有损耗左手材料模型的时域电磁分析

分析了电磁(EM)场在有损耗左手材料(LHM)模型中能量与损耗因子间的关系,推导了有耗LHM模型的时域有限差分法(FDTD)计算公式,数值模拟了EM场在该有耗LHM材料模型中的传播;对比无耗与有耗LHM模型的EM聚焦特性,分析EM场在不同损耗因子LHM材料中的传播.研究表明,数值结果与理论分析得到较好吻合.     

有耗介质中时域精细积分方法的数值色散分析

分析了时间步长、空间步长、电导率和电磁波传播方向对时域精细积分(PITD)方法的数值损耗和数值色散的影响。结果表明:PITD的数值损耗大于电磁波的真实损耗,其数值波速可以大于电磁波的真实波速。PITD的数值损耗和数值色散都基本上不受时间步长的影响。随着空间步长的减小,PITD的数值损耗和数值色散的误差都逐步减小。当电导率较小时,PITD的数值损耗和数值色散的误差比时域有限差分(FDTD)方法的大。但当电导率较大时,PITD的数值波速却比FDTD的数值波速更加接近于电磁波的真实波速。PITD的数值损耗和数值色散的各向异性在三维情况下的值要大于其在二维情况下的值。数值算例表明:对良导体而言,PITD比FDTD拥有更高的计算精度和更快的计算速度。     

单极天线和偶极子天线辐射特性数值计算*

采用时域有限差分法(FDTD)在柱坐标系下对同轴线馈电单极天线辐射特性进行数值计算,推导了二维扩展柱坐标下修正的Maxwell方程,应用辅助微分方程FDTD法对修正的Maxwell方程进行了差分离散,以TM波在自由空间中的传播为例,仿真了电磁波在自由空间中传播过程并分析了坐标伸缩完全匹配层的性能,建立了单极同轴线馈电天线仿真模型,仿真分析了同轴线馈电单极天线的近场、远场及阻抗特性。在三维直角坐标系下建立了偶极子天线仿真空间模型,数值计算了偶极子天线不同切面的远场方向图,仿真结果与客观实际相同,验证了空间模型及相关理论的正确性。     

基于左手材料提高微带天线方向性的研究

左手材料是介电常数和磁导率全为负值的新型人工合成电磁材料,在其中传播电磁波的群速度与相速度方向相反。利用左手材料的平板透镜聚焦特性,可以改善天线的辐射性能,提高天线的方向性。在此利用左手材料这一特性设计出基于左手材料的微带天线。研究结果显示,加载左手材料以后的微带天线半功率束宽减小29°。验证了左手材料能够提高天线方向性这一特性。     

填充左手介质矩形波导的截止频率研究

提出用时域有限差分法(FDTD)分析填充左手介质矩形波导的截止频率,给出了直角坐标系下无耗均匀左手介质中的二维时域有限差分法(FDTD)的差分公式.用FDTD法分析计算了填充无耗均匀左手介质的厚度和折射率对矩形波导TE模截止频率的影响,并与右手均匀介质填充进行比较,结果表明二者对TE模截止频率的影响正好相反,展示了左手介质所具有的奇特的电磁特性.     

PE模型预测蒸发波导中电波传播损耗

针对电磁波在蒸发波导中的异常传播现象,研究了电磁波在蒸发波导中的传播损耗,其传播损耗是电波传播的一个重要概念,并受到广泛关注。抛物模型(PE,Parabolic Equation Model)作为目前研究电波传播的主要模型,通过与Two-ray模型的对比分析验证了PE模型的可行性,且PE模型计算电磁波的传播损耗时可以克服其他模型预测粗糙海面时的不足。仿真分析表明,电波在蒸发波导中传播时的损耗值比在标准大气中的损耗值要小。     

利用表面电磁波进行能量分配的研究

研究了二维分界面上的表面电磁波,推导得出二维分界面上TE表面电磁波的电场强度、磁场强度和能流密度的表达式,得到分界面上表面波的存在条件,根据总能流把分界面分为左手分界面和右手分界面,对二维分界面上表面电磁波的传播进行仿真,最后提出利用表面电磁波进行能量分配,并给出了仿真结果.     

