散斑检测技术及其应用

综述了散斑计量中的主要检测技术。主题包括散斑照相技术、散斑干涉技术、电子散斑干涉技术、数字散斑相关技术和时间序列散斑检测技术。介绍了散斑计量在科学和工程研究中的一些重要应用。     

散斑干涉条纹图的总变分去噪方法

去除散斑条纹图中的噪声是电子散斑干涉测量技术的关键问题.提出将总变分图像去噪方法应用于电子散斑干涉条纹图滤波过程中,并对保真系数进行了改进.用总变分模型定义图像的能量函数,利用变分法求得满足能量函数的最优解,将图像去噪过程转化为求解偏微分方程的过程.分别对计算机模拟的条纹图和实验获得的条纹图进行了测试,定性和定量分析的结果表明该技术能够在显著滤波的同时保持条纹的对比度.     

散斑相关法标定电涡流传感器电压输出曲线

为了精确的测量电涡流传感器的距离-电压输出线性区间和线性位移精度,本文采用了显微散斑相关法对位移进行标定。首先,利用精度为5μm位移平台进行位移调节,得到位移和电涡流传感器输出电压的线性区间。然后,在线性区间内进行密集采样,通过显微照相系统采集散斑图,利用散斑相关法求出位移,得到更高精度的位移-电压曲线。分析了显微散斑照相的检测流程与检测精度;讨论了散斑尺寸对测量的影响。设计了测量光路参数：采用40×显微物镜配合20×读数显微镜可以实现64.5×的放大倍率。对40铬材料进行了位移-电压曲线标定实验,实验结果证明：本系统可以实现高精度的电涡流传感器位移标定,测量精度达到0.09μm,要实现更高精度的标定可以提高显微系统的放大倍率。     

电子散斑干涉法在铝合金材料结构内部柱状缺陷检测中的应用研究

采用电子散斑干涉法和相移技术研究了铝合金材料结构内部柱状缺陷.设计了实验试件,并运用气压对试件进行加载,比较试件在相同直径,深度位置不同缺陷时的变形情况.利用有限元对实验进行模拟计算,与实验结果进行比较,结果小于8.81%.研究为结构检测提供了新的方法,拓展了电子散斑干涉法的应用领域.     

电子错位散斑干涉系统中错位量的研究

电子错位散斑检测系统中,错位量对测量精度、灵敏度以及条纹对比度有很大影响。本文介绍了电子错位散斑干涉原理,研究了错位量与测量精度、灵敏度和条纹对比度之间的对应关系,并利用MATLAB模拟出不同错位量下干涉条纹图,将错位散斑模拟条纹图与理论分析有效结合,总结出选取错位量的方法,并将其应用于轮胎变形检测实验,取得了良好的实验效果。本文研究工作对无损检测中错位量定量选取具有实际指导意义。     

用于高精确度位移测量的散斑全息干涉术(英文)

传统的双曝光散斑照相术用于位移测量存在着某些弱点:其一是在再现中由于衍射爱里斑对杨氏条纹数的限制,使测量灵敏度不能太高;其二是照相术本身意味着不能实时测量;其三是杨氏干涉的机理使得横向位移的测量范围不可能很大。本文提出了用散斑全息干涉术进行高灵敏度的位移测量,进而提出用散斑莫尔术进行实时测量,并对它们从理论上和实验上作了论证。作者认为,上述方法的精确度高于双曝光散斑照相术,而且简便易行,可用于生产及科研中的横向小位移精密测量。     

全息空间三维显示研究

本文基于计算全息、光电衍射再现及散射成像等技术,研究全息空间三维显示,利用随机相位抑制全息空间三维再现像的散斑噪声,实现高分辨率全息空间三维显示。同时,测试不同厚度的散射介质屏对三维成像的影响,探究全息空间三维显示的亮度变化规律。     

