基于麦克风阵列的罐装食品真空度在线检测

声音频谱峰值法被广泛应用于罐装食品真空度检测领域,但是当检测环境出现声音强度较大且与罐盖振动产生的声音的频段相同的噪声时,该方法可能做出误判。为此,提出声学阵列法:由麦克风阵列采集多路混合声信号,采用稀疏半非负矩阵分解从混合声信号中分离出干净的罐盖振动产生的声音,再利用声音频谱峰值法判断真空度是否合格。该文研究稀疏半非负矩阵分解的数学模型,并且推导求解稀疏半非负矩阵分解的迭代优化函数。实验结果表明,无噪声环境下,声音频谱峰值法和声学阵列法的真空度检测结果均准确,但在噪声环境下,声音频谱峰值法出现误判时,声学阵列法仍能做出准确判断。     

光孤子通信系统的色散控制研究

光纤色散特性是支撑光纤孤子通信的决定性因素。比较了目前的几种色散补偿方案后,着重对相位共轭控制的色散控制方式进行了分析研究,该方式利用光纤非线性四波混频产生与输入光脉冲信号相位共轭的输出光脉冲信号,光脉冲的频谱以泵浦光频为中心进行反转,构建成相位共轭器,实现了对放大自发辐射(ASE)噪声、孤子相互作用与色散波等的控制,达到提高系统传输速率、距离和通信容量的目的。     

单模硫系玻璃光纤的制备及其超连续谱的产生特性

硫系玻璃具有独特的红外光学性能和极高的光学非线性等特点, 使得硫系光纤成为中红外超连续谱产生的优选材料。基于二次挤压法制备了单模As-S光纤, 并利用飞秒脉冲和光参量放大器作为泵浦源研究了该光纤的中红外超连续谱的产生特性, 包括光纤长度、泵浦波长、泵浦功率对超连续谱产生的影响。结果表明该单模光纤具有较低的传输损耗和较小的材料色散分布; 相比于传统零色散点波长附近泵浦, 在正常色散区且杂质吸收峰附近泵浦也可获得脉冲的极大展宽(泵浦参数: 4.5 μm, 1 kHz, 150 fs, 光纤长度23 cm, 输出谱宽为1.5~8.7 μm@60 dB带宽); 较短长度的硫系光纤便可产生超宽频谱输出, 相反, 光纤长度越长输出频谱越窄且平坦性变差。     

基于LabWindows/CVI和DSP的高精度频谱分析系统

介绍一种以LabWindows/CVI为软件平台,PC和DSP为硬件平台的虚拟仪器系统。该系统能够实现信号实时采集,对信号进行时域分析和频域分析,并可通过相位差法等四种频谱校正方法实现频谱校正,以此提高系统频谱分析的精度。     

光纤布拉格光栅型色散补偿模块的校准方法研究

基于相移法和微分相移法的传统色散校准方法无法满足梳状谱条件下的光纤布拉格光栅(FBG)型色散补偿模块的校准需求,提出了针对FBG型色散补偿模块的校准方法,将色散校准系统中的宽带光源用高波长分辨力、高输出功率的可调谐光源替代,通过波长的连续扫描实现窄波长范围的色散测试与量值溯源,并且借助可调谐光源的高功率和信噪比性能显著提高了色散测试的动态范围。     

能量色散X—荧光谱仪测定黄金饰品

众所周知,黄金饰品具有经济价值和使用价值。为了识别饰品伪真和质量,产生了许多检测方法:火试金法是检验K金含量的标准法,但操作复杂,技术性强和具有破坏性,故把它作为一种仲裁方法。密度法是测定已知杂质含量的黄金成色。虽然它是无损检测,但有一定的技术难度,所以用得较少。用得较多是x—荧光谱法(波长色散x—荧光谱仪和同位素x—荧光仪等等)。但随着科学技术的发展,尤其电脑的发展。波长色散x—荧光谱仪能满足各项分析要求。但该仪器较复杂,价格昂贵以及对周围环境要求较高等等。     

声光频谱分析技术研究

介绍利用我们研制的以声光滤光器（ＴＡＯＦ）作为色散元件的声光频谱分析装置［１－４］，对若干透明固体和液体的频谱进行测试的结果。实验表明，各种物体所固有的声光（ＡＯ）频谱是不相同的，这可作为对物体的微细结构分析的一种鉴别方法。     

基于频谱相似度的ICA不确定性快速消除

为了消除ICA估计的排序、相位、幅值等盲不确定性,提出一种基于快速傅立叶变换与频谱最大相似度为准则的ICA估计源校正方法.借助于观测信号的混合特征和频谱特性以及估计信号的频谱特性的分析,成功地消除汽车变速箱振动估计信号的不确定性.仿真结果证明该方法的有效性,也表明该法在源的识别和重构方面具有较大的应用潜力.     

