Precision measurement and suppression of low-frequency noise in a current source with double-resonance alignment magnetometers

Low-noise high-stability current sources have essential applications such as neutron electric dipole moment measurement and high-stability magnetometers. Previous studies mainly focused on frequency noise above 0.1 Hz while less on the low-frequency noise/drift. We use double resonance alignment magnetometers(DRAMs) to measure and suppress the low-frequency noise of a homemade current source(CS) board. The CS board noise level is suppressed by about 10 times in the range of 0.001-0.1 Hz and is reduced to 100 n A/√Hz at 0.001 Hz. The relative stability of CS board can reach2.2 × 10^(-8). In addition, the DRAM shows a better resolution and accuracy than a commercial 7.5-digit multimeter when measuring our homemade CS board. Further, by combining the DRAM with a double resonance orientation magnetometer,we may realize a low-noise CS in the 0.001-1000 Hz range.

Six-Degree-of-Freedom Measurement of Plate Anchors in Centrifuge by Magnetometers

The six-degree-of-freedom movement of an offshore plate anchor is essential to evaluate anchor performance.As an emerging technology,magnetometer has shown its potential in measuring the six-degree-of-freedom movement of offshore anchors under 1-g model laboratory tests.The paper presents the feasibility of adopting a magnetometer system in geotechnical centrifuge testing.Interference factors that may affect the measuring accuracy of the magnetometer system are investigated.The results demonstrate that the magnetometer system can accurately catch the anchor movement in the soils with the restrictions of:(1)the model anchor was made with stainless steel;(2)the system was placed at least 30 cm away from the side wall of soil model tank;(3)started the measurement when the artificial acceleration by centrifuge was stable.

Sensitive Single-Level Magnetometers of High T_(c) dc SQUIDS

We have developed a simple sintering system to prepare the yttria-stabilized-zirconia(YSZ)bicrystals.Grain-boundary junctions made from the epitaxial YBa_(2)Cu_(3)O_(7-δ) films on the bicrystal substrates demonstrated Josephson behavior.Using new square washer design,single-level magnetometer of dc superconducting quantum interference.device(SQUID)has been fabricated.Owing to the flux focusing effect of the large washer,the magnetic field sensitivity of the devices has been enhanced.The magnetic field resolution of the magnetometer is IpT/Hz^(1/2) at 10Hz,and increases to 3pT/Hz^(1/2) at 1Hz at 77K.

Tl_(2)Ba_(2)CaCu_(2)O_(x) Bicrystal Junction DC-SQUID Magnetometers Operating in Unshielded Environment

We fabricated direct-current superconducting quantum interference device magnetometers with single layer epi-taxial Tl_(2)Ba_(2)CaCu_(2)O_(x) films on 36.8° SrTiO_(3) bicrystal substrates.The white Aux noise and the field-flux transformation coefficient of the devices are 1.5 × 10^(-5)Φ0/√Hz and 40 nT/Φ0,respectively.The magnetometers can work in unshielded environment.

A Deep Learning Approach for Landmines Detection Based on Airborne Magnetometry Imaging and Edge Computing

Landmines continue to pose an ongoing threat in various regions around the world,with countless buried landmines affecting numerous human lives.The detonation of these landmines results in thousands of casualties reported worldwide annually.Therefore,there is a pressing need to employ diverse landmine detection techniques for their removal.One effective approach for landmine detection is UAV(Unmanned Aerial Vehicle)based AirborneMagnetometry,which identifies magnetic anomalies in the local terrestrial magnetic field.It can generate a contour plot or heat map that visually represents the magnetic field strength.Despite the effectiveness of this approach,landmine removal remains a challenging and resource-intensive task,fraughtwith risks.Edge computing,on the other hand,can play a crucial role in critical drone monitoring applications like landmine detection.By processing data locally on a nearby edge server,edge computing can reduce communication latency and bandwidth requirements,allowing real-time analysis of magnetic field data.It enables faster decision-making and more efficient landmine detection,potentially saving lives and minimizing the risks involved in the process.Furthermore,edge computing can provide enhanced security and privacy by keeping sensitive data close to the source,reducing the chances of data exposure during transmission.This paper introduces the MAGnetometry Imaging based Classification System(MAGICS),a fully automated UAV-based system designed for landmine and buried object detection and localization.We have developed an efficient deep learning-based strategy for automatic image classification using magnetometry dataset traces.By simulating the proposal in various network scenarios,we have successfully detected landmine signatures present in themagnetometry images.The trained models exhibit significant performance improvements,achieving a maximum mean average precision value of 97.8%.

