Nombre total de résultats : 255
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Complexity reduction of ultrasound sub-ultra-harmonic modeling by an input modified volterra approach

Fatima Sbeity, Sébastien Ménigot, Emma Kanbar, Nesrine HOUHAT, Jamal Charara, Jean-Marc Girault  (2017)

Contrast of echographic images has been highly improved by the injection of microbubbles, due to their nonlinear behavior. However, this contrast enhancement is limited by the nonlinear acoustic propagation in tissue. To overcome this drawback, sub and ultra-harmonic contrast imaging can be used, since only microbubbles can generate these components. Nonlinear modeling is a primordial step in the analysis of microbubble signals for sub and ultra-harmonic imaging. Nonlinear models like Volterra model has been applied in harmonic imaging to model harmonics optimally. However, it can model harmonics only. For sub and ultra-harmonic modeling, a multiple input single output (MISO) Volterra has been proposed. The aim of this study is to propose a simpler alternative for the modeling of sub and ultra-harmonics. We propose a modified single input single output (SMISO) Volterra model based on input demodulation. The model is tested using simulated and experimental signals. Results showed that sub and ultra-harmonics are modeled. The number of kernels is reduced to its half using SMISO model compared to MISO model. The relative mean square error between the simulated signal and the modeled signal with SMISO Volterra model is -15.8 dB and it is -60.7 dB for experimental signals. The computational time is reduced by a factor of 4 and 5 in simulated and experimental cases respectively. SMISO model can make easier the sub and ultra-harmonics modeling. Voir les détails

Mots clés : Non lineaire acoustics, contrast enhancement


Aicha ZIOUCHE (2018)
Thèse de doctorat

Le but de cette étude est l’évaluation et la caractérisation par les méthodes non destructives, les courantsde Foucault et les courants de Foucault pulsés, l’effet des traitements thermiques sur des aciersfaiblement alliés et des aciers inoxydables duplex ainsi que sur des couches minces élaborés parélectrodéposition.Des caractérisations structurales par microscope électronique à transmission (MET), des caractérisationsmécaniques (dureté, résilience,…) et électrochimiques ont été effectuées sur les aciers traités.Les couches minces protectrices contre la corrosion sont élaborées à partir d'un bain de nickel et del'alumine avec une variation de la quantité d'alumine de 5-20g / l. La morphologie de la surface et lamicrostructure des revêtements Ni-Al2O3 ont été déterminées au moyen de la microscopie électroniqueà balayage (MEB) et de la diffraction des rayons X (XRD). Les résultats obtenus de la mesure de ladureté par nano-indentation, la mesure de l'épaisseur et les essais électrochimiques ont abouti à uneaugmentation de la résistance à la corrosion lorsque la quantité d'alumine augmente. Il a été trouvé unebonne corrélation entre les résultats obtenus à partir des essais non destructifs et les méthodestraditionnelles. Voir les détails

Mots clés : corrosion, revêtement, traitement thermique, contrôle non destructif, couches minces.


Wahiba Djerir, Tarek Boutkedjirt  (2018)

In order to carry out reliable measurements of pulsed ultrasonic fields, the use of a piezoelectric hydrophone as receiver is recommended. However, due the finite size of the receiver aperture the measured acoustic pressure is affected by spatial averaging on the surface active face. The aim of this work is to deconvolve the spatial effects of the receiver hydrophone in order to reconstruct the pulsed ultrasonic field with a better spatial resolution. Hereby, the linear pulsed pressure field radiated in water by wideband planar transducers of 19 mm diameter, with central frequencies fc=2.25 MHz and fc=15 MHz are considered. The receivers are PVDF membrane hydrophones of 25 µm - thickness with rectangular and circular apertures. The results of this study show the strong dependency of the reconstruction quality upon the signal-to-noise ratio (SNR). Generally, the quality of the reconstruction decreases with decreasing SNR. Good reconstruction quality has been obtained with correlation coefficient larger than 0.9936 when the “acquired” signals are not too much noisy (SNR=60dB). In this case, improvement of the spatial resolution by a factor of 5 and 9 respectively could be reached. The reconstruction quality depends also upon the hydrophone dimensions, the axial distance to the source, the central frequency and the spectral frequency bandwidth of the pressure pulse. Voir les détails

Mots clés : Super-resolution, spatial inverse filter, spatial Wiener filter, PVDF hydrophone, pulsed ultrasonic field, ultrasonic field reconstruction.