复杂变速箱齿根裂纹诊断

本文针对齿轮出现裂纹后其振动信号特征，选用时域同步平均参数法和倒频谱的方法，对某型坦克变速箱的齿轮裂纹信号进行了分析。结果表明，在无载荷条件下，时域同步平均后的时域参数法较倒频谱法对齿根裂纹诊断更有效。     

改进MBCV法在滚动轴承故障诊断中的应用EI北大核心CSCD

针对传统最大类间方差法(Maximum Between‑Class Variance,MBCV)在分离轴承故障信号过程中存在的分割阈值适应性差、分离效果不佳的问题,提出一种基于MBCV动态阈值曲线的滚动轴承故障诊断方法。该方法通过MBCV法获得频谱均分子区间的各分割阈值,然后高阶拟合各部分阈值进而获得动态阈值曲线,再通过调整优化频谱分段数量并以分离信号与原信号之间的均方根误差最小化为目标确定最优阈值曲线;依据最优动态阈值曲线将信号频谱分割为高、低两部分,对低幅值部分进行傅里叶逆变换及平方包络谱分析进而诊断故障。此方法能有效消除强干扰成分,最大化提取轴承故障特征。实验分析结果表明,相比于传统MBCV法,该方法提取的故障特征更加明显。     

FBMC/OQAM水声通信系统的适应性成型脉冲设计

水声信道是一个时变的双扩散信道,不仅会引起传输信号的时频扩展,而且会造成严重的信息损失。由于滤波器组多载波/交错正交幅度调制(Filter Bank Based Multicarrier/Offset Quadrature Amplitude Modulation, FBMC/OQAM)系统可通过改变发送信号的成型脉冲来减小时频扩展带来的符号干扰和子载波干扰,因此更适合快速时变的水下声信道。为了降低现有成型脉冲设计算法的优化难度,提出了一种快速且易于实现的成型脉冲设计方法,该方法根据信道时频统计特性对扩展高斯函数(Extend Gaussian Function, EGF)进行了优化,实现了期望信号能量最大化,并在时域符号间加入适当的保护间隔,进一步增强了抗多途干扰的能力。仿真结果表明,无论在高频散信道还是在低频信道下,相比于其它成型脉冲算法,该算法在降低计算量的同时,改进了的FBMC/OQAM系统的传输性能,误码率降低了2～3 dB。     

模态声发射在结构材料缺陷定位中的研究

针对在役结构材料中间时存在静态和动态缺陷时难于进行缺陷平面定位的问题，利用声发射技术实时记录声发射波形时域信号的特点，结合薄板中Lamb波的频散特性和Gabor小波时频分析方法，研究并提出了一种新的实用定位方法。该方法通过先后采用三角形和椭圆平面定位方法可分别反演动态缺陷、静态缺陷的位置，并利用低频时频散不明显的对称模态波速和同一时域信号的相对时差来避免波速变化与各传感器间灵敏度差异和门槛值不同对椭圆定位精度的影响。经过实验研究证明，应用这种方法反演得到的缺陷位置和实际缺陷位置一致。     

Simulation of acoustic wave propagation in dispersive media with relaxation losses by using FDTD method with PML absorbing boundary condition

We present a method to incorporate the relaxation dominated attenuation into the finite-difference time-domain (FDTD) simulation of acoustic wave propagation in complex media. A dispersive perfectly matched layer (DPML) boundary condition, which is suitable for boundary matching to such a dispersive media whole space, is also proposed to truncate the FDTD simulation domain. The numerical simulation of a Ricker wavelet propagating in a dispersive medium, described by second-order Debye model, shows that the Ricker wavelet is attenuated in amplitude and expanded in time in its course of propagation, as required by Kramers-Kronig relations. The numerical results also are compared to exact solution showing that the dispersive FDTD method is accurate and that the DPML boundary condition effectively dampens reflective waves. The method presented here is applicable to the simulation of ultrasonic instrumentation for medical imaging and other nondestructive testing problems with frequency dependent, attenuating media.     

Study of linear wave motions using FFT and its potential application to non-destructive testing

The dispersive characteristics of longitudinal, flexural and surface waves in beams, plates and thick blocks are constructed by applying the Fast Fourier Transform (FFT) to the measured transient waves. The so-constructed dispersion curves of various types of waves are in good agreement with the analytical predictions. An iterative method for estimating the material properties of the medium using the dispersive characteristics of the waves is also developed. The method provides a reasonable estimation on the properties of the medium.     

