Field strength prediction of electromagnetic wave propagation along semicircular arched mine roadway based on mirror principle

In order to analyze the propagation characteristics of electromagnetic waves along the mine roadwat better, so as to deploy the mine mobile communication system and improve its wireless communication quality more effectively, a method for predicting the field strength of electromagnetic wave along semicircular arched mine roadway based on the mirror image principle is proposed.Mirror image method is a ray tracing method based on the geometrical optics theory.It regards the high-frequency electromagnetic wave as the ray of light wave.Through the phenomenon such as direct and reflection of light, it finds out the effective transmission path of electromagnetic wave between the transmitting point and the receiving point to simulate the propagation process of electromagnetic wave along the mine roadway.Firstly, the effective reflection cross-section required by the mirror image method is obtained by dividing the semicircular arched top surface with the proposed field strength prediction method, then the plane equation of each cross-section is established.A method is put forward to determine the primary reflection point, secondary reflection point and tertiary reflection point of each section, as well as a statistical method for the number of primary reflection, secondary reflection and tertiary reflection rays when the positions of the transmitting point and receiving point are determined in the mine roadway.Based on the plane equation of the segmented section, the calculation method of the incident angle of the incident wave at the reflection point of each section is proposed, and the reflection coefficients of the vertical and horizontal polarization waves of the incident wave can be obtained.Moreover, the calculation methods of the field strength vectors of primary, secondary and tertiary reflection rays at the receiving point are put forward, from which the sum of the field strength vectors of each reflection wave and the total field strength vectors at the receiving point can be obtained.The simulation results show that the number of each reflection rays can be counted and the field strength can be predicted at the receiving point effectively when the transmitting point and receiving point are in different positions in the semicircle arched mine roadway with the proposed field strength prediction method.For example, the field strength distribution curve with 6 and 9 sections to divide the semicircular arched top surface is consistent with the general law of electromagnetic wave propagation along the mine roadway and is also consistent with the trend of some classical test results.In addition, the proposed field strength prediction method can also be used to determine the location of the "breakpoint" of the field strength distribution curve which divides the curve into near-source and far-source regions when the electromagnetic wave propagates along the semicircular arched mine roadway.In the near-source region, the electromagnetic wave attenuates quickly, and in the far-source region, the electromagnetic wave attenuates slowly.The study plays an important role in the design of underground mobile communication system. © 2020, Editorial Office of Journal of China Coal Society. All right reserved.