Investigation On The Influence Of Magnetically Biased Graphenes On Guided-wave Modes

Graphene is a monolayer carbon-atom structure with two-dimensional honeycomblattices. In recent years, with the improvement of technology, a diameter of up to30cmgraphene sheet can be manufactured, opening up the possibility of applications ofgraphene in the field of microwave and millimeter wave. The unique atom structure ofgraphene leads to its linear non-gap electronic band structure, thus forming the uniquecharacteristic of graphene. Similar to the dispersion relation of photons in free space, thelinear energy-momentum dispersion relation graphene makes electrons just like zero-massparticles, so the mobility of electron up to15000cm2/Vs. Furthermore, the non-gapstructure of graphene leads to a unique bipolar field, i.e., the inversion of energy carriertype, transforming from the electron to holes or from the hole to the electron. Because ofthese characteristics graphene has been applied to various structures such as transistors,frequency multipliers and so on. The utilization of graphene into antennas and passivecomponents leads to miniaturization, efficient dynamic tuning, and even mechanicalflexibility. Recent studies have shown that a single-layer or multi-layer graphene sheetswill show Faraday rotation effect with a bias magnetic field, which will be applied to thepropagation of electromagnetic waves in microwave bands. Based on this background, thispaper mainly studies the effect of graphene with a biased magnetic field placed incross-section of a rectangular waveguide on the transmission, reflection and coupling ofwaveguide modes.The main work and innovation can be summarized as:1. Investigation on gyrotropic effect of magnetically biased graphene sheet inrectangular waveguide. The main work in this section includes:a graphene-loaded rectangular waveguide transmission system model is designed,and the graphene sheet is biased with a static magnetic field perpendicular to thecross-section of the rectangular waveguide. Determining the number of patterns within afrequency band according to the dimensions of the rectangular waveguide. Then thecoupling matrix of these modes is calculated based on their the eigen functions. Thus thesurface conductivity matrix of the graphene is obtained. Then we can calculate theS-parameter matrix according to transfer matrix of the whole system. Finally, the effect of the value of the biased static magnetic field and the electron chemical potential on thecharacteristics of waveguide mode is discussed.2. Effect of supporting substrate on mode characteristics of graphene-loadedrectangular waveguide. The novelty includes the following points:Firstly, a model of rectangular waveguide loaded with multiple graphene sheets isdesigned. Each graphene sheet is synthesized and then transferred on a quartz substrate.The graphene sheets are biased with a static magnetic field. For the reasons that thedielectric constant of the medium is higher than air, some conducting modes in quartzmedium will be cut-off in air. When transforming the transfer matrix into thecorresponding S-matrix, an important thing should be noticed. The wave impedances ofsome higher-order modes will have purely imaginary values when they are cutoff for theair-filled waveguide. In order to overcome this problem and simplify the analysis, weterminate the equivalent ports, except for those corresponding to H10-and H01-modes, withthe wave impedances. Finally, this paper mainly research the effect of the value of thebiased static magnetic field and the electron chemical potential on the transmission,reflection and coupling between H10-and H01-mode.According to the research, there are many factors affect the transmission, reflectionand coupling of the rectangular waveguide modes, including the biased magnetic field,chemical potential and the selected quartz substrate. In the case of the substrate, theself-transmission and the self-reflection of the pattern becomes large, while the couplingbetween the modes is small. These parameters can be adjusted in order to achieveoptimistic results of rectangular waveguide modes propagation.