Guided wave expansion in warped curvelet frames

Lamb wave testing for structural health monitoring (SHM) often relies on analysis of wavefields recorded through scanning laser Doppler vibrometers (SLDVs) or ultrasonic scanners. Damage detection and characterization with these techniques requires isolation of defect-induced reflections in the wavefield from the injected wave packet and from scattering events associated with structural features such as boundaries, rivets, joints, etc. This is a challenging task when dealing with complex structures and multimodal, dispersive propagation regimes, whereby various wave contributions in both the time/space and the frequency/wavenumber domain overlap. A new mathematical tool named warped curvelet frames (WCFs) is proposed to effectively decompose the recorded wavefields. The presented technique results from the combination of two operators, i.e., the curvelet transform (CT) and the warped frequency transform (WFT). The CT provides an optimally sparse representation of nondispersive wave propagators. Combining the CT with the WFT allows for a flexible analysis of multimodal wave propagation in dispersive media. Exploiting the spatial and temporal localization of curvelets, as well as the spectro-temporal adaptation of the analysis frame to the characteristics of each propagating mode, provided by frequency warping, a convenient decomposition of guided waves is achieved and relevant contributions can be effectively isolated. The proposed approach is validated through dedicated simulations and further tested experimentally to demonstrate the effectiveness of the method in separating guided wave modes corresponding to acoustic events in close spatial proximity.     

Study of band structure of one-dimensional photonic crystal composed of dispersive and nonlinear dielectric materials

The analysis of band structure of one-dimensional (1-D) photonic crystal containing dispersive and non-linear dispersive materials has been presented. The band spectra for the different combination of photonic crystals have been calculated by the well-known plane wave expansion method. The effect of the dispersive and non-linear materials on the band structures has been determined. The third-order nonlinearity has been considered in the non-linear material, and Lorentz–Drude model has been taken for dispersive material. The band gaps of considered photonic crystal are affected by the nonlinearity in the presence of dispersive material like gold. We have observed that the normalized frequency difference between photonic bands decreases on increasing intensity of input beam. This work may be useful in optical switching devices.     

含裂纹故障的齿轮系统动力学特性研究及其故障特征分析

考虑齿轮的时变啮合刚度、传动误差和轴承支撑刚度的影响,建立含齿根裂纹故障的齿轮系统多自由度力学模型,基于动力学方法对其故障机理进行研究。通过材料力学的方法计算齿轮在正常和含裂纹两种情况下的啮合刚度,对比两种刚度曲线的变化趋势,便于进行精确的动力学特性分析;对建立的模型求解系统的动态响应,结果表明当齿根存在裂纹时,其时域波形中会出现周期性的冲击现象,频谱中在啮合频率的基频及其倍频等地方形成一系列等间隔的边频谱线,其间隔大小等于故障齿轮的转频;这些边频成分幅值较低,能量分散且分布不均匀,在不同频带的幅值大小存在差异。针对上述特点,通过正交小波包方法对信号的频带进行分解,应用倒频谱分析各子频带信号的边频成分;结果表明,该方法能够有效的提高信号的信噪比,有助于识别和提取信号中由裂纹故障引起的边频成分。     

Multiple target detection using split spectrum processing and groupdelay moving entropy

The split spectrum processing technique obtains a frequency-diverse ensemble of narrow-band signals through a filterbank then recombines them nonlinearly to improve target visibility. Although split spectrum processing is an effective method for suppressing grain noise in ultrasonic nondestructive testing, its application was mainly limited to the detection of single targets or multiple targets having similar spectral characteristics. In this paper, the group delay moving entropy technique is introduced primarily to enhance the performance of split spectrum processing in detecting multiple targets which exhibit different spectral characteristics (i.e., variations in target signal center frequency and bandwidth). This is likely to occur in complex, dispersive, and nonhomogeneous media such as composites, layered, and clad materials, etc. The analysis shows that the group delay moving entropy method can be used effectively to select the optimal frequency region for split spectrum processing when detecting such targets. Based on an iterative procedure that combines group delay moving entropy and split spectrum processing, multiple targets can be identified one at a time, and subsequently eliminated by using time domain windows. The removal of the dominant target improves the detection of the remaining weaker targets. Simulation results are presented which demonstrate the feasibility of the multistep split spectrum processing technique for detecting multiple targets in such materials     

Fracture source location in thin plates using the wavelet transform of dispersive waves

A new signal processing approach was presented for acoustic emission source location using the dispersive waves in a thin plate. For wave propagation in dispersive media, the accuracy of source location can be improved by using the arrival times of a single frequency component in the output signals at an array of sensors. The wavelet transform (WT) was used to resolve this problem. By utilizing the time-frequency data of the WT, the frequency-dependent arrival time traveling with the group velocity was shown to be easily determined. Experiments were performed using a lead break as the simulated fracture source on the surface of an aluminum plate. Two plate modes corresponding to the S(0) and A(0) Lamb waves were identified, and their group velocities were accurately measured. The source location results based on the WT method agreed well with the true locations. The WT method was also compared with the cross correlation technique, and both methods provide similar results.