Suppression of the Ferromagnetic Boundary Coupling and Precision Control of Magnetic Field with the Self-Shielding Method

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.