| Terahertz technology has become the world’s leading technology,and terahertz functional devices are also widely used in various fields such as communication,security and biomedicine.As one of the important functional devices,filter plays an important role in signal detection,modulation and transmission process.The filters with low transmittance,polarization insensitivity,broadband and controllability are the current research hotspots.Due to the poor dynamic response characteristics of traditional materials in terahertz band,it is difficult to meet the requirements of rapid parameter regulation.Graphene is a new nonnatural material with unique electromagnetic properties,and its superior physical properties and photoelectric tunability have important application value in the dynamic regulation of terahertz parameters.This paper focuses on the resonance mechanism of he filter and the unique properties of metamaterials.Two excellent filter devices are designed,and the dynamic regulation of the filter is realized by using graphene.The specific research contents of this paper are as follows:1.In order to solve the problems of narrow bandwidth,shallow modulation depth and unregulability of traditional filters,this paper designs a multilayer S-shaped tunable filter based on graphene according to the principle of multi-frequency resonance superposition and equivalent circuit model.The simulation results show that the five-layer filter formed by the superposition of the unit layer structure generates two wide stopbands within0.1～3THz,with the bandwidth of 0.56 THz at low frequency and 0.68 THz at high frequency,which effectively broadens the filtering bandwidth compared with other layer structures.The maximum modulation depth of the filter is-64.2d B and the in-band transmittance is lower than 1.2%,which deepens the modulation depth and reduces the in-band transmittance.At the same time,the average steepness of the five-layer filter on both sides of the stopband reaches-490 d B/THz and 240 d B/THz respectively,which improves the response speed of the pass-to-stopband.In addition,by changing the Fermi energy level of graphene,the filter moves dynamically in the range of 0.1～3THz,showing good tunable characteristics.2.To solve the problems of small stopband number,complex material structure design and uncontrollability in the application of traditional filters,this paper designs a multiplex structure tunable filter based on graphene according to the coupling effect between dipoles.The simulation results show that the filter can change the number of power resonant units to increase the transparent window,so that the filter can generate two stopbands in the range of10～40THz,and the resonant frequency points of the filter are 17.5THz and 34.6THz respectively.Similarly,changing the Fermi level of the graphene layer can effectively control the movement of multiple resonant center frequencies of the filter within 10～40THz,which is dynamically controllable.In addition,the center frequency of the filter is sensitive to the refractive index of the surface medium,which can be used for refractive index-based sensor design.The filter can also be flexibly applied in the low frequency band of 0.5～5THz by changing the structure size,which has a certain universality and greatly improves the application range of the filter.The terahertz dynamic tunable filters based on graphene are expected to be applied to terahertz communication,sensing,medicine and electromagnetic stealth,which can meet the application requirements in different scenarios. |
