Electromagnetic propagation along a wire in a tunnel-approximate analysis

The propagation of electromagnetic waves along an axial wire in an underground tunnel is analyzed from a perturbation theory point of view. The formulation is compared with that of J. R. Wait in which he solves an exact mode equation approximately, and a modified tunnel wall admittance is thus identified. Attenuation computed on the basis of the approximate formulation is compared with exact results of Wait and Hill.