Analysis of the natural modes of the 3-D eddy current problem based on the finite integration technique

Low-frequency, broadband electromagnetic induction (EMI) sensors have been shown to be highly effective at detecting and classifying buried conducting targets. Even the simplest inductive sensors are capable of easily detecting the presence of buried metal. It is difficult, however, for most inductive sensors to discriminate between targets of interest, and the ubiquitous metallic clutter that might be buried alongside it. One attractive solution to this discrimination problem is to invert the broadband frequency data collected by the EMI sensor, finding a pole-expansion representation of the scattering transfer function known as its discrete spectrum of relaxation frequencies (DSRF). A target´s low-frequency scattering behavior can then be compactly described by a set of relaxation frequencies that are the poles of the transfer function and their coefficients that are the corresponding amplitudes. Discrimination can be achieved by comparing the inverted data to a dictionary that contains the theoretical DSRFs of targets of interest. In this paper, a computational method will be presented for modeling the DSRF of arbitrarily-shaped three-dimensional conducting targets.