Study On Algorithms For Scattering Characteristics Of The Complex Targets Covered By Plasma

The stealth technology of plasma has attracted much attention from many countries around the world, due to the potential application of plasma as absorbers of electromagnetic waves. At the same time, the plasma stealth is also a promising and complex system engineering, it involves in many subjects, such as: the plasma generator technique, the theory and engineering of electromagnetic field, radar theory, mechanical and electrical engineering, and so on. But with the development of the science and the technology, the plasma stealth must exhibit expansive future.The research works of this dissertation are at the three parts: the scattering of unmagnetized plasma, the scattering of anisotropic magnetized plasma and the scattering modeling method of complex targets. The alternating direction implicit finite difference time domain (ADI-FDTD) method is applied to analyze the scattering of unmagnetized plasma. The RCS reduction for the two dimensional, three dimensional conducting target coated by unmagnetized plasma is studied. Furthermore, the finite difference time domain (FDTD) method is applied to analyze the scattering of anisotropic magnetized plasma. The RCS reduction for the two dimensional, three dimensional conducting target coated by anisotropic magnetized plasma is studied. The main innovations of this paper are as follows:The ADI-FDTD method has a larger dispersion error compared with the regular FDTD method. To improve the accuracy of the ADI-FDTD method, we introduce the higher order ADI-FDTD method. The dispersion relation of the higher order ADI-FDTD method can be derived by analyzing the phase. In addition, a new perfectly matched layer based on the auxiliary differential equation is presented for the ADI-FDTD method. The ADE-PML formulations only require two additional auxiliary variables per field component in the PML region without the need of splitting the field in the time domain. Two dimensional numerical examples are included to validate the proposed formulations.The ADI-FDTD method is extended to dispersive media based on the Z-transform method. Two-dimensional ADI-FDTD formulations for dispersive media are derived. And the same time, a method based infinite-impulse response digital filter (IIR) is presented to reduce memory requirements. The proposed method is applicable to arbitrary Mth-order dispersive media. Finally, some examples are calculated, the numerical results of ADI-FDTD for dispersive media are in good agreement with the results obtained by conventional FDTD method, but compared with conventional FDTD method, the proposed method is efficient without requiring additional memory.The ADI-FDTD method is extended to dispersive media—isotropic plasma based on the PLJERC(Piecewise Linear JE Recursive Convolution) method. Two-dimensional ADI-FDTD formulations for isotropic plasma are derived. Two examples are calculated, the numerical results of the ADI-FDTD method for isotropic plasma are compared to those obtained by the FDTD method to show the efficiency of the proposed method. And this method is applied to study the scatteing characteristics of two dimensional, three dimensional unmagnetized plasma.An analytical technique for solving the scattering of an anisotropic nonuniform plasma cylinder is presented. The plasma model chosen for the study is cold, nonuniform, collisional and magnetized. The nonuniform plasma cylinder is represented by a number of concentric cylindrical shells and each has a fixed electron density. The overall density profile follows any prescribed distribution function. The effect of the plasma parameters such as the number of layers, the collision frequency, and the central density on the backscattering cross section is investigated.The JE convolution fmite-difference-time-domain (JEC-FDTD) method is extended to the anisotropic magnetized plasma which incorporates both anisotropy and frequency dispersion at the same time, enabling the transient solution of the electromagnetic wave propagation in anisotropic magnetized plasmas. Two-dimensional JEC-FDTD formulations for magne-tized plasma are derived. The back scattering radar cross section (RCS) of a perfectly conducting cylinder coated by a layer of magnetized plasmas is calculated.The JEC-FDTD method is extended to three dimensional anisotropic dispersive media—magnetized plasma. The problem which incorporates both anisotropy and frequency dispersion at the same time is solved for the electromagnetic wave propagation. The three dimensional JEC-FDTD formulations for anisotropic magnetized plasma are derived. The method is applied to the electromagnetic scattering of dihedral corner reflector and sphere-cone coated with anisotropic magnetized plasma. By simulating the interaction of electromagnetic wave with magnetized plasma, some numerical results are obtained, which indicate that an appropriate plasma coating may efficiently reduce the RCS of a metallic target.As a supplement to the FDTD meshing technique based on solid model, which is not easy to combine with the FDTD program, a new meshing technique based on surface model was put forward. Using this technique, we can mesh most of the target models without caring about what file format they use or where they come from. The electromagnetic characteristics of the three dimensional large complex military objects coated by anisotropic mangtized plasma are investigated. Two models are calculated. They are the missile model and the airplane model coated by anisotropic magnetized plasma.