Complex Envelope Crank-Nicolson Nearly PML Algorithm for the Left-handed Material FDTD Simulations

Unconditionally stable complex envelope (CE) absorbing boundary conditions (ABCs) are presented for truncating left handed material (LHM) domains. The proposed algorithm is based on incorporating the Crank Nicolson (CN) scheme into the CE finite difference time domain (FDTD) implementations of the nearly perfectly matched layer (NPML) formulations. The validity of the formulations is shown through numerical example carried out in one dimensional Lorentzian type LHM FDTD domain.     

Simple and Efficient PML Algorithm for Truncating Nonlinear FDTD Domains Based on the Z -Transform Method

Based on the Z-transform method, a simple, efficient and unsplit-field implementation of the Stretched Coordinate Perfectly Matched Layer (SC-PML) is proposed for truncating the nonlinear dispersive Finite Difference Time Domain (FDTD) lattices. In addition, the nonlinear FDTD formulations using the Z-transform method are reformulated with the advantage of a simple derivative process. The proposed algorithm is validated through two numerical examples carried out in one dimensional and two dimensional domains which include Lorentz dispersion as well as Kerr and Raman nonlinearities.     

Unsplit-Field PML Algorithm for Truncating Nonlinear FDTD Domains

In this paper, unsplit-field Perfectly Matched Layer (PML) formulations are presented for truncating nonlinear dispersive Finite Difference Time Domain (FDTD) grids. The proposed scheme is based on incorporating the nonlinear Z-transform FDTD algorithm into the Auxiliary Differential Equation PML (ADE-PML) formulations. Numerical example carried out in one dimensional domain which includes Lorentz dispersion as well as Kerr and Raman nonlinearities is included to show the validity of the formulations.     

高斯波束在双负媒质中的传播特性分析

 提出了一种基于Drude色散媒质模型的2维TM模时域有限差分法，数值模拟了高斯波束从自由空间垂直入射和斜入射到双负媒质(介电常数和磁导率同时为负)平板后的折射现象，并给出了平板内外的电场强度分布。模拟结果显示：垂直入射时，双负媒质平板对高斯波束具有汇聚作用，通过改变媒质的折射率，可以控制高斯波束通过组合平板的传播时间而不发生衰减；斜入射时，折射波束与入射波束均位于法线的同一侧，高斯波束在双负媒质与空气交界面处发生了负折射。     

Unconditionally Stable Complex Envelope Wave Equation PML Algorithm for Band Limited FDTD Simulations

Unconditionally stable complex envelope (CE) perfectly matched layer (PML) absorbing boundary conditions (ABCs) are presented for truncating the scalar wave-equation finite difference time domain (WE-FDTD) grids. The formulations are based on incorporating the alternating direction implicit (ADI) scheme into the CE FDTD implementations of the scalar wave-equation derived in the PML region at the domain boundaries. Numerical example carried out in two dimensional domain shows that the proposed formulations are more accurate than the classical ADI scalar wave equation PML formulations when it is used for modelling band limited electromagnetic applications.     

基于Z变换的高阶完全匹配层实现

基于拉伸坐标完全匹配层(SC-PML)公式和Z变换方法,提出以非分裂场形式来实现具有多极点的高阶完全匹配层的高效算法,来截断时域有限差分(FDTD)网格.在吸收性能方面,高阶PML同时具有传统PML和复频率偏移完全匹配层(CFS-PML)二者的优点.提供的数值算例是二维TE极化电磁波与无限长且有限宽度的理想电导体(PEC)薄片的相互作用.仿真结果显示,高阶PML公式在衰减低频行波和隐失波及减少后期反射方面效果好,比传统SC-PML和复频率偏移的卷积完全匹配层(CPML)算法有更好的吸收性能.     

一种双开口谐振环结构的新型双负介质

 提出了一种双开口谐振环结构的新型双负介质单元模型,该模型集电、磁谐振于一体,结构简单。用时域有限差分法和CST软件对该新型结构进行了模拟对比,并对其物理机理进行了分析,解释了其双负效应发生的原因。从电磁波理论出发,导出了波导中双负介质参数的反演公式,推广了通常提取介质参数的NRW方法,并由此提取了新型双负介质的等效电磁参数。结果表明：在频率10.3 GHz附近其等效介电常数和等效磁导率的实部同时为负值,确定了其双负效应的存在。     

An effective-medium model for high-impedance surfaces

We show that high-impedance surfaces with complex microstructures can be well described by a double-layer effective-medium model consisting of an anisotropic meta-material layer (with a dispersive permeability μ) put on top of a metal sheet. We predict that a complete surface wave (SW) gap exists in such a system when the condition 0<μ<1 is fulfilled, and we verify this prediction by finite-difference-time-domain (FDTD) simulations on realistic structures. We argue that opening a SW gap in the in-phase reflection regime requires an additional mechanism for such kinds of systems, and demonstrate this argument via FDTD simulations on two commonly adopted structures. PACS 41.20.Jb; 78.20.Bh     

