Vector Magnetic Field Measurements Research Articles

Macau Scientific Satellite‐1 Initial Magnetic Field Model

AbstractEight months of vector magnetic field measurements from the Macau Scientific Satellite‐1 (MSS‐1), supplemented by higher latitude field intensity measurements from the Swarm satellites, are used to derive an MSS‐1 Initial Field Model (MIFM). Robust root‐mean‐square misfits between MIFM and the three components of the MSS‐1 vector field data are found to be below 3.3 nT. MIFM agrees well with the CHAOS‐7 field model and we find even better agreement with an identically parameterized model derived only from Swarm data. MSS‐1 and Swarm vector data can moreover be fit simultaneously with only a small increase in misfit (by less than 0.2 nT). We show that both lithospheric anomalies and core surface field changes can be studied using MSS‐1 data. With its fast coverage of local times MSS‐1 is a valuable addition to the global geomagnetic observing system.

Highly sensitive fiber vector magnetic field sensor based on an open-cavity Mach-Zehnder interferometer filled with magnetic fluid

In this paper, we proposed and demonstrated a highly sensitive fiber vector magnetic field sensor utilizing an open-cavity Mach-Zehnder interferometer (MZI) filled with magnetic fluid. The MZI sensor was fabricated using large-offset splicing technique to form an open cavity, facilitating the easy introduction of magnetic fluid samples into the open cavity. The MZI sensor was then encapsulated in a glass capillary containing diluted magnetic fluid. As the applied magnetic field varies, the refractive index of the magnetic fluid undergoes a corresponding change, subsequently inducing a shift in the transmission spectrum of the MZI. By monitoring the wavelength shift of the transmission spectrum, we can accurately detect the intensity of the magnetic field. The proposed sensor can achieve vector magnetic field measurement because of the axially asymmetric open-cavity MZI. The maximum sensitivity to magnetic field direction is 0.260 nm/°. Notably, the proposed sensor achieves an ultrahigh sensitivity, reaching an value of −17.306 nm/mT within the range of 4 mT to 7 mT. In addition, a temperature sensitivity of 2.236 nm/℃ is obtained within the temperature range of 30 ℃ to 65 ℃. Given its advantages, including high sensitivity, compact size and low cost, our MZI sensor holds immense potential for diverse applications in magnetic field measurement.

Phase-error-free atomic magnetometer and vector measurement method based on demodulated signal phase in geomagnetic environment

The performance of double-beam atomic magnetometer in the geomagnetic environment is greatly affected by the vectorial direction of magnetic field, which leads to the shift of the phase of the demodulation signal. We propose a phase-error-free scalar double-beam atomic magnetometer. When the RF field is along the direction of probe beam, the fluctuation of the phase of the demodulation signal can be avoided. For the practical measurement environment, we propose a phase extraction method for atomic magnetometer. Additionally, based on the phase of the demodulated signal when the RF field is applied in the directions of pumping, probing, and perpendicular to the pumping-detection plane, we propose a method for vector magnetic field measurement. The measurement results indicate that under a 10 μT bias magnetic field, the deviations θ and φ are within 0.1°. The theory and method proposed are of great significance to the application of magnetometer in geomagnetic magnetic field.

Research on Precise Attitude Measurement Technology for Satellite Extension Booms Based on the Star Tracker

This paper reports the successful application of a self-developed, miniaturized, low-power nano-star tracker for precise attitude measurement of a 5-m-long satellite extension boom. Such extension booms are widely used in space science missions to extend and support payloads like magnetometers. The nano-star tracker, based on a CMOS image sensor, weighs 150 g (including the baffle), has a total power consumption of approximately 0.85 W, and achieves a pointing accuracy of about 5 arcseconds. It is paired with a low-cost, commercial lens and utilizes automated calibration techniques for measurement correction of the collected data. This system has been successfully applied to the precise attitude measurement of the 5-m magnetometer boom on the Chinese Advanced Space Technology Demonstration Satellite (SATech-01). Analysis of the in-orbit measurement data shows that within shadowed regions, the extension boom remains stable relative to the satellite, with a standard deviation of 30′′ (1σ). The average Euler angles for the “X-Y-Z” rotation sequence from the extension boom to the satellite are [−89.49°, 0.08°, 90.11°]. In the transition zone from shadow to sunlight, influenced by vibrations and thermal factors during satellite attitude adjustments, the maximum angular fluctuation of the extension boom relative to the satellite is approximately ±2°. These data and the accuracy of the measurements can effectively correct magnetic field vector measurements.

