Electronique
Rational Function Approximationof a Fundamental Fractional OrderTransfer Function
This paper introduces a rational function approximation of thefractional order transfer function ; for 0 to 0:5. Thisfractional order transfer function is one of the fundamental functions of thelinear fractional system of commensurate order corresponding to pure complexconjugate poles or eigenvalues, in sa. Hence, the proposed approximation willbe used in the solution of the linear fractional systems of commensurate order.Illustrative examples are given to show the exactitude and the efficiency of theapproximation method. Voir les détails
Mots clés : Fractional power zero Linear fractional system Irrational transfer function Rational transfer function
The solution of state space linear fractionalsystem of commensurate order withcomplex eigenvalues using regularexponential and trigonometric functions
In a previous work, we have derived the generalsolution of the state space linear fractional system of commensurate order for real simple and multiple eigenvalues ofthe state space matrix. The obtained solutions of the homogeneous and non-homogeneous cases have been expressed as alinear combination of introduced fundamental functions. Inthis paper, the above work has been extended to solve thestate space linear fractional system of commensurate orderfor complex eigenvalues of the state space matrix. First, suitable fundamental functions corresponding to the differenttypes of complex eigenvalues of the state space matrix areintroduced. Then, the derived formulations of the resolutionapproach are presented for the homogeneous and the nonhomogeneous cases. The solutions are expressed in terms ofa linear combination of the proposed fundamental functionswhich are in the form of exponentials, sine, cosine, dampedsine and damped cosine functions depending on the commensurate fractional order. The results are validated by solving anillustrative example to demonstrate the effectiveness of theproposed analytical tool for the solution of the state spacelinear fractional system of commensurate order. Voir les détails
Mots clés : Complex eigenvalues · Fractional differential equation · Fundamental functions · Modal decomposition · Rational function · State space representation
Quantum and conversion efficiencies optimization of superstrate CIGS thin-films solar cells using In2Se3 buffer layer
In this present contribution, AMPS-1D device simulator is employed to study the performances of superstrate SLG/TCO/p-Cu(In,Ga)Se2(CIGS)/n-ODC/n-In2Se3/Metal thin film solar cells. The impact of theTCO and Metal work functions on the cell performance has been investigated. The combination of optical transparency and electrical property for TCO front contact layer is found to yield high efficiency. The obtained results show that the TCO work function should be large enough to achieve high conversion efficiency for superstrate CIGS solar cell. Nevertheless, it is desirable for Metal back contact layer to have low work function to prevent the effect of band bending in the n-In2Se3/Metal interface. Several TCOs materials and metals have been tested respectively as a front and back contact layers for superstrate CIGS solar cells. An efficiency of 20.18%, with Voc ≈ 0.71 V, Jsc ≈ 35.36 mA/cm2 and FF ≈ 80.42%, has been achieved with ZnSn2O3-based as TCO front contact layer. In the case of SnO2:F front contact and indium back contact layers, an efficiency of 16.31%, with Voc ≈ 0.64 V, Jsc ≈ 31.4 mA/cm2 and FF ≈ 79.4%, has been obtained. The present results of simulation suggest an improvement of superstrate CIGS solar cells efficiency for feasible fabrication. Voir les détails
Mots clés : Cu(InGa)Se2 material, Superstrate solar cells, Transparent conducting oxides, Barrier height, AMPS-1D
Rolling bearing faults diagnosis based on empirical mode decomposition: Optimized threshold de-noising method
The faults of rolling bearings frequently occur in rotary machinery, therefore the rolling bearings fault diagnosis is a very important research project. The vibration signal is usually noisy and the information about the fault in the early stage of its development can be lost. A threshold de-noising method based on Empirical Mode Decomposition (EMD) is presented in this paper. Firstly, the signal is decomposed into a number of IMFs using the EMD decomposition. Secondly the algorithm based on the energy to determine the trip point is designed for IMF selection, then, by comparing the energy of the selected IMFs with excluded IMFs, singular selected IMFs are treated with soft threshold function, and finally the de-noised signal is obtained by summing up the selected IMFs, it is proved that the best IMFs can be summed up and properly de-noised by the proposed method. The results show the effectiveness of the proposed technique in revealing the bearing fault impulses and its periodicity and amelioration the sensibility of scalar indicator for real rolling bearing vibration signals Voir les détails
Mots clés : bearing fault detection, EMD, threshold Denoising, IMF selection, Singular IMF
Fast algorithm for hybrid region-based active contours optimisation
Active contours are usually based on the optimisation of energy functionals that are built to attract the curve towardsthe objects' boundaries. This study describes a hybrid region-based active contours technique that uses global means to definethe global fitting energy and local means and variances to define the local fitting energy. The optimisation of the functional isperformed by applying a sweeping-principle algorithm, which avoids solving any partial differential equation and removes theneed for any stability conditions. Furthermore, sweeping-principle algorithm is not based on the computation of derivatives,which allows using a binary level set function during the minimisation process instead of the signed distance function,consequently this removes the need for the distance regularisation term, avoiding its subtle side effects and speeding up theoptimisation process. Successful and accurate segmentation results are obtained on synthetic and real images with a significantgain in the CPU execution time when compared with the minimisation via the commonly used gradient descent method. Voir les détails
Mots clés : image segmentation
Fast Level Set Algorithm for Extraction and Evaluation of Weld Defects in Radiographic Images
The classification and recognition of weld defects play an important rolein weld inspection. In this paper, in order to automate inspection task, we proposean aide-decision system. We believe that to obtain a satisfied defects classificationresult, it should be based on two kinds of information. The first one concerns thedefects intensity and the second one is about its shape. The vision system containsseveral steps; the most important ones are segmentation and feature computation.The segmentation is assured using a powerful implicit active contour implementedvia fast algorithm. The curve is represented implicitly via binary level set function.Weld defect features are computed from the segmentation result. We have computedseveral features; they are ranked in two categories: Geometric features (shapeinformation) and Statistic features (intensity information). Comparative study, onsynthetic image, is made to justify our choice. Encouraging results are obtained ondifferent weld radiographic images. Voir les détails
