Integrated YBa2Cu3O7−x magnetometer for biomagnetic measurements

An integrated dc superconducting quantum interference device (SQUID) magnetometer has been fabricated using a YBa2Cu3O7−x–SrTiO3–YBa2Cu3O7−x multilayer process. The magnetometer consists of a 8.3 mm×8.6 mm pickup coil coupled inductively to a small washer‐type SQUID with 9 Ω bicrystal junctions via an integrated 101/2‐turn input coil. Using simple direct‐coupled read‐out electronics with additional positive feedback, a noise level of 9.7 fT/√Hz at 1 kHz and 53 fT/√Hz at 1 Hz was measured inside a magnetically shielded room. Due to the low noise level biomagnetic heart and brain signals with high quality and the very weak signals of the peripheral nerve system were recorded.