Magnetic compensation coils are often used to improve the effectiveness of a magnetically shielded room (MSR), but a distortion of the field is caused by the shielding layer consisting of high-permeability material, which leads to a reduction in compensation capacity. To solve this problem, a new method is presented in this article based on a target-field method, an image method, and particle swarm optimization. By this way, a magnetic compensation system composed of biplanar coils is designed and fabricated to compensate the background field for a wearable magnetoencephalography device inside the MSR, and the coupling effect between the magnetic shielding material and the compensation field is effectively avoided. Experimental data show that these compensation coils produce uniform fields and field gradients with the inhomogeneity of less than 3.8%, consistent with the simulation results. In addition, this system realizes a real-time compensation to the residual field and field gradient in the MSR.

Magnetic field shields are important for electronic equipment, ultrahigh-sensitivity sensors, and electrical instruments. For ultrahigh-sensitivity atomic sensors, in particular, ferrite shields with low intrinsic magnetic noise are widely used. In this article, the calculation methods of longitudinal and transverse magnetic noise, which are calculated by loss, are analyzed. The experimental results confirm the feasibility of the model. Using the loss separation method, it is proved that the loss of ferrite magnetic shielding is mainly hysteresis loss, which is below 100 Hz. To effectively reduce the magnetic noise, we analyze the effect of structure parameters on the longitudinal and transverse magnetic noise, and the optimized parameters are obtained. The results show that the longitudinal magnetic noise decreases with the increasing aspect ratio and stabilize eventually. When the aspect ratio exceeds 1, the transverse magnetic noise remains practically unchanged. When the external diameter is fixed, by optimizing the thickness of the magnetic shield, the optimal solution for the longitudinal and transverse magnetic noise is obtained.

In order to improve the performance of surface permanent magnet synchronous motor (PMSM) drives, a novel sensorless drive scheme is proposed in this paper, which is based on the virtual third-harmonic back-EMF incorporating a fraction-N phase-locked loop (FN-PLL) and a synchronous frequency-extract filter (SFF). A simple low-pass filter based circuit is used to obtain the commutation points through the virtual third-harmonic back-EMF. After that, an FN-PLL is applied to catch continuous rotor position angles. On this basis, the SFF-based compensation is proposed to compensate the detecting error adaptively. Meanwhile, the field vector control loop for surface PM motor is proposed, which is based on the proposed rotor position detection link and compensation link. An experimental high-speed magnetically suspended blower platform is built. The effectiveness and the feasibility of the proposed method are validated with experimental results.

Functional imaging equipment based on miniaturized atomic magnetometers with array arrangement exhibits promising prospects in biomagnetic scenarios. However, crosstalk from the modulated magnetic field between adjacent sensors degrades the imaging accuracy. To address this issue, this study proposes an all-optical dual-axis zero-field atomic magnetometer using light-shift modulation. We utilize an acousto-optic modulator to modulate a detuned circularly polarized beam for pumping the atomic spin ensembles. This beam allows for the optical modulation of spin polarization and meanwhile generates a light-shift modulation, effectively replacing the conventional magnetic field modulation. By using a probe beam to detect the optical rotation angle perpendicular to the direction of the pump beam, we construct an all-optical configuration of a longitudinally modulated atomic magnetometer, enabling dual-axis magnetic field measurements. Experimental results demonstrate dual-axis sensitivities of 29 and $15\mathrm{fT}/{\mathrm{Hz}}^{1/2}$, respectively. This method eliminates the need for conventional coil-based magnetic field modulation, thereby paving the way for potential applications in magnetocardiography and magnetoencephalography.

Atomic magnetometers operated in spin-exchange relaxation-free (SERF) have the potential to replace superconducting quantum interference devices (SQUIDs) in the field of biomagnetism. Here, we demonstrate the dual-axis closed-loop control of a single-beam SERF magnetometer that allows sensing of two orthogonal magnetic fields simultaneously and independently with suppressed crosstalk effect, achieved by applying a rotating modulation field and using the negative feedback. Operating in the dual-axis closed-loop mode with a miniature 4 $\times $ 4 $\times $ 4 mm ⁸⁷ Rb cell, we achieve the magnetic field sensitivity of 20 fT/Hz ^1/2 and a bandwidth of 1.8 kHz. In addition to the experimental study of the sensitivity and bandwidth, we perform a theoretical analysis of the dual-axis response and develop an effective decoupling method. The implementation of closed-loop control enables the magnetometer to be robust against the disturbance of the ambient field, which could enlarge the dynamic range, enhance the systematic stability, and suppress the crosstalk effect. Such a simple, yet high-performance SERF magnetometer could be suitable as a promising candidate in the field of biomagnetism, allowing for a denser sensor array and opening up new possibilities for noninvasive biomagnetic imaging.

The uniform field and field gradient coils can be utilized for nulling the background field inside a magnetic shielding room (MSR), but the desired field produced by the coils is inevitably distorted due to the coupling effect of the magnetic shielding material. To overcome this problem, an improved method is proposed based on the image method and target field method (TFM). Directed by this method, a series of biplanar coils (BCs) are designed to produce the uniform fields and field gradients for an active compensation in an MSR. Then, their finite element models and practical experiment are established to verify the effectiveness. Compared with the conventional TFM, the proposed method shows significant effects for both uniform field coils and field gradient coils. Uniformities of the B _x and B _z increase by 79.9% and 72.5%, and the dB _x / dz and dB _z / dz improve by 89.6% and 63.2%, respectively. It demonstrates that this method is adopted to design the BCs fixed in MSR and holds great promise for the active compensation of environmental magnetic field in the measurement of magnetoencephalogram (MEG).