Vector magnetic field measurement based on fiber ring microwave photonic filter with the Vernier effect

A vector magnetic field sensor based on enhanced Vernier effect is experimentally demonstrated. The Vernier effect is generated from two microwave photonic filters (MPFs) with close free spectral range (FSR), which is constructed by the fiber ring (FR) and the optical carrier microwave interferometry (OCMI). Linear chirped fiber Bragg grating (LCFBG) is inserted in the FR to act as the dispersion element to provide time delay. By attaching the fiber Bragg grating (FBG) on the magnetostrictive material (MA), the magnetic field can be transferred into the wavelength shift, as well as the time delay of the FR and the frequency response of the FR-MPF. By choosing opposite dispersion of LCFBGs and closer FSRs, cascaded FR-MPFs based sensor can greatly improve the sensitivity. The sensitivities for the magnetic field intensity and direction are 127.71 kHz/Oe, the magnification factor of which is 432, and 418.16 kHz/deg. The proposed scheme has merits of high sensitivity and interference immunity, which is suitable for high precision measurement.

Copper permalloys for fluxgate magnetometer sensors

Abstract. Fluxgate magnetometers are commonly used to provide high-fidelity vector magnetic field measurements. The magnetic noise of the measurement is typically dominated by that intrinsic to a ferromagnetic core used to modulate (gate) the local field as part of the fluxgate sensing mechanism. A polycrystalline molybdenum–nickel–iron alloy (6.0–81.3 Mo permalloy) has been used in fluxgates since the 1970s for its low magnetic noise. Guided by previous investigations of high-permeability copper–nickel–iron alloys, we investigate alternative materials for fluxgate sensing by examining the magnetic properties and fluxgate performance of that permalloy regime in the range 28 %–45 % Cu by weight. Optimizing the alloy constituents within this regime enables us to create fluxgate cores with both lower noise and lower power consumption than equivalent cores based on the traditional molybdenum alloy. Racetrack geometry cores using six layers of ∼30 mm long foil washers consistently yield magnetic noise around 4–5 pT/Hz at 1 Hz and 6–7 pT/Hz at 0.1 Hz, meeting the 2012 1 s INTERMAGNET standard of less than 10 pT/Hz noise at 0.1 Hz.

Machine learning techniques for estimation of Pc5 geomagnetic pulsations observed at geostationary orbits during solar cycle 23

