频闪剪切散斑干涉术的研究

提出了一种用于振动研究的方法——频闪剪切散斑干涉照相法。该方法由于采用了剪切镜,能得到较为精确的散斑剪切图,提高了测量的精度,是一种用于振动研究较为理想的散斑照相的新方法。讨论了频闪剪切散斑干涉术的基本原理,给出了频闪剪切散斑图的全场分析的平均光强分析的解析式,并给出了实验结果。理论和实验都表明频闪剪切散斑干涉照相法要优于时间平均剪切散斑干涉照相法。该方法在全场滤波分析时,能给出任一瞬时物体振动信息,得到清晰的、高衬比的全场干涉条纹图,是一种实用可行的方法。     

Vibration analysis by means of digital shearography

Digital shearography, also called digital speckle pattern shearing interferometry, is described as a robust measuring method due to its simple optical setup and the relative insensitivity against ambient noise. It has been applied for nondestructive testing and strain measuring. This paper explores its possibilities for vibration analysis. The measuring device performing both continuous (time-average method) and stroboscopic illuminations is described. The selection of the illumination mode is made by adjusting a controller and performed simply by a computer. The real-time observation with refreshing reference frame technique and the quantitative evaluation with the phase shift technique are presented. The results show this measuring device is well suited for both qualitative and quantitative vibration analysis.     

基于单幅数字散斑投影及图像相关的离面振动测量

采用单幅数字散斑图投影及高速数字图像采集技术,研究了动态离面位移的测量。采用商用液晶投影仪将计算机产生的模拟散斑图投影到待测动态变形物体表面,由高速数字图像采集设备摄取并保存变形散斑图,采用时间序列数字图像相关软件计算出物体表面各点随时间变化的离面位移。这种方法用于振动分析时不仅可以获得振型分布,而且还可以获得各点的振幅值。与现有的激光频闪照相测振及激光多普勒测振等方法相比,具有光学系统简单,可全场定量测量。悬臂梁振动实验结果证实了该方法的有效性。     

An electro-optic holographic technique for the measurement of the components of the strain tensor on three-dimensional object surfaces

An electro-optic holographic technique (also called electronic speckle pattern interferometry or TV holography) for the measurement of displacements and strains on three-dimensional object surfaces is presented. The three components of the displacement vector, in a fixed coordinate system, are separated using four independent illumination beams. The interferometric phase for each illumination beam is extracted using the phase stepping technique. Displacements in the fixed coordinate system are projected on to the object surface using the tensor transformation law. Equations for the computation of surface strains using the projected displacements and the surface geometry are developed. The technique is applied for the measurement of strains on the surface of a cylindrical vessel subjected to internal pressure.     

数字散斑干涉技术在振动分析中的应用

首次将相移技术应用于频闪数字散斑干涉计量中,对物体的振动进行了定量分析.实验证明,这种方法有广泛的实用价值.另外,介绍了一套自动分析系统,讨论了各参数对测量结果的影响.     

Further reduction of recording time in stroboscopic holographic interferometry

Except for the extreme positions, a vibrating object passes twice through a position in each vibration cycle. It is suggested that this fact can be used to reduce the recording time during the pulsed illumination in stroboscopic holographic interferometry by providing two light pulses per vibration cycle for a given subject position.     

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.     

Dynamic measurement of volume contraction and phase change of submerged visco-elastic bodies using ESPI

This paper outlines the application of electronic speckle pattern interferometry (ESPI) to the measurement of dynamic bulk modulus of elastomers. This is achieved by direct measurement of the volume contraction of submerged specimens subjected to sinusoidal pressure changes. Also outlined is the stroboscopic operation of ESPI for the identification of phase delays between peak loading and maximum deformation, characteristic of the response of viscoelastic materials.     

利用电子散斑相移技术测量物体三维面形的方法

为了获得准确的面形测量,提出了一种相移电子散斑干涉技术测量物体面形的测量方法.利用电子散斑干涉产生载波条纹,该载波条纹受到物体表面高度的调制变得弯曲,引起载波条纹相位的变化,可运用相移技术提取物体的相位信息,最后根据高度和相位之间的关系得到物体的面形.介绍了该方法的原理,利用该方法对球冠物体进行了面形测量,证明该方法测量物体面形是可行性的.由于是采用散斑干涉的方法产生干涉条纹,因此该方法测量物体面形具有灵敏度高的优点.     

Continual deformation analysis with scanning phase method and time sequence phase method in temporal speckle pattern interferometry

If a laser beam illuminates a continual deformation object surface, it will lead to a temporal speckle pattern on the observation plane. Recording this time-dependent speckle pattern the deformation of the surface of an object can be obtained. Two methods, scanning phase method (SPM) and time sequence phase method (TSPM), have been introduced for measuring the displacement caused by the deformation in temporal speckle pattern interferometry (TSPI). Their principle is that by capturing a series of speckle interference patterns related to the object deformations, the fluctuations in the intensity of the interference patterns can be obtained. Through scanning these fluctuations and estimating both the average intensity and modulation of the temporal speckle interference patterns, the phase maps for whole-field displacements are calculated. In this way one is capable of quantitatively measuring continual displacements simply using a conventional electronic speckle pattern interferometry (ESPI) system without phase shifting or a carrier. The elaboration on the new methods is given in this paper and experiments are performed to demonstrate their performance with a conventional ESPI system.     