用于测振的电子散斑剪切干涉术

电子散斑剪切干涉术作为一种高精度全场测量技术,已被广泛应用于无损检测(NDT)、应变分析、振动检测和流场分析等领域．主要分析了电子散斑剪切干涉术在振动检测领域的应用,分析了它利用时间平均法检测振动的原理,并为实现物面振动的大面积检测进行了电子散斑剪切干涉仪光学结构的参数设计,一次可以检测大小为669 mm×502mm的矩形物面．利用计算机模拟产生随机高斯相关表面的高度分布函数及振动散斑剪切条纹图．结果表明电子散斑剪切干涉术用于振动检测．     

非银图象记录技术动向

本文摘自去年国际摄象会议非银盐录象技术专论。 1.电子照相的高感光度化利用低表面电位实现电子照相的高感光度化。这种低电位型的电子照相,是在基村上先镀—铟—锡氧化物,然后再镀单结晶的硫化镉作为感光层。具有全色性、连续阶调再现性,可作为胶版印刷的高感度制版材料。显象后感光体的表面经亲水处理,能印200线的画象25万份以上。这种感光膜是印刷市场发展的中心。     

流体温度场测量中的电子散斑干涉技术

电子散斑干涉是一种利用全电子记录和计算机图象处理系统替代传统照相干版进行测量的先进技术。本文在简要介绍其应用于流体温度场测量的理论与实验的基础上,着重描述了如何通过调整光学系统参数配置来获取最佳质量原始干涉图象的途径,并给出对比分析结果。     

Through-the-thickness displacements measurement in laminated composites using electronic speckle photography

This paper describes an application of electronic speckle photography to measurement of through-the-thickness displacements in composites. Purpose is to assess the accuracy of this technique in presence of the strong gradients and rotations at the layer interfaces of these materials. The software for data acquisition and processing was in-home developed. Experimental results quantifying the thickness distribution of in-plane and transverse displacements in laminated beams are reported for some kinds of beams with metallic, polymeric and carbon fibre layers, to assess the influence of different constituent materials and optical properties. The experimental results are compared with the predictions of a theoretical model previously developed by the author, substantiated by the exact elasticity solution. In all the examined cases, electronic speckle photography appeared suited to accurately measure displacements with a magnitude of technical interest.     

Completely passive method of speckle reduction utilizing static multimode optical fibre and two-dimensional diffractive optical element

ABSTRACT

In this paper, we present experimental results on speckle noise suppression using a completely passive method. The passivity of the method is achieved owing to the absence of any mechanical, electronic, or other dynamic influences on the optical scheme elements. In the experiment, a multimode semiconductor 520?±?5-nm laser with a spectral bandwidth of 2?nm, static two-dimensional (2D) and 2?×?1D diffractive optical elements (DOEs), as well as multimode single-core optical fibre and multimode optical fibre bundle were used. The dependence of the speckle reduction efficiency as a function of the optical fibre type and optical fibre length was measured for different DOEs. A speckle contrast of 0.148 and speckle reduction coefficient of 2.38 were obtained for a 2.5-m-long multimode optical fibre bundle. The experimental results confirmed that it is possible to construct completely passive optical circuits with reduced speckle noises using static multimode optical fibres and diffraction optical elements.     

Accuracy in electronic speckle photography

Electronic speckle photography is an accurate, easy-to-use, video-based technique for the analysis of two- and three-dimensional deformation fields and in-plane strain fields, based on numerical cross correlation. Through the use of statistical optics, simulated speckle patterns, and experiments the accuracy in electronic speckle photography was found to depend on correlation, speckle size, window size, and correlation filter. The estimated correlation was found to be the combined effect of three mutually competing factors because of classical speckle correlation, subimage overlap, and displacement gradients. In many applications white-light speckle patterns provide a more accurate estimate of the displacement field than do laser speckle patterns.     

Three-dimensional deformation field measurements with simultaneous TV holography and electronic speckle photography

The ordinary recordings of TV holography (phase-stepped electronic speckle interferometry), arranged for out-of-plane sensitivity, are recombined and also analyzed by use of electronic speckle photography for simultaneous measurements of all three components of the deformation vector field. The principles of this technique are presented. Experimental results showing the opening of a slot in a perspex plate are also presented.     

