Liste des communications
MODELISATION DU FONCTIONNEMENT EN RECEPTIOND’UN HYDROPHONE PIEZOELECTRIQUE A PVDF
les hydrophones en PVDF sont reconnues comme les capteurs les plus appropriés pour la mesure du champ acoustique émis par les appareils ultrasonores, pour cela une connaissance parfaite de leurs caractéristiques est nécessaire, nous proposons dans ce travail une étude théorique des propriétés de transmission temporelle d’un hydrophone à polyvinylidene fluoride qui se traduit par la détermination de sa réponse impulsionnelle dans le domaine temporel ou par sa fonction de transfert dans le domaine fréquentiel (sensibilité en réception ) et la détermination de son impédance électrique équivalente. Voir les détails
Mots clés : hydrophones en PVDF, réponse impulsionnelle
Robustness study of detection algorithms of multiple Imperfections in coarse grains materials
In this work, we propose to develop algorithms based on the Split Spectrum Processing (SSP) method associated with the multi-steps method based on "Group delay moving entropy" (GDME) allowing detecting and locating multiple imperfection echoes drowned in the structural noise of materials. In fact, GDME is based on the fact that defect echoes have a constant group delay while the noise has a random group delay. The investigation is performed with 4 known defect echoes with different characteristics (position, center frequency and bandwidth). The defect echo frequency is varied around the frequency of the input signal in order to evaluate, by SNR calculation, the robustness of the detection method. The grain noise signal is generated first, by a simple clutter model which consider the noise, in the time domain, as the superimposed of signal coming from backscaterers in the medium and second, experimentally by a material with coarse grains. Voir les détails
Mots clés : Ultrasonic NDE, split spectrum processing, Signal to noise ratio, Structure noise
New discrepancy measures for segmentation evaluation.
In this paper, we propose new evaluation measures for scene segmentation results, which are based on computing the difference between a region extracted from a segmentation map and the corresponding one on an ideal segmentation. The proposed measures take into account separately both under and over detected pixels. It also associates in its computation the compactness of the region under investigation. Voir les détails
Mots clés : Image segmentation evaluation, Discrepancy methods., Difference measures, Refence segmentation
Représentations Temps Fréquence et Temps Echelle Appliquées au Contrôle Non Destructif par Ultrasons des Matériaux
Dans cet article, nous contribuons par le développement de quelques techniques de traitement des signaux basées sur les représentations temps-fréquence et temps-échelle afin d'ameliorer le rapport signal sur bruit, mesurer les fines épaisseurs des matériaux et caractériser les défauts en nature (plan ou volumique). Voir les détails
Mots clés : contôle non destructif, ultrasons, temps-fréquence, temps-echelle
Signal processing techniques applied to ultrasonics NDE
In this paper, we contribute by the development of some signal processing techniques based on time frequency and wavelet transform in order to enhance the sensibility of flaw detection, to measure thin materails thickness and to characterize defects in nature (plan or volumic). Voir les détails
Mots clés : Ultrasonics, time frequency, Wavelet transform, Flaw detection
Time Frequency and Wavelet Transform Applied to Ultrasonics NDE
In this paper, we contribute by the development of some signal processing techniques based on time frequency and wavelet transform in order to enhance the sensibility of flaw detection, to measure thin materails thickness and to characterize defects in nature (plan or volumic). Voir les détails
Mots clés : Ultrasonics, NDE, time frquency, Wavelet transform
Classification of weld defects detected by ultrasonics using signal processing techniques
Discriminatory features from temporal and spctral signals of detected echo are extracted. the compact feature vector obtained will be then classified by different methods: K Nearest Neighbour algorithm, statistical bayesian algorithm and artificial neural network. other disciminatory features using a multiresolution analysis technique, callled discret wavelet transform are also extracted. then, the obtained feature vector will be also classified by the same algorithms. experimental results obtained from a data bank constitued by echoes detected in welds will be compared and discussed. Voir les détails
Mots clés : NDT, Ultrasonics, defects classification, digital wavelets transform, neural networks
Signal to noise enhancement using wavelets and split spectrum processing. Application to defect detection by ultrasonics
In ultrasonic techniques, information on defects characterization possibilities have required more evolved techniques development than classical methods. to obtain a high probability of defect detection, these methods use signal processing algorithms in order to enhance signal to noise ration. In this paper, some signal processing algoritms mike split spectrum processing (SSP) and wavelets are developed and implemented on computer allowing their utilization in ultrasonics NDT results processing. Voir les détails
Mots clés : NDT, Ultrasonics, Split spectrum techniques, digital wavelets transform, Signal to noise ratio
Classification des défauts détectés par Ultrasons par la méthode des KPPV et la méthode Bayesienne
Dans cet article nous developpons une methode de mesure d'atributs obtenus à partir des signaux de défauts qui sont regroupés dans une banque de données. ensuite deux methodes de classification à savoir la methode des K plus proches voisins et la methode bayésienne sont implémentées permettant la classification des défauts de soudure. ces algorithmes sont appliqués au contrôle non destructif des materiaux par ultrasons. Voir les détails
Mots clés : contôle non destructif, ultrasons, traitement du signal, classification
Flaw Detection in Ultrasonics Using Wavelets Transform and Split Spectrum processing
In ultrasonic techniques, information on defects characterization possibilities have required more evolved techniques development than classical methods. to obtain a high probability of defect detection, these methods use signal processing algorithms in order to enhance signal to noise ration. In this paper, some signal processing algoritms mike split spectrum processing (SSP) and wavelets are developed and implemented on computer allowing their utilization in ultrasonics NDT results processing. Voir les détails
Mots clés : NDT, Ultrasonics, Split spectrum techniques, continuous wavelets transform, digital wavelets