HIGH-T-C DC-SQUID SYSTEM FOR NONDESTRUCTIVE EVALUATION

We developed different types of thin film high temperature superconduc tor (high-T-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 mu-metal shielded chamber. The planar galvanically coupled gr adiometers based on step edge or bicrystal Josephson junctions were in vestigated in shielded and unshielded environment, We discuss the infl uence of junction type and SQUID parameters depending on the device ge ometry on the sensitivity of our complete testing system, Oar interest is focused in particular on the noise properties and magnetic field r esolution at 77 K. Measurements of ac and dc current distributions wil l be shown as well as measurements of magnetic moments of different sa mples.