Study On Characteristics Of Elliptical Metal Wire Plasmon Of Terahertz Wave

The terahertz (THz) wave has a large number of potential applications inimaging, sensing, communication, and biomedicine, so it obtains much attention inrecent years as one of the hottest academic frontier. Due to its large attenuationcoefficient in the air, the goal of a long-range propagation of THz radiation has onlybeen achieved in some waveguide systems. Previous studies of THz waveguidessuggest that, metal wire THz waveguide has distinguishing characteristics of lowloss, low dispersion and simple structure, and should be designed into an effectiveTHz waveguide. The propagation properties of metal wire THz waveguide can beexplained by surface plasmon characteristics. Surface plasmon has been a researchhotspot in recent years, which is similar to THz wave itself. The metal wire plasmonof THz wave is the intersection of these two research hotspots, so it obtains muchattention. Before, researchers have done a lot of work on the characteristics of THzwire. This article is about the characteristics of plasmon of elliptical metal wireunder THz wave.The research content of this paper is divided into the following two mainaspects:(1) theoretical analysis of the characteristics of surface plasmon of singleelliptical THz metal wire, and numerical simulation by using the finite elementmethod (FEM), and comparison of difference between the surface plasmon of singleellipse and circular metal wire;(2) we designed a dual elliptical THz metal wirewaveguide connector, which is used to couple an approximate plate waveguide THzwave into the dual circular metal wire waveguide efficiently. And we calculated thecoupling efficiency by WKB approximation and numerical simulation. Itsinnovations are as following:1. By numerical simulation of THz surface plasmon of the circular metal wire,it has been confirmed that the simulation results are consistent with theexperimental results, which verifies the feasibility of the numericalsimulation method. Then we built a geometric model of single elliptic metal wire, and carried on numerical simulation. We found that with the increase ofthe ratio of long and short axis, the field of elliptic metal wire splits up andgradually focuses to the ellipse tips, and the loss also significantly reduces inthis gradual process. The results show that, compared with circular metalwire, surface plasmon of single elliptic metal wire has the characteristic ofstronger localization while maintaining its characteristics of low loss and lowdispersion. The elliptic metal wire waveguide gets more degree of freedom indesign due to the introduction of long and short axis.2. According to the characteristics of dual circular THz metal wire, we designeda dual elliptical THz metal wire waveguide connector. The ratio of long andshort axis is set much greater than1at the input end of the connector. At theoutput end of the connector, the length of the long axis equals exactly to theshort one. Between the input and output end, the length of the ellipse longaxis is linearly reducing. First, we use the2-D simulation and obtain thecoefficient of equivalent by selecting the air-metal boundary condition to bean impedance boundary condition. Then we work out the coupling efficiencyby using both numerical simulation and coupling efficiency equation inducedby WKB approximation, and analyze its relations with some relatedparameters. Finally, the results show that this structure could be used as aTHz waveguide connector, which couples an approximate plate waveguideTHz wave into a dual circular metal wire waveguide efficiently, the couplingefficiency should reach about94%.