References of "Languy, Fabian"
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See detailDeformation measurements by ESPI of the surface of a heated mirror and comparison with numerical model
Languy, Fabian ULg; Vandenrijt, Jean-François ULg; Saint-Georges, Philippe et al

in Proceedings of SPIE (2017, June 26), 103291M

The manufacture of mirrors for space application is expensive and the requirements on the optical performance increase over years. To achieve higher performance, larger mirrors are manufactured but the ... [more ▼]

The manufacture of mirrors for space application is expensive and the requirements on the optical performance increase over years. To achieve higher performance, larger mirrors are manufactured but the larger the mirror the higher the sensitivity to temperature variation and therefore the higher the degradation of optical performances. To avoid the use of an expensive thermal regulation, we need to develop tools able to predict how optics behaves with thermal constraints. This paper presents the comparison between experimental surface mirror deformation and theoretical results from a multiphysics model. The local displacements of the mirror surface have been measured with the use of electronic speckle pattern interferometry (ESPI) and the deformation itself has been calculated by subtracting the rigid body motion. After validation of the mechanical model, experimental and numerical wave front errors are compared. [less ▲]

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See detailNondestructive inspection of aerospace composites by a fiber-coupled laser ultrasonics system
Vandenrijt, Jean-François ULg; Languy, Fabian ULg; Thizy, Cédric ULg et al

in Proceedings of SPIE (2017, June)

Laser ultrasonics is a technique currently studied for nondestructive inspection of aerospace composite structures based on carbon fibers. It combines a pulsed laser impacting the surface generates an ... [more ▼]

Laser ultrasonics is a technique currently studied for nondestructive inspection of aerospace composite structures based on carbon fibers. It combines a pulsed laser impacting the surface generates an ultrasound inside the material, through the nondestructive thermoelastic effect. Second a detection interferometer probes the impacted point in order to measure the displacement of the surface resulting from the emitted ultrasound wave and the echo coming back from the different interfaces of the structure. Laser ultrasonics is of interest for inspecting complex shaped composites. We have studied the possibility of using frequency doubled YAG laser for the generation and which is fiber-coupled, together with a fiber-coupled interferometric probe using a YAG laser in the NIR. Our final system is a lightweight probe attached to a robot arm and which is able to scan complex shapes. The performances of the system are compared for different wavelengths of generations. Also we have studied some experimental parameters of interest such as tolerance to angle and focus distance, and different geometries of generation beams. We show some examples of inspection of reference parts with known defects. In particular C-scans of curved composites structures are presented. [less ▲]

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See detailArtificial defects in CFRP composite structure for Thermography and Shearography nondestructive inspection
Blain, Pascal ULg; Vandenrijt, Jean-François ULg; Languy, Fabian ULg et al

Poster (2017, April)

Locating defects in CFRP composite materials is a hot topic in nondestructive inspection (NDI). Beside classical NDI technique, such as ultrasound testing (UT), contactless techniques are actively studied ... [more ▼]

Locating defects in CFRP composite materials is a hot topic in nondestructive inspection (NDI). Beside classical NDI technique, such as ultrasound testing (UT), contactless techniques are actively studied. Generally manufacturers of CFRP structure incorporate artificial defects in the bulk, with different extents and depths, in order to study the performance of a specific NDI technique to detect the defect. One of the most common defects in CFRP is delamination between two layers. This is simulated by inserting teflon sheets which, like air, acts as ultrasound blocker in UT. When such reference part is used to assess NDI performance of thermography or shearography, we only observe respectively the thermal or mechanical response of teflon with respect to external loading used with these techniques. In this work, we assess other possibilities for artificial defects in CFRP matrix. For that a CFRP structure was developed and which incorporates teflon, flat-bottom holes and delamination obtained by the pull-out method. We experimentally studied the signals and we discuss the difference between the various artificial defects methods. [less ▲]

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See detailUltrasons par laser pour l'inspection de matériaux composites. Comparaison entre génération à 532 nm et 10,6 µm. Effet de la géométrie du faisceau de génération
Vandenrijt, Jean-François ULg; Languy, Fabian ULg; Walter, Julien et al

Conference (2017, March)

Un système de contrôle non destructif basé sur la génération d'ultrasons par laser à 532 nm et de détection par laser, entièrement fibré et robotisé, est développé au CSL. Nous le comparons à un système ... [more ▼]

Un système de contrôle non destructif basé sur la génération d'ultrasons par laser à 532 nm et de détection par laser, entièrement fibré et robotisé, est développé au CSL. Nous le comparons à un système équivalent du CTA basé sur la génération plus classique avec un laser CO2 (10,6 µm). De plus nous montrons les résultats d'investigations concernant différentes géométrie du faisceau de génération. [less ▲]

