基于二氧化钒的太赫兹双频多功能编码超表面

Vanadium dioxide based terahertz dual-frequency multi-function coding metasurface

提出了一种基于二氧化钒且工作频段可切换的太赫兹编码超表面.该编码超表面由金属-二氧化钒复合层、聚酰亚胺介质层、金属反射层构成,主要通过对顶层双裂环谐振器和十字结构的参数进行设计,获得其所需的性能;而二氧化钒材料的引入,巧妙地使其可工作于双频点,进而实现不同功能的切换.仿真结果表明:当二氧化钒处于绝缘态时,在f1=0.34 THz的圆极化波垂直入射下,设计的编码超表面可以视为3-bit Pancharatnam-Berry相位编码超表面,通过对单元中双裂环谐振器设计卷积编码序列,使该编码超表面具有以特定角度出射拓扑荷数l=±1涡旋波束的功能;当二氧化钒处于金属态时,在f2=0.74 THz的正交线极化波垂直入射下,设计的编码超表面可以视为2-bit各向异性编码超表面,通过对单元中十字结构分别设计随机编码序列和棋盘格编码序列,使该编码超表面具有雷达散射截面缩减和波束分束的功能.其可为太赫兹电磁超材料多功能器件的设计提供一定的参考.

Terahertz(THz)wave has the advantages of low photon energy,high resolution,large communication bandwidth,etc.It has broad application prospects in security detection,high-resolution imaging,high-speed communication,and other fields.In recent years,as a new way to control THz wave,THz metasurface functional devices have attracted extensive attention of researchers.In this work,vanadium dioxide(VO2),a phase change material,is introduced into the coding metasurface.By regulating a circularly polarized wave and the orthogonal linearly polarized waves independently,a multi-function coding metasurface that can work at dual frequency points is obtained.It is composed of three layers.The top layer is a metal-VO2 composite structure.The middle is a polyimide dielectric layer.The bottom is a metal ground.Under certain conditions,the double split ring resonator(DSRR)and the cross structure in the top layer are relatively independent.Designing the coding sequences for them enable the coding metasurface to have multiple functions.The electromagnetic simulation software CST is used to establish model and conduct simulation,and the obtained results are as follows.When the VO2 is in an insulating state and a circularly polarized wave at 0.34 THz is incident vertically,the characteristics of coding metasurface elements are mainly affected by the DSRR.The DSRR is rotated to meet the requirements of 3-bit Pancharatnam-Berry phase coding.The coding sequence is designed to generate vortex beams with the topological charge l=±1 at a specific angle.The VO2 state is changed into a metallic state,and the DSRR can be equivalent to a metal ring.When the orthogonal linearly polarized wave at 0.74 THz is incident vertically,the characteristics of coding metasurface elements are mainly affected by the cross structure.Because of its anisotropy,four different 2-bit coding metasurface elements can be obtained respectively by changing the length of the horizontal arm and the vertical arm.The design of appropriate coding sequences can reduce the radar cross section of the x-polarized wave and the beam splitting of the y-polarized wave,and the results have broadband characteristics.Multiple coding sequences can be designed by special characteristics of the coding metasurface,then various expected functions can be realized on the same metasurface.It solves the problem of single function of ordinary metasurface devices to a certain extent,and paves a novel way to the development of THz multi-function systems.