Damage identification in concrete using impact non-linear reverberation spectroscopy

High amplitude non-linear acoustic methods have shown potential for the identification of micro damage in brittle materials such as concrete. Commonly, these methods evaluate a non-linearity parameter from the relative change in frequency and attenuation with strain amplitude. Here, a novel attenuation model is introduced to describe the free reverberation from a standard impact resonance frequency test, together with an algorithm for estimating the unknown model coefficients. The non-linear variation can hereby by analyzed over a wider dynamic range as compared to conventional methods. The experimental measurement is simple and fully compatible with the standardized free-free linear impact frequency test.     

基于Timoshenko梁理论的回传射线矩阵法在传感器优化布置中的应用研究

由于结构存在阻尼现象,弹性波在传播过程中信号强度必然会随传播距离而衰减.据此提出弹性波极限传播距离与传感器极限布置间距概念,考虑到在高频率处剪切变形引起的转动惯量对结构动力特性的影响比较大,基于Timoshenko梁理论,结合经典回传射线矩阵法,提出使用局部散射矩阵确定结构损伤检测中的传感器布置极限间距,并将其应用到传感器优化算法中.针对指定检测系统,以桥梁结构Benchmark模型为例,验证算法的有效性.     

多冲载荷下激光涂层等截面上应力波特性分析

根据多冲载荷下激光涂层应力波的传播过程研究了涂层全覆盖基体试样在受冲击载荷下的变形情况.首先分析了多冲载荷下激光涂层等截面上弹性应力波的反射与透射的形成,并对弹性应力波的反射系数与透射系数、声阻抗比进行了计算和讨论.结果表明:涂层全覆盖基体的试样在多冲载荷下弹性应力波由激光熔覆涂层到基体的传播周期规律是:压缩波→拉伸波→压缩波→拉伸波…….     

Modeling of EMI response of damaged Mindlin–Herrmann rod

To ensure high sensitivity to incipient damages, electromechanical impedance (EMI) is measured at high frequencies for damage detection. In the working high-frequency range, very high vibration modes, of the order of the thousandth mode or higher, of a structural member are likely to be activated. This imposes a great difficulty on the accurate modeling of EMI response of a structure. In this paper, the reverberation matrix method (RMM) is adopted to study the dynamics of a Mindlin–Herrmann rod with surface piezoelectric patches. The rod is inhomogeneous along the axial direction so that damage-induced reduction of cross-section or Young's modulus could be easily incorporated in the model. A piecewise-homogeneous rod model is subsequently introduced to approximate the inhomogeneous rod, along with a shear lag model of interfacial bonding between the lead zirconate titanate (PZT) patches and the host rod. An analytical expression for the electric impedance (or admittance) of the coupled model of PZT patch-bonding layer-host rod system is derived. Comparison with other established results is presented. Parametric investigations are also performed to show the dynamic properties of the coupled smart structural system. The analysis in this paper provides necessary theoretical basis for damage detection of rod via the EMI signatures.     

EASE4.4新增中国吸声材料数据库介绍

长期以来EASE软件吸声材料数据库一直为美、欧公司的声学产品所占据,给中国国内用户在声学设计中造成不便.介绍声学设计软件EASE4.4新增的中国吸声材料数据库中20款产品的说明和吸声数据等,为在不同场合下使用国内吸声产品提供参考指南.     

Acoustic evaluation and adjustment of an open-plan office through architectural design and noise control

Arranging office space into a single open room offers advantages in terms of easy exchange of information and interaction among coworkers, but reduces privacy and acoustic comfort. Thus, the purpose of this work was to evaluate the acoustic quality of a real open-plan office and to propose changes in the room to improve the acoustic conditioning of this office. The computational model of the office under study was calibrated based on RT and STI measurements. Predictions were made of the RT and STI, which generated the radius of distraction r(D), and the rate of spatial decay of sound pressure levels per distance doubling DL(2) in the real conditions of the office and after modifications of the room. The insertion of dividers between work stations and an increase in the ceiling's sound absorption improved the acoustic conditions in the office under study.     

Reverberation Chamber技术应用于手机OTA量测

一般混响室多用于EMC测试中,文章针对手机的OTA全辐射功率与全性灵敏度在混响室中测试方法提出说明,并针对小型的多输入多输出天线于多重路径环境测试测试方式说明。     

基于镜像对称的多馈源混响室扩展方法研究

提出了基于镜像对称的多馈源混响室扩展方法,给出了镜像对称扩展混响室改善工作区域场性能的原理,对单混响室及镜像混响室模型进行数值模拟计算,并设计了3组仿真实验从场强大小和场均匀性两个方面验证镜像混响室改善工作区域场性能的可行性.实验结果表明:单混响室镜像对称组合扩展后,在成倍扩展混响室及工作区域体积的同时,工作区域场强增大,场均匀性有所提高,解决了混响室体积扩展与场强减小以及变频场均匀性恶化的矛盾;通过发射天线同时馈入相同功率即多个小功放合成的方法解决了混响室高场强问题,降低对功率放大器的要求,进而降低混响室的测试成本.     

Investigation of time selectivity of wireless channels through the use of RVC

A potential candidate that can be used for emulating different propagation environments is the reverberation chamber (RVC). Since mobility is of primary concern for wireless communication systems, understanding of its consequences is crucial. Mobility causes spectral broadening whose impact is generally evaluated through the observation of Doppler spectrum. In this study, investigation of Doppler spectrum characteristics through the use of an RVC and the methods for the purpose of its manipulation are presented. This study verifies that the Doppler spectrum can be manipulated in various ways. However, unless a precise setup is established it is almost impossible to obtain very specific Doppler shapes in RVCs such as widely known Jakes’ spectrum. Also, a different interpretation of mobility for wireless channels is given by the use of a new concept called motion intensity. This concept is elaborated in terms of both its technical aspects and its impact on wireless channel characterization.     

一种适用于混响环境的双传声器自适应指向性算法

在许多语音信号处理系统(如助听器)中,都采用了指向性算法处理在空间上相互分离的信号,但在客厅、会议室等室内环境中混响的存在严重影响了指向性系统的降噪性能,现有的去混响算法不能有效地抑制干扰噪声。该文提出一种适用于混响环境的自适应双传声器指向性算法,采用两个间距很小的全向性传声器,将自适应零限波束形成(ANF)结构和利用概率模型抑制混响的方法相结合,实现了在混响环境中的自适应指向性。与现有指向性和抑制混响算法相比,该算法采用一个简单的结构同步实现了指向性和抑制混响,具有较低的复杂度和较强的实时性。仿真验证了算法在混响环境中的指向性降噪性能。