Pierre Maréchal | Université du Havre (original) (raw)

Papers by Pierre Maréchal

La synthèse des activités de recherche présentée porte sur l'acoustique ultrasonore. Ces rech... more La synthèse des activités de recherche présentée porte sur l'acoustique ultrasonore. Ces recherches, développés à travers deux axes de recherche que sont l'évaluation et le contrôle non-destructifs (ECND) et les structures phononiques (SP), portent sur les assemblages multicouches de matériaux viscoélastiques et/ou piézoélectriques et les propriétés qui en découlent. Plus précisément, cette Habilitation à Diriger les Recherche comporte trois chapitres.Le premier chapitre porte sur l'étude des structures multicouches périodiques, dites structures phononiques. L'étude théorique, basée sur des formulations matricielles inconditionnellement stables numériquement, porte sur les propriétés spectrales de réflexion, transmission et atténuation résultantes d'une combinaison périodique de couches viscoélastiques. La non-réciprocité de la réflexion sur de telles structures périodiques viscoélastiques est démontrée théoriquement et expérimentalement. Le contrôle actif de tel...

HAL (Le Centre pour la Communication Scientifique Directe), Apr 11, 2022

HAL (Le Centre pour la Communication Scientifique Directe), Aug 24, 2009

La matrice S d'une multicouche plane périodique immergée dans un fluide est construite à partir d... more La matrice S d'une multicouche plane périodique immergée dans un fluide est construite à partir des coefficients de réflexion et de transmission. Les termes de transition obtenus à partir de ses valeurs propres sont associés soit à des modes de période soit à des modes de structures. L'influence de ces modes sur la position et la largeur des bandes interdites sont étudiées dans le cas d'une multicouche de N périodes composées de deux plaques isotropes.

-Les programmes mis en oeuvre ici visent à soulever certains détails des signaux que nous utiliso... more -Les programmes mis en oeuvre ici visent à soulever certains détails des signaux que nous utilisons au quotidien. La qualité des signaux que nous recevons via nos terminaux résultent d'un choix a priori par des experts compétents en la matière, mais dont l'utilisation est trop souvent relayée à des utilisateurs pressés par la simplicité et l'efficacité. Que ces préoccupations soient légitimes n'empêche pas, qui plus est dans une formation universitaire de s'intéresser au codage de l'information et d'en analyser les mécanismes et les limites. Les sons ont cette qualité de faire appel à nos sens, et nos perceptions de soulever la question de la qualité d'un signal. Parmi les outils à disposition, les logiciels libres permettent de faire des choix de compression audio (https://lame.sourceforge.io/index.php), et de constituer des éléments de décision et d'analyse quantitative (https://www.scilab.org/). La question de la compression est très souvent relayée à l'arrière plan bien que centrale dans nos usages, d'où l'intérêt de sensibiliser et former les étudiants à ces questions auxquelles ils sont implicitement confrontés, que ce soit dans leur vie personnelle, leur vie d'étudiant et leur vie professionnelle. Les signaux en question sont compressés pour des raisons historiques de limites de mémoire et de débit. S'intéresser au format MP3 (https://en.wikipedia.org/wiki/MP3), c'est s'intéresser aussi à l'histoire logicielle, celle des formats de fichiers et des motivations de diffusion (https://museumofportablesound.com/mp325-timeline/). Bien que de nombreuses limites matérielles aient été dépassées, le compromis compression/qualité demeure une préoccupation majeure pour les hébergeurs et diffuseurs de contenus. Les vertus d'un codage et d'une compression optimale constituent donc un sujet majeur pour la formation au choix de compromis techniques, économiques, mais aussi éthique au sens de l'amélioration continue de l'utilisation des ressources à disposition. Mots-Clés-Logiciel libre, compression audio, qualité du signal.

HAL (Le Centre pour la Communication Scientifique Directe), Dec 1, 2020

This work explores a wood-polymer composite (WPC) made of a polypropylene (PP) polymer combined w... more This work explores a wood-polymer composite (WPC) made of a polypropylene (PP) polymer combined with olive wood flour (OWF). The longitudinal wave propagation is proposed as an evaluation mean of the WPC viscoelastic properties. Depending on the OWF ratio

The polymerization of a resin is the main interest during the fabrication of a composite material... more The polymerization of a resin is the main interest during the fabrication of a composite material. In the case of a Resin Transfer Molding (RTM) process, the monitoring of resin polymerization can inform about the evolution of the process parameters. In this work, ultrasonic velocity and attenuation in the resin are monitored using a broadband ultrasonic transducer. Using this method, the time dependence of the characterized parameters allows determining the polymerization characteristics such as the beginning, the end or the inflexion point of the studied parameter. Through these measurements, the evolution of polymerization could be related to the process and environmental conditions (such as temperature) in order to consider improvements to the RTM technique.

Smart Materials and Structures, Dec 1, 2022

A one-dimensional piezoelectric phononic crystal (PPC) consisting of a periodic pattern made of t... more A one-dimensional piezoelectric phononic crystal (PPC) consisting of a periodic pattern made of two perfectly bonded materials: one active (piezoelectric), the other passive (elastic) and exhibiting a strong acoustic impedance contrast is studied. We are interested in the tunability of piezoelectric inclusions in order to control the propagation of ultrasonic waves in the MHz range from a nonlinear electrical component connected to the terminals of the piezoelectric elements. After modeling the dynamic resistance of the Schottky diode, based on the piezoelectricity equations, a one-dimensional analytical model is proposed to take into account the resistive impedance effect of this diode connected to the electrodes of the active plate. Thus, we have shown that the application of various electrical boundary conditions (EBCs) on the electrodes (open-circuit, short-circuit, connecting an electrical load) allows to change the effective properties of the piezoelectric plate in particular and those of the PPC in general. The dispersion of the waves is then electrically tuned and, depending on the applied EBCs, we have demonstrated numerically the possibility of opening Bragg or hybridization gaps in the PPC band structure.

HAL (Le Centre pour la Communication Scientifique Directe), Nov 1, 2019

Electromechanical impedance monitoring is investigated to quantify changes in physical and mechan... more Electromechanical impedance monitoring is investigated to quantify changes in physical and mechanical properties during the ageing of composite plates. In this context, an experimental measurement protocol is proposed, on the basis of a broadband 1 MHz center frequency piezoelectric transducer. After a preliminary characterization of the parameters of the transducer itself, the acoustical impedance of the front medium is deduced. More particularly, the acoustical properties such as longitudinal wave velocity and attenuation are identified in the studied composite carbon/epoxy plates. From the electrical measurement results in the MHz frequency range, the acoustical impedance of the plate is plotted in the complex plane, showing characteristic signatures corresponding to the actually monitored composite plate. The ageing is quantified, showing the effectiveness of this non-destructive evaluation method. First, the acoustical parameters of a plate made of a carbon/epoxy composite are modeled in order to study their sensitivity. During the ageing, those acoustical properties are known to evolve significantly, i.e. a decrease of the wave velocity and an increase of the attenuation, which can both be related to the increase of the porosity level in the plate. Secondly, these acoustical properties are evaluated on a set of samples which were submitted to a range of ageing duration from 500 to 5000 h performed at a thermostated temperature of 180°C. The feasibility of the evaluation of the ageing is demonstrated, and the precision of this measurement is discussed both in terms of temperature dependency and reproducibility.

