Vector Magnetometer Research Articles

Fiber Vector Magnetometer Based on Balloon-Like Fiber Structure and Magnetic Fluid

A compact vector magnetometer based on balloon-like fiber structure functionalized by magnetic fluid (MF) was proposed. To fabricate the sensor, the single mode fiber (SMF) was bent into a balloon-like structure, and then the shape was fixed by using the alcohol lamp flame. Because of the bending, the fiber core mode leaks into the cladding, thereby forming higher order cladding modes that are sensitive to the variations of external refractive index. When the structure is encapsulated in MF, due to the anisotropic distribution of ferromagnetic nanoparticles under magnetic field, the refractive index around the fiber structure also presents anisotropy. By measuring the refractive index of the MF under different magnetic-field directions and intensities, both the measurement of the magnetic field intensity and direction can be achieved. The experimental results show that a high magnetic field intensity sensitivity of 0.78 nm/mT and a high magnetic-field direction sensitivity of 0.094°/mT were obtained. Due to the simple fabricating method, low cost, and highly sensitivity, the proposed fiber vector magnetometer has potential applications in the navigation, aviation, and electric power industry.

Vector Overhauser magnetometer POS-4: experience and prospects of application

The results of practical use of a POS-4 vector magnetometer, developed by the Research Laboratory of Quantum Magnetometry, UrFU (Yekaterinburg) and based on POS Overhauser sensors, are presented. Continuous measurements by POS-4 have been carried out at the Paratunka observatory (IKIR FEB RAS, Kamchatka) since 2015, were done at the Saint Petersburg observatory (GC RAS / IZMIRAN SPb Branch, Leningrad Region) in 2017-2018 and have been performed at the Arti observatory (Institute of Geophysics, UB RAS, Sverdlovsk Region) since 2020. On the new high-latitude observatory White Sea (IAGA code WSE, GC RAS / MSU, Nikolai Pertsov White Sea Biological Station , Karelia), POS-4 is used as a main variometer for magnetic measurements. In April 2019, the magnetometer was successfully used for field measurements on ice during the TRANSARCTIC expedition in the Barents Sea (AARI, Roshydromet). At the beginning of 2021 IZMIRAN started testing two POS-4 magnetometers at the Moskow observatory. According to the results of field and observatory measurements it was possible to identify the advantages and disadvantages of the magnetometer and provide the information for its developers for further modernization in order to improve its efficiency and reliability. Many years of experience in POS-4 application determine the areas where its scientific and applied usage will provide important results, for example, for magnetic measurements in the Arctic regions or for monitoring of active zones around volcanoes.

Modeling and Reduction of the Initial Orientation Error of a Coil Vector Magnetometer

The initial orientation error of a coil vector magnetometer directly determines the measurement accuracy of the magnetic field direction. The traditional initial orientation method requires auxiliary manually operated instruments. To solve this problem, we propose an electrical orientation method based on applying bias fields. To analyze quantitatively the orientation error of the proposed method, a physical model for the coil orientation indicator and measurement errors of the magnetic direction was developed that exploits measurements of the deflected field obtained after applying two oppositely directed bias fields. The simulation results show that, when the difference indicator is 0.7 nT, the measurement error of the magnetic direction is less than 9°. Moreover, when the bias field strength is greater than 30% of the geomagnetic field strength during the orientation operation, the influence of the change in strength of the bias field on the measurement error of the magnetic direction diminishes significantly. The indirect effect of the measurement error of the total-field sensor on the measurement accuracy of the magnetic direction was also analyzed. To verify this method, we designed an experimental setup and conducted a comparative experiment. The results show that as the difference indicator increases, the measurement error of the magnetic direction increases accordingly. When this indicator is adjusted to about0.7 nT, the measurement error of the magnetic direction is less than 11.16'', which is in agreement with theoretical results.

Calibration-Free Vector Magnetometry Using Nitrogen-Vacancy Center in Diamond Integrated with Optical Vortex Beam.

We report a new method to determine the orientation of individual nitrogen-vacancy (NV) centers in a bulk diamond and use them to realize a calibration-free vector magnetometer with nanoscale resolution. Optical vortex beam is used for optical excitation and scanning the NV center in a [111]-oriented diamond. The scanning fluorescence patterns of NV center with different orientations are completely different. Thus, the orientation information on each NV center in the lattice can be known directly without any calibration process. Further, we use three differently oriented NV centers to form a magnetometer and reconstruct the complete vector information on the magnetic field based on the optically detected magnetic resonance(ODMR) technique. Compared with previous schemes to realize vector magnetometry using an NV center, our method is much more efficient and is easily applied in other NV-based quantum sensing applications.

