Application On EM Scattering With Alternative Direction Implicit Finite Difference Time Domain (ADI-FDTD) And Its Hybrid Algorithm

This dissertation is concerned with the improved algorithm of Finite Difference Time Domain (FDTD) method -- Alternative Direction Implicit FDTD (ADI-FDTD). The history, actuality and disadvantage of the FDTD scheme are introduced firstly, the basis equations and some key techniques are presented. Moreover the temporal and spatial dispersive relations are also discussed and the criteria of their steps are derived, which is so-called CFL constraint condition in this paper.It is the CFL constraint conditions that influence the efficiency of conventional FDTD. To circumvent this, we make a professional research on the ADI-FDTD scheme and derive the basis equations from the original Maxwell equations and ADI technique. At the same time, the analytical investigation of numerical stability for one, two and three dimensional equations are given. Due to the complexity of ADI-FDTD update equations, this method is not suitable for the electromagnetic scattering analysis. Therefore, this paper build up a new method named SADI-FDTD scheme which combines the split field equations in perfect matched layers with original ADI-FDTD equations. The improved ADI-FDTD method simplifies the absorbed and adjacent boundary condition greatly and has a higher efficiency in electromagnetic scattering problem. The numerical examples shows that the time exhausted in SADI-FDTD is only 1/7-1/8 of that in conventional FDTD.The other new hybrid methods with ADI-FDTD are presented here also. One is used to analysis the scattering of dispersive media. The Auxiliary Differential Equations (ADEs) is one of flexible methods in dispersive media. This new algorithm is based on the ADEs and SADI-FDTD, which is used here to simulation the scattering of Debye media. The result shows that the method has a good agreement with the analytical solution. The other method is ADI-MRTD which is related to another improved method of FDTD - Multi Resolution Time Domain. We derived the basis ADI-MRTD equations and discuss the key techniques such as the absorbing and adjacent boundary condition.It is well known that the effect between circumstance and the object is very complicated but has an important role in EM scattering. We have some research on this topic by FDTD method. When the scattering model is composed with the ground and the metallic object which has a moderate height from the earth, the spatial step is set according to the wavelength in the soil in FDTD computation region. On the other hand, the computation zone is rather large because it should include the object and the earth, which will occupied a large number of RAM. In the dissertation, we present theapproximation simulation technique which is called Separated Model Method. It has the advantage of reduction resources such as the Center Processing Unit (CPU) time and RAM greatly with the negligible error. Finally, the scattering of random rough surface is discussed to simulation more naturally circumstance.