Study Of Terahertz Transmission Lines

The special position of terahertz (THz) in the electromagnetic spectrum brings itmany excellent characteristics. Now, terahertz science and technology (THz S&T) andits applications have being attracting much attention from scientists and researchers ofvarieties fields worldwide. With the in-depth research on THz, the rich scientificconnotation and unique features of it are deplored, it can be employed in a wide areassuch as Physics, Chemistry, electric information, biomedicine, material science,astronomy, atmosphere and environment monitoring, communication and radar,National security and anti-terrorism, etc. As one of the strategic interdisciplinaryfrontier research areas, the development of THz S&T is of significant to modern scienceand technology, national economy and national defense. It is now become a scientifictop priority in the world. With the development of THz S&T, THz waveguides suitablefor different applications are urgent due to the strong vapor absorption of THz waves inthe open air, which drives varieties of waveguides based on the technology ofmicro/millimeter waves and optics are researched. Among these waveguides, thedesirable transmission properties of metal transmission line(s) at THz frequency attractresearchers; the paper of THz wave transmission on single metal wire was published inNature magazine. With a general analysis on most of the exist waveguides, this paperpay its emphasis on the research of dual-wire metal transmission line, single wire metaltransmission line and mimicking surface plasmon transmission line, a initialexperimental study on single metal wire are also presented. The results obtained in thepaper will present a good reference and benefit the research of these transmission line(s)on application systems.Dual-Wire Waveguide (DWW) can be used at Terahertz (THz) frequency regionsuccessfully with advantages of no dispersion, low loss, etc. It is also easy fabricationand good coupling with common THz sources. However, from the point of view ofphysics, the usually theoretical studies on the DWW at low frequencies are based on thetraditional electrostatic methods, but for its modern applications at THz or even higherfrequencies, rigorous analysis method suitable for high frequency application is necessary. In this paper, making use of the Bipolar Coordinate System (BCS), therigorous analytical theory of DWW is worked out, and some important physical andoptical characteristics of DWW including the rotating behavior etc. are revealed, theequivalent impendence and the ohmic loss for the gold DWW are calculated, the resultsshows the limitation of the traditional electrostatic methods. As for the dispersion modes(TE and TM modes), they are proved cannot be excited or exist on DWW analyticallyand simulately, an eigenvalue problem is presented from the point of view ofMathematical-Physics. The above obtained results will help to get a deep-goingunderstanding of DWW and explore its application at high frequency including THz.The single metal wire (SW) becomes attractive for its potential applications interahertz and higher frequency region. Gripping the properties of the Surface PlasmonPolaritons (SPPs) on single metal wire is the key to explore its application on THztransmission. However, the study of it seems far from enough, most studies are only onthe symmetrical modes based on the metal characteristics defined by the classical Drudemodel. In this paper, making use of the Modified Drude Model (MDM) based on theSommerfeld metal theory, the transmission behaviors of SPPs along SW relate to theproportion of wavelength and the diameter of the wire are systemically investigatedtheoretically, some important physical phenomena such as the modes transformation,the lifetime of radiative modes and the resonance frequency are revealed, and themechanisms of their occurrence have been explored from the viewpoint of physics. Asthe most simple and typical SPPs transmission line, the results obtained in the paper willfacilitate the general understanding on the features and the physics of the SPPstransmission, not only for SW itself but also for other SPPs transmission lines.Numerical study on cylindrical corrugated Mimicking Surface Plasmons (MSPs)Terahertz (THz) transmission line with and without gradually changed geometricparameters was carried out by means of the finite element method. The detailedtransmission characteristics of the MSPs on the corrugated cylindrical wire are revealed.The results show that the gradual increased size of corrugates both in depth and widthwill help the confinement of the electromagnetic energy transmission on the surface ofthe wire, and the structure also has the function of concentration the propagation wave,which brings forth enhancement of the surface plasmon wave during its transmissionalong the wire. The obtained results will favor the applications of THz transmission, near-field imaging, spectroscopy and sensing.