混响室条件下临界辐射干扰场强计算模型

为解决均匀场与混响室内辐射敏感度测试结果相关性较差的问题,利用统计学理论对混响室内场强直角分量及天线接收功率的统计特性进行分析,理论推导出基于受试设备干扰概率的混响室条件下临界辐射干扰场强计算模型。为验证该模型的正确性,以ETS 3142E型天线为受试设备分别在混响室及均匀场中进行临界辐射干扰场强测试,实验结果表明,利用该计算模型得出的临界辐射干扰场强值与均匀场测试结果吻合良好,平均相对误差可控制在2 dB以内,可将该模型应用于实际辐射敏感度测试。     

频率搅拌混响室原理及应用

从理论上分析了混响室采用频率搅拌的可行性,仿真计算和试验测量了频率搅拌混响室内部电场的均匀性和统计特性,探索了在屏蔽效能测试中的应用。研究结果表明:频率搅拌方法能够得到空间统计均匀的电场分布,电场直角分量的模值服从瑞利分布,并且频率越高电场的均匀性和统计特性越好。在频率搅拌混响室内部测试得到开缝小尺寸屏蔽体在1~10GHz频段的屏蔽效能约为15dB,与机械搅拌混响室测试结果基本一致。     

混响室的混沌特性及其场统计分布

采用有限元数值方法计算了理想和实际结构混响室的本征频率,将其本征频率间隔分布与量子混沌理论不同系综的理论分布进行对比分析,证明了实际结构混响室的系综为高斯正交系综,混响室为混沌系统。在此基础上,利用随机平面波假设将理想金属混响室内电场矢量本征函数表示为随机平面波的线性叠加,进而将混响室内电场表示为与横电磁波两种可能的极化方式对应的矢量本征函数展开式。根据矢量本征函数的概率分布得到了电场任一笛卡尔坐标分量服从2自由度的Rayleigh分布,总场服从6自由度的Rayleigh分布。用ETS HI-6105光纤电场探头对某混响室进行了电场分量值测量,比较了测量数据与理论模型的累积概率分布。结果表明,试验结果与理论模型符合较好,证明了电场统计分布模型的有效性。     

运动平台混响的时空耦合统计模型

混响时空耦合特性是空时处理混响抑制方法中的关键问题之一。传统方法不是建立在统计模型基础上的,对实际海洋混响扩展、海洋混响环境影响及基阵非理想性导致的混响时空耦合分析缺乏有效性。论文在混响概率模型基础上,推导了运动平台的混响时空耦合关系,进一步给出了复杂水声混响环境及具体阵列指向特性下的混响时空耦合规律的统计模型。利用该模型,推导了理想窄波束基阵混响的时空耦合关系。理论解析结果和计算机仿真清晰地展示了理想阵列流形的混响时空分布规律,验证了本文理论推导结果的正确性。最后采用数值计算方法分析非理想基阵的混响空时耦合关系及空时分布规律,结果表明利用本文的混响空时耦合模型,能获得实际基阵的混响空时分布规律,可为空时处理混响抑制算法与系统设计提供一定的理论支撑。      

再入飞行器驻点流光辐射特性的理论建模

本文用直接模拟蒙特卡罗法，对再入体驻点区域的流场、光辐射特性进行了研究．针对头部锥体驻点区（包括激波层），建立了流场中的化学反应模型，中性粒子和等离子体的热运动、粒子间碰撞的理论模型，碰撞激发辐射和化学发光辐射的物理模型．给出了样本粒子运动方向和速率、粒子碰撞对的选择等蒙特卡罗法概率模型和计算方法．     

基于贝叶斯分层模型的MCMC方法在闪光图像重建中的应用

针对闪光图像得到的光程数据,采用贝叶斯分层模型建立了后验概率模型,运用Gibbs抽样动态构造马尔可夫链;进而获得了关于线吸收系数的统计结果及其不确定度,并与约束共轭梯度(CCG)方法进行对比分析。数值实验结果表明,马尔可夫链蒙特卡罗(MCMC)方法对理想光程图像的重建结果与真值近似完全一致;在含模糊和噪声时,重建结果与CCG方法相当;当含模糊且噪声干扰较大时,MCMC方法的重建结果要略优于CCG;更重要的是MCMC方法能够给出重建结果的不确定度。     

利用多馈源激励改善混响室的场均匀性

 研究了多馈源激励对混响室内场分布的影响。根据理想封闭矩形腔体内电磁场表达式,分析了混响室内场分布的影响因素;通过对比电场的最大值、分布标准差及各向同性等统计特征,重点研究了多馈源激励对腔体内场分布的影响。研究结果表明:采用多馈源激励可以有效地提高场均匀性,有利于构造均匀的电磁场环境。同时也证明了利用该方法在混响室中研究高功率微波效应的可行性。     

连续能量共轭加权蒙特卡罗动态参数计算

本文开展基于连续能量共轭加权蒙特卡罗的堆芯动态参数计算研究,这些参数主要包括缓发中子有效份额、瞬发中子代时间和瞬发中子衰减常数,在目前普遍采用的迭代裂变概率（IFP）的基础上,扩展原有IFP方法中共轭通量的选择,比较径迹长度估计、碰撞估计、吸收估计和tally记数估计的差别,及协方差和方差权重计算.同时,给出多个概率区间的动态参数分布范围,对迭代裂变概率法进行深入的研究,对比并给出下一代事件估计计数和不同中间代迭代裂变概率估计计数对计算结果的影响,从中得出合适的迭代代数.相关程序在计算完成后自动输出各种粒子分布状况统计.     

