纳米尺度金属-氧化物半导体场效应晶体管沟道热噪声模型

随着CMOS工艺的发展,热载流子效应对沟道热噪声的影响随着器件尺寸的降低而增大,传统热噪声模型未能准确表征沟道的热噪声.本文通过解能量平衡方程,得到电子温度表达式,并结合沟道漏电流表达式,建立了沟道热噪声模型.利用建立的电子温度表达式,该热噪声模型考虑了热载流子效应的影响,并且在计算热噪声的过程中考虑了电子温度对迁移率降低的影响以及温度梯度对热噪声的影响.通过分析与计算,结果显示,随着器件尺寸的减小,温度梯度对电子温度产生显著影响,使得热载流子效应的影响增大,热载流子效应对热噪声的增长作用超过了迁移率降低对热噪声的减小作用,最终导致热噪声增大.本文建立的沟道热噪声模型可应用于纳米尺寸金属-氧化物半导体场效应晶体管器件的噪声性能分析及建模.     

真空绝热板边缘热桥效应数值分析及实验研究

真空绝热板的热桥效应对其自身导热系数及使用寿命具有重要的影响。真空绝热板产生热桥效应是由于外部阻隔膜和内部芯材导热系数相差较大,热量传递不均匀所致。通过理论分析、数学建模、实验研究等方式量化分析线性热桥和点热桥。实验结果表明,线性热桥占真空绝热板有效导热系数的5%—15%,而点热桥占比不到1%。基于实验结果得到线性热桥在实际应用中不可忽视的结论。量化分析组成热桥效应的各个部分有利于深入研究热桥效应的传热机理,进而实现对真空绝热板更加高效的利用,增加其使用寿命。该研究工作为实际应用时降低真空绝热板的热桥效应提供一种新思路和参考价值。     

功率型GaN基发光二极管芯片表面温度及亮度分布的物理特性研究

基于电流连续方程、欧姆定律及定性三维热流传导模型研究发光二极管(LED)芯片 的电流密度分布、热量、温度之间的相互交叉关系,进而测试分析GaN基蓝光 LED电流扩展效应和亮度分布的关系,认为芯片亮度变化趋势可作为判别电流扩 展性能的有效手段. 由于芯片表面温度、亮度分布和电流密度之间存在紧密的联结 关系,通过测试芯片表面温度或亮度分布就可定性了解器件电流扩展性能, 从而为优化电极结构提供一种判定依据. 在不同电流和热沉温度下,进一步 讨论了电流密度非均匀性和亮度分布的关系, 电流密度拥挤将导致芯片局 部区域热量堆积,非辐射复合作用增强,限制出射光子数目, 因此热 量是影响亮度分布的重要因素之一. 通过载流子传输机理进一步说明 温度影响亮度均匀性的原因,并通过实验说明理论分析的可行性. 通过优化电极结构能改善器件的电流扩展效应以及亮度均匀性, 对提高大功率LED的可靠性具有重要作用.     

热惯性对热弹性行为影响的渐近分析

当热作用时间或受热器件结构尺寸呈现微尺度特征时, 热流运动的惯性效应将对热量的传递过程产生显著地影响. 基于热质的概念, 依据牛顿力学原理引入用于描述热质运动的热波方程, 结合各向同性材料的本构关系, 构建了计及热流运动惯性效应的广义热弹性动力学模型. 利用超常传热的微尺度特征, 采用解析的方法对半无限大体外表面受热冲击作用的一维问题进行了渐近求解. 通过对热波、热弹性波的传播和各物理场分布的分析以及与已有广义热弹性理论预测结果的对比, 揭示了热流运动的惯性效应对热弹性行为的影响. 结果表明：热量的传递除了受到热流加速的时间惯性影响之外, 热流运动的空间惯性也对传热行为产生影响, 当计及空间惯性时, 热波、热弹性波的波速、波前位置, 各物理场的建立时间、阶跃峰值及阶跃间隔均受到不同程度的影响. 关键词： 热惯性 热质运动 广义热弹性动力学模型 渐近分析     

惯性约束聚变中内爆混合的模型构建

从热斑质量方程和能量守恒方程入手,重新计算考虑混合后聚变燃料的比内能和比热容等热力学参数,分析混合效应在轫致辐射损失等能量输运方面的作用,构建有杂质混合情况的热斑燃烧动力学模型.根据静态模型中的热斑燃烧的功率平衡条件,研究烧蚀层杂质混合比例与点火阈值和热斑自持燃烧的关系.理论分析和数值计算表明,混合效应导致热斑中的轫致辐射增强是点火失败的重要因素之一.通过调整不同掺杂材料、混合浓度及混合方式,得到壳层混合与热斑面密度、热斑离子温度的演化之间的关系.最后,基于模拟结果给出两种降低混合影响的方法.     

