Electromagnetic Characteristics Modeling And Theoretical Analysis Of Graphene-based Frequency Selective Surfaces For Wave Absorbers And Wave Polarizers

Graphene-based frequency selective surface,denoted as GFSS,has broad application prospects in the fields of intelligent electronics,stealth materials,and optoelectronic devices.In this dissertation,the electromagnetic response characteristics mechanism of GFSS wave absorber and wave polarizer and its electromagnetic characteristic mathematical model were extensively investigated.Combined with full-wave electromagnetic simulation,theoretical analytical method,equivalent circuit method,and their theoretical framework and analysis methods for wave absorbers and wave polarizers were put forward.By establishing a reasonable mathematical and physical model by way of appropriate analytical methods,GFSS surface conductivity type absorber,GFSS medium type absorber and GFSS surface conductivity type polarizer are designed over the range of microwave and terahertz band.The main results of overall investigations are outlined as follows:At first,GFSS surface conductivity and equivalent medium electromagnetic parameters were theoretically established.According to the mathematical and physical modeling,the electrostatic field and static magnetic field bias effects of GFSS are discussed.It is found that GFSS can control dynamically the electromagnetic wave response,which provides potential possibilities for implementing electromagnetic wave intelligent control equipment.Electrostatic field biasing of the GFSS can change the graphene chemical potentialc?,thereby changing the impedance characteristics of the GFSS to achieve tunability of the frequency or amplitude of the electromagnetic wave.The GFSS static magnetic field bias effect can change the main diagonal and sub-diagonal conductivity components of graphene to achieve polarization tunability of electromagnetic waves.Secondly,according to the GFSS mathematical and physical modeling,the electromagnetic absorption and electromagnetic polarization control characteristics of GFSS are extensively explored.A broadband GFSS surface conductivity type absorber was designed by using GFSS surface conductivity modeling.It was found by transfer matrix method(TMM)that changing the surface resistance of graphene can make the absorber continuous dynamical tunable in 2.2 ? 14.5 GHz.A GFSS medium-type absorber was designed by GFSS equivalent medium modeling.The full-wave electromagnetic simulation method was used to study the chemical potentialc? of graphene.The absorption intensity and bandwidth of the absorber can be dynamically tuned at 1.7 ? 4.5 THz.A wideband GFSS surface conductivity type polarizer operating at 2.7 ? 3.5 THz was designed by using GFSS surface conductivity modeling.The maximum energy conversion efficiency of single layer polarizer was found to be 50% by equivalent circuit method.It has also been found that the energy conversion efficiency of the polarizer can be greatly improved by reasonable stacking of the single layer polarizer.Thirdly,a generalized transfer matrix method(TMM)to analyze single-layer or multilayer GFSS absorbers were extensively described.Each layer of the structure can be characterized and analyzed by a multi-dimensional transmission matrix.The reflection,transmission and impedance characteristics of this layer relative to the incident wave are embedded in the matrix.The overall characterization of the structure can be obtained by cascading the transmission matrix of the layers.TMM is a theoretical analytical method that can calculate the impedance characteristics of each layer and its combination.The Smith chart is used to simply and intuitively display the impedance characteristics and reflection coefficients in the same graph.This graphical approach gives an intuitive physical picture and optimum solution to focus on impedance matching toward the center point of Smith chart.Finally,the problem of oblique incidence of electromagnetic waves is explored,and a method to improve the oblique incidence performance is presented.It is found that the resonant frequency of the electromagnetic wave moves to a high frequency under oblique incidence,and the impedance matching properties of the electromagnetic wave become mismatch,resulting in deterioration of the performance of the electromagnetic device.Loading a layer of dielectric between the periodic arrays or between the periodic surface and the metal can pull the operating resonant frequency from the high frequency back to the low frequency to stabilize the operating frequency.A dielectric plate having a thickness of ?4 or slightly larger is applied to the outer layer of the periodic array as a quarterwavelength impedance converter for a constant bandwidth over a wide angle range.Therefore,the proposed method of stabilizing oblique incidence is of great significance for GFSS engineering applications.The systematic theoretical studies show that the GFSS electromagnetic parameterization modeling can give a guideline for the design of GFSS wave absorbers and wave polarizers.The theoretical framework and technique of electromagnetic characteristics modeling and analysis of GFSS absorbers and polarizers has laid the foundation for the application of GFSS in the defense field.