Transient propagation in anisotropic laminated composites

A detailed analysis of the transient response of an electromagnetic pulse (EMP) and a Gaussian pulse in anisotropic laminated composites is presented. To this end, both the equivalent transmission line circuit (ETLC) model and the finite-difference-time-domain (FDTD) method are adopted in the time-domain analysis. Numerical results are presented for graphite/epoxy laminates, based on a model which treats each lamina as a homogeneous and anisotropic sheet. The factors that influence the transient response of anisotropic laminated composites, such as laminate thickness, fiber orientation, and the angle, frequency contents, and polarization of the incident wave, are also investigated     

The correct ETLC model for anisotropic lossy materials-a comment on "Transient propagation in anisotropic laminated composites"

S. He comments on a paper by Lin et al. (IEEE Trans. Electromagn. Comp., vol.25, no.3, p.357-65, Aug. 1993). Lin et al. wanted to calculate the transient response for a plane wave obliquely incident on a multilayered structure consisting of anisotropic lossy materials. They first derived an equivalent transmission-line-circuit (ETLC) model for the anisotropic lossy materials, and then used a standard circuit analysis program (PSPICE) to calculate the transient response. The method is efficient and it enables one to use the existing computer code. However, He believes that the Lin et al. ETLC model for anisotropic lossy materials is not correct. He derives and presents the correct one.<>     

Properties of and generalized full-wave transmission line modelsfor hybrid (Bi)(an)isotropic waveguides

In this paper single and coupled equivalent transmission lines are developed for the propagation of modes in reciprocal and nonreciprocal, anisotropic, bi-isotropic, and bi-anisotropic waveguides. The transmission lines are described by the generalized telegrapher's equations. In order to develop these transmission line models some properties related to reciprocity, bi-directionality, and mirroring, of general waveguides and generalized transmission lines are investigated. The transmission line models are based on the reciprocity theorem and are valid for arbitrary frequencies     

Transmission Characteristics of Sandwiches (Correspondence)

The radome design equations which are in common use are based on the transmission characteristics of sandwiches. Transmission line techniques provide a convenient method for determining these characteristics. The transmission line analogy of wave propagation has been discussed by Ramo and Whinnery. A restricted application of this analogy is given in a report by Snow. In this note, a more general application will be discussed.     

基于四值脉冲参数模型的单粒子瞬态传播机理与软错误率分析方法

随着工艺尺寸的不断缩小,由单粒子瞬态(Single Event Transient, SET)效应引起的软错误已经成为影响宇航用深亚微米VLSI电路可靠性的主要威胁,而SET脉冲的产生和传播也成为电路软错误研究的热点问题。通过研究SET脉冲在逻辑链路中的传播发现:脉冲上升时间和下降时间的差异能够引起输出脉冲宽度的展宽或衰减;脉冲的宽度和幅度可决定其是否会被门的电气效应所屏蔽。该文提出一种四值脉冲参数模型可准确模拟SET脉冲形状,并采用结合查找表和经验公式的方法来模拟SET脉冲在电路中的传播过程。该文提出的四值脉冲参数模型可模拟SET脉冲在传播过程中的展宽和衰减效应,与单参数脉冲模型相比计算精度提高了2.4%。该文应用基于图的故障传播概率算法模拟SET脉冲传播过程中的逻辑屏蔽,可快速计算电路的软错误率。对ISCAS89及ISCAS85电路进行分析的实验结果表明:该方法与HSPICE仿真方法的平均偏差为4.12%,计算速度提升10000倍。该文方法可对大规模集成电路的软错误率进行快速分析。     

FD-TD modeling of digital signal propagation in 3-D circuits withpassive and active loads

Most existing computer-aided circuit design tools are limited when digital clock speeds exceed several hundred MHz. These tools may not deal effectively with the physics of UHF and microwave electromagnetic wave energy transport along metal surfaces such as ground planes or in the air away from metal paths that are common at or above this frequency range. In this paper, we discuss full-wave modeling of electronic circuits in three dimensions using the finite-difference time-domain (FD-TD) solution of Maxwell's equations. Parameters such as stripline complex line impedance, propagation constant, capacitance per unit length and inductance per unit length can be easily computed as a function of frequency. We also discuss FD-TD Maxwell's equations computational modeling of lumped-circuit loads and sources in 3-D, including resistors and resistive voltage sources, capacitors, inductors, diodes, and transistors. We believe that this approach will be useful in simulating the large-signal behavior of very high-speed nonlinear analog and digital devices in the context of the full-wave time-dependent electromagnetic field     

Some effects of group-velocity dispersion on parametric interactions

Three-wave parametric interactions are studied in media exhibiting group-velocity dispersion. Under certain conditions these interactions may be described by the same equations that govern pulse propagation in a two-level resonant system. This analogy suggests the existence of steady-state pulse solutions in the three-wave parametric system. Such solutions are found, and are analogues of pi and two-pi pulses. The variety of solutions in the parametric system is greater than in the resonant case.     

