The China Seismo-Electromagnetic Satellite (CSES) is the first platform of China’s earthquake observation system in space and the first satellite of China’s geophysical field detection missions. The ...high precision magnetometer (HPM), which contains two fluxgate sensors and a coupled dark state magnetometer (CDSM), measures the vector of the Earth’s magnetic field with a bandwidth from DC to 15 Hz. The two fluxgate sensors are in a gradiometer configuration in order to reduce satellite interferences. Additionally, the CDSM sensor measures the scalar value of the magnetic field with higher accuracy and stability. Several data processing and calibration methods have been prepared to get accurate vector magnetic field data. This includes the calibration of each of the three sensors, the absolute vector correction algorithm, the spacecraft magnetic interference elimination and the coordinate transformation method. Also the instrument performances based on ground calibration activities are shown in this article.
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 (1
σ
) 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.
Multifunctional magnetometers enable high-precision observations of the geomagnetic direction and total magnetic field, which have broad applications in geoscience research and space weather ...forecasting. However, inconsistencies still occur between the optical and magnetic axes of classic multifunctional magnetometers, and few studies have investigated their direct detection. To address this issue, we propose a novel method for the detection of the optical-magnetic axis inconsistency. The magnetic azimuths for the magnetic axis and the optical axis of the multifunctional magnetometer are determined through the bias field loading and fluxgate theodolite, thereby allowing direct detection of the inconsistency. The proposed method is also modeled to quantify the detection errors introduced by the total-field sensor and the observation operation. In addition, we develop a dedicated experimental platform and conduct comparative tests at a geomagnetic observatory to validate the practicality and performance of the method. The experimental results show that the proposed method can significantly reduce the deviation of the declination curve measured by the multifunctional magnetometer relative to the curve measured by the fluxgate theodolite from <inline-formula> <tex-math notation="LaTeX">3959{}^{\prime \prime } </tex-math></inline-formula> to <inline-formula> <tex-math notation="LaTeX">19{}^{\prime \prime } </tex-math></inline-formula>, achieving a 99.5% reduction rate.
Featuring chapters written by leading experts in magnetometry, this book provides comprehensive coverage of the principles, technology and diverse applications of optical magnetometry, from testing ...fundamental laws of nature to detecting biomagnetic fields and medical diagnostics. Readers will find a wealth of technical information, from antirelaxation-coating techniques, microfabrication and magnetic shielding to geomagnetic-field measurements, space magnetometry, detection of biomagnetic fields, detection of NMR and MRI signals and rotation sensing. The book includes an original survey of the history of optical magnetometry and a chapter on the commercial use of these technologies. The book is supported by extensive online material, containing historical overviews, derivations, sideline discussion, additional plots and tables, available at www.cambridge.org/9781107010352. As well as introducing graduate students to this field, the book is also a useful reference for researchers in atomic physics.
•The fundamental physical characteristics of how the modulation amplitude affects OPM performance are investigated.•A model is established to reveal the relationship between the optimal modulation ...amplitude and operating parameters of OPM.•We recommend using the lower operating temperature for OPM in practical applications.•By adjusting OPM operating points and modulation coil current, the modulation field crosstalk was successfully suppressed.
Crosstalk between neighboring optically pumped magnetometers (OPMs) limits the localization accuracy of the magnetoencephalography systems based on high-density OPMs. In this study, we develop a comprehensive model to describe the relationship between the optimal modulation-field amplitude of OPMs and their operating parameters. Our model reveals that sensors have distinct optimal modulation amplitudes under different operating parameters. Meanwhile, by appropriately reducing the vapor temperature or increasing the pump intensity, the susceptibility of OPM response to change in the modulation amplitude can be significantly reduced and thus decreasing the influence of the crosstalk. Furthermore, considering the layout of our high-resolution OPM array, the calculation equation for the coil magnetic field is improved for achieving the optimal modulation amplitude for each sensor. Consequently, we successfully suppress the crosstalk associated with the modulation-field amplitude. Our approach facilitates the rapid and accurate suppression of the crosstalk between channels, paving the way for OPM array applications.
Parametric-resonance magnetometer is a high-sensitivity quantum sensor characterized by applying the non-resonant radio-frequency (RF) fields to the atomic ensemble. The RF fields lead to crosstalk ...in the multi-sensor design, thus disturbing the magnetic-field measurement results. We propose an optically modulated alignment-based sup.4He parametric-resonance magnetometer. By using the fictitious field generated by the modulated light shift, parametric resonance is realized, and crosstalk caused by the magnetic RF field is prevented. The relative intensity noise of the lasers is suppressed to optimize the sensitivity of the magnetometer. Our magnetometer experimentally demonstrates a magnetic-field noise floor of 130 fT/Hzsup.1/2 in both open- and closed-loop operations and has the potential to reach 70 fT/Hzsup.1/2 when compared with the optimized magnetic RF scheme. It provides near-zero magnetic-field measurements with a 2 kHz bandwidth at room temperature, which is useful for high-bandwidth measurements in biomagnetic applications.
In the current article, we present a new kind of magnetometer for quantitative detection of magnetic objects (magnetic nano- and submicron particles) in biological fluids and tissues. The sensor is ...based on yttrium-iron garnet film with optical signal registration system. Inheriting the working principle of a fluxgate magnetometers, the sensor works at a room-temperature, its wide dynamic range allows the measurements in an unshielded environment. A small size of sensitive element combined with a short recovery time after the excitation coils are off provide us with a potentially high spatial and temporal resolution of measurements. We show the feasibility of the developed devices by sensing the remanent magnetization of magnetic nanoparticles (MNPs) both in vitro (test tubes, dry MNPs) and in vivo (local injection of the MNPs into mice).
In this paper, we propose a method to estimate the position, orientation, and gain of a magnetic field sensor using a set of (large) electromagnetic coils. We apply the method for calibrating an ...array of optically pumped magnetometers (OPMs) for magnetoencephalography (MEG). We first measure the magnetic fields of the coils at multiple known positions using a well-calibrated triaxial magnetometer, and model these discreetly sampled fields using vector spherical harmonics (VSH) functions. We then localize and calibrate an OPM by minimizing the sum of squared errors between the model signals and the OPM responses to the coil fields. We show that by using homogeneous and first-order gradient fields, the OPM sensor parameters (gain, position, and orientation) can be obtained from a set of linear equations with pseudo-inverses of two matrices. The currents that should be applied to the coils for approximating these low-order field components can be determined based on the VSH models. Computationally simple initial estimates of the OPM sensor parameters follow. As a first test of the method, we placed a fluxgate magnetometer at multiple positions and estimated the RMS position, orientation, and gain errors of the method to be 1.0 mm, 0.2°, and 0.8%, respectively. Lastly, we calibrated a 48-channel OPM array. The accuracy of the OPM calibration was tested by using the OPM array to localize magnetic dipoles in a phantom, which resulted in an average dipole position error of 3.3 mm. The results demonstrate the feasibility of using electromagnetic coils to calibrate and localize OPMs for MEG.
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