Nicholas W. Damiano

NIOSH-Sponsored Research in Through-the-Earth Communications for Mines: A Status Report

This paper presents the results of recent contractual research sponsored by the National Institute for Occupational Safety and Health that aimed at demonstrating the feasibility of through-the-earth (TTE) wireless communication in mining. TTE systems, developed by five different contractors, are discussed with a focus on technical approach, prototype hardware, and field test results. System features include both magnetic and electric field sensing, loop and line antennas, digital and analog processing, noise filtering and cancelation, and direction finding. The systems were demonstrated at commercial mine sites. The results of these tests are characterized by transmission range and power levels. This paper concludes with a discussion of issues that remain to be resolved as TTE communications are implemented. These include text versus voice format, acceptable time delays, portability, ease of deployment, an interface with existing communications systems, permissibility, and the effect of geological variations.

NIOSH-sponsored research in through-the-earth communications for mines-a status report-

This paper presents the results of recent contractual research sponsored by the National Institute for Occupational Safety and Health that aimed at demonstrating the feasibility of through-the-earth (TTE) wireless communication in mining. TTE systems, developed by five different contractors, are discussed with a focus on technical approach, prototype hardware, and field test results. System features include both magnetic and electric field sensing, loop and line antennas, digital and analog processing, noise filtering and cancelation, and direction finding. The systems were demonstrated at commercial mine sites. The results of these tests are characterized by transmission range and power levels. This paper concludes with a discussion of issues that remain to be resolved as TTE communications are implemented. These include text versus voice format, acceptable time delays, portability, ease of deployment, an interface with existing communications systems, permissibility, and the effect of geological variations.

Simulation and measurement of through-the-earth (TTE), extremely low-frequency signals using copper-clad, steel ground rods

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.

Statistical analysis and modeling of VLF/ELF noise in coal mines for through-the-earth wireless communications

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 systems performance at a specific mine site.

Comparison of medium frequency propagation characteristics of a transmission line measured from both ends in a coal mine entry

An underground coal mine medium frequency (MF) communication system generally couples its electromagnetic signals to a long conductor in a tunnel (entry). The entry plus the conductor acts as a transmission line (TL). Transceivers exchange signals along the line. The propagation characteristics of the TL, which is generally the longest signal path, play a major role in determining the system performance. In this paper, we present MF measurements of TL characteristics as measured from both ends of the TL in a coal mine entry. The characteristic impedances from both ends have some significant differences, but the other propagation parameters are very similar.

E-fields of electrode-based through-the-earth (TTE) communication

An electrode-based through-the-earth (TTE), or linear TTE, communication system sends its signal directly through the earth overburden of a mine by driving an AC current into the earth. The resultant current, present at the receiver, is detected as a voltage and communication is established. The electrode-based TTE system may achieve a considerably large transmission range >305 m (1000 ft). This kind of system may be implemented for emergency communication close to an area such as a refuge alternative or other strategic location to establish communication between underground miners and the surface. Since it does not rely on extensive infrastructure underground, this communication would provide an alternate path out of the mine. Given the attenuation characteristics of the earth-which is the major factor determining the performance of TTE systems-the receiver sensitivity, transmitter antenna length and orientation, working frequency, and transmitted current required for communication can be estimated and determined. In an effort to estimate the earth attenuation, the analytic solution for the electrical field distribution of an electrode-based TTE communication system in a homogenous half-space is derived. A prototype system was built and tested at a mine site. The test data is compared with the modeling results, and a close agreement is found between them.

Characterization of medium frequency propagation on a twin-lead transmission line with earth return

This work presents research in the development of medium frequency communications systems that the National Institute of Occupational Safety and Health (NIOSH) is performing in support of the 2006 MINER Act. In this work, a 280 m twin-lead transmission line (TL) is used to measure complex input impedance and line currents resulting from open and shorted terminations at medium frequencies (MF). The line is placed in free space and positioned close to a lossy earth surface such that two line configurations can be chosen in order to control the extent to which the grounds presence affects MF propagation. In this way, the effects of the earth return may be characterized and modeled. Further, full-wave computational models using moment methods are used to compare with the experimental measurements as a way to determine the material properties of the ground medium. In the future, these experiments will be conducted in underground mines in an effort to develop and improve MF communication systems for mining operations and emergency response.

Simulation of a Medium Frequency Mesh Network for Communications in Underground Mines

Signals at the lower end of the medium frequency range (300 kHz to 3 MHz) propagate with relatively low attenuation along existing metallic infrastructure in an underground mine, such as cables, pipes and rails. Exploiting this capability, low-bandwidth medium frequency mesh networks are being developed to extend digital voice and data communications throughout a mine. This paper presents a network modeling and simulation tool that can be used to plan and evaluate medium frequency mesh networks in mines. Examples are given of mine communication scenarios that can be modeled and the quantitative analysis that can be performed using communication performance metrics such as end-to-end delay and packet delivery rate.

Simulation and measurement of medium frequency signals coupling from a line to a loop antenna

The underground-mining environment can affect radio-signal propagation in various ways. Understanding these effects is especially critical in evaluating communications systems used during normal mining operations and during mine emergencies. One of these types of communications systems relies on medium-frequency (MF) radio frequencies. This paper presents the simulation and measurement results of recent National Institute for Occupational Safety and Health (NIOSH) research aimed at investigating MF coupling between a transmission line (TL) and a loop antenna in an underground coal mine. Two different types of measurements were completed: 1) line-current distribution and 2) line-to-antenna coupling. Measurements were taken underground in an experimental coal mine and on a specially designed surface test area. The results of these tests are characterized by current along a TL and voltage induced in the loop from a line. This paper concludes with a discussion of issues for MF TLs. These include electromagnetic fields at the ends of the TL, connection of the ends of the TL, the effect of other conductors underground, and the proximity of coal or earth. These results could help operators by providing examples of these challenges that may be experienced underground and a method by which to measure voltage induced by a line.

Mathematical modeling and measurement of electric fields of electrode-based through-the-earth (TTE) communication

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.