| The wireless communication system of mine rescue is one of the important parts of’modem mine enterprises’emergency rescue equipment.In order to determine the mine rescue wireless communication relay equipment related parameters and provides the theory basis for reasonable layout,this paper uses the actual research,analysis of the basic theory,numerical calculation and simulation and field experiment study the way of combining analysis of the main factors influencing underground roadway electromagnetic wave propagation,the attenuation of electromagnetic wave propagation characteristics of roadway,reveals the mine rescue multimedia communication signal transmission attenuation law.The transmission of electromagnetic wave signals in the mine roadway belongs to the propagation in the confined underground space,and the energy attenuation and loss in the propagation process are mainly affected by the number and form of roadway support,roadway section size,roadway wall roughness,roadway bending radius,dust concentration and other factors.Among them,the size and shape of the roadway section,the concentration of dust in the roadway and the roughness of the roadway wall have a great influence on the normal propagation of electromagnetic wave.In the process of electromagnetic wave propagation in the mine roadway,the dielectric parameters related to coal and rock mass in the roadway,such as conductivity,permeability and dielectric constant,also have a certain impact on the attenuation and loss of electromagnetic wave propagation,but the contribution rate to electromagnetic wave is relatively small.Based on Maxwell’s electromagnetic equation,the variation trend of magnetic field component in x,y and z directions with time in the propagation process of electromagnetic wave in waveguide is analyzed,and the variation and attenuation law of electromagnetic field transmission are preliminarily obtained.The formula of mode attenuation of electromagnetic wave in rectangular waveguide is derived theoretically,and the cut-off frequency of electromagnetic wave transmission under different tunnel section size and mode order is calculated theoretically,and the corresponding influence curve is obtained.The shape factor of the mine roadway is one of the main factors affecting the wireless Mesh attenuation.In the design of the roadway,the cross-sectional area and the ratio of width to height can be fully considered to make the cross-sectional area of the roadway as large as possible within the allowable range of conditions,and the shape factor is close to 2,which can effectively reduce the attenuation of the wireless Mesh signal.In the curved roadway,the frequency of 900 MHz is selected to properly alleviate the signal attenuation caused by dust in the wireless Mesh The roadway wall can cause Mesh electromagnetic wave to produce rough loss,tilt loss and mode attenuation. |
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