Performance of a planar filter using a 0/spl deg/ feed structure

The advantage of using a 0/spl deg/ feed structure in filter design is that two extra transmission zeros are created in the stopband while the passband response remains unchanged. This feed structure is analyzed by using transmission matrices. A new lumped-circuit model for a coupled resonator filter is then proposed to take into account the effects of this feed structure. Finally, the feed structure is applied to the design of a cross-coupled filter. All the theoretical analysis and design procedures have been successfully verified by experiment results.     

Domain-integral analysis of channel waveguides in anisotropicmultilayered media

A domain-integral equation method is presented to determine both propagation constants and the electromagnetic field distributions of guided surface wave modes in integrated optical waveguides. Both the waveguide and its multilayered embedding are anisotropic. The permittivity tensor of the embedding is assumed to be piecewise homogeneous. The kernels of the domain-integral equations consist of Green's tensors. The integral equations form an eigenvalue problem where the electric field strength represents the eigenvector. This problem is solved numerically by applying the method of moments. Numerical results are presented for an anisotropic ridge waveguide, embedded in an anisotropic multilayered medium     

Propagation of electromagnetic pulse having a Gaussian envelope in longitudinally inhomogeneous anisotropic ionized media

For radio-wave communication with ionospheric propagation, it is useful to study the distortion of signals propagating through a plasma medium. The problem is discussed of finding the distortion of a pulse after it has propagated through a longitudinally inhomogeneous anisotropic ionized medium whose electron density varies linearly in one direction. As a model of the incident pulse source, the Gaussian envelope carrier pulse is considered. Dependence of the electromagnetic pulse distortion upon the duration of the pulse, the gradient of the electron density, the magnetostatic field, and the carrier frequency is mathematically studied in detail.     

Combinational static CMOS networks

We develop mathematical switch-level models for static combinational CMOS networks. In contrast to other available MOS models and theories, our models capture design principles that are special to CMOS, such as the use of transmission gates. First we study networks consisting of cascade connections of CMOS cells realizing negative functions. We then extend this model to incorporate transmission gates. Finally, we develop a more complex CMOS graph model which includes a ternary transient analysis and is capable of handling some unconventional, but commercially used, combinational networks. Such designs cannot be properly explained by presently available theories. Also, we discuss several general design approaches.     

Analysis of the Collocation Method for Simulating the Propagation of Optical Pulse Sequences

In analogy to the standard Split-Step Fourier algorithm for calculating the signal transmission through optical fibers, a Split-Step collocation algorithm is applied and analyzed in terms of its capability to calculate the propagation of pulse sequences in optical fibers. The method uses a point matching technique for the representation of short optical pulse sequences with Hermite-Gauss functions as basis. This special basis renders time consuming Fast Fourier Transformations (FFT) within the calculation unnecessary. The method is analyzed using realistic NRZ pulse sequences in the simulations. Accuracy and computational effort are evaluated in comparison to the Split-Step Fourier method.     

色散对光纤中高斯光脉冲传播特性的影响

从麦克斯韦方程组出发,建立了光脉冲在光纤中传播的理论模型。在只考虑色散效应的情况下,对该理论模型进行进一步的研究,数值模拟出高斯光脉冲在光纤中的传输状态,并讨论了色散对光脉冲传播特性的影响。结果表明,群速度色散会增加光脉冲的宽度而波形保持不变;三阶色散会引起光脉冲的畸变。该结论对光纤的色散补偿具有一定的理论参考价值。     

External field coupling to MTL networks with nonlinear junctions:numerical modeling and experimental validation

The problem of predicting the voltages and currents induced on a printed circuit multiconductor transmission line (MTL) network by an impinging transient plane wave electromagnetic field is considered. The MTL network contains nonlinear circuit elements and test cases with various dielectric substrates are examined. Numerical predictions based on quasi-TEM models of the MTL and modified nodal analysis (MNA) models of the lumped element junctions are compared to experimental results obtained in the time domain using a GTEM cell. As has been done in the past, the effect of the incident plane wave is introduced as forcing functions in the MTL equations. The primary goal of this paper is to quantify the accuracy of the various commonly used quasi-TEM mathematical time-domain models. It is shown that when modeling the forcing function terms, it is important to take into account the perturbation of the incident plane wave due to the dielectric substrate. (The experimental-numerical comparisons herein are shown for the case of end-fire illumination since it best demonstrates this point.) Neglecting the dielectric effect on the incident transient pulse, even for substrates with low dielectric constant, produces poor results     

Numerical simulation of thermal wave propagation during laser processing of thin films