Enhanced measurement precision with continuous interrogation during dynamical decoupling

Dynamical decoupling(DD)is normally ineffective when applied to DC measurement.In its straightforward implementation,DD nulls out DC signal as well while suppressing noise.This work proposes a phase relay method that is capable of continuously interrogating the DC signal over many DD cycles.We illustrate its efficacy when applied to the measurement of a weak DC magnetic field with an atomic spinor Bose-Einstein condensate.Sensitivities approaching standard quantum limit or Heisenberg limit are potentially realizable for a coherent spin state or a squeezed spin state of 10000 atoms,respectively,while ambient laboratory level noise is suppressed by DD.Our work offers a practical approach to mitigate the limitations of DD to DC measurement and would find other applications for resorting coherence in quantum sensing and quantum information processing research.

Performance optimization of a SERF atomic magnetometer based on flat-top light beam

We explore the impact of pumping beams with different transverse intensity profiles on the performance of the spinexchange relaxation-free(SERF) atomic magnetometers(AMs). We conduct experiments comparing the traditional Gaussian optically-pumped AM with that utilizing the flat-top optically-pumped(FTOP) method. Our findings reveal that the FTOP-based approach outperforms the conventional method, exhibiting a larger response, a narrower magnetic resonance linewidth, and a superior low-frequency noise performance. Specifically, the use of FTOP method leads to a 16% enhancement in average sensitivity within 1 Hz–30 Hz frequency range. Our research emphasizes the significance of achieving transverse polarization uniformity in AMs, providing insights for future optimization efforts and sensitivity improvements in miniaturized magnetometers.

Response optimization of a three-axis sensitive SERF magnetometer for closed-loop operation

Most triaxial-vectorial magnetic field measurements with spin-exchange relaxation free(SERF)atomic magnetometer(AM)are based on the quasi-steady-state solution of the Bloch equation.However,the responding speed of these methods is greatly limited because the frequency of the modulation signal should be slow enough to ensure the validity of the quasi-steady-state solution.In this work,a new model to describe the response of the three-axis sensitive SERF AM with high modulation frequency is presented and verified.The response of alkali-atomic spin to high-frequency modulation field is further investigated by solving the Bloch equation in a modulation-frequency-dependence manner.This solution is well verified by our experiments and can offer a reference for selection of modulation frequencies.The result shows a potential to achieve a SERF AM operating in a geomagnetic field without heavy aluminum shielding when the modulation frequencies are selected properly.

VCSEL frequency stabilization for optically pumped magnetometers

Optically pumped magnetometers(OPMs)have developed rapidly in the bio-magnetic measurement field,which requires lasers with stable frequency and intensity for high sensitivity.Herein we stabilize a vertical-cavity surface-emitting laser(VCSEL)without any additional setup except for the parts of an OPM.The linewidth of the absorption spectrum as a frequency reference is broadened to 40 GHz owing to pressure broadening.To enhance performance,the VCSEL injection current and temperature are tuned simultaneously using a closed-loop control system.The experiments reveal that the VCSEL frequency stability achieves 2×10^(-7) at an average time of 1 s,and the intensity noise is 1×10^(-6)V/Hz^(1/2) at 1-100 Hz.This approach is useful for suppressing OPM noise without additional sensor probe parts.

