Research On Tunable Absorber And Polarization Converter Based On Graphene Metamaterial

Graphene is a two-dimensional material which consists of one unique monolayer of carbon atoms arranged in a hexagonal lattice,it has excellent and unique properties in terms of electrical,mechanical and thermal properties and it also plays an important role in materials and physics.Graphene has been widely used in the optoelectronic equipment with its own special properties,making the miniaturization and integration of optoelectronic devices a reality.Meanwhile,graphene has been widely applied in different fields,especially in tunable absorbers,modulators,converters and other adjustable devices which operate in frequencies ranging from terahertz to infrared ranges,because it has the ability to support propagation of surface plasmon polaritons and tunable conductivity.With the rapid development of electromagnetic stealth technology,the research of absorber with tunable characteristics and polarization converter has important research value and application prospect.On the basis of the tunable material properties,this paper will propose several tunable absorbers and converters to study their characteristics.The main research contents of this article are demonstrated as follows:1.We briefly introduce the application background of electromagnetic stealth technology,introducing graphene materials from Electromagnetic materials and the excellent properties of graphene,and conducting electromagnetic characteristics of graphene.The structural design of traditional metamaterial-based absorbers and polarization deflectors are reviewed.Apart from that,the current research status of the absorbers and polarization converters based on graphene-based is introduced,and the theoretical model for designing graphene-based optical devices is also summarized.2.We numerically demonstrate a novel route to effectively enhance multi-band terahertz absorption enabled by a variety of tunable polarization-insensitive multiband terahertz absorbers based on composite graphene and metal microstructures.By setting the proper height of the dielectric spacer between graphene and metal reflector.It is interesting that all absorbers exhibit exactly the identical absorption properties regardless of the shapes of microstructures.The absorption band of the absorber also shows obvious independence under normal incident polarization,and the absorption peak can be flexibly adjusted by changing the chemical potential of graphene.Through the analysis of interference theory and effective impedance matching theory,the inherent physical laws of the graphene plasmon enhancement effect are explored.Based on the electric field distribution of the graphene layer,the principle of multi-band absorption of the absorber is analyzed,In addition,we figure out the relationship between the absorptivity of terahertz absorbers,polarization,and angle of incidence,and also study the graphene in terms of its the adjustable absorptivity and the chemical potential of graphene.3.We have proposed and numerically demonstrated two novel terahertz absorbers,Simulation results show that the proposed absorber has a terahertz absorption with a narrow-band near unity,ultra-wide frequency reconfigurability,and angular stability.We first study the terahertz absorption spectrum,frequency reconstruction,and angular stability of a single-layer graphene array based absorber.Then,in order to achieve a wider frequency reconstruction range,we propose a double-layer graphene band array absorber and study its performance.By using a double-layer graphene structure of the absorber,the tuning frequency range can be significantly increased.Finally,an analytical fitting model was proposed to accurately predict the reconfigurable absorption peak frequency of this type of absorber.Besides,the effective impedance matching theory is used to explain the absorption mechanism of the absorber,and the absorption principle is demonstrated in the combination of the electric field distribution.At the same time,we also discuss the dependence of the incident angle,the polarization method,as well as the dependency relationship between the graphene chemical potential and the absorption.4.We design two tunable reflective cross-polarization converters,which are dualband and wide band reflective cross-polarization converter.The proposed reflective cross-polarization converter can convert the polarization state of the incident wave from a linear polarization state to a cross-polarization state at the operating frequencies and the efficient polarization conversion rate(PCR)is up to 100%.In addition,Through the combination of theoretical analysis and numerical simulation,the new structure of graphene polarization converter with plasmon enhancement effect is explored.In addition,we study the internal principle of polarization conversion,the structure size,incidence method,graphene effect of chemical potential and relaxation time on conversion characteristics.The results of this paper verify the effectiveness and feasibility of the graphenebased tunable absorber and polarization converter in the field of electromagnetic stealth by combining theoretical analysis with numerical simulation,which is of great significance for further research on various stealth technologies.