Two-Stage Compensation System Based on Decoupled Biplanar Coils for Near-Zero Magnetic Field Environments

To achieve the near-zero magnetic field environment necessary for magnetoencephalography (MEG) measurements, a two-stage magnetic compensation (TMC) system for background magnetic field compensation in a magnetic shielding room is proposed in this article. The TMC system utilizes decoupled biplanar coils (DBCs) to create two types of regions in magnetically shielded room (MSR): uniform region (UNIR) and decoupled region (DECR). In the first stage, the Helmholtz coil is arranged outside the MSR and a fluxgate for the measurement is placed in the decoupled region where the current in the DBC coil does not generate a magnetic field. Compensation in this stage can decrease residual magnetic field and guarantee optically pumped magnetometer (OPM) function within the spin-exchange relaxation-free (SERF) regime. In the second stage, DBCs inside the MSR use OPMs for closed-loop feedback, generating spatially uniform magnetic fields. The TMC system effectively reduces residual and peak magnetic fields within the MSR, providing a suitable background magnetic field for MEG measurements.