resulting in the offset current overload. Therefore, the CFCT is currently only applied for steady-state direct-current measurements. In this article, an approach is proposed to eliminate the false balance of the CFCT in the dynamic process by adding a feedforward branch, which provides a follow-up bias point for the CFCT to make the CFCT always work in a small-signal range, where a risk of magnetic saturation does not arise. The zero-flux state of the CFCT still only depends on the feedback branch, so its high measurement accuracy is maintained. The experiments prove that the CFCT can measure a flat-top pulsed current with an accuracy of the ppm level by this method.

In order to calibrate the tri-axis magnetometer errors, an attitude-independent calibration method based on adaptive filtering is proposed. This method can estimate all the error parameters precisely without the need of external equipment to provide stable magnetic field and reference attitude information. In this paper, incremental meta-learning Incremental Delta-Bar-Delta (IDBD) algorithm is applied to adaptive filtering to achieve magnetometer calibration instead of the traditional least squares (LS) algorithm. The results of this calibration method will be compared with the classical calibration method in the earth’s magnetic field as well. The experiments show that the sensor error after calibration by the proposed method is significantly suppressed and reduced by more than 93 % compared with that before calibration and the calibration effect of IDBD algorithm is much better than that of LS algorithm. The proposed method in this paper can not only effectively improves the measurement accuracy of the tri-axis fluxgate sensor, but also is potentially applicable to various kinds of three-axis sensors.

The work is devoted to the description of the design of the magnetovariation station, created on the basis of a three-component fluxgate sensor. This station is designed for geomagnetic work in stationary observation points, as well as for field expeditionary work.

The Low Orbit Pearl Satellite series consists of six constellations, with each constellation consisting of three identical microsatellites that line up just like a string of pearls. The first constellation of three satellites were launched on 29 September 2017, with an inclination of ∼ 35.5∘ and ∼ 600 km altitude. Each satellite is equipped with three identical fluxgate magnetometers that measure the in situ magnetic field and its low-frequency fluctuations in the Earth's low-altitude orbit. The triple sensor configuration enables separation of stray field effects generated by the spacecraft from the ambient magnetic field (e.g., Zhang et al., 2006). This paper gives a general description of the magnetometer including the instrument design, calibration before launch, in-flight calibration, in-flight performance, and initial results. Unprecedented spatial coverage resolution of the magnetic field measurements allow for the investigation of the dynamic processes and electric currents of the ionosphere and magnetosphere, especially for the ring current and equatorial electrojet during both quiet geomagnetic conditions and storms. Magnetic field measurements from LOPS could be important for studying the method to separate their contributions of the Magnetosphere-Ionosphere (M-I) current system.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2021-06-03, 資料番号: PA2210003000

High precision magnetometer (HPM) is a magnetic field detection payload onboard China Seismo-Electromagnetic Satellite (CSES), including two fluxgate magnetometers (FGM) and a coupled dark state magnetometer (CDSM). Observations show that FGM appears to be influenced when tri-band beacon (TBB) is powered on and emits electromagnetic waves. The interference phenomenon is further validated based on both in-orbit observation analysis and electromagnetic compatibility (EMC) tests on the ground. A joint correction algorithm based on the least square fitting and first-order difference method according to scalar magnetometer data is proposed to eliminate the interference. The algorithm significantly improves the consistency of HPM data. After correction, the average scalar deviation error could be reduced from 9.0 nT to around 0.7 nT.

This review paper explores the most common technologies of vector magnetic field sensors. Specifically, the AMR, GMR, TMR, GMI, Hall, Fluxgate, Search Coil and SQUID sensors are considered. The physical phenomena that permit their operation as well as the structure and operating principles of each sensor are presented. In addition, the basic linear, time-invariant error sources of magnetic sensors are described along with some popular calibration techniques. Finally, some representative application examples of each sensor are described.

As vector sensors, such as the fluxgate magnetometer, are more and more widely used in magnetic anomaly signal detection and location, researchers find that the error of sensors has become an essential obstacle in the application. To solve this problem, we established a calibration model with three kinds of error. A new optimization algorithm called Partition Beetles Antennae Search is provided to solve the model parameters. Simulation results show that the new algorithm can consider both accuracy and computational complexity. Besides, we set up a single three-axis fluxgate sensor experimental platform for sensor calibration and conducted related experiments. The results further prove the effectiveness and practicability of the method. The work of this article suggests an effective way to calibrate three-axis magnetometers.

Exploration of deep mineralization, particularly where the mineralization of interest is covered by a conductive overburden, is still a challenge for the conventional transient electromagnetic (TEM) method, which measures TEM response using induction coils as the sensor. However, sensors such as fluxgate and superconductive quantum interfere device (SQUID) magnetometers can measure the B-field directly, which can provide more reliable deep information for mineralization exploration. In this paper, we report on the research and development of our newly developed high-temperature superconductor (HTS) SQUID magnetometer, which is cooled by liquid nitrogen at 77 K, and its application in TEM measurement for deep exploration in a gold deposit in China. This improved SQUID magnetometer version has a good performance with noise (60 fT/ $$\sqrt {{\rm{Hz}}} $$ ), slew rate (0.8 mT/S), dynamic range (100 dB), sensitivity (6.25 mV/nT), and bandwidth (DC-20 kHz). To find deep and peripheral ore in the Baiyun gold deposit located in Liaoning Province, NE China, both the SQUID magnetometer and induction coil were used for TEM data acquisition. Results show that TEM can detect the distribution of local strata and the faults contained within them. Results also indicate that the SQUID magnetometer has superior response performance for response over geological targets with slower decay time when compared to the induction coil signals. The SQUID magnetometer is more sensitive at observing the induced-polarization effect which is closely related to the ore-controlling faults.