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See detailInterférométrie de speckle à 10.6 µm et shearographie à 532 nm en temps réel temps moyenné et décalage de phase. Comparaison et application pour identification des modes de vibrations sur shaker industriel
Vandenrijt, Jean-François ULg; Languy, Fabian ULg; Thizy, Cédric ULg et al

Conference (2017, March)

Deux méthodes interférométriques sont comparées pour l'identification des modes de vibration en temps réel-temps moyenné avec décalage de phase. Il s'agit d'une part de l'interférométrie de speckle (ESPI ... [more ▼]

Deux méthodes interférométriques sont comparées pour l'identification des modes de vibration en temps réel-temps moyenné avec décalage de phase. Il s'agit d'une part de l'interférométrie de speckle (ESPI) à 10,6 μm et, d'autre part, de la shearographie à 532 nm. La comparaison sur une aube de vibration en laboratoire nous a conduit à sélectionner la shearographie en lumière visible pour l'application avec un shaker en milieu industriel, où les conditions de travail ne permettent pas d'utiliser des techniques interférométriques plus conventionnelles. [less ▲]

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See detailHolographie numérique en infrarouge lointain - Applications aérospatiales
Georges, Marc ULg; Vandenrijt, Jean-François ULg; Languy, Fabian ULg et al

Conference (2016, November)

L'holographie numérique en infrarouge lointain, utilisant un laser CO2 émettant vers 10 µm et des caméras thermiques à microbolomètres, permet la mesure de grandes déformations et de s'affranchir des ... [more ▼]

L'holographie numérique en infrarouge lointain, utilisant un laser CO2 émettant vers 10 µm et des caméras thermiques à microbolomètres, permet la mesure de grandes déformations et de s'affranchir des perturbations environnementales plus facilement qu'en lumière visible. Nous l'appliquons dans le cas de structures spatiales subissant des cyclages thermiques en régime cryogénique sous vide, ce qui induit des déplacements de grande ampleur. Nous passerons en revue les différentes expériences effectuées au Centre Spatial de Liège et discuterons des recherches en cours, notamment pour utiliser des longueurs d'onde plus grande (ondes Terahertz) [less ▲]

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See detailLaser Ultrasound for NDT: investigation of the generation beam shape
Languy, Fabian ULg; Perrard, Aurélie; Vandenrijt, Jean-François ULg et al

Poster (2016, July)

Usually laser ultrasonic systems use an infrared laser operating at 10 µm to generate the ultrasound in CFRP objects. However this system suffer from an important drawback: optical fiber cannot be used to ... [more ▼]

Usually laser ultrasonic systems use an infrared laser operating at 10 µm to generate the ultrasound in CFRP objects. However this system suffer from an important drawback: optical fiber cannot be used to transport the high energy beam from the laser output to the target which limits the flexibility of the system to investigated complex shaped objects. To overcome this issue, visible light can be used to generate ultrasound. In our case we use a fiber-coupled laser operating at 532 nm. The output end of the optical fiber is placed on an industrial robot arm. The investigated object remains stationary while the optical fiber mounted on the robot arm scan the object. This system offers large flexibility but laser generation at 532 nm is known to be less efficient than CO 2 system emitting at 10 µm. Increasing the visible pulse power is one of the options but optics and CRFF object will be damaged before the same echo level as CO2 generation can be obtained. An alternative solution consists in the investigation of the generation beam size and shape. We recently developed an optical design composed of an axicon lens able to generate annular beam. The diameter of the beam can be adapted. If the axicon lens is removed the optical system provides a disk whose diameter can also be adapted onto the investigated object. Ray-traycing simulations performed with ASAP and experimental beam profile investigated with a beam profiler show good agreement between theoretical and experimental optical design. An experimental comparison between ring and disk shapes will be presented. The comparisons take into account the beam diameter and the beam intensity but also the effect of the angle of incidence will be presented. [less ▲]

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See detailVibration mode shapes visualization in industrial environment by real-time time-averaged phase-stepped electronic speckle pattern interferometry at 10.6  μm and shearography at 532 nm
Languy, Fabian ULg; Vandenrijt, Jean-François ULg; Thizy, Cédric ULg et al

in Optical Engineering : The Journal of the Society of Photo-Optical Instrumentation Engineers (2016), 55(12), 121704

We present our investigations on two interferometric methods suitable for industrial conditions dedicated to the visualization of vibration modes of aeronautic blades. First, we consider long-wave ... [more ▼]