本期重点推荐论文北大核心

《水下光场的蒙特卡罗法求解》针对水下光电成像的应用需求,建立光子水下传输概率模型,利用蒙特卡罗方法求解水下光子照度随深度的分布特性,并与文献迭代法的计算结果进行比对,验证了该方法的有效性。在此基础上,模拟分析了水下点光源形成的光子照度随深度的分布特性,论文有关结果对实际工作有一定参考价值。     

用传输线和时域有限差分法计算电缆X射线响应

 介绍了时域传输线和时域有限差分两种计算电缆X射线瞬态响应的方法，并利用电缆芯线总电荷以及介质层的电荷分布，结合实验结果，分别给出了时域传输线模型中的电流源和时域有限差分模型中电流密度的计算方法。作为例子，在60 keV单能X射线垂直于电缆轴向辐照的条件下，采用两种方法计算了电缆两端接匹配负载时负载上的电流响应；采用传输线方法计算了不同能量X射线辐照电缆时的芯线负载电流响应。计算结果表明，两种方法计算的电缆X射线瞬态响应是一致的；电缆介质层中存在静电场；X射线能量不同时，电缆芯线负载电流存在最大值。计算中，电缆与X射线的作用采用蒙特卡罗方法计算。     

Coupled reverberation chambers for emulating MIMO channels

This article describes a new experimental set up for emulating MIMO channels, based on two mode stirred reverberation chambers (MSRC), coupled together with a waveguide. This guide allows one to control the order of the channel diversity, the chambers generating a Rayleigh environment. This set up could thus be used to perform tests of MIMO communication systems in perfectly defined environments and thus under reproducible conditions. After a brief recall of the advantages and drawbacks of using a single reverberation chamber, we describe the theoretical approach and the experimental results for the analysis of two coupled chambers.     

基于柔性屏蔽材料混响室的设计与应用

利用柔性屏蔽材料不平整性使屏蔽腔内场环境易于满足各向同性、均匀分布、随机极化统计特征的特点,研究了三种不同柔性屏蔽材料搭建的模式搅拌混响室的可行性。在Z字形搅拌器的作用下通过测量得到低频场均匀性和高频归一化电场的概率密度函数,根据IEC 61000-4-21-2011标准和理想混响室模型验证了所搭建混响室的有效性。在此基础之上,通过实验测量分析了搅拌器转速、天线高度、天线位置对归一化电场概率密度函数(PDF)的影响,并利用所搭建混响室对加载开孔电大金属腔的电磁屏蔽效能进行了测试。研究结果表明利用柔性屏蔽材料搭建混响室具有较好的可行性。     

Fast estimation of speech transmission index using the reverberation time

The paper presents the function of STI in the domain of reverberation time. Through the application of the said function, we can quickly estimate the speech transmission index, knowing only the time of room reverberation. For that purpose we applied a known method which consists in physical estimation of speech intelligibility basing on the modulation transfer function (MTF) determined in a room. Then, the STI was described using a logarithmic function whereof argument was the room reverberation time. To verify the model, reverberation times of six rooms were measured. The selected rooms were very different deliberately. They had different cubature and shape. The selection included a small cuboid, lecture halls and a church. Then, the same rooms were modeled in the ODEON version 11.23 and their reverberation times were determined. Furthermore, the STI was determined in the ODEON and then compared with the reverberation time obtained in effect of fast estimation. The statistical verification with the use of correlation index and regression equation has demonstrated that the fast estimation yields results close to those obtained in the computer simulation in ODEON. We obtained the correlation index at the level close to 1. Furthermore, the test probability at the level lower than 0.05 bespeaks of a statistically significant linear relation for the confidence level of 95%.     

Statistical characteristics of some standard reverberant sound field measurements

The space and time fluctuations of $\text{1}\text{3}\text{-}\text{octave}$ band sound pressure level and reverberation time measurements in hard-walled chambers have been investigated experimentally with the aim of determining characteristic probability density functions and typical variances. The basic random variables observed (that is, the mean square pressure and the reverberation time estimates) are acceptably described by a gamma distribution given in a paper by D. Lubman. A specific sampling procedure has been used for the experiments: the samples were taken in randomly chosen discrete positions and a time averaging performed in each position so that the time variances thus obtained were much smaller than the spatial variances. Such a sampling procedure leads to the statistical characteristics of the random variables being independent of any specific equipment used. With the aid of the basic probability density function, statements of precision with regard to time and space fluctuations can be made from the data obtained in this way. Confidence intervals for standard measurements of sound pressure level, reverberation time, sound pressure level difference, sound power level and transmission loss are presented. The typical variances in various possible situations are not always well-known, which means that one has to use estimated values of the variances in the derivation of the respective confidence statements. This fact causes some uncertainty, and one must regard the confidence statements thus obtained as approximate only. From the results obtained in these investigations, it appears that the degree of this uncertainty would be quite acceptable in a normal measurement situation.     

