Physique
Application de la Technique de Focalisation par Ouverture Synthétique (F-SAFT) pour l’amélioration de la résolution latérale d’images échographiques
Dans le présent travail, la technique de Focalisation par ouverture synthétique (Synthetic Aperture Focusing Technique ou SAFT) a été utilisée afin de montrer son efficacité quant à l’amélioration de la résolution latérale d’images échographiques. Une étude expérimentale a été effectuée sur un bloc en acier comportant des défauts (trous) de diamètres variés séparés par différentes distances. Les images échographiques en B-scan des données brutes ainsi que ceux reconstruites par l’algorithme SAFT sont présentés. Voir les détails
Mots clés : ultrasons, Technique de Focalisation par Ouverture Synthétique, SAFT, résolution latérale
Ultrasonic Backscatter Coefficient Estimates in a Soft Tissue Mimicking Phantom
The ultimate goal of characterization methodsbased on the backscatter coefficient (BSC) estimates isto obtain structural information about samples independentlyof the measurement system. In the current study,measurements of the BSC were obtained from TissueMimicking Materials (TMM) or phantoms. These consistedof a mixture of gelatin and distilled water containingmicroscopic graphite particles with a mean radius of 18micrometers, which were randomly distributed. Phantomsconcentrations ranged from 50 to 200 g of graphite per literof gelatin. Two BSC estimation methods were used andtheir results were compared to Faran’s scattering theorywhich allowed the estimation of the number density ofgraphite particles in the phantoms. Moreover, measurementsof the attenuation coefficient and the ultrasonicpropagation velocity in phantoms were performed. Theevolution of the attenuation coefficient and the BSC as afunction of frequency and scatterers’s concentration in afrequency range from 1.5 MHz to 6 MHz will be presentedusing two transducers of nominal frequencies 2.25 MHzand 5 MHz. Decreasing of the attenuation coefficient withfrequency and graphite concentration will be showed. Voir les détails
Mots clés : Ultrasound, Attenuation, backscattering, TMM
Propagation of Lamb Waves on an Immersed Plate Containing a Periodic Grating: Experimental study
In this paper the propagation of Lamb waves in an aluminum plate with a roughness on only one side is studied. The interaction between the incident Lamb wave and the grating gives rise to reflected converted waves. This phenomenon is studied experimentally in the case of an immersed plate in water. Our objective is to show that retroconverted waves radiating into the water are detectable although their energies are small. The damping coefficient of the propagating Lamb wave in the plate is evaluated. Preliminary numerical simulation by using a finite elements method is performed in order to help experiments. Voir les détails
Mots clés : Liquid–solid interfaces, Rough plate, Periodic grating, Lamb waves, Converted modes
Frequency and concentration dependence of the ultrasonic backscatter coefficient in a soft tissue mimicking material
In medical ultrasound, the backscatter coefficient is used to quantify the scattering properties of biological tissues. It is defined as the differential scattering cross section per unit volume for a scattering angle of 180 °.In this study, measurement of backscatter coefficient are made on Tissue mimicking Materials. These are materials whose acoustic properties (velocity, attenuation, diffusion) are close to those of biological tissues.Measurements of this coefficient have been achieved in a mixture of gelatin and distilled water containing microscopic graphite particles with mean radius of 18µm randomly distributed. Samples concentrations ranged from 50 to 200g of graphite per liter of gelatin. The backscatter coefficient was evaluated using both Sigelman and Reid and Chen methods in frequency range around 5 MHz. The evolution of this coefficient as a function of frequency and concentration of scatterers will be presented. Comparison of experimental values with those obtained from Faran theory permits estimation of number density of graphite particles in TM material. Voir les détails
Mots clés : Ultrasound, Bakscatter coefficient, Tissue mimicking material
Graphene: Material description, elaboration methods and main properties
Nanomaterials containing carbon have open new ways for the development of interesting and innovator applications. Among these materials, the mother of all graphite shapes, the graphene, is becoming a material of a great interest because of their remarkable properties (physical, chemical and electrical ones). Currently, the graphene presents a great promise for potential applications in many technological fields such as: sensors, composites, transparent conducting films, solar cells, storage medium of gas, saturable absorber for pulsed laser etc.The development of graphene is a technological challenge; the methods of current production are required with a balance between the facility of the production and the quality of materials. Our present work consist on a digest of the most significant works and protocols presented by the scientific community. It selects ones which ensure a graphene with optimal properties; it also discuss the main physical and chemical phenomenon responsible of the graphene formation. Solvothermal technique is an interesting way to synthesize graphene sheets. Firstly Graphene Oxide (GO) is elaborated, followed by its reduction in different solvents (for example: hydrazine, L-glutathione, Dimethylhydrazine, aluminum powder, etc.). This last approach is regarded as more suitable because of its simplicity, reliability, adequacy on a large scale and production at low cost. Voir les détails
