Theory of the transmission of electromagnetic waves down a mine hoist


  • James R. Wait,

  • David A. Hill


Using an idealized coaxial model, we consider the transmission, in the frequency range from 20 to 1000 kHz, down a mine hoist shaft from a symmetric source at the surface. The shaft is circular in cross section and the metal hoist cable is represented by a concentric conductor. To facilitate the analysis, the source is idealized as a voltage-excited annular slot in a circular ground plane that is located in the air-earth interface. The earth itself is taken to be a homogeneous conducting half space. Using a modal type analysis, the total power supplied to the annular slot is calculated as the sum of the power delivered to the lower half space, the power dissipated at the air-earth interface and the power radiated into the atmosphere. Using these results, the relative power transmitted down the shaft to a specified depth is estimated. The resulting transmission efficiency is found to be almost completely dependent on the attenuation characteristics of the dominant TEM mode in the shaft.