Application of the holographic carrier fringe and FFT technique for deformation measurement

This paper describes a holographic system based on the use of fibre optics and automatic spatial carrier fringe pattern analysis. Carrier fringes are generated by simply translating the object beam between two exposures. Single-mode optical fibres are used to transfer both the object and reference beams. The fast Fourier transform method is used to process the interferograms: it extracts phase from fringe patterns resulting from the interference of tilted wavefronts. The method is illustrated by measuring the deformation of an arbitrarily clamped, uniformly loaded circular plate. The results are given for the perspective plot of the out-of-plane deformation field, the maps of wrapped and unwrapped phase, and a contour map of the unwrapped phase.     

Radio frequency field intensity mapping using a composite spin-echo sequence

A novel radio frequency (RF) field intensity mapping or imaging method using a composite NMR spin-echo sequence is proposed. A composite spin-echo RF pulse with 90 degrees y-180 degrees x-90 degrees y sequence makes phase change in the final image depending on the RF field intensity on the object. The resultant phase change or phase map can be used to obtain the actual RF flip-angle map for a given condition which includes the status of tuning and RF inhomogeneity, etc. Bloch equation has been solved numerically to obtain the effects of the RF field intensity as well as the main magnetic field inhomogeneity and the results are used for the mapping (imaging) of the RF field intensity. Phantom studies have been performed using a 1.5 Tesla whole body MRI system and the results are presented.     

A quasi-one-frame phase-unwrapping algorithm through zone-switching and zone-shifting hybrid implementation

This study presents a wrapped-data-switching model and a corresponding regional unwrapping algorithm for 2D phase fields retrieval. In contrast to earlier techniques, which only produce successive frames of transient unwrapping, the proposed method can produce correct unwrapping in quasi-one frames. The approach tolerates isolated phase inconsistencies, and thus is quite effective for unwrapping speckle-coded contour map with numerous discrete inconsistencies. Since the analysis is based on a wrapped-data-switching model, the proposed criterion is path independent and error-propagation free. Additionally, the criteria are simple, concise, efficient, and easily implemented. The criteria and characteristics of the algorithm are demonstrated by simulating ideal and problematic cases, as well as by conducting experiments.     

Characterization of axially tilted fibres utilizing a single-shot interference pattern

We proposed a method to solve the problem of extracting meaningful phase information for a single-shot interference pattern taken for an axially tilted fibre sample. Conventionally such interference patterns can be not evaluated with appropriate accuracy. Here, such an interference pattern is considered to be a special hologram since it contains information about light propagated through a laterally fixed sample located at different axial planes. Thus, part of the test object in such a hologram is in focus and the other parts are out of focus. The proposed method can be considered as two complementary steps. In the first step the complex amplitude across the hologram plane is recovered using an adaptive spatial carrier frequency method. This is followed by the second step where the complex amplitude is numerically propagated within a given volume. Thus, planes where the test object is in focus are defined. Consequently, the phase distributions corresponding to all of these planes are together stitched. Thus a complete focus phase map for the fiber sample under test is obtained. From the obtained phase map the two dimensions refractive and the two dimensions birefringence of isotactic polypropylene fibre were calculated.     

A new method for generating and analysing digital speckle shearing correlation fringe patterns

A method for generating a high visibility digital speckle shearing fringe pattern is proposed. A three-step phase shifting technique which involves the introduction of arbitrary phases is utilized. The phase shifting technique is carried out using a rotating mirror and a theoretical model which involves a linear correlation algorithm is discussed. Experimental results showing correlation fringe patterns and a deformation phase map are presented.     

Fast fourier transformed electronic speckle contouring for diffuse surfaces profilometry

A method of contouring three-dimensional objects using an out-of-plane sensitive ESPI apparatus with optical fibers is presented. The contour map is obtained by shifting the object illumination beam. A Fourier transform method is suggested for automatic quantitative analysis of specklecorrelograms in terms of phase. An example of application is presented.     

