Study On The Multi-band Terahertz Absorber Based On Graphene Metamaterial

Metamaterials are composite materials that have artificially designed structures and exhibit extraordinary physical properties not found in natural materials.The use of metamaterials can achieve arbitrary "cutting" of electromagnetic wave performance,and thus can obtain strange electromagnetic properties such as negative refractive index,perfect lenses,and invisibility cloaking.In recent years,terahertz perfect absorbers based on graphene metamaterials have attracted widespread attention from researchers.Compared with traditional metal metamaterials,the most fascinating feature of graphene metamaterials is that they can actively tune their electromagnetic properties through external excitation,thereby achieving tuning of absorption performance.However,how to design a graphene metamaterial terahertz perfect absorber with multi-band,simple structure,flexible tuning way and wide tuning range is a challenge.In this paper,multi-band and dual-broadband terahertz absorbers based on patterned and unpatterned graphene metamaterials are designed,and their absorption characteristics are analyzed through software numerical simulation.The main research contents are as follows:1.The terahertz metamaterial absorber based on patterned graphene.Firstly,a dual-band terahertz absorber based on disk-and ring-shaped graphene stacked.Numerical simulation results show that the absorber achieves near perfect absorption at4.58 THz and 7.89 THz.Benefiting from the optical response of the two layers can be separated,the Fermi energy of each layer of graphene can be adjusted by applying an external voltage to achieve active and independent adjustment of the two absorption peaks,corresponding frequency shifts of 29.5% and 54.1%.In addition,the absorber is insensitive to the polarization direction of the incident light.Under TE and TM polarization,the absorption remains above 90% at the incidence angle of 0o~50o.secondly,the four-band and dual-broadband absorber based on multi-size disk-and ring-shaped graphene structure stacked.Based on the study of the above mentioneddual-band terahertz absorber,two sizes of disk-and ring-shaped graphene are combined to form a symmetrically distributed supercell structure.The simulation results show that the structure has four absorption peaks with absorption than 90%.Further,by changing the geometry of the disk-and ring-shaped graphene.The two low-frequency and high-frequency absorption peak of the four-band absorber are merged,respectively.This achieves dual-broadband absorption with bandwidths of 0.39 THz and 0.48 THz,respectively.Finally,the Fermi level of graphene is tuned to achieve broadband tunability.2.The terahertz absorber based on unpatterned graphene.It consists of a four-layer structure of "cross" dielectric,single layer of complete graphene,dielectric layer,and metal substrate.We can observe resonance peaks at 1.25 THz and 2.81 THz,and their absorption rates are 97.81% and 97.96%,respectively.The absorption mechanism is discussed through the principle of impedance matching and the distribution of the electric field.It is shown that the entire dual-band absorption spectrum is the combined effect of multiple resonance modes.The Fermi level is adjusted from 0eV to 0.8eV by applying an external bias voltage,and the low-frequency and high-frequency modulation depths reach 66.16% and 80.78%,respectively.In addition,it achieves the switch from perfect absorption of single band to perfect absorption of dual-band.