Design Of Bifunctional Terahertz Metamaterials Based On Transparency And Fano Effects

Terahertz waves are electromagnetic waves with many advantages,but its direct interaction with matter is weak.Metamaterials can greatly enhance the interaction between terahertz light and matter by providing unique properties that natural materials cannot achieve.In recent years,metamaterial resonance devices working in terahertz band have attracted the attention of many researchers.Terahertz metamaterials based on transparency(such as electromagnetic induced transparency,plasma-induced transparency)and Fano resonance effects have been extensively reported.Dual-function/multifunction devices have a wider application prospect,but there are relatively few reports based on dual-function/multifunction devices.In this paper,several terahertz metamaterial resonance devices are optimized by means of finite difference time domain numerical simulation method and related fabrication techniques,and various factors affecting device performance are analyzed and studied.The main work can be divided into the following three parts.(1)A dual-function terahertz metamaterial device with both electromagnetically induced transparency and Fano resonance effect is studied.A double π-shaped metamaterial resonator is designed.The upper and lower π-shaped resonators have opposite openings,and the sizes of the two resonators are different.By controlling the arm length of a single π-shape resonator to introduce the breaking,both the double transparency and the Fano resonance effects can be achieved simultaneously.The transmission spectrum reflects the performance of the metamaterial resonator.In the process of symmetry breaking increasing,the Fano resonance gradually increases,the intensity of the second transparent peak gradually weakens,and finally becomes the effect of single transparency and Fano resonance.A metamaterial resonator composed of three metal strips is designed.The coupling effect of incident terahertz light through the device is generated to form a transparent peak.By slightly breaking the symmetry of the structure and introducing a discrete state at the transparent peak,the transparent peak can be split and the transparent and Fano resonance effects can be realized at the same time.The strength of Fano resonance can be adjusted by moving transverse metal strips up and down.When the deviation degree is large,the Fano phenomenon disappears and the structure becomes a double transparent metamaterial.Other structural parameters have little effect on the performance.Changing the size of the opening spacing G and the length of the metal strip will cause a frequency shift in the transmission spectrum,causing a slight change in the resonance intensity.(2)Suspension metamaterial used to enhance the refractive index sensing dual-function terahertz devices are studied.Metamaterials are sensitive to their surroundings and can be used as refractive index sensors.This parts focuses on the influence of environmental change on device performance.A single resonance is presented,which is directly excited by terahertz wave irradiation on the classical double-open ring structure,and clearly demonstrates the frequency shift change of transmission spectrum under the influence of environment.A double-open ring resonator was designed and the refractive index sensing performance of metamaterial devices was compared between the planar design and the suspension design.It is found that the suspension design improves the refractive index sensing performance of the metamaterial by 2.1 times.At the same time,a simpler relief metamaterial structure is studied.Compared with the suspended structure,the refractive index sensitivity of relief metamaterial is increased by 2 times,but it is easier to prepare experimentally.Changing the size of the opening spacing will affect the near-field distribution.The larger the opening spacing is,the larger the near-field distribution range will be,and the sensitivity of the refractive index of the device will also be improved.(3)Theoretical simulation and experiment verify the design and study of a dual-function terahertz metamaterial filter element with conductive connection type.This part provides a new idea for expanding the design of multifunctional metamaterial devices.Different from the traditional single mode superposition,more resonance modes are introduced in the design of conductance connected structure.The two U-shaped open rings are connected by metal strips.The connecting metal strips will introduce a variety of new resonance modes in the whole structure,and the transmission spectrum of the structure changes from single-channel filtering to three-channel filtering.The device performance is studied by changing the size of the connecting metal bar and U-shaped resonator.In this kind of connected structure design,the dependence between the resonances is high.Changing the parameters of a single structure will produce frequency shift and intensity change of all resonances.The mechanism of resonance generation is analyzed by the near field distribution of each resonance position.The metamaterial device was prepared by further experiments,and the transmission spectra measured by experiments matched well with the simulation data.