单幅对称变形相位图分离二维变形分量的相移电子散斑干涉技术

提出了利用相移电子散斑干涉测量物体二维变形分量的方法.单光束照明的传统电子散斑干涉技术,测量得到的是一幅物体变形的混合相位场.当物体具有对称变形时,可由这一幅相位图求得二维变形分量.方法是将该相位图镜像翻转得到第二幅相位图,通过二幅相位图的叠加、复位和分离运算,获得物体的二维变形场的分量值.利用三点加载的简支梁进行了实验,给出了实验结果,并与对称光照明实验结果进行了对比,验证了该方法的正确性.     

Shape identification using phase shifting interferometry and liquid-crystal phase modulator

A phase shifting technique using a Michelson interferometry system is presented and applied to surface contour measurement. Hyperbolic fringes are produced by the interference of two spherical wavefronts expanded from a beam expander. The fringe pattern is projected on an object surface and the deformed grating image is captured by a CCD camera for subsequent analysis by a PC. Phase variation is achieved by a liquid-crystal device incorporated in the Michelson interferometry system. Results obtained using the proposed method for objects of various shapes and sizes compared well with those from a conventional profilometer.     

Strain mapping of semiconductor specimens with nm-scale resolution in a transmission electron microscope

The last few years have seen a great deal of progress in the development of transmission electron microscopy based techniques for strain mapping. New techniques have appeared such as dark field electron holography and nanobeam diffraction and better known ones such as geometrical phase analysis have been improved by using aberration corrected ultra-stable modern electron microscopes. In this paper we apply dark field electron holography, the geometrical phase analysis of high angle annular dark field scanning transmission electron microscopy images, nanobeam diffraction and precession diffraction, all performed at the state-of-the-art to five different types of semiconductor samples. These include a simple calibration structure comprising 10-nm-thick SiGe layers to benchmark the techniques. A SiGe recessed source and drain device has been examined in order to test their capabilities on 2D structures. Devices that have been strained using a nitride stressor have been examined to test the sensitivity of the different techniques when applied to systems containing low values of deformation. To test the techniques on modern semiconductors, an electrically tested device grown on a SOI wafer has been examined. Finally a GaN/AlN superlattice was tested in order to assess the different methods of measuring deformation on specimens that do not have a perfect crystalline structure. The different deformation mapping techniques have been compared to one another and the strengths and weaknesses of each are discussed.     

基于多混沌系统的双图像光学加密算法

为了扩展双图像光学加密算法的密钥空间,克服双随机相位加密系统中随机相位掩模作为密钥难于存储、传输和重构的问题,突破传统图像加密的研究思路,提出了一种基于多混沌系统的双图像加密算法,构造了光学加密系统。系统增加混沌系统参数作为密钥,利用混沌加密密钥空间大和图像置乱隐藏性好的特点,构建基于Logistic混沌映射的图像置乱算法,利用Kent混沌映射生成的伪随机序列构造出一对随机相位掩模,分别放置在分数傅里叶变换光学装置的两端,图像经加密系统变换后得到密文。数值仿真结果表明,算法的密钥敏感性极高,能够有效地对抗统计攻击,具有较高的安全性。     

Application of the FFT method for the quantitative extraction of information from high-resolution interferometric and photoelastic data

This paper describes the application of a digital Fourier transform to phase encoded intensity distribution. Attention is drawn to a method of extracting quantitative information automatically from the interferometric fringe data. To achieve this, a set of carrier fringes has been added to interferometric fringe data. This has made it possible to form a phase map using a FFT (fast Fourier transform) algorithm. A minimum spanning tree (MST) phase unwrapping strategy has been used to create a contiguous map of the whole fringe field. Finally, the measurement parameter related to the fringe field has been calculated from one single image. Experimental results are given for the burner flames, a compressible flow and photoelastic fringe data. It has been shown that the methods developed have the potential for use as reflection analysis systems suitable for applications to non-stationary objects and complicated fringe fields.     

