# Mining Contract: Through-The-Earth Wireless Real-Time Two-Way Voice Communications

Keywords:CommunicationsNoise cancellationPersonnel trackingThrough-the-earth communications systemsUndergroundWireless node communications systems

| Contract #                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 200-2008-25720 |
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| 8/1/2008                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| 8/31/2010                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| The goal of this project is to design, build, and demonstrate a battery-powered, through-the-earth wireless voice communication system for overburdens of up to 600 feet. Work to extend the range to 1,200 feet will also be specified. The design will be intrinsically safe for use in a methane environment. Besides voice communication, it will feature:
- text messaging  - Text messaging transmission requires less energy than voice. When battery power is low, switching from voice to text can conserve energy.
- beacon transmission  - A key will be provided which, when pressed, will transmit a tone. This will provide a beacon to help locate trapped miners.
- instrument data output transmission  - Terminals will be provided to transmit, in binary code, data from instruments such as oxygen, carbon monoxide, or methane gas monitors, or temperature monitors.

The technical approach will use magnetic coupling between transceivers underground and on the surface. The mining environment is electromagnetically very noisy both inside and outside the mine. Electromagnetic noise originates from both man-made machinery and natural atmospheric disturbances. To meet Mine Safety and Health Administration regulations for intrinsically safe equipment, transmitter power is greatly restricted. Consequently, advanced filtering and noise cancellation will be employed to extract the signal from noise. |
| - Emergency Communications and Tracking                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |

## Contract Status & Impact

This contract is complete. To receive a copy of the final report, send a request to mining@cdc.gov.

A prototype, through-the-earth communication system was constructed and tested in the laboratory. The system worked as expected without the presence of external electrical noise. It was also tested at a stone mine through 200 feet of overburden. However, when simulated noise was introduced, reception by the surface transceiver was adversely affected. The design was revised to incorporate appropriate noise filtering and cancellation techniques to make the system usable for field tests.

The through-the-earth unit was then tested at the NIOSH Experimental Coal Mine in Pittsburgh on November 5, 2009. The system delivered two-way, real-time voice, through-the-earth communication when the transmitting antennas and receiving antennas were directly in-line vertically (approximately 100 feet), as well as when the surface transceiver was moved about 300 feet off the vertical axis. In a follow-up demonstration on April 16, 2010, real-time, two-way voice and text communications were successfully established between a point outside the portal of the Experimental Mine and a point inside the mine, approximately 1,000 feet away.

In-mine tests of the prototype communication system were conducted at a mine in southwestern PA on August 10, 2010. The cover was approximately 580 feet. Two-way communications were established via beacon, text, and real-time voice at relatively low power levels (antenna currents were approximately 1.5 amps). Electrical noise sources were nearby both underground and on the surface. The transceiver on the surface was in proximity to the elevator and power lines approximately 100 feet away. The underground transceiver was located near the trolley line. Voice reception on the surface was judged to be of excellent quality; underground voice reception was marginal and was attributed to a design deficiency in the underground receiver.

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          - Advanced Tutorial on Wireless Communication and Electronic Tracking: Appendix B
          - Advanced Tutorial on Wireless Communication and Electronic Tracking: Communication System Performance
          - Communication Systems Research At Bruceton Safety Research Mine
          - Medium Frequency Radio System Modifications for Refuge Chamber Situational Awareness
          - Mine Communications and Tracking Glossary
          - Mine Communications Engineering and Compatibility Guidelines
          - Propagation of EM Signals in Underground Mines
          - Technology News 544 - New Measurement Tool to Validate Wireless Communications and Tracking Radio Signal Coverage in Mines
          - Through-the-Earth Communication Systems for Underground Coal Mines: Product Final Development and Standardized Interface Definition
          - Wireless Through-The-Earth Modeling and Support

July 18, 2016

September 17, 2012

National Institute for Occupational Safety and HealthMining Program

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