Pc5 geomagnetic pulsations can accelerate electrons in the radiation belts, which can pose adverse threats to both astronauts and satellites in space. The estimation of Pc5 waves in space is crucial to radiation belt dynamics studies and will help mitigate these challenges. Here, we explore the advantages of the Feed-forward Neural Network (FFNN) and Random Forest (RF) algorithm for effective estimation of Pc5 geomagnetic pulsations observed in space at geostationary orbit during solar cycle 23. The dataset used in this study is the vector magnetic field measurements retrieved from the Geostationary Operational Environmental Satellite-10 (GOES-10) and the solar wind parameters: Bz and Vx component of the solar wind in the Geocentric Solar Ecliptic (GSE) coordinate system, proton density, flow pressure, and plasma beta obtained from the OMNI Web database during part of solar cycle 23. Pc5 geomagnetic pulsations were extracted from the toroidal component of the magnetic field time series using a bandpass Butterworth filter. The continuous wavelet transform (CWT) was utilized to study the characteristics of the extracted wave in the time-frequency domain for its validation. The validated Pc5 events were used as the target in the model's development, with the solar wind parameters as the inputs. In addition to the solar wind parameters, we included an attribute of the magnetic field time series as an input variable in the model. The dataset is carefully divided to ensure effective training and testing of the models. Finally, we trained both models using the same inputs and targets and explored their estimation abilities. The model was tested during the maximum, descending, and minimum phases of solar cycle 23. Both the FFNN and RF models have a similar estimation, with average cross-correlation score (R) values of 0.74 and 0.73 and corresponding average root mean squared error (RMSEs) of 0.16 nT and 0.67 nT, respectively. The model was deployed to investigate the response of Pc5 waves during three storm days in each testing year. The machine learning (ML) model outputs showed good coherence with the observed Pc5 waves. To validate the models, we studied the correlation between the estimated Pc5 events with the Kp index, and a good correlation was seen to exist between both events. This validates the good performance of the developed models. This work will aid in the study of radiation belt dynamics and the construction of electron depletion regions in the radiation belt.

Measurements of Spatial Angles Using Diamond Nitrogen-Vacancy Center Optical Detection Magnetic Resonance.

This article introduces a spatial angle measuring device based on ensemble diamond nitrogen-vacancy (NV) center optical detection magnetic resonance (ODMR). This device realizes solid-state all-optical wide-field vector magnetic field measurements for solving the angles of magnetic components in space. The system uses diamond NV center magnetic microscope imaging to obtain magnetic vector distribution and calculates the spatial angles of magnetic components based on the magnetic vector distribution. Utilizing magnetism for angle measuring enables non-contact measuring, reduces the impact on the object being measured, and ensures measurement precision and accuracy. Finally, the accuracy of the system is verified by comparing the measurement results with the set values of the angle displacement platform. The results show that the measurement error of the yaw angle of the system is 1°, and the pitch angle and roll angle are 1.5°. The experimental results are in good agreement with the expected results.

Joint quantum sensing of vector magnetic field and temperature with nitrogen-vacancy centers in diamond

Quantum diamond sensors of multiple physical quantities, especially magnetic field and temperature, have great application prospects in materials science, biophysics, and engineering. Here, we demonstrate joint quantum sensing of vector magnetic field and temperature based on ensembles of nitrogen-vacancy (NV) centers in the diamond. Combining the intrinsic C3ν symmetry of diamond crystals and multiple-frequency excitation technique, we can directly measure frequency-modulated optically detected magnetic resonance (ODMR) spectra for three different NV orientations and then obtain the Zeeman splittings and the center frequency movement of the electron spin. An artificially generated underlying external magnetic field is used to eliminate degeneracy and facilitate coordinate transformations. The six-channel phase-locked amplification technology enables simultaneous detection of vector magnetic field and temperature with a sensitivity of about 0.87 nT/Hz1/2 and 0.32 mK/Hz1/2; meanwhile, a 23 dB isolation between magnetic and temperature signals is kept. This technology realizes the simultaneous measurement of arbitrary vector magnetic field and temperature, which can be used to study the temperature-varying magnetic phase transition.

A machine learning approach combined with wavelet analysis for automatic detection of Pc5 geomagnetic pulsations observed at geostationary orbits