Deformation and profile measurement using the digital projection grating method

This paper presents a digital projection grating method for full field measurement of out-of-plane deformation and shape of an object. Two grating patterns on an object before and after deformation are captured by a CCD camera and stored in a computer. With the aid of Fast Fourier Transform (FFT) and signal demodulating techniques, a wrapped phase map is generated. The phases are expanded in the range of 0–2π and compared with the resulting moiré pattern. An unwrapping procedure is used to obtain a continuous phase. In addition, a digital method for fractional fringe multiplication is also developed. Results on deformation and object profile measurements are presented.     

Photoelasticity stress analysis using carrier fringe and FFT techniques

A novel carrier fringe technique for photoelasticity stress analysis is described and verified experimentally. Linear carrier fringes generated by using a quartz wedge are superimposed on fringes formed by the stressed model. The resultant fringe pattern is then captured using a charge coupled device camera and stored in a digital frame buffer. A fast Fourier transform method is then used to process the complete photoelastic fringe image over the whole surface of the model. The experiment also uses a minimum spanning tree phase unwrapping strategy to create a continuous map of the whole stress field. Finally, the whole principal stress difference field has been calculated and plotted from one single exposure showing the methods' potential for use as a reflection analysis system suitable for application to nonstationary objects and complicated stress patterns.     

Automatic window size selection in Windowed Fourier Transform for 3D reconstruction using adapted mother wavelets

Fringe pattern analysis in coded structured light constitutes an active field of research. Techniques based on first projecting a sinusoidal pattern and then recovering the phase deviation permit the computation of the phase map and its corresponding depth map, leading to a dense acquisition of the measuring object. Among these techniques, the ones based on time-frequency analysis permit to extract the depth map from a single image, thus having potential applications measuring moving objects. The main techniques are Fourier Transform (FT), Windowed Fourier Transform (WFT) and Wavelet Transform (WT). This paper first analyzes the pros and cons of these three techniques, then a new algorithm for the automatic selection of the window size in WFT is proposed. This algorithm is compared to the traditional WT using adapted mother wavelet signals both with simulated and real objects, showing the performance results for quantitative and qualitative evaluations of the new method.     

Virtual fields method coupled with moiré interferometry: Special considerations and application

The virtual fields method (VFM) is a novel highly efficient non-iterative tool for the identification of the constitutive parameters of materials. The VFM can obtain several constitutive parameters based on the full-field deformation of the specimen measured in a single test. However, the available results demonstrate that the accuracy of the identification result is strongly dependent on the quality of the deformation field, which is generally measured using optical methods. Especially, in the case where a small deformation is applied under elastic loading, the image noise and measurement error will exhibit a significant influence on the identification results. By combining the VFM with moiré interferometry (MI), a MI-based VFM is used to identify the parameters of an orthotropic linear elastic material. A numerical experiment is conducted to examine the feasibility of this method. From the analysis results, we determine that two factors exhibit an influence on the identification accuracy. The reinforcement direction of the orthotropic material is one factor, and the other is the noise in the deformation field. This MI-based VFM is then applied to determine the mechanical parameters of a unidirectional carbon fiber composite material. In the measurement, a three-point bending load is applied to the specimens. A high density grating with a frequency of 1200 line/mm grating is replicated on the specimen surface and used for measuring the in-plane deformation fields using a moiré interferometer. The obtained deformation fields are taken as the inputs of the VFM identification process, and the elastic properties of the materials are identified. The obtained results verify the advantage of the proposed method with respect to high accuracy and good noise immunity.     

Digital image watermarking using gyrator transform and chaotic maps

We propose a new method for digital image watermarking using gyrator transform and chaotic maps. Four chaotic maps have been used in the proposed technique. The four chaotic maps that have been used are the logistic map, the tent map, the Kaplan-Yorke map and the Ikeda map. These chaotic maps are used to generate the random phase masks and these random phase masks are known as chaotic random phase masks. A new technique has been proposed to generate the single chaotic random phase mask by using two chaotic maps together with different seed values. The watermark encoding method in the proposed technique is based on the double random phase encoding method. The gyrator transform and two chaotic random phase masks are used to encode the input image. The mean square error, the peak signal-to-noise ratio and the bit error rate have been calculated. Robustness of the proposed technique has been evaluated in terms of the chaotic maps, the number of the chaotic maps used to generate the CRPM, the rotation angle of the gyrator transform and the seed values of the chaotic random phase masks. Optical implementation of the technique has been proposed. The computer simulations are presented to verify the validity of the proposed technique.     

