Applications Of Metamaterials In Electromagnetic Wave Absorption And Helical Beam Generation

Metamaterials,defined as artificial engineered materials with particular characteristics which are not found among natural materials,have been a hot research topic in recent years.Metasurface is regarded as the two dimensional form of metamaterial,which has been considered to be an important extension of metamaterial.Metasurface has been widely used to control electromagnetic wave-fronts arbitrarily by manipulating subwavelength artificial unit-cells.Due to the advantage of designability of electromagnetic parameters,many practical devices based on metamaterials have been proposed,including both for civil and military applications.Among them,the emergence of the electromagnetic absorbers based on metamaterial has been wildly concerned.In this thesis,researches on water-based broadband metamaterial absorbers have been carried out.In the meantime,we also propose and experimentally demonstrate a metasurface for the generation of helical beam.The contents are arranged as:1.We analyze the dielectric permittivity and loss tangent of water in microwave frequency domain.A novel water-droplets-based metamaterial absorber is proposed,which is based on the periodic dielectric holes filled with water.And it is demonstrated that the absorption performance can be tuned by manipulating the volume of the water droplets.In addition,we also design a water-column-based metamaterial absorber.The structure and principle of the design are analyzed in detail.The absorption performances of the proposed water-based broadband metamaterial absorbers both have been simulated and experimentally demonstrated at microwave domain.With the merits of excellent absorption performance,low profile,easy fabrication,the proposed designs may be a promising opportunity to achieve novel broadband absorbers.2.Based on the theory of orbital angular momentum,we propose a reflective metasurface which can generate helical beam.The design has been verified by both simulation and experiment.The proposed metasurface can convert the incoming plane wave into a helical beam with topological charge of l=1 at 10 GHz.The presented reflective metasurface may pave a new way to generate the helical beams for microwave communication applications.