The CHAOS-7 geomagnetic field model and observed changes in the South Atlantic Anomaly

We present the CHAOS-7 model of the time-dependent near-Earth geomagnetic field between 1999 and 2020 based on magnetic field observations collected by the low-Earth orbit satellites Swarm, CryoSat-2, CHAMP, SAC-C and Ørsted, and on annual differences of monthly means of ground observatory measurements. The CHAOS-7 model consists of a time-dependent internal field up to spherical harmonic degree 20, a static internal field which merges to the LCS-1 lithospheric field model above degree 25, a model of the magnetospheric field and its induced counterpart, estimates of Euler angles describing the alignment of satellite vector magnetometers, and magnetometer calibration parameters for CryoSat-2. Only data from dark regions satisfying strict geomagnetic quiet-time criteria (including conditions on IMF B_z and B_y at all latitudes) were used in the field estimation. Model parameters were estimated using an iteratively reweighted regularized least-squares procedure; regularization of the time-dependent internal field was relaxed at high spherical harmonic degree compared with previous versions of the CHAOS model. We use CHAOS-7 to investigate recent changes in the geomagnetic field, studying the evolution of the South Atlantic weak field anomaly and rapid field changes in the Pacific region since 2014. At Earth’s surface a secondary minimum of the South Atlantic Anomaly is now evident to the south west of Africa. Green’s functions relating the core–mantle boundary radial field to the surface intensity show this feature is connected with the movement and evolution of a reversed flux feature under South Africa. The continuing growth in size and weakening of the main anomaly is linked to the westward motion and gathering of reversed flux under South America. In the Pacific region at Earth’s surface between 2015 and 2018 a sign change has occurred in the second time derivative (acceleration) of the radial component of the field. This acceleration change took the form of a localized, east–west oriented, dipole. It was clearly recorded on ground, for example at the magnetic observatory at Honolulu, and was seen in Swarm observations over an extended region in the central and western Pacific. Downward continuing to the core–mantle boundary, we find this event originated in field acceleration changes at low latitudes beneath the central and western Pacific in 2017.

Dependence on sensitivity patterns of bias fields for vector measurements using optically pumped vapor magnetometers

The optical light shift effect is an all-optical technique to create magnetic bias fields to determine the vector components of the magnetic field using a scalar optically pumped magnetometer. We show that the measurement of the induced bias fields is affected by the response pattern of the scalar magnetometer. The sensitivity of the magnetometer affects the minimum total field resolution as well as the angular resolution of the vector measurement. Three configurations of multiple-laser, optically pumped cesium vapor vector magnetometers are characterized for their spatial sensitivity patterns. Each configuration has a unique response level as a function of the relative magnetic field orientation. Thus, the formulations used for angular determination are dependent on the magnetometer configuration, and the angular resolution of the vector measurement is dependent on the relative angle between the magnetic field and the optical probe beam. The spatial dependence of the light shift signals is measured, and the equations describing their responses are presented for each configuration. Equations for determining the field angles from the bias field responses are derived.

Light-ellipticity and polarization-angle dependence of magnetic resonances in rubidium vapor using amplitude-modulated light: Theoretical and experimental investigations

We report on experimental and theoretical investigations of the polarization dependence of magnetic resonance generated by synchronous optical pumping. Magnetic resonances with narrow linewidth are generated experimentally using a rubidium vapor cell with octade-cyltrichlorosilane (OTS) antirelaxation coating on inner walls. We studied the effect of light ellipticity on the amplitudes and widths of magnetic resonances by matching the light modulation frequency with 2 {\Omega}_L (alignment) and {\Omega}_L(orientation) in a Bell-Bloom interaction geometry, where {\Omega}_L corresponds to the Larmor frequency. Both 2 {\Omega}_L and \OmegaL resonance amplitudes showed a strong dependence on the light ellipticity. In addition, we showed that the duty cycle of light modulation changes the slope of amplitude variations in 2{\Omega}_L and {\Omega}_L resonances with light ellipticity. As a potential application, we showed that the difference between 2{\Omega}_Land {\Omega}_Lresonance amplitudes can be used for in situ measurement of light ellipticity. We also studied the dependence of 2{\Omega}_L and {\Omega}_L resonance amplitudes on the polarization angle of linearly polarized light. These amplitudes oscillate periodically with the polarization angle. We found this oscillatory behavior to be sensitive to the tilt in magnetic field direction from the polarization plane. Such a property could be used to realize a vector magnetometer. A density matrix based theoretical model is developed to simulate the magnetic resonance spectrum for different light polarizations. Our theoretical model accurately reproduces the above mentioned experimental observations.

