Examinando por Autor "Belenguer, T."
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Ítem Applications of spatial light modulators in speckle interferometry(SPIE-INT SOC OPTICAL ENGINEERING, 2012-01-01) Bodendorfer, T.; Restrepo, R.; Belenguer, T.; Koch, A.W.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaHigh resolution spatial light modulators (SLM) have been used in many different ways during the last years. Regarding speckle interferometry, different applications can be realized by integrating SLMs in interferometric setup. In this work the influence of a liquid crystal based phase-only SLM on the measurement quality concerning deformation and shape measurement using two wavelengths is discussed. © 2012 Copyright SPIE.Ítem Consumed fatigue life assessment of composite material structures by optical surface roughness inspection(Trans Tech Publications Ltd., 2013-01-01) Zuluaga, P.; Frövel, M.; Restrepo, R.; Trallero, R.; Atienza, R.; Pintado, J.M.; Belenguer, T.; Salazar, F.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaA strong knowledge of the fatigue state of highly advanced carbon fiber reinforced polymer composite (CFRP) structures is essential to predict the residual life and optimize intervals of structural inspection, repairs, and/or replacements. Current techniques are based mostly on measurement of structural loads throughout the service life by electric strain gauge sensors. These sensors are affected by extreme environmental conditions and by fatigue loads in such a way that the sensors and their systems require exhaustive maintenance throughout system life. This work is focused on providing a new technique to evaluate the fatigue state of CFRP structures by means of evaluating the surface roughness variation due to fatigue damage. The surface roughness is a property that can be measured in the field by optical techniques such as speckle and could be a useful tool for structural health monitoring. The relation between surface roughness and fatigue life has been assessed on CFRP test specimens. A tensile fatigue load with an R=0.1 (T-T) and a maximum load of 60% of the material ultimate strength has been applied. The surface roughness of the specimens has been determined from the surface topography measured by a high precision confocal microscope. Results show that the surface roughness of the specimens increases with the accumulation of fatigue cycles in such a way that the roughness could be taken into account as a fatigue damage metrics for CFRP. © (2013) Trans Tech Publications.Ítem Electronic speckle pattern interferometry technique for the measurement of complex mechanical structures for aero-spatial applications(SPIE-INT SOC OPTICAL ENGINEERING, 2010-01-01) Restrepo, R.; Uribe-Patarroyo, N.; Garranzo, D.; Pintado, J.M.; Frovel, M.; Belenguer, T.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaUsing the electronic speckle pattern interferometry (ESPI) technique in the in-plane arrangement, the coefficient of thermal expansion (CTE) of a composite material that will be used in a passive focusing mechanism of an aerospace mission was measured. This measurement with ESPI was compared with another interferometric method (Differential Interferometer), whose principal characteristic is its high accuracy, but the measurement is only local. As a final step, the results have been used to provide feedback with the finite element analysis (FEA). Before the composite material measurements, a quality assessment of the technique was carried out measuring the CTE of Aluminum 6061-T6. Both techniques were compared with the datasheet delivered by the supplier. A review of the basic concepts was done, especially with regards to ESPI, and the considerations to predict the quality in the fringes formation were explained. Also, a review of the basic concepts for the mechanical calculation in composite materials was done. The CTE of the composite material found was 4.69X10-6 ± 3X10-6K-1. The most important advantage between ESPI and differential interferometry is that ESPI provides more information due to its intrinsic extended area, surface deformation reconstruction, in comparison with the strictly local measurement of differential interferometry. © 2010 Copyright SPIE - The International Society for Optical Engineering.Ítem High dynamic range imaging method for interferometry(ELSEVIER SCIENCE BV, 2011-01-01) Vargas, J.; Restrepo, R.; Quiroga, J.A.; Belenguer, T.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaWe demonstrate a method to easily and quickly extend the dynamic range imaging capabilities of the camera in a typical interferometric approach. The camera dynamic range is usually low and limited to 256 gray levels. Also, it is well known that one may have over or under-exposed regions in the interferogram (due to non-uniform illumination) which makes these image regions not reliable. In our proposed method it is not necessary to obtain or use the non-linear camera response curve in order to extend the camera dynamic range. We obtain a sequence of differently exposed interferograms, typically five or six; after that, we compute the corresponding normalized fringe patterns and modulation maps using a typical normalization method. These normalized patterns are combined through a temporal weighted average using as weights the corresponding modulation maps. We show a set of experimental results that prove the effectiveness of the proposed method. © 2011 Elsevier B.V. All rights reserved.Ítem Improvement of the signal-to-noise ratio in interferometry using multi-frame high-dynamic-range and normalization algorithms(ELSEVIER SCIENCE BV, 2012-01-01) Restrepo, R.; Uribe-Patarroyo, N.; Belenguer, T.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaUsing both high dynamic range (HDR) and normalization methodologies, we show a method to improve the fringe pattern contrast in interferometric measurements normally used for phase recovering. In a simulated interferogram that mimics the main effects that can be found in an interferometric process (stray-light, photon noise, electronic noise, scattering phenomena, etc.) it was possible to improve the contrast of the fringes and to decrease the root mean square error by more than 35%. The method proposed is applied to experimental interferograms to measure wavefront error and retardance changes on liquid crystal (LC) devices. It is done by using a Mach-Zehnder set-up in which we used different polarization areas. The proposed method increases the quality of the phase recovered and decreases the root mean square error by 50%. © 2011 Elsevier B.V. All rights reserved.Ítem Inspection of an extended surface by an active 3D multiresolution technique(Springer-Verlag Berlin Heidelberg, 2009-01-01) Vargas, J.; Restrepo, R.; Quiroga, J.A.; Belenguer, T.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaReliable inspection of large surfaces with low depth recovery error is needed in a wide variety of industrial applications, for example in deformation measurement or defect inspection of extended surfaces as communication antennas. Active triangulation measurement systems present a compromise between the depth recovery error and the measured area. For an optimized active three-dimensional measuring system the expected ratio between the depth resolution and the inspected area is in the rage of 10-4. Therefore, if we want to scan a large object with a high level of detail we need multiresolution techniques. In this work we demonstrate the application of an active triangulation multiresolution method for the inspection of communication antennas. The technique is based on a standard camera-projector system. The result is a global measurement formed by a set of superposed local measurement with high depth resolution. © 2009 Springer-Verlag Berlin Heidelberg.Ítem Shack-Hartmann spot dislocation map determination using an optical flow method(OPTICAL SOC AMER, 2014-01-27) Vargas, J.; Restrepo, R.; Belenguer, T.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaWe present a robust, dense, and accurate Shack-Hartmann spot dislocation map determination method based on a regularized optical flow algorithm that does not require obtaining the spot centroids. The method is capable to measure in presence of strong noise, background illumination and spot modulating signals, which are typical limiting factors of traditional centroid detection algorithms. Moreover, the proposed approach is able to face cases where some of the reference beam spots have not a corresponding one in the distorted Hartmann diagram, and it can expand the dynamic range of the Shack-Hartmann sensor unwrapping the obtained dense dislocation maps. We have tested the algorithm with both simulations and experimental data obtaining satisfactory results. A complete MATLAB package that can reproduce all the results can be downloaded from [http://goo.gl/XbZVOr]. © 2014 Optical Society of America.