E3S Web of Conferences

In this paper, we studied the propagation of acoustic waves in an acoustic ramified system. Our p... more In this paper, we studied the propagation of acoustic waves in an acoustic ramified system. Our proposed system contains an input waveguide of length d0 and three output lines (three channels), each output line contains a semi-infinite waveguide. The theoretical analysis is based on the Transfer Matrix Method (TMM), which allows us to calculate the three transmission rates T1, T2, T3 and the reflection rate R. We demonstrate that our proposed three-output channels system can be used to design a multifunctional device that functions as an amplitude splitter: an incident sound wave is splited to three output channels. This system is capable of achieving various waveguiding characteristics with perfect channels transmissions.

Journal of Composite Materials, 2021

Although piezocomposite (PC) materials have increasingly attracted researchers, there is still a ... more Although piezocomposite (PC) materials have increasingly attracted researchers, there is still a need to properly and easily derive their properties. We develop a generalized homogenization model (GHM) that accounts for Smith and Cha approaches to evaluate the equivalent characteristics of piezocomposites. This method could be applied to all connectivities patterns, but restricted herein to 2-2 and 1-3 piezocomposites for comparison with Smith (1-3) and Cha (2-2) analytical results. In the proposed GHM is a parameter θ, is changed for various connectivities. The 1-3 and 2-2 PZT-7A/Araldite D (PCs) data are used and equivalent characteristics of these Pcs are determined as function of volume fraction of PZT-7A piezoelectric. Results show that the electromechanical coefficients are well fitted by Voigt and Reuss models. Results obtained for some parameters show that the proposed GHM is consistent with the analytical existing models used for the 1-3 and 2-2 connectivities and is in lin...

Le Centre pour la Communication Scientifique Directe - HAL - Diderot, Nov 1, 2019

Electromechanical impedance monitoring is investigated to quantify changes in physical and mechan... more Electromechanical impedance monitoring is investigated to quantify changes in physical and mechanical properties during the ageing of composite plates. In this context, an experimental measurement protocol is proposed, on the basis of a broadband 1 MHz center frequency piezoelectric transducer. After a preliminary characterization of the parameters of the transducer itself, the acoustical impedance of the front medium is deduced. More particularly, the acoustical properties such as longitudinal wave velocity and attenuation are identified in the studied composite carbon/epoxy plates. From the electrical measurement results in the MHz frequency range, the acoustical impedance of the plate is plotted in the complex plane, showing characteristic signatures corresponding to the actually monitored composite plate. The ageing is quantified, showing the effectiveness of this non-destructive evaluation method. First, the acoustical parameters of a plate made of a carbon/epoxy composite are modeled in order to study their sensitivity. During the ageing, those acoustical properties are known to evolve significantly, i.e. a decrease of the wave velocity and an increase of the attenuation, which can both be related to the increase of the porosity level in the plate. Secondly, these acoustical properties are evaluated on a set of samples which were submitted to a range of ageing duration from 500 to 5000 h performed at a thermostated temperature of 180°C. The feasibility of the evaluation of the ageing is demonstrated, and the precision of this measurement is discussed both in terms of temperature dependency and reproducibility.

Normandie Université ; Université de Sfax (Tunisie), Sep 11, 2020

Ce travail de thèse porte sur l'élaboration et la caractérisation de nouveaux matériaux composite... more Ce travail de thèse porte sur l'élaboration et la caractérisation de nouveaux matériaux composites à base de fibres naturelles. Cette étude consiste à exploiter des renforts végétaux résultant du travail du bois d'olivier introduit sous forme de farine de bois d'olivier (FBO) dans une matrice polymère en polypropylène (PP). Ainsi, deux types de bio-composites PP/FBO ont été fabriqués : les combinaisons polypropylène avec les fibres de farine de bois d'olivier non traitées ou traitées avec de l'amino-silane avec un taux de charge massique de 3%. Suite au traitement chimique, les caractérisations des fibres traitées ont montré une augmentation de taux de cellulose, de la rugosité, de la stabilité thermique et aussi de la cristallinité. Les échantillons de matériaux composites étudiés ont été fabriqués à partir des matières premières PP et FBO, par extrusion bi-vis suivie d'une injection en variant le taux de charge en FBO de 0 à 30%. Les micrographies des facettes de rupture réalisées au microscope électronique à balayage (MEB) montrent une meilleure adhésion entre la matrice et les fibres traitées par rapport à celles non traitées. Dans l'objectif d'une caractérisation des propriétés élastiques, des méthodes de caractérisation destructive par essais mécanique et non destructive par ultrasons, sont confrontées afin d'en établir la correspondance, mais aussi les limites. Il en résulte que la rigidité des bio-composites PP/FBO a été améliorée avec l'augmentation du taux de fibres et l'ajout d'un agent de couplage. Un facteur de corrélation entre les modules de Young estimés est établi entre les valeurs ultrasonores et les valeurs mécaniques. Les vitesses longitudinale et transversale augmentent dans les mêmes proportions que la teneur en fibres et que l'ajout d'un agent de couplage. Enfin, la structure interne des échantillons de bio-composites PP/FBO a été évaluée par réflectométrie ultrasonore et la tomographie par rayons X.

During the Resin Transfer Molding (RTM) process, bubbles can appear and move between fibers and m... more During the Resin Transfer Molding (RTM) process, bubbles can appear and move between fibers and meshes. In this study, a monitoring method for the size and velocity of air bubbles using an ultrasonic phased array transducer is proposed. This method is tested in a flow of a known viscous silicone oil along a sample of fiber preform. By ultrasonic imaging the fiber preform immersed in a viscous flow, a position-time map (x fl , t) is obtained for each acquisition date t acq. These data could be converted to (x fl , z, t acq) data. The bubble motion is extracted from the raw data by separation of the static component from the dynamic part of the signal. As a result, a modified C-scan is obtained and both the instantaneous position and velocity of a bubble could be extracted in the (x, z) plane. Through these measures, the evolution of the bubbles is related to the processes that generate them in order to consider improvements to the RTM technique.