Description of the solid method of BaTiO3 ceramics elaborations

Guessoum Mounia, Boukazouha Faiza, Sedda Kamel  (2018)
Article de conférence

Abstract— There are two major methods of the barium titanate ceramic BaTiO3 elaboration, the solid and the liquid methods (Hydrothermal, sol-gel processing, and Coprecipitation) [1, 2, 3].In this work, we present a theoretical study to describe the solid method of BaTiO3 elaboration, it is the most method used in the industry, because it is very economical, inexpensive and easier to implement. Voir les détails

Mots clés : component formatting; style; styling; insert

Synthesis, characterization and structural study of perovskite ceramics for piezoelectric applications

K. Sedda, R. Djafar, K. Boumchedda, F. Boukazouha, M. Guessoum, A. Badidi Bouda  (2018)
Article de conférence

In this work we have prepared lead-free ceramics BaTiO3, CaTiO3 and Ba0.85Ca0.15Ti0.9Zr0.1O3 successfully from different raw materials barium carbonate (BaCO3) calcium carbonate (CaCO3) dioxide of titanium (TiO2) and zirconium dioxide (ZrO2) by the conventional solid state reaction technique at different sintering temperatures. These materials are mixed for 6 hours and sintered at temperatures of 1200 °C to 1300 °C for 2 hours. The sintering temperature has been varied to study its effects on microstructure and structural properties. Structural parameters were analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM). Differential thermal analysis coupled with thermogravimetric analysis (ATG-ATD) was performed mainly to follow the process of precursor decomposition and formation of the perovskite phase. The XRD analysis results clearly show the synthesis of the perovskite phase as well as highlighting the formation of the Ba2TiO4 phase in addition to the BaTiO3 phase. The diffractogram obtained shows that the BCTZ symmetry is both Cubic with a space group Pm-3m and orthorhombic with a space group R3m. The calculated phase rates are: 10% and 90% respectively. Voir les détails

Mots clés : Lead free ceramics, synthesis, microstructure, Perovskite

Modeling and simulation of In0.15 Ga0.85 N/GaN strainquantum well structure for solar cells application

S. Dehimi, S. Kahla, A. Kellai, L.Kaba, N.Hammouda, A.Boutaghane  (2018)
Article de conférence

Quantum well solar cells based on III-V nitride semiconductor materials are a great technological interest by means to their physical and optical properties. In this study the effect of quantum well number on the characteristics (J-V), (P-V) and efficiency for the structure GaN/In 0.15 Ga0.85 N/ GaN was studied. our result showed that, the increase in the number of wells is accompanied by the increase of the light current density and the efficiency, for example with 50 wells we found Jight = 14(mA /cm2) and a efficiency 28%. Voir les détails

Mots clés : Quantum well, solar cell, GaN, InGaN

Melt Surface Temperature Monitoring In Tiltable Induction Furnace

Aouabdi Salim, BENDJAMA Hocine, boutasseta nadir, Ramzi Boulkroune  (2018)
Article de conférence

The supervision of the induction furnace is the subject of increasing development because of the rising demand on reliability and safety. An essential aspect of the pyrometers of induction furnace is the determination of the exact temperature on the melt surface related to the current and frequency flow resulting from optimum coil position depending on the applied actual power. With the aid of the mathematical model that describes the appearance and development of the temperature change in the area of inductive cold wall crucible melting, with the use of the automatic control methods it is possible to determine the change of temperature variation corresponding to direct visualization of a meniscus forms on the melt surface under the energy created by the induction coil, the latter can fully or partly influence the meniscus. To solve the problem of pyrometer temperature variation we propose the determination and the study of the total interaction force related to the operating current of the induction generator. This contribution presents an application for melt temperature change detection through a case study of the tiltable induction furnace with induction generator MFG-20. The study indicates that the pyrometer of the measurement temperature is powerful device related to the development of a new control method. Voir les détails

Mots clés : Tiltable induction Furnace, cold wall crucible melting, pyrometer measurements, Infrared thermography measurement.

