Mining Contract: Magnetic Communication System
This contract will (1) enhance key features of the through-the-earth prototype previously developed under contract 200-2007-22843 ("TE Communication & Trapped Miner Beacon System"), to improve its usability, (2) investigate design changes to comply with mine safety standards, (3) ruggedize the hardware, and (4) demonstrate performance at coal mine sites. The prototype durability and reliability will be improved by making the hardware resistant to humidity, mechanical shock, dust, and water. The power usage of the amplifier will be reduced to increase battery life while maintaining transmission range. MSHA and IEC standards will be examined to determine what changes are need to ensure safety in potentially hazardous mine atmospheres. Usability will be enhanced by adding several key features. A beacon mode will be developed to assist rescuers to detect the presence of a transmitter at long ranges where data and voice transmissions are not possible. A collision avoidance protocol will minimize message collisions when multiple transceivers are active. A radio relay capability will allow interoperability with conventional hand-held radios. A remote activation mode will be investigated to activate units from a remote location. Automatic frequency selection will be studied to negotiate carrier frequency and data rate to automatically establish a communication link. The improved prototypes will be demonstrated at several mine sites of varying depth and overlying strata. Research results will be documented in a final report.
Contract Status & Impact
This contract is completed. To receive a copy of the final report, send a request to OMSHR@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.