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.

To achieve the nearly zero-field environment, demagnetization is an indispensable step for magnetic shields composed of high-permeability material, which adjusts the magnetization of the material to establish magnetic equilibrium with the environmental field and improve the shielding performance. The ideal demagnetization can make the high-permeability material on the anhysteretic magnetization curve to have a higher permeability than on the initial magnetization curve. However, inappropriate parameters of degaussing field cause the magnetization state to deviate from the anhysteretic magnetization curve. Therefore, this article proposes a new assessment criterion to analyze and evaluate the parameters of degaussing field based on the difference between the final magnetization state after demagnetization and theoretical anhysteretic state of the shielding material. By this way, the magnetization states after demagnetizations with different initial amplitude, frequency, period number and envelope attenuation function are calculated based on the dynamic Jiles–Atherton (J–A) model, and their magnetization curves under these demagnetization conditions are also measured and compared, respectively. The lower frequency, appropriate amplitude, sufficient period number and logarithmic envelope attenuation function can make the magnetization state after demagnetization closer to the ideal value, which is also consistent with the static magnetic-shielding performance of a booth-type magnetically shielded room (MSR) under different demagnetization condition.

Biomagnetic field measurements necessitate magnetic shields of high performance, particularly for quasi-static and low-frequency fields. These largely rely on the magnetic properties of the shielding material. Magnetic shaking can enhance the material's permeability by reducing hysteresis loss, though this method introduces field interference into the shielding device, complicating the magnetic environment. In this study, an attenuation coefficient is introduced into the Jiles–Atherton model to quantify the suppression effect of magnetic shaking on hysteresis loss, based on measurements of magnetic properties under the shaking fields. To improve shielding performance while minimizing additional interference, the frequency of magnetic shaking is increased and applied only to the outermost layer of the shielding device. Through testing and fitting results, the impact of various magnetic shaking conditions on a cubic magnetic shielding device is examined. By applying a shaking field of 200 Hz solely to the outermost layer, the shielding factor (@0.01 Hz) of a three-layer device increases by 77.4% without additional magnetic noise. This method is also applied to a magnetically shielded room, enhancing its shielding factors by more than two times.

Generally, a permalloy sheet is applied as the major shielding material for weakening the environmental magnetic field interference in a field of high-precision measurement. The demagnetization for a permalloy sheet determines its shielding performance; therefore, an enhanced method for measuring the magnetic properties under degaussing excitation is proposed in this article. The excitation apparatus and a feedback control system are designed for regulating the $B$ curve of a permalloy sheet as the desired amplitude and waveform. Furthermore, a method for applying degaussing excitation is proposed, and the corresponding measurement approach under such magnetic conditions is investigated. Finally, the dynamic Jiles–Atherton model is combined with a finite element method (FEM) algorithm for applying the tested data to the residual magnetic field calculation of a scaled-down model. The agreement between the calculated and tested remanence distribution indicates that the proposed measurement method is reliable and applicable.

The cylindrical magnetic shield (CMS) with the advantages of easy process, low cost, and portable mobility is widely utilized in magnetocardiography (MCG) for recording the weak biomagnetic field of cardiac. The one-side-open structure of CMS leads to excessive flux leakage and uneven-distributed magnetic field, which cause extra degradation of sensitivity and signal noise ratio of MCG test. Therefore, an enhanced magnetic suppression technique for reducing the asymmetric-distributed remanence and magnetic noise inside CMS is proposed in this article. This method introduces the Fourier series with half-angle component for asymmetric compensation field generation and combines the analytic method to model and weaken coupling effect impact. The feedback control is employed in the compensation system for static and dynamic magnetic interference containment. The asymmetric-distributed remanence ${B} _{y}$ and $B_{z}$ is suppressed near zero, and the magnetic noise of ${B} _{y}$ and Bz at 0.01 Hz is restrained from 59.3 to 0.06 ${pT/Hz}^{1/2}$ and 92.7–0.24 ${pT/Hz}^{1/2}$ with the inhibition rate of 29.95 and 25.87 dB, respectively. The MCG test with high signal-to-noise ratio is then realized inside the MCS with the asymmetric compensation system.