| Given coal is main energy in China,the scientific production of coal plays an important role in the modernized development.But in recent years,coal mining accidents have happened more frequently in China,and it has been a great damage to casualties and economic losses.Therefore,to protect the lives of miners and state property,the establishment of a scientific,reliable and effective through-to-earth communication system has an important practical significance.Due to the complex structure of the stratum and the influence of earth medium with electrical conductivity,there is a serious attenuation of electromagnetic wave transmission.Thence,it is necessary to research transmission characteristics of electromagnetic wave in the channel of stratum medium for the establishment of a robust mine communication system.At the moment,the research on the transmission characteristics of the electromagnetic wave in the complex stratum medium channel is still insufficient.In this thesis,the characteristics of electromagnetic wave transmission and attenuation in the medium channel are deeply studied.The main contributions and conclusions are as follows:(1)Aiming at the shortcomings of the existing layered stratum modeling algorithms,a Kriging interpolation method based on Particle Swarm Optimization-Genetic Algorithm(PSO-GA)is proposed.Using this method,the parameters of the variation function are optimized and the layered medium model is established.The simulation results show that the Kriging interpolation method based on PSO-GA can be used to establish the layered medium model of the stratum communication for better performance and stability.Simultaneously,based on the proposed algorithm,the profile of stratum layered model is realized in VC6.0.It is important to analyze the electromagnetic wave penetrating stratum medium by using the layered stratum of profile.(2)According to the layered model of the stratum,in addition to the complexity of the transmission medium when the electromagnetic wave transmits through the earth,the stratum model is also irregular.Therefore,this dissertation creatively establishes the layered model of the irregular stratum.By analyzing the geometrical relationship between the incident angle of electromagnetic wave and the inclined angle of layered stratum,the attenuation of the electric field intensity and the magnetic field intensity in the forward and backward transmission of electromagnetic wave in irregular stratum is derived.The simulation results show that the attenuation of forward transmission and backward transmission is usually different,which is not only related to the irregularity of layered stratum,but also to the entering order of electromagnetic wave in forward and backward transmission;and the attenuation rate of the electric field intensity is generally greater than the attenuation rate of the magnetic field intensity,especially the electromagnetic wave just enters the initial stage of the stratum.(3)A pseudo-spectral time domain(PSTD)method is given to solve the problem of the accuracy and stability of the finite difference time domain(FDTD)method when it's used to do simulation of electromagnetic wave through-the-earth communication.In this thesis,the basic principle of the PSTD method and the absorbing boundary conditions suitable for lossy medium are described,and the numerical model of the medium is established.The simulation results show that the method can simulate the transmission attenuation of electromagnetic waves in the layered model of the lossy medium more precisely and stably.Moreover,the transmission of electromagnetic waves at the interface of the stratum medium is related to the electrical parameters of the medium.The bigger the electrical parameter,the more serious the attenuation,and the less the transmittance. |
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