Asymmetric Cylindrical Coils Design for Uniform Magnetic Field

With the deepening research in atomic sensors, extremely weak magnetic detection has shown great advantages in the biomedical field. To achieve high detection sensitivity, the uniform field coil is used in the magnetic detection system to maintain a uniform and stable working environment for the atomic sensors. This article presents a design method for an asymmetric cylindrical uniform field coil based on the boundary element method (BEM) and optimized by the particle swarm optimization (PSO) algorithm. The BEM could find optimal coil paths on arbitrary geometries, which is fit for the asymmetric configuration in an optically pumped magnetometer-based magnetocardiogram (OPM-MCG) device. However, the BEM used in the coil design would cause an ill-posed mathematical problem. A Tikhonov regularization combined with a penalty function approach is proposed to solve the ill-posed problem and smooth the coil winding patterns, and the correction weights are optimized by PSO within constraints. The calculation results show that the absolute maximum relative error in the target region is optimized to 0.0124% by the proposed method when compared with the target field method (TFM) coil (0.023%). Meanwhile, it illustrates that the high uniformity region is enlarged through the utilization of asymmetric structure. In addition, through experiments, the test performance of the designed coil is verified to be consistent with the theory. As the proposed method contributes a high-performance uniform field coil on arbitrary structures, it has important significance in extremely weak magnetic field measuring devices such as the MCG and magnetoencephalogram (MEG).