We first provide an overview of 3-D shape measurement us- ing various optical methods. Then we focus on structured light tech- niques where various optical configurations, image acquisition tech- niques, data postprocessing and analysis methods and advantages and limitations are presented. Several industrial application examples are presented. Important areas requiring further R&D are discussed. Finally, a comprehensive bibliography on 3-D shape measurement is included, although it is not intended to be exhaustive. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)00101-X)

Overview of three-dimensional shape measurement using optical methods

Shearography is a full-field speckle interferometric technique used to determine surface displacement derivatives. For an interferometric technique, shearography is particularly resilient to environmental disturbances and has hence become an invaluable measurement tool outside of the optics laboratory. Furthermore, the inclusion of additional measurement channels has turned shearography from a qualitative inspection tool into a system suitable for quantitative surface strain measurement. In this review article we present a comprehensive overview of the technique, describing the principle of operation, optical configurations, image processing algorithms and applications, with a focus on more recent technological advances.

/pdf/shearography-technology-and-applications-a-review-383g7ymz1d.pdf

Shearography technology and applications: a review

This article reviews shearography and its applications. Shearography is a laser-based technique for full-field, non-contacting measurement of surface deformation (displacement or strain). It was developed to overcome several limitations of holography by eliminating the reference beam. It does not require special vibration isolation; hence, it is a practical tool that can be used in a field/factory environment. Shearography has already received considerable industrial acceptance, in particular, for non-destructive testing. In non-destructive testing, shearography reveals defects in an object by identifying defect-induced deformation anomalies. Other applications of shearography include strain measurement, material characterization, residual stress evaluation, leak detection, vibration studies and 3-D shape measurement.

Shearography: An optical measurement technique and applications

We review profile measurement methods using shearography. Traditionally, shearography implies the use of small image shearing, which yields first-order derivatives of displacements or of spatial coordinates. We demonstrate that the use of large image shearing is equivalent to holography, since displacement-related, or spatial coordinate-related, phase fringes are generated. Hence, the technique of shearography can appropriately be perceived as an optical technique that directly measures displacements (or spatial coordinates) and surface strains (or surface slopes). Unlike holography, shearography does not require special vibration isolation since a separate reference beam is not required; hence, it is a practical tool that can be used in the field/ factory environment. Examples of the use of small and large image shearing for surface profiling are given. Finally, a novel method for computing phase derivatives for the determination of curvatures of object surfaces from shearographic measurements is discussed.

Surface profiling using shearography

Evaluating the soundness of bonding using shearography

Slope measurement by two-wavelength electronic shearography

Phase stepping by wavelength modulation of the optical source is demonstrated in a path-length unbalanced shearing interferometer. A magnification difference, which accompanies the path-length imbalance in the interferometer, introduces an unwanted radial shear, which is shown to be compensated by inclusion of a block of high-refractive-index material in the longer interferometer arm. The block also increases the phase shift obtained for a given wavelength change. The phase-stepping technique is demonstrated with a three-step algorithm to measure out-of-plane strain on a flat metal plate.

Phase-stepped speckle shearing interferometer by source wavelength modulation.

A technique for the slope measurement of objects by using an electronic shearography system is presented. To detect the gradients of an object shape, a laser diode is modulated to produce two wavelengths on successive image frames. These two frames are then subtracted to generate the correlation fringes which depict the slope variation. The theory of this technique is derived and objects of conical, cylindrical, and spherical shapes are measured. Experimental results are demonstrated.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optoelectronic shearography: two wavelength slope measurement

Direct injection-current modulation of a diode laser source is demonstrated for phase-stepping, heterodyning and
stroboscopic illumination in a shearing interferometer. The techniques are proposed as an alternative to the use of mechanical
phase-shifters such as piezoelectric transducers, offering the advantages of ease of implementation, extended measurement
bandwidth and elimination of active elements from the measurement head. The phase-stepping and heterodyning techniques
require the interferometer to be unbalanced, which introduces an unwanted magnification mismatch into the shearing
interferometer. A compensation technique using a block of high refractive-index material is described, and experimental
demonstrations of each of the three techniques are presented.

Source modulation for phase shifting in static and dynamic speckle shearing interferometry

Material testing is an important task during product design, manufacturing and inspection processes. Speckle techniques are increasingly used as effective tools for this work. In this paper, we discuss the use of speckle interferometric techniques such as electronic speckle pattern interferometry (ESPI) and shearography for non-destructive testing (NDT) of composite materials. Three test coupons of the same composite material with different defects were tested, and the experimental results by using these two methods were compared.

J.-R. Huang

Papers

Slope measurement by two-wavelength electronic shearography

Phase-stepped speckle shearing interferometer by source wavelength modulation.

Optoelectronic shearography: two wavelength slope measurement

Source modulation for phase shifting in static and dynamic speckle shearing interferometry

Speckle techniques for material testing