Technique for compensating excessive rigid body motion in nondestructive testing of large structures using shearography

A major limitation of speckle interferometry techniques including shearography is that the occurrence of rigid body motion produces a decorrelation of speckle patterns which destroys the fringe visibility. This paper demonstrates that digital shearography can tolerate much greater rigid body translation than a speckle size as predicted by the conventional speckle decorrelation theory. Excessive rigid body translation in digital shearography can be compensated by either translating the sensor/camera or digitally shifting one of the speckle patterns.     

光源编码的白光散斑剪切干涉计量术

本文提出了一种用非相干光源照明进行剪切干涉计量的方法—光源编码的白光散斑剪切干涉计量术.它采用光栅对光源进行编码以提高空间相干性,使物体的两个剪切像的波面部分相干叠加,以实现剪切干涉.     

Direct measurement of curvature and twist of plates using digital shearography

A method of determining the second-order derivatives of displacement using digital shearing speckle interferometry is presented in this paper. A phase-shifting technique is incorporated and demonstrated to yield good quality fringe patterns that depict either the second-order derivative separately or a combination of first- and second-order derivatives. The optical set-up of this method is similar to that of conventional phase-shifting shearography, thus enjoying a simple and practical configuration. Qualitative comparison shows acceptable agreement of the generated fringe patterns with theoretical results.     

A dual-function ESPI system for the measurement of out-of-plane displacement and slope

A dual-function ESPI system is developed for the measurement of out-of-plane displacement and its slope change. The proposed system is convenient and also efficient to switch over from an out-of-plane sensitive configuration to shearography. A difference-of-phase method with a five-step algorithm is used for speckle fringe analysis.     

Measurement of small displacement based on surface plasmon resonance heterodyne interferometry

This paper proposes an optical method for measuring small displacements using the surface plasmon resonance (SPR) heterodyne interferometry. A heterodyne light beam reflected by a mirror passes through a hemisphere glass and then enters into a surface plasmon resonance apparatus at the resonant angle. A small displacement of the mirror will introduce a phase-difference variation between p- and s-polarizations of the light emerging from the SPR apparatus. The phase-difference variation can be precisely measured with the heterodyne interferometric technique, and the associated displacement can be estimated. The feasibility of this method was verified by experiment, and the displacement measurement resolution of about 1.4 nm over a traveling range of 6 μm was achieved. Our method of measurement has the merits of both common-path interferometry and heterodyne interferometry.     

融合散斑干涉技术的阵列式洛伦兹力微颗粒探测方法

提出了一种阵列式洛伦兹力微颗粒探测法,该方法结合了散斑干涉技术的全场位移测量、分辨率高等特性与洛伦兹力微颗粒探测法中探测量为矢量、可探测内部缺陷等优势,探索了一种实时、在线、原位的缺陷检测方法.针对阵列式洛伦兹力微颗粒探测法中阵列式排布的多个悬臂梁位移测量问题,设计了大剪切数字散斑干涉系统,使来自于被测悬臂梁和安装悬臂梁的横梁的反射光发生干涉,形成剪切干涉,通过对相位差进行分析获得悬臂梁的绝对位移,并且以洛伦兹力及悬臂梁末端的位移量为中间量建立了散斑干涉相位差与缺陷体积之间的关系.本文通过实验成功获得了悬臂梁全场位移量以及缺陷的体积,通过散斑干涉的方法测量悬臂梁位移量理论分辨率可达30 nm,这使洛伦兹力微颗粒探测法具备了微米级缺陷的探测能力.     

Comparison between instantaneous and integral intensities in dynamic speckle pattern interferometry

A new speckle measurement technique called temporal speckle pattern interferometry or time sequential speckle pattern interferometry has been developed recently. Its principle is that by capturing the temporal speckle patterns related to the object deformation or displacement, the whole-field displacement, the amplitude of the vibrating object and the shape of the tested object can be calculated through speckle intensity fluctuation scanning technique or Fourier-transforming method. In this paper, we combine the analytical and numerical methods to simulate the properties of the time demodulation in temporal speckle patterns interferometry techniques. The performance of three kinds of temporal phase sequences, power, exponential and harmonic phase sequences, are studied with the parameters of temporal speckle intensity fluctuation, the value of the spatial phase term, optical integral time of the recording camera and the initial phase of the temporal speckle intensities. The results indicate that the normalized value and period change of the instantaneous intensity are nearly coincident with that of the integral intensity for the harmonic temporal phase sequences and are different for the power and exponential temporal phase sequences.     

