Study on the Terahertz High Refractive Index Metamaterial and the Sensing Characteristics of the Metamaterial Absorbers
Author:Tan Si Yu
Supervisor:yan feng ping
With the rapid expansion of the demand for radio spectrum resources in the information era,the spectrum resource is facing increasingly fierce competition as a national strategic resource.In the entire electromagnetic spectrum,the development and utilization of terahertz band between 0.1 THz-10 THz has aroused significant interests.Previous studies have revealed that terahertz technology has great potential in many fields such as spectroscopy,broadband communication,medical imaging,environmental monitoring,safety scanning and defense and military.Natural materials that can respond to terahertz waves are usually expensive and scarce,largely hindering the development of terahertz technology.Therefore,the use of terahertz metamaterials to replace natural materials to produce terahertz devices has aroused great interest.The combination of the requirements of terahertz technology and the flexibility of metamaterials can greatly promote the practical process of terahertz technology,which has high research value and development potential.Permittivity and permeability are the most fundamental parameters for characterizing the electromagnetic properties of materials.By rationally designing the resonating structure,the permittivity,permeability and refractive index of metamaterials can be "tailored" by changing the geometrical dimensions of the element structure,which greatly improves the design flexibility of the functional devices to effectively manipulate electromagnetic wave.Based on the theoretical analysis of the electromagnetic resonance characteristics of the metamaterial,a series of theoretical,simulation and experimental investigation have been carried out on the effects of the electromagnetic response on the equivalent refractive index and absorption characteristics of the metamaterials.The main innovative achievements are as follows:(1).A Z-shaped high refractive index metamaterial at terahertz frequencies with strong nearest neighbor coupling is proposed.By reducing the spacing between the resonant units,the coupling between the nearest neighbors is effectively enhanced to excite the strong electric dipole resonance.The diamagnetic response is suppressed by the structural optimization therefore a high refractive index of 14.36 is realized at 0.315 THz.The experimental results are in good agreement with the numerical calculations.The influence of the geometrical parameters on the effective refractive index and resonant characteristics of the structure is systematically analyzed by characterizing the Z-shape structure with different gap width and the equivalent circuit model analysis.(2).A broadband metamaterial absorber based on two interlaced fishnet layers is proposed.Different from the three-layer structure of the conventional metamaterial absorber,the resonating structure of the proposed broadband absorber is replaced by two interlaced fishnet layers,which produces near-perfect absorption peaks at three closely located frequencies respectively.The broadband absorption of 0.99 THz is realized near 2.3 THz by merging the absorption peaks.Further simulations have revealed that the proposed structure was angular insensitive under TM polarized incidence.(3).A broadband metamaterial absorber based on asymmetric crossed slot is proposed.By introducing symmetry breaking characteristic in the crossed structure,the original symmetric structure is separated into two independent resonators,therefore generating multiple absorption peaks simultaneously.Furthermore,a meta-molecular is designed with four resonators with different degrees of asymmetry and geometrical dimensions.By merging the asymmetric absorption peaks excited by the sub-resonators,a broadband absorption with 0.526 THz is realized near 1.2 THz.(4).A multispectral metamaterial absorber sensor based on the composite structure is proposed.The photoresist was spin-coated on the absorber surface as the sensing analyte.And the influence of the thickness and refractive index of the sensing analyte on the resonance frequency of the absorber was studied by numerical simulations and experimental measurements.Based on a equivalent circuit model,the drift of the resonant frequency of the metamaterial absorber is derived from the equivalent capacitance of the resonant structure changed by the added analyte.Furthermore,a multi-band absorber sensor is designed using a double-split-ring resonator and a metal cut wire.The sensitivities of the refractive index of each resonance mode of the multi-band sensor are investigated experimentally and numerically,and the highest sensitivity obtained is 26.2%RIU"1.(5).A high sensitivity sensor design based on three-dimensional terahertz absorber is proposed.A high-resolution metamaterial absorber sensor is designed using three-dimensional split ring resonator and metallic ground plane.Benefiting from the high-quality resonant characteristic,the proposed absorber sensor shows extremely high sensitivity to the thickness and refractive index of the sensing analyte,and its refractive index sensitivity is up to 34.40%RIU-1.By comparing the sensing performance of the designed absorber sensor with the metamaterial sensor in same structure,the proposed three-dimensional sensor has shown obvious advantages in both resonant quality factor and the refractive sensitivity.