We present our investigations on two interferometric methods suitable for industrial conditions dedicated to the visualization of vibration modes of aeronautic blades. First, we consider long-wave infrared (LWIR) electronic speckle pattern interferometry (ESPI). The use of long wavelength allows measuring larger amplitudes of vibrations compared with what can be achieved with visible light. Also longer wavelengths allow lower sensitivity to external perturbations. Second, shearography at 532 nm is used as an alternative to LWIR ESPI. Both methods are used in time-averaged mode with the use of phase-stepping. This allows transforming Bessel fringes, typical to time averaging, into phase values that provide higher contrast and improve the visualization of vibration mode shapes. Laboratory experimental results with both techniques allowed comparison of techniques, leading to selection of shearography. Finally a vibration test on electrodynamic shaker is performed in an industrial environment and mode shapes are obtained with good quality by shearography. [less ▲]

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See detailInvestigation of spectral impacts on the performance of a concentration device using a Fresnel lens combined with a double junction cell
Loicq, Jerôme ULg; Galante, Nicolas ULg; Thibert, Tanguy ULg et al

in Proceedings of SPIE (2014, May 15)

This experimental study was carried out within the context of high concentration photovoltaics. The paper presents the results of an experimental investigation relating to the quantification of the ... [more ▼]

This experimental study was carried out within the context of high concentration photovoltaics. The paper presents the results of an experimental investigation relating to the quantification of the impacts of the chromatic effect on the performance of a double junction GaInP/GaAs solar cell. Chromatic effects are the result of material dispersion caused by the refractive optics component. This study aims to evaluate the effect of the spectral modification of the incident beam on the whole solar concentrator system performance. Such considerations are fundamental in producing a highly accurate design, with which to achieve the best possible system performance. Efficiency is evaluated within the vicinity of the focus of a Fresnel lens designed for concentration. On the optical axis, rays with different wavelengths are not focalized at the same points. The spectral content of the beam depends, therefore, upon the position of the cell along the optical axis. It is assumed that spectral content modification may have an impact on cell performance and, as a consequence, on system efficiency as a whole. Efficiency of the optical Fresnel lens and of the cell were evaluated in relation to spectral content modification. [less ▲]

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See detailSpectral splitting planar solar concentrator : Design and Experimental testing Preliminary results
Blain, Pascal ULg; Michel, Céline ULg; Clermont, Lionel ULg et al

in Proceedings of SPIE (2014, May 15), 9140

We present a new concept in solar concentrator: spectral splitting. It implies reflective, refractive and diffractive elements that allow two spectrally differentiated beams to reach different and/or ... [more ▼]

We present a new concept in solar concentrator: spectral splitting. It implies reflective, refractive and diffractive elements that allow two spectrally differentiated beams to reach different and/or unmatched lattice solar cells. Those cells efficiencies are then enhanced. The aimed geometrical concentration factor is 5× and the theoretical optical efficiency of that concentrator concept reaches 82%. [less ▲]

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See detailOptical study of a solar concentrator for space applications based on a diffractive/refractive optical combination
Michel, Céline ULg; Loicq, Jerôme ULg; Languy, Fabian ULg et al

in Solar Energy Materials & Solar Cells (2014), 120PA

This paper presents a new design of a planar solar concentrator for space applications. The concentrator focuses light onto two spatially separated photovoltaic cells, allowing for independent control of ... [more ▼]

This paper presents a new design of a planar solar concentrator for space applications. The concentrator focuses light onto two spatially separated photovoltaic cells, allowing for independent control of the output power of each cell. Thanks to a blazed diffraction grating superimposed on a Fresnel lens, advantages of both spectral splitting and light focusing can be combined. The theoretical model of the optical design is presented, with the optimization of either element. Moreover, configuration improvement is proposed: a symmetrical configuration composed of two lenses. First numerical results are presented, highlighting the possibility to design a concentrator at about 10× for each cell, with an optical efficiency of about 75% and less than 10% of losses for tracking errors lower than ±0.9°. [less ▲]

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See detailNonimaging achromatic shaped Fresnel lenses for ultrahigh solar concentration
Languy, Fabian ULg; Habraken, Serge ULg

in Optics Letters (2013), 38(10), 1730-1732

The maximum concentration ratio achievable with a solar concentrator made of a single refractive primary optics is much more limited by the chromatic aberration than by any other aberration. Therefore ... [more ▼]

The maximum concentration ratio achievable with a solar concentrator made of a single refractive primary optics is much more limited by the chromatic aberration than by any other aberration. Therefore achromatic doublets made with poly(methyl methacrylate) and polycarbonate are of great interest to enhance the concentration ratio and to achieve a spectrally uniform flux on the receiver. In this Letter, shaped achromatic Fresnel lenses are investigated. One lossless design is of high interest since it provides spectrally and spatially uniform flux without being affected by soiling problems. With this design an optical concentration ratio of about 8500× can be achieved. [less ▲]

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See detailStudy of a solar concentrator for space based on a diffractive/refractive optical combination
Michel, Céline ULg; Loicq, Jerôme ULg; Mazzoli, Alexandra ULg et al

