MAGNETO-CARDIOGRAM MEASUREMENT USING A HIGH-T-C SQUID MAGNETOMETER

We made Superconducting Quantum Interference Devices (SQUIDs) coupled with large pickup loops (directly coupled SQUIDs) by using single-laye r YBCO thin films on SrTiO3 bicrystal substrates. The I-V characterist ics of the SQUIDs showed Resistively Shunted Junction type (RSJ-type) behavior, and the measured IcRn values were in the 100 similar to 300 mu V range. The rms field resolution of a directly coupled SQUID measu red in liquid nitrogen was 0.9 pT/Hz at 1 Hz and 0.1 pT/Hz at 1 kHz. U sing this directly coupled SQUID, we have developed a SQUID magnetomet er system operating in liquid nitrogen, and we used that system in a m agnetically shielded environment to measure biomagnetic signals from h uman heart.