Researchon Tunable Bifunctional Metasurfaceabsorber/Converter With Graphene/VO₂

Metasurface is a two-dimensional artificial metamaterial with the advantages of thin thickness,small volume and high integration.Rapid progress has been made in the realization of electromagnetic regulation such as absorption,polarization conversion and imaging.However,the traditional metasurface function is fixed,the working bandwidth is narrow,and the frequency offset is prone to occur,which cannot be flexibly adjusted according to the demand,which limits its application scenarios in practice.In view of the above problems of fixed functions and narrow working bandwidth,this thesis proposes two function-switchable metasurfaces based on vanadium dioxide(VO2)and graphene,one realizes broadband polarization conversion and broadband absorption switching based on VO2,and the other realizes the switching of dual-band absorption and broadband absorption based on VO2 and graphene.The main research contents are as follows:1.A dual-function ultra-thin metasurface with broadband polarization conversion and broadband absorption switching is designed.The metasurface consists of gold-VO2 resonators located on the same plane.When the temperature of VO2is increased from room temperature to 68℃,the switch between polarization conversion and broadband absorption is achieved.The physical mechanism of this metasurface is elaborated by eigenmode decomposition,current electric field distribution and impedance matching theory,and its operating performance shows good robustness at wide incidence angles.The proposed metasurface only uses VO2 as a phase change material,which reduces the thickness of the metasurface,and the tuning method is simple and flexible,and the working bandwidth is also improved while the dual-function is guaranteed,which has potential application prospects in switches,absorbers,polarization converters and isolators.2.A frequency-bandable terahertz absorption metasurface based on VO2 and graphene hybrid materials was designed.When VO2 is in the insulating state and graphene is in metallicstate,the absorption rate of the absorber reaches 97.65%and 98.07%at 1.34 THz and 2.84 THz,respectively,which realizes the function of dual-band absorption,and the regulation of the dual-band absorption band and absorption intensity can be realized by adjusting the Fermi energy level and relaxation time of graphene.When VO2 is in a metallic state and graphene is in insulating state,the absorption rate of the absorber exceeds 90%in the 4.44～11.97 THz frequency band,and the relative bandwidth is 91.77%,which realizes the function of broadband absorption,and can still maintain good working characteristics when the incident angle and polarization angle are changed.The switchable absorber can be used in areas such as stealth,terahertz imaging,and sensing.