Study On Absorbers And Multifunctional Devices Based Metasurfaces

Metamaterials are favored by researchers because of their unique electromagnetic properties that surpass natural materials.Its two-dimensional form,metasurfaces,have rapidly developed and became an efficient means of regulating electromagnetic waves in the past few decades due to their compact size,high design freedom,and extraordinary physical properties.Its appearance makes up for the deficiency of the response of natural materials to electromagnetic waves:a thin layer of sub-wavelength structure can achieve perfect absorption of electromagnetic waves and electromagnetically induced transparency effect（EIT）,which overcomes the disadvantages of traditional materials:heavy volume and harsh experimental conditions.Therefore,metasurfaces will have great application potential in the field of electromagnetic field and microwave technology.Such as:metasurface absorbers and metasurface EIT-like effects can be widely used in stealth,modulators,sensors,switches,optical storage and other fields.In this thesis,wide range tunable metasurface absorbers and multifunctional metasurfaces are designed and studied.The main works are as follows:（1）A wide range tunable metasurface absorber based on bulk Dirac semimetal（BDS）and graphene is studied.Simulation results show that dual-peak with more than 90%absorption is achieved at 3.97 THz and 7.94 THz.The absorption frequency can be tuned between 3.97 THz and 9.28 THz by changing the Fermi energy of graphene and BDS,and the two absorption peaks also show the independent characteristics of incident angle and polarization angle.Changing the refractive index around the metasurface reveals that the first absorption peak is unaffected,while the second absorption peak is frequency shifted and has a sensitivity of 2 441 nm/RIU.Therefore,it can be used for anti-interference perfect absorber or refractive index sensor.（2）The graphene-based plasmon induced transparency（PIT）effect is studied.A PIT metasurface composed of graphene split ring resonator and graphene ribbon is designed by means of“bright-bright mode”coupling.The mechanism of PIT generation is described in detail and the reasons for the effects of different structural parameters on PIT are explained.Introducing the coupled oscillator model,it is proved that the increase of graphene Fermi energy enhanced the coupling,broaden transparency window,and also enhanced slow light effect.In addition,remaning the polarization direction of the incident wave unchanged and increasing the incident angle to 30°,the slow light effect is almost affected,and then the slow light effect is gradually enhanced by continuing to increase the incident angle.（3）A bifunctional tunable metasurface is designed for PIT and perfect absorption.On the basis of the previous PIT metasurface,vanadium dioxide（VO₂）substrate is added and the thickness of the dielectric is optimized.The phase transition characteristics of VO₂ is used to realize the switching of bifunctions:perfect absorption with dual-peak is realized when VO₂ is in the metallic state,and the PIT effect is realized when VO₂ is in the insulating state.The dynamic tunable of the two functions can be achieved by changing the graphene Fermi energy.Finally,the sensing properties of the metasurface are investigated:When the PIT function is realized,the sensitivity is 18 219 nm/RIU.When the perfect absorption function is realized,the sensitivities of the two absorption peaks are 20 541 nm/RIU and 23166 nm/RIU,respectively.