Research On Characteristics Of LF/VLF Electromagnetic Wave Propagation In The Earth-ionosphere Cavity And Its Applications

In recent years,low frequency(LF)and very low frequency(VLF)electromagnetic wave have been widely used in many fields,such as submarine communication,geological exploration,oil exploitation and earthquake prediction.At the same time,the propagation of electromagnetic wave in earth-ionospheric waveguide has become a hot topic in theoretical research field.Based on the theoretical research results published by W.Y.Pan and Kai Li in 2014 and the expressions of the earth-anisotropic ionospheric waveguide propagation[1],the parameters of LF/VLF electromagnetic wave are calculated.With the characteristics of LF wave in time domain and VLF wave in the multimodes interference region,the application of LF/VLF is studied systematically.The innovative research results of this paper are summarized as follows:First,based on the research method of LF electromagnetic wave in the earth-ionospheric waveguide excited by vertical electric dipole,the analytical expressions of electromagnetic field excited by magnetic dipole and horizontal electric dipole are derived.On this basis,approximate expressions of the propagation of sky waves under the excitation of horizontal electric dipole are present.Secondly,the frequency and time domain responses of the sky wave propagation excited by vertical and horizontal electric dipole are given,respectively.It shows that the propagation characteristics of the sky wave excited by the horizontal electric dipole are affected by the propagation distance and the launching height..Finally,propagation characteristics of VLF wave in the earth ionosphere waveguide are calculated,the formula of the phase velocity and attenuation rate are given,also,the performance of multimode interference of VLF electromagnetic wave and spatial distribution of electric field are simulated in the daytime and nighttime conditions.In conclusion,LF electromagnetic wave in the earth-ionospheric waveguide is propagated mainly by superimposing the multimode of the ground wave and the sky wave.For the VLF wave in a isotropic ionosphere waveguide,the multimode interference phenomenon happened in the daytime and nighttime.At last,comparison between isotropic and anisotropic,the multimode interference in the anisotropic condition is more complicated.In this paper,the research contents are calculated and discussed with the purpose of showing the physical value of these complex mathematical expressions,it also provides some reference data theoretically for the recognition and location of electromagnetic radiation.