A multimodal approach to the analysis of the attenuation properties of MF communication systems in mine tunnels

Abstract

Low-attenuation medium-frequency communications are still utilized in mine tunnels as useful backup systems. Previous research on the topic has addressed the evaluation and measurement of the wave propagation parameters of these communication structures considering the presence of a single conductor inside the tunnel. In this work, the presence of multiple conductors is considered and a multimodal approach is developed to determine the expected attenuation as a function of the distance and frequency. The examples provided in the paper concern a three-conductor structure, consisting of one power cable and two rail tracks, where three basic modes propagate. Simulation results show that the expected attenuation depends on the set of initial currents injected into the conductors and that, in the case of randomly injected currents, the expected attenuation constant decreases with distance, tending to the attenuation constant of the least attenuated mode.

Keywords:

• medium frequencies
• modal analysis
• multiconductor transmission-line systems
• tunnel communications
• wave propagation parameters

Acknowledgements

The Fundação para a Ciência e a Tecnologia (Project PEst-OE/EEI/LA0008/2013), and the Instituto de Telecomunicações (Project PC226), sponsored this work.