耦合空间的声学研究进展

近年来由于混响室在演艺厅堂工程上的应用,唤发了对耦合空间声场研究的广泛兴趣。本文简短地回顾了马大猷先生对室内声学简正模态理论的贡献,对近代特别是最近15年来室内声学研究在耦合空间方面的发展,做了综述性讨论,包括简正模态分析和模态分解法、统计声学方法、几何声学方法、扩散方程、以及高分辨率实验技术和贝叶斯概率分析在耦合空间研究的应用。值马大猷先生诞辰一百周年之际,以此文缅怀德高望重的声学前辈。      

Effects of edge screens on the absorption of blocks of theatre chairs

This paper reports new measurement results investigating the use of screens around samples of theatre chairs to minimize edge effects when measuring theatre chair absorption in reverberation chambers. The absorption measurements included both full scale and scale model measurements in reverberation chambers and a model recital hall. The use of screens has been proposed to better approximate the sound absorption of the larger blocks of chairs in auditoria. The method of measuring the absorption of blocks of chairs with screens around their edges and located in the corner of a reverberation chamber did not give results indicative of the values obtained for larger areas in auditoria. The addition of screens around samples of chairs did not eliminate the variation of absorption coefficients with perimeter/area ratio. The results of extrapolations from measurements of blocks of screened chairs to infinite samples gave lower absorption coefficients than found for blocks of unscreened chairs. The absorption of chairs in large performance halls can best be predicted using the P/A method to extrapolate from reverberation chamber measurements of smaller samples of unscreened chairs, with a range of P/A values, to the larger samples and lower P/A ratios of blocks of chairs typical of performance spaces.     

频率搅拌嵌套混响室场分布的统计特性

为明确频率搅拌方式下嵌套混响室内的场分布,在混响室电磁统计特性的基础上,对嵌套小室内外的场分布进行了理论研究,重点对小混响室开窗大小对场分布的影响进行了分析。当窗口为电大尺寸时,小混响室内外均服从瑞利分布;为电小尺寸时,参考车-车链路通信的统计特性,小混响室内部应满足双瑞利分布。在某大型混响室内,借助矢量网络分析仪,通过测试收、发天线间的散射参数S21,实现了样本数据的快速采集,并将样本数据与理论分布模型进行了拟合优度检验(KS检验),检验结果证明了假设分布的正确性。     

浅海混响建模的声束跟踪理论

研究建立了基于声束跟踪理论的浅海混响强度计算方法和混响时间序列仿真方法。给出了混响强度计算的简要理论推导,并进行了模型计算值与实验值的比较。建立了一种混响时间序列仿真模型,给出了其实现框架和方法。结合实验数据与文献研究结果,进行了混响序列相关特性的检验与分析。结果表明:建立的混响强度计算模型能很好地进行浅海混响强度的预报,混响序列仿真模型能仿真具有不同包络分布的混响序列,且其相关特性符合实验与文献研究结果。      

On the angular error of intensity vector based direction of arrival estimation in reverberant sound fields

An acoustic vector sensor provides measurements of both the pressure and particle velocity of a sound field in which it is placed. These measurements are vectorial in nature and can be used for the purpose of source localization. A straightforward approach towards determining the direction of arrival (DOA) utilizes the acoustic intensity vector, which is the product of pressure and particle velocity. The accuracy of an intensity vector based DOA estimator in the presence of noise has been analyzed previously. In this paper, the effects of reverberation upon the accuracy of such a DOA estimator are examined. It is shown that particular realizations of reverberation differ from an ideal isotropically diffuse field, and induce an estimation bias which is dependent upon the room impulse responses (RIRs). The limited knowledge available pertaining the RIRs is expressed statistically by employing the diffuse qualities of reverberation to extend Polack's statistical RIR model. Expressions for evaluating the typical bias magnitude as well as its probability distribution are derived.     

The combined effects of reverberation and nonstationary noise on sentence intelligibility

Listening conditions in everyday life typically include a combination of reverberation and nonstationary background noise. It is well known that sentence intelligibility is adversely affected by these factors. To assess their combined effects, an approach is introduced which combines two methods of predicting speech intelligibility, the extended speech intelligibility index (ESII) and the speech transmission index. First, the effects of reverberation on nonstationary noise (i.e., reduction of masker modulations) and on speech modulations are evaluated separately. Subsequently, the ESII is applied to predict the speech reception threshold (SRT) in the masker with reduced modulations. To validate this approach, SRTs were measured for ten normal-hearing listeners, in various combinations of nonstationary noise and artificially created reverberation. After taking the characteristics of the speech corpus into account, results show that the approach accurately predicts SRTs in nonstationary noise and reverberation for normal-hearing listeners. Furthermore, it is shown that, when reverberation is present, the benefit from masker fluctuations may be substantially reduced.