La propagation d’une onde ultrasonore de compression au travers d’une distribution de particules ... more La propagation d’une onde ultrasonore de compression au travers d’une distribution de particules solides identiques localisees aleatoirement dans un liquide visqueux est etudiee. La longueur d’onde de l’onde de compression est supposee grande devant le rayon des particules, et les proprietes effectives dynamiques du milieu sont recherchees.Les coefficients de diffusion d’une sphere solide isolee sont etudies pour differentes polarisations des ondes partielles de mode n incidentes et diffusees. Des expressions approchees en sont donnees pour tout n dans le regime de diffusion de Rayleigh.Dans le cas de particules spheriques, le milieu est modelise par un noyau elastique, de meme materiau et rayon que les particules, et entoure d’une coque emplie du fluide hote. L’ensemble est insone, dans le milieu effectif, par une onde de compression partielle de mode n. Les proprietes effectives sont recherchees par minimisation de la diffusion pour differentes valeurs de n. Le module d’elasticite...

Revue Européenne des Éléments Finis, 1993

Physics Procedia, 2015

Abstract Active materials are investigated as a tuning possibility for phononic crystals. Electro... more Abstract Active materials are investigated as a tuning possibility for phononic crystals. Electromechanical properties of piezoelectric materials electrical and mechanical variables are coupled. Thus, the propagation properties of elastic waves can be tuned using electrical impedance load connected to the piezoelectric layer. In this study, a theoretical one-dimensional model is proposed to calculate the electrical impedance of an active layer located inside a finite periodic structure including both piezoelectric and passive layers. Depending on the electrical impedance load, various effects on the position and the amplitude of the electrical resonance are observed in very good agreement, between experimental and theoretical results.

The polymerization of a resin is of the main interest during the fabrication of a composite mater... more The polymerization of a resin is of the main interest during the fabrication of a composite material. In the case of a Resin Transfer Molding (RTM) process, the monitoring of resin polymerization can inform about the evolution of the process parameters. In this work, ultrasonic velocity and attenuation in the resin are monitored using a broadband ultrasonic transducer. Using this method, the time dependence of the characterized parameters allows determining the polymerization characteristics such as the beginning, the end or the inflexion point of the studied parameter. Through these measurements, the evolution of polymerization, could be related to the process and environmental conditions (such as temperature) in order to consider improvements to the RTM technique.

La synthèse des activités de recherche présentée porte sur l'acoustique ultrasonore. Ces rech... more La synthèse des activités de recherche présentée porte sur l'acoustique ultrasonore. Ces recherches, développés à travers deux axes de recherche que sont l'évaluation et le contrôle non-destructifs (ECND) et les structures phononiques (SP), portent sur les assemblages multicouches de matériaux viscoélastiques et/ou piézoélectriques et les propriétés qui en découlent. Plus précisément, cette Habilitation à Diriger les Recherche comporte trois chapitres.Le premier chapitre porte sur l'étude des structures multicouches périodiques, dites structures phononiques. L'étude théorique, basée sur des formulations matricielles inconditionnellement stables numériquement, porte sur les propriétés spectrales de réflexion, transmission et atténuation résultantes d'une combinaison périodique de couches viscoélastiques. La non-réciprocité de la réflexion sur de telles structures périodiques viscoélastiques est démontrée théoriquement et expérimentalement. Le contrôle actif de tel...

HAL (Le Centre pour la Communication Scientifique Directe), Apr 11, 2022

HAL (Le Centre pour la Communication Scientifique Directe), Aug 24, 2009

La matrice S d'une multicouche plane périodique immergée dans un fluide est construite à partir d... more La matrice S d'une multicouche plane périodique immergée dans un fluide est construite à partir des coefficients de réflexion et de transmission. Les termes de transition obtenus à partir de ses valeurs propres sont associés soit à des modes de période soit à des modes de structures. L'influence de ces modes sur la position et la largeur des bandes interdites sont étudiées dans le cas d'une multicouche de N périodes composées de deux plaques isotropes.

-Les programmes mis en oeuvre ici visent à soulever certains détails des signaux que nous utiliso... more -Les programmes mis en oeuvre ici visent à soulever certains détails des signaux que nous utilisons au quotidien. La qualité des signaux que nous recevons via nos terminaux résultent d'un choix a priori par des experts compétents en la matière, mais dont l'utilisation est trop souvent relayée à des utilisateurs pressés par la simplicité et l'efficacité. Que ces préoccupations soient légitimes n'empêche pas, qui plus est dans une formation universitaire de s'intéresser au codage de l'information et d'en analyser les mécanismes et les limites. Les sons ont cette qualité de faire appel à nos sens, et nos perceptions de soulever la question de la qualité d'un signal. Parmi les outils à disposition, les logiciels libres permettent de faire des choix de compression audio (https://lame.sourceforge.io/index.php), et de constituer des éléments de décision et d'analyse quantitative (https://www.scilab.org/). La question de la compression est très souvent relayée à l'arrière plan bien que centrale dans nos usages, d'où l'intérêt de sensibiliser et former les étudiants à ces questions auxquelles ils sont implicitement confrontés, que ce soit dans leur vie personnelle, leur vie d'étudiant et leur vie professionnelle. Les signaux en question sont compressés pour des raisons historiques de limites de mémoire et de débit. S'intéresser au format MP3 (https://en.wikipedia.org/wiki/MP3), c'est s'intéresser aussi à l'histoire logicielle, celle des formats de fichiers et des motivations de diffusion (https://museumofportablesound.com/mp325-timeline/). Bien que de nombreuses limites matérielles aient été dépassées, le compromis compression/qualité demeure une préoccupation majeure pour les hébergeurs et diffuseurs de contenus. Les vertus d'un codage et d'une compression optimale constituent donc un sujet majeur pour la formation au choix de compromis techniques, économiques, mais aussi éthique au sens de l'amélioration continue de l'utilisation des ressources à disposition. Mots-Clés-Logiciel libre, compression audio, qualité du signal.

HAL (Le Centre pour la Communication Scientifique Directe), Dec 1, 2020

This work explores a wood-polymer composite (WPC) made of a polypropylene (PP) polymer combined w... more This work explores a wood-polymer composite (WPC) made of a polypropylene (PP) polymer combined with olive wood flour (OWF). The longitudinal wave propagation is proposed as an evaluation mean of the WPC viscoelastic properties. Depending on the OWF ratio

The polymerization of a resin is the main interest during the fabrication of a composite material... more The polymerization of a resin is the main interest during the fabrication of a composite material. In the case of a Resin Transfer Molding (RTM) process, the monitoring of resin polymerization can inform about the evolution of the process parameters. In this work, ultrasonic velocity and attenuation in the resin are monitored using a broadband ultrasonic transducer. Using this method, the time dependence of the characterized parameters allows determining the polymerization characteristics such as the beginning, the end or the inflexion point of the studied parameter. Through these measurements, the evolution of polymerization could be related to the process and environmental conditions (such as temperature) in order to consider improvements to the RTM technique.

