Factors affecting temperature measurement using phase measurement interferometry in small scale devices

This paper presents full-field temperature measurements of buoyancy opposing mixed convection flow within a miniscale fluidic geometry. The technique used is phase measurement interferometry and a Mach–Zehnder layout is employed. The popular two-dimensional microfluidic geometry of three streams merging at a junction is chosen for this analysis. The apparatus set-up is described and measures taken to limit experimental errors discussed. Also presented, are corresponding flow visualization images for comparison with the interferometric results. The results are compared for similar boundary conditions over the range of Richardson numbers of 0.5–1.7. The results of the interferometric study are presented in the form of full-field temperature maps depicting the type of thermal plume structure present through isotherms and are seen to compare well with the results of the flow visualization study. Some factors affecting the measurement technique at this scale are then discussed. These include the effect of using different transparent materials for sealing the fluidic device and temporal vibrations caused by either varying boundary conditions or by slight pulsations in the flow supplied. Also, due to discrepancies that exist in the literature for the temperature coefficient of the refractive index of the working fluid, thermocouples are embedded in the flow field and used to convert the measured phase change to a corresponding temperature change. The corresponding values of refractive index change with temperature are discussed and compared to published values. Overall, PMI is demonstrated to provide excellent full-field temperature plots that can be used to measure local heat transfer rates from this non-intrusive measurement technique.     

对流传热边界层温度分布的激光干涉测量

本文介绍利用双镜干涉仪测量对流传热边界层中二维温度分布的方法。当冷空气流经热板模型时,附面层内的干涉条纹发生弯曲。根据条纹弯曲偏移量,由折射率与温度的关系,画出空气温度的二维分布图。整个过程由光学方法及微计算机全盘处理,是一种无接触测量方法。     

数字全息干涉相位导数计算的研究

应变测量对材料评估与分析非常重要。通过计算数字全息干涉的相位导数可实现应变测量。本文针对数字全息干涉相位导数提取问题,对数字剪切法和基于二维伪维格纳法进行研究。数字剪切法通过对干涉复相量的数字平移实现剪切,确定干涉相位导数,而二维伪维格纳法则通过对干涉复相量的二维伪维格纳分布变换,由变换模极值对应的频域参数确定相位导数。数字剪切法需干涉复相量的数字剪切过程,还需相位去包裹。由于激光散斑噪声的影响,直接数字剪切法处理效果较差,通过对剪切干涉复相量滤波,能较好消除散斑噪声影响。二维伪维格纳法无需数字剪切和相位去包裹,就可同时得到2个方向的干涉相位导数,但处理时间较长,处理效果较差。最后,用数字全息干涉法对四周固定、中心加载铝圆盘进行了实际测量,并分别用数字剪切法和二维伪维格纳法进行了分析。结果表明,滤波数字剪切法处理时间适中,处理效果较好。     

Calibrated multichannel electronic interferometry for quantitative flow visualization

Calibrated multichannel electronic interferometry, a new technique for quantitative flow visualization of transient phenomena, is discussed. This technique uses an interferometer combined with diffraction gratings to generate three phase shifted interferograms simultaneously which are used to perform multichannel phase shifting. The optical system is calibrated with no phase object present using standard piezoelectric phase shifting, and this calibration information is stored as an electro-optic hologram. The calibration information is used along with the three phase-shifted interferograms that exist with a phase object present to perform time-resolved phase shifting. Examples using natural convection and separated flows are presented.     

A laser interferometric measurement of the temperature distribution in convective thermal transfer boundary layers

By means of a double mirror interferometry a two-dimensional temperature distribution measurement in convective thermal boundary layers is presented. When the cold air flows along a hot plate model, the interferometric fringe inside the boundary layer will bend. According to the displacement of the fringe and the relation between temperature and index of refraction, a two-dimensional temperature profile is obtained. All is accomplished by optical device with the help of micro-computer without any contact with the flow field. The project supported by the National Natural Science Foundation of China     

Image reconstruction of three dimensional temperature field from projections in optical tomography

It is well known that determination of temperature fields by holographic interferometry is a successful method in the measurement of thermophysics. In this paper, some practical algorithms for image reconstruction from projections are presented to produce the temperature field. Algorithms being developed include that the Radon transform integral equation is directly solved by a grid method, and that the Radon inversion formula is numerically evaluated by two-dimensional Fourier transform technique. Some examples are given to verify the validity of the above methods in practice. A heat air flow above conbustor with a rectangular hole is investigated by holographic interferometric system, and temperature distributions of two sections in the air flow field have been reconstructed by this methods.     

