Magnetic Field Compensation Research Articles

Bias Calibration of Optically Pumped Magnetometers Based on Variable Sensitivity

Optically pumped magnetometers (OPMs) functioning in the spin-exchange relaxation-free (SERF) regime have emerged as attractive options for measuring weak magnetic fields, owing to their portability and remarkable sensitivity. The operation of SERF-OPM critically relies on the ambient magnetic field; thus, a magnetic field compensation device is commonly employed to mitigate the ambient magnetic field to near zero. Nonetheless, the bias of the OPM may influence the compensation impact, a subject that remains unexamined. This paper introduced an innovative bias calibration technique for OPMs. The sensitivity of the OPM was altered by adjusting the cell temperature. The output of the OPM was then documented with varying sensitivity. It is assumed that the signal exhibits a linear correlation with the environmental magnetic field, and the statistical characteristics of the magnetic field are identical for both measurements, upon which the bias of the OPM is assessed. The bias was subsequently considered in the feedback magnetic field compensation mechanism. The results indicate that this technique might successfully reduce environmental magnetic fluctuations and enhance the sensitivity of the OPM. This technique measured the magnetic field produced by the human heart, confirming the viability of the ultra-weak biomagnetic field measurement approach.

Disturbance Suppression Based High-Precision Magnetic Field Compensation Method for Magnetic Shielding Cylinder

Disturbance Suppression Based High-Precision Magnetic Field Compensation Method for Magnetic Shielding Cylinder

Magnetic Measurement System and Environmental Magnetic Field Compensation at CEM

Magnetic Measurement System and Environmental Magnetic Field Compensation at CEM

Non-uniform dynamic magnetic field compensation for a lightweight magnetically shielded room based on distributed differential coils

Abstract Due to the influence of material characteristics and engineering imperfections, the residual magnetic fields including static and dynamic field in a lightweight magnetically shielded room (MSR) present non-uniform distribution characteristic. To effectively reduce the residual static field, a non-uniform field compensation method based on distributed coils has been proposed. This method takes the L2-norm of the magnetic field at the target array points as the objective function, to optimize the compensation current in each of the designed distributed coils, achieving non-uniform field compensation. To further achieve compensation for non-uniform residual dynamic field, a closed-loop control system containing a voltage divider and multi-channel amplifiers is designed in this paper. Additionally, the coil constant of the distributed differential coils and the initial magnetic field distribution vector for dynamic compensation are redefined. In conjunction with a PI controller, dynamic compensation is achieved using a single optically pumped magnetometer (OPM) as the feedback component. The experimental results indicate that the average dynamic field decreased from 376.75 pT to 27.80 pT over the central volume of (300 mm)³ in MSR, achieving a near-zero magnetic environment. This method has universal applicability for compensating non-uniform residual field under different working conditions.

In-situ magnetic fields monitoring and compensation for zero-field atomic magnetometers

Zero-field atomic magnetometers (AMs) offer high sensitivity in compact size, making them versatile for various applications. However, magnetic field variations within shielded environments, especially in challenging conditions, can disrupt the zero-field, exceeding the AM’s linear range and reducing its accuracy and sensitivity. Conventional solutions rely on auxiliary sensors or an in-situ close-loop mode, leading to increased financial and spatial costs or interference among sensors. This study proposes an in-situ monitoring and compensation method, thereby establishing a monitoring-compensation loop mode for zero-field AMs without additional sensors. The proposed mode enhances conventional AMs by integrating not only the first but also the second harmonic of the longitudinal polarization, enabling real-time monitoring and rapid online compensation of triaxial magnetic fields. The high sensitivity is maintained and sensor interference is suppressed as AMs operate similarly to conventional ones near the zero-field. When field variations arise, rapid online compensation is triggered to restore the zero-field, covering a range of up to 120 nT with an accuracy of 8pT. Particularly, artificial intelligence algorithms are introduced to achieve simultaneous triaxial online compensation, enhancing the efficiency. This study supports the cost-effective and highly sensitive use of zero-field AMs in space-limited or challenging magnetic environments.

Noise suppression for an aeromagnetic measurement system on an unmanned helicopter.

