Real-time color holographic interferometry devoted to 2D unsteady wake flows

A new optical technique based on real time holographic interferometry in true colors has been implemented around the transonic wind tunnel of the ONERA-Lille center to analyze 2D unsteady wake flows. Tests realized in color interferometry, real time and double exposure, use simultaneously three wavelengths of a continuous waves laser (argon and krypton mixed) and holograms are recorded on silver-halide single-layer panchromatic Slavich PFG03c plates. The very principle of real-time true color holographic interferometry uses three primary wavelengths (red, green and blue) to record, under no-flow conditions, the interference among the three measurement beams and the three reference beams simultaneously on a single reference hologram. After the holographic plate is developed, it is placed on the test setup again in the position it occupied during exposure and the hologram is illuminated again by the three reference beams and three measurement beams. A flat, uniform color can then be observed behind the hologram. So a horizontal, vertical, or even circular fringe pattern can be formed and the achromatic central fringe can be made out very clearly. The single color is used to determine the path difference zero on the interferograms. The flow studied was the unsteady flow downstream of a cylinder placed crosswise in the test section. A sequence of hundred interferograms was recorded on the flow around the cylinder at Mach 0.37. The vortex formation and dissipation phases can be seen very clearly, along with the fringe beat to either side of the cylinder.     

单周期条纹双四步相移投影仪的标定方法

针对投影仪标定方法中存在畸变及倾斜投影引起条纹周期、条纹级数变化的问题,提出一种单周期条纹双四步相移投影仪的标定方法.设计生成横向和纵向各两组单周期条纹图像,经投影仪投影到带有圆形标识的标定板上,相机同步采集标定板图像,叠加由双四步相移获得的两幅相位主值图,对叠加相位主值图相位展开,利用展开的绝对相位值计算投影仪像素坐标值,最终将投影仪标定转换为成熟的相机标定.实验结果表明:仿真投影仪标定实验准确度的最大重投影误差约为0.4pixel,均方根误差为0.132 96pixel;实际投影仪标定实验准确度的最大反投影误差约为0.46pixel,均方根误差为0.143 12pixel;实验结果与仿真结果的最大反投影误差相差15%,均方根误差相差7.6%.与现有的采用三频相位展开进行投影仪标定的方法相比,投影光栅图像数可减少8幅.该方法改善了现有投影仪标定方法的不足,标定准确度和标定效率均得到提高.     

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.     

大剪切电子散斑干涉的载频调制与位移场测量

将电子散斑干涉场的载波调制引入到大剪切电子散斑干涉中,通过对参考物的微小偏转引入载波条纹;利用傅里叶变换法,解调出了变形场的相位,从而实现了物体变形场的精确测量。讨论了大剪切载频的调制机理,理论分析表明,调制条纹的空间频率与参考面偏转的角度成正比;因此,控制参考面的偏转角度可实现不同位移量系统的调制。利用中心加载周边固定圆盘进行了典型实验,实验结果证明在大剪切电子散斑干涉技术中可以通过参考面的旋转高质量地实现电子散斑干涉条纹的调制,求解位移场。该系统具有系统简单,不需要专门引入参考光,条纹质量好等优点。该技术可扩展电子散斑干涉的应用范围,有一定的实际应用价值。     

Simultaneous estimation of unwrapped phase and phase derivative from a closed fringe pattern

We propose a new approach for the direct estimation of the unwrapped phase from a single closed fringe pattern. The fringe analysis is performed along a given row/column at a time by approximating the phase with a weighted linear combination of linearly independent basis functions. Gaussian radial basis functions with equally distributed centers and a fixed variance are considered for the phase approximation. A state space model is defined with the weights of the basis functions as the state vector elements. Extended Kalman filter is effectively utilized for the accurate state estimation. A fringe density estimation based criteria is established to select whether the phase estimation is performed in a row by row or column by column manner. In the seed row/column decided based on this criteria, the optimal basis dimension is computed. The proposed method effectively renders itself in the simultaneous estimation of the phase and the phase derivative. The proposed phase modeling approach also allows us to successfully demodulate the low density fringe patterns. Simulation and experimental results validate the practical applicability of the proposed method.     

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.     

