High T-c SQUID sensor system for non-destructive evaluation

Magnetic field mapping measurements were performed using commercial high-T- c superconducting quantum interference device (SQUID) sensors. The sensors are incorporated in a fully computerized scanning system and were found to be operative only when encased inside a double-layer mu-metal shield. This allowed us to measure signals of the order of 0.5 nT. In all cases, the fie ld map obtained was consistent with the theoretically expected images, In m easurements with two samples, the relative orientation and center-to-center separation of the samples could be easily deduced from the field map. Surf ace flaw detection of unglazed ceramic tiles under an externally applied ma gnetic field is also discussed. (C) 2000 Elsevier Science S.A. All rights r eserved.