Theoretical Research On The Tunable Plasma-Induced Transparency Based On Graphene-Metal Metamaterials

Terahertz functional devices are an important part of terahertz research.However,very few natural materials(elements)exist that have strong responses to terahertz waves,and this has hampered the development of terahertz technology based on the corresponding functional devices.Through artificial design and assembly,metamaterials,from concept to reality,can exhibit novel electromagnetic properties that traditional materials do not,thus providing a broad platform for the progress of terahertz functional devices.Meanwhile,graphene exhibits unique tunable photoelectric properties,which makes it possible to dynamically control terahertz waves and promote the diversified development of terahertz functional devices.Plasmon-induced transparency(PIT)is a phenomenon wherein surface plasmon coupling in the metamaterial structure causes the transparent transmission of electromagnetic waves that should be absorbed by the medium at the resonance frequency.PIT has various engineering applications in the fields of sensors,radar,and communication.The terahertz PIT metamaterial is one of terahertz functional devices with important application prospects.The only route for the development of these devices is from the passive to active type.In this dissertation,to obtain active PIT devices with excellent performance,based on the research of metal metamaterials,graphene is organically integrated into a metal metamaterial structure as a control unit in the THz frequency domain.Various graphene-metal tunable PIT metamaterials have been theoretically studied by combining numerical calculations with theoretical model analysis.The related research results provide theoretical guidance and a scientific basis for the design of active PIT devices.In this dissertation,the main work is divided as follows:1.Two types of single-band PIT terahertz metamaterials based on graphene-metal were designed.The first type is used to achieve dynamic tuning of the PIT effect using graphene to manipulate the dark mode,achieving a maximum modulation depth of 83.1%of the PIT transmission peak and exhibiting the function of dynamic on(amplitude transmission of 0.89)and off(amplitude transmission of 0.15)for incident terahertz waves at 0.58 THz and adjustable slow-light characteristics(maximum group delay tg=19.1 ps).The influence of the number of graphene layers on resonance was discussed.The sensing characteristics of the structures were analyzed.The modulation mechanism of the PIT effect is revealed from the electric field layout and the equivalent circuit model.The second type is used to realize the dynamic modulation of the PIT effect by manipulating the bright mode with graphene,and the influence of split-ringresonator size on the propagation characteristics of PIT was studied.The classical two-particle coupling model was used to elucidate the source of the transmission spectrum modulation.2.By introducing the polarization dimension,two types of metal-graphene-tailoring PIT metamaterials were designed.In the first case,the structure has quadruple symmetry and thus exhibits polarization independence.The tunable characteristics of transmission and absorption were discussed using numerical simulations.The formation and tunability mechanisms of the PIT response were discussed based on the electric field layout.Through theoretical fitting,the role of graphene in the novel interaction between THz resonant modes was revealed.The second case is a tunable polarization-dependent PIT structure.The PIT resonance intensity and accompanying slow light delay can be controlled by double dimensions(incident polarization and graphene Fermi energy),and the number of transparency windows can be adjusted through polarization.A RLC coupling circuit model is constructed,which describes the additional induced loss of graphene through a series variable resistor,reveals the mechanism through which graphene modulates the PIT effect from a specific perspective,and provides a theoretical basis for the design of active PIT devices using graphene.3.Based on the graphene-metal structure,an independent tunable dual-band terahertz PIT metamaterial was proposed to broaden its application scenarios.Based on structure geometry parameter optimization,by integrating graphene layers with adjustable conductivity under two dark mode resonators,the dual-window PIT effect characteristics(transmission and group delay)can be independently and dynamically modulated simultaneously.In addition,the classical twoparticle coupling model is extended to the three-particle coupling model,which accurately reproduces the destructive interference characteristics between bright and dark resonators and the PIT transmission curve and clarifies the physical mechanism of the structural electromagnetic response tunability.