Due to the potential of SQUID (superconducting quantum interference device) to detect small defects in material and structure and changes in magnetic properties caused by degradation of materials, the use of SQUIDs for non-destructive evaluation (NDE) using SQUID has attracted interest. Recently several SQUID systems for NDE have been developed including high Tc SQUID systems. Some preliminary experiments were carried out using these systems to explore the ability of SQUID for NDE. In this paper, the sensitivity and spatial resolution of a SQUID system are described in association with the liftoff distance and the size and configuration of the pick-up coil. SQUID systems and scanning SQUID microscopes are reviewed. Some preliminary experimental results are presented.
