The New Theoretical Calculation Method Of Extremely Low Frequency Propagation In Earth-Ionosphere Wave Guide

In order to investigate the low layer earthquake,the geological stratum survey,the communication and navigation technology of the submarine,we need to further understand the wave propagation characteristic in SLF/ELF frequency band. Because the wavelength of ELF is compared to the earth circumstance, in this case, the propagation space between the earth and ionosphere can't already be regarded as a " wave guide ", and should be regarded as a " shell ". The presented wave guide theory can not be used in the ELF frequency band. In order to solve this difficulty,Barrick has expanded the fields in the wave guide as the spherical harmonic series in 1999. He calculated directly the electromagnetic fields in the wave guide by using a kind of speed numerical convergence algorithm. Barrick has only educed the calculating formulary of vertical electric dipole under the ideal conductor condition. We have further developed Barrick's method,and derived the calculating formula of both the vertical electric dipole and horizontal electric dipole under the imperfectly conductor condition. This algorithm is based on separately deducting and adding the asymptotic expression under the ideal conductor condition to the primitive strict spherical harmonic series expression of every field component. This series of asymptotic expression can already be summed analytically,and the difference of the spherical harmonic series expression and asymptotic expression series will convergent faster than itself. This method will improve the convergence speed of the spherical harmonic series,and it can get higher calculating precision and higher calculating efficiency than the directly calculating spherical harmonic series. The numerical calculation shows that the electromagnetic fields in the wave guide are the standing wave, and the variation of the amplitude verse frequency coincides with the Schumann resonance in ELF frequency band.In order to let this algorithm may be used directly by engineers and technicians, we have established a computation software by utilizing this algorithm. It has obtained the application in studying the earthquake electromagnetic radiation.