Automatic generation of starting values for the simulation ofmicrowave oscillators by frequency domain techniques

A new approach to the start-up problem inherent to the large-signal analysis of autonomous circuits in the frequency domain is presented. By insertion of a simple network, depending on one parameter, the oscillator is damped to the stability limit where a linear analysis yields good results. The steady state of the undamped oscillator is then obtained by a continuation method corresponding to the successive removal of the damping network. With this procedure the degenerate solution may be excluded in a straightforward manner     

A coupled efficient and systematic full-wave time-domain macromodeling and circuit Simulation method for signal integrity analysis of high-speed interconnects

This paper presents an accurate and systematic approach for analysis of the signal integrity of the high-speed interconnects, which couples the full-wave finite difference time domain (FDTD) method with scattering (S) parameter based macromodeling by using rational function approximation and the circuit simulator. Firstly, the full-wave FDTD method is applied to characterize the interconnect subsystems, which is dedicated to extract the S parameters of the subnetwork consisting of interconnects with fairly complex geometry. Once the frequency-domain discrete data of the S parameters of the interconnect subnetwork is constructed, the rational function approximation is carried out to establish the macromodel of the interconnect subnetwork by employing the vector fitting method, which provides a more robust and accurate solution for the overall problem. Finally, the analysis of the signal integrity of the hybrid circuit can be fulfilled by using the S parameters based macromodel synthesis and simulation program with integrated circuits emphasis (SPICE) circuit simulator. Numerical experiments demonstrate that the proposed approach is accurate and efficient to address the hybrid electromagnetic (interconnect part) and circuit problems, in which the electromagnetic field effects are fully considered and the strength of SPICE circuit simulator is also exploited.     

A Theoretical Method for Design and Realization of Fixed Amplitude Sinusoidal Oscillators

In this paper, a new method for design and realization of a sinusoidal oscillator is proposed. The oscillator has fixed amplitude. As we know, the design of this kind of oscillator is very difficult because of its sinusoidal form and fixed amplitude. Design is done in state space domain. After designing, oscillator is realized base on the concepts of trees and links. In fact, we design a nonlinear system such that its phase portrait corresponds to oscillation and also prespecified amplitude of the oscillation. Then we transfer it to time domain. The design of appropriate nonlinear system is base on equipotential curves.     

Influence of noise intensity on the spectrum of an oscillator

This paper investigates the influence of high-intensity noise on the correlation spectrum of a two-dimensional (2-D) nonlinear oscillator. An exact analytical solution for the correlation spectrum of this 2-D oscillator is provided. The analytical derivations are well suited for oscillators with white noise of any intensity, but computational constraints on the solution of the partial differential equation may make it impractical for cases where the number of state variables exceeds three. The spectral results predicted by our analytical method are verified by numerical simulations of the noisy oscillator in the time domain. We find that the peak of the oscillator spectrum shifts toward higher frequencies as the noise intensity is increased, as opposed to the fixed oscillation frequency predicted in the existing literature. This phenomenon does not appear to have been reported previously in the context of phase noise in oscillators.     

Pattern Nulling in Coupled Oscillator Antenna Arrays

An optimization method is presented for constrained beam steering with null formation in linear coupled oscillator arrays. The method is based on a perturbation model of the far field of the array that includes both amplitude and phase perturbations, to accommodate prescribed nulls. Moreover, it takes into account the array nonlinear dynamics through a first-order approximation model of the array steady state. The optimization results are verified by harmonic balance simulations. Also, the stability of the optimized solutions is examined by perturbing the steady state solution and is verified with envelope transient. Design examples are used to demonstrate the validity and limitations of the proposed method     

Two mathematical models of unconfined detonation and their numerical solution

We consider the numerical solution of an unconfined detonation problem modelled by differential/algebraic equations in a boundary value format. The problem has index one throughout the interval of integration, except at a free boundary point, where it has index two. Moreover, a nonlinear constraint is active at the free boundary point. We consider a simple mathematical model, as well as a more realistic and functionally complex model. In both cases, the resulting boundary value problem is solved directly, using a collocation method. This approach compares favorably with the solution techniques proposed previously in the literature and enables us to examine some interesting properties of the solution to the detonation problem.     