Volume-grating phase-shifting digital speckle pattern interferometry used for measurement of out-of-plane displacement field

A new digital speckle pattern interferometry, called volume-grating phase-shifting digital speckle pattern interferometry, is discussed in this paper. The out-of-plane displacement field of a bent plate can be quantitatively measured using volume-grating phase-shifting digital speckle pattern interferometry proposed in this paper. Theoretical and experimental results, as well as absolute errors, are given.     

双目视觉DIC测量系统的离面位移测量精度

采用离面位移测量精度达到10 nm~20 nm的电子散斑干涉测量系统验证了双目视觉数字散斑相关测量系统的离面位移测量精度。分别用电子散斑干涉测量系统和双目视觉数字散斑相关测量系统同时测量了平板离面位移,并对所测量的位移最大值进行了分析处理及比较。结果表明,双目视觉数字散斑相关测量系统的物体离面位移分布云图与电子散斑干涉测量系统的结果基本相同,且两者位移均方根相差为2.76 m~3.56 m,相对误差为4.59%~7.60%。因此,当被测量物体的离面位移大于4 m时,双目视觉Q400测量系统精度可达到电子散斑干涉测量系统的精度。     

用于多参数同时测量的散斑干涉仪

本文描述了一种新的散斑干涉仪,它可以同时对表面应变物体的面内位移、离面位移、位移梯度和莫尔曲率进行测量;由于利用了取向滤波方法,在滤波系统输出平面同时得到了与这些参数对应的散斑条纹.还利用散斑空间运动规律较好地解释了散斑干涉与散斑剪切干涉之间的关系.     

Stroboscopic digital speckle pattern interferometry for vibration analysis of microsystem

In this paper, vibration measurement and analysis of microsystems, such as micro-electro-mechanical systems (MEMS) by using stroboscopic digital speckle pattern interferometry (DSPI) is presented. Because of the speckle interferometry, the technique is suited for samples which have a rough surface or whose surfaces can be sprayed into a scattering surface. A laser speckle microinterferometer incorporated with optoelectronic devices for a stroboscopic illumination and a synchronization of the signals between excitation and stroboscopic illumination is described and demonstrated. The system can measure both out-of-plane and in-plane displacement under either a static or dynamic loading. The fundamental is explained and some applications are demonstrated.     

剪切散斑干涉技术及应用研究进展

剪切散斑干涉技术是一种非接触测量物体变形缺陷的光学无损测量方法,其通过计算物体变形前后的散斑图中的相位获取被测物的应变缺陷信息。近年来该技术在航空、航天等工业无损检测领域得到了广泛的应用。本文从系统关键技术、散斑图像处理技术两方面介绍了剪切散斑干涉技术的研究进展,详细论述了多种剪切装置实现大视角测量、空间载波实现动态测量、多种图像处理算法的一系列剪切散斑干涉技术;最后介绍了剪切散斑干涉技术的国内外应用进展,展望了剪切散斑干涉技术在动态测量、光滑表面测量及定量反算形变量等方面的发展趋势。     

Measurement of the off-plane displacement of carbon steel corrosion with twin-object-beam electronic speckle interferometry

In this paper, twin-object-beam electronic speckle interferometry is used to study the longitudinal corrosion of carbon steel. The displacement expression of this technique is deduced and optical fibers are used to reduce the influence of the optical system and improve the quality of speckle pattern. Twin-object-beam electronic speckle interferometry cannot only quantitatively cipher out off-plane displacement as a result of corrosion, but also estimate the change of corrosion speed.     

