SQUIDs and Inverse Problem Techniques in Nondestructive Evaluation of Metals

Superconducting Quantum Interference Devices coupled to gradiometers were used to detect aws in metals. We detected aws in aluminum samples carrying current, measuring elds at lift-o distances up to one order of magnitude larger than the size of the aw. Con gured as a susceptometer we detected surface-braking aws in steel samples, measuring the distortion on the applied magnetic eld. We also used spatial ltering techniques to enhance the visualization of the magnetic eld due to the aws. In order to assess its severity, we used the generalized inverse method and singular value decomposition to reconstruct small spherical inclusions in steel. In addition, nite elements and optimization techniques were used to image complex shaped aws.