General noise analysis of nonlinear microwave circuits by thepiecewise harmonic-balance technique

This paper presents a self-consistent set of algorithms for the numerical computation of noise effects in forced and autonomous nonlinear microwave circuits. The analysis relies upon the piecewise harmonic-balance method, and thus retains all the peculiar advantages of this technique, including general-purposeness in the widest sense. The noise simulation capabilities include any kind of forced or autonomous nonlinear circuit operated in a time-periodic large-signal steady state, as well as microwave mixers of arbitrary topology. The limitations of the traditional frequency-conversion approach to noise analysis are overcome. The analysis takes into account the thermal noise generated in the passive subnetwork, the noise contributions of linear and nonlinear active devices, and the noise injected by sinusoidal driving sources of known statistical properties. The nonlinear noise models of two representative families of microwave devices (FET's/HEMT's and Schottky-barrier diodes) are discussed in detail, and several applications are illustrated     

基于FWCM的非线性动态电路时域稳态模拟

本文提出一种基于快速小波配置法（ＦＷＣＭ）的非线笥动态电路时域稳态模拟方法。该方法可以对电路瞬态响应过程用大步长（低阶小波）模拟,而对稳态响应过程用小步长（高阶小波）模拟,从而避免了为得到电路稳态响应而在瞬态响应时期花费的大量的模拟时间。并且,该方法具有较低的计算复杂度。一些模拟结果证明,本文的方法是一种十分有效的方法。     

The transient evolution of AM mode locking a TEA CO2laser

The evolution of the pulse in an AM mode-locked TEA CO2laser has been investigated. The experiments have been performed by injecting the mode-locked pulses in a high-pressure slave oscillator at various time intervals after the initiation of the mode-lock process. This technique allows the measurements of the pulse widths independent on the pulse energies. A numerical solution of a dynamic model for the mode-locking process accurately predicts the transient evolution. It is shown that the build-up time to reach steady state can be, depending on the modulation depth, considerably larger than the duration of the pulse train.     

Nonlinear design of multiple-cavity switchable dielectric-resonator oscillators

The application of nonlinear CAD techniques to the design of multiple-cavity dielectric-resonator oscillators is demonstrated. The circuit topology consists of an FET oscillator which can be coupled to one of several dielectric resonators by means of a diode switching network. The circuit is numerically designed as a whole making use of a novel broadband optimisation technique especially devised for autonomous nonlinear circuits. At each fundamental frequency of interest the steady state of oscillation is determined by harmonic-balance analysis and at the same time the oscillator is tuned to the prescribed frequency by changing a parameter of the corresponding resonator. The electrical performance is simultaneously specified at all the fundamentals, and the optimisation is carried out with respect to the circuit parameters of the frequency-invariant part of the network.<>     

Time-Domain Analysis of Lumped-Distributed Networks

A new method for time-domain analysis of networks containing transmission lines and lumped linear/nonlinear elements is presented. A key feature of the method is a procedure for generating a system matrix in a manner that involves only sums of subnetwork (or element) terms (no products or quotients). Numerical integration algorithms are used to reduce the problem to a solution of sparse algebraic equations.     

A Genetic Algorithm and Analysis of Designing Large Enterprise Network Topology

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考虑热松弛时间的半无限粘弹性压电杆的热冲击问题

基于具有一个松弛时间的广义热粘弹性理论,研究了半无限压电杆热冲击问题。利用现代控制理论中状态空间法求解了偏微分控制方程,获得了拉普拉斯变换域内的精确解。利用数值反变换方法,得到了位移、温度和应力的分布曲线,同时将广义理论和传统耦合理论做了对比。从这些结果来看,当所考察时间的量级短到与材料热松弛时间量级相同时,热松弛影响着所有场变量的分布。材料粘性性质不影响温度分布,但在时间很短时对应力分布影响显著,而对位移分布的影响为时间愈长愈明显。     

模拟大规模电路的快速频域小波配置法

提出了一种求解状态方程的方法:频域快速小波配置法.通过将状态方程转入频域求解,并对输出变量直接进行小波展开.这一方法比原有的时域快速小波配置法大大减少了未知变量的数目,从而使计算速度和存储空间都有很大程度的改善.由于小波函数及其反变换均有显式的数学表达式,这一方法在得到频域解析近似解的同时就可以获得时域解析近似解,无须在计算过程中进行耗时的数值积分反变换.同时通过自适应算法的引入,这一方法可以有效提高计算效率.     

