色散媒质中ADI-FDTD

基于交替方向隐式(ADI)技术的时域有限差分(FDTD)法是一种非条件稳定的计算方法，该方法的时间步长不受Courant稳定条件限制，而由数值色散误差决定。与传统的FDTD相比，ADI-FDTD增大了时间步长，从而缩短了总的计算时间。本文采用递归卷积方法将ADI-FDTD推广应用于色散媒质，推导了二维情况下色散媒质中的ADI-FDTD迭代公式。应用推导公式计算了色散土壤中目标的散射，并与色散媒质FDTD结果对比，在大量减少计算时间的情况下，两者结果符合很好。     

色散媒质二阶时域参量的演绎

为了实现色散媒质二阶时域参量的变换, 提出将色散媒质二阶参量演绎为时域参量的方法.以德拜媒质水为对象, 依据其本构参量和平面波在空气-水分界面上频域反射和透射系数, 先建立其频域超越方程式; 再依据易于得到的本构时域参量和待求的时域参量建立起其相应的时域超越方程式, 对其用迭代方法可演绎出二阶时域参量.通过时-频变换技术已证明方法的有效性.给出演绎过程和技术要点, 并对所得结果进行了讨论, 展示了因果关系.本演绎技术具有拓展延伸的潜力.     

色散媒质中ADI-FDTD的PML

基于交替方向隐式(ADI)技术的时域有限差分法(FDTD)是一种非条件稳定的计算方法,该方法的时间步长不受Courant稳定条件限制,而是由数值色散误差决定。与传统的FDTD相比, ADI-FDTD增大了时间步长, 从而缩短了总的计算时间。该文采用递归卷积(RC)方法导出了二维情况下色散媒质中ADI-FDTD的完全匹配层(PML)公式。应用推导公式计算了色散土壤中目标的散射,并与色散媒质中FDTD结果对比,在大量减少计算时间的情况下,两者结果符合较好。     

色散媒质中采用Z变换的ADI-FDTD方法

基于Z变换方法将ADI-FDTD推广应用于色散媒质,得到了二维情况下色散媒质中的迭代差分公式,同时给出了一种采用ⅡR滤波器结构来减少存储量的方法.本文方法适合于任意M阶色散媒质,最后,给出了一个算例,数据仿真结果表明,本文的算法与传统色散媒质中的FDTD相比,在计算结果吻合的情况下,存储量相当,计算效率却更高,时间步长仅仅由计算精度来决定.     

N阶色散媒质的FDTD法与数学信号处理技术

提出了一种新的Ｎ阶色散媒质的时域分析方法,并将其表征为一组无限冲击响应滤波器,将色散媒质在ＦＤＴＤ中的表述问题转化为数字滤波器（ＩＩＲ）的设计问题。改进ＦＤＴＤ能分析处理与频率有关的电磁场问题。为验证此方法的有效性和可靠性,用此方法计算了高斯平面波脉冲入射Ｎ阶色散媒质的情况,计算结果与解析值非常吻合。     

色散媒质中的完全匹配层吸收边界

将Ａ．Ｐ．Ｚｈａｏ提出的与媒质无关的完全匹配层吸收边界推广到色散媒质中,推导出了用于色散媒质的无反射完全匹配条件。并对导电媒质进行了数值实验,结果十分理想。与Ｑ．Ｈ．Ｌｉｕ的方法相比,该方法可以应用到更复杂的媒质中。而与Ｓ．Ｄ．Ｇｅｄｎｅｙ的各向异性媒质吸收层相比,在角区的处理要简单得多,更适合于时域有限差分法,对于三维问题更是如此。     

色散媒质覆盖导电体的瞬时散射

本文提出了修正的时域有限差分法（ＦＤＴＤ）来分析计算色散媒质中瞬变场问题，并采用普郎尼近似法使时域卷积可转化为违推计算，是充分利用现代计算机技术解决时域和宽带电磁场问题的一种有效手段。同时运用此方法对色散媒质中及色散媒质覆盖的导体目标瞬时域散射场进行了计算和分析，直观可靠地反映了其特性，并与传统的（非色散）ＦＤＴＤ方法计算的结果进行了比较，差别是显而易见的，为此必须重视色散媒质对瞬变场分析的影响。     

各向异性媒质中光子带隙结构色散特性的时域伪谱法分析

本文采用时域伪谱(PSTD)法分析复杂媒质中的光子带隙(PBG)结构,建立了电磁波色散特性的统一数学模型,经数值计算绘出色散曲线.在各向同性媒质情况下所得的曲线,与时域有限差分法及平面波展开法的结果相一致.在各向异性媒质情况下,能展宽原各向同性媒质PBG结构的第一阻带、并增多阻带条数.     

瞬变电磁波在色散媒质中的传播与散射

色散媒质中瞬变电磁波的传播与散射等问题的计算分析是比较困难的，特别是在时域直接分析更加困难，本文采用时域的有限差分析来分析色散媒质中的瞬变场能直观可靠地反映其特性，为色散媒质中瞬变场的分析与研究和对目标识别，电磁兼容和隐形技术等领域的理论及应用研究提供了一种简便有效的数值计算方法。     

N阶色散媒质的瞬态散射特性

本文提出了Ｎ阶色散媒质瞬态特性的时域分析方法，结合Ｚ变换对常规的时域有限差分（ＦＤＴＤ）法进行了修正，改进后的ＦＤＴＤ法能分析和与频率有关的电磁场问题，具有方法简洁、易实现等优点。为验证此方法的有效性和可靠性，对Ｎ阶色散媒质的反向系数进行了分析与计算，并与已知的解析结果进行了比较，同时，采用此时域方法对Ｎ阶色散媒质和导体覆盖Ｎ阶色散媒质散射场进行了计算和分析。     

Time-domain Wave Propagation in Dispersive Media^①

The equation of time-domain wave propagation in dispersive media and the explicit beam propagation method are presented in this paper.This method is demonstrated by the short optical pulses in a directional coupler with second order dispersive effect and shows to be in full agreement with former references.This method is simple,easy and practical.     

