Research On Terahertz Metamaterials Functional Device Based On Electromagnetically Induced Transparency Like And Absorber Switchable

Electromagnetic metamaterials are composed of periodically arranged artificially designed unit structures,whose size is far smaller than the working wavelength,and have negative dielectric constant and negative magnetic permeability.Through reasonable design and optimization of the metamaterial structure can make the propagation of the electromagnetic waves in the metamaterial appear negative refraction effect,electromagnetically induced transparency（EIT）,and other exotic properties.EIT is a nonlinear quantum interference effect occurring in a three-level atomic system,resulting in a transparent window in the spectral absorption region of the original opaque medium,accompanied by a slow light effect.Using metamaterial to simulate the EIT phenomenon,which is called electromagnetically induced transparency-like（EIT-like）,breaks through the rigorous experimental conditions of traditional EIT and expands the idea for people to study the EIT effect and develop applications.In this dissertation,based on graphene-tunable EIT-like metamaterials,vanadium dioxide（VO₂）material is introduced based on studying EIT-like metamaterials’slow light characteristics and related applications.A terahertz multifunctional device with electromagnetically induced transparency and absorber switchable can be realized by using the phase change characteristics of VO₂.The main work of this paper is as follows:（1）A polarization-insensitive EIT-like metamaterial is designed.Two graphene square rings with different sizes act as the bright mode,and the EIT-like effect is produced by the near-field coupling of the two bright modes.The EIT-like window and the corresponding group delay can be adjusted by changing the Fermi level of graphene.The theoretical fitting results based on Lorentz model are in good agreement with the numerical simulation results.Then,by introducing vanadium dioxide based on this metamaterial,the metamaterial can realize the conversion from electromagnetically induced transparency-like to dual-band absorber by taking advantage of the phase transition characteristics of VO₂.When VO₂ is in the insulating state,the metamaterial structure achieves the EIT-like effect.When VO₂ is in the metallic state,the metamaterial structure can realize the dual-band absorption function,with the absorption rate reaching 63.2%and 99.6%at 0.96 THz and 1.89 THz,respectively.The dynamic adjustment of the frequency response characteristics of both functions can be achieved by changing the Fermi level of graphene.In addition,the performance of the proposed metamaterial as a sensor for detecting the refractive index of surrounding media was discussed,and the maximum sensitivity of the metamaterial sensor was calculated to be 0.4845 THz/RIU.This design provides a feasible method for developing slow light devices,sensors,absorption,and multifunction devices.（2）A tunable double EIT-like metamaterial based on single layer graphene is designed.Different length graphene bands and rotating graphene square rings act as bright modes,and the near-field coupling between the two bright modes produces the EIT-like effect.The theoretical fitting results based on Lorentz model are consistent with the numerical simulation results.By changing the Fermi level of graphene,it can not only realize the EIT-like window and corresponding group delay dynamic modulation,but also realize synchronous or asynchronous switching with high modulation depth and low insertion loss switching function.On the basis of tunable double EIT-like metamaterials,VO₂ substrate is introduced and its phase transition characteristics can be used to realize the functional conversion between double electromagnetically induced transparency-like and triple-band absorber.When VO₂ is in the insulating state,the designed metamaterial produces a double EIT-like effect.When VO₂ is in the metallic state,the designed metamaterial realizes the three-band absorption function,with absorption rates of 91.02%,95.81%,and 80.37%at resonance frequencies of 2.152 THz,3.076 THz,and 3.741 THz,respectively.The simulation results show that the dynamic adjustment of the two functions can be realized by changing the Fermi level of graphene.（3）A terahertz multifunctional metamaterial device based on graphene and VO₂materials is proposed.When VO₂ is in the insulating state,the metal rings of different sizes in the designed multi-functional metamaterials act as the bright mode,and the coupling of the“bright-bright mode”produces the EIT-like effect.The amplitude regulation of the electromagnetically induced transparent window can be achieved by adjusting the VO₂ conductivity and the Fermi level of graphene.When the VO₂ is in the metallic state,the designed multifunctional metamaterial can achieve broadband absorption,with the absorption rate exceeding 90%and the relative bandwidth reaching63.4%in the frequency range of 1.211-2.335 THz.In addition,the proposed broadband absorber has the characteristics of polarization independence and large incidence angle,and its broadband absorption performance can be adjusted by changing the VO₂conductivity.