High T-c SQUIDs and eddy-current NDE: a comprehensive investigation from real data to modelling

The interest in magnetometry for eddy-current non-destructive testing, e.g. of planar conductive structures encountered in the aircraft industry, usin g high-temperature superconducting quantum interference devices (SQUIDs) is primarily due to their high sensitivity to magnetic flux even at very low frequencies. Here it is shown how theoretical, numerical and measurement ma chineries are combined to get reasonable synthetic and experimental data an d to reach a good understanding of the interaction of diffusive wavefields with a damaged non-magnetic metal plate las a first step towards the retrie val of pertinent features of the defects). The measurement modalities are c onsidered first. It is illustrated in some detail how laboratory-controlled experiments are performed by a SQUID-based probe displaced above artificia lly damaged plates. Experimental data are then confronted with simulation r esults in order to evaluate the accuracy and reliability of this measuremen t system. Simulations are carried out by a computationally fast vector volu me integral method dedicated to a planar layering affected by a volumetric defect, which involves the construction of the dyadic Green system of the l ayering.