基于FDTD算法在PBG-PCFS中色散对TE波与TM波能量转移特性分析

通过二维Yee氏元胞割分法中的时域有限差分(FDTD)法对光子晶体光纤中二维导行电磁波在TE波,TM波中x,y,z方向矢量数值变换以此来建立入射激励光源在光子晶体中传播行为的基本理论模型,为此通过对Courant稳定条件及BS-PML吸收边界等参数进行设定与计算机程序数值仿真相结合的方式分析了入射光波在不同时间段不同色散值所产生的电场波与磁场波之间特性关系.研究结果表明:即色散数值偏大时,其光子晶体光纤中TM波能量转移更为显著.     

色散金属的时域有限差分方法

表面等离子体激元具有使光场局域化和局域电磁场增强等特性,在纳米光子学和微观检测等诸多领域显示出广泛的应用潜力.时域有限差分（FDTD）数值计算方法能仿真激光与亚波长金属微结构相互作用的表面等离子体效应.金属具有色散性质,其相对介电常数模型有Drude模型和Lorentzs模型及它们相结合的Drude-Lorentzs模型,能拟合金属在可见光和近红外部分或全部波段的色散特性.FDTD数值计算要采用增加辅助变量和相应的辅助差分方程的方法使FDTD迭代计算稳定.     

基于FDTD方法的无线电波透地传输特性的研究

介绍了时域有限差分法(FDTD)的基本原理；模拟了电磁波在大地非均匀介质信道中的传播，研究了透地通信系统中的电磁波在有耗大地分层面的反射和透射，得出了对透地通信系统设计有重要意义的反射系数和透射系数，说明了FDTD方法是解决电磁波在复杂媒质中传播的一种有效方法。     

非线性左手材料中的背向参量放大

基于电磁场理论,推导了非线性左手材料中的差频耦合波方程,以及相位匹配条件下介质内信号波与闲频波放大过程和场分布。发现有限厚度的非线性左手介质,可补偿损耗的影响,能够得到比右手介质更大的信号波和闲频波能量输出。提出非线性左手背向参量振荡器,在一定的泵浦条件下,不需要外加谐振腔也可以产生振荡。这为非线性左手材料在参量放大器中的应用奠定了理论基础。     

FDTD Simulation of Electromagnetic Pulse Interaction with a Switched Plasma Slab

This paper deals with the Finite Difference Time Domain (FDTD) simulation of interaction of an electromagnetic wave with a switched plasma slab. In formulating the simulation the well-known concepts of (a) total-field/scattered-field formulation (b) and PML lattice truncation are adapted to suit the simulation under consideration. FDTD is particularly well suited to handle the switched (time-varying) medium (including sudden switching) since the time varying parameters of the medium can be easily interpreted in the algorithm. The technique is applied to the difficult problem of interaction of an electromagnetic pulse source wave of frequency ω₀ and a gaussian envelope with a newly created plasma slab of time-varying and space varying electron density profile. The creation of a pulse of Wiggler magnetic field in the slab is illustrated.     

电磁波在周期性结构星型波导中的传输特性

提出一种新型波导结构,在二维周期性结构平板介质中引入两条线缺陷形成星型波导,在波导中加入介电常数不同的介质点阵形成缺陷,采用时域有限差分法(FDTD)对该结构的导波特性进行数值模拟。计算结果表明,该星型结构波导的透射频谱比入射波频谱的带宽更窄,说明此结构具有窄带滤波作用。当改变该星型波导中缺陷结构介电常数取值时,透射过该波导的电磁波中心频率随缺陷介质介电常数的增大而减小,呈良好的线性关系。当改变中心介质柱直径时,透射电磁波的中心频率随缺陷介质柱直径的增大而减小。这种周期性结构星型波导可作为一种窄带滤波和选频器件。     

A novel FDTD formulation for dispersive media

A novel FDTD formulation for dispersive media called piecewise linear JE recursive convolution (PLJERC) finite-different time-domain (FDTD) method is derived using the piecewise linear approximation and the recursive convolution relationship between the current density J and the electric field E. The high accuracy and efficiency of the PLJERC method is confirmed by computing the reflection coefficients of an electromagnetic wave through a collision plasma slab in one dimension.     

