UNSHIELDED USE OF THIN-FILM NB DC SUPERCONDUCTING QUANTUM INTERFERENCE DEVICES AND INTEGRATED ASYMMETRIC GRADIOMETERS FOR NONDESTRUCTIVE EVALUATION

Novel nondestructive evaluation measurements made using niobium de sup erconducting quantum interference devices with integrated asymmetric f irst-order gradiometers are described. Comparative theoretical and exp erimental studies of their spatial response have been described, and i t is shown that the gradiometric response makes operation possible in an unshielded and electromagnetically noisy environment. As a demonstr ation of their capabilities, subsurface defects in a multilayer alumin um structure have been located and mapped using induced eddy currents at 70 Hz, with no magnetic shielding around the specimen or cryostat. (C) 1997 American Institute of Physics.