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Detecting unexploded ordnance with time domain electromagnetic induction Pasion, Leonard Rodriguez

Abstract

In this thesis I assume that the Time Domain Electromagnetic (TEM) response of a buried axisymmetric metallic object can be modelled as the sum of two dipoles centered at the midpoint of the body. The strength of the dipoles depends upon the relative orientation between the object and the source field, and also upon the shape and physical properties of the body. Upon termination of the source field, each dipole is assumed to decay as k (t + α)-β e-t/γ. The parameters k, α, β and γ depend upon the conductivity, permeability, size and shape of the object, and these can be extracted from field or laboratory measurements by using a nonlinear parametric inversion algorithm. An investigation carried out using an analytic solution for a sphere and laboratory measurements of steel and aluminum rectangular prisms, suggest the following methodology. The value of β might be used as a diagnostic to assess whether the metallic object is non-magnetic or magnetic. If the object is thought to be magnetic, then the ratios of k1/k2 and β1/β2 are diagnostic indicators as to whether the geometry is plate-like (uninteresting) or rod-like (a high candidate for being a UXO). [Scientific formulae used in this abstract could not be reproduced.]

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