Grating holographic interferometry

A holographic interferometric technique, combining an image hologram with a grating approach, is proposed for three-dimensional deformation measurements on opaque planar object surfaces. In this technique, the holographic plate is brought close to the object surface, onto which a high-frequency crossed-line diffraction grating has been replicated. The grating surface produces multiple object waves rather than the usual diffusely reflected object waves. The double-exposed single holograms can be reconstructed at multiple off-axis angles. Four independent high-contrast fringe patterns are extracted simultaneously. Displacement vectors over the entire measurement area are separated in three orthogonal directions. The resultant displacements are presented as three-dimensional meshed plots and topographic contour maps. The optical system for both recording and reconstruction of the holograms has been simplified compared to conventional holographic interferometry. Experimental errors associated with fringe readout and system geometry are reduced because of the sharp images and the well-defined spatial orientation in the reconstruction system.     

Evaluation of three techniques for wall-shear measurements in three-dimensional flows

Recent improvements in three techniques for measuring skin friction in two- and three-dimensional turbulent wall-bounded shear flows are presented. The techniques are: oil-film interferometry, hot wires mounted near the wall, and surface hot-film sensors based on MEMS technology. First, we demonstrate that the oil-film interferometry technique can be used to measure the skin-friction magnitude and its direction in two- and three-dimensional wall-bounded shear flows. Second, a simple method is outlined to measure the skin friction with a wall wire located outside of the viscous sublayer. Finally, a systematic study of the parameters influencing wall-friction measurements with MEMS sensors is presented. The results demonstrate that accurate measurements of the mean skin friction with MEMS sensors are possible in two- and three-dimensional wall flows. Measurements by the three techniques are compared to each other and to past measurements in the same facility.     

Study of failure modes of microelectronic packaging modules by holography quasi projection moire method

In this paper, a novel interferometric method with a wide range of sensitivities, called holography quasi projection moire, is proposed. It combines the features of the variated double projection moire method and the holographic interferometry method. This technique is used to study the failure modes of microelectronic packaging modules. The project supported by the National Natural Science Foundation of China     

Comparative holographic interferometry: A nondestructive inspection system for detection of flaws

Comparative holographic interferometry addresses a key problem of nondestructive evaluation: comparison of the resistance to strength in real time of two nominally identical specimens. After outlining the basis of comparative holography in flaw detection, the present paper reports on some new and complementary developments in comparative holographic interferometry. The proposed systems stand out by their ability to store the master displacement field in the interferometric setup. The integration of the storage capacity in the instrument considerably augments its potential in nondestructive routine inspection tasks. The visual display of the fringes contouring the difference in mechanical response is shown to improve considerably with the addition of auxiliary phase difference satisfying certain conditions. Methods for the generation of corresponding fringes are considered and their localization investigated in brief. Particular attention is devoted to the formation of the holographic moiré fringes. The influence of system misalignment on the moiré fringe interpretation is examined. A potential application of comparative holography to the quantitative evaluation of fatigue is described. Experimental evidence supporting the operational feasibility of the technique along with the results obtained in application to flaw detection are finally presented.     

Digital interferometry: techniques and trends for fluid measurement

Interferometric based measurement techniques have long played a significant role in enabling insight and understanding into the flow and heat transfer processes in a wide range of fluid flow situations. In recent years, with the advent of digital processing techniques, full field quantitative data can be obtained from interferometric data with relative ease and a high degree of accuracy. However, these developments seem not to have percolated through to experimental fluids practitioners. This paper sets out to review the various processing and acquisition techniques for quantitative and qualitative measurement using interferometry. Full field phase measurement interferometry (PMI) and differential interferometry (DI) are discussed. PMI is demonstrated for diffusing mixing in a mini-channel and DI is demonstrated for heat transfer measurement in a convecting fluid.     

