Nombre total de résultats : 261
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Wahiba Djerir, Tarek Boutkedjirt (2018)
Article de journal

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 nitridesemiconductor materials are a great technological interest bymeans to their physical and optical properties. In this study theeffect of quantum well number on the characteristics (J-V), (P-V)and efficiency for the structure GaN/In 0.15 Ga0.85 N/ GaN wasstudied. our result showed that, the increase in the number ofwells is accompanied by the increase of the light current densityand 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

Structural study of Al-doped ZnO thin films produced by the sol-geltechnique

Fayssal BOUFELGHA, N. Brihi, A. BOUAINE, R. Zellagui, N. OUAFAK, et A. BOUGUELLOTE (2018)
Article de conférence

In this work we studied the effect of aluminum doping concentration on the structural properties of zinc oxidethin films, we deposited samples of ZnO and aluminum doped ZnO with a doping rate of 1, 2, 3, 4 and 5%,on glass substrates by the spin coating technique. The structural characterization of the samples is done by theXRD and SEM techniques, the XRD spectra show that the layers are polycrystalline with a hexagonalwürtzite structure, and a preferred orientation in the plane (002), and for the doping 5% the structure is almostmonocrystaline (002). SEM images are used to confirm grain sizes and surface conditions. Opticalcharacterization is done by UV-visible spectroscopy, gives a good visible transmittance up to 80% andexceeds 90% for 2% doping, and the gap varies with the doping variation with a small gap for the samedoping (2%)Voir les détails

Mots clés : Thin films, spin coater, ZnO / Al, XRD, SEM, UV-visible

Electrical Circuit Constants Determination andVoltage Gain Measurement of Unloaded RosenType Piezoelectric Transformer Operating inFirst Mode

F. Boukazouha1, H. Barkat2, A. Herbadji2, A. Rouabha2. M. Guessoum1 and K. Sedda1 (2018)
Article de conférence

Abstract- In this paper a voltage gain of 155 for anunloaded Rosen type piezoelectric transformer operatingat the first mode was successfully measured with aprecision of 5%. For this purpose, it was necessary toensure a good impedance matching along the measuringcircuit. Also, using the admittance circles obtained fromthe measured admittances, the PT equivalent circuitconstants were determined experimentally and foundmatching the calculated ones (model 1D). Precisions lessthan 10% have been reported.Voir les détails

Mots clés : Index Terms- Acoustic wave, Equivalent circuit, High voltage, Measurements, Piezoelectric transformer, Voltage gain.

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.

Optimal Stochastic Excitation for Linear Flaw Detection in a Solid Material

N. HOUHAT, S.MENIGOT, T. Boutkedjirt, R.Drai, J.M. GIRAULT (2018)
Article de conférence

The field of ultrasonic nondestructive testing has known a great development during the recent years. In order to increase the flaw detection sensitivity, many improvements have been made in the equipment and the sensors technology. In the present work, the optimal command which maximizes the flaw detection is investigated experimentally. A parametric optimization consisting of finding the optimal excitation frequency which maximizes the Euclidean distance between a reference medium and a medium with a linear flaw has been obtained automatically by using the gradient descent algorithm. Moreover, the waveform excitation optimization has been considered. A set of stochastic signals have been transmitted to the medium. A closed loop optimization process based on a genetic algorithm allowed to find the optimal excitation without a priori knowledge on the shape of the signal. This optimal excitation converged to a sinusoidal pulse with the optimal frequency found by the parametric optimization.Voir les détails

Mots clés : Optimal command, nondestructive testing, Gradient descent algorithm, Genetic algorithm, Ultrasound

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)
Article de journal

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