Fluxgate magnetometers are widely used for in-situ magnetic field measurements in the context of geophysical and solar system studies. Like in most of experimental studies, magnetic field measurements using the fluxgate magnetometers are constrained to the associated uncertainties. To evaluate the performance of magnetometers, the measurement uncertainties of calibrated magnetic field data are quantitatively studied for a spinning spacecraft. The uncertainties are derived analytically by perturbing the calibration procedure, and are simplified into the first-order expression including the offset errors and the coupling of calibration parameter errors with the ambient magnetic field. The error study shows how the uncertainty sources combine through the calibration process. The final error depends on the ambient environment such as the magnitude of magnetic field relative to the offset error and the angle of magnetic field to the spacecraft spin axis are important factors. The offset uncertainties are the major factor in a low-field environment, while the angle uncertainties (rotation angle in the spin plane, sensor non-orthogonality, and sensor misalignment to the spacecraft reference directions) become more important in a high-field environment in a proportional way to the magnetic field. The error formulas serve as a useful tool in designing high-precision magnetometers in future spacecraft missions as well as in data analysis methods in geophysical and solar system science.

The article shows the need for high-quality demagnetization of the axle of the wheelset, which is one of the most critical parts of the rolling stock. The main task of demagnetization is to bring the remanent magnetization to such a value at which the ferromagnetic particles formed during processing would not be retained on the surface of the axle, as a result of which its service life will significantly increase. The method of comparative analysis was used to assess the effectiveness of methods for demagnetizing the axle of a wheelset, which ensures the durability and operational reliability of the rolling stock. Based on the results of the analysis, three main methods of demagnetizing ferromagnetic parts and products are identified: a reverse pulse, a free oscillatory process and a pulse method. A method of demagnetization based on cyclic magnetization reversal by a sinusoidal changing magnetic field with an amplitude smoothly decreasing to zero has been selected and substantiated. The basic requirements for the device for demagnetizing the axles of wheelsets have been determined and analyzed. The proposed implementation of the device, which guarantees the required quality of demagnetization of the axle of a wheelset based on its magnetic state. The magnetization of the axis material is proposed to be estimated indirectly from the results of measuring the tangential component of the magnetic field strength on the axis surface with a fluxgate. To compensate for external magnetic fields, a second flux gate is used, located at some distance from the first. The output signals of the flux gates are connected according to the differential circuit. The difference signal of the flux gates is amplified and fed to a recording device, depending on the readings of which the demagnetizing field is corrected. The proposed implementation of the device, which guarantees the required quality of demagnetization of the axle of a wheelset on the basis of determining its magnetic state. The magnetization of the axis material is proposed to be estimated by an indirect method based on the results of measuring the fluxgate tangential component of the magnetic field strength on the axis surface. The direction of further research is the automation of the demagnetization process.

The objective of this study is to improve the detection capability of eddy current testing by developing a novel eddy current probe. The developed probe is composed of six excitation coils made at different areas and suitably aligned with a single-axis sensitive DRV425EVM fluxgate sensor. The distribution of magnetic field intensity and eddy current density of the developed probe were calculated using ANSYS 2019R3 (Maxwell-3D) simulation software. The simulation results revealed that the new probe design enhances the detection capability and the spatial resolution compared to the conventional design that uses a double-D coil. Experiments were carried out using the double-D coil as reference, under the same input parameter to detect flaws with various sizes and locations. The experimental results validated the simulation results and showed that the sensitivity and spatial resolution of the developed sensor are much better than those obtained by the conventional probe.

The coils in a three-axis fluxgate magnetometer have been investigated to enhance the noise and power performance for the use in geomagnetic stations. The turn number of the excitation and pickup coils in the fluxgate sensors is carefully optimized by measuring the equivalent magnetic noise spectral density of the magnetometers. Correspondingly, the values of the tuning and demodulation capacitors are delicately designed to match the optimized coils. The noise of the fluxgate magnetometer is 6 pT/ $\surd $ Hz at 1 Hz with a power consumption lower than 360 mW. The size of the packaged magnetometer is $30 \times 30 \times 113$ mm3, and its weight is less than 80 g (without cable). The features of the fluxgate magnetometer make it a suitable instrument for geomagnetic stations and other applications.

