Research On Design And Application Of THz Programmable Metasurface Based On Phase Change Materials

The sixth generation of mobile communications(6G)will use the terahertz(THz)band to provide ultra-high-speed data transmission and ubiquitous wireless connectivity.Nevertheless,THz links have the disadvantages of high loss and line-of-sight transmission,communication transmission is greatly limited,so there is an urgent need for a device that implements the function of manipulating THz waves.As a subwavelength two-dimensional structure,the metasurface provides an ideal platform for the implementation of THz technology.However,most previous metasurfaces are designed to manipulate electromagnetic waves by adjusting the structure parameters.The structure is solidified after preparation,which cannot realize dynamic functions such as beam scanning.Therefore,programmable metasurface,i.e.,metasurface combined with tunable materials such as phase change materials,and digitally modulated using field programmable gate array(FPGA),is considered as an effective way to realize 6G wireless communication.Vanadium dioxide(VO2)is a reversible phase change material which can be excited by heat,light and electricity.It has the advantages of fast response speed and large modulation depth.In this paper,we propose two different digital coding and a THz programmable metasurface for broadband modulation based on VO2,and its beam modulation performance is analyzed and verified through simulation and theoretical calculations.The main research contents are as follows:First,two different digital coding VO2 metasurfaces are proposed to manipulate THz waves.In 1-bit coding,π phase difference is obtained before and after the phase change of the metasurface at 0.218 THz;in 2-bit encoding,π/2 phase difference is achieved at 0.220 THz using two units.The THz beam can be diffracted to different angles through real-time dynamic configuration of the coded sequence.Simulation results show that the 1-bit coding metasurface can achieve wide-angle beam modulation from-60° to+60°;the 2-bit encoded metasurface has more freedom in phase control and can double the diffraction efficiency by generating a single deflection angle.This work provides a technical reference for beam ruanipulation devices used for THz communications.Second,a THz programmable VO2 metasurface for broadband beam manipulation is proposed.In the bandwidth of 0.218 THz-0.232 THz,the reflection amplitude of the unit exceeds 0.8 before and after the phase change of VO2,and the phase difference reaches 180°±20°.Simulation results show that by changing the coding sequence,the metasurface can continuously diffract THz beams to different deflection angles within the 14 GHz bandwidth.Among them,the maximum deflection angle can reach 53°.This work provides a potential implementation solution for broadband manipulation of THz waves in 6G wireless communications.