Research On Multi-frequency Narrowband Absorber Based On Electromagnetic Metamaterials

With the in-depth research and exploration of terahertz waves,the demand for extending various functional devices from the microwave/radio frequency band to the terahertz band is also increasing.Electromagnetic metamaterial refers to an artificially designed periodic array structure and presents unique electromagnetic properties that other materials do not have.It is of great significance to functional devices in the terahertz band.Compared with traditional absorbers,metamaterial absorbers have the advantages of flexible structure design,light and thin thickness,and efficient absorption.Metamaterial absorbers are widely used in compressed sensing imaging,frequency selective thermal emitters,detectors and sensors.So it is of great value to carry out research on metamaterial-based terahertz absorbers.First,two dual-frequency absorbers are proposed.The first is a dual-frequency terahertz absorber based on a combination of "swastika" shape and a square metal ring superimposed structure.These two resonant structures can independently exhibit their comparative advantages.The strong absorption peaks form the top metal resonance layer after being superimposed in the horizontal direction,so as to achieve dual-frequency absorption.The absorption spectrum curve shows that the absorption rates at the resonance frequencies of 1.508 and 2.464 THz are respectively 98.9% and98.8%.The absorber has no limitation on the polarization mode of incident electromagnetic waves,and has no obvious change in the absorption performance of TE or TM electromagnetic waves.Stable absorption with an absorptivity higher than 90% under the incidence of electromagnetic waves in the range of 0-40° incident angle is still maintained.When the incident angle is 60°,the absorption peak at the resonance frequency of the absorption peak is still above 75%.Since the "swastika" shape is a relatively complex resonant structure,there are certain difficulties in the subsequent processing of absorber samples,so on the basis of this structure,the "swastika" shape structure is simplified to a square metal that is consistent with the outer ring structure.Under this structure,the absorption peaks at the resonance frequency of the two absorption peaks of the absorber are both improved by about1%,and it also has polarization insensitive characteristics and still has two strong absorption peaks under the incidence of electromagnetic waves with larger incident angles.In order to further expand the number of absorption peaks,according to the above-mentioned double-sided metal ring absorber,a square metal ring structure is continued to be superimposed on this basis to meet the three frequency absorption requirements.The absorption spectrum curve shows that the absorption rates at the resonance frequencies of 1.212,2.068,and 3.128 THz are respectively99.7%,95.8%,and 99.8%.The absorber has polarization insensitive characteristics,and it still maintains stable absorption under the incidence of electromagnetic waves in the range of 0-60°.If the absorption rate of the resonance frequency of the three absorption peaks is further increased,only from increasing the period of the unit structure,higher requirements are also put on the size of the device,so a ring structure similar to the square ring structure is adopted instead.Only by changing the size parameters of the inner circular metal ring structure,the absorption rates at the resonance frequencies of the three absorption peaks of the absorber are respectively 99.1%,99.1%,and 99.7%.The absorbers of these two structures are not sensitive to the polarization mode of terahertz waves,and still have three strong absorption peaks under electromagnetic waves with larger incident angles.The absorber studied in this paper has great significance and application value for high-sensitivity detectors.