The Industrial Internet of Things (IIoT), a concept that combines sensor networks and control systems, has been employed in several industries to improve productivity and safety. U.S. National Institute for Occupational Safety and Health (NIOSH) researchers are investigating IIoT applications to identify the challenges of and potential solutions for transferring IIoT from other industries to the mining industry. Specifically, NIOSH has reviewed existing sensors and communications network systems used in U.S. underground coal mines to determine whether they are capable of supporting IIoT systems. The results show that about 40 percent of the installed post-accident communication systems as of 2014 require minimal or no modification to support IIoT applications. NIOSH researchers also developed an IIoT monitoring and control prototype system using low-cost microcontroller Wi-Fi boards to detect a door opening on a refuge alternative, activate fans located inside the Pittsburgh Experimental Mine and actuate an alarm beacon on the surface. The results of this feasibility study can be used to explore IIoT applications in underground coal mines based on existing communication and tracking infrastructure.

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The through-the-earth (TTE) wireless communication system, in which the RF signal can directly penetrate the earth separating a transmitter and receiver, is likely to survive a mine disaster because it requires no cabling between the surface and underground. One of the biggest challenges for TTE communication is that the ambient electromagnetic (EM) noise can be significant and impose a limitation on the reception sensitivity. Both underground and surface RF noise characteristics were obtained and analyzed from experimental data collected at several coal mines. The results show the surface has a higher noise level than underground. Moreover, the parameters obtained in an empirical noise model can be used to predict a TTE system's performance at a specific mine site.

The underground mining environment can greatly affect radio signal propagation. Understanding how the earth affects signal propagation is a key to evaluating communications systems used during a mine emergency. One type of communication system is through-the-earth, which can utilize extremely low frequencies (ELF). This paper presents the simulation and measurement results of recent National Institute for Occupational Safety and Health (NIOSH) research aimed at investigating current injection at ELF, and in particular, ground contact impedance. Measurements were taken at an outside surface testing location. The results obtained from modeling and measurement are characterized by electrode impedance, and the voltage received between two distant electrodes. This paper concludes with a discussion of design considerations found to affect low-frequency communication systems utilizing ground rods to inject a current into the earth.

There are two types of through‐the‐earth (TTE) wireless communication in the mining industry: magnetic loop TTE and electrode‐based (or linear) TTE. While the magnetic loop systems send signal through magnetic fields, the transmitter of an electrode‐based TTE system sends signal directly through the mine overburden by driving an extremely low frequency (ELF) or ultralow frequency (ULF) AC current into the earth. The receiver at the other end (underground or surface) detects the resultant current and receives it as a voltage. A wireless communication link between surface and underground is then established. For electrode‐based TTE communications, the signal is transmitted through the established electric field and is received as a voltage detected at the receiver. It is important to understand the electric field distribution within the mine overburden for the purpose of designing and improving the performance of the electrode‐based TTE systems. In this paper, a complete explicit solution for all three electric field components for the electrode‐based TTE communication was developed. An experiment was conducted using a prototype electrode‐based TTE system developed by National Institute for Occupational Safety and Health. The mathematical model was then compared and validated with test data. A reasonable agreement was found between them.

-The underground mining environment can greatly affect radio signal propagation. Understanding how the earth affects signal propagation is a key to evaluating communications systems used during a mine emergency. One type of communication system is through the earth (TTE) that can utilize extremely low frequencies (ELF). This paper presents the simulation and measurement results of recent National Institute for Occupational Safety and Health (NIOSH) research aimed at investigating current injection at ELF , and in particular ground contact impedance. Measurements were taken at a surface testing location, outside. The results obtained from modeling and measurement are characterized by electrode impedance and the voltage received between two distant electrodes. The paper concludes with a discussion of design considerations found to affect low-frequency communication systems utilizing ground rods to inject a current into the earth.