Computer generated optical holographic fringe patterns for the analysis of vibrating structures

Optical holographic interference fringe patterns on rods and bars vibrating in ultrasonic resonance (standing waves) are predicted by computer simulations. The simulations are based on a combination of finite element calculations with calculations based on the theory of holographic interference fringe generation. The hypothetical fringe patterns are then compared to holographic fringe images obtained by the experiment (time average holograms). The holographic arrangement and the mechanical part of the ultrasonic system (transducer, horn and specimen) were fixed on a commercial rigid optical table supported on air bags to isolate it from ground vibrations. Thus it is shown that the scope of the study can be reached with a minimum of experimental effort, i.e., with basic laser optical equipment. It is shown that provided the system operates in the desired mode, good agreement between the theoretical and the real image is given. Finally examples of the possible influence of defects or of parasitic modes of vibration on the appearance of the fringe patterns are given.     

The evaluation of fracture mechanics parameters from electronic speckle pattern interferometric fringe patterns

Electronic speckle pattern interferometry has been used to calculate K_I and J for compact tension specimens. Automated fringe pattern analysis enables the full-field of data to be used with the minimum of operator intervention. Measurements are shown to be accurate to within 10%. The J-measurement procedure employed could form the basis of an automatic fault detection system.     

Computer aided evaluation of the p-T phase diagram of AgI using thermodynamic data

Abstract

The GeO-Calc computer program (Brown et al., Computers & Geosciences 14 (1988) 279) has been used for evaluating the p-T phase diagram of AgI in the pressure range up to 3 GPa and the temperature range 0 to 800°C. p-T phase diagrams were calculated using available thermodynamic data and compared to experimentally determined ones. The results of these compareisons were used to check the consistency of the data and to determine unknown quantities. A consistent set of data is presented.     

光学镜头基本结构计算机辅助设计

本文在ＡｕｔｏＣＡＤ平台的基础上对常用光学镜头基本结构进行参数化和模块化自动设计。根据光学系统外形尺寸可以一次性设计出结构装配图,而且可以从装配图方便地分离零件图。同时还提供了多种结构形式供设计者选择。     

Camera calibration with planar crossed fringe patterns

We introduced a novel crossed fringe pattern as the model plane for camera calibration. It can provide abundant control points, in extreme case each pixel on the CCD sensor can be taken as control points. Fourier Fringe Analysis is used to extract the phase distributions from the image of this pattern. Each control point consists of the locations of a pixel and the world coordinates, which can be calculated from the phase distributions. It avoids the complex extracting procedure of those classical control points and could produce abundant control points. Both computer simulation and real data have confirmed the proposed technique is easy to use, reliable and high accurate.     

Normalization and noise-reduction algorithm for fringe patterns

This paper presents a fringe pattern normalization and noise-reduction algorithm. Locally the background noise is suppressed, the modulation normalized and the noise smoothed. An expression to calculate the cosine-only term is formulated. It is related to the directional derivatives of the intensity fringes. Two-dimensional Fourier series are used to calculate the parameters needed for the algorithm. Experimental work is presented using diffraction and ESPI images. The programming is relatively simple and involves mainly local convolutions. The processing time using a 2 GHz computer to normalize an image of 256 × 256 pixels is approximately one second.     

铜蒸气激光器计算机辅助设计

 在已有的各种输出功率、激励条件参数和实际模拟程序基础上,对铜蒸气激光器计算机辅助设计进行改进,获得了适合于宽广参数条件下的模拟程序及实用曲线组。可在一定的激光输出功率条件下确定器件的激活体积;当口径选定后,可得铜蒸气激光器对应的电功率输入密度、激励电场、最佳重复频率和放电管壁温度值。     

载波全息干涉图的自动分析

用正交相干相位检测法实现了载波全息干涉图的自动分析.讨论了分析载波条纹图的边界效应,提出了一种易于在微机上实现的条纹图外插算法.最后给出了一幅实时法载波全息图的分析结果.     

Automatic processing of fringe patterns in integer interferometers

The purpose of this paper is to describe a new method for determination of the total phase difference of light waves without interference fringe counting. One can build up an interferometer for measurement of displacements in which the displacements are determined only by the final values of intensity regardless of the velocity and any prior displacements that caused the present one. The same thing holds true for vibration, relief parameters and other values to be measured. Such an interferometer is devisable thanks to two underlying ideas: first, the application of controllable phase shift, and secondly, the use of properties of integer divisability.     

铜蒸气激光器计算机辅助设计

在已有的各种输出功率、激励条件参数和实际模拟程序基础上,对铜蒸气激光器计算机辅助设计进行改进,获得了适合于宽广参数条件下的模拟程序及实用曲线组。可在一定的激光输出功率条件下确定器件的激活体积;当口径选定后,可得铜蒸气激光器对应的电功率输入密度、激励电场、最佳重复频率和放电管壁温度值。     

The identification of fringe positions in speckle patterns

This paper two methods of identifying fringe positions in speckle patterns. The first uses local directional averaging to track fringes, while the second uses standard image processing techniques to connect the patterns into a form where the fringes can be identified.     