Mots clés : Graphene, solvothermale technique, Chemical reduction
Characterization of the cementation layer by the ultrasonic pulse echo method
it is necessary to measure this layer with a sufficient precision.In this study, we use the ultrasonic pulse echo method as a non destructive testing in thecementation layer characterisation of 12 NC6 steels with a rang of 0.6 mm to 1.5 mm for thecementation thickness.The ultrasonic measurement are based on the reflection of signal at the interface of twomaterials having different impedance and on the determination of the longitudinal elastic wavesvelocity as well as the sound attenuation coefficients based on the Rayleigh model.The paper discuss also the microstructure influence on the ultrasonic measurement parametersand the precision obtained.We conclude our work by analysing the ability of the ultrasonic pulse echo for the cementationlayer measurement Voir les détails
Mots clés : Cementation process, ultrasonic attenuation, reflection coefficient, pulse –echo method
Passive control of tubes by crosscorrelation of ambient noise fields
The tube or pipeline are used for the routing of the uids such asgas, oil or water. The tubes deteriorate during its life. This dete-rioration can reveal defects, from where need for controlling of suchstructure. It is interesting to be able to detect damages in tubes byusing a passive control method. The goal of this work is to show inexperiments the possibility of using the function of cross correlation,between tow signals of noise, in order to make a passive control of thetubular structures. The noise in the tube was generated by ow of uid.The reproducibility of the function of cross correlation and its sensi-tivity to the presence of a defect, were checked for several frequenciesin the frequently band of [200 Hz, 35kHz]. Moreover, the movementof the uid in the tube generates a temperature variation; the inu-ence of this temperature variation on the cross correlation function wasstudied. Voir les détails
Mots clés : Green function, ambiant noise, cross corrélation, tube, flow fluide
Exploitation de la propagation réverbérante des ondes élastiques dans les structures : vers un concept de réseau de capteurs SHM à basse consommation
Les méthodes de CND et d’imagerie ultrasonores classiques utilisent des sources contrˆolées et synchronisées avecles récepteurs et n’exploitent en général que les premiers paquetsd’onde des signaux enregistrés aprés propagation dansle milieu. `A l’inverse, les travaux que nous présentons iciconsistent à exploiter les signaux acoustiques dans toute leur complexité, afin d’extraire le maximum d’information à partir d’un nombre limité de capteurs. Les codas ultrasonores, notamment,issues de trajets de propagation multiples et entrelacés dans les structures offrent un moyen original d’extraire des propriétés structurelles utiles (propriétés des matériaux, dimensions,localisation des sources, d´etection et caract´erisation ded´efaut) des signaux de réverbération excités par des sourcesconnues ou non. En particulier, la possibilité d’utiliser dessources acoustiques naturelles (on parle également de sources≪ ambiantes ≫, ou encore ≪ sources d’opportunité ≫) en lieu etplace de l’émission d’ondes ultrasonores, ouvre la voie vers des réseaux de capteurs ultrasonores passifs (récepteurs uniquement), donc basse consommation et potentiellement autonomes et peuintrusifs. Nous présenterons tout d’abord quelques résultats sur l’extraction d’informations globales à partir des moyennes d’ensemble des codas de réverbération. Puis nous illustrerons la détection de défauts par la méthode de corrélation de bruit pardes exemples d’applications sur différentes structures (plaques,tubes, rails,. . . ). Voir les détails
Mots clés : ondes ´elastiques, propagation réverbérante, SHM
Hollow circular cylinder: application to non destructive testing
Advanced research into non destructive control of industrial pipe works provides several acoustical methods for inspection of their structural integrity. The use of guided waves is one possible solution to detect and identify different flaws. In this paper, we are studying the propagation of guided waves in a tube and the correlation of these last by defects of surface. The dispersion curves of symmetrical modes (longitudinal and torsion) and asymmetrical mode (inflection) have been established. The mode chosen to generate it the second longitudinal mode, for this mode the radial element of displacement is very weak in front of the axial element in the point produced frequency thickness equal to 0.99 MHz.mm where from a weak attenuation, according to our experimental results the L (0, 2) mode is sensitive to the depth variation and the defect circumference. Voir les détails
Mots clés : guided waves, Hollow cylindre, NDT
Influence des forces d’entrainements sur la pénétration de bain de fusion lors le soudage TIG.
Dans ce travail nous nous intéressons à l’étude du comportement thermohydraulique du bain de fusion lors du soudage TIG sans métal d’apport. L’influence des forces d’entrainements sur la morphologie et la pénétration de bain de fusion sera mise au point. Le modèle intègre trois forces prédominantes indépendantes, la force de tension de surface (effet de Marangoni), la force de convection naturelle (flottabilité) et la force électromagnétique. Une simulation numérique 2D de soudage TIG d’une tôle en acier inoxydable 304L est donc menée, en utilisant le code du calcul Comsol Voir les détails
Mots clés : "Modélisation thermohydraulique, soudage TIG, forces d’entrainements, bain de fusion."