Commissioning of the multiparametric geophysical observatory at Shoal Bay, South Andaman and the preliminary results

The Indian Institute of Geomagnetism (IIG) is operating Multiparametric Geophysical Observatory (MPGO) at Port Blair in South Andaman. We report here on the commissioning of MPGO and the quality of data collected by this observatory. The base line values are regularly computed with the aid of the declination inclination magnetometer, in house developed proton precession magnetometer and the flux gate magnetometer. The total field computed by the vector magnetometer is all time compared with direct measurements from the scalar magnetometer. An attempt to co-relate the precursor seismo-electromagnetic emissions of the earthquake event by the induction coil magnetometer is made. The seismic station of the observatory is capable of recording seismic events within the vicinity of ≈200 km. Further MPGO is upgrading and some more experiments are planned for the future.

Calibration of AC Vector Magnetometer Based on Ellipsoid Fitting

AC vector magnetometers have recently become increasingly widespread. The calibration of ac vector magnetometers before use is critical. Based on traditional ellipsoid fitting, which is suitable for calibrating dc vector magnetometers, a method suitable for calibrating ac vector magnetometers is presented. Simulation analysis and experimental verification demonstrate that this method is effective in calibrating ac vector magnetometers, including scaling factors, angular misalignments, and offset errors.

Side-Polished Single-Mode-Multimode-Single-Mode Fiber Structure for the Vector Magnetic Field Sensing

A vector magnetometer, composed of a side-polished single-mode-multimode-single-mode fiber structure coated with ferrofluids, is proposed and investigated. The side-polishing of the multimode fiber can expose the evanescent field to the surrounding ferrofluids, whose refractive index in the vicinity of the polished surface can be tuned by both the intensity and direction of the applied magnetic field, thus in turn realizing the magnetic vector sensing. The sensing principles are illustrated in details, and the sensing performances, especially the dependence on the residual thickness (RT) of the side-polished multimode fiber, are well investigated experimentally. It is found that the decrease of the RT can significantly improve the sensitivity to both the magnetic field intensity and the direction, and the highest intensity and direction sensitivities of −0.053 nm/Oe and −5.68 nm/degree have been achieved respectively, when the RT reduces to 50.5 μm. The proposed vector magnetometer, featuring the advantages of simple structure, low cost, and ease of fabrication, can find the potential applications in the fields such as industry, military, and environment.

Herriott-cavity-assisted all-optical atomic vector magnetometer

We report an all-optical atomic vector magnetometer using dual Bell-Bloom optical pumping beams in a Rb vapor cell. This vector magnetometer consists of two orthogonal optical pumping beams, with amplitude modulations at $^{85}$Rb and $^{87}$Rb Larmor frequencies respectively. We simultaneously detect atomic signals excited by these two pumping beams using a single probe beam in the third direction, and extract the field orientation information using the phase delays between the modulated atomic signals and the driving beams. By adding a Herriott cavity inside the vapor cell, we improve the magnetometer sensitivity. We study the performance of this vector magnetometer in a magnetic field ranging from 100~mG to 500~mG, and demonstrate a field angle sensitivity better than 10~${\mu}$rad/Hz$^{1/2}$ above 10~Hz.

A calibration method for coil constants using an atomic spin self-sustaining vector magnetometer

The self-sustaining atomic magnetometer has the advantage of high sensitivity and long spin coherence lifetime, based on which we demonstrate a novel method to calibrate the magnetic coil constants precisely. Via non-destructive phase measurement and coherent optical pumping, the spin polarization of rubidium atoms is regenerated coherently and the Larmor precession signal is oscillating continuously. In this stable state, the calibrating capability is achieved by applying current to coils and scan the magnetic components along x- and y-direction. The magnetic field magnitude is obtained from precession frequency and the coil constants can be derived from the fitting equation directly. The constants of coils in the experiment are 246.010 ± 0.034 nT/mA and 197.452 ± 0.025 nT/mA in the x- and y-directions, respectively.