Measurement of slopes of structural deflections by speckle-shearing interferometry

A specimen illuminated by coherent light is imaged by a camera through a shearing mechanism so that the speckle from one point on the surface can be made to interfere with the speckle from a neighboring point. The resultant speckle pattern is recorded. By mechanically interfering the recorded speckle pattern corresponding to deformed and undeformed states of the specimen, respectively, using double-exposure technique, a speckle-moiré-fringe pattern is generated. These fringes which depict derivatives of deflections of the specimen are made visible by spatial-filtering technique. Speckle-moiré fringes can also be obtained in real time. This method is a new interferometry and will be referred to as “speckle-shearing interferometry”. Speckle-shearing interferometry has the same function as Ligtenberg's technique. However, it does not have the sometimes inconvenient requirement of Ligtenberg's technique that the surface of the specimen must be of mirror quality. The new technique will be particularly useful in studies of flexural deformation such as flexed beams and plates. Although speckle-shearing interferometry is an interferometric method, it overcomes several of the limitations associated with holographic and speckle interferometries, namely: (1) the setup is simple and does not need laborious alignments of optical components, (2) it does not require stringent mechanical and ambient stabilities, (3) coherent requirement of light is greatly relaxed, and (4) the sensitivity is reduced that somehow fills the gap in sensitivity between moiré techniques and holographic or speckle interferometry.     

Depth-resolved Imaging and Displacement Measurement Techniques Viewed as Linear Filtering Operations

The last 5 years have seen the emergence of a family of optical interferometric techniques that provide deformation measurements throughout three-dimensional (3-D) weakly scattering materials. They include wavelength scanning interferometry (WSI), tilt scanning interferometry (TSI), phase contrast spectral optical coherence tomography (PC SOCT) and hyperspectral interferometry (HSI) and can be thought of as a marriage between the phase sensing capabilities of Phase Shifting Interferometry and the depth-sensing capabilities of Optical Coherence Tomography. It was recently shown that some closely related 3-D optical imaging techniques can be treated as shift-invariant linear filtering operations. In this paper, we extend that work to include WSI, TSI, PC SOCT and HSI as spatial filtering operations and also relate the properties of their transfer functions in the spatial frequency domain to their spatial resolution and phase sensitivity, for depth-resolved displacement measurements.     

Automated fringe pattern analysis for moiré interferometry

The theory of an automated fringe-pattern analysis using temporal phase stepping method for moiré interferometry is presented. The automated method provides a fast and accurate strain measurement for moiré interferometry. Measurements on a tapered composite specimen with a dropped ply are shown to highlight the capability of this technique to obtain the strain distribution, particularly around the region with a dropped ply.     

Residual Stress Determination by Hole Drilling Combined with Optical Methods

An overview is provided of the use of eight different optical methods with hole drilling to determine residual stresses. The methods considered are: brittle and photoelastic coatings, Moire interferometry, holographic interferometry, electronic speckle pattern interferometry, interferometric strain rosette, digital image correlation and shearography. A number of applications are summarized, such as the use of hole drilling with holographic interferometry to investigate stresses in rock structures accessed by deep boreholes and to determine manufacturing-induced residual stresses in fillets of small radii.     

Tomographic reconstruction of shock layer flows

The tomographic reconstruction of supersonic flows faces two challenges. Firstly, techniques used in the past, such as the direct Fourier method (DFM) (Gottlieb and Gustafsson in On the direct Fourier method for computer tomography, 1998; Morton in Tomographic imaging of supersonic flows, 1995) or various backprojection (Kak and Slaney in Principles of computerized tomographic imaging, vol. 33 in Classics in Applied Mathematics, 2001) techniques, have only been able to reconstruct areas of the flow which are upstream of any opaque objects, such as a model. Secondly, shock waves create sharp discontinuities in flow properties, which can be difficult to reconstruct both in position and in magnitude with limited data. This paper will present a reconstruction method, matrix inversion using ray-tracing and least squares conjugate gradient (MI-RLS), which uses geometric ray-tracing and a sparse matrix iterative solver (Paige and Saunders in ACM Trans. Math. Softw. 8(1):43–71, 1982) to overcome both of these challenges. It will be shown, through testing with a phantom object described in tomographic literature, that the results compare favourably to those produced by the DFM technique. Finally, the method will be used to reconstruct three-dimensional density fields from interferometric shock layer images, with good resolution (Faletič in Tomographic reconstruction of shock layer flows, 2005). This paper was based on work that was presented at the 3rd International Symposium on Interdisciplinary Shock Wave Research, Canberra, Australia, March 1–3, 2006.     