An unmanned helicopter is one of the main platforms for conducting unmanned aerial vehicle aeromagnetic measurements and combines the advantages of rotary-wing and fixed-wing unmanned aerial vehicles. However, unmanned helicopter-based aeromagnetic measurement systems face complex static magnetic noise and maneuvering magnetic interference, which limit their practical performance. To address this issue, an improved multi-channel frequency measurement algorithm for the optically pumped magnetic sensor is proposed to suppress the static magnetic noise proportional to the frequency noise generated by the random quantization error and the airborne electromagnetic interference. A novel aeromagnetic compensation method for the maneuvering magnetic interference is then proposed to weaken the negative effects of the strong multicollinearity of the attitude parameters of the unmanned helicopter on the compensation accuracy and stability by introducing a regularization term and weight matrix. In addition, dedicated software is developed for the real-time calculation and compensation of magnetic interference fields. A dedicated unmanned-helicopter-based aeromagnetic measurement system is developed, and ground and flight experiments are carried out. The ground test results indicate that the static noise of the proposed system is only 0.000 82 nT. In the flight experiments, the system achieves an improvement ratio of 8.33, which is higher than the improvement ratio of 4.37 for a state-of-the-art commercial compensator. Furthermore, the dynamic noise after compensation decreases by 37.6% from 0.0157 to 0.0098 nT.

Filtering and Delay Compensation of Magnetic Field Caused by Eddy Current in Gyrotron With Flat-Top Pulsed Magnet

Filtering and Delay Compensation of Magnetic Field Caused by Eddy Current in Gyrotron With Flat-Top Pulsed Magnet

Low noise magnetic field compensation based on differential biplanar coils with small coil constant

Magnetic field noise is a key factor limiting the resolution of quantum precise measurement. In active magnetic field compensation systems, the large coil constant and fixed noise of the coil and current source, respectively, cause excessive noise. This study proposes a differential biplanar coils (DBCs) design method by comprehensively optimizing two sets of biplanar coils with differential evolution (DE) algorithm, which can reduce the coil constant by two magnitude orders while ensuring high uniformity. The peak-to-peak magnetic field at the center point is reduced to 0.8 pT, and the magnetic field noise is reduced to 8 fT/Hz, which is a reduction of 94.4%. The low noise active magnetic compensation system based on the differential biplanar coils can improve the accuracy of the magnetic shielding room (MSR) internal magnetic field control and reduce magnetic field noise effectively. The proposed method contributes to generating a near-zero magnetic field environment with low magnetic field noise, which is critical to promoting magnetoencephalography (MEG) measurements.

Highly Homogeneous and Low-Noise Magnetic Field Compensation Based on the High-Uniform Magnetic Field Coils With Small Coil Constant

Highly Homogeneous and Low-Noise Magnetic Field Compensation Based on the High-Uniform Magnetic Field Coils With Small Coil Constant

In Situ Magnetic Field Compensation Method for Optically Pumped Magnetometers Under Three-Axis Nonorthogonality

In Situ Magnetic Field Compensation Method for Optically Pumped Magnetometers Under Three-Axis Nonorthogonality

In Situ Triaxial Magnetic Field Compensation for the Spin-Exchange-Relaxation-Free Optically Pumped Magnetometer

In Situ Triaxial Magnetic Field Compensation for the Spin-Exchange-Relaxation-Free Optically Pumped Magnetometer

Method for control by orbital spacecraft magnetic cleanliness based on multiple magnetic dipole models with consideration of their uncertainty

Aim. Development of method for control by orbital spacecraft magnetic cleanliness based on multiple magnetic dipole models using compensation of the initial magnetic field with consideration of magnetic characteristics uncertainty. Methodology. Orbital spacecraft multiple magnetic dipole models calculated as solution of nonlinear minimax optimization problem based on near field measurements for prediction orbital spacecraft far magnetic field magnitude. Nonlinear objective function calculated as the weighted sum of squared residuals between the measured and predicted magnetic field. Weight matrix calculated as inverse covariance matrix of random errors vector. Values of magnetic moments and coordinates of placement of compensating magnetic dipoles for compensation of the orbital spacecraft initial magnetic field also calculated as solution of nonlinear minimax optimization problem. Both solutions of this nonlinear minimax optimization problems calculated based on particle swarm nonlinear optimization algorithms. Results. Results of prediction spacecraft far magnetic field magnitude based on orbital spacecraft multiple magnetic dipole models using near field measurements and compensation of the initial magnetic field with consideration of orbital spacecraft magnetic characteristics uncertainty for ensuring the orbital spacecraft magnetic cleanliness. Originality. The method for control by orbital spacecraft magnetic cleanliness based on multiple magnetic dipole models using compensation of the initial magnetic field with consideration of magnetic characteristics uncertainty is developed. Practical value. An important practical problem of ensuring orbital spacecraft magnetic cleanliness based on orbital spacecraft multiple magnetic dipole models using near field measurements and compensation of the initial magnetic field with consideration of orbital spacecraft magnetic characteristics uncertainty solved.

