NIOSH-sponsored research in through-the-earth communications for mines-a status report-

This paper presents the results of recent NIOSH-sponsored contractual research aimed at demonstrating the feasibility of through-the-earth wireless communications in mining. Through-the-earth systems, developed by five different contractors, are discussed with a focus on technical approach, prototype hardware, and field test results. System features include both magnetic and electric field sensing, loop and line antennas, digital and analog processing, noise filtering and cancellation, and direction finding. The systems were demonstrated at commercial mine sites. The results of these tests are characterized by transmission range and power levels. The paper concludes with a discussion of issues that remain to be resolved as through-the-earth communications are implemented. These include text vs. voice format, acceptable time delays, portability, ease of deployment, interface with existing communications systems, permissibility, and the effect of geological variations.