磁化铁氧体覆盖二维导体目标FDTD分析的移位算子方法

采用移位算子方法把时域有限差分法推广应用于二维磁各向异性色散介质—磁化铁氧体中.证明了电磁波横向入射二维轴向磁化铁氧体目标情形下,电磁波可按目标的轴向分解为横电波(TE波)和横磁波(TM波),且TE波的散射特性与铁氧体介质无关,而TM波的散射特性与介质电磁参量密切相关,同时对其物理原因进行了分析.通过采用移位算子方法处理磁化铁氧体频域本构关系,得到该情形下目标电磁散射的移位算子时域有限差的迭代计算公式,同时解决了电磁波在各向异性和频率色散介质中传播的问题.计算了轴向磁化铁氧体涂敷VonKarman型导体柱的TM波双站雷达散射截面,分析了铁氧体参量对目标双站雷达散射截面的影响.结果表明:恰当地选择铁氧体参量能有效地减少目标的雷达散射截面,本文时谐因子取exp〔jωt〕.     

一种适用于任意阶空间差分时域有限差分方法的色散介质通用吸收边界条件算法

基于伸展坐标完全匹配层方程和辅助微分方程 方法, 给出了一种在时域有限差分(FDTD) 计算中适用于常见色散介质的通用边界条件算法. 该算法适用于任意阶的FDTD空间差分, 并且由于所采用的D-H方程独立于计算区域, 所以可以被用于截断任意电介质. 数值试验结果表明, 与卷积完全匹配层 算法相比较, 所提出的吸收边界条件算法不仅通用性强、 计算复杂度低、 计算时间短, 并且吸收效果有明显的提高.     

An FDTD absorbing boundary condition for anisotropic media based on NPML

Based on the nearly perfectly matched layer (NPML) theory, a finite-difference time-domain (FDTD) absorbing boundary condition (ABC) is presented for truncating three-dimensional (3-D) anisotropic medium. In the proposed technique, the complex coordinate stretching in the NPML scheme and the spatial interpolation method are employed. The associated ABC formulations have the advantage of simplicity in the FDTD implementations. The radiation fields of an electric dipole in anisotropic media are calculated using the presented ABC. The results are numerically verified by the comparison with the reference solutions. Furthermore, in order to clearly show the effective absorbing performance of the proposed method, the reflection coefficient and time-dependent relative error for different layers NPML absorbing boundary are also simulated.     

PML-FDTD法在分析负折射率材料中的应用

将时域有限差分(FDTD)法引入了对负折射率材料物理现象的仿真研究.给出了二维TM波在负折射率材料中的时域差分方程,并且在吸收边界处使用了理想匹配层(PML).为了避免在迭代过程中出现的不稳定现象,在差分方程的推导中引入了Drude模型, 并对Pendry提出的由负折射率材料构成的平板透镜具有的完美成像现象进行了数值仿真验证.由仿真结果发现,完美成像现象只在平板透镜的折射率n=－1时出现,当n≠－1时则会出现近轴聚焦效应.     

二维各向异性磁等离子体的无条件稳定ADE-CNAD-FDTD算法

针对二维各向异性磁等离子体提出一种有效的无条件稳定算法,新算法结合了辅助微分方程(ADE)方法与Crank-Nicolson approximate-decoupling(CNAD)时域有限差分算法仿真各向异性磁等离子体介质。传统的ADE-FDTD方法应用在一维各向异性色散介质具有较高的精度和效率,将提出的新算法ADE-CNAD-FDTD应用到二维各向异性磁等离子体介质中不仅解决了电磁波在具有各向异性和频率色散特性介质中传播的仿真难题,而且去除了CFL稳定性条件。该算法在保留了原有的精度情况下大幅度地提高了计算效率并成为无条件稳定的形式。给出一个算例证明该算法的有效性,通过模拟电磁波在磁等离子体中的传播,仿真结果与传统的ADE-FDTD算法对比,证实了该算法的高效率、无条件稳定性和高精度。     

Numerical Analysis of Electromagnetic Fields in Multiscale Model

Modeling technique for electromagnetic fields excited by antennas is an important topic in computational electromagnetics, which is concerned with the numerical solution of Maxwell's equations. In this paper, a novel hybrid technique that combines method of moments(MoM) with finite-difference time-domain(FDTD) method is presented to handle the problem. This approach employed Huygen's principle to realize the hybridization of the two classical numerical algorithms. For wideband electromagnetic data, the interpolation scheme is used in the MoM based on the dyadic Green's function. On the other hand, with the help of equivalence principle, the scattered electric and magnetic fields on the Huygen's surface calculated by MoM are taken as the sources for FDTD. Therefore, the electromagnetic fields in the environment can be obtained by employing finite-difference time-domain method. Finally, numerical results show the validity of the proposed technique by analyzing two canonical samples.     

