Scanning DC-SQUID system with high spatial resolution for NDE

We have developed a scanning DC-SQUID system with a high spatial resolution for NDE. The SQUID system is composed of a concentric multi-loop DC-SQUID gradiometer using Nb/AlOx/Nb Josephson junction, anon-magnetic scanning stage, a cryostat and a computer for gathering data and controlling the system. We have developed the concentric multi-loop gradiometer (d(2)Bz/dr(2), r(2)=x(2)+y(2)) to have a higher spatial resolution and reduce background noise. The gradiometer was integrated on a single 3 x 3 mm(2) Si chip. To reduce the standoff distance between the specimen and the pick-up coil, a cryostat with a thin bottom space was developed. A scanning stage was made of nonmagnetic materials and was driven by air pressure using a rod-less cylinder to avoid making magnetic noise.