Literal solutions for the time-domain response of a two-conductortransmission line excited by an incident electromagnetic field

Analytical solutions of the transmission line equations for a lossless, two-conductor transmission-line with incident electromagnetic field illumination are obtained. The equations for the terminal voltages are in terms of symbols, rather than numerical values. This form of the solution gives insight into the various factors that contribute to the overall, time-domain response waveshape that would be obscured in a numerical solution. The results are specialized to uniform plane wave illumination and to electrically short lines     

An Equivalent Circuit for Quantum Cascade Lasers

A new simpler equivalent circuit model of a quantum cascade laser based on two level rate equations is presented. The model is valid for small and large signals. A realistic current voltage model based on experimental results is included in the circuit model. Incorporation of the current voltage characteristic makes the circuit model fully compatible with parasitics and drive electronics. The model is validated by comparison of simulated results with analytica results and large signal numerical results reported earlier.     

采用双自由曲面整形的无掩模光刻照明系统

为了实现无掩模光刻系统所需求的矩形准直平顶激光光束照明,提高照明系统的能量利用率,提出了一种利用双自由曲面整形的照明系统设计方法。根据光程守恒原理和折射定律,推导了积分形式的双自由曲面面形方程;采用数值解法求解积分方程,分别设计了含有双自由曲面的双透镜整形单元和单透镜整形单元的照明系统,使用光学设计软件对两种照明系统进行模拟,得到两种照明系统的照明均匀性在93%以上,能量利用率大于91%。结果表明,两种照明系统均能实现无掩模光刻系统的高均匀性、高能量利用率照明。     

Integration of wide-band service in time division multiplex systems

The authors present a TDM (time division multiplexing) channel access concept based on narrowband and wideband traffic requests which are queued in separated parallel queues. The system may be regarded as a part of a wideband integrated services digital network (ISDN). The channel access strategy follows the premise of allocating that type of customer first into service which fits best (fills out best) the nonoccupied channels. A Poisson arrival process and exponentially distributed service times for both are assumed for both traffic types, but they may have different bit rate requirements. The model involves four characteristic random variables; its joint probability is obtained by means of balance equations. Since it is difficult to determine the solution analytically, the authors develop the transition rate matrix and suggest a procedure for the numerical solution of the balance equations. Several numerical results are presented and discussed     

Characteristic lengths for steady-state transport in illuminated,intrinsic a-Si:H

The steady-state transport equations are solved for a general small-signal case. This solution leads to the spatial distribution of the carriers in the bulk of undoped hydrogenated amorphous silicon (a-Si:H) under illumination. The general small-signal differential equations for electrons and holes, including a local and/or external electric field, are first established. Subsequently, the analysis is restricted to the case with a negligible external electric field. Two characteristic lengths appear in the analytical solution. They are interpreted for the lifetime regime as the ambipolar diffusion length and the dielectric relaxation length. Depending on the material parameters, one or the other of these lengths dominates the transport. Illustrative numerical examples for typical solar-cell-quality a-Si:H are given     

彩色AC-PDP 显示单元的一维数值模拟

根据彩色AC－PDP放电机理的物理模型，提出了基于粒子流连续性方程和泊松方程的一维彩色AC－PDP放电单元和数值计算模型。然后由其数值解描述了放电过程和电子，各种离子及中性粒子浓度的时空分布，放电单元的放电电流随时间变化以及电场强度的时空分布。     

Modeling and simulation of InAs/GaAs quantum dot lasers

Based on the analysis of carrier dynamics in quantum dots (QDs), the numerical model of InAs/GaAs QD laser is developed by means of complete rate equations. The model includes four energy levels and among them three energy levels join in lasing. A simulation is conducted by MATLAB according to the rate equation model we obtain. The simulation results of PI characteristic, gain characteristic and intensity modulation response are reasonable. Also, the relations between the left facet reflectivity of laser cavity and threshold current as well as modulation bandwidth are studied. It is indicated that the left facet reflectivity increasing can result in reduced threshold current and improved modulation bandwidth, which is in accordance with experimental results. The internal mechanism of QD lasers is fully described with the rate equation model, which is helpful for QD lasers research.     