Mots clés : Code generation, State machine, Radiographic inspection, image segmentation, Level set, Region-based models, Features computation
An Automated Microemboli Detection and Classification System using Backscatter RF Signals and Differential Evolution
Embolic phenomena, whether air or particulate emboli, can induce immediate damages like heart attack or ischemic stroke. Embolus composition (gaseous or particulate matter) is vital in predicting clinically significant complications. Embolus detection using Doppler methods have shown their limits to differentiate solid and gaseous embolus. Radio-Frequency (RF) ultrasound signals backscattered by the emboli contain additional information on the embolus in comparison to the traditionally used Doppler signals. Gaseous bubbles show a nonlinear behavior under specific conditions of the ultrasound excitation wave, this nonlinear behavior is exploited to differentiate solid from gaseous microemboli. In order to verify the usefulness of RF ultrasound signal processing in the detection and classification of microemboli, an in vitro set-up is developed. Sonovue micro bubbles are exploited to mimic the acoustic behavior of gaseous emboli. They are injected at two different concentrations (0.025µl/ml and 0.05µl/ml) in a nonrecirculating flow phantom containing a tube of 0.8 mm in diameter. The tissue mimicking material surrounding the tube is chosen to imitate the acoustic behavior of solid emboli. Both gaseous and solid emboli are imaged using an Anthares ultrasound scanner with a probe emitting at a transmit frequency of 1.82 MHz and at two mechanical indices (MI) 0.2 and 0.6.We propose in this experimental study to exploit discrete wavelet transform (DWT) and a dimensionality reduction algorithm based on differential evolution (DE) technique in the analysis and the characterization of the backscattered RF ultrasound signals from the emboli.Several features are evaluated from the detail coefficients. It should be noted that the features used in this study are the same used in the paper by N. Aydin et al. These all features are used as inputs to the classification models without using feature selection method. Then we perform feature selection using differential evolution algorithm with support vector machines (SVM) classifier. The experimental results show clearly that our proposed method achieves better average classification rates compared to the results obtained in a previous study using also the same backscatter RF signals. Voir les détails
Mots clés : Embolic phenomena, whether air or particulate emboli
Design and simulation of Pyramidal Horn Antenna for NDT Applications
This paper describes a pyramidal horn antenna design which it works in a microwave domain. His operating frequency is 4.7 GHz. The parameters of the antenna were measured through its numerical modeling using HFSS (High Frequency Structure Simulator) electromagnetic simulation software. HFSS has the capability to calculate and plot a 3D image depicting the real beam of the gain. The obtained results show that an antenna gain of 12.90 dB was obtained at the frequency of 4.7 GHz, which means that the antenna is properly adapted to the transmission systems. This antenna will be used for non destructive testing (NDT) application, such as detection of cracks in different materials, materials characterization. Voir les détails
Mots clés : Pyramidal horn antenna, Finite Element Method, HFSS, Radiation Pattern, gain, non destructive testing (NDT).
Micrographic Image Segmentation using Level SetModel based on Possibilistic C-MeansClustering
Image segmentation is often required as afundamental stage in microstructure material characterization.The objective of this work is to choose hybridization betweenthe Level Set method and the clustering approach in order toextract the characteristics of the materials from thesegmentation result of the micrographic images. Morespecifically, the proposed approach contains two successivenecessary stages. The first one consists in the application ofpossibilistic c-means clustering approach (PCM) to get thevarious classes of the original image. The second stage isbased on using the result of the clustering approach i.e. oneclass among the three existing classes (which interests us) asan initial contour of the level set method to extract theboundaries of interest region. The main purpose of using theresult of the PCM algorithm as initial step of the level setmethod is to enhance and facilitate the work of the latter. Ourexperimental results on real micrographic images show thatthe proposed segmentation method can extract successfully theinterest region according to the chosen class and confirm itsefficiency for segmenting micrographic images of materials. Voir les détails
Mots clés : Level set, clustering approach, micrographic images;, image segmentation.
Contribution au Réglage de Correcteurs PIαDβ d’Ordre Fractionnaire
In this work, a new tuning method for fractional order PIλDµ controller was proposed. This method consists of designing a fractional PIλDµ controller, in unit feedback control loop, such that the closed loop system will be equivalent to the desired model. The reference model used in this work, which is Bode's ideal transfer function, is a widely used function in the fractional order control domain because of its iso-damping property, which is an important robustness feature. Indeed, the five parameters of PIλDµ are derived analytically from step response of theprocess to be controlled and the parameters of the desired system that was selected form design specifications, and therefore, six steps of calculation allows to calculate the five parameters of fractional PIλDµ. This analytical formulation make the method more practice and very simple. Illustrative examples were presented to validate this new approach. In the second part of this work is an extension of the proposed tuning method. The proposed strategy consists to apply a self-tuned PIλDµ for controlling a speed of a wind turbine in an electric power production plant. Indeed, by using a linearized model about a specified operating point, the controller's parameters were adjusted, with online implementation of the proposed tuning method, to get robust behavior of closed loop system in term of parameters variation. Voir les détails
Mots clés : Bode’s ideal function, fractional PIλDµ controller, iso-damping property, Robustness