Electronique
Computer aided weld defect delineation using statistical parametric active contours in radiographic inspection
A perfect knowledge of a defect shape is determinant for the analysis step in automatic radiographic inspection. Image segmentation is carried out on radiographic images and extract defects indications. This paper deals with weld defect delineation in radiographic images. The proposed method is based on a new statistics-based explicit active contour. An association of local and global modeling of the image pixels intensities is used to push the model to the desired boundaries. Furthermore, other strategies are proposed to accelerate its evolution and make the convergence speed depending only on the defect size as selecting a band around the active contour curve. The experimental results are very promising, since experiments on synthetic and radiographic images show the ability of the proposed model to extract a piece-wise homogenous object from very inhomogeneous background, even in a bad quality image. Voir les détails
Mots clés : Welded joint, Radiographic inspection, Active contours, local statistics-based model, band region selection
Bayesian Networks-Based Defects ClassesDiscrimination in Weld Radiographic Images
Bayesian (also called Belief) Networks (BN) is a powerfulknowledge representation and reasoning mechanism. Based on probabilitytheory involving a graphical structure and random variables, BN iswidely used for classification tasks and in this paper, BN is used as aclass discrimination tool for a set of weld defects radiographic imagesusing suitable attributes based on invariant geometric descriptors. Testsare performed on a database of few hundred elements where the resultsare outstanding and very promising, since they outperform those givenby powerful SVM classifiers. Voir les détails
Mots clés : Bayesian networks, weld defects, Geometric descriptors, radiography
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
Head Pose Classification Using a BidimensionalCorrelation Filter
Correlation filters have been extensively used in face recognition but surprisingly underused in head pose classification. In this paper,we present a correlation filter that ensures the tradeoff between three criteria: peak distinctiveness, discrimination power and noise robustness.Such a filter is derived through a variational formulation of these threecriteria. The closed form obtained intrinsically considers multiclass information and preserves the bidimensional structure of the image. The filterproposed is combined with a face image descriptor in order to deal withpose classification problem. It is shown that our approach improves poseclassification accuracy, especially for non-frontal poses, when comparedwith other methods. Voir les détails
Mots clés : Head pose classification, Bidimensional correlation filter
Vector Fourier transform analysis of stacked rectangular microstrip patches on isotropic and anisotropic substrates
Galerkin’s method in the vector Fourier transform domain is used for computing the resonant frequencies of two stacked rectangular patches embedded in a multilayered media containing isotropic and/or uniaxial anisotropic dielectrics. The proposed method for determining the dyadic Green’s functions of the stacked configuration leads to a new concise expression, allowing the computation of these dyadic easily by using simple matrix multiplications. Numerical results are presented for two stacked rectangular patches fabricated on a two-layered substrate. Numerical results are also obtained for another stacked configuration involving three patches and five layers. The set of TM modes of a rectangular cavity with magnetic side walls are used in the approximation of the currents on the patches. Through numerical convergence checks, it is found that for symmetrical patches, only one mode per patch suffices to obtain good convergence, while for unsymmetrical patches, additional basis functions should also be included in both the approximation of the current on the lower patch and the one on the upper patch. The validity of the solution is tested by comparing the computed results with the known experimental data. The numerical results indicate that the two constitutive resonators of the stacked structure, which determine the dual-frequency behavior of the antenna, depend on the relative sizes of the lengths of the patches. Also, the numerical results show that substrate dielectric anisotropy has a more pronounced effect on the lower resonance than on the upper resonance. With regard to the bandwidth, we show that in order to bring the stacked antenna the benefits of broad band, it is necessary that the antenna operates at its lower (upper) resonance when b2 > b1 (b2 < b1). Other results also indicate that the displacement of the upper patch along the resonant direction constitutes an efficient tool for widening the separation between the upper and lower resonances. Voir les détails
Mots clés : Stacked patches Unsymmetrical patches Dual-frequency operation Full-wave analysis
Enhancement of phased array ultrasonic signal in compositematerials using TMST algorithm
In this paper, we apply a new technique for the ultrasonic phased array signal enhancement. It is based on the threshold modifiedS-transform (TMST). The signal processing algorithms generally give very satisfactory results on synthetic signals verifying theimplicit or explicit hypotheses on which they are constructed. The obtained performances on the real signals can be howeverdifferent radically. Time–frequency analysis methods are mainly used to improve the defects detection resolution. Significantperformance enhancement is confirmed when the proposed approach is tested with the simulation of the B-scan signals contain acloser delamination to the front face. The experimental results show that the TMST Algorithm can enhance the quality of imageprovided by composite materials contained delamination defect. Voir les détails
Mots clés : Ultrasonic Phased Array, composite materials, S-transform, TMST Algorithm