A YBa/sub 2/Cu/sub 3/O/sub 7/ thin film SQUID gradiometer for measurements in unshielded space

Low-noise RF superconducting quantum interference device (SQUID) washers fabricated from YBa/sub 2/Cu/sub 3/O/sub 7/ epitaxial thin films have been used to construct a first-order electronic gradiometer operating at 77 K and suitable for biomagnetic measurements. Mechanical adjustment of one SQUID's plane in a gradiometric setup, which consisted of two SQUIDs separated by a vertical 6-cm base, made it possible to attenuate signals due to far DC magnetic field sources by three orders of magnitude. A magnetic field resolution of 280 fT/ square root Hz above 2 Hz was attained through the use of large thin-film and bulk flux focusers. The fine structure of human-heart magnetocardiograms could be recorded in unshielded space. In a shielded room, magnetoencephalograms were obtained. The system was used to obtain new data on the acoustically evoked cortical response.<
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