一种端接负载的同轴传输线特性阻抗时域测量方法

针对作为微波阻抗及散射参数标准的同轴线特性阻抗准确测量的热点和难点问题,提出了一种端接负载的同轴传输线特性阻抗时域测量方法,其测量结果可溯源至几何量等物理参数,实验验证结果的有效性En＜1,该方法可以作为同轴传输线特性阻抗量值准确测量的参考方法。     

基于特性阻抗的半主动吸声研究

提出了一种新的半主动吸声方法,并设计了一种新的半主动吸声系统.该系统由一层吸声材料和可以移动的刚性板组成,调节刚性板与吸声材料之间的空腔深度,使得吸声材料的表面特性阻抗和空气的特性阻抗相匹配,从而使吸声系数达到最大.最后进行了实验,实验结果表明了在中低频平面声波入射时,采用本方法的吸声效果改进比较明显,但在高频平面声波入射时,采用本方法的吸声效果就不是很明显,此时吸声主要是依靠吸声材料被动吸声.     

基于室内环境品质的空调列车车内空气参数标准研究

在分析国内外室内环境品质研究成果的基础上,首次引入了环境品质线的新概念,并结合空调列车车内空气参数的具体条件,提出了车内空气参数的一个建议性标准。     

基于TDR的特性阻抗时域测量系统的设计与实现

本文首先通过LabVIEW对TDR模块实行虚拟化设计,然后与MATLAB进行混合编程,完成了特性阻抗时域测量系统。实际操作和测量结果表明,本特性阻抗测量系统具有测量高效、操作简易、结果精确等优点,适用于PCB传输线特性阻抗流水线的测量。     

微波多层板基材的性能要求

介绍了微波多层板所用基材的性能参数,重点阐述了材料的介电常数、介质损耗、热胀系数、特性阻抗对多层板性能的影响。通过对微带线特性阻抗公式的理论计算,得出了带线的线宽W、导体层的厚度t、介质的厚度h以及介电常数ε1的精度对特性阻抗Z。的影响程度。这4个因素中,介质的厚度h和带线的线宽W对特性阻抗Z。的精度影响最大。总结了国内外微波介质材料的研究情况,优选了适合于制造微波多层板的材料。     

一种矢量网络分析仪测量同轴传输线特性阻抗的方法

本文提出了一种应用矢量网络分析仪直接测量同轴传输线特性阻抗新方法.通过建立数学模型,推导出特性阻抗的计算公式,然后经实验验证其方法和测量结果的正确性.     

基于材料表面特性阻抗的吸声系数测量研究

吸声材料的吸声系数是由吸声材料表面特性阻抗表征的,因此通过测量吸声材料的表面特性阻抗就可以得到吸声材料在某一频率的吸声系数。基于此,根据吸声材料表面的表面特性阻抗是吸声材料吸声系数的一个重要参数的原理,提出了一种新的测量吸声系数的方法。本系统的测量方法不仅简单,这对快速测量材料吸声系数具有重要的意义。     

波导阻抗传递标准——三厘米标准负载

阻抗标准在微波计量中属于基本标准一类,在已建立的三厘米波段微波阻抗国家标准装置中,作为一级阻抗标准的是一段尺寸极精确的标准波导段和电铸四分之一波长短路器。标准波导段提供准确的特性阻抗,被测阻抗值均以它作参考。四分之一波长短路器的反射系数模为1,其精确值可由几何尺寸及电导率计     

简析回波损耗RL的不良原因及解决对策

回波损耗RL是电缆链路由于阻抗不匹配所产生的反射,RL原理如图1所示。这种不匹配主要来自于两个方面：一是线缆与连接器的特性阻抗不匹配;二是线缆本身特性阻抗不均匀。现在我们从这两个来分析一下影响RL的几种原因及解决方法。     

横电磁波传输室分布电容和特性阻抗的计算

本文给出计算横电磁波传输室分布电容和特性阻抗的新方法。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。