Wideband electromagnetic induction for metal-target identification: Theory, measurement, and signal processing

A principal problem with traditional, narrowband EMI sensors involves target identification. As a consequence, in minefield or unexploded ordinance (UXO) detection, for example, each piece of buried metal must be excavated, causing significant false alarms in regions littered with anthropic clutter. Therefore, the principal challenge for the next generation of EMI sensors is development of electronics and algorithms which afford discrimination. To this end, in this paper we operate in the frequency domain, considering wideband excitation and utilize the complex, frequency-dependent EMI target response as a signature. To test the signature variability of different metal types and target shapes, as well as for calibration of an actual sensor, we have developed a full-wave model for the analysis of wideband EMI interaction with highly (but not perfectly) conducting and permeable targets. In particular, we consider targets which can be characterized as a body of revolution, or BOR. The numerical algorithm is tested through use of a new wideband EMI sensor, called the GEM-3. It is demonstrated that the agreement between measurements and theory is quite good. Finally, we consider development of signal processing algorithms for the detection and identification of buried conducting and permeable targets, using wideband data. The algorithms are described and then tested on data measured using the GEM-3, with results presented in the form of contour plots as a function of the number of discrete frequencies employed. ©2003 Copyright SPIE - The International Society for Optical Engineering.