Design And Study Of Broadband High Anti-reflection Meta-surface Based On Cone-shape Multilayer Structure

Meta-material is an artificial material with some special properties that do not exist in nature materials. They were made up by metal/ dielectric sub-wavelength micron/nanostructures, and their electromagnetic properties could be manipulated via the geometry and constituent components. Perfect absorbers based on meta-material could have a near 100% absorptivity in THz, infrared and the visible. Those special electromagnetic behaviors had attracted a lot of interested over the past decade. Unfortunately, narrow-band was not overcomed in previous results. Absorber with this disadvantage would reflect large part incidence energy, so it can not be applied to devices like solar cells which need high-band absorptivity. In this thesis, we take advantage of both the transverse and the longitudinal planes as the design degree, and propose a cone-shaped multilayer anti-reflection meta-surface. It is shown that it forms a broad-band, polarization independent effect, with incident angle up to 45. This thesis provides interpretation for the underlying mechanisms.This thesis has firstly studied common perfect absorbing property of transverse structures. The purpose is to know how perfect absorbtion happens, and how the resonant wavelength could be turned. Based on that, we design a cone-shape meta-surface structure composed of alternating metallic and dielectric multi-layer thin films along z axis. We use the finite element method(FEM) to calculate the reflectance spectrum. It is shown that the meta-surface supports ultrabroadband reflection spectrum. Effective medium theory(ETM) is applied to justify the results.To know the deep physical meaning of the above phenomenon, electric field, magnetic field, and Poynting vector of the cone-shape meta-surface structure have been examined for normal incidence. It is found that localized surface plasmon resonance, cavity resonance, and slow light effect, collectively lead to the ultrabroadband anti-reflection. It is further shown that the reflectance changes slightly when the angle and polarization of incidence light changes. Therefore, the cone-shape meta-surface structure is polarization-insensitive and has large incident angle tolerance, up to q=45 comparing with flat multilayer structure and cylinder meta-surface structure. The influences on the reflectance by the period of unit cell, the whole height of the unit cell, and the ratio of the height of metal and dielectric layers are provided.