Measurement of temperature using speckle shearing interferometry

A laser speckle shearing interferometric technique is used for measuring the temperature profile inside a gaseous flame. The experimental results are compared with the values obtained by a thermocouple and also by speckle photography. Good agreement is seen among the temperatures measured by speckle shearing interferometry, speckle photography, and the thermocouple. Speckle shearing interferometry is easier to implement than speckle photography. This is because in speckle shearing interferometry the accurate positions of the fringes can be known without point-by-point analysis and correction for the halo effect.     

Adaptive aperture defocused digital speckle photography

Speckle photography can be used to monitor deformations of solid surfaces. Its measuring characteristics, such as range or lateral resolution, depend heavily on the optical recording and illumination setup. I show how, by the addition of two suitably perforated masks, the effective optical aperture of the system may vary from point to point of the surface, accordingly adapting the range and resolution to local requirements. Furthermore, by illuminating narrow areas, speckle size can be chosen independently from the optical aperture, thus lifting an important constraint on the choice of the latter. The technique, which I believe to be new, is described within the framework of digital defocused speckle photography under normal collimated illumination. Mutually limiting relations between the range of measurement and the spatial frequency resolution turn up both locally and when the whole surface under study is considered. They are deduced and discussed in detail. Finally, experimental results are presented.     

Experimental Analysis of Thermo‐mechanical Behaviour of Electronic Components with Speckle Interferometry

Experimental investigations of thermo‐mechanical behaviour of electronic components may help to prevent catastrophic in‐service failures. Non‐contact optical techniques such as speckle and moiré interferometry are naturally suited for carrying out measurements on electronic equipment as they are non‐invasive techniques and provide high‐resolution full‐field information on displacements. In spite of its inherent ability to measure deformations at the nanometer level, there are few examples of application of speckle interferometry to true monitoring of thermo‐mechanical behaviour of electronic components in real time. For this reason, the paper presents a phase shifting electronic speckle pattern interferometry (PSESPI) experimental set‐up developed in order to monitor the time evolution of thermal deformations in electronic components for aerospace applications submitted to normal or anomalous working conditions. Cyclic loads are also analysed to assess fatigue behaviour. Experimental results obtained for whole electronic boards and single components mounted on board fully demonstrate the capability of PSESPI to detect even small differences in thermo‐mechanical response between normal and anomalous functioning.     

Effect of compensation for spherical aberration on the transverse displacement of laser speckle patterns

When a rough surface illuminated by coherent light is displaced perpendicularly to the optical axis of an imaging optical system the speckle pattern in the conjugate plane is transversally displaced too. This displacement has two components. The first one is proportional to the object displacement, and the second one depends on wave-front aberrations and, consequently, is strongly related to the optical system that is used. Usually, well-corrected photographic objectives are used for the measurement of transverse displacements by double-exposure laser speckle photography. Since in well-corrected objectives aberrations tend to compensate one another, it seems that the complementary displacement of the speckle pattern, caused by aberrations, is near zero and does not affect the accuracy of the measurement. Here it is analytically shown that the compensation of spherical aberrations does not guarantee a negligible complementary displacement. From the results obtained it follows that well-corrected objectives for laser speckle photography can be regarded as a particular class of photographic objectives, since they not only yield high-quality images but also minimize complementary displacement.     

Three-dimensional deformation field measurement with digital speckle correlation

Digital speckle correlation is based on a detailed analysis of changes in speckle images that are recorded from laser-illuminated rough surfaces. The two in-plane components are obtained by cross-correlation of corresponding subimages, a method also known as digital speckle photography. The local gradient of the hitherto inaccessible out-of-plane component is determined from the characteristic dependence of the speckle correlation on the spatial frequency. A detailed experimental study is carried out to analyze the new technique for systematic and random measuring errors. For moderate decorrelation the accuracy of the out-of-plane measurement is better than lambda/10 and thus comparable with interferometric techniques. Yet the extremely simple and robust optical setup is suited to nondestructive-testing applications in harsh environments. The quality of the deformation maps is demonstrated in a practical application.