Higher Order Anisotropic Impedance Boundary Conditions

Electromagnetic scattering from material coated objects has been an area of indepth research in low detectable techniques for many years. With the development of new materials and applications in electromagnetic area, investigating the electromagnetic scattering characteristics from anisotropic coated targets and optimal designing of multilayer radar absorbing materials (RAM), is becoming an urgent problem in low detectable design for various aero-crafts. In this dissertation, higher order anisotropic/tensor impedance boundary condition (HOTIBC) was derived and applied to anisotropic coated planar, cylindrical or bodies of revolution. The design of optimal RAM for several conical targets was considered.The exact impedance for single and multilayer arbitrary material coated conducting planar and cylindrical surface were build hi spectral domain. Based on approximating the impedance in terms of a ratio of polynomials in the transform variables, the corresponding HOIBCs were given.Adopting the spectral method, the one and two dimensional HOTIBC were derived for single anisotropic and multilayer complex material coated planar structures. HOTIBC's accuracy was improved after optimal method was introduced in the procession. By simulating the impedance and reflection coefficients on the boundary, the accuracy of the presented HOTIBC was discussed.The one dimensional HOTIBC was applied on cylindrical surface with locally planar approximation. The range of HOTIBC's validity and accuracy were discussed by simulating the bistatic RCS of anisotropic and isotropic coated cylinder. Conclusions were drawn out after comparing to the analytical solution.The case of scattering by anisotropic coated three-dimensional bodies of revolution (BOR) is considered. Firstly, the integral equation of anisotropic coated BOR was set up using Green's function in general uniaxial anisotropic material. By testing the equation using Galerkin's method, the exact numerical solution-moment of method (MoM) solution was given. Secondly, the two-dimensional HOTIBC was applied to the anisotropic coated BOR. Solutions for bistatic RCS based on a planar HOTIBC solution were compared to the MoM solution or the Mie series solution in isotropic case. Accuracy and limitations of HOTIBC imposed by the finite radii ofcurvature on the BOR such as sphere, and discontinues surface curvature such as cone-sphere were investigated.Radar Cross Section reduction of canonical conducting target such as planar, spherical and hemi-spherical was considered. The binary genetic algorithm was utilized in the optimization of radar absorbing material for planar multilayered surface. Float genetic algorithm was adopted in the process of optimal design for spherical and hemi-spherical RAM. Three improvements were proposed. That is: coding the chromosome with floating point numbers, selecting different optimal strategy according to the electric dimension of the target, utilizing subsection varying parameter genetic algorithm to avoid trapping in premature convergence. The optimization time was saved significantly after adopting these methods.