Performance of laser-ultrasonic F-SAFT imaging

Lévesque, Daniel; Blouin, Alain; Néron, C.; Monchalin, Jean‐Pierre

doi:10.1016/s0041-624x(02)00256-1

Cited by 75 publications

(35 citation statements)

References 10 publications

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“…For FSW defects, data acquisition across the weld line is made and numerical focusing is performed using the Fourier domain Synthetic Aperture Focusing Technique (F-SAFT) [15]. Lap and butt joints are examined along with metallographic analysis and validation by destructive mechanical testing.…”

Section: Figure 1 Near Herementioning

confidence: 99%

Laser ultrasonics for defect detection and residual stress measurement of friction stir welds

Lévesque

Dubourg

Blouin

2011

Nondestructive Testing and Evaluation

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Section: Figure 1 Near Herementioning

confidence: 99%

Laser ultrasonics for defect detection and residual stress measurement of friction stir welds

Lévesque

Dubourg

Blouin

2011

Nondestructive Testing and Evaluation

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“…T rec is the estimated virtual wave which is used in 2D and 3D to reconstruct the initial temperature distribution T 0;rec ðrÞ. As detection surfaces for the simulations and experiments are planes F-SAFT, [23][24][25] a wellknown ultrasound image reconstruction method was used, but the other methods such as time-reversal reconstruction also show similar results. 14 FIG.…”

Section: Simulation Results For 2d and 3d Heat Distributions Witmentioning

confidence: 99%

“…In laser ultrasonics, the propagation distances have to be doubled compared to photoacoustics, or alternatively, half of the sound velocity is taken. 24 Also, boundary conditions for the sample surface which are more realistic than the adiabatic boundary condition should be investigated in future. First results for a third kind boundary condition 43 are given in Burgholzer et al 34 Another assumption made in this publication, which can be changed in future work is the homogeneous thermal diffusivity.…”

Section: Discussion and Outlookmentioning

confidence: 99%

“…One reconstruction method which directly uses the time invariance of the virtual wave signal is time-reversal reconstruction, 14,21,22 and another one which works well for planar sample surfaces is the frequency domain synthetic aperture focusing technique (F-SAFT). [23][24][25] In this work, we introduce the concept of virtual waves for thermographic image reconstruction for the case of short excitation pulses. However, the introduced concept can be easily transferred to other temporal excitation schemes.…”

Section: Introductionmentioning

confidence: 99%

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Three-dimensional thermographic imaging using a virtual wave concept

Burgholzer

Thor

Gruber

et al. 2017

Journal of Applied Physics

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In this work, it is shown that image reconstruction methods from ultrasonic imaging can be employed for thermographic signals. Before using these imaging methods, a virtual signal is calculated by applying a local transformation to the temperature evolution measured on a sample surface. The introduced transformation describes all the irreversibility of the heat diffusion process and can be used for every sample shape. To date, one-dimensional methods have been primarily used in thermographic imaging. The proposed two-stage algorithm enables reconstruction in two and three dimensions. The feasibility of this approach is demonstrated through simulations and experiments. For the latter, small steel beads embedded in an epoxy resin are imaged. The resolution limit is found to be proportional to the depth of the structures and to be inversely proportional to the logarithm of the signal-to-noise ratio. Limited-view artefacts can arise if the measurement is performed on a single planar detection surface. These artifacts can be reduced by measuring the thermographic signals from multiple planes, which is demonstrated by numerical simulations and by experiments performed on an epoxy cube.Comment: 22 pages, 8 figures, 1 appendix, acceapted by JA

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“…Previous authors have used the synthetic aperture focusing technique (SAFT) with laser ultrasonics to improve detectability and enhance imaging [21,22], mainly in the destructive, ablation regime. The authors of the present paper have recently demonstrated [23] Laser Induced Phased Array (LIPA) imaging in post processing, by obtaining the full matrix of all possible transmitter receiver combinations in the array, at the non-destructive, thermoelastic regime.…”

Section: Introductionmentioning

confidence: 99%

Full matrix capture and the total focusing imaging algorithm using laser induced ultrasonic phased arrays

Stratoudaki

Clark

Wilcox

2017

AIP Conference Proceedings

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Abstract. Laser ultrasonics is a technique where lasers are used for the generation and detection of ultrasound instead of conventional piezoelectric transducers. The technique is broadband, non-contact, and couplant free, suitable for large stand-off distances, inspection of components of complex geometries and hazardous environments. In this paper, array imaging is presented by obtaining the full matrix of all possible laser generation, laser detection combinations in the array (Full Matrix Capture), at the nondestructive, thermoelastic regime. An advanced imaging technique developed for conventional ultrasonic transducers, the Total Focusing Method (TFM), is adapted for laser ultrasonics and then applied to the captured data, focusing at each point of the reconstruction area. In this way, the beamforming and steering of the ultrasound is done during the post processing. A 1-D laser induced ultrasonic phased array is synthesized with significantly improved spatial resolution and defect detectability. In this study, shear waves are used for the imaging, since they are more efficiently produced than longitudinal waves in the nondestructive, thermoelastic regime. Experimental results are presented from nondestructive, laser ultrasonic inspection of aluminum samples with side drilled holes and slots at depths varying between 5 and 20mm from the surface.

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Performance of laser-ultrasonic F-SAFT imaging

Cited by 75 publications

References 10 publications

Laser ultrasonics for defect detection and residual stress measurement of friction stir welds

Laser ultrasonics for defect detection and residual stress measurement of friction stir welds

Three-dimensional thermographic imaging using a virtual wave concept

Full matrix capture and the total focusing imaging algorithm using laser induced ultrasonic phased arrays

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