Eddy-current and current-channeling response to spheroidal anomalies

Abstract

We derive the electromagnetic induction (EMI) response to conducting anomalies of spheroidal shape embedded in a weakly conducting host medium. As one application, prolate and oblate spheroids are convenient shapes for modeling buried unexploded ordnance, landmines, and naval mines. Under the assumptions of a perfectly conducting or nonconducting target and the assumption of a uniformly incident field, simple analytical solutions are obtained. Both the eddy-current and the current channeling responses are derived for prolate and oblate spheroids. For example, in a marine environment the current-channeling contribution can be quite large. As expected, these responses differ depending on the direction of the incident field relative to the spheroidal symmetry axis. The problem is solved separately for axial and transverse incidence, with the general case being a superposition of the two. These solutions could be used for fitting a spheroidal model to EMI data in which a small number of parameters, such as the location, size, shape, and orientation of the object, are to be determined.