Time-domain Wave Propagation in Dispersive Media

Ｔｉｍｅ－ｄｏｍａｉｎＷａｖｅＰｒｏｐａｇａｔｉｏｎｉｎＤｉｓｐｅｒｓｉｖｅＭｅｄｉａ①ＪＵＺｈｅｎｌｅ，ＦＵＪｕｎｍｅｉ，ＦＥＮＧＥｎｘｉｎ（ＩｎｓｔｉｔｕｔｅｏｆＭｉｃｒｏｗａｖｅＥｎｇｉｎｅｒｉｎｇ＆ＯｐｔｉｃａｌＣｏｍｍｕｎｉｃａｔｉｏｎＴｅ...     

Phase-space asymptotic analysis of wave propagation in homogeneous dispersive and dissipative media

Arising naturally in the study of one-dimensional pulse propagation in homogeneous dispersive and/or dissipative media are certain classes of oscillatory and/or diffusion integrals which encompass the canonical diffraction catastrophe integrals due originally to Thorn and Arnold. This is especially evident within the framework of a phase-space asymptotic analysis. Depending on the order of approximation of the exact solution beyond the Liouville or "first-order quasiparticle" limit, one recognizes caustic-like structures smoothed over by hyperdiffusion. Asymptotic series for these structures, which essentially define new basic functions, have been derived, but will not be presented here. Only the salient features of these structures will be reviewed briefly, and they will be illustrated by means of several simple canonical problems. Also, their applicability to other physical areas (e.g., wave propagation in deterministically and/or randomly varying channels, diffraction, etc.) will be pointed out.     

FDTD modeling of wave propagation in dispersive media by using theMobius transformation technique

This paper introduces a technique for finite-difference time-domain modeling of wave propagation in general Mth-order dispersive media. Ohm's law in the Laplace domain with an Mth-order rational model for the complex conductivity is considered as a constitutive relation. In order to discretize this model, the complex conductivity is mapped onto the Z-transform domain by means of the Mobius transformation. This leads finally to a set of difference equations that is consistent with Yee's scheme. The resulting formulation is explicit, it has a second-order accuracy, and the need for additional storage variables is minimal. The numerical stability problem is discussed and the numerical dispersion equation for Mth-order media is given     

天波/地波组合传播模式下一阶海杂波特性分析

分析天波反射/地波绕射组合模式下一阶海杂波的产生机制、展宽原理,导出了一阶海杂波频移、展宽计算公式;结合距离换算、双基地角、擦地角计算公式,对组合模式下一阶海杂波频谱随距离、方位的分布特性及展宽特性进行了理论计算分析。实测信号频谱特征与理论分析结果的对比表明:实验结果与理论分析相符合,验证了天波反射/地波绕射集成概念是成立的,进一步证明了天波/地波集成探测技术原理可行。     

Time-domain optical wave propagation in disordered and nonuniformguiding structures

We formulate a time-domain numerical approach to optical wave propagation based on a locally one-dimensional implicit finite-difference approximation to the two-dimensional scalar wave equation and show how it can be used to study the nature of wave propagation in optical and optoelectronic devices with spatial nonuniformities and disorder. The technique is particularly well suited for the visualization of complex scattering and diffraction phenomena. We estimate the influence of interface roughness in semiconductor lasers with mirrors defined by etching processes as a function of a feature depth parameter and an in-plane correlation length. The reflectivity falls off exponentially with their product for small disorder yet remains close to its unperturbed value for the disorder scale attainable with the state-of-the-art etching technology. It is also shown how this approach can be applied to the design of an optically controlled heterojunction bipolar transistor, in which the Light enters from a lateral waveguide and must be absorbed in the base-collector depletion region     

平面光波导膜层厚度对传播损耗的影响

根据平面光波导损耗的波动理论，通过分析计算，对于传播损耗随波膜厚度的变化关系提出了新的看法，文中给出了一组以波导膜厚度为参变量的传播损耗曲线，说明在某些波导膜厚度范围内，不能有效地进行光波导传播。     

Pulsed-beam propagation in dispersive media via pulsed plane wavespectral decomposition

This paper is concerned with the behavior of transient wavefields due to a pulsed-beam (PB) wavepacket launched obliquely from a hypothetical aperture plane in a medium with generic dispersion k(ω) where k and ω are wavenumber and frequency, respectively. This generalizes our previous investigation of a PB launched normally from the hypothetical aperture plane. The problem is solved through spectral decomposition into plane waves in the frequency (ω) and spatial wavenumber (E) domains, followed by asymptotics on the spectral inversion integrals, with ω synthesis performed before ξ synthesis. Special attention in the transient spectral domain is given to paraxial PB approximations and to criteria for their range of validity, which are expressed in terms of critical nondimensional estimators that contain the beam parameters as well as the dispersion parameters of the medium. The resulting PBs can be used to synthesize transient wavefields excited by arbitrary space-time source distributions of finite support on a specified aperture plane in the medium