Analysis of induction responses from metal objects using the method of auxiliary sources

The method of auxiliary sources (MAS) is developed for analyzing the low frequency response of conducting and permeable objects. The method uses elementary auxiliary magnetic dipoles/charges to produce the unknown fields. Sources are located on virtual surfaces that usually conform to, but do not coincide with the real surface of the object, where application of the boundary conditions determines the unknown source coefficients. The source fields automatically satisfy Maxwell´s equations and, using point collocation on the real surface, one avoids all singularities and all integrations. The accuracy in satisfying the boundary conditions can be evaluated explicitly using non-collocation points. Highly efficient results here show the low frequency response of spheroids and cylinders depending on object size and shape. The method is of use for the detection of unexploded ordinance