Phase-evaluation methods in whole-field optical measurement techniques

Optical full-field measurement techniques have been widely studied in academia and applied to many actual fields of automated inspection, reverse engineering, cosmetic surgery, and so on. With the advent of color CCD cameras and DMD (Digital Micromirror Device) based color DLP (Digital Light Processing) projectors, their major red, green, and blue channels have been used as a carrier to code fringe patterns. Since three fringe patterns can be simultaneously projected and captured at one shot, the acquisition time reduces to 1/3 of the value by the gray fringe pattern projection. This chapter will introduce two kinds of applications of red, green, and blue as a carrier: 1) modulation and demodulation method of coding sinusoidal fringe patterns into RGB channels of a composite color image; and 2) modulation and demodulation method of coding sinusoidal and binary fringe patterns into RGB channels of multiple composite color images. Experiments on testing the two kinds of applications were carried out by measuring the shape of objects’ surface. The results confirm that red, green, and blue channels can be used as a carrier to reduce the acquisition time.

Conditions of the digital recording of the fringe pattern determine the phase reconstruction procedure, which in turn directly shapes the final accuracy and throughput of the full-field (non-scanning) optical measurement technique and defines the system capabilities. In this way, the fringe pattern analysis plays a crucial role in the ubiquitous optical measurements and thus is under constant development focused on high temporal/spatial resolution. It is especially valuable in the quantitative phase imaging technology, which emerged in the high-contrast label-free biomedical microscopy. In this paper, I apply recently blossomed two-frame phase-shifting techniques to the QPI and merge them with advanced adaptive interferogram pre-filtering algorithms. Next, I comprehensively test such frameworks against classical and adaptive single-shot methods applied for phase reconstruction in dynamic QPI enabling highest phase time-space-bandwidth product. The presented study systematically tackles important question: what is the gain, if any, in QPI realized by recording two phase-shifted interferograms? Counterintuitively, the results show that single-shot demodulation exhibited higher phase reconstruction accuracy than two-frame phase-shifting methods in low and medium interferogram signal-to-noise ratio regimes. Thus, the single-shot approach is promoted due to not only high temporal resolution but also larger phase-information throughput. Additionally, in the majority of scenarios, the best option is to shift the paradigm and employ two-frame pre-filtering rather than two-frame phase retrieval. Experimental fringe analysis in QPI of LSEC/RWPE cell lines successfully corroborated all novel numerical findings. Hence, the presented numerical-experimental research advances the important field of fringe analysis solutions for optical full-field measurement methods with widespread bio-engineering applications.

Few-fringe-based phase-shifting profilometry employing hilbert transform

In this paper, we obtain some new inequalities which reveal the further relationship between the inverse tangent function arctanx and the inverse hyperbolic sine function sinh−1x. At the same time, we give the analogue for inverse hyperbolic tangent and inverse sine.

Two practical computer-aided optical techniques for full-field surface shape measurement are presented, one for diffuse surfaces and the other for specularly reflective surfaces. The former technique is based on projecting a computer-generated fringe pattern onto a diffuse surface, and the latter is based on reflecting the fringe pattern from a specularly reflective surface. The fringe pattern is perturbed in accordance with the object surface with the fringe phase bearing information on the depth/slope of the object surface. The computer-generated fringe pattern conveniently enables the fringe phase to be manipulated, and hence the determination of the phase distribution using a phase extraction algorithm. Instead of deriving the mathematical relationship between the fringe phase distribution and the surface depth/slope, this relationship is obtained by calibration. The techniques described can be easily implemented for rapid measurement of 3-D surface shapes in an industrial setting.

Phase shifting profilometry (PSP) shifts the phase by projecting multiple fringe patterns with different initial phase values. Errors will be introduced when the dynamic object moves among the multiple fringe patterns. This paper presents a new 3D reconstruction method of moving object based on PSP by projecting single fringe pattern. The phase shift is caused by the object movement. Multiple images of the object with movement are captured. The object movement is tracked first; then, the phase variation caused by the movement in the single projected fringe pattern is analyzed and the reconstruction model describing the fringe pattern with movement is given; at last, the phase value is retrieved by utilizing the phase variation caused by the movement. The effectiveness of the proposed method is verified by the simulations and the experiment.

