Yan Lu

Cuboid magnetically shielded rooms (MSRs) are widely used in ultra-low magnetic field measurement systems. However, their unequal side lengths cause magnetic-flux shunting and eddy-current attenuation to vary with the direction of the external magnetic field, making dynamic shielding effectiveness (SE) difficult to evaluate accurately using conventional analytical models developed for symmetric shielding geometries. Finite element simulations can provide detailed numerical solutions but are computationally expensive for repeated design analysis. To address this limitation, this paper proposes a geometry-constrained analytical method for dynamic SE evaluation of anisotropic cuboid MSRs. The method separately formulates high-permeability magnetic shielding and high-conductivity eddy-current shielding, and integrates them through a hierarchical coupling framework for multilayer structures. For high-permeability layers, an anisotropic magnetic-circuit model is combined with a geometry-dependent eddy-current correction. For high-conductivity layers, a three-dimensional eddy-current attenuation model is established by explicitly incorporating cuboid geometric parameters into the dynamic formulation. The proposed method is validated by finite element simulations and experiments on three representative cuboid MSRs over 0.01–100 Hz. The maximum relative error is 4.47% against simulations and 8.47% against measurements, while the computation time is reduced by approximately two orders of magnitude compared with finite element simulations. The method provides an efficient analytical tool for rapid SE prediction and engineering design of cuboid magnetic shielding systems.

Rectangular magnetically shielded rooms (MSRs) are favored for their construction simplicity and efficient space usage. However, current rectangular MSRs lack an effective shielding factor (SF) theoretical system due to their inherent asymmetric geometry and process defects such as door gap. Therefore, an effective three-dimensional (3D) magnetic circuit method for calculating the SF of rectangular MSRs is proposed in this paper. Firstly, the theoretical model for the 3D magnetic circuit of rectangular MSRs is established, and the SF in three directions is derived. Secondly, the theoretical model is modified by introducing demagnetization factors to further improve the calculation accuracy of the SF based on the magnetization theory. Finally, formula systems for the SF considering door gap are derived, and their effect is also analyzed. To validate the proposed method, two rectangular MSRs with distinct structures are tested using a constructed experimental platform. The results show that the discrepancy between the calculated SF and the tested SF is less than 7%, affirming the efficacy of the proposed methodology. This method can be applied to rectangular MSRs of different sizes, and provide a valuable theoretical guidance for the construction of MSRs.

Investigating the state of cells in zero magnetic or near-zero magnetic environments is an important scientific issue. However, standard cell culture incubators can only provide general conditions such as constant temperature, constant humidity, sterility, and carbon dioxide, and cannot provide zero magnetic or near-zero magnetic environments for cell culture. To address this issue, an optimization method was proposed in this paper based on the combination of the particle swarm optimization algorithm (PSO) and the finite element method (FEM), achieving the optimization design of a magnetic shielding box (MSB) with a small volume, high shielding factor, and low residual field. Firstly, the high-permeability layer and high-conductivity layer were optimized respectively using the PSO and FEM. Then, the effectiveness of this method was analyzed through experiments. The experimental results show that the shielding factors in three directions at the center point of the optimized MSB are 786.8 (east-west), 2182.7 (north-south), and 1389.4 (vertical) respectively at 0.01 Hz. Meanwhile, the maximum residual field in the cubic region with a side length of 10 cm inside the MSB is 11.9 nT. Finally, the MSB designed by this method was placed in a standard cell culture incubator to cultivate cells in a zero-magnetic or near-zero magnetic environment. Then the Cell Counting Kit-8 (CCK8) experiments to evaluate the cytotoxicity of chemotherapy drugs on tumor cells in a weak magnetic environment (WMF). The results show that the lethality of paclitaxel (PTX) to Epidermal carcinoma cell (A431) increases by 25.96 times and the lethality of gemcitabine (GE) to Lung carcinoma cell (NCI-H460) increases by 24.23 times in a WMF. At the same time, the maximum proliferation inhibition rate of 5-fluorouracil (5-FU) on NCI-H460 cells in a WMF environment increased by 15.69%. That is, WMF could significantly improve the therapeutic effect of chemotherapy drugs on tumor cells.

Magnetic shielded cylinder (MSC) is crucial in various applications, especially in the realm of medical weak magnetic signal measurement. However, designing a small volume, low noise MSC is a multi-objective optimization problem, with the objectives conflict with each other. To address the complexity arising from numerous variables in the optimal design of MSC with a small volume and low-noise, this paper proposes an optimal design method based on non-dominated sorting genetic algorithm II (NSGA-II) to realize the optimal design of MSC with a high shielding factor, small volume and low-noise. Firstly, an analytical model for the shielding factor of the MSC is established, and a multi-objective optimization model is given. Then, the NSGA-II algorithm is employed to obtain a series of Pareto frontier optimal solutions. Finally, the efficacy of this method is evaluated through simulation and experimentation. The results reveal that the radial and axial shielding factors of the optimized MSC achieve maximum values of 8.6 × 10⁷ and 9.5 × 10⁶ respectively. Meanwhile, the average axial noise and radial noise of the MSC between 1 and 100 Hz are 22 fT/Hz^1/2 and 20 fT/Hz^1/2 respectively. Practice has proven that this method can be used to optimize the design of small-volume, low-noise magnetic shields to improve the performance of magnetic shields.

The permeability of permalloy at ultra-low-frequency magnetic field is a crucial and fundamental parameter for analyzing the low frequency shielding factor of magnetically shielded rooms. However, due to limitations in the accuracy of the existing magnetic flux signal measuring system, the permeability at ultra-low-frequency magnetic field is challenging to precisely determine. Therefore, a high-precision voltammetry method for measuring the permeability of permalloy at ultra-low-frequency magnetic field is proposed in this paper. First, the theory of the voltammetry method and the required level of induced voltage accuracy are derived and thoroughly analyzed. Then, the voltage acquisition module with ultra-low noise is designed by using four parallel instrumentation amplifiers, and the magnitude of the noise is quantified by establishing the noise analysis model for the voltage acquisition module. Finally, the system for measuring the permeability at ultra-low-frequency magnetic field is set up, and its feasibility is verified by comparing the measurement results of permeability at 10 Hz with the commercial soft magnetic instrument. The results show that the system is capable of measuring the permeability of permalloy at 0.01 Hz to 1 Hz, with repeatability error of less than 3%. The method can also be applied to measure the permeability of other soft magnetic materials.