Design Of Low-Scattering Metasurface Based On The Optimization Method

Metamaterials are artificial periodic structures composed by subwavelength electromagnetic resonators. Metamaterials have unusual constitutive parameters such as negative permittivity and permeability, which has become generally acknowledged by researchers. One important application of the metamaterials is to achieve electromagnetic invisibility or transparency, which can greatly reduce the radar cross section (RCS). In this thesis broadband low-scattering metasurface is designed based on the electromagnetic diffusion, which can provide additional surface reactance in order to generate different phase distribution. Due to randomly-distributed phase at the metasurface, the diffusion will occur for normal or oblique incidence, thus greatly reducing the RCS. Based on the theoretical derivation, numerical simulation and experimental test, we show the metasurface scatters the incident wave in off-normal or off-specular directions. The main contents and contributions of the thesis are as follows:(1) Several technologies on RCS reduction are discussed, and the mechanism of low-scattering metasurface is also presented. The limitation on the bandwith of metasurface is analyzed, and the factors to improving bandwith of unit are proposed. A metasurface for RCS reduction has been proposed, which is composed of double rings. By tailoring the phases of unit, the metasurface shows excellent scattering-suppressions as expected.(2) A new method to design metasurface for RCS reduction is proposed, where the particle swarm optimization and target’s RCS analysis are combined to achieve RCS reduction. This hybrid optimization algorithm greatly reduces the simulation costs compared to commercial software. The windmill shaped structure is selected as the basic element in order to improve bandwith. Full-wave simulation and measured results demonstrate that the metasurface can effectively decrease the backward scattering from 7 GHz to 14 GHz, which is important for stealth applications in the future. The results demonstrate the validity of hybrid optimization algorithm in designing low-scattering metasurfaces.