The magnetic gradient tensor system (MGTS) based on the fluxgate sensors array replaces partial differentials with the sensors reading difference to approximate the magnetic field gradient, but it introduces structural errors at the mean time. A good structure design with reasonable parameters can reduce structural errors and expand the theoretical detection range of the MGTS. From the analysis of the complete 18-uniaxial MGTS, five simplified structures of the MGTS were summarized, which include the plane cross, equilateral triangle, square, right-angle tetrahedron, and regular tetrahedron. The differential magnetic gradient tensor measurement matrixes of different structures were also provided, where we found the plane-cross structure produces the smallest structural error. Moreover, the theoretical detection limits expression of the MGTS to the magnetic dipole was derived. The detection limit boundary of the MGTS is related to the sensor’s accuracy, the array baseline distance, and the magnetization direction and magnetic moment magnitude of the source. In actual heading-line surveys, the magnetic moments of four typical small magnets were successfully estimated by the magnetic dipole positioning method, and the theoretical detection limits of the built plane-cross MGTS aiming at the four magnets were estimated. The results show that the estimation accuracy of the theoretical detection limits of MGTs is ±0.5 m.

Este estudo foca na análise das perturbações do campo geomagnético que estão relacionadas com o terremoto, e consequente tsunami, que ocorreram em 27 de fevereiro de 2010 em Maule, no Chile. O objetivo deste artigo é contribuir para uma melhor compreensão dos processos físicos envolvidos nos acoplamentos Tsunami-Atmosfera-Ionosfera (TAI) e Litosfera-Atmosfera-Ionosfera (LAI). Para isto, foram utilizados registros de magnetômetros fluxgate medidos em superfície fornecidos pelo projeto LISN (do inglês Low Latitude Ionospheric Sensor Network). A metodologia de filtragem do sinal por remoção da tendência relacionada à influência solar (linha de base Sq, do inglês Solar quiet) considerando os cinco dias geomagneticamente mais calmos foi aplicada. Os resultados mostraram distúrbios geomagnéticos, em ambas componentes H e Z, nos dados filtrados que ocorreram quase instantaneamente ou com atraso de até 100 minutos após a chegada do tsunami. Estes distúrbios são atribuídos aos mecanismos oceânico e ionosférico. Estudos como esse são importantes para uma futura condição de previsão e alerta de desastres dessa natureza.

This paper presents a new digital fluxgate current sensor based on second harmonic detection for DC and AC measurement. The sensor utilizes a feedback loop to obtain an almost zero-flux condition, i.e., a balance between the magnetic flux of the primary current and the feedback current, in which way the feedback current is proportional to the primary current. The AC magnetic flux is detected with an induction coil, and the DC zero-flux condition is realized by magnetic saturation effect method, where the magnetic core is periodically magnetized and then the second harmonic of the magnetization current is calculated as an indication of the DC magnetic flux. After theoretical derivation, the operating principle of the sensor was investigated using a numerical simulation model built with Simulink of MATLAB. In addition, a prototype sensor was developed and tested. The experiment results demonstrate that the current sensor works properly for DC and AC measurement. The average error is about 0.06% for DC measurement.

The aim of this study is to localize the electrode of the deep brain stimulation with three dimensional magnetic field measurements by applying the dipole fitting approach. The deep brain stimulation electrode was positioned successively at five increasing depths with well-known positions in a cylindrical head phantom and the magnetic field distribution was measured with a fluxgate magnetometer around the phantom. At each measuring point, the total magnetic field was measured by rotating the sensor in all three orthogonal directions. Finite element method was used to model the volume conduction of the phantom with its exact dimensions and electromagnetic simulations were performed to calculate the magnetic field distribution at the same measuring points around the phantom. The dipole fitting approach was then used to localize the position of the electrode by means of minimizing the normalized root mean square error between measured and calculated data. The results show an average localization accuracy of less than 1 mm over all performed measurements for both near surface and deep positions. Small deviations in the results can be explained by the measuring accuracy of the used fluxgate sensor. It can be concluded that the deep brain stimulation electrode can be precisely localized by three dimensional magnetic field measurements by using an accurate head volume conduction model and by applying the dipole fitting approach. The presented results are intended as preparatory work for real magnetic field measurements with patients implanted with deep brain stimulation electrodes.

The problems of using gradient measurements in magnetic exploration are considered. In many cases, to solve various geological problems, information on the intensity of the geomagnetic field and its gradients, as measured by special equipment, is important. The results of the development and construction of a three-component fluxgate magnetometer-gradiometer intended for measuring on the earth’s surface the absolute values of the three components of the geomagnetic field strength vector and the corresponding three components of the gradient are presented. Installation in the device of additional measuring sensors – accelerometers, enables one to calculate the orientation of these vectors in space. The device of the magnetometer-gradiometer is described, its functional diagram and the principle of operation are presented. The set of instrumental errors arising in the manufacture of three-axis systems of fluxgates and accelerometers designed for measuring the components of the geomagnetic field strength and determining the orientation of the device is considered. A method of finding instrument errors and algorithmic correction of information signals that come from measuring sensors is presented. It is shown that this method provides a significant increase in measurement accuracy. Examples of field testing of the device are given. The presented magnetometer-gradiometer can be used to accurately localize tectonic disturbances, low-power zones of magnetic mineralization, previously identified ore bodies and determine the details of their structure.

