Analysis Of Multi-band Terahertz Absorbers And Its Tunability

Since the end of last century,terahertz science and technology has made a leap forward.The development of terahertz band correlation technology has filled the gap between microwave band and infrared band.Artificial electromagnetic metamaterial absorbers have the advantages of perfect absorption,ultra-thin thickness and artificial design of absorption frequency,which have become an important means to detect and control terahertz waves.However,the traditional metamaterial absorbers determine their absorption characteristics once they are processed,which undoubtedly hinders the application of metamaterial absorbers in terahertz band.In most existing studies,the regulation of metamaterial properties is achieved by introducing active substances,changing the structure of the absorber or the surrounding media to achieve tunable properties.These methods can achieve tuning of absorption characteristics,however,adding complexity of regulation or complexity of structure.A convenient and effective means of regulation is particularly important.In this paper,a multi-band terahertz absorber based on the composited unit is proposed,which achieves absorption peak over 96% at 0.53 THz,0.94 THz and 1.59 THz.The electric field distribution,magnetic field distribution and current density distribution at the interface and within the structure of the terahertz metamaterial absorber are simulated.Further,the effects of incident polarization and oblique incidence on absorption characteristics are studied.The absorber still maintains good absorption characteristics when the incident angle rises to 50°.In addition,the interference theory is used to analyze the producing conditions of perfect absorption and to explain the physical mechanism of perfect absorption of metamaterial absorber based on metal-medium-metal three-layer structure.At the same time,the influence of structure parameters on absorption characteristics is also studied by combining the transmission line model and interference theory.The results of experiment,simulation,interference theory and transmission line theory are in good consistent.According to the influence of structure parameters on absorption characteristics and the analysis of polarization characteristics of metamaterial absorber,a tunable multi-band terahertz absorber based on the polarization state of incident terahertz wave is designed.The operating principle and tunability of the absorber were analyzed by numerical simulation,and the tunability of the absorber was verified by experiment.The results of simulation and experiment show that the designed absorber can achieve discrete tunability of absorption frequency at the four frequency points of 1.60 THz,1.71 THz,1.86 THz and 2.04 THz by changing its own rotation or the incident polarization state,and the main peak position can be switched by changing angle.In addition,the absorption amplitude is continuously tunable,the amplitude tuning range is 10%?99%,the modulation depth is 0.82.This work provides a concise way to achieve tunable absorption characteristics,which is available for implementation of sensors,detectors and switches in terahertz bands.