Last data update: Sep 23, 2024. (Total: 47723 publications since 2009)
Records 1-5 (of 5 Records) |
Query Trace: Waynert JA [original query] |
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Medium frequency propagation characteristics of different transmission lines in an underground coal mine
Li J , Waynert JA , Whisner BG . Int J Commun Antenna Propag 2015 5 (1) 7-15 A medium frequency (MF) communication system operating in an underground coal mine couples its signals to a long conductor, which acts as an MF transmission line (TL) in a tunnel to permit communications among transceivers along the line. The TL is generally the longest signal path for the system, and its propagation characteristics will have a major impact on the performance of the MF communication system. In this study, the propagation characteristics of three types of MF TLs in two layouts-on the roof and on the floor of a coal mine tunnel-were obtained in an effort to understand the propagation characteristics of different TLs in different locations. The study confirmed a low MF signal loss on all of these TLs. The study also found that the TLs in different layouts had substantially different propagation characteristics. The propagation characteristics of these different TLs in different layouts are presented in the paper. |
A hybrid approach for efficient modeling of medium-frequency propagation in coal mines
Brocker DE , Sieber PE , Waynert JA , Li J , Werner PL , Werner DH . IEEE Antennas Propag Mag 2015 57 (1) 164-176 An efficient procedure for modeling medium frequency (MF) communications in coal mines is introduced. In particular, a hybrid approach is formulated and demonstrated utilizing ideal transmission line equations to model MF propagation in combination with full-wave sections used for accurate simulation of local antenna-line coupling and other near-field effects. This work confirms that the hybrid method accurately models signal propagation from a source to a load for various system geometries and material compositions, while significantly reducing computation time. With such dramatic improvement to solution times, it becomes feasible to perform large-scale optimizations with the primary motivation of improving communications in coal mines both for daily operations and emergency response. Furthermore, it is demonstrated that the hybrid approach is suitable for modeling and optimizing large communication networks in coal mines that may otherwise be intractable to simulate using traditional full-wave techniques such as moment methods or finite-element analysis. |
An introduction to a medium frequency propagation characteristic measurement method of a transmission line in underground coal mines
Li J , Waynert JA , Whisner BG . Prog Electromagn Res B Pier B 2013 55 (55) 131-149 An underground coal mine medium frequency (MF) communication system generally couples its electromagnetic signals to a long conductor in a tunnel, which acts as a transmission line, and exchanges signals with transceivers along the line. The propagation characteristics of the transmission line, which is usually the longest signal path for an MF communication system, play a major role in determining the system performance. To measure the MF propagation characteristics of transmission lines in coal mine tunnels, a method was developed based on a basic transmission line model. The method will be presented in this paper along with the propagation measurements on a transmission line system in a coal mine using the method. The measurements con-rmed a low MF signal power loss rate, and showed the influence of the electrical properties of surrounding coal and rock on the MF propagation characteristics of the line. |
Measurements and modeling of through-the-earth communications for coal mines
Yan L , Waynert JA , Sunderman C . IEEE Trans Ind Appl 2013 49 (5) 1979-1983 This paper presents modeling results from the National Institute for Occupational Safety and Health research into through-the-earth (TTE) communications technology for underground coal mines. Research focuses on the factors controlling the propagation and coupling of radio signals between transmit and receive antennas separated by earth or coal. Most TTE systems use single or multiturn loops of conductor for the transmit antenna. We compare the magnetic field distribution predicted from analytical formulas to the predictions of a method of moments computational electromagnetic (CEM) code. The predictions are compared in free space, in a homogeneous earth, and with the effect of the presence of the surface of the earth. The evaluations are done with the transmit loop buried in the earth and with the loop above the surface. The analytic results are shown to agree reasonably well with the more detailed CEM predictions for the situations considered, reducing the need for expensive and complicated CEM codes in analyzing simple TTE configurations. The predictive methods are applied to TTE measurements made in 94 different coal mines by the Bureau of Mines in the 1970s, and the implications for the apparent conductivity of the earth are discussed. |
Measurements of medium-frequency propagation characteristics of a transmission line in an underground coal mine
Li J , Whisner B , Waynert JA . IEEE Trans Ind Appl 2013 49 (5) 1984-91 In underground coal mines, medium frequency (MF) communication systems couple their signals to metal infrastructures such as ac power cables and wire-based telephone lines, which guide the signals to propagate for a long distance. To better understand the propagation characteristics of MF signals, an easy-to-use measurement method was recently developed at the National Institute for Occupational Safety and Health. The method will be introduced along with an equivalent transmission line model for a long metallic infrastructure in underground coal mines. The model serves as the fundamental driver for the method development. Propagation measurements on a twisted pair of telephone lines in an underground mine were made using this method. The measurements confirmed the low MF signal attenuation rate and the dependence of the propagation characteristics of the line on the electrical properties of surrounding coal and rock as theoretical studies predicted. |
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