基于真实气体效应的湍流标度律特性

在量热完全气体、热完全气体和化学反应完全气体等3种气体模型假设下,利用Mach数为4.05、壁温为1 300 K的超声速槽道湍流的直接数值模拟（direct numerical simulation,DNS）结果,对标度律和自相似性做了详细分析.结果表明,不仅在量热完全气体模型下存在标度律和扩展自相似性,而且在热完全气体和化学反应完全气体模型下标度律和扩展自相似性仍然成立.压缩性的影响使得速度结构函数通过Favre平均获得更为合适.与热完全气体模型的结果相比,化学反应完全气体和量热完全气体模型的结果吻合更好.      

薄层稠油藏溶剂辅助蒸汽驱产量预测模型

通过分析生产数据和数值模拟结果,将薄层稠油油藏溶剂辅助蒸汽驱生产过程分为蒸汽前缘垂向扩展阶段、蒸汽前缘水平扩展阶段及冷凝水产出阶段.针对每个生产阶段,通过联合质量守恒方程、运动方程、能量守恒方程及溶剂扩散方程得到描述蒸汽前缘扩展和产油量解析模型.能量守恒方程属于典型的第二类Volterra 积分函数,首先对其进行Laplace变换;之后运用半解析方法对该模型进行求解.为验证模型的正确性,将模型的溶剂辅助蒸汽驱计算结果与数值模拟结果对比,整体误差仅为4%.新模型可以方便简单地分析不同溶剂性能和注采参数对溶剂蒸汽驱开发效果的影响.     

非对称HALO掺杂栅交叠轻掺杂漏围栅MOSFET的解析模型

为抑制短沟道效应和热载流子效应, 提出了一种非对称HALO掺杂栅交叠轻掺杂漏围栅MOSFET新结构. 通过在圆柱坐标系中精确求解三段连续的泊松方程, 推导出新结构的沟道静电势、阈值电压以及亚阈值电流的解析模型. 结果表明, 新结构可有效抑制短沟道效应和热载流子效应, 并具有较小的关态电流. 此外, 分析还表明栅交叠区的掺杂浓度对器件的亚阈值电流几乎没有影响, 而栅电极功函数对亚阈值电流的影响较大. 解析模型结果和三维数值仿真工具ISE所得结果高度符合.     

基于热质理论的广义热弹性动力学模型

具有微尺度传热特征的超常传热过程中,热流矢与温度梯度之间存在延迟效应,且热流的运动受到空间效应的影响.基于热质概念的普适导热定律,结合Clausius不等式和Helmholtz自由能公式,构建了计及热流矢和温度对时间和空间惯性效应的广义热弹性动力学模型,推导了各向同性材料超常传热行为的热弹性控制方程组.通过与已有广义热弹性动力学模型进行对比分析可得,当热流密度不大的条件下,热流矢与温度对空间的惯性效应可忽略时,基于热质概念的广义热弹性模型可分别退化为L-S,G-L和G-N的模型;对于尺度微观、稳态导热条件时,热流矢与温度对空间的惯性效应不可忽略,此时导热系数将受到热质运动惯性效应的影响,利用所建模型可揭示稳态导热时呈现的非傅里叶现象,并可避免基于已有广义模型得到的导热系数随结构特征尺寸变化的非物理现象.     

高功率电磁脉冲作用下MESFET热效应的时间尺度统一算法

提出高功率电磁脉冲作用下MESFET热效应分析的时间尺度统一算法.提高联合求解电磁场方程、热传导方程和载流子方程的效率.讨论利用时域有限差分法求解的数值稳定性和计算误差.通过一个计算实例,得出仿真结果与实验测量数据吻合,表明算法可行.     

定形相变墙板改善轻质墙体夏季隔热性能研究

本文提出了将定形相变蓄能墙板安装在轻质保温墙体内侧,取代传统重质材料,改善围护结构夏季隔热性能的方法.以北京地区为例,比较了定形相变蓄能墙板与重质混凝土在改善轻质围护结构隔热性能方面的差异,并从相变温度和相变墙板厚度两个方面对定形相变蓄能墙板的使用效果进行了优化.研究表明定形相变蓄能墙板能有效改善轻质保温墙体的隔热性能,而对建筑自身承重增加很小.     

