【作者】 吴松；

【导师】 江建军；

【作者基本信息】 华中科技大学 ， 微电子学与固体电子学， 2019， 博士

【摘要】 石墨烯基频率选择表面(GFSS)在智能电子、隐身材料、光电器件等领域具有广泛的应用前景。本研究系统地从理论上研究了GFSS吸波体和极化器的电磁响应机制及其电磁特性数理模型,结合全波电磁仿真法、理论解析法和等效电路法,构建了GFSS吸波体和极化器的研究理论框架和分析方法。应用建立的数理模型,分别针对微波段与太赫兹波段,设计了GFSS表面电导率型吸波体、GFSS介质型吸波体和GFSS表面电导率型极化器。本研究主要研究结果如下:首先,从理论上建立GFSS表面电导率和等效介质电磁参数数理模型。根据数理模型讨论了GFSS的静电场和静磁场偏置效应,研究发现GFSS可以动态控制电磁波响应,为实现电磁波智能控制设备提供了潜在的可能。对GFSS进行静电电场偏置可以改变石墨烯化学式cμ,从而改变GFSS的阻抗特性实现对电磁波的频率或幅度的可调谐。对GFSS静磁场偏置可以改变石墨烯的主对角线和次对角线电导率分量实现对电磁波的极化可调谐性能。其次,根据GFSS数理模型探究了GFSS的电磁吸收和电磁极化调控特性。应用GFSS表面电导率模型,设计并研究了一种宽带GFSS表面电导率型吸波体,通过传输矩阵法(TMM)研究发现改变石墨烯的表面电阻可以使吸波体在2.2～14.5 GHz实现动态可调谐。应用GFSS等效介质模型,设计并研究了一种GFSS介质型吸波体,通过全波电磁仿真方法研究发现改变石墨烯的化学式cμ,在1.7～4.5 THz可以动态调谐吸波体的吸收强度和带宽。应用GFSS表面电导率模型,设计并研究了一种工作在2.7～3.5 THz的宽带GFSS表面电导率型极化器,通过等效电路法研究发现单层极化器的最大能量转换效率为50%,还发现通过单层极化器的合理堆叠可以大幅度提高极化器的能量转换效率。第三,本研究提出了广义传输矩阵法(TMM)来分析单层或多层GFSS吸波体,结构的每一层可以单独用一个多维传输矩阵表征和分析,该层相对于入射波的反射、透射和阻抗特性嵌入在矩阵内。结构的总体特性表征可以通过级联各层的传输矩阵而获得。应用TMM理论解析方法,计算出GFSS吸波体的每一层及其组合的阻抗特性,结合史密斯圆图在同一个图中简单直观地显示阻抗特性和反射系数,这种图解的方式提供了直观的物理图像和指出了到达匹配中心点的路径。最后,研究了电磁波斜入射问题,并提出了改善斜入射性能的方法。研究发现斜入射下电磁波谐振频率向高频移动,并且电磁波的匹配特性变差导致电磁器件性能变差。在周期阵列之间或者周期表面与金属之间加载一层介质可以将工作谐振频率从高频拉回到低频,起到稳定工作频率的作用。在周期阵列的外层加载一层厚度为λ4或稍大一点的介质板,作为四分之一波长的阻抗变换器起到大角度范围内带宽恒定的作用。因此,所提出的稳定斜入射的方法对GFSS工程应用具有一定的实际意义。理论研究表明,本研究所提出的GFSS电磁参数数理模型可以指导GFSS吸波体和极化器设计。GFSS吸波体和极化器设计的电磁建模与分析理论研究为GFSS在电磁领域的应用奠定基础。更多还原

【Abstract】 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 potentialcμ,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 potentialcμ 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 λ4 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.更多还原