Self-marking phase-stepping electronic speckle pattern interfometry (ESPI) for 3D displacement measurement on cathode ray tube (CRT)-panels

This study demonstrates the feasibility of applying phase-shifting electronic speckle pattern interfometry to measure the deformation field of the front panel of a cathode ray tube, to support analysis to enhance the implosion-resistance capacity under violent collapse. Two effects, the air exhaustion and shrink band constraint effects, are comprehensively investigated. The angle of an adjustable mirror is switched, to provide three sensitivity vectors that are required in 3D-displacement measurement. A Fourier filtration is employed to remove speckle noise and establish a noise-free phase map. Inconsistent points are identified and masked to prevent any possible divergence during phase unwrapping. The results show that the accuracy of this method is satisfactory.     

基于AutoCAD和3DSMAX的虚拟校园三维场景构建研究

当前的虚拟校园三维场景构建方法是利用osgEarth获取GoogleEarth数据,构建虚拟校园三维地图,然后依据本地地形信息与三维场景模型完成对虚拟校园的三维场景构建。该方法在三维场景构建过程中没有考虑到校园后续建设发展,只凭现在所需进行三维场景构建,导致虚拟校园三维场景杂乱,存在虚拟校园三维场景构建顾虑不周的问题。为此,提出一种基于AutoCAD和3DSMAX的虚拟校园三维场景构建方法。该方法首先利用Kinect的RGB深度摄像头获取校园平面数据、影像数据和贴图资料,采用相机阵列合成算法对所得校园图像进行特征提取,然后依据非局部均值滤波方法对获取的校园图像进行去噪操作,最后利用边缘方向和梯度表示中的结构方向与强度,对校园图像外轮廓的纹理特征进行收敛,依据外轮廓纹理特征收敛实现校园图像内轮廓的准确定位,将校园图像与虚拟校园三维场景构建所需图像进行匹配,由此完成对虚拟校园三维场景的构建。实验结果证明,所提方法是虚拟校园三维场景构建领域革命性的突破,提高了学校的招生率,增加了校园文化历史的展现机会,为该领域的研究发展提供了有效依据。     

A least-squares method to cancel rigid body displacements in a hole drilling and DSPI system for measuring residual stresses

This paper presents the evaluation of a method to cancel rigid body displacements that can be introduced when a hole drilling and digital speckle pattern interferometry (DSPI) combined system is used to measure residual stresses. The proposed method is based on a least-square calculation of three correction parameters determined from two evaluation lines located near the edge of the phase map where the displacement field generated by the drilling process is supposed to be negligible. The errors introduced by the method for different residual stress levels and rigid body displacements are analysed using a numerical simulation. An application of the method to experimental data is also presented.     

Microscopic TV holography for MEMS deflection and 3-D surface profile characterization

Recent industrial demands for greater product quality in the fields of microelements and micro-electro-mechanical systems (MEMS) generate new challenges for metrology. The fast-growing MEMS industry requires a robust non-destructive quantitative measurement system for the characterization of their performance, reliability and integrity. A microscopic TV holographic system using a long working distance microscope with an extended zoom range has been developed for microelements and MEMS deformation and 3-D surface profile analysis. The system is capable of evaluating both rough and smooth surfaces. Noisy wrapped phase map is a usual problem in speckle interferometry. We have compared several phase-shifting algorithms for evaluation of speckle phase for their usefulness in generating less-noisy phase maps. The experimental results on a MEMS pressure sensor for out-of-plane deflection and 3-D surface profile analysis are presented.