A numerical model is developed to represent the thermal wave propagation during ultrashort pulsed laser processing of thin films. The model developed is based on the solution of non-Fourier heat conduction problem with temperature and thermal flux delays using discontinuous finite-element method. The mathematical formulation is described and computational procedures are given. The computer model is validated using the analytical solution for one-dimensional (1-D) thermal wave equations. Numerical simulations are performed to study the thermal wave propagation in a GaAs thin film exposed to ultrashort laser pulses. A wavelike behavior of the thermal signal propagation is observed, and the diffusive effect of the time relaxation in the temperature gradient is calculated and discussed. The thermal behavior of thin films under laser radiation is also studied as a function of various process parameters including pulse duration, laser pulse shapes and characteristic times of heat fluxes.     

Analytic solution of the anisotropic bidomain equations for myocardial tissue: the effect of adjoining conductive regions

The anisotropic bidomain model for the propagation of electrical activation in the human myocardium H consists of coupled elliptic-parabolic partial differential equations for the transmembrane potential Vm, intracellular potential phi(i), and extracellular potential phi(e) in H, together with quasi-static equations for the potential distribution phiB in the surrounding (passive) isotropic extracardiac regions B. Four local parameters sigma((i,e) (l,t)) specify the conductivities in the longitudinal (l) and transverse (t) directions with respect to cardiac muscle fibers. Continuous current flow is required at the interface S(H) between H and B. We derive analytic formulas for Vm, phi(e), phi(i), and phiB for plane wave propagation in a uniformly anisotropic slab surmounted by a homogeneous region of conductivity sigmaB. No assumptions are required regarding the anisotropy ratios of the conductivity coefficients. The properties of these solutions are examined with a view to providing insight into the effect of the passive region B on the propagation of Vm and phi(e) in H. We show that for a suitably chosen boundary condition, the problem can be reduced to solving the bidomain equations in H alone.     

典型场景下电波传播特性建模

为了解决某些典型场景(如海上、山区、丘陵、城区)下无法使用已有基础模型来全面表达电波传播特性的问题,建立了一种在典型场景下,基于确定性抛物方程、适用于多个传输场景的统一电波传播模型。把典型场景等效为损耗介质层来求解边界条件,利用Fourier分步步进法得到相应解,然后得到电波在典型场景下的传播损耗,并进行了理论分析和实验验证。结果表明,在不同传输场景下,将统一电波传播模型与Miller-Brown模型、射线追踪模型进行比较,结果较吻合,验证了其正确性。这一结果对建立一种求解典型场景下电波传播衰落问题的统一电波传播模型是有帮助的。     

单模光纤中洛伦兹脉冲传输特性研究

为了研究洛伦兹脉冲各参量在光纤中传输的演化特性,从麦克斯韦方程出发,建立光纤非线性传输方程,采用变分法进行了理论分析和数值模拟,得到了洛伦兹脉冲参量随传输距离的演化方程组以及振幅与脉宽、脉宽与啁啾之间的两个重要约束关系;并进一步得出了脉宽随传输距离演化的解析解;描绘了脉宽随传输距离演化的图形。结果表明,脉宽和振幅间满足绝热关系,初始啁啾会对洛伦兹脉冲的保形传输产生影响。     

Methods of theoretical analysis and computer modeling of theshaping of electrical pulses by nonlinear transmission lines andlumped-element delay lines

The mechanism by which high-power electrical pulses can be sharpened by propagation along nonlinear transmission lines and lumped-element delay lines is described with emphasis on the production of pulses with very fast leading or trailing edges. A survey of some of the mathematical techniques that have been applied to the propagation of electrical signals along nonlinear lines and ladder networks is presented, and the limitations of these techniques are discussed. The processes that both produce and limit pulse sharpening on nonlinear lumped-element delay lines are examined, and it is found that the wave equation, which describes the propagation of electrical signals along such networks, predicts that an electrical pulse will decompose into an array of solitons. An approximate formula for estimating the degree of pulse sharpening that can be produced on a delay line with a given number of sections is derived, and its accuracy is compared with experimental results. Numerical integration techniques for solving the nonlinear differential and difference equations that result from the mathematical analysis of nonlinear lines and networks are discussed, and the propagation of a voltage pulse along a lumped-element delay line containing nonlinear capacitors is simulated using a computer model based on an efficient algorithm     

Wave Propagation on Nonuniform Transmission Lines (Short Papers)

The problem of wave propagation on nonuniform transmission lines is studied. Equations are presented not only for the reflection coefficient but for the transmission and admittance properties as well. They are valid under the assumption that only one mode of propagation exists on the line and that the properties do not change so rapidly that the fundamental transmission line equations are no longer applicable. Since all equations are derived for arbitrary load conditions, an extremely versatile solution of the problem has been obtained.