Output Signal Prediction of an Eddy-Current Probe When Scanning Arbitrary-Shape Surface Cracks in Metals

This article proposes an efficient modeling technique to predict the output signal of an eddy-current (EC) probe when scanning arbitrary-shape surface cracks in metals. The probe is excited by an arbitrary-shape wire carrying an ac current of arbitrary frequency with no restriction on the crack depth profile or magnetic permeability of the metal. In the proposed technique, the equivalence principle is adopted to replace the crack with the equivalent electric and magnetic current densities, and the governing volume integral equations (VIEs) are derived using appropriate Green's functions. The VIEs are solved by the method of moments (MoM) for the unknown electric and magnetic fields inside the crack. This is done by expanding the electric and magnetic fields in terms of basis functions compatible with the problem. To support the validity of the proposed modeling technique, we compare the predicted output signals of various EC probes with their experimental counterparts and those available in the literature.