HTS-dcSQUID gradiometer for nondestructive evaluation

We have fabricated a HTS-dcSQUID gradiometer on the basis of a single YBa2C u3O7-delta film for a hand-held NDE system. The two loops of the gradiomete r 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 witho ut magnetic shielding. The effect of the small area of the SQUID loop on th e performance of the gradiometer was experimentally estimated. The performa nce of the SQUID gradiometer was investigated by measuring holes in a carbo n fiber reinforced plastic plate in a magnetically shielded room.