Mining Contract: Magnetic Communication System (MCS)

Contract Status & Impact

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

The contract was awarded on August 25, 2009, and a kickoff conference call was held on September 21, 2009. Lockheed Martin had previously developed a wireless, through-the-earth (TTE) prototype communication system under contract 200-2007-22843 ("TE Communication & Trapped Miner Beacon System"), based upon magnetic field generation and sensing. The enhanced system, developed under this new contract, consists of surface and underground transceivers. The receiving antennas are comprised of three ferrite core windings arranged orthogonally and housed in a portable case. Various sized single- and multiple-turn air core antennas are used for transmission from underground to surface, including a single loop of wire that can be deployed around a coal pillar. Voice and text messages are possible at signal transmission frequencies of 3200 and 330 Hz, respectively. Reception of either channel is automatic regardless of the transmission frequency selected. The surface and underground receivers have noise cancellation capability. The durability and reliability of the original prototype system were improved by making the hardware resistant to humidity, mechanical shock, dust, and water. The power usage of the amplifier was reduced to increase battery life while maintaining transmission range, and features were incorporated to enhance usability. A beacon mode was developed. A collision avoidance protocol minimizes message collisions when multiple transceivers are active, for example, having the underground transceiver trying to broadcast when the surface transceiver is also trying to broadcast. A radio relay capability allows interoperability with conventional hand-held radios. The voice message is stored and then transmitted at low frequency through the earth. Another TTE unit receives and stores the message, after which it is replayed.

The system was tested at the NIOSH Pittsburgh facility and at several coal mines in southwestern Pennsylvania, northern West Virginia, and Virginia. Prototype evaluations demonstrated ranges of 472.5 m for text, from the underground mine to the surface. In these tests, the surface transceiver was directly above the underground unit with the underground transmitting antenna operated at relatively low power comparable to intrinsic safety restrictions.

With the prototype operating at higher power levels, Lockheed demonstrated ranges, from the mine to the surface, of 305 m for voice and 594 m for low-rate text. Tests have also been conducted between two distant points, both within the mine. The maximum range achieved for the through-the-mine testing was 1,494 m for text, and 640 m for voice. Greater ranges are anticipated for the beacon mode signal. A surface direction finder was also demonstrated to estimate the origin of the underground beacon signal. The angular direction of the beacon signal was measured at multiple locations on the surface and, through triangulation, the approximate location of the transmitter antenna underground could be determined.