Design,fabrication,characterization and reliability study of CMOS-MEMS Lorentz-force magnetometers

This article presents several design techniques to fabricate micro-electro-mechanical systems(MEMS)using standard complementary metal-oxide semiconductor(CMOS)processes.They were applied to fabricate high yield CMOS-MEMS shielded Lorentz-force magnetometers(LFM).The multilayered metals and oxides of the back-end-of-line(BEOL),normally used for electronic routing,comprise the structural part of the MEMS.The most important fabrication challenges,modeling approaches and design solutions are discussed.Equations that predict the Q factor,sensitivity,Brownian noise and resonant frequency as a function of temperature,gas pressure and design parameters are presented and validated in characterization tests.A number of the fabricated magnetometers were packaged into Quad Flat No-leads(QFN)packages.We show this process can achieve yields above 95%when the proper design techniques are adopted.Despite CMOS not being a process for MEMS manufacturing,estimated performance(sensitivity and noise level)is similar or superior to current commercial magnetometers and others built with MEMS processes.Additionally,typical offsets present in Lorentz-force magnetometers were prevented with a shielding electrode,whose efficiency is quantified.Finally,several reliability test results are presented,which demonstrate the robustness against high temperatures,magnetic fields and acceleration shocks.

The Mars orbiter magnetometer of Tianwen-1:in-flight performance and first science results

The Mars Orbiter MAGnetometer(MOMAG)is a scientific instrument onboard the orbiter of China’s first mission for Mars—Tianwen-1.Since November 13,2021,it has been recording magnetic field data from the solar wind to the magnetic pile-up region surrounding Mars.Here we present its in-flight performance and first science results,based on its first one and one-half months’data.Comparing these early MOMAG observations to the magnetic field data in the solar wind from NASA’s Mars Atmosphere and Volatile EvolutioN(MAVEN)mission,we report that the MOMAG magnetic field data are at the same level in magnitude,and describe the same magnetic structures with similar variations in three components.We recognize 158 clear bow shock(BS)crossings in these MOMAG data;their locations match well statistically with the modeled average BS.We also identify and compare five pairs of datasets collected when Tianwen-1’s orbiter and the MAVEN probe made simultaneous BS crossings.These BS crossings confirm the global shape of modeled BS,as well as the south-north asymmetry of the Martian BS.Two cases presented in this paper suggest that the BS is probably more dynamic at flank than near the nose.So far,MOMAG performs well,and provides accurate magnetic field vectors.MOMAG is continuously scanning the magnetic field surrounding Mars.Data from MOMAG’s measurements complement data from MAVEN and will undoubt edly advance our understanding of the plasma environment of Mars.

A robust method for performance evaluation of the vapor cell for magnetometry

A robust performance evaluation method for vapor cells used in magnetometers is proposed in this work.The performance of the vapor cell determines the sensitivity of the magnetic measurement,which is the core parameter of a magnetometer.After establishing the relationship between intrinsic sensitivity and the total relaxation rate,the total relaxation rate of the vapor cell can be obtained to represent the intrinsic sensitivity of the magnetometer by fitting the parameters of the magnetic resonance experiments.The method for measurement of the total relaxation rate based on the magnetic resonance experiment proposed in this work is robust and insensitive to ambient noise.Experiments show that,compared with conventional sensitivity measurement,the total relaxation rate affected by magnetic noise below 0.9 n T,pump light frequency noise below 1.5 GHz,pump light power noise below 9%,probe light power noise below 3%and temperature fluctuation of 150±3℃deviates by less than 2%from the noise-free situation.This robust performance evaluation method for vapor cells is conducive to the construction of a multi-channel high-spatial-resolution cardio-encephalography system.

