HTS-dcSQUID gradiometer for nondestructive evaluation

We have fabricated a HTS-dcSQUID gradiometer on the basis of a single YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// film for a hand held NDE system. The two loops of the gradiometer are coupled directly to a SQUID arranged at the center of the pickup coil. The gradiometer worked at 77 K and at normal laboratory environment without magnetic shielding. The effect of the small area of the SQUID loop on the performance of the gradiometer was experimentally estimated. The performance of the SQUID gradiometer was investigated by measuring holes in a carbon fiber reinforced plastic plate in a magnetically shielded room.