Photoelastic stress pattern analysis using Fourier transform with carrier fringes: influence of quarter-wave plate error

The Fourier transform method, widely applied in photomechanics for the automated analysis of interferometric fringe patterns, has been recently extended to the photoelastic isochromatic fringe patterns analysis. Unfortunately, its use in photoelasticity involves some limitations that have not been completely highlighted in literature. This work deals with the influence of the quarter-wave plate tolerance on the evaluation of the retardation. Both theoretical and experimental analyses have shown that the quarter-wave plate error does not affect the retardation only if the principal stress directions in the model and in the carrier are aligned. In general, instead, the tolerance of the quarter-wave plates leads to an amplification of the retardation error due to the influence of the isoclinics with a subsequent restriction of the field in which the method can be applied. For instance, using common quarter-wave plates and tolerating a maximum retardation error of about 0.03 fringe order, than the Fourier transform method cannot be applied as a full-field technique but only in the model zones in which the misalignment between the principal stresses in the model and in the carrier is less than 15°.     

Automatic analysis of three-dimensional displacement field using ESPI

Electronic speckle pattern interferometry (ESPI) has been used to study the in-plane and out-of-plane displacements of the object. In order to improve the accuracy, a Fourier filtration algorithm has been used to remove the speckle noise and get the holographic-quality ESPI fringe pattern. The processing steps of this method are described in detail in this paper. In addition, a phase shifter, which is easily used with simplified structure and high stability, is also presented. It can be applied to various coherent arrangements in experiments to obtain phase shifted fringe patterns. Experiments of determining the 3D displacement field of a circular fixed plate with a uniform load have been carried out using these methods. The results presented in this paper indicate that the accuracy of this method is satisfactory.     

Free vibration of continuous polar orthotropic annular and circular plates

The free vibration of a polar orthotropic annular plate supported on concentric circles is analyzed by the Ritz method with use of Lagrange multipliers. A trial function for the deflection of the plate is expressed in terms of simple power series, and a frequency equation for the plate is derived by the condition for minimizing the total potential energy with the constraint equations included. In the numerical examples it is also shown that the method can directly yield quite accurate frequency values for a solid circular plate. Natural frequencies of annular and circular plates are calculated for wide ranges of the support location and orthotropic parameters.     

二维光子晶体缺陷模特性研究

用时域有限差分法计算了二维光子晶体的带隙和缺陷模,结果表明:在缺陷中心位置其强度达到最大值,离缺陷中心越远,强度越小.比较了方形介质柱与圆形介质柱光子晶体缺陷模:圆形缺陷缺陷模衰减的特征长度较小,但其缺陷模的品质因数较大.缺陷模的中心频率随缺陷介电常数的增大而变小,并近似成线性关系.     

Dislocation and disclination loops in the virtual-defect method

A method of virtual circular defect loops is developed for determining the elastic fields produced by defects in a bounded medium in the case of an axially symmetric geometry. In this method, continuously distributed virtual circular Volterra and Somigliana dislocation loops are adjusted in such a way as to satisfy the boundary conditions imposed at free surfaces and interfaces. Original calculations of the elastic fields of circular defect loops of different types are carried out. The elastic fields are found for the case of straight dislocations and disclinations in a plate that are perpendicular to the plate plane and for the case of circular disclination loops parallel to the plate plane or to an interface.     

Study on an automatic processing technique of the circle interference fringe for fine interferometry

The fringe center method (FCM) is an important digital processing technique of fringe patterns analysis for interferometry. In this paper, an improved automatic processing technique based on FCM was presented, which correlated the processing link and the looped feature of the circle fringe pattern. It also integrated several techniques including noise removal, the fringe thinning, the fringe patching, assignment of the fringe orders and wavefront reconstruction and can be executed orderly and automatically. Based on the new the algorithms of the fringe patching and assignment of the fringe orders, the fringe feature information was extracted automatically and the interference wavefront was reconstructed by Zernike polynomial fitting method. With the automatic processing technique, the circle interference fringe of the fine polished aluminum disks surface captured by the Twyman-Green interferometer was processed, and the surface profile and the parameters of the disk were obtained automatically. The experiments show that the improved automatic processing technique was more accurate and fast in measurement than the conventional one. It was convenient to use it in in-situ industry inspection.     

