Mining Contract: Emergency Seismic Communication System for the Mining Industry

Contract Status & Impact

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

This work explored the use of both oscillatory and impact seismic sources for underground through-the-earth communications applications. Initial tests were conducted in limestone mines where a text message was successfully transmitted and received through the rock mass over a distance of ~200 ft using the Terfenol-D (oscillatory) transducer as both source and receiver. Contract tasks were to refine the prototype equipment, quantify the path losses through both limestone and coal, and determine the maximum distance the Terfenol-D transducer could be used for communication purposes.

Previous tests in limestone indicated that a mechanical impact source could be detected and recorded at approximately 1,800 feet from the source. These results were reproduced in the contract effort at a second limestone mine. The prototype equipment was iteratively modified and retested for evaluation as a seismic source for greater distances. Path loss measurements were made in both limestone and coal environments.

During the tests, the maximum observed communication distance through limestone using the Terfenol-D transducer was 480 feet. Subsequent analyses predict that maximum achievable distance of the Terfenol-D transducer through limestone to be approximately 1,567 feet. The maximum observed communication distance through coal using the Terfenol-D transducer was 965 feet. Subsequent analyses predict that maximum achievable distance of the Terfenol-D transducer through coal to be approximately 1,040 feet.

Based upon the above results, the contractor indicated that the Terfenol-D transducer is not a practical seismic excitation source for the mining application. While impact sources offer potentially greater communication distances, the large amount of input energy necessitates the use of large batteries and heavy masses. Alternatively, communications could be relayed between multiple repeater locations that are closer together, using less powerful sources. Either approach escalates the total cost of the system, and its maintenance, to the extent that the contractor does not consider them practical as an application in a seismic-based communication system for use by the mining industry.