A miniaturized spin-exchange relaxation-free atomic magnetometer based on uniform light field

We experimentally study the dynamic characteristics of a miniaturized spin-exchange relaxation-free(SERF) magnetometer based on uniform light field. The ceramic ferrule is used to expand the Gaussian beam to improve light intensity uniformity, while the volume of the sensor is also reduced. This scheme makes the magnetometer have better sensitivity when the detected light intensity is less than 3.16 m W/cm^(2) at 120℃. When the temperature rises to 150℃ the sensitivity under the action of uniform light field is 18.5 f T/Hz^(1/2). The bandwidth of the sensor remains at the original level and meets application needs. The proposed structure improves transverse polarization uniformity within the miniaturized sensor, which is ideal for the magnetoencephalography and magnetocardiography imaging systems.

A compact and closed-loop spin-exchange relaxation-free atomic magnetometer for wearable magnetoencephalography

Atomic magnetometers operated in the spin-exchange relaxation-free(SERF)regime are the promising sensor to replace superconducting quantum interference devices(SQUIDs)in the biomagnetism field.The SERF magnetometer with compact size and good performance is crucial to the new generation of wearable magnetoencephalography(MEG)system.In this paper,we developed a compact and closed-loop SERF magnetometer with the dimensions of 15.0×22.0×30.0 mm^(3)based on a single-beam configuration.The bandwidth of the magnetometer was extended to 675 Hz while the sensitivity was maintained at 22 f T/Hz^(1/2).A nearly 3-fold enhancement of the bandwidth was obtained in comparison with the open-loop control.The implementation of the closed-loop control also greatly improved the dynamic range,enabling the magnetometer to be robust against the disturbance of the ambient field.Moreover,the magnetometer was successfully applied for the detection of humanα-rhythm and auditory evoked fields(AEFs),which demonstrated the potential to be extended to multi-channel MEG measurements for future neuroscience studies.

Measurement of T wave in magnetocardiography using tunnel magnetoresistance sensor

Several critical clinical applications of magnetocardiography(MCG)involve its T wave.The T wave’s accuracy directly affects the diagnostic accuracy of MCG for ischemic heart disease and arrhythmogenic.Tunnel magnetoresistance(TMR)attracts attention as a new MCG measurement technique.However,the T waves measured by TMR are often drowned in noise.The accuracy of T waves needs to be discussed to determine the clinical value of MCG measured by TMR.This study uses an improved empirical mode decomposition(EMD)algorithm and averaging to eliminate the noise in the MCG measured by TMR.The MCG signals measured by TMR are compared with MCG measured by the optically pumped magnetometer(OPM)to judge its accuracy.Using the MCG measured by OPM as a reference,the relative errors in time and amplitude of the T wave measured by TMR are 3.4%and 1.8%,respectively.This is the first demonstration that TMR can accurately measure the time and amplitude of MCG T waves.The ability to provide reliable T wave data illustrates the significant clinical application value of TMR in MCG measurement.

Low-noise,low-power-consumption seafloor vector magnetometer

The seafloor vector magnetometer is an effective tool for marine geomagnetic surveys and seafloor magnetotelluric(MT)detection.However,the noise,power consumption,cost,and volume characteristics of existing seafloor vector magnetometers are insufficient for practical use.Therefore,a low-noise,low-power-consumption seafloor vector magnetometer that can be used for data acquisition of deep-ocean geomagnetic vector components is developed and presented.A seafloor vector magnetometer mainly consists of a fluxgate sensor,data acquisition module,acoustic release module,glass sphere,frame,burn-wire release,and anchor.A new low-noise data acquisition module and a fluxgate sensor greatly reduce power consumption.Furthermore,compact size is achieved by integrating an acoustic telemetry module and replacing the acoustic release with an external burn-wire release.The new design and magnetometer characteristics reduce the volume of the instrument and the cost of hardware considerably,thereby improving the integrity and deployment efficiency of the equipment.Theoretically,it can operate for 90 days underwater at a maximum depth of 6000 m.The seafloor vector magnetometer was tested in the South China Sea and the Philippine Sea and obtained high-quality geomagnetic data.The deep-water environment facilitates magnetic field data measurements,and the magnetometer has an approximate noise level of 10 pT/rt(Hz)@1 Hz,a peak-to-peak value error of 0.2 nT,and approximate power consumption of 200 mW.The fluxgate sensor can measure the magnetic field in the lower frequency band and realize geomagnetic field measurements over prolonged periods.

