Liste des documents
Effects of stabilizer ratio on photoluminescenceproperties of sol-gel ZnO nano-structured thin films
Nanostructured ZnO thin films with different molar ratios of MEA to zinc acetate (0.5, 1.0, 1.5 and 2.0) have been deposited on glass substrates by a sol–gel dip coating technique. X-ray diffraction, Scanning Electron Microscopy, UV–visible spectrophotometry and photoluminescence spectroscopy have been employed to investigate the effect of MEA stabilizer ratio on structural, morphological, absorbance and emission properties of the ZnO thin films. Diffraction patterns have shown that all the films are polycrystalline and exhibit a wurtzite hexagonal structure. The c axis orientation has been enhanced with increasing stabilizer ratio. SEM micrographs have revealed that the morphology of the ZnO films depend on stabilizer ratio. The UV–visible absorption spectra have demonstrated that the optical absorption is affected by stabilizer ratio. The photoluminescence spectra have indicated one ultraviolet and two visible emission bands (green and red), while band intensities are found to be dependent on stabilizer ratio. ZnO thin films deposited at MEA ratio of 1.0 show the highest UV emission while the minimum UV emission intensity is observed in thin films deposited at ratio of 0.5 and the maximum green has been recorded for films deposited at MEA ratio of 2.0. Voir les détails
Mots clés : ZnO thin film, Sol–gel, Stabilizer ratio, Photoluminescence
An Effective Method for Bearing Faults diagnosis
The bearings are the most important mechanicalelements of rotating machinery. They are employed to supportand rotate the shafts in rotating machinery. An unexpected defectof the bearing may cause significant economic losses. For thatreason, the condition monitoring of these bearings has become afundamental axis of development and industrial research. Thefocus of this paper is to combine tow conventional methods:Hilbert Transform (HT) and Discrete Wavelet Transform (DWT)to develop a better method for detection and diagnosis the bearingfaults .This new method applied on real measurement signalscollected from an experimental vibration system. The monitoringresults indicate that the proposed method improves the bearingfaults diagnosis compared to other common techniques. Voir les détails
Mots clés : Vibration analysis, bearing Fault diagnosis, Hilbert Transform (HT), Envelope Analysis (EA), Discrete Wavelet Transform (DWT) ), Fast Fourier Transform (FFT)
Effects of a circular defect size and position on the damage progression in hybrid laminates under compressive loading.
The effects of a circular defect size and position on the post-damage response of the FMLs laminates under compressive loading have been studied. Compression tests are performed on composite plates comprising a hole having different diameters (8mm, 12mm and 16mm) and located at different positions (25%, 50% and 75%) in the loading direction. A numerical analysis using the finite element method FEM has permits the identification of the initiation zones and the description of the damage evolution in these laminates. The results of the numerical simulation are in good agreement with the experimental results. The FEM has well predicted the critical damage zones. Voir les détails
Mots clés : Defect, damage, hybrid laminate, FEM
Condition Monitoring and Fault Detection in Wind Turbine Based on DFIG by the Fuzzy Logic
oubly-fed induction generator is widely used in wind turbine conversion systems. Several research works are being made to efficiently approve existing condition monitoring and fault detection techniques for these systems. The condition monitoring ofthese systems becomes more and more important, the main obstacle in this task is the lack of an accurate analytical model to describe a faulty DFIG in the majority of the research tasks. In this paper, we present the monitoring strategy of short-circuit fault between turns of the stator windings and open stator phases in doubly-fed induction generator by fuzzy logic technique. The stator condition monitoring is diagnosed based on the root mean square values of current magnitude in addition to the knowledgeexpressed in rules and membership function. The proposed strategy is verified using simulations performed via the model of Doubly-fed induction generator built in MatLab ® SIMULINK. Voir les détails
Mots clés : Wind turbine, DIFG, Monitoring, Detection fault, Fuzzy logic.
