An Introduction to a Medium Frequency Propagation Characteristic Measurement Method of a Transmission Line in Underground Coal Mines

Abstract

Abstract-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 confirmed 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.

Accurate Electromagnetic Analysis of MF TL Backup Communications in Cylindrical Tunnels

“…Note: the parameterx s in (31) does not include the perturbation effect arising from small longitudinal displacement currents in the soil with permittivity ε s . This effect may be taken care by redefining q s and δ s in (18), replacing the soil conductivity by a complex conductivity,σ s = σ s + jωε s .…”

“…Analytical and numerical results concerning the attenuation, phase velocity, and characteristic impedance were presented, discussed, and compared with recently reported measurements [17], [18]. Also, in [21], a multimodal approach to the analysis of the attenuation properties of MF TL tunnel communication systems with several longitudinal conductors inside the tunnel was presented, where the randomness of the "injected" currents coupled to those conductors was considered.…”

Medium Frequency Propagation Characteristics of Different Transmission Lines in an Underground Coal Mine

“…The impedance measurement system introduced in [9]–[11] was used in the experiment. An Agilent E4980A LCR meter was used for the impedance measurements.…”

“…We have recently developed a method that was able to obtain all of the MF propagation parameters in a tunnel TL [9]–[11]. As indicated in the general voltage and current distribution functions (1) and (2) for a TL, the Z 0 ( f ) and γ( f ) are the basic parameters often needed for an analysis of signal propagation characteristics along the TL.…”

“…2β( f ) l in (6) is the input phase angle for a given line length of l . The detailed description on how to obtain 2β( f ) l can be found in [11]–[14]. …”