Smart Materials and Structures, Dec 1, 2022

A one-dimensional piezoelectric phononic crystal (PPC) consisting of a periodic pattern made of t... more A one-dimensional piezoelectric phononic crystal (PPC) consisting of a periodic pattern made of two perfectly bonded materials: one active (piezoelectric), the other passive (elastic) and exhibiting a strong acoustic impedance contrast is studied. We are interested in the tunability of piezoelectric inclusions in order to control the propagation of ultrasonic waves in the MHz range from a nonlinear electrical component connected to the terminals of the piezoelectric elements. After modeling the dynamic resistance of the Schottky diode, based on the piezoelectricity equations, a one-dimensional analytical model is proposed to take into account the resistive impedance effect of this diode connected to the electrodes of the active plate. Thus, we have shown that the application of various electrical boundary conditions (EBCs) on the electrodes (open-circuit, short-circuit, connecting an electrical load) allows to change the effective properties of the piezoelectric plate in particular and those of the PPC in general. The dispersion of the waves is then electrically tuned and, depending on the applied EBCs, we have demonstrated numerically the possibility of opening Bragg or hybridization gaps in the PPC band structure.

HAL (Le Centre pour la Communication Scientifique Directe), Nov 1, 2019

Electromechanical impedance monitoring is investigated to quantify changes in physical and mechan... more Electromechanical impedance monitoring is investigated to quantify changes in physical and mechanical properties during the ageing of composite plates. In this context, an experimental measurement protocol is proposed, on the basis of a broadband 1 MHz center frequency piezoelectric transducer. After a preliminary characterization of the parameters of the transducer itself, the acoustical impedance of the front medium is deduced. More particularly, the acoustical properties such as longitudinal wave velocity and attenuation are identified in the studied composite carbon/epoxy plates. From the electrical measurement results in the MHz frequency range, the acoustical impedance of the plate is plotted in the complex plane, showing characteristic signatures corresponding to the actually monitored composite plate. The ageing is quantified, showing the effectiveness of this non-destructive evaluation method. First, the acoustical parameters of a plate made of a carbon/epoxy composite are modeled in order to study their sensitivity. During the ageing, those acoustical properties are known to evolve significantly, i.e. a decrease of the wave velocity and an increase of the attenuation, which can both be related to the increase of the porosity level in the plate. Secondly, these acoustical properties are evaluated on a set of samples which were submitted to a range of ageing duration from 500 to 5000 h performed at a thermostated temperature of 180°C. The feasibility of the evaluation of the ageing is demonstrated, and the precision of this measurement is discussed both in terms of temperature dependency and reproducibility.

E3S Web of Conferences

In this paper, we studied the propagation of acoustic waves in an acoustic ramified system. Our p... more In this paper, we studied the propagation of acoustic waves in an acoustic ramified system. Our proposed system contains an input waveguide of length d0 and three output lines (three channels), each output line contains a semi-infinite waveguide. The theoretical analysis is based on the Transfer Matrix Method (TMM), which allows us to calculate the three transmission rates T1, T2, T3 and the reflection rate R. We demonstrate that our proposed three-output channels system can be used to design a multifunctional device that functions as an amplitude splitter: an incident sound wave is splited to three output channels. This system is capable of achieving various waveguiding characteristics with perfect channels transmissions.

Journal of Composite Materials, 2021

Although piezocomposite (PC) materials have increasingly attracted researchers, there is still a ... more Although piezocomposite (PC) materials have increasingly attracted researchers, there is still a need to properly and easily derive their properties. We develop a generalized homogenization model (GHM) that accounts for Smith and Cha approaches to evaluate the equivalent characteristics of piezocomposites. This method could be applied to all connectivities patterns, but restricted herein to 2-2 and 1-3 piezocomposites for comparison with Smith (1-3) and Cha (2-2) analytical results. In the proposed GHM is a parameter θ, is changed for various connectivities. The 1-3 and 2-2 PZT-7A/Araldite D (PCs) data are used and equivalent characteristics of these Pcs are determined as function of volume fraction of PZT-7A piezoelectric. Results show that the electromechanical coefficients are well fitted by Voigt and Reuss models. Results obtained for some parameters show that the proposed GHM is consistent with the analytical existing models used for the 1-3 and 2-2 connectivities and is in lin...

Le Centre pour la Communication Scientifique Directe - HAL - Diderot, Nov 1, 2019

Electromechanical impedance monitoring is investigated to quantify changes in physical and mechan... more Electromechanical impedance monitoring is investigated to quantify changes in physical and mechanical properties during the ageing of composite plates. In this context, an experimental measurement protocol is proposed, on the basis of a broadband 1 MHz center frequency piezoelectric transducer. After a preliminary characterization of the parameters of the transducer itself, the acoustical impedance of the front medium is deduced. More particularly, the acoustical properties such as longitudinal wave velocity and attenuation are identified in the studied composite carbon/epoxy plates. From the electrical measurement results in the MHz frequency range, the acoustical impedance of the plate is plotted in the complex plane, showing characteristic signatures corresponding to the actually monitored composite plate. The ageing is quantified, showing the effectiveness of this non-destructive evaluation method. First, the acoustical parameters of a plate made of a carbon/epoxy composite are modeled in order to study their sensitivity. During the ageing, those acoustical properties are known to evolve significantly, i.e. a decrease of the wave velocity and an increase of the attenuation, which can both be related to the increase of the porosity level in the plate. Secondly, these acoustical properties are evaluated on a set of samples which were submitted to a range of ageing duration from 500 to 5000 h performed at a thermostated temperature of 180°C. The feasibility of the evaluation of the ageing is demonstrated, and the precision of this measurement is discussed both in terms of temperature dependency and reproducibility.

