Mayssa Karray

Real-time three-sensitivity measurements based on three-color digital Fresnel holographic interferometry

This Letter presents a method for real-time 3D measurements based on three-color digital holographic interferometry. The optical setup is considerably simplified, since the reference beams are combined into a unique beam. A convolution algorithm allows the three monochrome images to be superposed to provide simultaneous full-field 3D measurements. Experimental results confirm the suitability of the proposed method.

Evaluation of surface acoustic waves on the human skin using quasi-time-averaged digital Fresnel holograms

This paper proposes a first attempt to visualize and analyze the vibrations induced by a bone-conduction device and propagating at the surface of the skin of a human face. The method is based on a new approach in a so-called quasi-time-averaging regime, resulting in the retrieval of the vibration amplitude and phase from a sequence of digital Fresnel holograms recorded with a high image rate. The design of the algorithm depends on the ratio between the exposure time and the vibration period. The results show the propagation of vibrations at the skin surface, and quantitative analysis is achieved by the proposed approach.

Some figures of merit so as to compare digital Fresnel holography and speckle interferometry

This paper presents a detailed analysis of figures of merit to compare digital Fresnel holography and speckle interferometry. The analysis is based on both theoretical and experimental analyses. A theoretical analysis of the influence of the aperture and lens in the case of speckle interferometry is developed. Compared to digital Fresnel holography, this element is a critical point influencing Shannon conditions, spatial resolution, spatial filtering and photometric efficiency. Optimal filtering and image recovering conditions are thus established. The theoretical analysis is validated by experimental results. The influence of the speckle decorrelation is estimated for the measurement of mechanical deformations. The same mechanical loading has been applied for both experimental configurations. The probability density of the noise map is then estimated. Fitting the curves along the theoretical analysis results in an objective comparison of the decorrelation degrees, and gives keys to compare the decorrelation sensitivity of the methods.

Digital holographic nondestructive testing of laminate composite

Abstract. Optical digital holographic techniques can be used for nondestructive testing of materials. Digital holographic nondestructive testing essentially measures deformations on the surface of the object. However, there is sufficient sensitivity to detect subsurface and internal defects in metallic and composite specimens. We investigate and discuss the vibration analysis of laminated composite glass-epoxy using time averaging in digital Fresnel holography to visualize the modes of vibration and to test the integrity of the structures of studied materials.

Dielectric relaxation phenomena in flax fibers composite

In this work, a study of the dynamic dielectric analysis of the unidirectional epoxy composite: flax-fibre-reinforced epoxy (FFRE) was investigated. In this composite, three relaxation processes were identified. The first one is the water dipoles polarization imputed to the presence of polar water molecules in flax fiber. The second relaxation process associated with conductivity occurs as a result of the carriers charges diffusion. As for the third dielectric relaxation associated with the interfacial polarization effect is attributable to the accumulation of charges at the fibers/matrix interface. The analysis of the Maxwell-Wagner-Sillars (MWS) and the water dipoles polarizations using the Havriliak-Negami model revealed the high adhesion of flax fibers in the matrix. This analysis was supported by the thermal properties using a Differential Scanning Calorimety (DSC).

Investigation of crack initiation with a three color digital holographic interferometer

This paper proposes a three-color holographic interferometer devoted to the deformation analysis of a composite material submitted to a short beam shear test. The simultaneous recording of three laser wavelengths using a triple CCD sensor results in the evaluation of shear strains at the lateral surface of the sample. Such an evaluation provides a pertinent parameter to detect premature crack in the structure, long before it becomes visible on the real time stress/strain curve, or with a classical microscope.

Reference-free metric for quantitative noise appraisal in holographic phase measurements

This paper presents a reference-free metric for quantitative appraisal of de-noising algorithms for phase measurements in digital holography. In the literature, quality metrics are not self-contained because they require a noise-free reference phase fringe pattern in order to be computed. In practical situations, no exact phase is available to evaluate the quality of processing. In order to bypass such limitations, one needs a metric directly capable of providing information on how efficient the filtering is, without any help from any reference measurements and by only considering the measured available phase data. This paper presents a novel reference-free metric, called estimated phase error for quantitative appraisal of de-noising algorithms for noisy phase data processing. This metric is based on the computation of an estimator of the standard deviation of the phase error between data processed with an external algorithm and that from the evaluated algorithm. A benchmark, including 37 different de-noising algorithms, demonstrates that the proposed metric is capable of producing the same rankings as those obtained with classical metrics, requiring a reference phase. Application to phase data from mechanical testing demonstrates that the ranking obtained from experimental phase data is similar to that obtained during the benchmarking with simulated data.

The iterative 2D windowed Fourier transform: A SOS approach to speckle noise reduction in digital holography

This paper addresses the problem of the reduction of speckle noise corrupting phase images from laser digital holography technique. It present an iterative denoising algorithm based on the 2-D windowed Fourier Transform. The algorithm is a new approach based on the SOS procedure recently proposed by Y. Romano and M. Elad adapted to phase processing. The approach is proposed in the case of the 2-D windowed Fourier Transform algorithm applied to phase maps which constitutes the state of the art in the field of digital holography. The reason is that the sum and difference operations used in the SOS procedure cannot be computed directly on phase maps but using a sine and cosine representation in order to avoid 2n phase jumps. Results on simulated phase maps including realistic noise conditions encountered in digital holography show the advantage of the proposed iterative approach. The paper proposes the application of the method to denoising of phase images from digital three color holography applied to cracks characterization of a composite materiel under mechanical strength test.

A new criterion for quantitative appraisal of de-noising algorithms in digital Fresnel holography

This paper presents a reference-free metric for quantitative appraisal of de-noising algorithms for digital Fresnel holography. In literature, lots of reported metrics are based on the availability of the noise-free reference phase to obtain ranking of selected de-noising algorithms. When such information is no longer available, other metrics must be chosen. The problem is that obtained rankings could be quite different than those using noise-free phase maps. This is the case for example with the signal-to-distortion ratio criterion. In order to avoid such problem, we propose a new criterion based on the use of a robust estimator of the speckle noise phase map using the 2D windowed Fourier transform. On one hand, correlation diagram between PSNR (using a noise-free reference) and our new metric (without any noise-free reference), and on the other hand, comparison of the rankings computed on selected de-noising algorithms demonstrate the validity of the proposed reference-free approach.

Effect of ecological treatment on adhesion of woven flax fibers in epoxy matrix

Surface treatment of woven flax fibers was investigated as means of improving their adhesion in epoxy matrix. Flax fibers were treated in two ways : (i) with enzymatic treatments using pectinase enzymes and (ii) with pectinase enzymes/detergent, respectively. For this reason, dielectric measurements were performed in the frequency range from 10-1 Hz to 106 Hz and temperature interval from 40 °C to 200 °C. Studies of dielectric relaxations in these composites revealed the presence of three relaxation processes namely the orientation polarization imputed to the presence of polar water molecules in flax fibers, the relaxation process associated with conductivity occurring as a result of the carriers charges diffusion noted for high temperature above glass transition and low frequencies, and interfacial polarization effect or Maxwell-Wagner-Sillars (MWS) relaxation that is attributable to the accumulation of charges at the flax fibers/epoxy resin interfaces. Analysis of this latter using the Havriliak-Negami model revealed that the adhesion fibers/matrix was improved by the addition of the detergent treatment to the enzymatic one.