Improving the shielding effectiveness of large magnetically shielded rooms via calibrated finite-element modeling and compensation current optimization

In large magnetically shielded rooms (MSRs), material hysteresis and environmental magnetic field variations can cause discrepancies between finite-element simulation results and actual conditions. Discrepancies between sample-level material properties and the magnetic response of the assembled MSR reduce the reliability of compensation-current optimization and limit further shielding improvement. To address these discrepancies, this study proposes a calibration-driven finite-element simulation framework for a large cylindrical-cap MSR with a 4 m radius, 1.33 m cylindrical-section height, 4.22 m total height, and eight optimized compensation-current variables. The Jiles–Atherton (JA) parameters were calibrated from coil-excited magnetic-field responses of the assembled MSR to better capture its device-level magnetic behavior. This calibration reduced the root mean square error of the predicted magnetic field response by 84.46 %. Next, an equivalent background magnetic field was reconstructed from external fluxgate array measurements and applied as the simulation model's boundary condition. Using this calibrated model, compensation currents were optimized to reduce the residual magnetic field and improve field uniformity inside the MSR. The optimized compensation currents achieved a post-compensation average residual magnetic field of 12.53 nT, corresponding to an absolute reduction of 9.50 nT from the pre-optimization value of 22.03 nT and a relative reduction of 43.12 %. Additionally, 81.78 % of the evaluated area exhibited a residual magnetic field within 7.5–17.5 nT, indicating improved field uniformity. The proposed workflow integrates JA parameter calibration and background magnetic field reconstruction, providing a consistent measurement basis for compensation current optimization in large hybrid passive–active magnetic shielding systems.