Four‐channel YBa2Cu3O7−y dc SQUID magnetometer for biomagnetic measurements

A four‐channel YBa2Cu3O7−y thin film dc SQUID magnetometer was fabricated. Biomagnetic measurements were performed by using the four‐channel system at 77 K in a magnetically shielded room. We have successfully measured four‐channel magnetocardiac signals clearly in real‐time mode. The best magnetic field resolution of the four SQUIDs was 370 fT/Hz1/2 at 10 Hz and 200 fT/Hz1/2 in the white noise region.