Research on the Design of Nonuniform Field Coils With Ferromagnetic Coupling in Magnetically Shielded Cylinder for Magnetocardiogram

To reduce the influence of remanence and interference on magnetocardiogram (MCG) measurements, an approach to designing nonuniform field coils (NUFCs) considering ferromagnetic coupling effects is proposed. First, a magnetic field analytical model considering the coupling effects between the magnetically shielded cylinder (MSC) and coils is established based on the distribution of the magnetic vector potential combined with the image method (IM). Subsequently, using the target field method (TFM), the NUFCs are designed inversely according to the distribution of remanence and interference, by which the problem that existing uniform field coils (UFCs) are difficult to compensate for nonuniform magnetic fields is solved. Furthermore, to improve the performance of the NUFCs, the adaptive inertia weight particle swarm optimization (PSO) method is introduced for optimizing the regularization parameters. Finally, finite-element simulations and experiments are carried out to verify the proposed method. The results from the experiments demonstrate that the remanence within the measurement area is reduced from 60 to below 10 nT by designed NUFCs, while magnetic field interference is effectively suppressed from 37 to 11 pT. These results prove the effectiveness of the designed NUFCs in enhancing the magnetic field performance of MCG devices.