Normandie Université ; Université de Sfax (Tunisie), Sep 11, 2020

Ce travail de thèse porte sur l'élaboration et la caractérisation de nouveaux matériaux composite... more Ce travail de thèse porte sur l'élaboration et la caractérisation de nouveaux matériaux composites à base de fibres naturelles. Cette étude consiste à exploiter des renforts végétaux résultant du travail du bois d'olivier introduit sous forme de farine de bois d'olivier (FBO) dans une matrice polymère en polypropylène (PP). Ainsi, deux types de bio-composites PP/FBO ont été fabriqués : les combinaisons polypropylène avec les fibres de farine de bois d'olivier non traitées ou traitées avec de l'amino-silane avec un taux de charge massique de 3%. Suite au traitement chimique, les caractérisations des fibres traitées ont montré une augmentation de taux de cellulose, de la rugosité, de la stabilité thermique et aussi de la cristallinité. Les échantillons de matériaux composites étudiés ont été fabriqués à partir des matières premières PP et FBO, par extrusion bi-vis suivie d'une injection en variant le taux de charge en FBO de 0 à 30%. Les micrographies des facettes de rupture réalisées au microscope électronique à balayage (MEB) montrent une meilleure adhésion entre la matrice et les fibres traitées par rapport à celles non traitées. Dans l'objectif d'une caractérisation des propriétés élastiques, des méthodes de caractérisation destructive par essais mécanique et non destructive par ultrasons, sont confrontées afin d'en établir la correspondance, mais aussi les limites. Il en résulte que la rigidité des bio-composites PP/FBO a été améliorée avec l'augmentation du taux de fibres et l'ajout d'un agent de couplage. Un facteur de corrélation entre les modules de Young estimés est établi entre les valeurs ultrasonores et les valeurs mécaniques. Les vitesses longitudinale et transversale augmentent dans les mêmes proportions que la teneur en fibres et que l'ajout d'un agent de couplage. Enfin, la structure interne des échantillons de bio-composites PP/FBO a été évaluée par réflectométrie ultrasonore et la tomographie par rayons X.

During the Resin Transfer Molding (RTM) process, bubbles can appear and move between fibers and m... more During the Resin Transfer Molding (RTM) process, bubbles can appear and move between fibers and meshes. In this study, a monitoring method for the size and velocity of air bubbles using an ultrasonic phased array transducer is proposed. This method is tested in a flow of a known viscous silicone oil along a sample of fiber preform. By ultrasonic imaging the fiber preform immersed in a viscous flow, a position-time map (x fl , t) is obtained for each acquisition date t acq. These data could be converted to (x fl , z, t acq) data. The bubble motion is extracted from the raw data by separation of the static component from the dynamic part of the signal. As a result, a modified C-scan is obtained and both the instantaneous position and velocity of a bubble could be extracted in the (x, z) plane. Through these measures, the evolution of the bubbles is related to the processes that generate them in order to consider improvements to the RTM technique.

La propagation d’une onde ultrasonore de compression au travers d’une distribution de particules ... more La propagation d’une onde ultrasonore de compression au travers d’une distribution de particules solides identiques localisees aleatoirement dans un liquide visqueux est etudiee. La longueur d’onde de l’onde de compression est supposee grande devant le rayon des particules, et les proprietes effectives dynamiques du milieu sont recherchees.Les coefficients de diffusion d’une sphere solide isolee sont etudies pour differentes polarisations des ondes partielles de mode n incidentes et diffusees. Des expressions approchees en sont donnees pour tout n dans le regime de diffusion de Rayleigh.Dans le cas de particules spheriques, le milieu est modelise par un noyau elastique, de meme materiau et rayon que les particules, et entoure d’une coque emplie du fluide hote. L’ensemble est insone, dans le milieu effectif, par une onde de compression partielle de mode n. Les proprietes effectives sont recherchees par minimisation de la diffusion pour differentes valeurs de n. Le module d’elasticite...

Revue Européenne des Éléments Finis, 1993

Physics Procedia, 2015

Abstract Active materials are investigated as a tuning possibility for phononic crystals. Electro... more Abstract Active materials are investigated as a tuning possibility for phononic crystals. Electromechanical properties of piezoelectric materials electrical and mechanical variables are coupled. Thus, the propagation properties of elastic waves can be tuned using electrical impedance load connected to the piezoelectric layer. In this study, a theoretical one-dimensional model is proposed to calculate the electrical impedance of an active layer located inside a finite periodic structure including both piezoelectric and passive layers. Depending on the electrical impedance load, various effects on the position and the amplitude of the electrical resonance are observed in very good agreement, between experimental and theoretical results.

The polymerization of a resin is of the main interest during the fabrication of a composite mater... more The polymerization of a resin is of the main interest during the fabrication of a composite material. In the case of a Resin Transfer Molding (RTM) process, the monitoring of resin polymerization can inform about the evolution of the process parameters. In this work, ultrasonic velocity and attenuation in the resin are monitored using a broadband ultrasonic transducer. Using this method, the time dependence of the characterized parameters allows determining the polymerization characteristics such as the beginning, the end or the inflexion point of the studied parameter. Through these measurements, the evolution of polymerization, could be related to the process and environmental conditions (such as temperature) in order to consider improvements to the RTM technique.

Analytical models can be useful tools to develop efficient transducers dedicated to a specific ap... more Analytical models can be useful tools to develop efficient transducers dedicated to a specific application field. This work proposes a homogenization technique for establishing the effective coefficients and parameters of 1-3 piezocomposite whose both phases are piezoelectrically active. Such piezocomposite materials may have homogenized electromechanical properties resulting from positive hybrid effect. A numerical simulation of the effective parameters resulting from a PZT-5A / PVDF-TrFE composition shows that, volume fraction influences significantly on the properties of the piezocomposite and consequently on its behaviour in service. As an end-user application for ultrasound imaging, those piezocomposite materials are effectively integrated in a piezocomposite transducer, coupled with a dedicated backing. The resulting characteristics in terms of impulse response and associated electroacoustic echo are compared and discussed for typical configurations. A method for the optimization of the design of such piezocomposite transducer is presented. Specific estimators based on the bandwidth flatness BWF and bandwidth amplitude product BWA are proposed as stable and smooth criteria for an optimization procedure.

Abstract Detecting porosities of different scales, both micro and macro, is a current problem in ... more Abstract Detecting porosities of different scales, both micro and macro, is a current problem in the development of composite materials. This is especially true for composite materials manufactured using Resin Transfer Molding (RTM). When injecting resin in the fibrous preform porosities appear, originating essentially because of air trapped in the fiber matrix. Consequently, the interaction between air bubbles and fibers has been the subject of several numerical investigations. In this study, we propose an original experimental method to monitor the interaction of air bubbles with a fibrous matrix. A 10 MHz center frequency ultrasonic phased array transducer is used to monitor air bubbles in the millimeter range. The ultrasonic imaging method is first tested only with bubbles ascending in a channel containing silicone oil. Then it is tested again in a sample of fiber matrix immersed in the same channel. The results prove the effectiveness of the measurement process. These results then can be used to find a correlation between the appearance of porosities and the processes that generate them in order to consider how to improve RTM. They can also be used to understand the interaction phenomena between bubbles and folds in order to improve RTM process.