Propriétés Optique de TiO2 et Application de la Méthode de Swanepoel pour la Détermination de l’Épaisseur Optique et de l’Indice de Réfraction

K. Bedoud, R. Graine, H. MERABET  (2018)
Article de conférence

Dans ce travail, des nano-films de dioxyde de titane « TiO2 » ont été déposés par pulvérisation cathodique en utilisant une cible en céramique de Ti pur de 3" de diamètre et 0,250" d'épaisseur avec une pureté de 99,99% sur des substrats en verre à des épaisseurs (e) différents. Nous visons par ce travail d’étudier l’effet de l’épaisseur sur les propriétés optiques de TiO2 nano films. Pour cela, nous avons utilisé la spectroscopie de transmittance optique UV-Visible pour la caractérisation optique. La variation du gap optique des films est inversement proportionnelle à la variation de l’épaisseur de 3,6 eV à 3,8 eV, respectivement. Pour la détermination de l'indice de réfraction et l'épaisseur du film nous avons utilisé la méthode proposée par Swanepoel, qui s’articule sur l’utilisation des franges d’interférence. On observe que, l'indice de réfraction n augmente avec l’augmentation de l'épaisseur de la couche déposée. Voir les détails

Mots clés : couches minces, pulvérisation, semi-conducteur, TiO2, nano-films, UV-Vis, épaisseur, indice de réfraction, Swanepoel.

Numerical simulation study of a high efficient AlGaN-based ultraviolet photodetector

F. Bouzid, L. Dehimi, F. Pezzimenti, M. HADJAB, A. HADJ LARBI  (2018)

In this paper, a two-dimensional (2D) numerical simulation study of a p+-n-n+ AlGaN-based ultraviolet (UV) photodetector, which is designed to achieve true solar blindness with a cutoff wavelength of 0.31 µm, is presented. The device performance is evaluated by investigating both the current density-voltage characteristics and the spectral response (SR). The proposed structure is optimized in terms of the fundamental geometrical and doping parameters. During the simulations, it was found that the detector is sensitive to the UV rays in the 0.155-0.37 µm wavelength range and the spectral response can reach 0.156 AW-1 under a light intensity of 1 Wcm-2 at zero-bias voltage and room temperature. This SR peak value increases further under reverse bias conditions. The temperature effect on the detector SR and the impact of an explicit trap concentration located into the p+ and n-region are also investigated. The spectral response decreases for a temperature exceeding 420 K. At the same time, the SR reference values begin to be affected only for acceptor and donor trap densities that are much higher than the local (total) doping concentration. Voir les détails

Mots clés : AlGaN, Numerical simulation, Photodetector, Spectral response, Trap Density

Elaboration et caractérisation des dépôts Aluminium sur Silicium(Al/Si(400))

Fayssal BOUFELGHA (2008)
Mémoire de magister

Dans ce travail nous nous sommes intéressés à la croissance et la diffusion superficielle de l’Aluminium sur un substrat de Silicium (400). Ce travail comporte deux parties :Le première partie consiste à réaliser sous-vide et à température ambiante des dépôts de différentes épaisseurs d = 240, 510, 720, 870 et 1050 A°. Ces dépôts ont été analysés quantitativement par DRX. L’Aluminium semble croisse sur le silicium selon le mode de Frank-van Der Merwe.La deuxième partie de notre travail est consacrée à l’étude de l’effet de la température de recuit sur la morphologie des dépôts réalisés à température ambiante. Les températures de recuits sont : 100,150, 200, 250, 300, 350 et 400C°. d’après les résultats d’analyse par DRX des dépôts traités, les îlots (2D) d’Aluminium formés à température ambiante se transforment en augmentant la température de recuit, en îlots (3D) plus hauts et plus ramenés. Voir les détails

Mots clés : Évaporation thermique, Silicium, Aluminium, diffusion, DRX.