Analytical Bases for Electromagnetic Sensing of Coal Properties

A number of theoretical problems have been studied that are relevant to the electromagnetic probing of the environment in coal mines. Particular emphasis was given to methods of determining the roof structures in underground workings. Essentially the idea is that the structure is illuminated by a source of primary field and the secondary response is detected. This secondary field is then related to the roof structure. The following approaches were employed: (i) low frequency induction wherein the induced eddy-currents give rise to a secondary measurable field, (ii) direct current excited by probes that interact with the inhomogeneous roof structure, (iii) microwave coupling to the roof by resonant loops, (iv) microwave reflection and scattering by horn antennas. The collected results presented here are intended to provide an analytical framework for further work in this area.