The objectives of this study are to present a 2-D optical method for measuring gross kinematics of porcine anterior column units (ACUs) exposed to swelling with no applied load, provide a detailed error analysis of the 2-D optical measurement technique, and present a 2-D radiographic technique for measuring the distribution of x-ray intensity through an axial slice of the disc. The 2-D optical technique was sufficient for detecting the flexion-extension behavior of the ACUs tested. The error analysis concluded that the use of a second camera to quantify out of plane movement of the specimen would greatly improve the accuracy of the measurement of angle. The 2-D radiographic technique provided limited information on changes in intradiscal material. It was also limited in its accuracy and dependability (i.e., only 5 out of 13 specimens provided radiographs suitable for this analysis). The results of this study indicate that a relationship might exist between the flexion-extension behavior observed from swelling and intradiscal shifts of matter. Further work is needed to confirm this relationship.

Flight tests of new or modified aircraft are a necessary part of the design process and provide the final validation of the full scale aircraft design. Flight testing for certification is a critical phase as all trials proving compliance, with respect to specifications and regulations must be completed in the shortest possible time, while maintaining high standards in the certification process. Usually significant instrumentation is installed to validate the predicted behaviour of the aircraft and also to detect unforeseen problems so that, if necessary, fast modifications can be done. Optical measurement techniques can minimize the installation effort and reduce the testing time as they are able to capture a large number of parameters within a short time. The EU funded research project -Advanced ln-flight Measurement (contract ASTS-CT-2006-030827 funded within the 6th Framework Programme) and the follow on project -Advanced ln-flight Measurement Techniques 2 (contract 266107 funded within the 7th European Programme), proved the principal feasibility to apply modern optical measurement techniques from industrial wind tunnels to flight testing and started to further develop those methods. AIM2 primarily focused on developing reliable and easy to use, dedicated measurement systems and on defining design and application rules for these new in-flight measurement techniques. The prime objective was to enable aerospace industries to use such measurement systems in future tests to reduce testing time and costs. This special issue focusses on the work completed in AIM2 and presents a total of eight papers. The papers present an overview on optical methods for in-flight flow and structural measurements as weil as state-of-the-art methods. In the work presented, the optical measurement techniques are continuously developed throughout the project. These techniques include the structural shape and deformation measurement method IPCT (Image Pattern Correlation Technique), the flow field measurement techniques PIV (Particle Image Velocimetry), IRT (lnfraRed Thermography) and LIDAR (Light Detection And Ranging), as weil as the method of lnterferometric Laser lmaging for Droplet Sizing (ILIDS) and pressure and strain sensors based on optical fibre sensor technology. Therefore we hope you will enjoy reading these papers and would encourage you to directly contact the authors of the papers and the editors for your feedback and to get information about the latest developments. lt has been our pleasure tobe part of the outstanding AIM and AIM2 projects and finally be the Guest Editors of this special issue. We would like to thank all project partners and the authors of the papers for their excellent contributions. We also extend our thanks to the referees in devoting their time and effort, on a volunteer basis, in order to ensure high quality contributions. Finally, we would like to thank the journal Editors for enabling this special issue.

Review of optical measurement techniques for measuring three-dimensional topography of inner-wall-shaped parts

