微型样品局部弹性的声显微成象研究

对微型样品或微掺杂复合材料样品的声学和机械特性进行了声显微成象研究,利用扫描声学显微镜对陶瓷基体内掺杂氮化硼纤维的复合材料进行了研究,在单根纤维内和基体中纤维－基体界面附近出现一系列明暗相间的圆环,分析了其形成机理,它是由于声显微镜输出信号中漏泄瑞利表面波信号同从纤维－基体界面反射的漏泄瑞利表面波信号之间相互干涉的结果。通过对干涉环的分析和研究,可求出瑞利波的声速,由此对微型样品的声学特性、弹性特性和力学性质进行研究和评价。     

500 MHz反射式机械扫描声学显微镜的研究和试制

本文叙述了500MHz反射式机械扫描声学显微镜的研究试制工作。介绍了显微镜的基本结构,分析和讨论了声透镜的分辨率和显微镜的实际分辨能力。测试结果证明该显微镜的分辨率已达2μm。文章最后给出一些样品的声学图像和声学特征曲线。结果说明它具有一些独特功能和广泛的应用前景。     

合成语声的声学分析及识别特征算法*

目的 当前社会新型犯罪中电信诈骗案件频发，急需一种能够自动有效区分语音真伪的方法。为进一步增强目前深度学习领域识别合成语音的能力，为保障语音信息安全提供技术上的支持。方法 本文针对合成语音声学特性上异于真实语音的特点，分析对比合成语音和真实语音的声学特性，设计了一种声学特征RMSA量化语音音强变化程度，结合FFV和SNS声学特征进行融合，量化了声学特性差异，聚焦了合成语音中关键声学信息。结果 在神经网络模型中融合输入声学特征，在FoR数据集的验证集上得到了0.6%的等错误率，在测试集上最好结果达到了10.8%的等错误率。结论 成功实现了对合成语音的识别，证实了声学特征的有效性和本文研究方案的可行性，在一定程度上拓宽了合成语音特征设计的研究思路。     

金属薄板缺陷的超声多途Lamb波检测

金属薄板在动车等现代化设计中应用广泛,其是否存在缺陷等检测具有很重要的意义。为此,利用超声多途提供的额外数据来检测金属薄板的缺陷,提出相应的算法,多途路径在直接反射的路径上是可以预测和识别的,直接反射路径是相对比较容易识别的。同时利用ANSYS有限元建模不同的薄板缺陷模型,在不同的传感器位置、缺陷位置、缺陷大小情况下分别进行仿真。通过ANSYS仿真和实验检测都得出了良好的结果,误差在可控制范围之内,证明了超声多途应用与金属薄板Lamb波检测的是可行的;仿真和实验表明超声多途通过实际和多途虚拟扩展的传感器数据的分析证明了超声多途能够对薄板缺陷进行定位并检测其大小。提出的超声多途检测方法,通过单次测量即可检测出薄板缺陷的位置和大小,具有良好的检测性能。     

Delta掺杂制备p-GaN薄膜及其电性能研究

采用Delta掺杂技术制备了p型氮化镓薄膜，并利用原子力显微镜、霍尔测试、X射线衍射、荧光光谱等测试手段对样品的形貌和电导性能进行了分析，发现Delta掺杂样品比均匀掺杂样品晶体质量和电导性能都有很大提高，说明Delta掺杂可有效抑制缺陷，并对缺陷抑制机理进行了讨论；最后，对掺杂前的预通氨过程作了深入的研究，结果发现，预通氨对掺杂不益. 关键词： 氮化镓 LEDs MOCVD Delta掺杂     

超声检测中人工神经网络对缺陷定量评价

分析了均匀各向同性介质的超声检测中,耦合因素和仪器因素造成的脉冲回波幅度的差异,提出了误差校正方法。以校正后的缺陷回波和底面反射波的峰－峰值为特征量,利用人工神经网络进行缺陷类型识别和大小评价。为模拟自然缺陷的二基本要素——光滑曲面和带棱边的平面,用有机玻璃制作了代表性的横穿孔和平底孔缺陷样品共１８个．对１８个缺陷样品的缺陷回波和底面反射波的峰－峰值测量了四次,并进行的校正．用人工神经网络对这组缺陷样品进行的处理结果表明：（１）设定的缺陷类型全部准确识别。（２）估计缺陷大小与标称孔径吻合较好。最后,对测量误差和缺陷大小估计误差进行了分析。     

连接时序分类准则声学建模方法优化

对基于连接时序分类准则(connectionist temporal classification,CTC)的端到端声学建模方法进行研究和优化。研究分析了不同声学特征、建模单元以及神经网络结构对CTC声学模型性能的影响,针对CTC模型中blank符号共享导致的建模缺陷提出了建模单元相关的非共享blank方法进行改进,并引入融合建模单元关联信息的模型初始化方法进一步提高CTC模型的性能。在300小时标准英文数据集Switchboard的实验结果显示,结合非共享blank、时延神经网络以及融合建模单元关联信息的初始化方法,CTC声学模型相对于基线系统在词错误率上取得绝对1.1%的下降,同时在训练速度上取得3.3倍的提高,实验结果证明本文针对端到端声学建模提出的优化方法是有效的。      

局域共振型声学超材料机理探讨

本文以二维固体薄板中的弹性波传播为例, 对基于共振子结构的声学超材料带隙机理进行了探讨, 证明在声学超材料中带隙形成既与共振子对波的散射相位有关, 也与波在共振体之间的几何传播相位有关. 通过调节散射相位和几何传播相位均能实现对色散关系的调控. 基于这一理解, 探究了弹性波超材料中的次波长缺陷态和负折射现象的实现条件.     

