Ultra Low Frequency Electromagnetic Fire Alarm System for Underground Mines

摘要

Recent research by the U.S. Bureau of Mines has demonstrated that ultralow frequency electromagnetic signaling can be used for an underground mine fire alarm. In field tests of prototype equipment at five mines, electromagnetic signals of from 630 Hz to 2,000 Hz were transmitted through mine rock for distances as great as 1,645 m to an intrinsically safe receiver. Theoretical analysis indicates a capability to transmit signals effectively from the surface to the lowest level of most American mines, 90 pct of which are less than 900-m deep. The prototype system uses off-the-shelf components and state of the art technology to insure high reliability and low cost. When utilized, the technology would enable simultaneous and instantaneous warning of all underground personnel, regardless of their location or work activity, thereby increasing the likelihood of their successfully escaping a mine. The report presents the theoretical basis for through-the-rock ultralow frequency electromagnetic transmission, design of the prototype transmitter and receiver, and the results of in-mine tests of the prototype system.