The presence of axial and circumferential defects on a coiled tubing (CT) surface leads to high risks of failure when the CT is used under acidic conditions in high-pressure and high-temperature wells. As the CT cannot rotate, it is difficult to identify the axial defects using traditional magnetic flux leakage methods. In this paper, a new method based on fluxgate sensor weak magnetic detection technology is proposed for detecting arbitrary direction defects under non-magnetization conditions. The method uses tri-axial fluxgate sensors and avoids complicated designs such as rotating magnetization. A data acquisition system is designed, and the amplitudes and coordinates of magnetic anomalies are obtained using the magnetic field gradient method. Sample tubes with arbitrary direction defects are tested. The test results show that the method can quickly locate and identify the arbitrary direction defects in the CT. The magnetic induction intensity signals obtained from the pre-fabricated arbitrary direction and circumferential defects show noticeable variations. The measured signal strength also varies significantly with the same lift-off height and different types of defects. The tri-axial fluxgate detection method can solve the problem of arbitrary direction defect detection.

Recently the two-spacecraft mission BepiColombo launched to explore the plasma and magnetic field environment of Mercury. Both spacecraft, the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO, also referred to as Mio), are equipped with fluxgate magnetometers, which have proven to be well-suited to measure the magnetic field in space with high precisions. Nevertheless, accurate magnetic field measurements require proper in-flight calibration. In particular the magnetometer offset, which relates relative fluxgate readings into an absolute value, needs to be determined with high accuracy. Usually, the offsets are evaluated from observations of Alfvénic fluctuations in the pristine solar wind, if those are available. While Mio's orbit will indeed partially reside in the solar wind, MPO will remain within the magnetosphere at most times during the main mission phase. Therefore, we examine an alternative offset determination method, based on the observation of highly compressional fluctuations, the so-called mirror mode technique. To evaluate the method performance in the Hermean environment, we analyze four years of MESSENGER magnetometer data, which are calibrated by the Alfvénic fluctuation method, and compare it with the accuracy and error of the offsets determined by the mirror mode method in different plasma environments around Mercury. We show that the mirror mode method yields the same offset estimates and thereby confirms its applicability. Furthermore, we evaluate the spacecraft observation time within different regions necessary to obtain reliable offset estimates. Although the lowest percentage of strong compressional fluctuations are observed in the solar wind, this region is most suitable for an accurate offset determination with the mirror mode method. 132 hours of solar wind data are sufficient to determine the offset to within 0.5 nT, while thousands of hours are necessary to reach this accuracy in the magnetosheath or within the magnetosphere. We conclude that in the solar wind the mirror mode method might be a good complementary approach to the Alfvénic fluctuation method to determine the (spin-axis) offset of the Mio magnetometer. However, although the mirror mode method requires considerably more data within the magnetosphere, it might also be for the MPO magnetometer one of the most valuable tools to determine the offsets accurately.

The China Seismo-Electromagnetic Satellite (CSES) was launched in February 2018 into a polar, sun-synchronous, low Earth orbit. It provides the first demonstration of the Coupled Dark State Magnetometer (CDSM) measurement principle in space. The CDSM is an optical scalar magnetometer based on the coherent population trapping (CPT) effect and measures the scalar field with the lowest absolute error aboard CSES. Therefore, it serves as the reference instrument for the measurements done by the fluxgate sensors within the High Precision Magnetometer instrument package. In this paper several correction steps are discussed in order to improve the accuracy of the CDSM data. This includes the extraction of valid 1 Hz data, the application of the sensor heading characteristic, the handling of discontinuities, which occur when switching between the CPT resonance superpositions, and the removal of fluxgate and satellite interferences. The in-orbit performance is compared to the Absolute Scalar Magnetometer aboard the Swarm satellite Bravo via the CHAOS magnetic field model. Additionally, an uncertainty of the magnetic field measurement is derived from unexpected parametric changes of the CDSM in orbit in combination with performance measurements on the ground.

Magnetic measurements with an unmanned aerial vehicle are ideal for filling the gap between ground and airborne magnetic surveying. However, to obtain accurate aeromagnetic data, the compensation of magnetic effects of the unmanned aerial vehicle is a challenge. Typically, scalar magnetometers are towed several metres under the unmanned aerial vehicle to minimize its magnetic field. In this study, a fluxgate three‐component magnetometer is attached 42 cm in front of the unmanned aerial vehicle at the tip of a composite pipe. Using a scalar calibration, the sensor can be calibrated, and the permanent and induced magnetic fields of the unmanned aerial vehicle can be compensated. The contributions of the magnetic measurements at different altitudes to the unmanned aerial vehicle results were tested over an area of 1 km² in the Northern Vosges Mountains. The area is located in a hamlet surrounded by a forest where few geological outcrops are observed. Three magnetic surveys of the same area are obtained at different altitudes: 100, 30 and 1 m above the ground. The unmanned aerial vehicle magnetic data are compared with a helicopter aeromagnetic survey at 300 m above the ground and a ground magnetic survey using upward continuations of the maps to compare the results. The magnetic maps (300, 100, 30 and 1 m above the ground) show very different magnetic anomaly patterns (e.g. amplitude, shape, wavelength and orientation). The magnetic data at different altitudes improve the understanding of the geology from the local to more general scales.