Interferometry and reconstruction of strongly refracting fields in two-dimensional boundary layer flow

 Optical methods like interferometry as non-intrusive experimental techniques are used for fine analysis of flowfields. The accuracy of the measuring method is very important for the applicability of its results to CFD validation. A common evaluation method to reconstruct interferograms is based on the assumption, that the object ray propagates along a straight line. But the strong bending of rays that occurs, e.g. in supersonic boundary layer flow, cannot be neglected without losses in reconstruction quality. Since the reconstruction of a two-dimensional boundary layer flow can be considered as an one-dimensional problem, the phase difference of the object and reference ray at the interferogram can be related analytically to the refractive-index distribution using a Taylor series expansion. The resulting interferometric equation is an ordinary non-linear second-order differential equation, which can be integrated by numerical methods. By application of this interferometric equation on the one hand, the error in the “classical” interferometry resulting from the ray bending neglection can be estimated. On the other hand, the accuracy in evaluation of interferograms of two-dimensional boundary layer flow can be improved by solving this equation. Received: 23 May 1996 / Accepted: 21 September 1996     

撞击载荷下数字散斑干涉法中位相的自动计量

在撞击载荷下的数字散斑干涉法（DSPI）中，本文联合应用加法和减法两种模式提出了位相测试技术，以矩形板对称轴承受撞击集中载荷为例，测量了位移场的位相分布，为了采集红宝石脉冲激光形成的数字散斑场，提出瞬态数字图像采集技术。     

Instantaneous phase-stepping interferometry using polarization imaging with a micro-retarder array

An instantaneous phase-stepping and subsequent phase analysis method, using a CCD camera with a form-birefringent micro-retarder array, is proposed for interferometry. An optical setup of a polarization interferometry using a Twyman-Green interferometer with two polarizers is constructed to analyze the distribution of out-of-plane displacement. Light emerging from the interferometer is recorded using a CCD camera that has micro-retarder array on the CCD plane. This micro-retarder array has four different principal directions. That is, an image obtained by the CCD camera contains four types of data corresponding to four different optical axes of the retarder. The four images separated from the image recorded by the CCD camera are reconstructed using gray-level interpolation. Then, the distributions of the Stokes parameters that represent the state of polarization are calculated from the four images. The phase distribution of the interference fringe pattern produced by the Twyman-Green interferometer is then obtained from these Stokes parameters. This method is applicable to time-dependent phenomena because multiple exposures are unnecessary for sufficient data acquisition in the completion of phase analysis.     

A method to provide statistical measures of large-scale instantaneous particle clusters from planar images

Particle clusters are preferential accumulations of a solid, secondary phase that can be caused by turbulence. It is well known that particle clusters can influence the performance of systems employing suspension flows, such as pulverised fuel combustion systems. However, statistical analysis of clusters is limited by available methods to quantify them. In the current study, a method to identify planar slices of large-scale particle clusters from planar images of instantaneous particle distributions is presented. The method employs smoothing of instantaneous particle scatter images by a length scale, L _S , to produce pseudo-scalar fields of particle distributions. The scalar fields are compared with mean (not smoothed) images to produce cluster masks that are then multiplied by the original instantaneous image to produce a map of the locations of cluster slices. The sensitivity to the smoothing length scale is assessed parametrically for its influence on the statistical measures of the following parameters characterising slices of large-scale clusters in four representative flows: the physical locations of the cluster slice centroids; the area of the cluster slice; and the number of cluster slices per image. While the results are influenced by the selected value of smoothing length scale, L _S , the sensitivity is low in a physically reasonable range and the method performs well in this range for the four different flow cases. The method could be extended to provide volumetric measurements with suitable volumetric imaging systems.