Imaging of small defects in nonmagnetic tubing using a SQUID magnetometer

SQUIDs for nondestructive evaluation

“…With this arrangement it was shown that the magnetic field due to the edges of the sample plate are essentially cancelled and the interfering signal due to the current cables is remarkably reduced. The cancellation principle was also studied [39] for transverse and longitudinal currents flowing in tubes and rods and later applied [40] to such samples. One of the key elements in the research at Vanderbilt has been the development of theoretical modelling in parallel with experimental work.…”

“…The effectiveness of SQUID susceptometry was further demonstrated in a novel NDE technique called surface decoration susceptometry. In this technique, the surface of a nonmagnetic sample is decorated with a ferromagnetic [40,101] or a superparamagnetic [102] tracer, and a high-resolution magnetometer or susceptometer is used to image the remanent magnetization or susceptibility distribution respectively of the decorated sample. An analysis of the resulting image is then utilized for detection of very fine surface-breaking cracks.…”

“…In other experiments, they utilized the FEM to compute the current distributions in a superconducting and normal state YBa 2 Cu 3 O 7−x , thin film [154]. To investigate the current distribution in flawed conducting tubes, Wikswo's group adopted lead field analysis [101] for inverting the measured magnetic field data. In this experiment, current flowed axially along a 12.1 mm metal tube with a 4 mm diameter hole in the wall of the tube.…”

“…The perception is that small items are cheaper to replace than inspect so they are of little interest. In fact some critical components are small and SQUID work aimed at nuclear reactor fuel rods [40] and microchips [75,77] has been performed. Inexpensive small items may also be a possibility provided they can be scanned very quickly.…”