Through-the Earth Wireless Communications
Radio Communications and Tracking System (RadCAT) is a two-way wireless radio system for use in both emergency and operational situations in underground mines. A complete RadCAT system provides two-way voice and text messaging communications among roving miners, mine rescue team members, and between a surface monitoring center and all underground personnel. It also provides tracking capability of roving, trapped, and barricaded miners in the event of a mine disaster. Stolar’s recent development work on the communication technology was partially funded by NIOSH and field tested at several hardrock and coal mining sites between August and October 2010. Preliminary testing in the western U.S. has proven that Stolar’s TTE technology can provide communication through a variety of rock types, with maximum depth capabilities ranging from 800 to 1,400 feet. The maximum depth at a mine is dependent on overburden rock type, thickness of layering, and the rock’s physical and electrical properties.
The most recent demonstration of Stolar’s TTE technology was performed in southwest Pennsylvania, in the Pittsburgh Coal Seam, and was completed the day of the Chilean rescue. This demonstration achieved two-way text messaging in the deepest part of the mine (nearly 800 feet) with ample signal strength remaining; the maximum range at this site is projected to be nearly 1,100 feet. This demonstration was supervised by technical teams from NIOSH and mine safety groups. After this demonstration, Stolar is continuing research and development to add synthetic voice capability, reduce the size of the antennas and acquire full MSHA approvals.
Stolar has designed a through-the-earth (TTE) system based largely on previous Mine Safety and Health Administration (MSHA) approved safe (IS) and flameproof enclosures, as well as other critical MSHA-approved components. The system features a state-of-the-art, narrow bandwidth, co-polarized gradiometer receiver antenna array on the mine surface. A surface transmitter, and resonating horizontal magnetic dipole antennas with electrostatic shields are at the underground transmitter/receiver locations. A battery pack, which has been MSHA-approved for operation in methane degasification boreholes, powers the underground electronics. An MSHA-approved flameproof enclosure with an MSHA-approved battery protection circuit enables the battery to be exchanged even when the ventilation is disrupted or when the TTE system must operate in a return entry or passageway.
The resonating magnetic dipoles are enclosed in a radio frequency signal transparent MSHA-approved electrical cable interconnection hose. Two compression glands seal the radiating magnetic dipole electrical conductors within an MSHA-approved flameproof enclosure. The enclosure contains a lexan cover for viewing an alphanumeric color graphics display for text messaging and escapeway information designation. An MSHA-approved four-key flameproof control mechanism is integrated in the enclosure. As an option, a transceiver carried on a miner’s belt, which allows a trapped miner to communicate with the transmitter mounted in the flameproof enclosure via a Bluetooth protocol at distances up to 100 feet, has also been approved by MSHA. A flameproof IS battery enclosure interconnects via a port in the housing. The TTE system data transmission rate is 80 bits per second with maximum transmission distances of nearly 2,000 feet.
For more information on Stolar's radio geophysics: LAR@stolarhorizon.com