Using a 77 K SQUID to measure magnetic fields for NDE

A bare HTS SQUID of commercial design was used in 77 K experiments concerning NDE. The SQUID was operated with flux-locked instrumentation to provide a noise floor of 80 pT//spl radic/Hz. The effective sensor area was measured to be approximately 70 /spl mu/m/sup 2/ equivalent to an ideal point detector for NDE. The SQUID was used unshielded in a normal laboratory environment in a special purpose LN/sub 2/ cryostat positioned above a motorized computer-controlled scanning system. We measured magnetic fields associated with current flowing in wires and compared them with calculations. We also detected a simulated flaw in an aluminum plate using an eddy current technique and made a preliminary depth assessment by frequency sweeping. Although developments in electronic gradiometers and gradiometric SQUID´s should make the use of single bare magnetometer SQUID´s unnecessary, we show that these already have sufficient sensitivity for NDE research, even without flux-focusing washers or pick-up coils.<>