On the Use of Aeromagnetism for Geological Interpretation: 1. Comparison of Scalar and Vector Magnetometers for Aeromagnetic Surveys and an Equivalent Source Interpolator for Combining, Gridding, and Transforming Fixed Altitude and Draping Data Sets

AbstractAirborne magnetic surveys are common in geosciences. High‐precision surveys are usually performed at a low altitude, draping the topography, using scalar absolute magnetometers and active compensation systems to correct the disturbances generated by the carrier. Another solution is to measure the total magnetic intensity using vector magnetometers, which allows compensation for aircraft fields to be calculated directly, without compensation systems. This study uses data of an industrial airborne survey and of a vector magnetometer survey with a small overlapping area in the Vosges (France) to compare both data sets and shows that both solutions provide results of the same overall precision. This paper also addresses the issue of combining fixed altitude and draped level data sets as well as topographic effect management by proposing an equivalent source interpolator based on a set of simple dipole sources. A synthetic case shows that the equivalent source interpolator allows to compute grids of the magnetic anomaly as well as potential field transforms from a draped data set with an error level a few orders of magnitude lower than could be obtained with minimum curvature, a classically applied interpolator. The interpolator is also tested on a case study in the Vosges massif of which geological interpretation is presented in Bertrand et al. (2020, https://doi.org/10.1029/2019JB017688). The results confirm the observations made on the synthetic case and show that the equivalent source interpolator is more tolerant to navigation errors (altitude) than minimum curvature and allows more rigorous computation of potential field transforms of draped data sets.

A Merged Search‐Coil and Fluxgate Magnetometer Data Product for Parker Solar Probe FIELDS

AbstractNASA's Parker Solar Probe (PSP) mission is currently investigating the local plasma environment of the inner heliosphere (<0.25 R⊙) using both in situ and remote sensing instrumentation. Connecting signatures of microphysical particle heating and acceleration processes to macroscale heliospheric structure requires sensitive measurements of electromagnetic fields over a large range of physical scales. The FIELDS instrument, which provides PSP with in situ measurements of electromagnetic fields of the inner heliosphere and corona, includes a set of three vector magnetometers: two fluxgate magnetometers (MAGs) and a single inductively coupled search‐coil magnetometer (SCM). Together, the three FIELDS magnetometers enable measurements of the local magnetic field with a bandwidth ranging from DC to 1 MHz. This manuscript reports on the development of a merged data set combining SCM and MAG (SCaM) measurements, enabling a high fidelity data product with an optimal signal‐to‐noise ratio. On‐ground characterization tests of complex instrumental responses and noise floors are discussed as well as application to the in‐flight calibration of FIELDS data. The algorithm used on PSP/FIELDS to merge waveform observations from multiple sensors with optimal signal‐to‐noise characteristics is presented. In‐flight analysis of calibrations and merging algorithm performance demonstrates a timing accuracy to well within the survey rate sample period of ∼340 μs.

Microwave-Free Vector Magnetometry with Nitrogen-Vacancy Centers along a Single Axis in Diamond

Sensing vector magnetic fields is critical to many applications in fundamental physics, bioimaging, and material science. Magnetic-field sensors exploiting nitrogen-vacancy (NV) centers are particularly compelling as they offer high sensitivity and spatial resolution even at nanoscale. Achieving vector magnetometry has, however, often required applying microwaves sequentially or simultaneously, limiting the sensors' applications under cryogenic temperature. Here we propose and demonstrate a microwave-free vector magnetometer that simultaneously measures all Cartesian components of a magnetic field using NV ensembles in diamond. In particular, the present magnetometer leverages the level anticrossing in the triplet ground state at 102.4 mT, allowing the measurement of both longitudinal and transverse fields with a wide bandwidth from zero to megahertz range. Full vector sensing capability is proffered by modulating fields along the preferential NV axis and in the transverse plane and subsequent demodulation of the signal. This sensor exhibits a root mean square noise floor of about 300 pT/Hz^(1/2) in all directions. The present technique is broadly applicable to both ensemble sensors and potentially also single-NV sensors, extending the vector capability to nanoscale measurement under ambient temperatures.

