The optimized asymmetric self-shielded uniform magnetic field coils in extremely weak magnetic field detection

Magnetic shielding with coil system could establish a weak and stable background field for extremely weak magnetic detection. However, the coupling effect between the shielding layer and the coils could not be ignored. To solve this problem, a novel design method of asymmetric self-shielded uniform field coil applied in the magnetocardiogram device is proposed in this paper, which could attenuate the magnetic field outside while ensuring the uniform performance inside. Equivalent magnetization current (EMC) is introduced to find optimal coil paths on the asymmetric surface in the magnetocardiogram device. Combined with quantum particle swarm optimization (QPSO), the optimal parameters to smooth the coil current paths could be obtained with a promoted computation efficiency, which improves the coil performance. The coils calculation results show that after self-shielding the absolute maximum relative error of the target magnetic field in the shielding layer is optimized from 0.937% to 0.240%, and the reaction factor reflecting the coupling effect reduces from 1.356 to 1.003. Moreover, the designed performance of the self-shielded coil is verified through experiments, and the shielded environment is significantly improved by the designed coil. As the proposed self-shielded coil provides a high performance uniform field while solving the coupling problem, it has great significance in extremely weak magnetic field detection.