Research On Tunable Terahertz Broadband Absorbers Based On Metamaterials

With the continuous development and maturity of terahertz light source and detection technology,the research on terahertz functional devices has also been developed rapidly.Terahertz absorber,as one of the important terahertz functional devices,is now widely used in electromagnetic stealth and terahertz imaging fields because of its excellent absorption characteristics.Metamaterials are artificially designed subwavelength periodic unitary structure materials with different properties from natural materials,which are widely used in the fields of optics and electromagnetism.The study of tunable,high absorption performance,polarization-insensitive,wideband absorbers with large angular incidence is a hot research topic.The application of metamaterials to terahertz absorbers has important academic significance and practical value.In this paper,an"H"shaped metamaterial broadband absorber is designed based on the principle of multi-frequency resonant superposition.The absorption rate of the absorber is 99.5%at 5.53 THz and 96.5%at 5.78 THz,and the absorption rate of the absorber is more than 90%in the frequency band from 5.4 THz to 5.9 THz.Although its structure is simple and easy to process,the absorption performance of this absorber will be affected by the polarization state of the incident wave.In order to solve the problem of absorber polarization sensitivity,a broadband absorber with a circular metal sheet multilayer structure is designed.The simulation calculation shows that the three absorption frequency points are 6.04THz,6.53THz,and 6.69THz,and the absorption rate corresponding to each absorption frequency point is 99.91%,99.46%,and 99.89%,respectively,and the broadband absorption range is 5.86THz-7THz,and the absorption rate in the broadband reaches more than 95%.In addition to the polarization insensitive characteristics,the absorber has superior absorption performance and wider broadband range,and still has better broadband absorption performance at large angle incidence,but the design of the multilayer structure will make it difficult to produce and process.Finally,a tunable metamaterial terahertz broadband absorber is designed by using two-dimensional tunable graphene material.The resonant structure on top of the absorber dielectric layer is a combination of graphene circular patch and square ring.Simulation results show that the absorber reaches peak absorption at 7.89 THz with 96.5%absorption,and achieves broadband absorption of2.06 THz in the broadband range of 7.08 THz-9.14 THz with more than 95%absorption in the frequency band.When the applied voltage makes the absorber surface graphene Fermi energy level E_f reach 1.8e V high Fermi energy level state,the absorber’s absorption rate is less than 20%in the terahertz band,therefore,the absorber can be switched between absorber/reflector operation mode,which greatly improves its application range.The absorber adopts a three-layer structure,which is simpler and easier to process,and satisfies the superior characteristics of tunability,polarization insensitivity,and large-angle incidence,etc.It has a wide application prospect and important value in the field of electromagnetic stealth.