Research On Dynamic Tunable Filter Based On Graphene

Terahertz?THz?wave has the advantages of instantaneousness,high transmission and broadband with a frequency range of 0.1THz-10THz.In recent years,it has significant application prospects in communications,imaging and biomedicine.Metamaterial,an artificial material with special electromagnetic properties,has opened up a new direction for the realization and development of terahertz devices.Combining with grapheme,the dynamic tuning function can been realized based on the resonance mechanism and filtering characteristics of metamaterial filters.the main research work of this thesis as follows:1.U-shaped metal-graphene metamaterial stop-band filter is proposed.The filter has a stop-band bandwidth of 2.4THz and a modulation depth of 25.23dB in the 32.4THz-34.8THz band.Enlarged the structure size of the filter,the filtering characteristics of the center frequency of 3.92THz,the stop-band bandwidth of 0.22THz are realized in the terahertz band.On this basis,a nested double U-shaped metal unit structure is designed to implement a dual stop-band filter.The stop-band bandwidths in the 29.8THz-41.9THz band are 1.9THz and 1.2THz,respectively,and the modulation depth is 24.01dB.By changing the graphene layer gate voltage to tune the graphene Fermi level,real-time dynamic tuning of the performance of the stop-band filter can be achieved.2.A stop-band filter with a mouth-shaped metal structure is proposed,and single-layer and double-layer mouth-shaped resonant structure filters are studied respectively.The single-layer mouth-shaped stop-band filter has a stop-band bandwidth of 3.8THz and a modulation depth of 34.32dB in the 37.6THz-42.7THz frequency band.The filter can be dynamically tuned by tuning the graphene Fermi level.The double-band mouth-shaped stop-band filter has a stop-band bandwidth of 14.3THz in the 27.3THz-42THz frequency band,achieving broadband filtering,with an average transmittance in the stop-band of less than 0.1 and a modulation depth of 35.89dB.The two resonant structures are universal and can be adapted to the terahertz frequency band by optimizing the size of structure.The terahertz filter with a single-layer structure has a stop-band bandwidth of0.5THz in the 2THz-5THz frequency band.The terahertz filter with double-layer structure forms a stop band with a bandwidth of 1.4THz in the range of 2THz-4.7THz.The mouth-shaped filter has a wider bandwidth than the U-shaped filter,and due to the symmetry of the structure,it is insensitive to the polarization direction of the incident wave.The stop-band bandwidth of the mouth-shaped filter with double-layer structure is further increased,and the double-layer structure can independently control the Fermi level of each layer of graphene to realize the real-time tuning function of the application stop band3.Analyzing the phase change mechanism of VO₂,determining the conductivity parameters of VO₂ at different temperatures,a field-shaped structured switching filter combining VO₂ and metamaterials and a connected field-shaped structured switching filter are proposed to realize the electric heating method Switching filter.VO₂ can change from non-metallic state to metallic state to implement adjustable filters by electric heating.In the normal temperature state?20??,VO₂ behaves as a non-metallic state,and the filter 42.9THz-47.4THz achieves an average transmittance of more than 90%of the pass-band.In the high temperature state?70??,VO₂ behaves as a metal state,the resonance center frequency of the filter is 45.8THz,and the bandwidth is 5.7THz.Both states can be freely adjusted by means of electric heating.The switching filter function is realized in the 42.9THz-47.4THz frequency band.It has been verified that the field-shaped structure filter is still applicable in the terahertz frequency band.