Investigations of the variable magnetic moment automatic compensation efficiency improving possibility of three-phase electrical equipment currents

An analysis and review of known parametric systems for automatic compensation of electrical equipment the external magnetic field was carried out. It was found that the known parametric electrical equipment automatic compensation systems of the external magnetic field do not take into account the change in the order of alternating power phases when the level of the external magnetic field changes, which reduces the effectiveness of the three-phase electrical equipment magnetic field compensation by two to three times. The parametric system of three-phase electrical equipment sinusoidal currents magnetic moment automatic compensation with the phase alternation order sensor was improved, the distinguishing features of which are the preliminary determination of the phases alternation order in the power circuit of three-phase electrical equipment and the formation electromagnets compensators currents taking into account this order, which allows to increase the efficiency of three-phase electrical equipment currents magnetic moment compensation and use such a system in a three-phase distribution device containing a plurality of three-phase feeders. The system parameters bench adjustment method of the sinusoidal currents magnetic moment automatic compensation of three-phase electrical equipment with the phase alternation order sensor has been improved, which differs from known methods in that the phases order in the power circuit is determined in advance and the currents of the electromagnets compensators are formed taking into account this order and only then the power is supplied in turn, in each independent circuit of the electrical equipment power circuit an electromagnet compensator oriented along the selected axis is simultaneously turned on, the component of the total magnetic moment along the same axis is measured, and depending on its value, the magnitude and phase of the compensation currents signals are adjusted, then the sequence of alternating phases is changed and the rest of the operations are repeated. It is recommended to improve the non-sinusoidal currents magnetic moment system automatic compensation of three-phase electrical equipment with the phases alternating order sensor to ensure high efficiency of the magnetic moment compensation and the external magnetic field regardless of the power supply phases alternating order of three-phase electrical equipment.

A Fast Determination Method for Transverse Relaxation Rate of Minimized SERF Atomic Magnetometer

The sensitivity and bandwidth as the primary criteria of spin-exchange relaxation-free (SERF) atomic magnetometer (AM) are closely related to the transverse relaxation rate of atomic ensemble. In this study, we show an effective method for transverse relaxation rate measurement drawing on golden section algorithm. With no requirement of offline fitting, the measuring time of this method is only 7s. This is especially advantageous for reducing measurement errors due to the drifts of spatial magnetic field and light intensity and employing multiple measurements to better monitor the performance of magnetometers. Moreover, the reset after measuring is optimized as the sensitive axis magnetic field correction, ensuring the integrity of measurement while improving the accuracy of magnetic compensation. Furthermore, we find that the acquired experimental data by using this method can be adopted for the evaluation of magnetic field compensation performance and the monitoring of magnetic anomaly states. This determination method for transverse relaxation rate is anticipated to play a greater important role in multi-channel SERF AMs arrays.

Characteristic analysis and compensation of eddy current interference field of rotating projectile

The accurate measurement of the attitude of the ballistic correction projectile is the precondition for accurate correction. In order to solve the measurement accuracy problem of the strapdown-connected projectile magnetic sensor, the eddy current magnetic field is considered on the basis of the traditional error compensation model. A simplified mathematical model of the eddy current magnetic field of the pure rolling projectile was established, and the influence of the eddy current magnetic field interference on the magnetic measurement at different rotational speeds was simulated and analyzed. Aiming at the necessity of eddy current magnetic field compensation, a parameter estimation method of the non-independent attitude comprehensive compensation model based on Kalman filter algorithm is proposed. The normalized evaluation of the magnetic correction effect shows that the error of the parameter estimation result does not exceed 0.01%, and the magnetic measurement error after compensation converges to 0.19nT. The compensation effect is obvious and meets the laboratory magnetic measurement compensation requirements.

Speedy in-situ magnetic field compensation algorithm for multiple-channel single-beam SERF atomic magnetometers

The currently employed algorithms for the magnetic field compensation of single-beam spin-exchange relaxation-free atomic magnetometers are excessively slow and unstable, which limits the use and commercialization of magnetometer arrays for biological magnetic measurement. This study proposes an improved trisection algorithm (ITSA) to compensate for the magnetic field around the vapor cell in an attempt to resolve these limitations. Through the constant monitoring of the intensity of light emitted from a laser, the proposed algorithm reduces the time required to compensate for magnetic fields to 0.85 s in a single magnetometer, which is nine times faster than the traditional algorithm, and to 26 s in 36-channel magnetoencephalography equipment, which is 15.5 times faster than the traditional algorithm. In addition, an approximately 16% increase in measuring sensitivities is achieved based on the ITSA compared with the traditional algorithm. These improvements can promote the usage efficiency and commercialization of biological magnetic measurement instruments. Furthermore, the ITSA is verified using an experimental setup and the mathematical analysis and comparable experimental results demonstrate the effectiveness of the proposed algorithm.