改进的牛顿法确定大气消光系数边界值

在用激光雷达方程反演大气消光系数时,大气消光系数边界值对反演精度影响较大,而在低层大气中该值较难确定。文中提出了一种基于改进牛顿法的大气消光系数边界值确定方法,其核心思想是,把确定大气消光系数边界值的问题转化为求非线性方程的数值解。首先,根据大气消光系数边界值与激光雷达回波信号功率以及大气光学厚度之间的关系,假设大气消光系数边界值为x,构建一个非线性方程。其次,采用改进的牛顿法求非线性方程的数值解,得到大气消光系数边界值。使用香港天文台装置在香港国际机场的多普勒激光雷达回波信号数据,对该方法的可行性和可靠性进行了验证。结果表明:利用该方法确定边界值,可以较为准确地反演出低层大气消光系数。该方法收敛速度快,迭代次数少,并且不需要计算导数值,极大地减少了运算量,具有较强的实际应用价值。     

基于FDTD方法的微带线耦合噪声研究

基于时域有限差分（FDTD）方法,采用单轴各向异性介质完全匹配层为吸收边界条件,用上升沿为200ps、稳态值为1v的斜坡信号为激励源,在微带线间距保持不变,激励源及负载与微带线特性阻抗相匹配的情况下,研究微带宽度、PCB介质基板厚度和相对介电常数等参数对平直微带线近端耦合噪声和远端耦合噪声的影响,其次,研究微带线中部的直角弯曲对不同参数微带线耦合噪声特征的影响规律,和当微带线直角弯曲被45&#176;斜切后,前述不同参数微带线耦合噪声特征的变化,结果有助于微带线的优化设计。     

Three-dimensional electrical impedance tomography: a topology optimization approach.

Electrical impedance tomography is a technique to estimate the impedance distribution within a domain, based on measurements on its boundary. In other words, given the mathematical model of the domain, its geometry and boundary conditions, a nonlinear inverse problem of estimating the electric impedance distribution can be solved. Several impedance estimation algorithms have been proposed to solve this problem. In this paper, we present a three-dimensional algorithm, based on the topology optimization method, as an alternative. A sequence of linear programming problems, allowing for constraints, is solved utilizing this method. In each iteration, the finite element method provides the electric potential field within the model of the domain. An electrode model is also proposed (thus, increasing the accuracy of the finite element results). The algorithm is tested using numerically simulated data and also experimental data, and absolute resistivity values are obtained. These results, corresponding to phantoms with two different conductive materials, exhibit relatively well-defined boundaries between them, and show that this is a practical and potentially useful technique to be applied to monitor lung aeration, including the possibility of imaging a pneumothorax.     

基于导热反问题的复合材料内壁不规则缺陷Ansys二次开发红外诊断识别

针对人工编程数值建模进行缺陷识别反问题求解存在编程复杂、分析效率低的局限性,提出了采用通用有限元数值计算软件Ansys结合共轭梯度算法进行二次开发对复合材料内壁不规则缺陷进行红外诊断定量识别的方法,并引入了相对敏感系数的概念用于比较评估试件检测状态对缺陷边界形状定量识别的影响。通过相对敏感系数分析发现,不同检测状态下内壁不规则缺陷的可检测性并不相同,采用检测面达到最大温差时刻点的瞬态检测比稳态检测更具优越性。数值试验验证了Ansys二次开发红外诊断识别的可行性和相对敏感系数比较评估的有效性。     

Transients on lossy transmission lines with arbitrary boundary conditions

In this work the problem of transients on a lossy transmission line terminated by an arbitrary, including nonlinear, load is formulated. The tranmission line parameters are the constantsR, L, G, andC. The exact relation between the input and output voltages and currents in the form of two coupled integral equations is derived by the Laplace transform method. It is shown that the kernels of the integral equations may be represented in terms of either Lommel functions or integrals involving zeroth order modified Bessel functions. Simultaneous (numerical) solutions of these integral equations fulfilling the boundary conditions at the input and output of the line yields the input and output voltages and currents on the line. Finally the exact analytical relations in time domain of the voltage and current at an arbitrary point on the line (and the voltages and currents at the input and output terminals) are derived. In all parts, the problem has been formulated in such a way as to impose the causality condition explicitly.