Simple calibration of a phase-based 3D imaging system based on uneven fringe projection

Phase-based fringe projection metrology systems have been widely used to obtain the shape of 3D objects. One vital step is calibration, which defines the relationship between the phase and depth data. Existing calibration methods are complicated because of the dependence of the relationship on the pixel position. In this Letter, a simple calibration procedure is introduced based on an uneven fringe projection technique, in which the relationship between phase and depth becomes independent of the pixel position and can be represented by a single polynomial function for all pixels. Therefore, given a set of discrete points with a known phase and depth in the measuring volume, the coefficient set of the polynomial function can be determined. A white plate having discrete markers with known separation is used to calibrate the 3D imaging system. Experimental results demonstrate that the proposed calibration method is simple to apply and can build up an accurate relationship between phase and depth data.     

铁矿选矿产品中低微量钍的X射线荧光光谱分析

本文介绍用粉末内标压片Ｘ射线荧光光谱法测定铁矿选矿工艺流程产品中的低微量钍，方法简便、快速、准确、经济，较之化学分析法，有它独到之处，满足了选矿研究对于分析的快速、准确的要求。本法以钼为内标元素，硼酸为低吸收粘结剂，与粉末试样混合均匀后，用１５吨压片机压制成直径２５ｍｍ的圆片状的样品，即可进机测量。     

Adaptive quadrature filters for multiple phase-stepping images

We present a new technique for the recovery of local phase from multiple phase-stepping fringe images that uses adaptive quadrature filters constructed by use of Bayesian estimation theory and complex-valued Markov random fields as prior models. It is shown that with this technique it is possible to perform accurate phase reconstructions even for extremely noisy fringe images and that the performance of this technique is nearly independent of the particular noise model, as long as the noise spectrum is wideband.     

双折射晶体在偏振光杨氏干涉实验中的应用

在正交偏光系统中置入一天然解理的双折射晶块和会聚透镜,可获得清晰的偏振光干涉分布图样。该文利用双折射晶体的偏振分束原理对干涉图样的产生和条纹分布进行具体的分析和计算。     

Reconstruction of a complex-shaped defect from the known arrival time of the reflected ultrasonic wave

The problem of reconstructing the boundary of an arbitrarily shaped defect formed inside an elastic body from the measured time of arrival of the reflected ultrasonic wave in the echo method is considered. The characteristic size of the defect is assumed to be greater than the wavelength, and the defect is irradiated from the far-field zone, which means that the incident wave can be considered as plane. An algorithm is developed for reconstructing the convex envelope of a nonconvex defect from the arrival times of echo signals measured at different angles with the use of circular scanning.     

用于缺陷定量的超声散射信号去相关分析及贝叶斯反演方法

针对结构中缺陷定量识别问题,建立了椭圆缺陷超声散射仿真模型,研究了缺陷偏转角度及尺寸对散射信号去相关特性的影响.结果表明,超声信号去相关系数矩阵与缺陷几何状态(如尺寸及角度)存在很大关联性,但并非线性相关.结合参数化有限元分析与贝叶斯理论,发展了一种基于超声散射信号去相关分析的缺陷反演方法,开展了缺陷反演数值仿真及检测...     

Limitation of carrier fringe methods in digital photoelasticity

The carrier fringes method has been proposed in digital photoelasticity in combination with techniques such as Fourier transform and phase shifting method, without considering the influence of the isoclinics on the isochromatic patterns analysis. Unlike other optical methods as moiré and holographic interferometry, in photoelasticity the light intensity emerging from a circular polariscope is related to both the isochromatic retardation and the isoclinic parameter. As it is shown by the theoretical analysis, owing to the misalignment between the principal stresses in the model and in the carrier, the computed retardation is affected by an error which is the same for all photoelastic methods based on the use of carrier fringes. Consequently, the photoelastic analysis carried out by methods that use carrier fringes cannot be applied as a full-field technique. In detail, numerical simulations show that the retardation error is comparable (less than 0.05 fringe orders) with that of other photoelastic methods provided that the misalignment between the principal stresses in the model and in the carrier is less than 30°. On the contrary, in the model zones where the misalignment is higher than 30°, the retardation measurement can be affected by non negligible errors (up to 0.25 fringe orders).     

Response of a mindlin plate with trunnion

The vibratory response of a circular plate with a central trunnion is considered. A harmonic force is allowed to act on the trunnion in a plane parallel to the surface of the plate. The model allows for arbitrary location of the center of mass of the trunnion and the line of action of the exciting force. The plate equations include the effects of transverse shear deformations and rotatory inertia, which makes the analysis useful for either thick or thin plates at acoustic frequencies. Application of the model in the control of noise and vibration of rotating machinery is illustrated.