A Marine Magnetometer Based on TMR

TMR (tunneling magnetoresistance) has the characteristics of high sensitivity, large linear range, low power consumption, and easy miniaturization, and has received great attention in the field of miniaturized and high-performance magnetic sensors. Widely used in marine magnetic field detection, earthquake monitoring, industrial control, and other fields. In this paper, A TMR marine magnetometer with AC modulation and magnetic field feedback compensation is proposed, designed, and manufactured, which can be used for the measurement of weak marine magnetic fields. After testing, its measurement range is ±100,000nT, the noise fluctuation level is 0.27nT, and nonlinearity level reaches 0.07%. It works by means of ac modulation and real-time compensation of feedback magnetic field, which greatly reduces magnetic hysteresis and increases the linearity. Compared with the nonlinearity of TMR material (more than 20% within ±1Oe, more than 7% within ±0.3Oe), it has been significantly improved.

Nested Magnetic Field Compensation With Regulated Coefficients for Bio-Magnetic Field Measurement

For a spin-exchange relaxation free (SERF) optically pumped magnetometer (OPM) that obtains its best performance in a zero magnetic field, an operation environment with approximately zero magnetic field is desired. This article proposes a nested magnetic field compensation system for a magnetic shielding room (MSR) to suppress the magnetic field. Two sets of coils, one set located outside of the MSR and the other one placed inside of the MSR, are combined in the system. The magnetic fields outside of the MSR are measured by tunneling magnetoresistance (TMR) sensors, while the fields inside the MSR are monitored by SERF OPMs. The two kinds of sensors complement each other in terms of measurement range and sensitivity. A nested two-stage proportional-integral (PI) closed-loop control strategy is employed to compensate for the magnetic field inside the MSR. The control parameters are regulated by the magnitude of the magnetic field to take advantage of the two kinds of sensors. The effect of the proposed system is experimentally tested. The three-axis field fluctuations are reduced by 97.52%, 98%, and 98.64% by the proposed method, respectively. The proposed method is compared with a conventional two-stage series PI control system. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> -axis magnetic field fluctuations of the conventional PI control system and the proposed system are 75.81 and 11.71 pT, respectively. The magnetic fluctuation of the proposed system is about 15.5% of the fluctuation of the conventional PI system. To validate the feasibility of the proposed magnetic field compensation system for ultra-weak bio-magnetic field measurement, magnetocardiography (MCG) and magnetoencephalography (MEG) signals are measured.

Simultaneous in-situ compensation method of residual magnetic fields for the dual-beam SERF atomic magnetometer

Near-zero magnetic field condition is essential to keep the spin-exchange relaxation-free (SERF) regime for the atomic magnetometer. We analyzed the output response variations of the dual-beam SERF magnetometer under different DC residual magnetic fields. Considering the problem that the gradient coil may introduce an additional DC magnetic field when compensating the gradient field, we propose a novel method of simultaneous in-situ compensation of gradient and DC residual magnetic field with high precision. The sensitivity and effectiveness of the compensation method for residual magnetic fields under 1 nT were verified by simulation and experiment. The precision of the gradient residual magnetic field compensation is better than 2 pT/mm. We built a dual-beam SERF atomic magnetometer platform to validate the proposed method. The magnetic field measurement sensitivity is 7 fT/Hz1/2 after residual magnetic fields compensation by the method mentioned in this paper, which is 4 times higher than the sensitivity of 36 fT/Hz1/2 without residual magnetic fields compensation.

High-sensitivity pump–probe atomic magnetometer based on single fiber-coupled

In this paper, we demonstrate an all-optical spin-exchange relaxation-free atomic magnetometer based on optical-fiber coupling, which simultaneously transmits orthogonally coupled pump and probe beam to an alkali vapor cell through a single polarization-maintaining fiber. The extinction ratios of the two pump–probe beams propagating along the fast- and slow-axis of the polarization-maintaining fiber were measured experimentally. To achieve the best sensitivity of the magnetometer, we theoretically analyze and experimentally optimize the triaxial magnetic compensation and optical parameters. Based on this scheme, it is proved that the compensation of the background magnetic field and the acquisition of three-axis magnetic field information can be achieved using only a pair of pump–probe beams. By optimizing the bias magnetic field Bx, Bz and optical parameters, we achieved bandwidths of 85 Hz, 42 Hz, and 48 Hz and magnetometer sensitivities of 18 fT/Hz1/2, 12 fT/Hz1/2, and 26 fT/Hz1/2 in the x-, y-, and z-axis, respectively. The proposed miniaturized configuration will be beneficial to developing magnetocardiography and magnetoencephalography instrumentation based on atomic magnetometers.