基于Gabor小波和阈值分析的声发射源定位方法

针对声发射信号多模态特性和信噪比低的特点,提出了一种将小波变换和阈值分析相结合的声发射源定位方法。对采集到的声发射信号进行信号频谱分析,提取信号主要频率成分之一的小波变换幅值,得到含有多峰值的时域波形。为消除多峰值的影响,将小波变换最大幅值的80%设为阈值。在时频空间下,确定声发射信号中同一频率下同种模态的波到达传感器的时间差,并测量该模态波在板面传播的群速度,实现声发射源定位。在大理石板上进行声发射两点线定位实验,结果证实该方法的确能提高声发射源定位精度,是一种有效的声发射源定位方法。     

局部放电声信号采集电路的设计和实现

声发射作为无损检测方法已经越来越多地在石油化工、电力工业和材料检测等领域得到应用。本文针对管道电缆巡检机器人研制项目中对管道内敷设电缆所产生的局部放电信号进行采集,提出研制机器人可携带的小型声发射检测装置。     

光纤法布里珀罗声发射传感系统

实现了一种由多个光纤法布里珀罗传感器构成的声发射传感系统,可用于变压器局部放电的检测与定位.该系统利用光纤法布里珀罗声发射传感器实现信号采集,利用门限检测的方法实现信号检测,并通过计算信号达到不同传感头的时延差实现放电源的空间定位,具有传感头尺寸小、系统结构简单、抗电磁干扰性能强等优势.     

基于FBG传感网络和时间反转聚焦成像方法的声发射定位技术研究

针对传统声发射定位系统存在的结构复杂、难以组网、定位精度低等问题,设计了一种基于光纤布拉格光栅(FBG)传感器网络和时间反转聚焦成像的声发射定位方法。在对时间反转聚焦定位原理分析的基础上,利用四个FBG传感器构建四点定位系统,并采用窄带激光边缘滤波技术实现信号解调。利用Morlet小波提取信号中特定频率成分,并计算模值和时差。通过建立时间反转聚焦模型实现声发射源定位,并在铝合金板结构上对整套成像定位方法进行验证。实验结果表明,该方法能有效地对400mm×400mm监测区域进行声发射定位成像,定位误差小于20mm,耗时小于2s。为声发射检测和定位提供了一种新的方法。     

基于广义S变换的声发射信号分析及定位

针对声发射信号分析和声源定位问题,提出了基于广义S变换的声发射信号分析方法和三维空间定位方法,推导出了广义S变换的实现过程,使用广义S逆变换对信号进行去噪重构.为保证各传感器时差的准确性,本文利用广义S变换分析声发射信号,提取其主频带能量序列曲线上峰值所对应的时间进行时差计算,然后结合三维空间定位方法对声发射源进行精确定位.仿真实验结果表明该算法能够实现声发射信号的特征提取和准确定位,且误差小,可靠性好.     

基于红外、超声和紫外技术的局部放电联合检测方法研究

利用图像配准与融合技术实现了一种超声、红外、 紫外联合的便携式局部放电在线检测系统。分别提出了这三种技术的检测原理和模块 化结构,然后利用计算机对三种局部放电检测信号进行了融合处理,并将该信号置入了由摄像头获取的设 备图像之中,从而建立了与设备图像的位置对应关系。本文系统不仅可以分别显示超声、红外、紫外三种信号的定 位成像视频,而且还可以将这三种信号融合到一个视频界面中,从而直观地显示出三种检测方法中的局部放电 位置及其变化情况。结果表明,该系统具有携带方便、检测快速等优点,能够及时发现电力设备的故障,因此具有 比较广泛的应用价值。     

充液管道中声发射波的传播及衰减特性研究

分析了声发射波在液体载荷作用下管道中的声学特性,并对钢管中的几种不同模态的声发射波在液体管道中的传播和衰减特性进行了测量。以一条长41.4 m的充水管道为例,对水载作用下的声发射管道泄漏检测及定位技术进行了研究,当管道内压力为0.6 MPa,两传感器相距40 m时,采用相关分析等信号处理方法,可检测到直径1 mm的针孔形泄漏,相对定位误差为2.9%。     

超声技术在变压器局部放电检测中的应用

对比了变压器局部放电的几种检测方法,简要介绍了利用超声技术测量变压器局部放电的原理,详细阐述了变压器局部放电超声定位系统的设计方法。结果表明,利用超声法测量变压器局部放电比其它方法更为有效。     