计算机辅助测定微波反射式速调管特性

提出了计算机辅助测量微波反射式速调管特性的方案,对用声卡采集实验数据的方法,以及用ＭＡＴＬＡＢ绘制三维图形作了具体的介绍。     

投影物镜小比率模型的计算机辅助装调

针对小比率模型光学系统光学元件数量较多,无法用每个补偿量去补偿对应失调量的问题,提出利用计算机辅助装调方法,通过建立系统的灵敏度矩阵找出偏心失调量和倾斜失调量的内在联系来缩小补偿量的选择范围。根据失调量敏感度的分析,提出了只用4个补偿量补偿系统波像差的想法,并对所选补偿参量的补偿效果进行仿真,以此近一步验证想法的可行性。光学系统初装完成后,将实际测得的系统波像差以36项Fringe Zernike多项式的形式代入灵敏度矩阵,计算得到补偿参量的补偿值和移动方向,用驱动器实现像质补偿。实验结果表明：系统波像差（RMS）由50.864 nm提高到25.993 nm,优于技术指标要求,证明了所选的4个补偿量的正确性和有效性。     

Adaptive monogenic filtering and normalization of ESPI fringe patterns

A technique is presented for filtering and normalizing noisy fringe patterns, which may include closed fringes, so that single-frame demodulation schemes may be successfully applied. It is based on the construction of an adaptive filter as a linear combination of the responses of a set of isotropic bandpass filters. The space-varying coefficients are proportional to the envelope of the response of each filter, which in turn is computed by using the corresponding monogenic image [Felsberg and Sommer, IEEE Trans. Signal Process. 49, 3136 (2001)]. Some examples of demodulation of real Electronic Speckle Pattern Interferometry (ESPI) images patterns are presented.     

Fringe projection profilometry based on complementary color-encoded fringe patterns

3D measurement techniques based on color-encoded fringe pattern projection have been widely used in various fields of engineering recently. There is one problem that the surface color of measured object may interfere with the color of projected fringe pattern. To solve this problem, a novel method based on complementary color-encoded fringe projection is proposed. Two color-encoded fringe patterns whose fringe colors are complementary are designed. The first pattern is with the sinusoidal fringe embedding into the green color channel which is used to evaluate phases by Fourier transform method. The fringe color of the captured image is established with the help of the complementary color fringe pattern, which is based on the feature of color complementation. Thus, the influence brought by the color of object surface can be eliminated, and decoding errors can be further reduced. Experiment results indicate that the proposed method is valid and can be applied to the measured colorful objects.     

Center positioning of circular interference fringe patterns for fine measurement

A kind of center positioning method of the circular interference fringe patterns was reported in this paper. The whole process was programmed by Matlab for processing the gray-scale images without denoising preprocessing and binary format transformation. The gradient vector field (GVF) based on a complex-valued cost function was used to extract the skeletons of circular interference fringe patterns, and the coordinate of the center was calculated by statistical method in which partial skeletons were selected to calculate the center according to the space topological relationship. Finally, subpixel accuracy and perfect anti-noise ability of the proposed method are demonstrated by the simulation and experimental fringe patterns, respectively. Thus the technique can be used in precision measurement and fine interferometry.     

Patch-wise denoising of phase fringe patterns based on matrix enhancement

We propose a new approach for the denoising of a phase fringe pattern recorded in an optical interferometric setup. The phase fringe pattern which is generally corrupted by high amount of speckle noise is first converted into an exponential phase field. This phase field is divided into a number of overlapping patches. Owing to the small size of each patch, the presence of a simple structure of the interference phase is assumed in it. Accordingly, the singular value decomposition (SVD) of the patch allows us to separate the signal and noise components effectively. The patch is reconstructed only with the signal component. In order to further improve the robustness of the proposed method, an enhanced data matrix is generated using the patch and the SVD of this enhanced matrix is computed. The matrix enhancement results in an increased dimension of the noise subspace which thus accommodates more amount of noise component. Reassignment of the filtered pixels of the preceding patch in the current patch improves the noise filtering accuracy. The fringe denoising capability in function of the noise level and the patch size is studied. Simulation and experimental results are provided to demonstrate the practical applicability of the proposed method.     

Computer aided measurement of biomechanical characteristics of cadaverous lumbar spines

Special computer-aided equipment was designed for measurement of biomechanical characteristics of lower part of the spine (L1-L5). When the stress is applied, it is necessary to observe the shift of the sample elements, together with measurement of the spine rigidity. This shift is determined with the help of circular targets fitted to the appropriate vertebra. The targets, illuminated by lamp or laser light, are monitored and their digitalized images are scanned by CCD camera is stored as computer media. The two dimensional Fourier transform of the digital optical signal is obtained by the fast Fourier transform algorithm. The period and direction of the interference fringes determine the size and the direction of the sample shift.     

Phase recovery from fringe patterns using the continuous wavelet transform

Interferometry is well established as an optical technique in which a measurand is encoded as the phase of a periodically varying intensity pattern. In view of the inherent accuracy of interferometry, many methods have been developed to retrieve the phase from images of the fringe pattern. Our focus in this paper is one such technique—the continuous wavelet transform (CWT). We begin by reviewing the CWT and the space–spatial–frequency localisation properties of wavelets. We show that a path which follows the maximum modulus of the CWT (the wavelet ridge) gives the instantaneous fringe frequency as a function of spatial displacement. The phase is automatically and trivially obtained, without discontinuities, by integration. Examples of practical wavelets are given and algorithms to isolate the wavelet ridge reviewed.     

Computer aided design of inverted strip dielectric waveguide millimeter-wave couplers

A computer aided design technique has been developed for the design of a beam splitter coupler and a distributed type coupler using inverted strip dielectric waveguides. The optical beam principle has been used for the beam splitter coupler. Numerical results for these couplers at 80 GHZ with minimum directivity of 30 dB and VSWR of 1.15 have been presented.This work was supported by the Faculty Research Committee of the University of North Dakota under research Grant Number 1813/0909/2369.