High-T/sub c/ DC-SQUID system for nondestructive evaluation

We developed different types of thin film high temperature superconductor (high-T/sub c/) DC-SQUID magnetometers and gradiometers for application in a nondestructive testing system. We used these sensors in a liquid nitrogen dewar mounted above a computer controlled x-y table within a compact /spl mu/-metal shielded chamber. The planar galvanically coupled gradiometers based on step-edge or bicrystal Josephson junctions were investigated in shielded and unshielded environment. We discuss the influence of junction type and SQUID parameters depending on the device geometry on the sensitivity of our complete testing system. Our interest is focused in particular on the noise properties and magnetic field resolution at 77 K. Measurements of ac and dc current distributions will be shown as well as measurements of magnetic moments of different samples.