Mining and mineral exploration play important roles in the global economy. In mining operations, communication systems play vital roles in ensuring personnel safety, enhancing operational efficiency and process optimization. Over the period 1920-2012, this article surveys the evolution of wireless communications in underground mines, the developments of the underlying technology, and progress in understanding and modeling the underground wireless propagation channel. Current and future trends in technology, applications and propagation modeling are also identified. About ninety relevant references have been reviewed that consider: 1) the emergence of technology and applications, 2) analytical, numerical and measurement-based propagation modeling techniques, and 3) implications of the physical environment, antenna placement and radiation characteristics on wireless communication system design. Affected systems include narrowband, wideband/ultra-wideband (UWB) and multiple-antenna systems. The paper concludes by identifying open areas of research.

A Survey of Wireless Communications and Propagation Modeling in Underground Mines

After a recent series of unfortunate underground mining disasters, the vital importance of communications for underground mining is underlined one more time. Establishing reliable communication is a very difficult task for underground mining due to the extreme environmental conditions. Until now, no single communication system exists which can solve all of the problems and difficulties encountered in underground mine communications. However, combining research with previous experiences might help existing systems improve, if not completely solve all of the problems. In this survey, underground mine communication is investigated. Major issues which underground mine communication systems must take into account are discussed. Communication types, methods, and their significance are presented.

Underground Mine Communications: A Survey

This paper presents an electromagnetic energy harvesting scheme by using a composite magnetoelectric (ME) transducer and a power management circuit. In the transducer, the vibrating wave induced from the magnetostrictive Terfenol-D plate in dynamic magnetic field is converged by using an ultrasonic horn. Consequently more vibrating energy can be converted into electricity by the piezoelectric element. A switching capacitor network for storing electricity is developed. The output of the transducer charges the storage capacitors in parallel until the voltage across the capacitors arrives at the threshold, and then the capacitors are automatically switched to being in series. More capacitors can be employed in the capacitor network to further raise the output voltage in discharging. For the weak magnetic field environment, an active magnetic generator and a magnetic coil antenna under ground are used for producing an ac magnetic field of 0.2–1 Oe at a distance of 25–50 m. In combination with the supply management circuit, the electromagnetic energy harvester with a rather weak power output (about 20 μW) under an ac magnetic field of 1 Oe can supply power for wireless sensor nodes with power consumption of 75 mW at a duration of 620 ms.

A magnetoelectric energy harvester and management circuit for wireless sensor network

This paper proposes a ferro-nickel (Fe-Ni)/PZT H-type fork magnetoelectric (ME) composite structure and an energy management circuit for ME energy harvesting. The resonant fork composite structure with a high Q value shows a higher ME voltage coefficient and a stronger power coefficient compared with the conventional rectangular composite structure. The resonant fork composite structure can obtain an output power of 61.64 μW at an ac magnetic field of 0.2 Oe. The ME sensitivity of the fork structure reaches 11 V/Oe. For weak magnetic-field environment, an active magnetic generator and a magnetic coil antenna underground are used for producing an ac magnetic field of 0.2-1 Oe at a distance of 25-50 m. A management circuit of the power supply with matching circuit, energy-storage circuit, and instantaneous-discharge circuit is developed suitable for weak electromagnetic energy harvesting. The management circuit can continuously accumulate weak energy from the fork composite structure for a long period and provide a high-power output in a very short cycle. While the voltage across the storage supercapacitor is over 0.36 V, the instantaneous-discharge circuit can drive a wireless sensor network node with an output power of 75 mW at a distance of over 60 m.

A Magnetoelectric Composite Energy Harvester and Power Management Circuit

Underground mines are typically extensive labyrinths that employ many people working over an area of many square miles; extensive analysis of mine-communications systems has identified specific problem areas, in particular the excessive times required to locate key personnel underground, the inadequacy of existing phone systems in terms of capacity and privacy, and the inability to communicate with men on the move with wireless communications, as is taken for granted on the surface. A review is presented of the existing systems, the problem definition, and the various approaches that have been or are being investigated to solve these problems.

https://www.cdc.gov/niosh/mining/UserFiles/works/pdfs/umc.pdf

Underground mine communications

Research involved in the development of a radio communication system for use in coal mine disasters is described. Theoretically predicted field strengths for surface to mine and mine to surface propagation are compared with measurements in coal mines in Colorado and Pennsylvania. It is concluded that surface-to-mine voice communication is practical using a horizontal wire antenna operating at audio frequencies, and that mine-to-surface interrupted CW signaling is practical using multiple-turn horizontal loop antennas. This research has resulted in an emergency through-the-earth communication system that is being evaluated by the U.S. Bureau of Mines for use in mine rescue operations.

A. Farstad

Papers

Radio Transmission to and from Underground Coal Mines--Theory and Measurement