Pc5 geomagnetic pulsations are ultra-low frequency (ULF) waves whose period lies within 150–600 s. Their detection is crucial for accurate space weather modelling, monitoring, and analysis. Identification of these pulsations using manual approaches is difficult and time-consuming because of the smaller magnitudes and the limited durations within which they occur. To overcome this challenge, we propose a robust Cascade Forward Neural Network (CFNN) model combined with the wavelet technique for automatically detecting Pc5 events from satellite datasets observed at geostationary orbits. The dataset used in this study is the magnetic field vector measurements retrieved from the Geostationary Operational Environmental Satellite-10 (GOES-10) from 2000 to 2009. Pc5 geomagnetic pulsations were extracted from the toroidal component of the field perturbation using a bandpass Butterworth filter. Continuous wavelet transform (CWT) analysis using the mother Morlet wavelet was utilized to validate the integrity of the extracted signal in the time–frequency domain. The extracted Pc5 signal was decomposed into details and approximations using Daubechies wavelet transform to separate the intelligible signal from the incoherent noise that left their trace on the magnetic field time series. The detail signal was subjected to denoising using the heuristic Stein Unbiased Risk Estimate (SURE) approach with soft thresholding to obtain the denoised Pc5 events. The denoised Pc5 events were utilized as the target in the machine learning whereas the inputs were obtained from 5-dimensional space transformation of the toroidal component of the time series. The developed algorithm performed well and demonstrated a detection accuracy of 80 % and a Root Mean Square Error (RMSE) of 0.13 nT indicating a high performance in detecting Pc5 events. For effective validation of the model, Pc5 events detected by our model were correlated with the Kp index and the amplitude of the Pc5 events observed at geostationary orbit. A good correlation was obtained in both cases, making our model a practical and preferred choice for Pc5 pulsation detection in contrast to conventional frequency analysis tools which take much time for signal processing on large data sets.

Construction and Experimental Verification of a New Miniature Low-Noise Hall Sensor for Wide-Range Vector Magnetic Field Measurements

Construction and Experimental Verification of a New Miniature Low-Noise Hall Sensor for Wide-Range Vector Magnetic Field Measurements

Interplanetary Coronal Mass Ejections and Stream Interaction Regions Observed by Tianwen-1 and MAVEN at Mars

The Tianwen-1 spacecraft is China's first Mars exploration mission. The Mars Orbiter Magnetometer (MOMAG) is a scientific instrument on board the Tianwen-1 mission that is designed to study magnetic fields at Mars, including the solar wind to the magnetosheath and the ionosphere. Using the first Tianwen-1/MOMAG data that is publicly available, we present an interplanetary coronal mass ejection (ICME) and stream interaction region (SIR) list based on in situ observations at Mars between 2021 November 16 and 2021 December 31. We compared the magnetic field intensity and vector magnetic field measurements from Tianwen-1/MOMAG and Mars Atmospheric Volatile EvolutioN (MAVEN)/Magnetometer (MAG) during the ICME and SIR interval and found a generally good consistency between them. Due to MAVEN's orbital adjustment since 2019, the Tianwen-1/MOMAG instrument is almost unique in its status as an interplanetary magnetic field monitor currently at Mars. The observations indicate that the MOMAG instrument on Tianwen-1 is performing well and can provide accurate measurements of the vector magnetic field in the near-Mars solar wind space. The multipoint observations combining MOMAG, MINPA, and MEPA on board Tianwen-1 with MAG, SWIA, and STATIC on board MAVEN will help develop systematic studies of the characteristics of ICMEs and SIRs at Mars, and their influences on the Martian atmosphere and ionosphere.

A customized control and readout device for vector magnetometers based on nitrogen-vacancy centers.

A customized control and readout device, which is developed to perform real-time measurement for vector magnetometers based on nitrogen-vacancy centers, is presented in this paper. A dual-channel analog-to-digital-converter chip, which has a 25 MSa/s sampling rate and a 16 bits amplitude resolution, is integrated for analog signal acquisition. The data processing and the system control are realized using a Xilinx Kirtex-7 field-programmable-gate-array chip. Eight independent lock-in modules, a four-channel proportional-integral-derivative controller, a reference generator, and a vector field reconstruction module are integrated with the Kirtex-7 device in order to perform the real-time vector magnetic field measurement. The device has a bright future to be applied in practical applications.

Magnetic Field Sensing Using Tapered Small-Core Optical Fibre Surrounded by Different Concentrations of Magnetic Fluid.

