Research On Terahertz Wave Control By Multi-bit Coding Metasurfaces

Nowadays,the research on coding metasurfaces is increasingly fierce.For the design of coding metasurface unit cells,patterned metal is generally used as the surface layer to provide varying phases.In order to achieve real-time control,a new method of combining an electronic control element such as a diode with a metal patch into an adjustable unit.However,considering the characteristics of the terahertz band and the complexity of actual experiments,this paper introduces graphene as a tunable material on the basis of metals.Combining the theorem in digital signal processing with the coding sequence of coding metasurface,several new methods of coding metasurface are designed.First,based on the theoretical guidance of coding metasurfaces,this paper proposes a multi-bit coding metasurface based on metal patches.In the study of the 1-bit coding,it was found that X_m and Y_n encoded in only one direction can generate two beams of axisymmetric waves,and X_mY_n encoded in both directions can generate four beams of centrally symmetric reflected waves.Research on the different values of m and n for X_mY_n shows that the azimuth?can be changed with different periods.In the study of higher-bit coding metasurfaces,it was found that both 3bit and 2-bit coding can generate a single beam of deflection wave,and 3-bit coding refines the control of?by 2-bit coding.Secondly,in response to the problems faced by metal patches,this paper proposes a new tunable coding metasurface on an uneven substrate based on graphene.In the research of 1-bit coding,two methods for constructing 1-bit coding unit are proposed for the first time.One is to use the substrate thickness H as a variable,and the other is to use the Fermi level E_f as a variable.The first method is when the Fermi energy level is changed from 0.85e V to 0.05e V,the frequency band can be changed from3.4THz?4THz to 6.5THz?9.2THz in real time.In the 2-bit coding,the convolution of the deflection waves in two directions finally realized the expansion of the azimuth?of the reflected wave.Finally,this paper combines metal and graphene to design a new broadband tunable coding metasurface based on metal and graphene.In the research of 1-bit coding,the real-time adjustment of the broadband frequency band of four continuous working frequency bands is realized.2-bit coding studies the influence of periodicity,and the convolution calculation is used to realize the 360°real-time adjustment of the single beam deflection wave?.At the same time,comparing the deflection of 3-bit coding to any reflected wave with 2-bit coding,the results show that any reflected wave can be almost lossless after being deflected.