“…From a purely modelling perspective, the computationally most efficient way of exciting a waveguide is through a slot in an external wall from a waveguide feed. Although this is not practical in large scale mining or geological operations the model is not unreasonable, see Sangster et al (2011), since a suitably aligned slot provides strong magnetic coupling into the seam. In practice the slot, plus the feed waveguide, would be replaced by a current loop embedded in the coal.…”