Modeling and estimation of earth electrical conductivity from through-the-earth electromagnetic transmission data from 94 mines.
Yan-L; Waynert-J; Sunderman-C
30th Annual Review of Progress in Applied Computational Electromagnetics, March 23-27, 2014, Jacksonville, Florida. Monterey, CA; Applied Computational Electromagnetics Society, 2014 Mar; :489-494
The electrical conductivity of earth overburden is a critical parameter in the design and application of through-the-earth (TTE) wireless communication systems. TTE systems have been called the only true wireless communication system for underground coal mines and may be the communication system most likely to survive an underground disaster. The overburden conductivity is a major factor controlling the maximum depth to which these systems can operate. In this paper, we investigate several modeling approaches to determining the attenuation in the magnetic field strength from loop antenna-based TTE systems. We compare the model predictions to data taken from 94 mine sites distributed over the U.S. by the Bureau of Mines in the 1980s. Previous investigators have shown that the apparent conductivity is somewhat dependent on mine depth. However, a Bureau of Mines study that sampled the mine data for only 27 out of 94 sites did not quite predict the magnitude of decrease in apparent conductivity with frequency. In this paper, the TTE data from all 94 mines are analyzed to determine the apparent conductivity of the overburden based on three different electromagnetic (EM) models: half-space homogenous model, thin sheet model, and the attenuation factor or Q-factor model. The Q-factor model is particularly simple because it requires only two parameters: the estimated earth conductivity .... and the conductivity thickness product .... of the conducting thin sheet. Results from the various models are compared and discussed. The Q-factor model is shown to predict the dependency of conductivity on both depth and frequency by carefully choosing the properties of the thin sheet. The agreement between the model and measurement results leads to a better understanding of the behavior and limitations of TTE radio signal propagation.
Mining-industry; Underground-mining; Radio-waves; Electromagnetic-wave-transmission; Coal-mining;
Author Keywords: through-the-earth; conductivity; coal mine; overburden; wireless; VLF/ULF
Lincan Yan, The National Institute for Occupational Safety and Health (NIOSH), Pittsburgh, PA, 626 Cochrans Mill Road, Pittsburgh, PA, USA
30th Annual Review of Progress in Applied Computational Electromagnetics, March 23-27, 2014, Jacksonville, Florida