In this paper, a high-sensitivity magnetic field sensor based on a single-mode-tapered small-core-single-mode (STSCS) optical fibre structure is investigated. The tapered small-core section of STSCS is surrounded by magnetic fluid (MF) containing ferromagnetic particles (FMPs) of different concentrations. The FMPs align themselves along the magnetic field, depending on the strength of the magnetic field. This alignment of FMPs changes the refractive index around the tapered small-core section, which in turn changes the output spectral response of the STSCS optical fibre structure. The change in spectral response is then calibrated for sensing the magnetic field strength. This paper also investigates the effect of both the taper waist diameter of the STSCS optical fibre structure and the concentration of MF surrounding it on the magnetic field sensitivity. The maximum sensitivity demonstrated in this paper is 0.46 nm/mT for a taper waist diameter of 10 μm surrounded by 1.22% FMPs in the MF. The magnetic sensor demonstrates reversible results, and its effects on the orientation of the magnetic field along the X-Y, X-Z and Y-Z axes are also investigated, which suggest that the sensor is capable of vector magnetic field measurement.

Analysis and Suppression of the Cross-Axis Coupling Effect for Dual-Beam SERF Atomic Magnetometer

Spin-exchange relaxation-free (SERF) atomic magnetometers operated under a near-zero magnetic field are used for vector magnetic field measurements with high sensitivity. Previously, the cross-axis coupling error evoked by a nonzero background magnetic field has been verified to be adverse in modulated single-beam magnetometers. Here, in a dual-beam unmodulated SERF magnetometer, we propose a somewhat different solution model for the cross-axis coupling effect where the field of interest couples with the interference field. Considering two cases where the transverse or longitudinal background field exists, the cross-axis coupling effect dependence on multiple factors is investigated here based on the dynamic response under a background magnetic field within ±5 nT. The theoretical and experimental investigation suggests that it has an adverse impact on the output response amplitude and phase and tilts the sensitive axis by several degrees, causing a measurement error on the dual-beam magnetometer. To suppress this effect, the background magnetic field is compensated through the PI closed-loop control. The coupling effect is effectively suppressed by 1.5 times at the 10–40 Hz low-frequency band and the sensitivity reaches 2.4 fT/Hz1/2.

Optic-fiber vector magnetic field sensor utilizing magneto-shape effect of magnetic fluid

In this work, an optic-fiber sensor utilizing magneto-shape effect of magnetic fluid (MF) has been put forward to measure magnetic field direction. MF magneto-shape effect has been presented, simulated and verified through experiments as a magneto-optical effect. The sensor consists of a capillary glass tube, two single-mode fibers (SMFs) and MF. The interface between MF and air is concave because the glass tube is attractive to MF. As magnetic field rises, the concavity degree becomes more obvious, in other words, edge length of MF cavity is extended and central length of cavity is shortened. The interference wavelength of sensor will change with magnetic field, so as to achieve the purpose of monitoring magnetic field. The phenomenon is defined as the magneto-shape effect of MF. Due to the magnetic field direction dependence of pressure difference between the MF and air, the magneto-shape effect of MF has different perception of axial magnetic field and radial magnetic field, realizing vector magnetic field measurement. Results of experiment are shown as follows: the sensor can easily react to field strength and orientation. The wavelength shows the shape of number “8″ with magnetic field direction changing. The field sensitivity reaches up to 296.1 pm/Gs from 22.6 Gs to 121.8 Gs in the axial field. Moreover, direction sensitivity reaches 311.6 pm/° at 104.4 Gs. The wavelength shift in the axial direction is 25.5 times higher than that of the radial direction. The presented sensing structure could monitor vector magnetic field without constructing a non-circular symmetrical structure. The proposed sensing structure is provided with characteristics of simple to make, highly-sensitive and little fabrication consumption. It possesses potential applications in electronic power industry and aerospace.

Single NV centers array preparation and static magnetic field detection.