采用窄带特征提取方法提高声发射源定位精度

针对提高声发射源定位精度的需要,提出了利用小波变换从宽带非平稳声发射信号中提取稳定的窄带响应信息的方法,可降低环境噪声和波速色散效应的影响;进一步根据Hilbert变换提取窄带信号的包络,可根据第一个包络峰值正确判定应力波到达时刻.介绍了该方法的实现原理,组建了应力波源定位实验系统.采用十字定位法确定发射源位置.结果表明,采用新的窄带特征提取技术后,定位误差从原来的15 mm减少到4.9 mm.     

基于统计特征的变压器超高频局部放电信号识别与分析

变压器中局部放电由于随机性强且易受外界干扰所以难以检测,基于120MVA变压器进行长期超高频局部放电信号监测,通过放电信号绝对数量和相对分数两个特征量,从统计行为的角度分析了不同局部放电信号的统计行为特征。结果表明变压器中存在 3种主要局部放电信号源,其中一种相对分数达48％的信号具有放电绝对数量多、幅值高、放电数量随时间变化稳定的特点,由此得出其主导了变压器中的局部放电活动,该分析方法能有效识别局部放电模式和放电行为特征。     

Planar location of the simulative acoustic source based on fiber optic sensor array

A fiber optic sensor array which is structured by four Sagnac fiber optic sensors is proposed to detect and locate a simulative source of acoustic emission (AE). The sensing loops of Sagnac interferometer (SI) are regarded as point sensors as their small size. Based on the derived output light intensity expression of SI, the optimum work condition of the Sagnac fiber optic sensor is discussed through the simulation of MATLAB. Four sensors are respectively placed on a steel plate to structure the sensor array and the location algorithms are expatiated. When an impact is generated by an artificial AE source at any position of the plate, the AE signal will be detected by four sensors at different times. With the help of a single chip microcomputer (SCM) which can calculate the position of the AE source and display it on LED, we have implemented an intelligent detection and location.     

Wavelet-based identification of delamination defect in CMP (Cu-low k) using nonstationary acoustic emission signal

Wavelet-based multiscale analysis approaches have revolutionized the tasks of signal processing, such as image and data compression. However, the scope of wavelet-based methods in the fields of statistical applications, such as process monitoring, density estimation, and defect identification, are still in their early stages of evolution. Recent literature contains some applications of wavelet-based methods in monitoring, such as tool-life monitoring, bearing defect monitoring, and monitoring of ultra-precision processes. This paper presents a novel application of a wavelet-based multiscale method in a nanomachining process [chemical mechanical planarization (CMP)] of wafer fabrication. The application involves identification of delamination defect of low-k dielectric layers by analyzing the nonstationary acoustic emission (AE) signal and coefficient of friction (CoF) signal collected during copper damascene (Cu-low k) CMP process. An offline strategy and a moving window-based strategy for online implementation of the wavelet monitoring approach are developed. Both offline and moving window-based strategies are implemented on the data collected from two different sources. The results show that the wavelet-based approach using the AE signal offers an efficient means for real-time detection of delamination defects in CMP processes. Such an online strategy, in contrast to the existing offline approaches, offers a viable tool for CMP process control. The results also indicate that the CoF signal is insensitive to delamination defect.     

FBG-based ultrasonic wave detection and acoustic emission linear location system

The ultrasonic (US) wave detection and an acoustic emission (AE) linear location system are proposed, which employ fiber Bragg gratings (FBGs) as US wave sensors. In the theoretical analysis, the FBG sensor response to longitudinal US wave is investigated. The result indicates that the FBG wavelength can be modulated as static case when the grating length is much shorter than US wavelength. The experimental results of standard sinusoidal and spindle wave test agree well with the generated signal. Further research using two FBGs for realizing linear location is also achieved. The maximum linear location error is obtained as less than 5 mm. FBG-based US wave sensor and AE linear location provide useful tools for specific requirements.     