A lens-focused single-element transducer designed for high-resolution medical imaging requires a ... more A lens-focused single-element transducer designed for high-resolution medical imaging requires a high ratio of radius of curvature to source radius. Therefore, classical models neglecting the radial contribution may not be accurate. The objective of this study is to evaluate the contribution of radial displacement to the pressure response of the transducer, both in terms of focal spot and pulse response characteristics. To achieve this objective, two finite element method calculations (FEM) were performed (commercial ATILA software), namely those for free and clamped radial displacements. A propagation code adapted to an axisymmetric transducer geometry was implemented to compare the radiated fields, and FEM results for the transducer surface were used as inputs to obtain the radiated fields. Subsequently, the differences between the results of the two calculations results were determined. However, it was demonstrated that the radial displacements slightly affect the propagated field and can therefore be neglected in realistic transducer designs. Moreover, the effects of lens acoustic properties were studied for realistic configurations in terms of resolution and sensitivity to obtain an optimal ultrasound image quality.

Recent fundamental results concerning the ultimate performance of electromagnetic absorbers were ... more Recent fundamental results concerning the ultimate performance of electromagnetic absorbers were adapted and extrapolated to the field of sound waves. It was possible to deduce some appropriate figures of merit indicating whether a particular structure was close to the best possible matching properties. These figures of merit had simple expressions and were easy to compute in practical cases. Numerical examples illustrated that conventional state-of-the-art matching structures had an overall efficiency of approximately 50% of the fundamental limit. However, if the bandwidth at
6 dB was retained as a benchmark, the achieved bandwidth would be, at most, 12% of the fundamental limit associated with the same mass for the matching structure. Consequently, both encouragement for future improvements and accurate estimates of the surface mass required to obtain certain desired broadband properties could be provided. The results presented here can be used to investigate the broadband sound absorption and to benchmark passive and active noise control systems.

Solidly mounted integrated transducers with a Bragg cell inserted between the piezoelectric film ... more Solidly mounted integrated transducers with a Bragg cell inserted between the piezoelectric film and the substrate are investigated for high frequency ultrasonic applications. A numerically stable recursive one dimensional transmission/reflection model was used to analyze the behavior of the periodic structure. This theoretical analysis includes the study of the influence of the acoustic properties of the constitutive layer, the effect of the number of cells and their arrangement. A 35 MHz integrated transducer consisting in a PZT ceramic laid down on a Au/PZT Bragg cell deposited on a porous substrate was fabricated and characterized. Both theoretical and experimental results highlight the interest of using a periodic structure for high frequency ultrasonic applications.

In this study, the real time ultrasonic monitoring is investigated to quantify changes in physica... more In this study, the real time ultrasonic monitoring is investigated to quantify changes in physical and mechanical properties during the manufacture of composite structures. In this context, an experimental transmission was developed with the aim of characterizing a high temperature polymerization reaction and post-curing properties using an ultrasonic method. First, the monitoring of ultrasonic parameters of a thermosetting resin is carried out in a device reproducing the experimental conditions for manufacturing a composite material with a process known as RTM, that is to say an isothermal polymerization at T = 160°C. During this curing, the resin is changing from its initial viscous liquid state to its final viscous solid state. Between those states, a glassy transition stage is observed, during which the physical properties are strongly changing, i.e. an increase of the ultrasonic velocity up to its steady value and a transient increase of the ultrasonic attenuation. Second, the ultrasonic inspection of the thermosetting resin is performed during a heating and cooling process to study the temperature sensitivity after curing. This type of characterization leads to identifying the ultrasonic properties dependence before, during and after the glassy transition temperature T g . Eventually, this study is composed of two complementary parts: the first is useful for the curing optimization, while the second one is fruitful for the post-processing characterization in a temperature range including the glassy transition temperature T g .

In this paper, a theoretical and experimental study of the electric impedance of a piezoelectric ... more In this paper, a theoretical and experimental study of the electric impedance of a piezoelectric plate connected to a negative capacitance is performed in the MHz frequency range. The negative capacitance is realized with a circuit using current conveyors (CCII+). This circuit allows us to achieve important values of negative capacitance, of the same order of the static capacitance of the piezoelectric plate studied. Mason’s model is considered for the theoretical characterization of the piezoelectric plate connected to the negative capacitance circuit. The experimental results show a large tunability of the frequency of the piezoelectric parallel resonance over a range of 1.1 MHz to 1.28 MHz. Moreover, according to the value of the negative capacitance, the effective electromechanical coupling factor of the piezoelectric plate is evaluated. With a very good agreement with the theoretical estimation, an increase of approximately 50% of the effective electromechanical coupling factor is experimentally measured.

High frequency electrical impedance measurements on PZT thick film structures were used to charac... more High frequency electrical impedance measurements on PZT thick film structures were used to characterise thin layers of parylene for acoustic matching applications. The parylene properties (i.e. longitudinal wave velocity and acoustic impedance) were obtained in a realistic configuration for transducer applications. The measured parylene properties were compatible with medical imaging requirements, in particular for high frequency, since the deposited thickness can be controlled with high accuracy (around 1 µm). The mean longitudinal wave velocity was measured at 2135 m/s and corresponding acoustic impedance was 2.75 MRa. Three high frequency single element transducers were simulated to show that using parylene as a matching layer is a good trade-off between transducer performance and the technical process.

A successful fabrication process of textured ceramics by homo-template grain growth (HTGG) is des... more A successful fabrication process of textured ceramics by homo-template grain growth (HTGG) is described. Two samples fabricated with this technique were characterised. Functional properties obtained are competitive with for example a thickness coupling factor over 50%. Different characteristics were compared with those obtained by a unit cell model previously developed for piezocomposites and extended to the case of two piezoelectric phases. Behaviours of several connectivities (0-3, 3-0 and 3-3) are calculated and results show that the spatial arrangement does not have a great influence on effective parameters. A transducer based on a textured ceramic sample has been fabricated and characterised. The measured performance shows the efficiency of these new piezoelectric materials. Finally, electroacoustic responses of identical single element transducer configurations have been simulated. They show that a sensitivity increase of 3 dB can be obtained at equivalent relative bandwidth of 40% with textured ceramic sample in comparison with PMN-PT ceramic used as a matrix in the textured ceramic.

Piezoelectric textured ceramics obtained by homo-template grain growth (HTGG) were recently demon... more Piezoelectric textured ceramics obtained by homo-template grain growth (HTGG) were recently demonstrated. A simple model with several assumptions has been used to calculate effective parameters of these new materials. Different connectivities have been simulated to show that spatial arrangements between the considered phases have little influence on the effective parameters, even through the 3-0 connectivity delivers the highest electromechanical thickness factor. A transducer based on a textured ceramic sample has been fabricated and characterised to show the efficiency of these piezoelectric materials. Finally, in a single element transducer configuration, simulation shows an improvement of 2 dB sensitivity for a transducer made with textured ceramic in comparison with a similar transducer design based on standard soft PZT (at equivalent bandwidths).

