Suppression of the gradient disturbance and hybrid control of magnetic field with the frequency separation method for weak biomagnetic signal measurement

Measurement of weak biomagnetic signals holds great significance for in-depth understanding of physiological activities and disease states, but the detection of weak biomagnetic field signal requires a high uniformity and low noise magnetic field environment. Gradient induced by ferromagnetic boundary effect and magnetic field disturbance in magnetic shielding room are the key factors that limit the residual magnetic field uniformity and control accuracy, thereby ultimately reducing the measurement accuracy. Typically, gradient suppression and residual magnetic field compensation have strong coupling effects. To address the above issues, uniform and gradient bi-planar coils in different directions are first designed to generate the corresponding magnetic field in the target region, respectively. Then a hybrid control method is proposed, which incorporates the frequency separation method and the designed coils to address both gradient distribution suppression and residual magnetic field reduction in the magnetically shielded room. We describe the theory in detail and verify its feasibility through experiments. The proposed method can provide new ideas for improving the accuracy in the weak biomagnetic signal measurement.