&lt;title&gt;Fiber optical single-frame speckle interferometer for measuring industrial surfaces&lt;/title&gt;

Kranz, J.; Lamprecht, Juergen; Hettwer, Andrea; Schwider, Johannes

doi:10.1117/12.323335

Cited by 7 publications

(4 citation statements)

References 3 publications

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“…Although this method can perform dynamic measurements, the system is complicated, has a large error, and the setting of the phase shift between multiple cameras is difficult to implement, making the method unsuitable for practical applications. A method of obtaining spatial phase shift using only a single CCD camera was later proposed [29]. One method of doing this is to divide a single CCD into at least three imaging regions, then introduce a fixed phase difference between each region.…”

Section: Multichannel Spatial Phase-shift Shearographymentioning

confidence: 99%

Digital Shearography for NDT: Phase Measurement Technique and Recent Developments

et al. 2018

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Composite materials have seen widespread use in the aerospace industry and are becoming increasingly popular in the automotive industry due to their high strength and low weight characteristics. The increasing usage of composite materials has resulted in the need for more effective techniques for nondestructive testing (NDT) of composite structures. Of these techniques, digital shearography is one the most sensitive and accurate methods for NDT. Digital shearography can directly measure strain with high sensitivity when combined with different optical setups, phase-shift techniques, and algorithms. Its simple setup and less sensitivity to environmental disturbances make it particularly well suited for practical NDT applications. This paper provides a review of the phase measurement technique and recent developments in digital shearographic NDT. The introduction of new techniques has expanded the range of digital shearography applications and made it possible to measure larger fields and detect more directional or deeper defects. At the same time, shearography for different materials is also under research, including specular surface materials, metallic materials, etc. Through the discussion of recent developments, the future development trend of digital shearography is analyzed, and the potentials and limitations are demonstrated.

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Section: Multichannel Spatial Phase-shift Shearographymentioning

confidence: 99%

Digital Shearography for NDT: Phase Measurement Technique and Recent Developments

et al. 2018

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“…The system was used for transient flow visualisation with a camera operating at 82 frames per second. A binary grating has been used to separate the images for spatial phase stepping, but ancillary polarizing elements were used to introduce the phase step [17,18].…”

Section: Experimental Demonstrationmentioning

confidence: 99%

High-speed, sub-Nyquist interferometry

Wu¹,

Valera²,

Moore³

2011

Opt. Express

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The velocity measurement limit in dynamic interferometry is vNyq, the velocity at which the interferogram is sampled at the Nyquist limit. We show that vNyq can be exceeded by assuming continuity of the surface motion and unwrapping the velocity modulo 2vNyq. The technique was demonstrated in a high-speed speckle pattern interferometer with spatial phase stepping. Surface velocities of 4vNyq were measured experimentally. With a reduced exposure, high-speed sub-Nyquist interferometry could be implemented up to a maximum acceleration of vNyq/ts, where ts is the detector frame period.

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“…. , 3}2 which is defined by (t1,t2) = (i1 + 1)) j2 ((t2 + 1)) (1) for all t E jp2 where qi,q2,q3 : IR -* JR are given by i() = (t -1)2, q2(t) = -(1 -1)2 + , and 3(t) = corresponding to the B-spline basis on [0, 1] with knot sequence [-2, -1, 0, 1, 2,3] (middle polynomial segment). Herewith, the system matrix of the corresponding least squares problem is defined by A = (ak) E pjlxM with akj = jij(sk) where the least squares problem can be stated as II4x-yf2 mm!.…”

Section: Local Approximation 21 Tile Processing Strategymentioning

confidence: 99%

<title>Hybrid algorithm to reconstruct out-of-plane surface deformations from interferometric image data</title>

Schwarz

1999

SPIE Proceedings

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Interferometric methods are of particular interest in industrial quality assurance to detect material defects via deformation and vibration analysis. One of their main advantages is contact-free surface examination and the possibility to provide full-field information with sub-micron sensitivity. When examining intensity images provided by a phase-shifting speckle interferometer, the measuring range is limited because the phase wrapping effect occurs in combination with high speckle noise levels. In this paper, a new hybrid approach for the phase unwrapping problem is presented which significantly extends the measuring range, and, in addition, reduces the computational effort. This is achieved by a specific tile processing strategy combining a polynomial based local phase-unwrapping approach and a Fourier based strategy to form a hybrid algorithm. The hybrid approach assures time efficient tile processing using polynomial approximation in image areas of low fringe density on the one hand and carefully directed high performance slope computations in noisy or strongly deformed areas on the other hand. In these strongly deformed areas a Fourier based approach can still find the correct affine linear approximation. With the resulting set of local affine linear approximations, a global spline model of the underlying deformation profile is obtained by an iterative region-growing technique combined with a 0(n) data transformation.

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<title>Fiber optical single-frame speckle interferometer for measuring industrial surfaces</title>

Cited by 7 publications

References 3 publications

Digital Shearography for NDT: Phase Measurement Technique and Recent Developments

Digital Shearography for NDT: Phase Measurement Technique and Recent Developments

High-speed, sub-Nyquist interferometry

<title>Hybrid algorithm to reconstruct out-of-plane surface deformations from interferometric image data</title>

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