Magnetic Field-based Eddy-Current Probe Design, Modeling and Computing Methods for Edge Defect Detection

This paper presents the methods to design and model an eddy-current (EC) probe composed of one or more electromagnets and a magnetic flux density (MFD) sensor for detecting defects near the edge of a conductive workpiece. Both cavity and crack defects are considered, the former characterized by a conductivity field and the latter modeled as two overlapping boundaries, and their perturbed effects on the EC-generated MFD field are analyzed using a distributed current source (DCS) computing method. Two approaches, defect-free subdomain formulation and dimension-reduction for analyzing defect-perturbation, are presented to shorten the time to compute the DCS solutions to the defect-detection problem. The accuracy and computational efficiency of these proposed approaches have been numerically evaluated, which demonstrate significantly improved performance with greatly reduced computation when compared with finite-element analysis (FEA) and can further shorten the time to compute the matrix inversion. The effectiveness of the magnetic field-based method has been experimentally verified with two prototype EC probes designed to overcome limitations associated with impedance-based EC probes commonly designed using a lumped-parameter approach.