强激光辐照PC型探测器的动态响应

基于载流子输运和强激光辐照会产生热效应造成探测器的温升,建立了描述光导(PC)型半导体探测器对激光辐照动态响应的动力学模型及非线性耦合方程组。通过进行数值模拟计算,得到了激光辐照PC型半导体探测器的动态响应情况,数值模拟结果与实验结果相吻合。该模型能适用于任何强度的激光辐照,弱激光辐照时结果与传统模型一致,强激光辐照时能描述探测器的信号饱和效应。     

位积分方程组矩量法用于精确计算非均匀介质柱的电磁散射

位积分方程组的主要特点是以电磁位为未知函数,这些未知函数在具有不同电磁参数的介质分界面处是连续的,因而在矩量法的实现过程中能够非常方便地应用高阶插值基函数来展开未知函数,以便获得高精度的解。但是,经典的点匹配方案使该模型的数值稳定性较差。本文用位积分方程组矩量法模型计算任意截面非均匀介质柱的电磁散射,采用三角形离散方案和高阶插值基函数,在测试过程中应用新提出的测试方法,克服了原位方程组矩量法模型的数值不稳定性。对矩量法矩阵中自阻抗元素的奇异性处理方法也作了详细介绍。文中提供的数值结果表明,该方法是精确、稳定的。     

Optimum cylindrical near fields for illuminating a spherical reflector

A spherical reflector antenna can be illuminated by a radiating line source along its symmetry axis. The optimal fields on a cylinder around this axis are found using a modal expansion technique. The optimal fields are expressed as combinations of cylindrical harmonics with unknown mode coefficients and set equal to the required illumination on the sphere. The resultant integral equations are solved using steepest descent methods, giving the mode coefficients. These coefficients are then checked by numerical integration. The optimal cylindrical fields are found from these mode coefficients both by integrating numerically and by steepest descent methods. The results of both techniques are checked by numerical integration. The results give theoretical aperture efficiencies of greater than 90 percent at sufficiently short wavelengths.     

强光注入锁定半导体激光器的理论分析

通过速率方程建立了强光注入半导体激光器的理论模型,研究了注入光强与从激光器注入锁定频率范围的关系.结果表明,强光注入增大了半导体激光器的注入锁定范围.同时对半导体激光器进行了时间特性的数值模拟,计算结果表明,无论是强光注入还是弱光注入,激光器的输出最终都趋于稳定,通过强光注入锁定条件与弱光注入条件下的对比,得出强光注入能有效地抑制弛豫振荡,缩短达到稳定的时间.     

A three-dimensional iterative scheme for an electromagneticcapacitive applicator

An efficient iterative method for solving quasi-static electromagnetic field problems is presented. A relaxation function is introduced in the quasi-static field equations. Then, the resulting equations can be solved by iteration. The method is similar to the one of solving a Laplace equation by computing the stationary state of a diffusion equation. Next, for a radially layered configuration the numerical results are compared with the results from an existing integral equation method. Subsequently, for a realistic three-dimensional model of a human knee numerical results are arrived at.     

Freeform optical element for uniform illumination

The energy from a source was rearranged through reflection or refraction by a freeform optical element in order to get the desired uniform illumination.The numerical results of first-order partial differential equation sets had been investigated to obtain the freeform optical element, and the equations could be used to get the characteristics of the light source and the desired illumination. For example, a light emitting diode (LED) with a Lambertian light emitting surface of 1 mm × 1 mm was applied as the light source. Two kinds of freeform reflectors and one freeform lens were designed for different illuminations, and the simulated uniformity was near to 90%. Considering the size of these freeform optical elements, the illumination system can be very compact and efficient if the freeform optical element is applied in the illumination system of projectors with LED as source.     

