EDDY-CURRENT NONDESTRUCTIVE MEASUREMENTS WITH DIFFERENT HTS-SQUID SPATIAL ORIENTATIONS

Superconducting QUantum Interference Devices (SQUIDs) are extremely se nsitive detectors for the measurement of magnetic flux. III particular the high critical temperature SQUIDs, which can be operated at liquid nitrogen temperature with easy cryogenic requirement, are well suited for nondestructive evaluation (NDE) of cracks and corrosion which res ult from the machining process or aging of electrically conductive str uctures. The main characteristics of SQUIDs as eddy-current NDE sensor s are: high sensitivity even in unshielded environments, a large frequ ency range of operation which allows the detection of surface and subs urface flaws and high spatial resolution. We performed magnetic field measurements on the eddy-current double-D inducing coil, used in many NDE experimental systems, and on 200x100x4 mm(3) Al plates with a 6mm surface-breaking hole using high critical temperature SQUIDs in unshie lded environments. The sensitivity to the anomalous magnetic field rel ated to the defect along the three spatial directions is discussed in terms of unperturbed magnetic field distributions due to the eddy-curr ent source.