| As a kind of artificial composite material with periodic arrangement structure,metamaterial has attracted much attention because of its novel electromagnetic properties different from natural materials,such as negative refractive index,electromagnetic stealth and inverse Doppler Effect.The electromagnetic properties of metamaterials can manipulate and change the propagation direction,amplitude and polarization of incident electromagnetic waves.Therefore,metamaterials are widely used in the researches of terahertz waves,which greatly makes up for the weak interaction between terahertz waves and natural materials.The emergence of terahertz metamaterials with subwavelength size promotes the integration and miniaturization of optical devices and fills the research gap in terahertz band.In recent years,a kinds of functional devices based on terahertz metamaterials have been widely proposed,including absorbers,filters and sensors.The EIT effect is an interference phenomenon observed in a three-level atomic system.Due to the stringent experimental conditions,such as coherent pumping and low temperature environment,its development and application are seriously limited.With the electromagnetic coupling between different resonant modes,the EIT effect can be easily realized in terahertz metamaterials.The EIT effect is always accompanied by steep dispersion and low group velocity,and can effectively enhance the light-matter interaction.Therefore,it shows great potential in the research of slow light devices,optical switches and filters.The terahertz metamaterial resonator with multi-band transparency effect shows higher application potential and can be used in the design of multi-band optical switches and sensor filters.This paper designed three different metamaterial resonators,which can produce three transparent peaks in the terahertz band.Moreover,the dynamic tuning of the resonant performance of the metamaterial resonator can be realized by adding phase change materials to the resonator.In addition,the potential applications of metamaterial resonators in the fields of optical switches and refractive index sensors are discussed.The designed metamaterial resonators are divided into the following three types:（1）A three-band electromagnetically induced transparency effect metamaterial resonator composed of two groups of arc-ring resonators is designed,which can produce three EIT transparent peaks in the terahertz band.Through the research of the electric field distribution at the transparent peak,it is found that the coupling between the resonant modes of different arc rings leads to the generation of the transparent peak.In addition,the effects of arc length and radius and the width of the air layer between the inner and outer arc rings on its resonance are studied.By introducing photosensitive silicon with adjustable conductivity into the metamaterial structure,the dynamic tuning of EIT transparent peak are realized.The results show that with the change of the conductivity and position of photosensitive silicon,the resonator shows the dynamic switching from three-band to dual-band or from triple-band to single-band.Finally,the refractive index sensing performance of metamaterial resonators are also discussed.Therefore,the metamaterial resonator has excellent characteristics such as simple structure design and active modulation,which is of great significance for the designs of optical switches,sensors and filters in terahertz band.（2）The paper designed a metamaterial resonator composed of three U-shaped split rings,which can produce three transparent peaks in the 0.1THz～1.33THz range.By comparing the resonance performance of a single U-shaped split ring and the field strength distribution at the resonant trough and transparent peak of the three-band transparency effect,it is found that the generation of the three transparent peaks is mainly attributed to the coupling between the resonant modes of different split rings.The influence of the change of structural parameters of metamaterial resonator on its resonant performance is discussed.By replacing different split rings with photosensitive silicon,changing the conductivity of photosensitive silicon can dynamically adjust the number of resonant dips of metamaterial resonators and realize the dynamic transformation of resonant troughs from four to one.The sensing response of the metamaterial resonator as a refractive index sensor to the thickness of the analytical layer and the change of refractive index is also analyzed.The results show that the maximum sensing sensitivity is 333.6 GHz RIU-1 in a small range of refractive index variation.The design is expected to be used in the sensing detection of solution concentration changes,and will provide important inspiration for the design and research of photoelectric switches,sensors and filters.（3）A metamaterial resonator composed of three open rings is designed,which can produce three-band transparency effect in the 0.1THz～1.5THz frequency range.By studying the electric field distribution at the corresponding frequency point,it is determined that the formation of the transparent peak of the three-band transparency effect mainly comes from the conductance coupling between resonant modes of the substructure.The resonant dip is caused by the resonant modes on different substructures in the metamaterial structure.Finally,the influence of the structural parameters of the metamaterial resonator on its resonant performance is discussed. |
