A Research Of The Tuning Characteristic Of Composite Right/left-handed Metasurface

Metamaterials have opened new research directions in the area of electromagnetic waves,and have offered new approaches of of manipulating electromagnetic waves for various applications.This kind of artificial materials can exhibit exotic electromagnetic properties that do not exist in natural material,making them attractive for both fundamental and applied researches.The composite right/left-handed metamaterial is a novel artificial material which exhibits a unique dispersion with right-handed modes in one frequency band and left-handed modes in another.Besides,it has low lossy and wide bandwidth and has been applied in a variety of novel microwave devices such as guided-wave devices and radiated-wave devices in early works.Recently,this microwave metamaterial was scaled to terahertz and mid-infrared frequency range,based on which several optical devices were reported.To date,most CRLH metamaterial demonstrations have been based on static designs with a fixed static dispersion.Tunable CRLH metamaterial has not yet been realized in optical frequencies including terahertz and mid-infrared region.In this thesis,we demonstrated a mid-infrared CRLH metasurface with tunable dispersion for the first time,which could be useful for beam scanning for a fixed frequency and molecular detection in mid-infrared applications.The main works and achievements are summarized below:Firstly,we designed a new type of tunable CRLH metasurface incorporating phase-change VO₂.The metasurface consists of a top‘H'-shaped gold pad,two dielectric layers of a SiO₂ film and a VO₂ phase-change material,a bottom metallic ground plane.We simulated the structure by using Ansys's high frequency structural simulator?HFSS?in driven mode.The results of our simulations show that the metasurface has composite right/left-handed dispersion,which can be tuned by optical parameters of VO₂.Next,we fabricated the VO2 CRLH metasurface in experiment.The fabrication process includes firstly evaporating thick Cu film on the silicon by using electron beam evaporation,then depositing SiO₂ film on Cu film by using chemical vapor deposition,and then depositing VO₂ film on the SiO₂ film by reactive magnetron sputtering method,finally fabricating an array of‘H'-shaped Au antennas standard electron-beam lithography.The SiO₂ thick film is used to facilitate the adhesion of VO₂ film on Cu film.Finally,characterized the VO2 CRLH metasurface,and revealed the tunable CRLH mode dispersion..The absorption of our metasurface was characterized with angle-variable Fourier transform infrared?FTIR?reflection spectroscopy.After analyzing the reflection spectrum,we confirmed that the CRLH modes of the metasurface work in the range of 23 THz³1.1 THz.Because of the reflection dips of right-handed mode and left-handed mode partly overlaps,we used two Lorentz line-shaped functions to fit the spectra and extracted the two modes.To study tuning property of the metasurface,we thermally triggered the VO₂ insulator-to-metal phase transition and measured the reflection spectra at different temperatures.The dispersion at each temperature was extracted,which is in agreement with theoretical calculations.Besides,we fitted the measured dispersion curves with a loss-less circuit mode,which shows that the circuit parameters can be tuned by temperature.The extracted variable lumped capacitance elements intuitively explain the physical mechanism of the tunability.