The industrial investment in unmanned aerial vehicles (UAVs) is soaring due to their multiple autonomous applications, such as aerial photography, rescue operations, surveillance, and scientific data collection. Current sensing is critical for determining battery capacity in charging and discharging process and alerting for system fault during the flight. Shunt resistors and Hall-effect sensors are traditionally used in UAVs. Recently, magnetoresistive (MR) sensors are gaining enormous attention from researchers. MR sensors tend to consume less power, and they are smaller in size than the Hall-effect sensors. In this paper, a number of off-the-shelf MR sensors were investigated to evaluate the possibility of applying them for UAVs. Another type of magnetic sensor (fluxgate) and shunt resistor was also studied and compared as a reference. The relative scoring method is adopted to evaluate the sensor performance under different metrics, and the results disclose that the MR sensors are highly suitable for current sensing of UAVs due to their higher accuracy, lower energy consumption, wider temperature endurance, smaller size, and less weight than other magnetic current sensors. They are also very competitive with traditional shunt resistors through the overall comparison. The remanence, thermal stability, and cross-field sensitivity of MR sensors are further discussed. This finding provides insight into the selection strategy of current sensors for UAVs and can enhance the industrial development of UAV potentially.

Attempts to improve the osteointegration, fixation and stability of Ti-base implants have been focused by producing a significative surface roughness that enhances the surface area available for bone/ implant apposition. In this research study, it shows the experimental data by synchrotron radiation X-ray diffraction (SR-XRD) of the main material surface properties (residual stress and cold work) that changed significantly during the application of different surface treatments such as grit blasting and laser shock peening in a biometallic Ti–6Al–4V alloy. The ratio of residual stress to cold work is primarily determined by the material and the specific surface treatment applied. In order to establish how they alter the recorded magnetic signatures and to validate that the residual stress and cold work effects govern the outcome of the magnetic measurements, we used a nondestructive magnetic method. It was displayed that the magnetic method provides the unique capability of nondestructively sensing the thermomechanical relaxation below the treated surface only calculating the normal and tangential magnetic intensities induced by thermocurrents using a fluxgate magnetometer.

This article describes the characterization of the SQUID-based time domain electromagnetic (TDEM) system for use in geophysical applications. This system has been characterized near the laboratory where the background noise, especially the cultural noise, is relatively low. A transmitter loop in the form of a square (2 × 2 m) with the excitation current of 0.212 A in the form of modified square pulses with a frequency of 2.5 Hz has been used to induce eddy currents in a nearby conducting target. A three-axes low Tc dc SQUID magnetometer and its associated fast readout electronics have been used to record the transient response of the target. Meanwhile, as part of this developmental work and to get the field experience, the TDEM measurements have been performed in the field with transmitter loop size of 100 × 100 m and fluxgate magnetometer as a receiver. Here, we observed that the decay of the secondary magnetic field has always unexpectedly reached a negative value even at the earlier time windows. Subsequently, the TDEM experiments with fluxgate as the receiver have been repeated with the same configuration as done in the past with SQUID, and the performance of the magnetometers, such as fluxgate and SQUID, have been compared. The experimental results were analyzed in detail and show that the fluxgate magnetometer behaves as the combination of magnetic field sensor and induction coil at earlier decay times, and magnetic field sensor only at later decay times.

Fluxgate magnetometer is an important device for weak magnetic-field measurements. By adding a large dc bias excitation current, the performances of fluxgate can be highly improved. In this article, based on the assumption of the single-domain state within the probe core wire, the quasi-static Stoner–Wohlfarth model (SW model) was used to construct a mathematic model for the output signal of the orthogonal fluxgate probe operated in fundamental mode (FM-OFG). The dynamic hysteresis loop characteristics were also considered here, and the expected first-harmonic output signal corresponding to the theoretical analysis was obtained from our model. A prototype FM-OFG probe was fabricated by using a 20 mm-long Co–Fe–Nb–Si–B amorphous microwire as core wire and a 1500-turn solenoid as pickup coils. Output performances were analyzed at different external fields, ac excitation currents, and dc bias currents. A good agreement between the modeling results and the experimental ones was found. The noise level was reduced down to 9.01 pT/rt (Hz).@.1 Hz. The simulation method and experiment results provide theoretical guidance for the subsequent design and improvement of the FM-OFG.

Residence times difference (RTD) fluxgate magnetometers measure the magnetic field using the time difference between positive and negative pulses of the induced voltage signal in the time domain. Sensitivity is one of the most important parameters to evaluate the performance of the magnetometers. According to our best knowledge of existing literature, for the RTD fluxgate sensors, there are no available models that can clearly set up relationships between physical parameters of an RTD fluxgate and the sensor sensitivity. Moreover, the relationship between the sensitivity and the excitation conditions is very complicate, thus the sensitivity calibration process is time-consuming. This paper presents a sensitivity model at a near-zero magnetic field. According to the model, by using relevant parameters of the excitation coil and driving signal, and the hysteresis state of the magnetic core, accurate predictions of sensitivity for the sensors can be made. RTD fluxgates with different structures were designed and built to experimentally verify the presented sensitivity model. The testing results indicates that the model is valid and the relative error of its prediction on sensitivity is less than 4%. Using the proposed sensitivity model, we can not only study situations of various excitation signals but also have a theoretical foundation to miniaturize the RTD fluxgate sensors.

