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Mining Contract: Through-the-Earth Communication Antenna Feasibility Demonstration

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Contract #200-2014-58688
Start Date9/1/2014
End Date8/31/2015
Research Concept

New antenna configurations are needed to improve performance and utility of through-the-earth (TTE) communications systems once deployed in underground coal mines. One concept is a small form factor antenna housed in an explosion-proof enclosure. Such an antenna would allow the underground transmission power to exceed the intrinsic safety limits of an open loop antenna. This new design is anticipated to maintain or improve the performance of an existing communication system while affording portability and increased potential to survive an emergency event.

Topic Area

Contract Status & Impact

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The most capable magnetic TTE fully wireless two-way voice and data radio systems offer communication ranges in excess of 1,000 feet. These systems employ large loop antennas to provide the necessary magnetic field strength (moment) while limiting energy at the coil terminals to intrinsically safe levels so that the communication systems may continue to operate even if contaminants in the mine atmosphere approach or exceed explosive levels. The strength of the magnetic moment is a function of area enclosed by a length of wire and the current that flows through it. Unfortunately, the resulting loop antenna length (on the order of hundreds of feet) makes these antennas cumbersome to deploy and vulnerable to damage under both routine and emergency underground conditions.

Raytheon UTD was contracted to leverage prior research and existing technology to conduct a feasibility demonstration of a compact Very Low Frequency (VLF) transmitting antenna. The goal of this research project was to design and build a novel, compact VLF magnetic antenna deployed in a volume of less than 5 ft3 (approximately a cube 20 inches on a side) to support communications through overburden to ranges in excess of 1,000 feet. The design was based on the Hitachi FINEMET® nanocrystalline alloy toroidal cores. The unique combination of low loss and high saturation flux density of this material allows higher performance levels than previously possible with conventional ferromagnetic materials. Since the VLF signal has very low loss when penetrating a metal enclosure, it could be housed in an MSHA-approved explosion-proof enclosure. Therefore the power would not be limited to the intrinsically safe levels of conventional systems.

Testing was conducted with an 80-core antenna in open air and inside a simulated explosion-proof enclosure at an underground mine. The enclosure was built out of mild steel plates of 0.25” thickness and approximately 18” X 16” X 2”. The testing showed that an enclosure greater than 30 ft3 (20” X 20” X 10’) may be required to achieve a TTE communication range of 1,000.