A. Cochran et al., 1ST-GENERATION SQUID-BASED NONDESTRUCTIVE TESTING SYSTEM, IEE proceedings. A, Science, measurement and technology, 140(2), 1993, pp. 113-120
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
.