1ST-GENERATION SQUID-BASED NONDESTRUCTIVE TESTING SYSTEM

The paper is an overview of the results of an investigation of a first -generation SQUID NDT system working on the principle of the detection of magnetic inhomogeneities. The system incorporates a superconductin g field generation coil - to apply a static magnetic field perpendicul ar to the test subject - and a differential two-coil planar pick-up co il connected to a SQUID, acting as the detector. These components are operated in a LHe cryostat in a normal (unscreened) laboratory environ ment. Test subjects are inspected by passing them beneath the cryostat during computer-controlled data acquisition. Typical experimental res ults are presented, and postprocessing techniques are outlined. Theore tical descriptions of the static field distortion technique have also been developed, based on the numerical solution of integral equations which model flaws as combinations of magnetic dipoles. The equations a re presented, and results are compared with those obtained experimenta lly. Despite significant limitations it is concluded that potential ap plications for SQUID NDT exist and further investigation is worthwhile .