Optical frequency dependence of the light shift effect for vector magnetometry with cesium.

Atomic vapor magnetometers have demonstrated very high sensitivity to the magnitude of the magnetic field. Vector field measurements are possible using bias fields applied to the vapor. For remote operation, the bias field can be generated using the optical light shift (LS) effect created with an optical beam delivered through optical fiber. Here, it is shown that the optical frequency of the LS effect for an optically pumped vapor vector magnetometer causes an angular error in the measured field orientation when it is tuned near the absorption resonances, countering the benefit of higher response. This angle-shifting effect is dependent on the LS beam power. The LS response, normalized to the LS power, is higher for lower powers due to a saturation effect but also shows a dependence on the LS optical frequency. We show that it is necessary to carefully choose the LS optical frequency and power to maximize the LS effect while avoiding potential angular error.

Reconfigurable Magnetoresistive Sensor Based on Magnetoelectric Coupling

AbstractMeasurement of magnetic signal from an arbitrary direction is of vital importance for applications in magnetic navigation, space science, indoor positioning, and magnetic gesture recognition. However, magnetoresistive sensors, as vector magnetometers, are only suitable for detection of magnetic signals along the magnetic hard axis. Magnetoelectric coupling is introduced to control the magnetic anisotropy of a magnetoresistive pattern, realizing a 90° rotation of the magnetic hard axis and thus the sensing direction of the tunable sensor. The sensitivity along the initial magnetic easy axis can be enhanced 12.7‐fold while that along the initial hard axis can be depressed to be only 4.7% of the original value through magnetic anisotropy engineering. The tailorable directional sensitivity of the electric‐field reconfigurable sensor speaks to the strong potential of this system for practical applications requiring testing of localized magnetic fields, for example, magnetic diagnosis or biomagnetic characterization.

Orientation of a Vector Magnetometer Optically Referenced to an External Coordinate System

We present a new method to realize a vector magnetometer that has been optically referenced to an external coordinate system. The vector magnetometer is made up of three Hall sensors attached to the orthogonal faces of a glass cube. When placed in a homogeneous magnetic field, rotating the vector magnetometer around two axes allows the orientation of each sensor to be determined with respect to the glass cube. The orientation of the glass cube is detected by an autocollimator and optically referenced to an external coordinate system. A direction uncertainty below $130~\mu $ rad (which is traceable to angle standards) is achieved.

SQUID Array With Optimal Compensating Configuration for Magnetocardiography Measurement in Different Environments

We developed a 51-channel magnetocardiography (MCG) system based on weakly damped dc superconducting quantum interference device (SQUID) magnetometers. In previous works, the system consisted of 36 sensing magnetometers, 12 reference magnetometers, and a three-component vector magnetometer. In this paper, we have describe the optimizing processes of software gradiometer configurations in different magnetically shielded rooms (MSRs). Using a simulated MCG signal generated by a small coil driven by electrocardiograph, we have quantitatively evaluated the signal quality through four key performance indices, which are 1) correlation in time domain, 2) correlation in frequency domain, 3) relative heights of different peaks, and 4) magnetic field map of simulating coil. After data processing and analysis of these four parameters, optimized software gradiometers of first or second order can be formed by using specific reference magnetometer signals to compensate the signals of 36 sensing magnetometers in each MSR. Also, the MCG signals of an adult have been detected by using these optimized configurations. The magnetic field maps and typical parameters at T-peak have been extracted and compared, and the results with high consistency confirm the effectiveness of optimization processes.

Voigt-effect-based three-dimensional vector magnetometer

We describe a method to dispersively detect all three vector components of an external magnetic field using alkali atoms based on the Voigt effect. Our method relies on measuring the linear birefringence of the radio frequency dressed atomic medium via polarization homodyning. This gives rise to modulated polarization signals at the first and second harmonic of the dressing frequency. The vector components of the external magnetic field are mapped onto the quadratures of these harmonics. We find that our scheme can be utilised in both cold and hot atomic gases to detect such external fields in shielded and unshielded environments. In the shielded hot vapour case we achieve field sensitivities well below 1~pT$/\sqrt{\textrm{Hz}}$ range for all 3 vector components, using pump-probe cycles with 125 Hz repetition rate, and limited by the short coherence time of the cell. Finally, our scheme has a simple single axis beam geometry making it advantageous for miniature magnetic field sensors.