Ferromagnetic boundary coupling is one key factor that limits the control accuracy of the residual magnetic field in the magnetic shielding room. Usually the image method is utilized to suppress the coupling, but the tolerance for door slit and holes of the image method is poor. Here, we propose the self-shielding method for suppressing the ferromagnetic boundary coupling with higher coupling suppression ability and better tolerance for door slit and holes. Two sets of biplane coils for one axis are designed for achieving uniform magnetic field in the target area and nearzero magnetic field in the shielding area near the passive metal shielding layer simultaneously. We have determined the analysis method and design process of the self-shielding method, and verified its feasibility by experimental test. The proposed method can provide new ideas for improving the control accuracy of the residual magnetic field in the magnetic shielding room, ensuring the smooth progress of magnetoencephalography measurement.

This study proposes a hybrid method for improving the magnetic shielding performance of a magnetic shielding room (MSR) with few permalloy layers. In this method, two types of compensating coils are combined, one placed outside the MSR and the other placed inside. The coupling effect between the outside coil and the permalloy layer is used to adjust the residual field distribution characteristics of the MSR, and the inside coil is used to compensate for the adjusted residual field. This method has been verified with an MSR with two permalloy layers and an inner space of 1.3 × 1.3 × 2.2 m. According to the result, the residual field was reduced to less than 2.5 nT in a cube with a 0.4-m side length, which is seven times lower than that without compensation, and the inner space utilization rate was also improved by two times compared with existing MSRs with a comparable space size. The proposed method is of great significance in the development of magnetic shielding technology.

The biplane coils (BCs) based on the inverse-design method are crucial for creating the near-zero magnetic environment in magnetic shielding room (MSR), but multi-parameters optimization remains a key factor that limits the performance of the BCs. This study proposes a funnel algorithm (FA) to solve the issue of multi-parameter optimization in the design. The upper and lower limits of the parameters are dynamically adjusted based on the previous calculating step. By gradually reducing the upper and lower limits, we achieve the BCs with optimal performance. This method has been verified by both the theoretical analysis and experimental test. Compared with other methods, the designed coils show a higher space utilization ratio (SUR) and smaller relative errors, with the SUR improved from 1.6% to 3.75% and the relative errors all less than 2%. Based on the designed BCs, the total residual magnetic field is stabilized below 40.4 pT at the central point of the MSR, with the noise reaching the intrinsic noise of the flux-gate magnetometer in the frequency range of interest. The proposed method can significantly improve the performance of the BCs, thus reducing the space and construct cost of the MSR and promoting the magnetoencephalogram (MEG) measurement based on the quantum technology.

Active magnetic compensation technology can effectively reduce magnetic field disturbances within a magnetic shielding room (MSR) and improve the signal-to-noise ratio of magnetoencephalography (MEG) measurement. But, for small-sized MSRs with external compensation coils, achieving high-precision magnetic field control is challenging, because it is difficult to establish an accurate mathematical model. In this article, an active magnetic compensation system is constructed based on model-free adaptive control with a radial basis function neural network (MFAC-RBFNN) method, which addresses the limitations of magnetic field control accuracy caused by the requirement for precise system model information. The nonlinear and coupling characteristics of the active magnetic compensation system were analyzed, and a model-free adaptive control (MFAC) controller is designed based on the input current and output magnetic field, and the utilization of radial basis function neural network (RBFNN) for estimating magnetic field disturbances. The experimental results are given to prove that the algorithm proposed can achieve high-precision control of magnetic field within the MSR without an accurate system model, and compared with proportional–integral–derivative (PID), the magnetic field disturbance reduction effect is improved by $2.4\times $ . It contributes to generating a near-zero magnetic field environment with low magnetic field disturbance.

The Magnetoencephalography (MEG) based on atomic magnetometer has high demand for the uniformity in the measurement area. Due to the door and holes of the magnetically shielding room (MSR), the distribution of residual magnetic field is non-linear, introducing much trouble into the magnetic field compensation. This study proposes a method for improving the uniformity of the residual magnetic field in the compact MSR by injecting different currents into the two coils in each pair of the outside compensation coils. The model and theoretical analysis method have been established, the feasibility has been verified both by the simulation and the experimental test. Results show that the maximum of the three components of the residual magnetic field in the direction of the three axes can be reduced by 18 times, 10.6 times and 8.1 times, respectively, when compared with the results without compensation, and 2.4 times, 2.3 times and 2.2 times, respectively, when compared with the results compensated with the same current. This study can provide certain help for achieving ultra-weak magnetic environment with high uniformity for the MEG measurement Note to Practitioners —In this article, we focus on the problem of compensating the residual magnetic field in the compact MSR with high efficiency and low cost, which remains the key factor that limits the promotion of the MEG. Method based on the compensation coils in series outside the MSR only deals with the linear or symmetric components, but has nothing to do with the non-linear and asymmetric one caused by the door. We propose a new method for compensating the residual magnetic field based on the coupling between the active and passive shielding, high compensation efficiency and uniformity can be achieved. In future work, we will aim at applying this method to create an ultra-weak magnetic field environment with high uniformity for the MEG measurement.