基于黄金分割搜索算法的行波管测量方法

为了提供声学材料的测试环境,该文通过有源吸声技术在行波管中建立了一套测量系统,声管中实现了模拟无限水域的行波场环境,从而对样品的声学参数进行测量。提出了一种利用黄金分割搜索算法对最佳时延与幅值进行搜索从而完成行波场建立的方法。在上述行波场建立的基础上,利用双水听器法分别对水柱与钢板样品的声学参数进行了声学测量,透射系数测量值与理论值符合较好。该方法为声学参数的测量方法提供了有意义的参考。     

基于数据融合的风电机组噪声预测

根据风电机组噪声信号检测复杂的情况,研究风电机组非声学参数的信息熵特征,对机组噪声进行多源数据融合预测。分析基于信息熵的非声学参数的特征提取方法,并对传统的基于遗传算法的支持向量机回归(GA-SVR)的缺陷提出改进,结合实际应用的非声学参数的信息熵特点平衡遗传算法(GA)的终止条件。通过统计分析完成了输入变量的筛选,去除了对预测影响较大的共线性因素,并实现了输入降维提高预测精度和速率。最后应用数据的信息熵特征,训练改进的GA-SVR建立最终的多源数据特征级融合预测模型。通过对比表明基于多源数据融合的预测方法精度最高,预测结果的相对误差平均值为0.7757%,具有实际可行性。     

An ultra-thin acoustic metasurface with multiply resonant units

In this paper, we propose an ultra-thin acoustic metasurface constructed of multiply resonant units to manipulate reflected wavefront. As a counterpart to the Helmholtz resonator (with monopolar resonance) and membrane-type resonator (with dipolar resonance), the multiply resonator are used in metamaterials to induce strong quadrupolar resonance. Here we use the multiply resonator as a new kind of building blocks to make acoustic metasurfaces. The used multiply resonant unit is composed of solid materials, and the acoustic metasurface can work in a water background. We demonstrate that the proposed acoustic metasurface achieves good performance in anomalous reflection, focusing, and carpet cloaking. The thickness of the acoustic metasurface is about two orders of magnitude smaller than the acoustic wavelength in water. A design of unit group is further proposed to avoid the phase discretization becoming too fine in such a long-wavelength condition.     

Design, simulation and structural optimization of a longitudinal acoustic resonator for trace gas detection using laser photoacoustic spectroscopy (LPAS)

The design of the acoustic resonator is critical for the optimization of the sensitivity of laser photoacoustic spectroscopy (LPAS) in trace gas detection applications. In this paper, an LC circuit model is used for the simulation of a 1D acoustic resonator. This acoustic resonator is designed for CO photoacoustic spectroscopy. The effects of the structural parameters, quality factor and resonant frequency on the performance of the device are theoretically analyzed. The role of the buffer volume as an acoustic filter is investigated and optimized dimensions of the buffer volume, to achieve minimum noise transmission coefficient, are calculated. The effects of the ambient temperature, variety of pressure and gas flow velocity on the resonant frequency of photoacoustic resonator and PA signal are simulated. The temperature dependence of the microphone sensitivity is also introduced.     

光声池径向共振模式耦合系数理论分析

光声光谱法是基于红外吸收光谱原理的一种高灵敏度的微量气体探测技术。它使用声共振腔来实现微弱声信号的共振放大。通过调节激光的调制频率,当它等于腔的某个共振频率时,在腔内形成声驻波,而腔本身的作用相当于一声放大器。共振腔的放大作用取决于当前被激活的共振模式、腔的品质因素、声传感器的状态以及电磁辐射与腔共振模式的耦合作用。值得关注的是,红外激光相对于声共振腔的入射方位不同则激励产生的光声信号幅值也不同。采用理论推导与数值计算相结合的方法,以圆柱形光声池为例,研究了径向共振模式下耦合系数受激光入射方位的影响。研究表明,激光入射角在0~π/2范围变化时耦合系数存在2个零点和2个极大值:入射角为0或tan-1(0.859 2×2R/L)时,耦合系数为零而径向共振失效;入射角为tan-1(0.556 8×2R/L)或tan-1(2R/L)时,耦合系数极大而径向共振最强。此处R为池径而L为池长。结果可用于指导光声池结构优化设计与安装调试,增强光声法检测微量气体的信号幅值,提高检测灵敏度。     