Digital speckle pattern interferometry (DSPI) with increased sensitivity: Use of spatial phase shifting

This paper presents a real-time digital speckle pattern interferometry system with twofold increase in sensitivity for the measurement of in-plane displacement and first order derivative of out-of-plane displacement (slope). Spatial phase shifting technique has been used for quantitative fringe analysis. The system employs a double aperture arrangement in front of the imaging system that introduces spatial carrier fringes within the speckle for spatial phase shifting. For in-plane displacement measurement, the scattered fields from the object are collected independently along the direction of illumination beams, and combined at the image plane. For slope measurement, a shear is introduced between the two scattered fields. Experimental results on an edge clamped circular plate subjected to in-plane rotation for in-plane displacement measurement and central loading for slope measurement are presented.     

Low-frequency harmonic vibration analysis with temporal speckle pattern interferometry

In this paper, the time sequence phase method (TSPM) has been applied to measure the displacement caused by low-frequency vibration in temporal speckle pattern interferometry (TSPI). The principle is that by capturing the temporal speckle patterns related to the object vibration, the whole-field displacement responses (amplitude and phase) of the vibrating object can be calculated through scanning these fluctuations. Thus, quantitative measurement can be carried out using a conventional ESPI system without a camera synchronized to the object vibration or a phase shifting system. The elaboration on the method is given and experimental results are presented.     

电子散斑归一化互相关法测位移

把粗糙物体表面受到相干光照明时产生的散斑场看作是一个稳态随机信号,在此基础上,本文提出了一种能做到大量程,高精度位移测量的新方法——电子散斑归一化互相关法测位移或称电子散斑照相法测位移.该法实质上是借助数字图像处理技术,通过物体位移前后二个散斑场之间的相关性来进行位移测量方法的发展.文中给出了理论分析和实验系统.实验结果表明,该法有诸如准实时,大量程(毫米级),高精度和线性可靠等优点.     

Investigation of glass panels thickness profile by all-fiber digital heterodyne interferometry

All-fiber digital heterodyne interferometry is a laser metrology technique employing pseudo-random codes phase modulated onto an optical carrier signal. In this heterodyne interferometer system, the optical signal includes signal reflected and transmitted from the sample, respectively. Compared with the conventional heterodyne interferometry, this enhanced optical system has much higher measurement sensitivity, and can distinguish the signal which reflected from the front and the rear surface of the sample. Analysis and simulation for the digital heterodyne interferometry are presented. It takes approximately 4 s to scan the whole surface with the diameter of 300 mm. The thickness profile of the sample is obtained in the experiment. The discussion about the experiment is given finally.     

Two wavelength simultaneous DSPI and DSP for 3D displacement field measurements

A novel optical system is proposed that implements digital speckle pattern interferometry (DSPI) and digital speckle photography (DSP) simultaneously using two wavelength illumination of an object for simultaneous measurement of all three components of the displacement vector field. A collimated red light illuminates both the object and a reference surface in a DSPI configuration which is sensitive to out-of-plane displacement field while a blue light illuminates the object in a DSP configuration which is sensitive to in-plane displacement fields. A color 3-CCD camera records the red and blue lights individually through its red and blue channels, respectively. Two reference images and one image in the deformed state of the object are required for quantitative measurement. Experimental results are presented to validate the system.     

Optical heterodyne grating shearing interferometry for long-range positioning applications

We develop a displacement measurement and positioning system with nanometer resolution over the millimeter traveling range. The method is based on a heterodyne grating shearing interferometry, a homemade lock-in amplifier and a servo control loop for displacement sensing and positioning. The quasi-common optical path configuration of our system provides better immunity against environmental disturbances. The experimental results demonstrate that our system can measure small and long displacement with nanometric resolution. The device achieves a positioning resolution of 2.3 nm over a traveling range of 20 mm.     

基于激光外差干涉术的薄膜厚度测量方法

针对光学薄膜厚度测量困难问题，提出了一种基于激光外差干涉术的薄膜厚度测量方法。采用经典迈克尔逊干涉光路，利用外差干涉原理将薄膜厚度差转换为光程差，以精密位移平台为扫描机构实现薄膜厚度的逐行扫描测量。测量系统在恒温实验条件下20 min内的漂移不超过8 nm，测量结果平均差小于1 nm，通过与椭圆偏振仪的测量结果比较，测量差值为12.97 nm，表明了该方法的可行性。