基于散斑干涉的光滑表面变形快速检测

针对目前光滑表面力学性能测试困难的情况,建立了一种改进的数字激光散斑干涉测量系统。首先通过新的散斑干涉光路设计实现散斑照射,同时采用空间载波傅里叶变换法,对光滑零件加载变形的动态散斑干涉图像进行处理,最后得到光滑表面的变形场分布情况。该方法不对被测表面进行任何处理,可实现光滑表面的高精度全场变形测量。实验结果表明:最大变形处为镜面板的中央,测得最大变形量分别为1.936、1.861和1.797μm,与中心变形预设值接近。该方法光路简单、测量方案切实可行,能够实现光滑表面变形的快速动态测量。     

Phase shifting speckle shearing polarization interferometer using a birefringent wedge

A digital speckle pattern shearing interferometer is presented which utilizes a single birefringent wedge. Two orthogonally polarized images of an object measured are sheared by the wedge, and the bias phase difference between two polarized images is shifted by translating the wedge. The phase shifting technique applied to speckle pattern shearing interferometry makes it possible to analyze a slope and surface strain numerically. The fringe formation in the present interferometer is analyzed with statistical theory. Experimental results are also presented in two cases: (1) measurement of a slope and normal displacement with a single illumination; (2) simultaneous and separate measurement of a slope and surface strain with two symmetrical illuminations.     

A novel interferometric method for contour mapping of optically rough surfaces

A new white light interferometric arrangement for contour mapping of light diffusing but not depolarising surfaces is presented and compared with related electronic speckle and holographic interferometry (ESPI and HI) methods. Using two angles of illumination of the tested surface, and modifying the light beam in the observation pupil it is possible to observe contour fringes with arbitrary sensitivity depending on the geometry of a chosen set-up.     

Dynamic out-of-plane profilometry for nano-scale full-field characterization of MEMS using stroboscopic interferometry with novel signal deconvolution algorithm

A dynamic 3D nano-scale surface profilometer using stroboscopic white-light interferometry with novel signal deconvolution was developed to deliver dynamic surface profilometry with a measurement bandwidth of up to a MHz scale and a vertical resolution reaching 1 nm. Previous work using stroboscopic microscopic interferometry for dynamic characterization of micro-(opto)electromechanical systems (M(O)EMS) has been limited in measurement bandwidth of less than a few hundred kHz due to physical length limitation of stroboscopic light. For high-resonance mode analysis, the stroboscopic light pulse is too lengthy to capture the moving fringes from dynamic motion of the detected structure. In view of this need, a novel deconvolution algorithm using correction of the light response was developed for removing potential image blurs caused by the unavoidable vibration of the tested parts. With this advance in technology, the bandwidth of dynamic measurement can be significantly increased without sacrificing measurement accuracy. A microcantilever beam used in AFM was measured to verify the capability of the system in accurate characterization of dynamic behaviors of M(O)EMS.     

Using Speckle Interferometry for Controlling the Units of Multi‐Mirror

Applications of speckle interferometry for measuring displacements of mirrors of multi‐mirror centimeter radiotelescopes are considered and analyzed in modeling experiments. The general principles of speckle photography, speckle interferometry, and the use of two-exposure speckle patterns for the analysis of displacements of rough surfaces (units of the radiotelescope mirrors) are worked out. Experiments are carried out for three possible displacements of the object surface: parallel shifts along the surface itself, rotations, and shifts in the perpendicular direction. The shape and structure of the displaced units do not change. The experiments prove that speckle interferometry is a rather effective and practical tool for measuring shifts and rotations of composite radiotelescope mirrors.     

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.     

Modulation analysis in spatial phase shifting electronic speckle pattern interferometry and application for automated data selection on biological specimens

In electronic speckle pattern interferometry (ESPI), for a fast and objective analysis of measurement data which occur with a high repetition rate, an automated data processing is of particular advantage. For this reason, investigations were carried out to determine if the modulation of speckle interferograms can be applied as a quality parameter for the selection of suitable interferogram data for further evaluation e.g. phase unwrapping when spatial phase shifting (SPS) is performed. Six methods for determining the modulation of speckle interferograms are characterised and compared. The applicability of the speckle interferogram modulation as a parameter for mask generation in the unwrapping process of the phase difference is demonstrated by the evaluation of measurement data obtained from experiments with a spatial phase shifting endoscopic ESPI system on a technical surface and on a human gastrectomy specimen.     

New fourth-order partial differential equations for filtering in electronic speckle pattern interferometry fringes

Partial differential equations (PDEs) based methods have been demonstrated to be a powerful tool for filtering in electronic speckle pattern interferometry fringe or wrapped phase patterns. In this paper, we derive the new fourth-order partial differential equations (NFOPDE) with a better performance for filtering in electronic speckle pattern interferometry fringe patterns based on the variational methods. We test the proposed models on two computer-simulated speckle fringe patterns and an experimentally obtained fringe pattern, respectively, and compare our models with the widely used, well-known the second-order selective degenerate diffusion PDE model (SOSDPDE) and the published fourth-order PDE model (PFOPDE). The proposed NFOPDE can overcome the shortages that both the SOSDPDE and PFOPDE encounter. In all cases, our NFOPDE outperforms SOSDPDE and PFOPDE.     

Application of ESPI to three-dimensional vibration measurements

There are many situation in vibration analysis where it is necessary or desirable to make three-dimensional measurements. By using three different illumination geometries around a single imaging system, electronic speckle pattern interferometry (ESPI) can be used to measure the orthogonal components of vibration amplitude independently. These can be combined to determine the three-dimensional amplitude and mode shape. Examples of experimental results are presented for volume vibrations of a thick cylinder, identification of vibration modes of a turbocharger blade, and observation of in-plane modes in a thin plate.