Influence des paramètres de traitement par brunissage sur la texture de la surface
Résumé : Le procédé de brunissage (galetage à la bille) est l’un des moyens de finition et d’amélioration de la texture de surface d’une pièce mécanique. La texture de la surface est matérialisée par la rugosité et l’orientation de la direction prédominante des stries en travers de la surface. Cette orientation est d’une grande importance dans un contact mécanique, elle peut être évaluée par le rapport d’aspect de texture " Str" appelé indicateur d’isotropie de la surface. Ce travail a pour objectif de mettre en relief, l’influence des paramètres de traitement par brunissage sur l’orientation des stries. Les paramètres considérés sont : l'effort appliqué " Py ", l'avance " f " et le diamètre de bille " Db ". Au moyen d’un modèle mathématique basé sur les plans factoriels de Box-behenken, un régime optimal offrant le meilleur rapport de texture " Str ", a été déterminé. Voir les détails
Mots clés : Modèle mathématique., paramètres de brunissage, paramètre de texture
CDR Antenna with Dual-Band 1.9/2.7 GHz for MIMO-LTE Terminals
In this letter, we present a compact dual-band dielectric resonator antenna for multi-input multi-output antenna is designed and fabricated. The proposed antenna consists of a single cylindrical dielectric resonator antenna (CDRA) excited from two orthogonal ports. The electromagnetic analysis is performed using the CST microwave studio software. To validate the proposed concept, experimental measurements are also performed. The measured results show that the CDRA provides two bands around 1.9 and 2.7 GHz, suitable for LTE applications. Moreover, the proposed design allows a very good isolation between the two ports and a low envelop correlation coefficient. Voir les détails
Mots clés : Dielectric resonator antenna, multi-input multioutput systems, LTE bands, isolation, envelop correlation coefficient
Integrated Flexible UWB/NB Antenna Conformed on a Cylindrical Surface
In this paper, an ultra-wideband (UWB) conformal monopole antenna integrated with a narrow-band (NB) rectangular slot antenna is designed and fabricated. The proposed structure consists of a circular disc monopole antenna printed on a cylindrical surface and fed by a coplanar waveguide line (CPW). A rectangular slot antenna, excited by a microstrip line, is integrated in the front of the UWB antenna. The simulations are performed using the CST Microwave Studio software. To validate the proposed antenna concept, an experimental prototype is fabricated and measured. The measured results show that the monopole antenna covers an ultra wideband from 2 GHz to 12GHz with S11 < −10 dB and provides a very good isolation with a transmission coefficient below −20 dB across the operating band. Compared to planar integrated antennas, the proposed conformed structure possesses an important wideband, which can be used in many wearable electronic applications and communication systems. Voir les détails
Mots clés : UWB, Conformal antenna
Enhanced Isolation MIMO Antenna with DGS Structures for Long Term Evolution Systems
In this communication, a new multi-antenna system based on two microstrip antennas is analyzed and proposed for LTE (Long Term Evolution) terminals. The multi-input multi-output (MIMO) antenna is printed on a FR4 substrate with size of 60×100×1.6 mm3. The proposed design, in its basic form, operates around 2.3 GHz, and provides a transmission coefficient of -19 dB. In order to improve the isolation between the two antenna ports, some rectangular and circular slots are inserted in the ground plane between the two antennas. With this modification, the mutual coupling of -59 dB was achieved, which are 40 dB improvements over the initial antenna. The simulated results are presented and discussed in term of reflection coefficients, transmission coefficients and radiation patterns. Voir les détails
Mots clés : MIMO antenna, mutual coupling, LTE (Long Term Evolution) terminals
High Isolation Microstrip MIMO Antennas for WLAN Systems
This paper introduces a novel design of aperture coupled microstrip antenna for MIMO array applications. The proposed antenna uses 2x4 patches excited from two ports via rectangular slots. HFSS (High Frequency Structure Simulator) and CST (Computer Simulation Technology)softwares are used to simulate the antennas performance. The results are given in term of S-parameters, radiation patterns and gain. In addition a parametric study is done to evaluate the effect of certain antenna parameters on the antenna performances. Form the simulated result, it is concluded that the proposed concept provides a good isolation between the two antenna ports (with low mutual coupling, S12/21). Voir les détails
Mots clés : High Isolation, MIMO antenna
Optimization of Distribution Functions for the Hysteresis Preisach Model by Genetic Algorithms
The description of hysteresis is one of the classical problems in magnetic materials. The progress in its solution determines the reliability of modeling and the quality of design of a wide range of contemporary devices, as well as devices that will be created in the future. The intensive investigations in hysteresis modeling were induced by the fact that accuracy models of magnetic hysteresis must be studied yet. In this paper, several identification procedures of the distribution functions of the Preisach model will be investigated by means of a genetic algorithm.The proposed approach has been applied to model the behavior of many samples and distribution functions are optimized which will give accurate results of the hysteresis loop. The results show the robustness and efficiency of genetic algorithm to model the phenomenon of hysteresis loop. This work can give solutions about the ferromagnetic material evaluations and shows the optimization of distribution functions according to the material behaviors. Voir les détails
Mots clés : Preisach Model, distribution functions, genetic algorithms GA, optimization