To solve the problem of static magnetic field detection accuracy and consistency, we prepared an array of single NV centers for static magnetic field vector and gradient detection using the femtosecond laser direct writing method. The prepared single NV centers are characterized by fewer impurity defects and good stress uniformity, with an average spatial positioning error of only 0.2 µm. This array of single NV centers can achieve high accuracy magnetic field vector and gradient measurement with GBZ≈-0.047 µT/µm in the Z-axis. This result provides a new idea for large-range, high-precision magnetic field vector and gradient measurements.

Vector Magnetic Field Imaging With High-Resolution TMR Sensor Arrays for Metal Structure Inspection

This paper proposes an eddy current testing (ECT) probe with high-resolution tunneling magnetoresistance (TMR) array sensors for vector magnetic field measurement. The probe consists of two printed circuit boards (PCBs), which are placed perpendicular to each other. Three arrays of TMR sensors are wire bonded on the two PCBs to measure the three components of the magnetic field. Each array contains 32 sensors and the distance between the centers of two adjacent sensors in an array is 0.5 mm. The 32 output signals of each array are multiplexed, amplified and filtered by using a circuit on the PCB. An experimental system is set up and aluminum samples with machined defects are imaged by the probe. It is seen that the patterns of the images along the x-, y- and z-axis are different, meaning the information in the three images can compensate each other to a certain extent. The images change their orientations if the defects are oriented along different angles. An image processing algorithm including image segmentation, normalization, edge detection and K-means classification is developed to class the defects. It is seen that the defects can be classified accurately with the algorithm. Then, the orientations of the defects are calculated from the images with a linear regression of the angles of the three axis images. It is found that the mean error of the orientation quantification is only 4.14°, which is much smaller than the mean error calculated from each axis image separately.

The magnetic topology of the inverse Evershed flow

Context. The inverse Evershed flow (IEF) is a mass motion towards sunspots at chromospheric heights. Aims. We combined high-resolution observations of NOAA 12418 from the Dunn Solar Telescope and vector magnetic field measurements from the Helioseismic and Magnetic Imager (HMI) to determine the driver of the IEF. Methods. We derived chromospheric line-of-sight (LOS) velocities from spectra of Hα and Ca II IR. The HMI data were used in a non-force-free magnetic field extrapolation to track closed field lines near the sunspot in the active region. We determined their length and height, located their inner and outer foot points, and derived flow velocities along them. Results. The magnetic field lines related to the IEF reach on average a height of 3 megameter (Mm) over a length of 13 Mm. The inner (outer) foot points are located at 1.2 (1.9) sunspot radii. The average field strength difference ΔB between inner and outer foot points is +400 G. The temperature difference ΔT is anti-correlated with ΔB with an average value of −100 K. The pressure difference Δp is dominated by ΔB and is primarily positive with a driving force towards the inner foot points of 1.7 kPa on average. The velocities predicted from Δp reproduce the LOS velocities of 2–10 km s−1 with a square-root dependence. Conclusions. We find that the IEF is driven along magnetic field lines connecting network elements with the outer penumbra by a gas pressure difference that results from a difference in field strength as predicted by the classical siphon flow scenario.

Intensity-demodulated fiber-optic vector magnetic field sensor based on fiber-optic evanescent field

A high-sensitivity intensity-demodulated fiber-optic evanescent field sensor is proposed for vector magnetic field measurement. The structure was fabricated by bending a section of single mode fiber into a U shape under the flame of alcohol burner, and then coated with magnetic fluid. By bending the fiber into a U shape, a non-centrosymmetric fiber-optic evanescent field is distributed on the cross section of fiber. Combing with the magnetic-field-dependent anisotropy of magnetic fluid, a high intensity sensitivity of 2.481 dB/mT and a high direction sensitivity of 0.182 dB/° were obtained. Due to the simple structure, high sensitivity and low cost, the proposed fiber-optic sensor has potential application in the vehicle navigation, aviation, and biomedical fields.