Study Of The Electromagnetic Scattering From The Objects Composed By Metal And Dielectric Materials

Using the accurate and efficient numerical methods to analyze the electromagnetic scattering properties of complex three-dimensional objects has been the focus work in the computational electromagnetics. Most of the practical application of three-dimensional complex targets are not simply made of metal or dielectric, but usually compounded by the metal and dielectric materials, so this dissertation mainly study the methods of computing electromagnetic scattering characteristics from mixed metal and dielectric objects. There are mainly four parts consisted of this dissertation, which are the fast solution for solving volume and surface integral equation, the electromagnetic scattering analysis from mixed metal and complex dielectric objects, the electromagnetic scattering analysis from thin coating objects and high-order Nystrom based volume and surface integral equation method.In the first part of this dissertation, the coupled volume and surface integral equation method for the electromagnetic scattering analysis from mixed metal and dielectric objects is studied. Firstly, the process of establishing the volume and surface integral equations, basis functions for discreting integral equations and the processing means of basis functions at the interface of different materials are studied in detailed. Secondly, the fast multipole method is applied to solve the coupled volume and surface integral equation, which can shorten the calculation time and reduce the computational memory effectively. Finally, according to the characteristic of impedance matrix resulted by volume and surface integral equation, a block matrix preconditioner is proposed. Compared with those traditional preconditioners, the block matrix preconditioner not only can reduce the number of iterations effectively, but also needs less time and memory for the construction.The electromagnetic scattering analysis of mixed metal and complex dielectric objects using the volume and surface integral equation is studied in the second part of this dissertation. Firstly, the volume and surface integral equations for the analysis of mixed metal and several complex materials are introduced. These complex materials include magnetic media and chiral media. The detailed forms of impedance matrix elements resulted by mixed metal and different materials are also given in this part. Secondly, the electromagnetic scattering analysis of metal targets in terahertz and far-infrared bands is studied. Based on the equivalent relative permittivity model of metal in the terahertz and far-infrared bands, metal targets can no longer consider as the perfect electric conductor simply. In this dissertation, the electromagnetic scattering analysis of several different metals is considered using the surface integral equation based on the impedance boundary condition. For the wavelength in terahertz and far-infrared bands is very small and can be comparable with the roughness of the metal surface, therefore the effect of roughness on the metal surface for the electromagnetic scattering analysis is studied.In the third part of this dissertation, the electromagnetic scattering analysis of conductor coated by thin dielectric coating is studied. Firstly, according the facts that the single-layer coating is backed by the metal and the thickness of coating layer is very thin, the tangent component of volume electric current density and vertical component of volume magnetic current density in the coating layer can be neglected, and the relationships between surface current on the metal surface and volume electric current, volume magnetic current in the coating layer are established. Similar to the single-layer coating, a numerical model without increasing extra unknowns for the multilayer coating is proposed, which can be used to analyze the scattering from the both closed and open structures with coatings. The error analysis is also given in this part. Secondly, the numerical model is used to analyze electromagnetic scattering problems when the coating is chiral material. Finally, the numerical model is applied for the electromagnetic scattering analysis of body of revolution. Using the rotational symmetry properties of the objects, the three-dimensional scattering problem can fall into a two-dimensional case, so that it can save computational time and memory.In the fourth part of this dissertation, the electromagnetic scattering problems from mixed metal and dielectric objects using volume and surface integral equation based on the high-order Nystrom method is analyzed. Compared with traditional methods based on the low-order RWG and SWG basis functions, the high-order Nystrom method not only has high-order error convergence, but also shows the grid-roubust ability. A high-order Nystrom solution is used for the analysis of inhomogenous objects based on the curvilinear tetrahedron modeling, and is also used for solving volume and surface integral equation to analyze the scattering problems from mixed metal and dielectric objects. The construction of interplation basis functions and the chosen for polynomial space terms are studied. The impedance matrix elements are given in detail, including the treatment for the singular term.