A multi-channel high- SQUID system and its application

A multi-channel high temperature superconducting interference device (high Tc SQUID) system has been developed. Step edge junctions were employed as weakly coupled Josephson junctions for the SQUID. The magnetic field resolution was 70 to 250fT/Hz1/2 at 1kHz. The SQUID was mounted on a special chip carrier and was sealed with epoxy resin for protection from humidity. We have developed a 32-channel high Tc SQUID system. We used it to measure magnetic signals of the human heart in a magnetically shielded box. We obtained clear multi-channel magnetocardiac signals, which showed clear so called Q, R, S and T wave peaks. Its clear isofield contour map was also obtained. We could observe activities of a stomach using a tiny steel ball as a tracer. These data indicated that the high Tc SQUID is feasible for these biomagnetic applications.