This work deals with the study of a plane periodic multilayer structure in which the elementary s... more This work deals with the study of a plane periodic multilayer structure in which the elementary stack consists of two plates in contact: one in aluminum (AL) and the other one in polyethylene (PE). These isotropic materials, present a high acoustic impedance contrast. The attenuation of the longitudinal and transverse waves is taken into account in the polyethylene but neglected in the aluminum plate. The effect of different defects is analyzed. Firstly, we focus on the effect of the presence of grease inclusion in the polyethylene plate (considering the two plates of the elementary stack in perfect contact). Secondly, the effect of disbond simulated by the insertion of a thin Teflon layer between the interfaces of the two layers constituting the elementary stack of the multilayer structure is investigated. Finally, the effect of the stacking sequences of the multilayer is analyzed. In order to obtain the effective acoustic parameters of polyethylene layer, allowing to evaluate the reflection and transmission coefficients using the stiffness matrix method developed by Rokhlin et al., four homogenization models are analyzed, then the best one to our configuration is chosen. The comparison of the simulation results is carried out.

Piezocomposite design for dedicated ultrasonic imaging applications requires precise homogenizat... more Piezocomposite design for dedicated ultrasonic imaging applications requires precise homogenization models for predicting the electromechanical characteristics of the new material. Thus, several homogenization models have been developed. As part of this work, we applied several analytical homogenization models for piezocomposite of 2–2 and 1–3 connectivities. To validate these analytical models, a comparative study was made between various models and experimental measurements. As a result, these homogenized electromechanical properties are effectively used for the calculation and comparison of electroacoustic response for typical transducers aimed at ultrasound imaging applications. An optimal design of transducer aimed at ultrasound imaging applications is proposed as a dedicated imaging performance index, elaborated through a trade-off between sensitivity and bandwidth.

Abstract In this paper the monitoring of ultrasonic parameters of a thermosetting resin during an... more Abstract In this paper the monitoring of ultrasonic parameters of a thermosetting resin during an isothermal curing process is described. The ultrasonic properties are studied within the context of the monitoring of composite plate production by resin transfer molding (RTM). These ultrasonic characteristics can be related directly to cure kinetic models. An ultrasonic method, based on the measurement of the elastic constant and associated mechanical loss has been developed to identify the variations of the phase transformation. To study the reaction kinetics, the time dependence of the elastic coefficient is modeled using a Weibull distribution. The approximate time derivative form of this Weibull model makes it possible to find the relationship between ultrasonic parameters and the chemical Kamal model. The ultrasonic monitoring of a cooling process was also performed to study the temperature sensitivity after curing. Thanks to experimental measurements of the ultrasonic velocity and attenuation, the power law coefficient variations and their temperature sensitivity can be examined. The resulting viscoelastic Cole-Cole parameters were estimated and a frequency-temperature (f, T) model was proposed.

We consider a disordered suspension of spherical silica particles in water. For a particle size o... more We consider a disordered suspension of spherical silica particles in water. For a particle size of a few hundred nanometres and concentration (volume fraction) around 0.15 to 0.2, experiments conducted in the MHz range have shown that the non ideal nature of water must be taken into account for the "longitudinal" coherent wave attenuation to be understood, because of wave conversions, from longitudinal to shear and then back to longitudinal, occurring at each pair of scattering events. We are interested here in the properties of the "shear" coherent wave that are given by the expansion of its squared wavenumber, around that in the absence of particles, in powers of the concentration. At 1 MHz and a particle radius of 0.05 μm, we show that convergence of the modal series involved in that expansion may be reached after three terms: we use ten terms subsequently. We study the evolution of both the effective shear velocity and attenuation with concentration, as well as that of the effective shear viscosity deduced therefrom.

Recent fundamental results concerning the ultimate performance of electromagnetic absorbers were ... more Recent fundamental results concerning the ultimate performance of electromagnetic absorbers were adapted and extrapolated to the field of sound waves. It was possible to deduce some appropriate figures of merit indicating whether a particular structure was close to the best possible matching properties. These figures of merit had simple expressions and were easy to compute in practical cases. Numerical examples illustrated that conventional state-of-the-art matching structures had an overall efficiency of approximately 50% of the fundamental limit. However, if the bandwidth at -6 dB was retained as a benchmark, the achieved bandwidth would be, at most, 12% of the fundamental limit associated with the same mass for the matching structure. Consequently, both encouragement for future improvements and accurate estimates of the surface mass required to obtain certain desired broadband properties could be provided. The results presented here can be used to investigate the broadband sound absorption and to benchmark passive and active noise control systems.

In linear acoustics, the pressure field transmitted through a plate immersed in water is commonly... more In linear acoustics, the pressure field transmitted through a plate immersed in water is commonly used to determine the characteristics of the object. The aim of this work is to extend the approach to the quasi-linear case. The so-called insertion/substitution method consists in comparing the amplitude of the transmitted field with and without the sample whose parameters are to evaluate. An initially sinusoidal plane wave normally incident upon the plate is considered. The second order pressure field is described analytically, based on the solution to the Westervelt equation, from series of reflected and transmitted waves at the interfaces. Attenuation, dispersion and diffraction effects for the fundamental component are included in the model. Firstly, it is shown that the derived expression can be separated into three components according that harmonic generation occurs before, in or beyond the plate. Secondly, the source terms for harmonic generation are identified. Furthermore, experimental data obtained from aluminum plates are compared to results from the analytical expressions. The ability to deduce the nonlinear coefficient of a solid plate from such an experimental configuration is discussed

Ultrasonic testing is a technique frequently used in the field of nondestructive evaluation given... more Ultrasonic testing is a technique frequently used in the field of nondestructive evaluation given the fact that ultrasonic waves are directly related to the mechanical behavior of materials. It is for this reason that mechanical waves are often involved in solid material testing and the evaluation of their mechanical properties. As such, ultrasonic velocity is often used to identify so-called healthy concrete in comparison to deteriorated concrete. The objective of the present study is to determine Young’s modulus of a bio composite using two methods: ultrasonic and mechanical methods. For this, a bio-composite based on polypropylene (PP) as a matrix and the olive wood flour (OWF) as a reinforcement was elaborated with extrusion using a twin extruder following by the injection in the form of 4 mm thick plate for ultrasonic control and standardized specimens for tensile testing. The longitudinal and transversal velocity of propagation of the wave in the plates is measured with the technique of immersion in water using transducer at 5 MHz center frequency in order to determinate the ultrasonic Young’s modulus. Results show that the ultrasonic Young’s modulus of the studied bio-composite is different than that mechanical Young’s modulus. The causes of this difference will be studied.

