Improved surface method for computing eddy-current modes

Broadband electromagnetic induction sensors are effective at detecting and classifying buried metal, such as landmines, by using an incident magnetic field to induce eddy currents in buried metal and measuring the secondary magnetic field they produce. A target's magnetic polarizability is a frequency dependent tensor that expresses the relationship between the incident magnetic field and the scattered field created by the eddy currents. Viewed as a singularity expansion, the magnetic polarizability can be decomposed into contributions from a set of eddy-current modes which relax at different frequencies. This decomposition provides a unique signature for targets of interest, allowing them to be effectively distinguished from clutter. In this paper, an improved, stream function -based numerical approach will be presented that can accurately compute the eddy-current modes that flow in thin conducting shells and their contribution to the singularity expansion of the magnetic polarizability.