Baseline optimization of SQUID gradiometer for magnetocardiography

SQUID gradiometer techniques are widely used in noise cancellation for biomagnetic measurements. An appropriate gradiometer baseline is very important for the biomagnetic detection with high performance. By placing several magnetometers at different heights along the vertical direction, we could simultaneously obtain the synthetic gradiometers with different baselines. By using the traditional signal-to-noise ratio (SNR) as a performance index, we successfully obtain an optimal baseline for the magnetocardiography (MCG) measurement in a magnetically shielded room (MSR). Finally, we obtain an optimal baseline of 7 cm and use it for the practical MCG measurement in our MSR. The SNR about 38 dB is obtained in the recorded MCG signal.