Ground calibration of the Mars orbiter magnetometer onboard Tianwen-1

Ground calibration experiments of the Mars orbiter magnetometer(MOMAG)onboard the orbiter of Tianwen-1 were performed to determine the sensitivity,misalignment angle,and offset of the sensors.The linearity of the applied calibrated magnetic fields and the output from the sensors were confirmed to be better than 10^(-4),and the sensor axes were orthogonal to each other within 0.5 degrees.The temperature dependencies of the sensitivity and misalignment angle were examined,but no clear signatures of temperature dependencies could be seen.Sensor offset and the stability of sensor offset drift with a temperature change were also determined by the rotation method.The stability of the sensor offset drift was less than 0.01 nT/℃.The ground calibration of MOMAG determines all the calibration parameters of the sensors for accurate magnetic field measurements in orbit with the appropriate corrections.

Results of Geomagnetic Studies on the Problem of Forecasting Strong Earthquakes in Uzbekistan

The article is devoted to the problem of forecasting strong earthquakes by the geomagnetic method. The geomagnetic method is widely used on this problem in seismically active regions of the world as one of the promising, informative and operational geophysical methods. The results of long-term geomagnetic studies on the problem of forecasting strong earthquakes in Uzbekistan are presented. Geomagnetic studies were carried out on the territories of the Tashkent, Ferghana, and Kyzylkum geodynamic polygons in the epicentral zones of strong earthquakes that occurred. Long-term, medium- and short-term precursors of earthquakes have been identified. Anomalous changes in the geomagnetic field associated with the decline in aftershock activity were also revealed. The dependence between the duration of the manifestation of long-term magnetic precursors and the magnitude of earthquakes is determined. Absolute proton magnetometers MMP-1, MV-01 (Russia), and G-856 (USA) were used to measure the geomagnetic field.

Observing the steady-state visual evoked potentials with a compact quad-channel spin exchange relaxation-free magnetometer

We observed the steady-state visually evoked potential(SSVEP) from a healthy subject using a compact quad-channel potassium spin exchange relaxation-free(SERF) optically pumped magnetometer(OPM). To this end, 30 s of data were collected, and SSVEP-related magnetic responses with signal intensity ranging from 150 fT to 300 f T were observed for all four channels. The corresponding signal to noise ratio(SNR) was in the range of 3.5–5.5. We then used different channels to operate the sensor as a gradiometer. In the specific case of detecting SSVEP, we noticed that the short channel separation distance led to a strongly diminished gradiometer signal. Although not optimal for the case of SSVEP detection, this set-up can prove to be highly useful for other magnetoencephalography(MEG) paradigms that require good noise cancellation.Considering its compactness, low cost, and good performance, the K-SERF sensor has great potential for biomagnetic field measurements and brain-computer interfaces(BCI).

Chinese Antarctic Magnetometer Chain at the Cusp Latitude

A Chinese Antarctic Magnetometer （CAM） chain from Zhongshan Station （ZHS） to Dome-A （DMA） has been established since February 2009. A regular magnetometer is operated at ZHS, and four low power magnetometers are operated along the interior route from ZHS to DMA in the cusp latitude, extending over a distance of 1260 km. These stations fill an important void in the Antarctic magnetometer network. Furthermore, the CAM chain is magnetically conjugated with the Arctic region reaching from the Svalbard archipelago to Daneborg, on the east coast of Greenland. Conjugate measurements using the Arctic and Antarctic magnetometers provide excellent opportunities to investigate phenomena related to the coupling of the solar wind to the magnetosphere and ionosphere, such as magnetic impulse events, flux transfer events, traveling convection vortices and ultra-low frequency waves.