Research Of Underwater Electromagnetic Field Analysis Algorithm Based On The Equivalent Principle

Water is a kind of lossy dispersive medium. The higher the propagation frequency of electromagnetic waves in the water, the faster the attenuation. In this case, only those signals with low-frequency or extremely low-frequency can propagate longer distances in the underwater environment. In dealing with the problem of low-frequency, if we discrete the target according to wavelength, it is difficult to describe the target accurately as the discrete intervals are too wide. In order to describe the target accurately, it is necessary to make the discrete unit small enough, which, however, will appear other problems in deal with the problem of large space. Traditional FDTD algorithm also exist the conflict of how to describe small target(such as antenna) and compute broad space. In order to solve this problem, it requires us to improve the existing algorithm to meet the need of the electromagnetic field calculation.In this paper, FDTD grid transformation technique is proposed to solve these problems. For this method, small-to-large grid transformation is realized by building up exchange surface, which is carried out by two separate FDTD simulations. Excitation source is modeled and tangential electromagnetic field on the surface is recorded in the first simulation with fine grids. In the second simulation, the equivalent source is added with coarse grids on the surface. This method can dramatically increase the ratio(N) of the grids, for example, N=10. Thus we can save computation time and reduces compational memory consumption.The work of this paper includes three parts:Firstly, according to the PMC equivalence princple, we have studied two-dimensional FDTD grid transformation technology. The theroy and examples are given in this paper.Secondly, two-dimensional FDTD grid transformation technology based on total field and scattered field theroy has introduced in the chapter 3. Examples of linear current and metal scattering are proposed, which verified the accuracy of the proposed method. A real underwater model is analyed by using the grid transformation technology.Finally, three-dimensional FDTD grid transformation technology are discussed in the chapter 4.