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.

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.

Magnetocardiogram (MCG) requires near-zero magnetic environment, which cannot be achieved by passive shielding structure, and needs to be combined with active compensation to reduce environmental magnetic field interference. However, the environmental magnetic field is multi-directional. In this study, a multiplex coil compensation system with a matrix-based expansion magnetic field model was constructed for near-zero magnetic field environments in MCG. First, a matrix-based expansion model was established to quantify magnetic field distribution that could be used as compensation. Second, by using the particle swarm optimization algorithm with adjustable weights, the best adjustive excitation vector of the proposed matrix was obtained, despite ill-posed problems, allowing the active compensation system to suppress residual magnetic fields. Simultaneously, the multiplex compensation system was employed to follow and reduce magnetic field fluctuations in the measurement signals. Finally, cardiac magnetic signals were measured and evaluated based on the effectiveness of creating a near-zero magnetic field environment and the improvement of the signal-to-noise ratio.

Direct current (DC) bias induced by the DC transmission and geomagnetically induced current is a critical factor in the abnormal operation of electrical equipment and is widely used in the field of power transmission and distribution system state evaluation. As the main affected component, the vector magnetization state of a transformer core under DC bias has rarely been studied, resulting in inaccurate transformer operation state estimations. In this paper, a dynamic vector hysteresis model that considers the impact of rotating and DC-biased fields is introduced into the numerical analysis to simulate the distribution of magnetic properties, iron loss and temperature of the transformer core model and a physical 110 kV single-phase autotransformer core. The maximum values of B, H and iron loss exist at the corners and T-joint of the core under rotating and DC-biased fields. The corresponding maximum value of the temperature increase is found in the main core limb area. The temperature rise of the 110 kV transformer core under various DC-biased conditions is measured and compared with the FEM (Finite Element Method) results of the proposed model and the model solely based on the magnetization curve B||H. The calculation error of the temperature rise obtained by the improved model is approximately 3.76–15.73% and is much less than the model solely based on magnetization curve B||H (approximately 50.71–66.92%).

The demand for spatial nonlinear magnetic fields (SNMF) spans diverse domains, encompassing medical applications like drug transportation and aerospace applications such as attitude control. Existing designs of magnetic field coils predominantly focus on uniform and gradient fields as the complexity of nonlinear magnetic field distribution often leads to intricate solution processes. This paper presents a novel approach to coil design, addressing the challenge of SNMF distribution by reconstructing the characteristic matrix within the traditional target field method (TFM). To solve the overdetermined equations involved, we incorporate an improved particle swarm optimization algorithm into the TFM framework. A pair of symmetrical and asymmetrical coils are designed and the effectiveness of this method is verified by comparing the simulated and experimental results.

A near-zero magnetic environment provided by magnetic shielding device (MSD) is essential for spin-exchange relaxation-free measurements and ultra-weak biomagnetic signal detection. Due to the high permeability, low coercivity, and low remanence, permalloy is widely used as the primary material in MSD. In practical applications, a demagnetization process is typically applied to permalloy to eliminate residual magnetization and restore its optimal magnetic performance, particularly before conducting sensitive measurements. However, it also exhibits four distinct magnetization conditions, which are characterized by significantly different hysteresis behaviors. These variations become particularly evident during the demagnetization process, where the magnetization state evolves continuously under a damped oscillating magnetic field. Traditional Jiles–Atherton (J–A) models mainly focus on single magnetization states and do not account for the variation of hysteresis characteristics across the full magnetization process. This paper proposes the reversible magnetization ratio increment (RMRI)-amplitude-responsive Jiles–Atherton (ARJA) algorithm, which integrates the RMRI criterion with an ARJA model. First, the RMRI criterion is proposed, which quantifies magnetization conditions and identifies states based on the reversible component ratio within a magnetization increment. With RMRI criterion, dynamic parameters are introduced into the J–A model to achieve a amplitude-responsive hysteresis model capable of sensing the current magnetization state and dynamically adjusting parameters accordingly. Next, a single-sheet tester system is developed to acquire full magnetization process data of permalloy, which is used to train and validate the RMRI-ARJA algorithm. Finally, the RMRI-ARJA algorithm is used to compute magnetic characteristics such as hysteresis loops, basic magnetization curves, remanence curves, and permeability curves across various magnetization conditions. Compared to the conventional hysteresis algorithm, the proposed approach significantly enhances calculation accuracy, particularly in modeling the hysteresis behavior of permalloy.