Dynamic field nulling method for magnetically shielded room based on Smith predictor assisted GADRC

Magnetically shielded room (MSR) creates a zero-field environment for magnetoencephalography (MEG) research. Given the high cost of high-permeability materials and the low shielding factor at low frequencies, compensation coils combined with closed-loop control system are necessary for further dynamic shielding. To enhance the capacity of dynamic shielding, this paper proposes a dynamic field nulling method based on Smith predictor assisted generalized active disturbance rejection control (GADRC). Each component of the dynamic nulling system is analyzed and a high accuracy closed-loop system model is established. Additionally, the time-delay of the optically pumped magnetometer (OPM) is addressed by the Smith predictor, and the controller is designed within the GADRC framework. The equivalent models are constructed to analyze system performance from frequency domain perspective. Experimental results demonstrate that the proposed method can reduce the peak-to-peak value of magnetic fluctuation from 130.4 pT to 0.98 pT after filtering out power frequency interference.