基于菱形光纤布拉格光栅传感阵列的声发射定位技术

声发射技术是结构损伤检测的重要手段,声发射源定位是损伤检测的首要环节。时差定位技术具有快速、高效、精确的特点,以此设计了由菱形阵列光纤布拉格光栅（FBG）传感器构成的声发射定位系统。采用小波变换和传统阈值法提取特征信号,结合互相关法获得传感器间的信号到达时差,然后根据几何定位模型求解非线性方程组得到声源可能存在的位置,最后根据时差的正负特性进一步确定声源的准确位置,有效避免了伪声源的情况。在铝合金板上,以对角线为48 cm48 cm的监测区域进行了10组测试实验验证,平均误差为1.29 cm。     

Analysis of Acoustic Events in Speech Signals Using Bessel Series Expansion

In this paper, we propose an approach for the analysis and detection of acoustic events in speech signals using the Bessel series expansion. The acoustic events analyzed are the voice onset time (VOT) and the glottal closure instants (GCIs). The hypothesis is that the Bessel functions with their damped sinusoid-like basis functions are better suited for representing the speech signals than the sinusoidal basis functions used in the conventional Fourier representation. The speech signal is band-pass filtered by choosing the appropriate range of Bessel coefficients to obtain a narrow-band signal, which is decomposed further into amplitude modulated (AM) and frequency modulated (FM) components. The discrete energy separation algorithm (DESA) is used to compute the amplitude envelope (AE) of the narrow-band AM-FM signal. Events such as the consonant and vowel beginnings in an unvoiced stop consonant vowel (SCV) and the GCIs are derived by processing the AE of the signal. The proposed approach for the detection of the VOT using the Bessel expansion is shown to perform better than the conventional Fourier representation. The performance of the proposed GCI detection method using the Bessel series expansion is compared against some of the existing methods for various noise environments and signal-to-noise ratios.     

基于EMD的声发射管道泄漏检测研究

针对管道泄漏声发射检测信号的非平稳特征,该文提出了基于经验模态分解(EMD)的声发射信号分析方法。该信号分析法将管道泄漏产生的复杂声发射信号分解成有限个固有模态信号(IMF),使Hilbert-Huang变换(HHT)的瞬时频率具有了实际物理意义,提高了管道泄漏检测的定位精度。结果表明,HHT法能准确描述声发射波形信号的非线性、非平稳时变特征,是声发射信号时频分析的有效工具。     

相关熵与循环相关熵信号处理研究进展

在无线电监测和目标定位等应用中,接收信号经常会受到脉冲噪声和同频带干扰等复杂电磁环境的影响,传统的基于2阶统计量的信号处理方法往往不能正常工作,基于分数低阶统计量的信号处理方法也由于对信号噪声统计先验知识的依赖性而遇到困难。近年来提出并受到信号处理领域普遍关注的相关熵和循环相关熵信号处理理论与方法,是解决复杂电磁环境下信号分析处理、参数估计、目标定位和其他应用问题的有效技术手段,有力促进了非高斯、非平稳信号处理理论方法和应用的发展。该文系统性地综述了相关熵和循环相关熵信号处理的基本理论和基本方法,包括相关熵与循环相关熵的起源背景、定义概念、性质特点,以及所包含的数学物理意义。该文还介绍了相关熵与循环相关熵信号处理在多个领域的应用问题,希望对非高斯、非平稳统计信号处理的研究和应用有所裨益。     

时频分析在雷达信号识别中的应用

针对目前雷达信号分选识别的问题,研究了时频分析的方法在信号识别方面的应用。该方法与其他雷达信号识别方法相比,能有效地分析非平稳信号。在时频分析相关理论的基础上,分别研究了基于短时傅里叶(STFT)变换和Wigner-Ville分布(WVD)方法对信号特征的分析和提取。通过仿真,分析对比了两种方法的优劣性, STFT可分析出信号的局部频域特性,而相同信噪比下, WVD比STFT受噪声影响小、聚合度高,能更好地体现时间和频率之间的关系,由此表明,两种方法均可较好地区分出调制信号特征。     

Selection of signal detection threshold in Doppler spectrum analyzer

It is shown, that for spectrum analyzer noise immunity increase, during processing of optical Doppler location signal with unknown frequency, random appearance time and low signal to noise ratio it is advisable to use methods of false alarm probability decrease, where decision about useful signal presence is made according to two pulses appearance at the matched filter output. These pulses have the same delay times with regard to signal analysis beginning time. This methodology application for signal detection allows to decrease a false alarm probability with regard to one period of analysis in case of the same values of threshold.