Design of low-noise coil for magnetocardiography based on differential magnetic coupling strength

A low-noise, near-zero magnetic field environment is essential for the accurate detection of cardiac magnetic signals. In active magnetic field compensation systems, large coil constant causes excessive noise. This study proposes a low-noise compensation coil design based on differential magnetic coupling. In the proposed configuration, the high degree of magnetic field homogeneity of nested saddle coils was combined with the low coil constant characteristic of differential saddle coils. Coupling effects with high-permeability shielding were incorporated by modeling the coil constant as a function of coil–shield distance. A hybrid particle swarm–genetic algorithm and differential magnetic coupling strength was employed to optimize the design. Compared with a conventional saddle coil, the proposed design reduces the coil constant by two orders of magnitude to 84.9 nT/A and improves field uniformity by 41.7%, and reduces magnetic noise (1–30 Hz) by 44.1%.