Experimental and computational investigation of coupled resonator–cavity systems

Launch vehicle noise is broadband in nature and the noise transmitted into the payload fairing is reduced by treating its interior with an acoustic absorption layer. The latest generation payload fairings are made from composite material which offer poor noise attenuation at low frequencies. One possible solution for reducing the low frequency noise is to use Helmholtz resonators tuned to a few of the dominant low frequency components, such as shell ring frequency or the first few cavity modes of the fairing. The paper presents a simplified modelling approach for numerical simulation of a coupled cavity–resonator system which is validated by experiments. The influence of damping and resonator volume fraction on the coupled system performance, to suppress the first axial mode in a cylindrical cavity, is shown and the resonator volume fraction required for significantly (more than 5 dB) suppressing the cavity axial mode is established.     

Compressibility-near-zero acoustic metamaterial

This letter theoretically analyzes and experimentally demonstrates a novel class of compressibility-near-zero (CNZ) acoustic metamaterials, achieved by using resonant-type metamaterials, namely the Helmholtz resonator. We first present a closed analytical formula for the effective compressibility of the proposed unit cell and then show that two frequencies exist which may support CNZ propagation. We demonstrate how the choice of the actual operating CNZ frequency depends on the properties of the host and finally experimentally verify CNZ propagation of acoustic waves.     

Transfer matrix methods for sound attenuation in resonators with perforated intruding inlets

A resonator with perforated intruding inlet (PII) is a superior silencer element, since the use of perforated inlet extensions can dramatically improve the acoustic performance. In this work, both a one-dimensional (1D) and a two-dimensional (2D) transfer matrix methods are developed to predict the transmission loss of the resonator without considering the mean flow. Based on the two groups of comparisons with tests, it is found out that the applicability of 1D method is limited by the resonator geometry even when the frequency is below the cut-off value of plane wave. Whereas the 2D approach is much more accurate while predicting the transmission losses within entire frequency range. Subsequently, five groups of resonators are chosen to determine the effects of structure parameters to transmission loss based on the 2D approach. The resonant frequency decreases and more resonant peaks appear when the length of inlet extension increases. A higher perforation rate leads to a shift of resonant peak towards higher frequencies. Besides, better acoustic performance could be obtained with the perforation being properly designed. Reducing the inlet/outlet radius can obviously improve the transmission loss without changing the frequency of resonant peak. The theories and conclusions in this study can be used for the design and optimization of resonators in various engineering applications.     

圆柱形光声池结构及环境因素对声学本征频率的影响

以典型的圆柱形光声池为研究对象,建立光声池声学仿真有限元模型,并在此基础上,研究了光声池中谐振腔、缓冲腔、进出气孔结构参数以及温度、湿度因素对其声学本征频率的影响规律.研究结果表明:圆柱形光声池的进、出口孔对其声学本征频率影响极不敏感,设计计算中可以忽略不计,谐振腔的长度影响最为敏感,其次为谐振腔的直径.此外缓冲腔的长度与直径对其亦有一定影响,因而在准确计算时需要加以考虑.温度与湿度对光声池声学本征频率的影响均呈现正线性增长规律,温度的影响随着谐振腔长度的增大而减小,湿度的影响随着温度的升高而增大,仅计算光声池的声学本征频率时,湿度的影响在室温环境下且湿度变动较小的条件下可以忽略.     

基于FW-H方程的Hartmann哨辐射声场数值研究*

该文基于声类比法,通过求解FW-H方程,对不同喷口与谐振腔位置关系的Hartmann哨的声场分布进行了分析,计算了不同位置关系的Hartmann哨的声指向性。得到了以下结论:喷口与谐振腔位置关系对Hartmann哨的发声基频几乎不产生影响。对称位置关系的Hartmann哨的声场呈对称趋势,且在垂直于喷流方向上达到最大;非对称位置关系的Hartmann哨不再呈现对称趋势。Hartmann哨的最大声压级随着偏离对称位置的距离的增加有小幅增加,最大声压级出现的方向向着谐振腔方向移动。     

Condition monitoring of a single-stage gearbox with artificially induced gear cracks utilizing on-line vibration and acoustic emission measurements

The condition monitoring of a lab-scale, single stage, gearbox using different non-destructive inspection methodologies and the processing of the acquired waveforms with advanced signal processing techniques is the aim of the present work. Acoustic emission (AE) and vibration measurements were utilized for this purpose. The experimental setup and the instrumentation of each monitoring methodology are presented in detail. Emphasis is given on the signal processing of the acquired vibration and acoustic emission signals in order to extract conventional as well as novel parameters-features of potential diagnostic value from the monitored waveforms. Innovative wavelet-based parameters-features are proposed utilizing the discrete wavelet transform. The evolution of selected parameters/features versus test time is provided, evaluated and the parameters with the most interesting diagnostic behaviour are highlighted. The differences in the parameters evolution of each NDT technique are discussed and the superiority of AE over vibration recordings for the early diagnosis of natural wear in gear systems is concluded.