Criticism of statistical energy analysis for the calculation of sound insulation: Part 2-double partitions

The theory of statistical energy analysis has been applied to the problem of estimating the transmission loss of a single finite panel. This theory was extended to the problem of a finite double-leaf partition structure.This paper deals with the degree of agreement of the measured values with the theoretical results of the sound insulation of double partitions according to this theory.In addition, the advantages and disadvantages of this method compared with classical methods are discussed. A comparison between the method of statistical energy analysis and classical methods for the calculation of the sound insulation of double partitions is given.     

真空绝热板在大型低温储罐上的应用

真空绝热板(VIP)由于其优良的绝热性能,已经在许多领域得到了广泛的应用,但在大型低温储罐上的应用并不多见。基于这一现状,从绝热效果、技术性以及经济性等方面,论述了真空绝热板在大型低温储罐中应用的可行性。分析表明,真空绝热板可以提高大型低温储罐的绝热效果,降低储罐建造难度和绝热层施工难度,而且还减少了绝热层厚度,降低了绝热成本,可以在大型低温储罐中逐步推广应用。     

四边简支含多孔材料双层板隔声特性

有限大含多孔材料和空气层复合板结构隔声特性的研究尚不充分。该文旨在研究四边简支边界条件下复合板结构隔声特性。首先基于流体饱和多孔弹性介质的声传播理论计算了声波在多孔介质中的传播波数；继而采用四边简支边界条件下板结构的模态函数，利用模态叠加法和伽辽金法推导了复合板结构隔声系数理论模型，并数值求解复合板隔声量。将理论模型得到的四边简支复合板隔声量与实验结果对比，验证了理论模型的正确性。最后，详细讨论了边界条件、板结构尺寸和多孔材料厚度等主要参数对隔声特性的影响。结果表明：四边简支复合结构隔声特性曲线上“谷值”出现得较少，并且简支复合板隔声特性的第一个“吻合频率”比固支支撑复合板更靠近低频，当频率超过3000 Hz以后，简支和固支边界条件复合板结构隔声特性趋于一致。     

基于拓展分离变量法的层合材料瞬态传热分析

层合材料各层热物理参数不同,难以用常规的分离变量法求解.针对此问题对常规分离变量法进行了拓展,将层合材料受热时的温度场在时间域上分成微小时间段,在每个微小时间段内层合材料交界处的温度可认为随时间正比变化,并假设比例系数,此时在微小时间段内对各层分别利用分离变量法单独求得解析解,根据交界处温度相等能量连续的关系可求出比例系数,进而求出该微小时间段内的温度场,通过循环求解可得整个时间段内的温度场.之后,利用拓展的分离变量法对常用层合隔热材料瞬态传热进行了分析,通过与有限元方法计算的结果比较,验证了本文方法的正确性,分析了隔热材料类型、厚度,材料表面对流换热系数,空气温度等参数对隔热效果的影响.拓展分离变量法利用解析的方式求解了层合材料瞬态传热问题,物理意义比常规的数值方法明确,计算效率也较高.     

分布式通风消声板特性研究*

在隔声板结构中,分布式内嵌大量小型消声单元,在入射声波被消声单元有效衰减的同时,气流可均匀通过整个板结构,形成一种分布式消声板结构。利用平面波理论和修正传递矩阵法,建立消声板简化模型,并预测模型传递损失。加工消声板样件,实验室内测试并验证其声学及通风性能。对比隔声测试结果与预测结果,验证修正传递矩阵法针对该结构的准确性,同时验证消声板结构的实际效果。结果显示,该分布式消声板结构具有良好的声学效果,修正传递矩阵法可应用于该结构的声学性能预测以及结构设计。     

Analytical evaluation of the acoustic insulation provided by double infinite walls

