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Distortion of amplitude and phase of alternating electromagnetic fields by presence of electrical conductors Mungall, Allan George

Abstract

This thesis discusses both qualitative and quantitative characteristics of the horizontal electromagnetic field produced by the flow of eddy currents in a conductor. The exciting field is supplied by a large horizontal loop carrying an alternating current, and the secondary horizontal field is measured by detecting the voltage induced in a small vertical search coil in the plane of the loop. Determinations of both the ratio of the horizontal field to the vertical, and the phase angle between them are made at various points along a diameter directly above the centre line of each conductor. Corrections to eliminate extraneous voltages induced in all parts of the measuring apparatus are applied to these measurements. The corrected values are then plotted as profiles of relative amplitude and phase for several positions of each conductor. The shapes of these curves and possible mathematical expressions relating them to the physical dimensions and position of the conductor are discussed, and some approximations of the configuration of surface current flow are suggested. The present results are compared with those obtained by previous experimenters and certain changes of fundamental concepts are suggested. Possible application of these results to qualitative interpretation of measurements taken over actual ore-bodies, and methods of accurate determination of size and depth of the bodies are proposed.

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