A Novel “Flying-Spot” Infrared Camera for Imaging Very Fast Thermal-Wave Phenomena

Wang, Y. Q.; Kuo, P. K.; Favro, L. D.; Thomas, R. L.

doi:10.1007/978-3-540-46972-8_5

Cited by 16 publications

(11 citation statements)

References 2 publications

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“…The procedure to size the width of an infinite crack consists in fitting the experimental temperature profile perpendicular to the crack and crossing the center of the laser spot to Equation (2). As can be seen in Equation ( 2), there are four free parameters to be fitted: a, l, ηP o /K, and KR th .…”

Section: Analytical Model: Vertical Cracks Of Infinite Depthmentioning

confidence: 99%

“…In the case of a vertical crack (typically, a fatigue crack) an abrupt temperature discontinuity along the length of the fissure appears in the thermogram, betraying the presence of the crack. By scanning the laser spot along the sample surface at constant velocity (the so-called flying spot thermography), large parts can be analyzed in a fast way [ 1 , 2 ]. This method is well suited to image cracks by showing the crack length along the surface [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ].…”

Section: Introductionmentioning

confidence: 99%

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Sizing the Depth and Width of Narrow Cracks in Real Parts by Laser-Spot Lock-In Thermography

Colom

Rodríguez‐Aseguinolaza

Mendioroz

et al. 2021

Materials

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We present a complete characterization of the width and depth of a very narrow fatigue crack developed in an Al-alloy dog bone plate using laser-spot lock-in thermography. Unlike visible micrographs, which show many surface scratches, the thermographic image clearly identifies the presence of a single crack about 1.5 mm long. Once detected, we focus a modulated laser beam close to the crack and we record the temperature amplitude. By fitting the numerical model to the temperature profile across the crack, we obtain both the width and depth simultaneously, at the location of the laser spot. Repeating the process for different positions of the laser spot along the crack length, we obtain the distribution of the crack width and depth. We show that the crack has an almost constant depth (0.7 mm) and width (1.5 μm) along 0.7 mm and features a fast reduction in both quantities until the crack vanishes. The results prove the ability of laser-spot lock-in thermography to fully characterize quantitatively narrow cracks, even below 1 μm.

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Section: Analytical Model: Vertical Cracks Of Infinite Depthmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sizing the Depth and Width of Narrow Cracks in Real Parts by Laser-Spot Lock-In Thermography

Colom

Rodríguez‐Aseguinolaza

Mendioroz

et al. 2021

Materials

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“…6 Some workarounds have led to a set of techniques where illumination of the imaged object has been used to detect subtle characteristics such as delamination and crack formations in surfaces. These methods include lock-in thermography 7 and flying spot thermography, 8 where the active illumination is either modulated or raster scanned, respectively.…”

Section: Introductionmentioning

confidence: 99%

Acquisition and Analysis of Hyperspectral Thermal Images for Sample Segregation

et al. 2020

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This study presents the first results of a new type of hyperspectral imager in the longwave thermal radiation range from 8.0-14.0 Âµm which is simpler than readily available Fourier transform infrared spectroscopy (FTIR) based imagers. Conventional thermography images the thermal radiation from hot objects, but an accurate determination of temperature is hampered by the often unknown emissivities of different materials present in the same image. This paper describes the setup and development of a hyperspectral thermal camera based on a low order scanning Fabry-PÃ©rot interferometer (FPI) acting as a bandpass filter. A three-dimensional hyperspectral datacube (two spatial and one spectral dimension) was measured by imaging a high emissivity carbon nanotube coated surface (Vantablack), black painted aluminium, borosilicate glass, Kapton Tape and bare aluminium. A principal component analysis (PCA) of the hyperspectral thermal image (HSTI) clearly segregates the individual samples. The most distinguishable sample from the PCA is the borosilicate petri-dish of which the Si-O-Si bond in borosilicate glass was the most noticeable. Additionally, it was found that the relatively large 1024x768x70 datacube can be reduced to a much smaller cube of size 1024x768x5 containing 92 % of the variance in the original dataset. The possibility of discriminating between the samples by their spectroscopic signature was tested using a logistic regression classifier. The model was fitted to a chosen set of principal components obtained from a PCA of the original hyperspectral datacube. The model was used to predict all pixels in the original datacube resulting in estimates with very high true positive rate (TPR). The highest TPR was obtained for borosilicate glass with a value of 99 % correctly predicted pixels. The remaining TPRs were 94 % for black painted aluminium, 81 % for bare aluminium, 79 % for Kapton Tape, and 70 % for Vantablack. A standard thermographic image was acquired of the same objects where it was found that the samples were mutually indistinguishable in this image. This shows that the hyperspectral thermal image contains sample characteristics which are material related and therefore outperforms standard thermography in the amount of information contained in an image.

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“…The use of new scanning systems based on a galvanometer mirror allows the easy control of the spatial and temporal displacements of a laser hot spot over a plane surface. Such systems are then suitable for use in developing new flying spot methods as alternatives to the initial flying spot technique, [1][2][3][4] which is based on a constant velocity of the spot. By contrast, instead of the single temperature measurement used in Ref.…”

Section: Introductionmentioning

confidence: 99%

Pulsed flying spot with the logarithmic parabolas method for the estimation of in-plane thermal diffusivity fields on heterogeneous and anisotropic materials

Gavérina

Batsale

Sommier

et al. 2017

Journal of Applied Physics

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A novel thermal non-destructive technique based on a Pulsed Flying Spot is presented here by considering in-plane logarithmic processing of the relaxing temperature field around the heat source spot. Recent progress made in optical control, lasers, and infrared cameras permits the acquisition of 2D temperature fields and localized thermal excitation on a small area instead of the entire recorded image. This study focuses on a new method based on spatial logarithm analysis of a temperature field to analyse and measure different parameters, such as the in-plane thermal diffusivity and localization of the spot. In this paper, this method is presented and the first results of heterogeneous anisotropic materials are depicted. The in-plane thermal diffusivity is estimated with an error lower than 4%, and the initial location of the heating spot is determined.

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A Novel “Flying-Spot” Infrared Camera for Imaging Very Fast Thermal-Wave Phenomena

Cited by 16 publications

References 2 publications

Sizing the Depth and Width of Narrow Cracks in Real Parts by Laser-Spot Lock-In Thermography

Sizing the Depth and Width of Narrow Cracks in Real Parts by Laser-Spot Lock-In Thermography

Acquisition and Analysis of Hyperspectral Thermal Images for Sample Segregation

Pulsed flying spot with the logarithmic parabolas method for the estimation of in-plane thermal diffusivity fields on heterogeneous and anisotropic materials

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