The acoustic insulation provided by infinite double panel walls, when subjected to spatially sinusoidal line pressure loads, is computed analytically. The methodology used extends earlier work by the authors on the definition of the acoustic insulation conferred by a single panel wall. It does not entail any simplification other than the assumption that the panels are of infinite extent. The full interaction between the fluid (air) and the solid layers is thus taken into account and the calculation does not involve limiting the thickness of any layer, as the Kirchhoff or Mindlin theories require. The problem is first formulated in the frequency domain. Time domain solutions are then obtained by means of inverse Fourier transforms using complex frequencies.The model is first used to compute the sound reduction provided by a double homogeneous brick wall, with identical panels, when illuminated by plane sound waves. The results are then compared with those provided by the simplified method proposed by London, which was later extended by Beranek (London-Beranek method). The limitations of the simplified London-Beranek model, namely, its applicability only to double walls with identical mass, subjected to plane waves, and its failure to account for the coincidence effect, are overcome by the method proposed.Time signatures are produced to illustrate the different sound transmission mechanisms. Several types of body and guided waves are originated, giving rise to a complex dynamic system with multiple reflections within the solid and fluid layers and the global resonance of the system. The effect of the cavity absorption is considered by attributing a complex density to the air filling the space between the two wall panels. Absorption attenuates the dips of insulation controlled by the cavity resonances. Several simulations are then performed for different combinations of wall and air layer thickness to assess the influence of this variable on the final acoustic insulation. The influence of the air cavity on sound reduction was found to be dependent on the frequency. At low frequencies a better performance was achieved for thicker air layers, while at higher frequencies a thinner air layer is preferable. The use of wall panels with different mass resulted in the wall performing better, particularly for high frequencies.     

钢结构装配式住宅墙板连接方式对隔声性能的影响*

为提升其隔声性能,通过有限元法数值分析,比较了不同位置墙板的连接方式对房间隔声性能的影响。结果表明：(1)侧墙墙板柔性连接处理对侧向传声的抑制作用显著,当侧墙墙板采用柔性连接后,房间的隔声量在低频段平均可以提升3 dB左右;(2)公共隔墙墙板的柔性连接对房间低频段隔声量提升不明显,甚至在160 Hz、400 Hz、500 Hz等频率下隔声量有所降低。最后,基于模拟分析结果对装配式墙体连接方式提出了改进策略。     

Sound insulation characteristics of multi-layer structures with a microperforated panel

Multi-layer structures have issues with sound insulation at low and mid-frequencies due to mass-air-mass resonance. The purpose of this study is to investigate improvements to the sound insulation performance of multi-layer structures using a microperforated panel (MPP), which can absorb well over a wide frequency range. Although MPPs have been investigated over the last several decades, almost all studies have been conducted in terms of sound absorption. Herein the sound transmission loss of multi-layer structures with flexible MPPs of infinite extent is theoretically investigated. The calculation is based on the wave equation and the equation of panel vibration including the effect of perforation of the panel. Additionally to consider a more realistic sound insulation performance, the effect of the directional distribution of the incident energy in a reverberation chamber is taken into account. Experiments are conducted using an acoustic tube to validate the calculated results and the reverberation chamber method to verify the actual sound insulation characteristics. Both experiments agree well with the theoretically calculated perforation effects. Consequently, MMPs are confirmed to improve the deterioration of sound insulation performance due to mass-air-mass resonance of multi-layer structures.     

A millimeter wave technique for measuring ice thickness on the Space Shuttle''s external tank

The external fueltank of the Space Shuttle contains extremely lowtemperature propellents. A layer of material known as SOFI (Spray-On Foam Insulation) covering the outside of the fueltank provides thermal insulation between the aluminum surface of the fueltank and the ambient air. In spite of this insulation, under certain conditions ice formation will occur on the surface of the SOFI. Ice on the external fueltank can be detrimental to the launch and it is important to detect its presence and measure its thickness. This paper describes the design of a millimeter-wave radiometer technique developed for this purpose. The design is based on model calculations and measurements of the emission properties of a panel from the external fueltank performed at 35, 94 and 140 GHz. Two sets of measurements were performed, one for the unmodified rough-surface SOFI panel and another for a panel whose surface was sanded down to produce a smooth surface interface with the ice cover. The latter was used to evaluate the results of radiative transfer calculations which are much easier to perform for multilayer structures with plane boundaries. We present experimental evidence demonstrating that the technique developed can accurately predict ice thickness in the case of the smooth-surface SOFI panel. For the original (rough-surface) panel, the emission levels observed were considerably higher than predicted by the model. Both cases however exhibited comparable sensitivities to ice thickness ( K/mm at 35 GHz, 4 K/mm at 94 GHz, and 5 K/mm at 140 GHz).