TIME DOMAIN ANALYSIS OF TRANSIENT PROPAGATION IN INHOMOGENEOUS MAGNETIZED PLASMA USING Z-TRANSFORMS

The electromagnetic propagation through an inhomogeneous magnetized plasma slab is studied using the Z-transform formulation of the Finite-Difference Time-Domain（FDTD） method. The direction of electromagnetic propagation is parallel to the biasing magnetic filed. To validate the Z-transform algorithm, the reflection and transmission coefficients for the right-hand circularly polarized wave of the homogeneous magnetized plasma slab are computed by means of discrete Fourier transform. The comparison between the reflection and transmission coefficients of the homogeneous plasma slab and analytical values indicates that Z-transform algorithm is very accurate. When the plasma frequency varies according to the square root and parabolic relations, the reflection and transmission coefficients of the inhomogeneous magnetized plasma slab are computed.     

FDTD implementation for magnetoplasma medium using exponential time differencing

The electromagnetic propagation in dispersive magnetoplasma medium is modeled using the finite-difference time-domain (FDTD) method based on the exponential time differencing (ETD). The ETD schemes with first-order and second-order accuracy are presented. The ETD algorithm is accurate and efficient. The reflection and transmission coefficients of the magnetized slab for the right-hand circularly polarized wave are computed.     

BI-FDTD: a novel finite-difference time-domain formulation for modeling wave propagation in bi-isotropic media

This paper presents a newly developed finite-difference time-domain (FDTD) technique, referred to as BI-FDTD, for modeling electromagnetic wave interactions with bi-isotropic (BI) media. The theoretical foundation for the BI-FDTD method will be developed based on a wavefield decomposition. The main advantage of this approach is that the two sets of wavefields are uncoupled and can be viewed as propagating in an equivalent isotropic medium, which makes it possible to readily apply conventional FDTD analysis techniques. The BI-FDTD scheme will also be extended to include the dispersive nature of chiral media, an important subclass of bi-isotropic media. This extension represents the first of its kind in the FDTD community. Validations of this new model are demonstrated for a chiral half-space and a chiral slab.     

Oscillating guided modes in a symmetric five-layer slab waveguide with anisotropic-dispersive left-handed material

A symmetric five-layer slab waveguide with anisotropic and dispersive left-handed material (LHM) in the core and righthanded material (RHM) in other layers is investigated. Through Maxwell’s equations and a transfer matrix method, the dispersion equations for the TE oscillating guided modes are obtained. Under consideration of two extremely anisotropic cases, some mode dispersion curves are plotted. The zero-order TE oscillating guided mode exists. Meanwhile, with the increase of mode number, their dispersion curves move to left or right, corresponding to positive or negative dielectric permittivity and magnetic permeability in the longitudinal direction. Besides, as the core thickness increases, mode dispersion properties change and three propagation properties appear: positive group velocity, negative group velocity and zero group velocity. The negative group velocity indicates the characteristics of the left-handed materials, and the zero group velocity implies that electromagnetic waves are trapped in the waveguide completely.     

瞬变等离子体中电磁波频率漂移特性研究

推导一维瞬变磁化等离子体的时域有限差分(FDTD)递推式,并以一维金属谐振腔作为计算模型,分析了瞬变等离子体中电磁波频率漂移特性。从理论分析出发,得到了一维瞬变等离子体对电磁波作用的解析解。通过选取相同的模型和参数,将FDTD数值解与解析解进行对比,验证了所用FDTD方法的准确性,在此基础上研究了瞬变等离子体中电磁波的频率漂移规律。     

Propagation Characteristics of a Novel NRD Guide with Double-Layer LHM Slab

A new waveguiding structure based on NRD (Nonradiative Dielectric) guide with a double-layer LHM (Left Hand Material) slab is carefully investigated. Rigorous multi-mode network treatment combining with mode matching method is carried out to analyze the propagation characteristics of the structure. Theoretical analysis results reveal that depending on the choice of permittivity and permeability of the two dielectric slabs, the guiding structure is of series distinct and interesting properties, such as anomalous dispersion, opposite polarization modes coupling, and the existence of complex mode. Besides, the new configuration can also be used as a leaky wave antenna working in the dominant or the first higher order mode. All these particular features create various applications in electromagnetic engineering.