An approach for small omnidirectional microstrip antennas based on the backward waves of double negative metamaterials

In this paper, a small omnidirectional microstrip antenna (MSA) is proposed based on a compact double negative (DNG) metamaterial, which is constructed by modified split ring resonators (MSRRs) and metal strips. First, the backward wave property of the DNG slab is investigated and illustrated by full-wave simulations. It is shown that the slab can exhibit double negative parameters and support backward wave in a broadband of 8.45 GHz∼11.05 GHz, so the existence of the DNG band is proven. Then the DNG unit cells are stacked and embedded into a host substrate to construct a phase-compensating substrate for the small MSA. By using the modified transmission line model (MTLM) and 3D full-wave simulation, a small MSA is modeled and characterized. Results show that the presence of the DNG fillings can indeed greatly reduce the physical dimensions from 0.5λ to 0.17λ, while its farfield pattern is significantly different from that of a conventional half-wave-length MSA. Lastly, the E-field distributions of the small MSA and a conventional half-wave-length MSA are contrasted and discussed to explain the functional mechanism of the small omnidirectional SMA. PACS 78.70.Gq; 81.05.Zx; 84.40.Ba     

Complete analysis of photonic crystal fibers by full-vectorial 2D-FDTD method

In this paper, an extended finite difference time domain (FDTD) algorithm for the full-vectorial analysis of photonic crystal fibers has been derived. For achieving a good convergence and high accuracy, a kind of modified conformal FDTD method has been applied. An anisotropic perfectly matched layer for truncation of boundary conditions has been introduced. Material and chromatic dispersions are numerically investigated for the photonic crystal fibers with different dimensions and geometrical parameters and different dispersion behaviors are exhibited.     

基于圆柱型硅光子晶体的1×2光下路分束器

本文设计了一个基于圆柱型硅光子晶体自准直环形腔的1×2光下路分束器.该光下路分束器由三个分光镜和一个反射镜构成,其中窄光束依赖自准直效应进行传输.利用多光束干涉理论分析了光下路分束器中不同出口的理论透射谱,并且利用时域有限差分法对光下路分束器透射谱进行数值模拟计算,其结果与理论预测基本一致.当下路波长为1 550 nm时,光下路分束器的自由光谱范围约为30 nm,几乎涵盖了整个光通信C波段.由于其小尺寸和全硅材料,本文设计的1×2光下路分束器有望应用于未来的集成光路中.     

基于圆柱型硅光子晶体的1×2光下路分束器(英文)

本文设计了一个基于圆柱型硅光子晶体自准直环形腔的1×2光下路分束器.该光下路分束器由三个分光镜和一个反射镜构成,其中窄光束依赖自准直效应进行传输.利用多光束干涉理论分析了光下路分束器中不同出口的理论透射谱,并且利用时域有限差分法对光下路分束器透射谱进行数值模拟计算,其结果与理论预测基本一致.当下路波长为1 550nm时,光下路分束器的自由光谱范围约为30nm,几乎涵盖了整个光通信C波段.由于其小尺寸和全硅材料,本文设计的1×2光下路分束器有望应用于未来的集成光路中.     

Perturbation Analysis for a New Omni-Directional Antenna Consisted of Circular Rod Corrugations Gloved with a DNG Shell

A new omni-directional leaky-wave antenna is proposed in the paper, which is consisted of circular rod corrugations gloved with a Double-negative (DNG) shell. The leaky characteristics of the new antenna are analyzed by improved perturbation method. The electromagnetic fields are described in terms of a radial transmission-line network, which tremendously simplifies the analysis procedure with good calculation accuracy and brings considerable physical insight into the overall behavior of the dielectric grating antenna. The case where the n = −1 space harmonic of TE₀₁ mode radiating into the space is carefully investigated, it is demonstrated that the gloved cylindrical DNG shell greatly enhances the leaky strength of the antenna. As a result, the dimension of the antenna could be largely reduced keeping the radiation efficiency unchanged, which is of practical significance for some applications.     

一种可用于分析任意介电常数张量的各向异性波导导模的二维时域有限差分模型

为分析具有任意介电常数张量的各向异性波导的导模，本文通过把简化的二维时域有限差分（２－ＤＦＤＴＤ）法扩展至任意各向异性介质，提出了一种以Ｄ、Ｅ和Ｈ场为基础的统一的简化２－ＤＦＤＴＤ模型．利用该模型，研究了简化的复数２－ＤＦＤＴＤ方法与实变数２－ＤＦＤＴＤ方法之间的关系．文中还讨论了复变数方法和实变数方法的激励技术．