Compared with ground magnetic measurement and aeromagnetic survey, downhole magnetic measurements can provide more abundant and accurate distribution information of ore deposits. Measurement of the full magnetic tensor gradient affords more information than either traditional magnetic total field or three, orthogonal axes, vector field measurements. Gradient field measurements are less influenced by any time and/or spatial changes of the Earth's magnetic field during the measurement period. CSIRO has developed the world first downhole magnetic full tensor gradiometer and carried out field tests. This gradiometer is based on a rotation of two fluxgate vector field sensors to enable frequency separation of the common mode from the gradient signals. Reposition of the gradiometer about three, nominally orthogonal axes, enables measurement of the full gradient tensor with one pair of fluxgate sensors. This paper describes a method to improve the accuracy of this type of gradiometer. System errors have been analyzed and classified according to the effect of the errors on the measurement accuracy. Major errors include scale factor error of the two fluxgates, misalignment and motion errors of these two sensors relative to the model system, and transformation errors when moving from the sensor to the instrument coordinate frame of reference. Minor errors include errors of finite length measurement parameters, errors associated with ignoring high-order tensors, the deviation of the rotation axis from ideal, and the temperature co-efficient of the fluxgates' signals. We have developed the error models for the major errors and calibrated the full-tensor gradiometer by using the two independent tensor rotation invariants. 1000 simulations with random errors show the root mean squares of relative error are less than 8% after calibration. The calibration technique was applied to field trail measurements made using a gradiometer that was re-oriented multiple times around a fixed point while measuring a known gradient. Applying the calibration method resulted in an improvement of the tensor magnitude accuracy by a factor of 3.74. This result validated the calibration method.

Currently, magnetic fluxgate circuits used for magnetic field measurements mostly adopt parallel excitation second harmonic generation. The magnetic fluxgate developed by this method cannot possess both low noise and high bandwidth at the same time. The orthogonal fundamental mode fluxgate is used in this paper: the excitation magnetic field is orthogonal to the magnetic field to be measured, and the external magnetic field is detected by measuring the voltage signal in the pick-up coil. The excitation magnetic field changes with the parallel excitation second harmonic method while the direction of the excitation magnetic field does not change in the orthogonal fundamental mode scheme, which can effectively reduce the influence of Barkhausen noise. The magnetic fluxgate circuit is designed based on the orthogonal fundamental mode scheme and its performance indexes are tested. The range of the magnetic fluxgate is ±100000 nT, the sensitivity is $100~\mu \text{V}$ /nT, the output noise is 8.9 pT/rt(Hz)@1 Hz, and the bandwidth is DC-15 kHz. The orthogonal fundamental mode fluxgate improves the bandwidth performance while enabling low-noise magnetic field measurements in practical applications.

An autonomous UAV-mounted 3-axis fluxgate vector magnetometer (FVM) was flown over a Golden, Colorado landfill to test map buried ferromagnetic objects and infrastructure. The flights test terrain following flight control software using active GNSS positioning over a fixed 1-meter (m) resolution LiDAR control surface, at slung sensor clearances that approach ground survey sensor heights. The FVM was first walked over the landfill with the sensor at a constant 2 m above the surface, to provide a high-resolution ground survey dataset for comparison. Both the UAV and ground FVM data are scalar calibrated on the ground through a full sphere to return error corrected and 360⁰ maneuver compensated total magnetic intensity (TMI). The comparison also includes UAV downward and ground survey upward continuation filtered (DCF and UCF) TMI respectively, to put the two surveys on approximately the same levels, providing two inverse-distance-magnetic-source viewpoints for both surveys, one at ground level and one at UAV level. The UAV survey DCF results indicate that low level flights might be considered as a replacement for coarser reconnaissance ground TMI surveys in some mapping situations. Lastly, the ground and UAV survey calibration data statistics are reviewed, and the FVM survey TMI images are compared with each other. These in turn, are compared with a highresolution alkali-vapor scalar magnetometer (AVM) benchmark TMI survey, walked on the same lines as the FVM. The AVM provides a reference standard to compare with both FVM surveys.

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.

The High Precision Magnetometer (HPM) is one of the main payloads onboard the China Seismo-Electromagnetic Satellite (CSES). The HPM consists of two Fluxgate Magnetometers (FGM) and the Coupled Dark State Magnetometer (CDSM), and measures the magnetic field from DC to 15 Hz. The FGMs measure the vector components of the magnetic field; while the CDSM detects the magnitude of the magnetic field with higher accuracy, which can be used to calibrate the linear parameters of the FGM. In this paper, brief descriptions of measurement principles and performances of the HPM, ground, and in-orbit calibration results of the FGMs are presented, including the thermal drift and magnetic interferences from the satellite. The HPM in-orbit vector data calibration includes two steps: sensor non-linearity corrections based on on-ground calibration and fluxgate linear parameter calibration based on the CDSM measurements. The calibration results show a reasonably good stability of the linear parameters over time. The difference between the field magnitude calculated from the calibrated FGM components and the magnitude directly measured by the CDSM is just 0.5 nT (1σ) when the linear parameters are fitted separately for the day- and the night-side. Satellite disturbances have been analyzed including soft and hard remanence as well as magnetization of the magnetic torquer, radiation from the Tri-Band Beacon, and interferences from the rotation of the solar wing. A comparison shows consistency between the HPM and SWARM magnetic field data. Observation examples are introduced in the paper, which show that HPM data can be used to survey the global geomagnetic field and monitor the magnetic field disturbances in the ionosphere.

