Theoretical Study On Terahertz Surface Wave Propagation Characteristics Of Metamaterial And Design Of Absorber

Electromagnetic metamaterials,as a new kind of artificial materials,have attracted more and more attention because of the unique electromagnetic properties and the structure that can be designed according to the requirements.The absorption mechanism and boundary conditions of electromagnetic metamaterials due to their properties allow different theoretical approaches to the study of electromagnetic phenomena near metal structures,especially the generation of surface plasmon polaritons（SPP）and the propagation of surface waves.Therefore,the study of surface waves has become a hot spot.Graphene can be a good substitute for metal conductors because of the metal-like properties.The devices combined with graphene and electromagnetic metamaterials have excellent functions and adjustability because the surface conductivity of graphene can be adjusted by chemical potential.Moreover,the special properties of electromagnetic metamaterials greatly enhance the absorption capacity of electromagnetic waves,and can effectively reduce the thickness of the absorber and optimize its structure.At the same time,electromagnetic metamaterials have been widely applied in the field of wave absorbing materials due to the proposed"perfect absorber"structure and the insensitivity of incident and polarization angles.The main work of this thesis is as follows:1.The propagation of surface plasmon polaritons over a graphene-covered metamaterial interface in the terahertz（THz）range has been investigated.The characteristic equation is derived from the electromagnetic field equation and impedance boundary conditions.The variable parameters are obtained by lossy dispersion rather than constant.The propagation behavior of surface wave can be well explained by numerical analysis.The results show that the propagation characteristics of surface plasmon polaritons can be adjusted by changing the bias voltage to change the chemical potential of graphene.The propagation length can be changed by regulating the chemical potential of graphene,but the total energy flux is not sensitive to the chemical potential.We have also compared the numerical results with the simulation,and proposed a new model to describe the excited electric field,which is more accurate than the previous theory.2.A new design of a tunable broadband THz metamaterial absorber（MMA）is proposed.The absorber has a sandwich-shaped structure with a metal pattern surface arranged periodically,a medium layer of dielectric that consumes energy,and a vanadium dioxide（VO₂）square ring layer at the bottom.The absorptivity can be adjusted through the conductivity of VO₂ which is controlled by the temperature,and the effective absorption bandwidth of 0.9 THz can be obtained at the optimum condition.The energy absorption mechanism was investigated by the study of the distribution of electromagnetic field and loss.The influence of the structure parameters of VO₂ square ring on the absorptivity was also investigated,and the insensitivity of the incidence and polarization angle of the MMA was discussed.The size of proposed MMA is small and structure is simple,with thickness of 6.85μm.The proposed absorber can be applied to a wide range of applications and provides a new idea for the subsequent research of similar structures.