Study On Metamaterial Absorbers Based On Graphene Disks

Electromagnetic metamaterials refer to artificial composite materials with extraordinary electromagnetic properties that natural materials can not achieve,such as left-handed materials and photonic crystals.Electromagnetic metamaterials have important applications in electromagnetic stealth,integrated optics and optical sensing by manipulating electromagnetic waves.Its electromagnetic properties is closely related to its shape structure,geometric parameters and material types.It has great operability and can be widely and deeply applied in many modern fields.Electromagnetic absorber is one of the important application fields.However,the traditional metamaterial absorbers' electromagnetic properties will not change after the physical shape and geometric parameters of its unit cell was determined,which leads to a great limitation of metamaterials' application.Therefore,It has become an inevitable trend in the development history of metamaterial to design a perfect metamaterial absorber with dynamically tunable electromagnetic properties and large modulation depth.The electrical conductivity of graphene can be adjusted by applying an voltage,its convenience has gradually entered the view of researchers,which brings significant advantages to the research of metamaterial absorbers in terms of absorption frequency,absorption peak,physical parameters,etc.At the mean time,It also has great potential for future applications.Therefore,the study of tunable metamaterial absorbers with simple structure,which can achieve single-band,multi-band and broadband absorption,has attracted great attention.Based on graphene disks,this paper has proposed two metamaterial absorbers,"gourd-shaped" and "petal-shaped",which can achieve perfect dual-band absorption by using the combination of graphene disks.This paper includes the following research contents:A "gourd-shaped" graphene metamaterial absorber was investigated.Firstly,under the same initial simulation conditions,the absorption peaks and corresponding resonant peak frequencies generated by disks with different radiuses are calculated.Next,according to the simulation calculation results of a single disk,two suitable disks are selected and combined into a metamaterial absorber with a surface shape of "gourd type".The calculation results have showed that at the resonant frequencies of 4.71 THz and8.97 THz,perfect absorption with absorption peaks reaching more than 99.9% has showed up.At the same time,the absorber can change the Fermi level of graphene by applying an voltage to achieve dynamic tunability of the absorption band.The study also found that the absorber can maintain high absorption in a large range of incident angles,and due to the anisotropy of the "gourd-shaped" graphene surface,the absorption band of the absorber also can be tunable by rotating the polarization angles.it has the characteristics of polarization sensitivity.Based on the previous research on the combination of two graphene disks into a "gourd-shaped" graphene metamaterial absorber,three graphene disks were further combined into a "petal-shaped" graphene metamaterial was studied.The calculation results have showed that under the TE wave and TM wave incident modes,not only can the absorber achieve dynamic tunability of the resonant peak frequency and absorption peak by changing the Fermi level and relaxation time of graphene,but also Operates over a wide range of incident angles.it is polarization insensitive,and can achieve high absorption over a wide range of polarization angles,with minimum absorption peaks exceeding 94% in both incident modes.Therefore,according to the polarization angles and the incident angles,a wide range of high-efficiency absorption can be achieved.In conclusion,the two shapes of graphene metamaterial absorbers that proposed in this paper have simple structures,can achieve perfect double-band absorption,and have flexible tunability,so the absorber have potential applications in sensors,optical switches,and stealth.