Thermal cycling treatment is the most effective treatment for increasing the reliability and durability of metal structures. In this work, an assessment of the effect of the structure of a metal with a different degree of dispersion, obtained during thermal cycling after a different number of processing cycles, on the mechanical properties of steels 08ps, St3 and 10KhSND was made. Additionally, the influence of the degree of cold plastic deformation on the change in the stray magnetic field strength Hp in low-carbon and low-alloy steels is considered. As a result, methods have been developed for assessing the effect of thermal cycling modes on the mechanical properties of structural steels, as well as the effect of acting stresses during cold plastic deformation of steels 08ps, St3 and 10KhSND on the stray magnetic field strength. Graphical dependencies of values are obtained. On the basis of the research results, the relationship between the structure, magnetic and mechanical parameters was revealed, which allows a reliable assessment of the structural state of the metal and the acting stresses in welded joints and elements of welded metal structures using other methods of passive fluxgate control method. The study is devoted to identifying which zones and places of the welded joint are the most dangerous, and which of them must be controlled first.

The initial structure of metals and alloys determines their mechanical properties. They can differ significantly in various elements of welded metal structures, as well as in the zones and sections of welded joints. Plastic deformation can occur in hazardous areas of stress concentration of elements of operated metal structures. In this work, studies were carried out on samples of low-carbon steel 08 ps and low-alloy steel 10KhSND, which were subjected to thermal cycling in the following conditions: as delivered state; as delivered + annealing at 900 °C; as delivered + cold rolling for the degree of deformation e = 50%. The formation of a fine-grained structure during thermal cycling was monitored by a passive fluxgate method, as well as by microstructural analysis and hardness testing. The value of the stray magnetic field strength Hp was measured. As a result of the conducted studies, a relationship was established between the magnetic parameter Hp and structural changes in steels during thermal cycling.

The available magnetic field data from the terrestrial magnetosphere, solar wind and planetary magnetospheres exceeds over $10^6$ hours. Identifying plasma waves in these large data sets is a time consuming and tedious process. In this Paper, we propose a solution to this problem. We demonstrate how Self-Organizing Maps can be used for rapid data reduction and identification of plasma waves in large data sets. We use 72,000 fluxgate and 110,000 search coil magnetic field power spectra from the Magnetospheric Multiscale Mission (MMS$_1$) and show how the Self-Organizing Map sorts the power spectra into groups based on their shape. Organizing the data in this way makes it very straightforward to identify power spectra with similar properties and therefore this technique greatly reduces the need for manual inspection of the data. We suggest that Self-Organizing Maps offer a time effective and robust technique, which can significantly accelerate the processing of magnetic field data and discovery of new wave forms., Accepted in "JGR: Space Physics - Technical Reports: Methods"

In this paper, the response of the fluxgate core is analyzed against different design parameters using finite element method simulations. Furthermore, the nonlinear characteristic of the core magnetic material is included during simulations to have reliable evaluation about the fluxgate core behavior under the investigated operating conditions. Results of the conducted numerical simulations reveal that at 100 KHz excitation frequency, a desired flux response was achieved for 20 μm radius' core with 100 mA ac current. Moreover, in addition to the 100 mA ac current, a dc bias of 100 mA was needed to achieve a desired flux response for 20 μm radius' core at 1 MHz excitation frequency. Furthermore, for a core radius of 40 μm, a desired flux response was achieved at 100 KHz, with the excitation ac and dc currents to be 60 mA, and 100 mA respectively.

The magnetic field created by technical devices is a source of information. This information could be used in contactless diagnostics and predictive maintenance or for resolving problems along with standard NDT (nondestructive testing) methods, especially if we consider large, slow-speed devices, such as electromotors, transmissions, or generators. Identification of causalities of device failure processes with near magnetic field is one of the suitable NDT methods improving sustainability of systems. The measurements presented in the article were performed with the VEMA 04 fluxgate vector magnetometer with the DC-250 Hz bandwidth and 2 nT sensitivity. Postprocessing of the results was performed in the means of standard methods of discrete Fourier Transform, spectrogram creation and Wavelet Transform. The article presents data gathered during the measurement of a pair of extraction fans with power of 140 kW each and maximum revolutions up to 740 rev/min controlled by frequency converters and a single semi-Kaplan water power plant with 400 kW peak power at 1005 rev/min maximum generator speed. The measurements were performed before and after repairs of one of the ventilators in the ventilation system at 60% and 100% of maximal output power. The rotating magnetic fields of the fan electromotor stator, fan rotor revolutions, rotor slip frequency and ball-bearing frequencies were identified in frequency spectrums in the distance of 700 mm from fan electromotor axis in both cases. During the measurements on the semi-Kaplan turbine, the changes in states of mechanical and electrical components of the machine were monitored in the magnetic fields with increase of the power in the range of 0–95%, before and after phasing to the electrical grid. Standard processing methods, Discrete Fourier Transform, spectrograms and Discrete Wavelet Transform were used. In the spectrograms of the measured magnetic fields, the 1st–4th harmonics of the turbine shaft, generator shaft and also their side frequencies were identified. Significant changes of magnetic fields in time were identified in the area of 60–95% power. With the help of the Wavelet, transform intervals were identified where it is desirable to operate the turbine. The analyses of magnetic fields measurements performed on the power plant were compared with vibro-diagnostic principles.

