Non Destructive Testing using the SQUID with Integrated Gradiometer

We have used the integrated SQUID gradiometer in an unshielded environment to make eddy current nondestructive testing measurement on a multi-layer aluminum structure. The sensor consists of a niobium dc superconducting quantum interference device (SQUID) and a first-order gradiometer pick up coil on the same substrate. As a demonstration of their capabilities, subsurface defects in a multilayer aluminum structure have been located and mapped using eddy current with no magnetic shielding around the specimen or cryostat