Poster (2013, April 16)

This paper presents a new design of a planar solar concentrator for space applications focusing on two spatially separated PV cells, allowing independent control of output power of each cell. It has the ... [more ▼]

This paper presents a new design of a planar solar concentrator for space applications focusing on two spatially separated PV cells, allowing independent control of output power of each cell. It has the advantages of both spectral splitting and solar concentration by the combination of a blaze transmission diffraction grating and a flat cylindrical Fresnel lens. An optical optimization has been realized and two variations of configuration have been developed to improve tracking tolerance: first, a design completed by secondary reflective concentrators and second, a symmetrical configuration composed of two lenses. First numerical results are presented, highlighting the possibility to design a concentrator at about 10×, with an electrical output power about 290W/m² lens and less than 10% losses for tracking errors lower than ±0.9°. [less ▲]

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See detailStudy of a solar concentrator for space based on a diffractive/refractive optical combination
Michel, Céline ULg; Loicq, Jerôme ULg; Languy, Fabian ULg et al

in AIP Conference Proceedings (2013), (1556), 97-100

This paper presents a new design of a planar solar concentrator for space applications focusing on two spatially separated PV cells, allowing independent control of output power of each cell. It has the ... [more ▼]

This paper presents a new design of a planar solar concentrator for space applications focusing on two spatially separated PV cells, allowing independent control of output power of each cell. It has the advantages of both spectral splitting and solar concentration by the combination of a blaze transmission diffraction grating and a flat cylindrical Fresnel lens. An optical optimization has been realized and two variations of configuration have been developed to improve tracking tolerance: first, a design completed by secondary reflective concentrators and second, a symmetrical configuration composed of two lenses. First numerical results are presented, highlighting the possibility to design a concentrator at about 10×, with an electrical output power about 290W/m² lens and less than 10% losses for tracking errors lower than ±0.9°. [less ▲]

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See detailAchromatization of nonimaging Fresnel lenses for photovoltaic solar concentration using refractive and diffractive patterns
Languy, Fabian ULg

Doctoral thesis (2012)

In the field of concentrated photovoltaics, the main disadvantage of lenses compared to mirrors lies in their chromaticity: Snell's law is related to the refractive index which is wavelength dependent ... [more ▼]

In the field of concentrated photovoltaics, the main disadvantage of lenses compared to mirrors lies in their chromaticity: Snell's law is related to the refractive index which is wavelength dependent. Consequently, even for purely collimated beams under normal incidence, the maximum concentration achievable with typical lenses made of PMMA is limited to ~1000×. This maximum value becomes even lower when considering Sun's angular aperture. Since the law of reflection is not wavelength dependent, mirrors can theoretically achieve the thermodynamic limit of concentration which is about 46'000×. This thesis aims at the design and the manufacturing of an achromatic Fresnel lens suitable for photovoltaic solar concentration, i.e. combining high concentration, low production cost and tolerance to manufacturing errors. Firstly, we investigated a hybrid lens made of a refractive lens and a diffractive lens. The investigations showed that the concentration ratio could be multiplied by 4. A full chapter is dedicated to the optimisation of blazed diffraction gratings to finally achieve the design of the diffractive lens. Nevertheless, a bilayer diffractive lens is needed to obtain a high diffraction efficiency which makes the diffractive lens highly sensitive to manufacturing errors and consequently not suitable for photovoltaic solar concentration. Purely refractive achromatic Fresnel doublets were then investigated and several designs were compared. They allow for very high concentration ratios in the case of collimated beams under normal incidence, higher than 100'000×. Therefore, contrary to singlets, Fresnel doublets are much more affected by the angular size of the source than by the chromatic aberration. Moreover, it was shown that they are tolerant to manufacturing error, change of temperature and uncertainty on the refractive index. It emerges from this thesis that the concept of achromatic doublets is a tolerant and low-cost production solution to achieve a highly concentrated white flux. Although bilayer diffractive lenses are not suitable for concentrated photovoltaics, the combination of refractive with diffractive structures seems to be promised to a bright future for spectrum splitting applications, including spectrum splitting for concentrated photovoltaics. [less ▲]

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See detailStudy of a solar concentrator for space based on a diffractive/refractive optical combination
Michel, Céline ULg; Loicq, Jerôme ULg; Languy, Fabian ULg et al

Conference (2012, November 12)

This paper presents a new design of a planar solar concentrator at 10× with spectral splitting focusing on two separated PV cells, allowing independent control. Optical elements, blazed diffraction ... [more ▼]

This paper presents a new design of a planar solar concentrator at 10× with spectral splitting focusing on two separated PV cells, allowing independent control. Optical elements, blazed diffraction grating and Fresnel lens, are optimized. [less ▲]

Detailed reference viewed: 70 (25 ULg)