Joseph Waynert

The Equivalence of the Ray Tracing and Modal Methods for Modeling Radio Propagation in Lossy Rectangular Tunnels

Ray tracing and modal methods are widely used for modeling RF propagation in tunnels. In this letter, we show that the two methods are mathematically equivalent and yield the same results. We also compare the theoretical predictions from both methods to field measurements at different frequencies (455, 915, 2450, and 5800 MHz) and find good agreement.

Measurements of medium frequency propagation characteristics of a transmission line in an underground coal mine

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.

Measurements and Modeling of Through-the-Earth Communications for Coal Mines

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

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.

Measurements and modeling of through-the-earth communications for coal mines

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.

AN INTRODUCTION TO A MEDIUM FREQUENCY PROPAGATION CHARACTERISTIC MEASUREMENT METHOD OF A TRANSMISSION LINE IN UNDERGROUND COAL MINES

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 conflrmed a low MF signal power loss rate, and showed the in∞uence of the electrical properties of surrounding coal and rock on the MF propagation characteristics of the line.

RF Propagation in Mines and Tunnels: Extensive measurements for vertically, horizontally, and cross-polarized signals in mines and tunnels.

This article reports measurement results on radiofrequency (RF) propagation in tunnels and mines for vertically, horizontally, and cross-polarized signals. Extensive measurements have been made in concrete tunnels, coal mines with rock dust and shotcrete, with and without conductive mesh, and hard-rock mines. The measurements include power attenuation over distances with and without line of sight (LOS) at four frequencies (455, 915, 2,450, and 5,800 MHz) that are common to underground radios, as well as swept wideband-frequency measurements from 30 MHz to 1 GHz at fixed separation distances to investigate the attenuation behavior as the waveguide cutoff frequency is approached. In addition, power loss associated with radio propagation around a 90? corner was measured for the four frequencies and two polarizations in an operational coal mine.

Modeling RF propagation in tunnels

As mandated by the 2006 Mine Improvement and New Emergency Response (MINER) Act, many underground coal mines have installed UHF radio systems to provide communications between personnel on the surface and underground. In an effort to better understand UHF signal propagation in tunnel environments, we made radio signal attenuation measurements in concrete tunnels at frequencies of 455 MHz, 915 MHz, 2.45 GHz, and 5.8 GHz. In this paper, a ray tracing method is used to model the channel. Although the tunnel has an arched roof, the model describes the propagation behavior very well using a rectangular tunnel with the same width. The measured data verify the ability of the ray tracing model to predict radio frequency propagation at all the four frequencies. In addition, the propagation constants for the different frequencies are investigated and shown to be consistent with the measured values.

An overview of underground coal miner electronic tracking system technologies

Since the passage of the Mine Improvement and New Emergency Response Act (MINER Act) of 2006, several electronic tracking systems that inform personnel on the surface of a coal mine about the location of miners underground have become commercially available. These systems can be broadly categorized into technology groups that are described in this paper. In addition, several other technologies have been identified by the National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR) that show promise to increase location accuracy, reduce installed infrastructure, or otherwise improve the performance of existing systems. This paper will describe tracking system technologies currently installed in US coal mines and discuss some emerging technologies.

Modeling the influence of wall roughness on tunnel propagation

At the ultra-high frequencies (UHF) common to portable radios, a mine tunnel is often modeled as a hollow dielectric waveguide. The roughness condition of the tunnel walls has an influence on radio propagation and therefore should be taken into account when accurate power predictions are required. In this paper, we derive a general analytical formula for modeling the influence of the wall roughness. The formula can model practical tunnels formed by four dielectric walls, with each having an independent roughness condition. It is found that different modes are attenuated by the same wall roughness in a different way, with higher order modes being significantly more attenuated compared to the dominant mode. The derivation and findings are verified by numerical results based on both ray tracing and modal methods.