Optical measurement techniques have evolved since the mid-2000's due to the advancement in computer processing and digital camera sensors. These techniques allow for the digitization of full three-dimensional (3D) surfaces and provide time-domain surface information data with high details not previously possible with more traditional measurement techniques. A variety of industries are using these technologies with a focus on high accuracy industrial applications including aerospace and automotive. This paper introduces optical measurements techniques used to provide quantifiable data and visual information of a woman's abdomen during various stages of pregnancy. Two non-invasive techniques are used for this study including structured light (SL) scanning and digital image correlation (DIC). An overview of these techniques, the process for data collection, results of the data, and opportunities for future studies are presented in this paper. The structured light scanning was used to capture a 3D surface of the woman's abdomen at four to six week intervals starting at week 15 of maternity and ending six days prior to birth. The results quantify growth during each stage of pregnancy along with full surface data in addition to postnatal results. The DIC data was collected during week 30 when the baby was very active in the womb and external deformations on the woman's abdomen were observed visually. The results from these studies were not intended to be a formal medical study but to provide feasibility of the SL and DIC process during the stages of pregnancy and encourage unique uses of otherwise industrial measurements.

Contour measurement by fibre optic fringe projection and Fourier transform analysis

In this paper, various methods for characterization of semiconductor charge carrier lifetime are reviewed and an optical technique is described in detail.This technique is contactless, all-optical and based upon measurements of free carrier absorption transients by an infrared probe beam following electron-hole pair excitation by a pulsed laser beam.Main features are a direct probing of the excess carrier density coupled with a homogeneous carrier distribution within the sample, enabling precision studies of different recombination mechanisms.The method is capable of measuring the lifetime over a broad range of injections (10 13 -10 18 cm -3 ) probing the minority carrier lifetime, the high injection lifetime and Auger recombination, as well as the transition between these ranges.Performance and limitations of the technique, such as lateral resolution, are addressed while application of the technique for lifetime mapping and effects of surface recombination are also outlined.Results from detailed studies of the injection dependence yield good agreement with the Shockley-Read-Hall theory, whereas the coefficient for Auger recombination shows an apparent shift to a higher value, with respect to the traditionally accepted value, at carrier densities below 2×10 17 cm -3 .Data also indicate an increased value of the coefficient for bimolecular recombination from the generally accepted value.Measurement on an electron irradiated wafer and wafers of exceptionally high carrier lifetimes are also discussed within the framework of different recombination mechanisms.

Researchers in the Department of Mechanical Engineering seek to obtain a means to measure less than 3 mg of H2O that adheres to a metal surface as condensate. The objective is to calibrate optical reflectance measurements of an aluminum surface as a function of the condensate thickness present. Collaboration with the Hazardous Substance Research Center at Michigan State University results in the development of an indirect static headspace gas chromatographic technique capable of measuring H2O in low-milligram quantities. The technique utilizes manual headspace sampling, a megabore capillary column, and a flame ionization detector. A correlation of r2 = 0.999 is obtained for the calibration of the indirect measurement technique. The calibration of the analytical instrument demonstrates adequate precision (< +/- 50 microg at a 95% confidence interval) for such a heterogeneous sample. The calibration samples consist of a strip of aluminum metal, H2O, and pulverized calcium carbide to convert the H2O to acetylene. A scaled calibration technique is used to simplify handling trace water volumes. The surface reflectance measurements are found to correlate well (r2 = 0.935) with measurements of the condensate mass. This result facilitates the development of an optical mass-transfer measurement technique. This study focuses on the analytical method and its relationship with engineering research.

Thanks to the improvements in manufacturing techniques, it is becoming more common to alter the functional performance of products by controlling the geometrical properties of technical surfaces. The required characterization of surfaces can be done by using different optical measurement techniques. In order to have reliable measurement results, one of the pre-requisite is the proper calibration of the instrument. Although new ideas, like 3D Siemens-Star are becoming available in surface metrology, complexity of optical measurement techniques makes it not easy to calibrate them. In this study, depending on the available guidelines, some effects on the calibration of optical measurement techniques are given.

In paper represented a new (alternate) method of solve algebraic quadratic equations or, by other words, a new method of compare two or more plane grids in interface between two crystals. Also entered and resolved a few mathematical problems with its main goal: compare two or more parabolas. A mathematical fundamental relation between algebraic and transcendental functions is obtained. Some new relations between some inverse trigonometric functions is obtained. Some new relations between some inverse trigonometric functions and function of square root are obtained too