We propose an unmanned aerial system fully dedicated to magnetic surveying in a variety of contexts ranging from small and shallow objects or pipelines detection to large-scale geological mapping: the Easymag system. Four major requirements are identified if one wishes to efficiently acquire quality magnetic data at such variable scales: 1- the accuracy of the magnetic acquisition must be better than the lowest expected signal according to the application (usually a few nT or lower); 2- the navigation and positioning must be precise enough to compete with ground operators with centimetre accuracy; 3- the flight flexibility must allow contrasting flight domains with topographic draping at any height; 4- the efficiency on the field must compete with existing carriers. Each of these aspects are investigated to demonstrate Terremys’ ability to perform efficient magnetic surveys. As a first case study, a drone magnetic acquisition for archaeological purposes is presented in comparison with a ground survey of the same area. Ground and drone surveys can lead to similar results. To demonstrate the ability to acquire magnetic data in different flight domains with the same system, a second case study focusing on a multiscale analysis is presented.

Traditional fluxgate sensors used in geomagnetic field observations are large, costly, power-consuming and often limited in their use. Although the size of the micro-fluxgate sensors has been significantly reduced, their performance, including indicators such as accuracy and signal-to-noise, does not meet observational requirements. To address these problems, a new race-track type probe is designed based on a magnetic core made of a Co-based amorphous ribbon. The size of this single-component probe is only Φ10 mm × 30 mm. The signal processing circuit is also optimized. The whole size of the sensor integrated with probes and data acquisition module is Φ70 mm × 100 mm. Compared with traditional fluxgate and micro-fluxgate sensors, the designed sensor is compact and provides excellent performance equal to traditional fluxgate sensors with good linearity and RMS noise of less than 0.1 nT. From operational tests, the results are in good agreement with those from a standard fluxgate magnetometer. Being more suitable for modern dense deployment of geomagnetic observations, this small-size fluxgate sensor offers promising research applications at lower costs.

Design, fabrication, characterisation and calibration of a three-axis, ring-core, second harmonic fluxgate magnetometer is described in detail. Owing to the good material selection, precise structural fabrication, and high-performance processing unit, in addition to implementation of a novel and effective calibration algorithm, the sensor features good characteristics such as $$0.1^{\circ }$$ non-orthogonality, 0.03% accuracy and 0.08% linearity. The power consumption of the fabricated sensor is 0.7 W. We have also compared the noise level of two types of commercial ring cores and shown that the experimental findings confirm our expectation about the noise level of the cores. In addition, a novel calibration method using the neural network was used to reduce errors of the fluxgate sensor.

Modern magnetic sensor arrays conventionally utilize state of the art low power magnetometers such as parallel and orthogonal fluxgates. Low power fluxgates tend to have large Barkhausen jumps that appear as a dc jump in the fluxgate output. This phenomenon deteriorates the signal fidelity and effectively increases the internal sensor noise. Even if sensors that are more prone to dc jumps can be screened during production, the conventional noise measurement does not always catch the dc jump because of its sparsity. Moreover, dc jumps persist in almost all the sensor cores although at a slower but still intolerable rate. Even if dc jumps can be easily detected in a shielded environment, when deployed in presence of natural noise and clutter, it can be hard to positively detect them. This work fills this gap and presents algorithms that distinguish dc jumps embedded in natural magnetic field data. To improve robustness to noise, we developed two machine learning algorithms that employ temporal and statistical physical-based features of a pre-acquired and well-known experimental data set. The first algorithm employs a support vector machine classifier, while the second is based on a neural network architecture. We compare these new approaches to a more classical kernel-based method. To that purpose, the receiver operating characteristic curve is generated, which allows diagnosis ability of the different classifiers by comparing their performances across various operation points. The accuracy of the machine learning-based algorithms over the classic method is highly emphasized. In addition, high generalization and robustness of the neural network can be concluded, based on the rapid convergence of the corresponding receiver operating characteristic curves., Accepted to IEEE Magnetics Letters

The operation of flux-gate magnetometers (FGMs) onboard moving carriers faces several difficulties that limit their application in geophysics. Specifically, when FGM is used onboard UAV (such as drone) it has essential space rotation. As we show in the paper, it may create interference up to the value overcoming the useful signal. We show that the obstacles limiting the FGM sensitivity threshold are the FGM axes non-orthogonality and its sensors transformation factor non-uniformity. A possible solution of this problem is proposed: not to try to make these values as small as possible, but to determine them after production at thorough calibration and then use them at data processing. A new method to determine the real FGM channels mutual orthogonality deflection and transformation factors non-identity with given precision is described and experimentally confirmed.