Study On Tunable Electromagnetic Absorbers Based On Graphene Metamaterials

Matematerials are a kind of artificial structure based compound materials with extraordinary electromagnetic properties,made by designing the key physical dimensions.The unusual electromagnetic properties of metamaterials are closely related to their artificial unit structure,arrangement and geometry size,thus they have extremely high design flexibility.Due to their singular characteristics,electromagnetic metamaterials have been fully applied in electromagnetic stealth,antenna,super-resolution imaging,microwave devices.Electromagnetic absorber is one of the important application fields.However,the electromagnetic properties of metamaterials will not change if the shape and physical dimensions of their unit structures are determined,which leads to the limitations of metamaterials in practical applications.Therefore,how to realize the dynamic adjustment of electromagnetic properties has become a hot spot in the research of metamaterials.The conductivity of graphene can be controlled by applying a voltage,which has caused great attention in the application of tunable metamaterials.The introduction of new materials graphene has brought new developments in electromagnetic absorbers in terms of absorption frequency and geometric size.Based on this,we propose two kinds of metamaterial absorbers with different structures to achieve single-frequency perfect absorption and double-frequency perfect absorption respectively.We use CST software to simulation analysis of the absorption characteristics of the absorber.This article contains the following two works:1.Study on absorption characteristics of single-frequency graphene absorber.The calculation results show that the structure has an absorption rate of 99.9% at the resonant frequency of 4.7 THz,that nearly achieved perfect absorption.The Fermi level of graphene can be controlled by applying a voltage,thus realizing the dynamic adjustment of the frequency of the metamaterial absorber.Studies have shown that when the length L in the X or Y direction changes,the absorption curve shows polarization sensitivity due to the symmetry of the entire structure is destroyed.In the TE and TM modes of the incident wave,the absorber has a high absorption rate in the range of 0°to 70°,which has high practical value in reality.2.Study on absorption characteristics of double-frequency graphene absorber.Firstly the resonance frequency generated by each size disk is calculated,and it is concluded that the overall dual-frequency absorption is superimposed by these resonance frequencies.Therefore,two nearly perfect absorption peaks are obtained at the resonance frequencies of 7.1 THz and 10.4 THz.The resonance frequency can be effectively tuned via controlling the graphene Fermi level;The absorber can achieve selectively frequency tunability and it can tune each resonance frequency independently by changing the radius of the disks.When the four surrounding graphene disks move on the diagonal of 2.0μm ?? d1μm,there is no significant invariant on the absorption frequency and intensity of the absorber.When the dielectric constant of the dielectric layer is changed in the study,the resonance frequency will shift and the absorption rate will not change significantly.Since the cell structure is symmetrical,the absorber exhibits polarization insensitivity.At the same time,the absorption rate of the proposed absorber is still high at an incident angle of 70°.