Simple magnetic charge model for representation of emi responses from a buried UXO

Abstract

Low frequency electromagnetic induction (EMI) sensing, operating from ten's of Hertz up to several hundred's of kHz, has been identified as one of most promising technologies for detection and discrimination of subsurface metallic objects, particularly unexploded ordnance (UXO's). In EMI sensing, which is a pure EM diffusion rather than wave phenomena, displacement currents within an object and its surrounding medium are negligible. Therefore the scattered field outside the object can be represented as a sum of quasi-static magnetic fields radiated by magnetic charges placed on a fictitious surface. This paper presents a simple surface magnetic charge model for fast and accurate representation of EMI signal for any metallic scatterer of interest. The magnetic charges and Green's function associated with them are much simpler than magnetic dipoles and their dyadic Green's functions. The simplicity and computational accuracy of the magnetic charge model makes it an alternative candidate to the simple dipole model for buried metallic object discrimination in EMI frequency range. In addition, for a given object the amplitudes of the magnetic charges are unique and they can be used to discriminate an object of interest from innocuous items. The amplitudes of the responding magnetic charges are determined from measured data. Several numerical results are presented to demonstrate the accuracy and superior computational speed of the proposed method. I. Introduction