High-T-c SQUID magnetometer with grain boundary junctions and its application in non-destructive evaluation

Vile have fabricated and tested high-ir, magnetometers based on DC supercon ducting quantum interference device (SQUID). The SQUID was made from YBa2Cu 3O7-delta thin film deposited on SrTiO3 bicrystal substrate. The noise spec trum was characterized at 77 K and showed that above 5 Hz, the magnetometer sensitivity is Limited by a white noise level of around 2 X 10(-5) Phi(0)/ Hz(1/2), which corresponds to a magnetic field sensitivity of 100 fT/Hz(1/2 ). Below 5 Hz, the noise is dominated by 1/f noise. The magnetometer was us ed for non-destructive evaluation (NDE) of conducting aluminum structures b y performing eddy current testing. By mapping out the field distribution wi th the SQUID magnetometer, flaws 10 mm below the surface can be clearly ide ntified. The system can operate in a magnetically unshielded laboratory env ironment. (C) 2000 Elsevier Science B.V. All rights reserved.