Development of SQUID-based system for nondestructive evaluation

This article describes the development of a superconducting quantum interference device (SQUID)-based system for nondestructive evaluation. The setup incorporates an in-house developed thin-film-based Nb SQUID with readout flux locked loop electronics and consists of a liquid helium cryostat with adjustable stand-off distance, a precision XY - theta scanner for studying both flat and cylindrical samples, and a data acquisition system. The system has been used for the detection of artificially engineered subsurface defects in aluminum plates and to track magnetic-to-nonmagnetic phase transformation in stainless steel [grade 316L(N)] weldment specimens subjected to low cycle fatigue deformation.