Active compensation of non-uniform residual static magnetic field in miniaturized magnetocardiography devices using coil array

The spin-exchange relaxation-free (SERF) atomic magnetometer, serving as the core sensor of a magnetocardiography (MCG) device, typically operates stably in an ultra-weak magnetic field environment below 10 nT. However, the miniaturization of the device makes it difficult for a single-ended magnetic shielding cylinder (SMSC) to achieve sufficient magnetic field attenuation within the sensor plane. To address this issue, a static magnetic field compensation method based on a coil array (CA) is proposed. First, a planar magnetic field mapping model is established to estimate the internal magnetic field from the external field on the plane. Then, considering the coupling effects of the SMSC, an analytical magnetic field model of the CA is constructed. Finally, the magnetic coupling among different coil units (CUs) is decoupled, and the optimal compensation currents are obtained through inverse computation. Both simulation and experimental results verify the effectiveness of the proposed compensation method. Experimental results show that, after active compensation, the three-axis static magnetic fields on the sensor plane are reduced from 23.64 nT, 1.73 nT, and 58.46 nT to 2.22 nT, 1.13 nT, and 4.21 nT, respectively. These results demonstrate that the proposed method can significantly reduce the residual static magnetic field on the sensor plane, which is of great significance for promoting the miniaturization of MCG devices.