Mining Contract: Electromagnetic Noise Data Acquisition for the Evaluation of TTE Communications in Coal Mines

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Contract #	211-2014-59075
Start Date	9/1/2014
End Date	3/31/2017
Research Concept	Unlike traditional methods, through-the-earth (TTE) radio systems based on low-frequency communication allow underground workers to communicate without having “line of sight” or a physical wired or fiber connection. The use of frequencies in the 10-9,000 Hz range may allow TTE radio systems to penetrate strata that block high-frequency radio signals (such as broadcast radio or cellular). One of the primary factors affecting the performance of TTE radios is background noise that is both man-made and naturally occurring. Extensive studies conducted by the Bureau of Mines and others in the 1970s showed that below-ground noise varied considerably from location to location. Furthermore, changes in the design and operation of electrical equipment since then have resulted in changes in the noise environment. Earlier data was also collected using a variety of equipment and measurement methods, making the data analysis complex.
Topic Area	Emergency Communications and Tracking

Contract Status & Impact

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

Improved performance is needed of TTE radio systems intended for use in coal mine emergency communications between the mine and the surface. To assess current and future TTE technology, it must be evaluated against a representative set of noise conditions and parameters in order to ensure it will operate under emergency conditions. Consistent and predictive performance will lead to adoption and greater safety. Consequently, it is necessary to collect fresh datasets from a range of different coal mines in an electronic, sampled data format that can be used to create reference conditions and to simulate and test modern TTE radio systems. To be representative, the data must be collected from as many mines as possible, covering different types (longwall, room and pillar) and the differing geologies of the United States used for sub-surface extraction. Current TTE radio systems use either magnetic induction or E-field (current injection). The receive antennas used in these systems respond to noise in the environment in different ways, and so, to be complete, the noise dataset must be collected using each method.

Vital Alert Communication, Inc., has developed commercially available TTE communications systems that can operate using either electromagnetic induction or E-field current injection. This technology has already been adapted to build a system used for the collection of TTE noise data. This system uses receivers and loop antennas or electrodes similar to those used for actual communications systems so that the noise samples collected closely match those “seen” by the actual communications equipment. The analog noise signals are amplified and then sampled, and the digitized data is then stored as a digital data file. These data files can be “played back” to re-create the original noise waveforms, or may be read directly by a simulation program. This equipment has already been used to collect hundreds of megabytes of magnetic induction noise data from coal mines and other test locations. An updated and fully automated version of this design—the Automated Noise Data Acquisition Unit (ANDAU)—will be developed under this contract research.

The ANDAU is a self-contained, portable battery-powered unit suitable for use in the coal mine environment. It has separate receivers for the magnetic field and E-field measurements, each optimized for the different antenna impedances. Vital Alert Communication has obtained agreement from two partners engaged in coal mine communications that will take noise measurements during routinely scheduled mine visits made by their technicians. A reliable means of obtaining E-field measurements without inserting electrodes into rock has been identified and will be prototyped and tested as part of the project.