双曲两步模型下金属薄膜的热行为

从双曲两步热传导模型出发,运用数值差分法求解了微尺度条件下热传递问题。利用特征值法对耦合的能量方程解耦,得到一组控制薄膜中的热波传播的特征方程,对特征方程组运用Godunov格式进行离散得到特征方程组的解。通过特征方程和原控制方程之间的关系,得到薄膜的温度响应并运用这种方法求解了薄膜的激光加热问题,揭示了在短脉冲激光加热条件下薄膜中热传递的波特性以及金属薄膜中电子气和晶格温度的非平衡态特征。     

一种改进型金属-半导体-金属光电探测器数学模型

以E.Sano的金属-半导体-金属光电探测器(MSM-PD)模型为基础,提出了一种改进型的模型.该模型以多个电流源和电容并联的形式构造,以吸收区过剩电子和空穴总数为研究对象,求解速率方程.另外计算了电容,给出了暗电流与端电压的非线性计算式,改进了传统模型中暗电流的线性计算方法.通过线性叠加给出了该模型光电流的数学解析解.通过在Matlab中的模拟计算,表明该模型具有计算量小、准确度高的特点,它不仅能反映一定偏压和光照下光电流的变化,而且能展示光电子在器件中的转化过程.这种模型也能较好地应用于微弱信号的检测模拟.     

用于室内照明的自由曲面均匀配光透镜设计

以非成像光学为基础,设计了一种在大发散角范围内均匀配光的大功率LED室内照明二次配光透镜方案。采用划分网格法建立光源LED和接收面的映射关系,推导透镜自由曲面面形的一般方程,采用差分法求解透镜面形方程获得面形轮廓数据,再用三维软件建立透镜模型,通过光学仿真软件对所建模型进行光线追迹。结果表明:此方案适用于40°～140°配光角度要求的均匀配光;仿真配光角度120°的照明系统,当透镜的口径与LED发光面直径之比大于等于10时,照明系统的均匀性优于0.9,能量利用率大于92%,且照明效果不受接收面高度的影响。该设计方法为实现大功率LED室内均匀照明系统的小型化和简单化提供了一种有效的途径。     

电磁数字模拟中时间衰落的辅助场研究

将一衰减因子引入麦克斯韦方程式，得到一随时间雕落的辅助场，文中讨论了它的特性，并给出了所满足的方程及其差分离散方程。给出的计算例子说明这种人工衰减技术在分析含高Q谐振电路系统中可得到与常规时域有限差分法相同的精度。     

基于标准数学规划的非光滑器件/电路的建模及仿真

针对非光滑器件/电路的非光滑特性,提出了一种基于标准数学规划问题的建模及仿真。首先将非光滑器件建模为具有可能发生状态跳变的分段线性函数;其次给出了由这些非光滑器件构成的电路的非光滑线性特性的动态系统方程;然后对这些非光滑动态系统方程进行时间离散化得到各种类型的一步非光滑问题,如(线性)互补问题或具有等式-不等式约束的非线性(或二次)规划,进而进行数值求解。仿真实验结果表明,本文所提出的数值建模方法对于具有大量事件的非光滑系统是有效的,对于模型参数的变化具有鲁棒性。     

基于LightTools的大口径积分球辐射特性仿真

为了研制辐射特性相对理想的大口径积分球,采用LightTools仿真分析了5种光源位置和3种照明模式,共15种直径为3 m积分球模型的辐照度面均匀性和朗伯特性。相比依靠经验设计积分球,计算机仿真研究具有周期短、成本低、重复性高等优点。仿真结果表明:照明模式和光源位置对积分球开口处辐照度面均匀性影响很小;而对开口处朗伯特性产生较大影响。首先,光源方向上的朗伯特性最差,其次,对称式照明模式则会改善朗伯特性,另外,随着光源与积分球前后半球交汇面的距离不断增加,积分球的朗伯特性逐步变优。最后,测试了直径为3 m积分球在不同照明模式下的辐照度面均匀性、光源方向和垂直方向的朗伯特性,实测辐射特性与仿真结果相吻合。