Electronique
Performance Evaluation of Omni-Directional Circular UWB Disc Antenna Conformed on a Cylindrical Surface
The cylindrical geometry can offer certain desirable antenna characteristics that are not provided by planar elements. In this paper a conformal omni-directional circular disc antenna which is mounted on a cylindrical surface feeding by a microstrip line is presented and proven to operate equally well compared to its planar rival. The return losses and the radiation pattern characteristics of the proposed antenna are studied using the commercially available electromagnetic software CST studio suiteTM , and high frequency structure simulator HFSS. Compared with the planar shape and the cylindrical conformal antenna existing, the proposed structure possesses an important wideband which is needed for many wearable electronics applications. Voir les détails
Mots clés : Conformal antenna, UWB antenna, CST simulator, HFSS simulator.
Experimental Investigations of an Omni-directional Dielectric Resonator Antenna for UWB Systems
In this paper, a new dielectric resonator antenna(DRA) is presented and investigated for ultra wideband (UWB)applications. The UWB antenna has a U-shape and excited by amicrostip fed monopole. The proposed antenna was simulatedand designed using two electromagnetic simulators. To validateour design, a prototype antenna was fabricated and measured.From the measurements, the U-shaped DRA has a 117.6 %impedance bandwidth (from 2.94 GHz to 11.34 GHz, for returnloss below -10 dB, largely covering the UWB spectrum band).Moreover, the proposed antenna provides an omni-directionalradiation pattern. With these features, the present antenna canbe used in ultra-wideband wireless systems. Voir les détails
Mots clés : Dielectric Resonator Antennas, Measurements, Radition Pattern, UWB applications.
Hybrid Shape Descriptors for an Improved WeldDefect Retrieval in Radiographic Testing
In this paper, four region-based shape descriptors well reported in the literature are used to characterize weld defect types ofcrack, lack of penetration, porosity and solid inclusion, usually encountered in radiographic testing of welds. The rectangularity and the roundness in the geometric descriptor (GEO) are used in order to propose anhybridization algorithm so that the hybrid descriptor issued from GEOand each of the other descriptors becomes more discriminant in suchapplication where, due to bad radiographic image quality and weld defect typology, the human film interpretation is often inconsistent andlabor intensive. According to the results given in the experiments, theefficiency of the proposed hybrid descriptors is confirmed on the welddefects mentioned above where, the retrieval scores are significantly improved compared to the original descriptors used separately. Voir les détails
Mots clés : Weld decfec, radiography, shape descriptor, hybridization
Filtrage des interférogrammes InSAR par separationdes sources
Les interférogrammes dans un processusinterférométrique sont souvent bruités, ils présentent desdiscontinuités au niveau des franges ; qui sont dueprincipalement à la décorelation spatiale, temporelle, etthermique, en plus des erreurs de recalage des couplesinterférométriques. Plusieurs méthodes de filtrage ont étédéveloppées. Dans ce travail nous sommes particulièrementintéressé aux techniques de filtrage interférométrique basées surla décomposition en sous espaces dont nous avons proposé uneméthode de sélection de sous espace optimal afin de conserverl’information physique particulièrement au niveau des zones detransitions des franges. La méthode a été testée sur desinterférogrammes de zones accidentées. Les résultats obtenussont comparés aux résultats de filtrage par les algorithmes deGoldstein et vecteur. Voir les détails
Mots clés : Interférogrammes; décorélation spatiale; temporelle; thermique; recalage de couple interférométriques; décomposition en sous espaces; Goldstein; vecteur
TwTwo-dimensional Modelling and Simulationof CIGS thin-film solar cell
Abstract: 2 D Silvaco Atlas software is used for the study of a CIGS thin film solar cell in the configuration:ZnO(200 nm)/n-type CdS(50 nm)/ p-type CIGS(350 nm)/Mo. The cell performance is evaluated by implementing thedefects created at the grain boundaries of the polycrystalline CdS and CIGS ma terial and at the interface CdS/CIGS. TheJ-V characteristics and the external quantum efficiency EQE are simulated under AM 1.5 illumination. The conversionefficiency η of 20.35 % is reached and the other characteristic parameters are simulated: the short circuit current density Jscequals 35.62 mA/cm2, the open circuit voltage Voc is of 0.69 V and the fill factor FF is of 82.7 %. The calculated externalparameters of the solar cell are in good agreement with the measured characteristics. The simulation results also showedthat the rise of the CdS thickness decreases all output parameters and the external quantum efficiency while the rise of theCIGS thickness improves all photovoltaic parameters and the external quantum efficiency. The highest efficiency of21.08 % is reached for the CIGS thickness of 5 μm. Voir les détails
Mots clés : Computer modeling, Silvaco Atlas, CIGS solar cell, solar cell parameters.
Elaboration des Couches Minces du ZnO Déposé par la Méthode Spray Pyrolysis à partir de Trois Sources : Application Capteur de Température.
