Traveling DC-SQUID gradiometry for nondestructive evaluation

We are reporting on the development of a self-propelled-type superconducting quantum interference device (SQUID) magnetic imaging system for nondestructive evaluation (NDE). We recently completed a novel SQUID instrument that can continuously travel back and forth by itself over the surface of sample during testing without using a magnetic shielding. Technically self-propelling is useful for enlarging an available scanning area of SQUID-NDE without limitation. The capability of the new SQUID instrument is strikingly demonstrated by the detection of weak ferromagnetism due to plastic deformation using type-304 austenitic stainless steels. The instrument is also useful in the evaluation of internal cracks artificially embedded in austenitic weld.