Aujourd’hui il existe une demande croissante sur des systèmes industriels plus sûrs et plus fiables qui sont essentiellement contrôlés par des capteurs de température, pour satisfaire cette demande, nous nous somme intéressés à la réalisation des capteurs à base de couches minces. A cet effet, nous avons choisi l’oxyde de zinc « ZnO » qui fait partie de la famille des semi-conducteurs et les oxydes conducteurs transparents « TCO ». Ce choix est justifié par le compromis entre les propriétés optiques et électriques d’oxyde de zinc, sa stabilité thermique et chimique très élevées, sa non toxicité ainsi que son abondance dans la nature et son coût bas. De plus, il présente un gap de 3,3 eV et une énergie de liaison excitonique de 60 meV. Dans ce travail, des couches minces de ZnO ont été déposées par la technique de spray pyrolyse, à partir de trois différentes sources « Chlorure de Zinc », « Acétate de Zinc » et « Nitrate de Zinc » avec une molarité de 0.1mol/l ou t = 5 min sur des substrats en verre chauffés à une température de 280°C.Notre travail porte sur l’étude de l’influence de la méthode de déposition ainsi que les sources utilisées sur les propriétés structurales, optiques et électriques de ces couches. Pour cela, nous avons utilisé la spectroscopie de transmission optique UV–Visible pour les caractérisations optiques, la technique de deux pointes pour les caractéristiques électriques et nous souhaitons faire la diffraction des rayons X pour les caractérisations structurales de nos couches. Voir les détails
Mots clés : couches minces, spray pyrolyse, propriétés optiques, semi-conducteur, ZnO.
Ultrasonic Flaw Detection in Composite Materials Using SSP-MPSD Algorithm
Due to the inherent inhomogeneous and anisotropy nature of the composite materials, the detection of internal defects in these materials with non-destructive techniques is an important requirement both for quality checks during the production phase and in service inspection during maintenance operations. The estimation of the time-of-arrival (TOA) and/or time-of-flight (TOF) of the ultrasonic echoes is essential in ultrasonic non-destructive testing (NDT). In this paper, we used split-spectrum processing (SSP) combined with matching pursuit signal decomposition (MPSD) to develop a dedicated ultrasonic detection system. SSP algorithm is used for Signal-to-Noise Ratio (SNR) enhancement, and the MPSD algorithm is used to decompose backscattered signals into a linear expansion of chirplet echoes and estimate the chirplet parameters. Therefore, the combination of SSP and MPSD (SSP-MPSD) presents a powerful technique for ultrasonic NDT. The SSP algorithm is achieved by using Gaussian band pass filters. Then, MPSD algorithm uses the Maximum Likelihood Estimation. The good performance of the proposed method is experimentally verified using ultrasonic traces acquired from three specimens of carbon fibre reinforced polymer multi-layered composite materials (CFRP). Voir les détails
Mots clés : Non-Destructive testing, Ultrasonics, Carbon fibre, Defects, Signal processing
Ultrasonic flaw detection using threshold modified S-transform
Interference noising originating from the ultrasonic testing defect signal seriously influences the accuracy of the signal extraction and defect location. Time–frequency analysis methods are mainly used to improve the defects detection resolution. In fact, the S-transform, a hybrid of the Short time Fourier transform (STFT) and wavelet transform (WT), has a time frequency resolution which is far from ideal. In this paper, a new modified S-transform based on thresholding technique, which offers a better time frequency resolution compared to the original S-transform is proposed. The improvement is achieved by the introduction of a new scaling rule for the Gaussian window used in S-transform. Simulation results are presented and show correct time frequency information of multiple Gaussian echoes under low signal-to-noise ratio (SNR) environment. In addition, experimental results demonstrate better and reliable detection of close echoes drowned in the noise. Voir les détails
Mots clés : Flaw detection, Ultrasonic signal, Time–frequency signal analysis, Modified S-transform
Characteristics of a high Tc superconducting rectangular microstrip patch on uniaxially anisotropic substrate
Resonant characteristics of a high Tc superconducting rectangular microstrip patch printed on uniaxially anisotropic substrate are investigated using a full-wave spectral analysis in conjunction with the complex resistive boundary condition. The uniaxial medium shows anisotropy of an electric type as well as anisotropy of a magnetic type. Both permittivity and permeability tensors of the substrate are included in the formulation of the dyadic Green’s function of the problem. The accuracy of the analysis is tested by comparing the computed results with previously published data for several anisotropic substrate materials. Numerical data of the resonant frequency and bandwidth as a function of electric anisotropy ratio are presented. Variations of the resonant frequency and bandwidth with the magnetic anisotropy ratio are also given. Finally, results showing the influence of the temperature on the resonant frequency and quality factor of the high Tc superconducting rectangular microstrip patch on a uniaxial substrate are also given. Voir les détails
Mots clés : superconducting microstrip patch, Anisotropic substrate, Permittivity and permeability tensors
Bacterial foraging optimisation and method of moments for modelling and optimisation of microstrip antennas
A novel technique applying bacterial foraging optimisation (BFO) in conjunction with the method of moments (MOM) is developed to calculate accurately the resonant frequency and bandwidth of rectangular microstrip antenna of any dimension and of any substrate thickness. The resonant frequency results obtained by using (BFO/MOM) algorithm are in very good agreement with the experimental results available in the literature. The computation time is greatly reduced as compared with the classical MOM. Furthermore, the idea of this paper can be used for calculating the various parameters of microstrip antennas of different structures and geometries. Voir les détails
Mots clés : method of moments, microstrip antennas, natural frequencies, bacterial foraging, Computation time, Different structure, Method of moments (MOM), Modelling and optimisation, Novel techniques, Rectangular-microstrip antennas, Substrate thickness