The polymerization of a resin is the main interest during the fabrication of a composite material... more The polymerization of a resin is the main interest during the fabrication of a composite material. In the case of a Resin Transfer Molding (RTM) process, the monitoring of resin polymerization can inform about the evolution of the process parameters. In this work, ultrasonic velocity and attenuation in the resin are monitored using a broadband ultrasonic transducer. Using this method, the time dependence of the characterized parameters allows determining the polymerization characteristics such as the beginning, the end or the inflexion point of the studied parameter. Through these measurements, the evolution of polymerization could be related to the process and environmental conditions (such as temperature) in order to consider improvements to the RTM technique.

During the Resin Transfer Molding (RTM) process, bubbles can appear and move between fiber strand... more During the Resin Transfer Molding (RTM) process, bubbles can appear and move between fiber strands and fiber folds. In this study, a monitoring method for the size and velocity of air bubbles using an ultrasonic phased array transducer is proposed. This method is tested in a flow of known viscous silicone oil along a sample of fiber preform. By ultrasonic imaging the fiber preform immersed in a viscous flow, a position-time map (xfl, t) is obtained for each acquisition date tacq. These data could be converted to (xfl, z, tacq) data. The bubble motion is extracted from the raw data by separation of the static component from the dynamic part of the signal. As a result, a modified C-scan is obtained and both the instantaneous position and velocity of a bubble could be extracted in the (x, z) plane. Through these measures, the evolution of the bubbles is related to the processes that generate them in order to consider improvements to the RTM technique.

Based on previous work, screen-printing technology was used to elaborate an improved integrated p... more Based on previous work, screen-printing technology was used to elaborate an improved integrated piezoelectric structure relatively to a reference sample [1]. An active PZT layer doped with PGO to lower sintering temperature at 800°C was printed on a porous unpoled PZT substrate which was chosen to withstand such a temperature. Moreover, the acoustical impedance of this substrate is close to that of the deposited piezoelectric thick film, making it an adequate backing for a wideband device. Thus, a short pulse-echo response is obtained, but the resonance frequency is lowered. Additional layers such as a back electrode and a dense barrier layer were interposed between the substrate and the piezoelectric film. These passive and active layers have a significant influence on the performance of the high frequency transducer. Therefore, their thickness and acoustic propeties must be controlled precisely for an optimization of the structure. The center frequency and active source radius of the transducer were increased in comparison to the reference sample, resulting in an improved radiation pattern. In vivo human skin images were performed with an imaging system for two of the prototype broadband high frequency transducer.

Le suivi ultrasonore de proprietes durant la fabrication de materiaux composites permet d’effectu... more Le suivi ultrasonore de proprietes durant la fabrication de materiaux composites permet d’effectuer un contrôle sante de pièces composites en cours de fabrication. Ce thème de recherche se situe dans le contexte du suivi en temps reel des proprietes, tant au niveau de la detection de defauts qu’au niveau de la qualite du produit fini. Un dispositif experimental à ete mis au point, visant à contrôler un pli de fibres de carbones, avec des defauts integres, à l’interieur d’un moule en aluminium. Un transducteur multi-element lineaire haute resolution est utilise pour obtenir une resolution optimale. Une première approche consiste à suivre le deplacement des fibres avec des C-scan en deux dimension (x, y). Une deuxième approche a ete proposee, avec des C-scan en profondeur (x, y, z), afin de localiser les defauts internes et de visualiser le profil des plis. Enfin, une cartographie des plaques composites permet d’obtenir un C-scan des proprietes ultrasonores: vitesse et attenuation.

Focusing ultrasound is needed for high resolution imaging applications such as non destructive te... more Focusing ultrasound is needed for high resolution imaging applications such as non destructive testing (NDT) or medical imaging. Its effects are explored in the case of a single-element transducer focused with a lens, and electrically driven with a broadband excitation. The electro-acoustic response very near the surface of the transducer is first modelled using a finite element method (ATILA). This response in the very near-field is then propagated in water thanks to two codes. These results are presented and compared. Using these tools, the electro-acoustic response is investigated at the focal point, as a function of the acoustic impedance of the lens.

Phonic crystals (PC) are of primary interest for their numerous applications and developments. A... more Phonic crystals (PC) are of primary interest for their numerous applications and developments. An area of investigation for periodic plane structures lead to selective filters, and more particularly to solidly mounted resonators (SMR). This study is aimed at showing the practical limits of viscoelasticity in one of the constitutive layers for the design of a reflection spectrum. Here, the studied configuration is designed for laboratory purpose, with an elementary period constituted of two layers n = 1, 2. Their properties are dn, Zn, and an, their thickness, acoustic impedance and attenuation, respectively. The N-periodic plane multilayer structure is immersed in water of acoustic impedance Z0. This immersed periodic structure could be summarized with the set of acoustic impedance Z0;(Z1;Z2)´N;Z0 and associated set of thickness (d1;d2)´N.

Les travaux presentes concernent la comparaison des traces theoriques et experimentaux des coeffi... more Les travaux presentes concernent la comparaison des traces theoriques et experimentaux des coefficients de reflexion et de transmission d’une multicouche plane periodique composee de N periodes (1<N<5), dans le domaine de frequences 0,5-3,5 MHz. La periode est constituee de deux plaques collees, l’une en aluminium, l’autre en polyethylène. Ces materiaux, supposes isotropes, presentent un fort contraste d’impedance. L’attenuation des ondes longitudinales et transversales est prise en compte pour le polyethylène et negligee pour l’aluminium. Theoriquement, les coefficients de reflexion et de transmission sont obtenus par la methode de la matrice des rigidites elaboree par Rokhlin et al.. Dans ce calcul, les plaques sont supposees en contact parfait, la presence de la colle etant negligee. On montre theoriquement que, suivant le cote d’insonation, les traces des coefficients de reflexion sont differents et ceux des coefficients de transmission sont identiques. Ces resultats sont verifies experimentalement. On constate par ailleurs que la prise en compte de l’attenuation attenue la formation de bandes d’arrêt sur les differents coefficients. Les courbes de dispersion theoriques et experimentales sont comparees pour differentes valeurs de N (nombre de periodes). Enfin, l’importance de la precision et de la regularite des proprietes acoustiques et geometriques des plaques constituant une periode est discutee ; une deperiodisation même legère peut influer fortement sur l’allure des traces.

In this paper, the use of a Bragg cell between the piezoelectric film and the substrate is invest... more In this paper, the use of a Bragg cell between the piezoelectric film and the substrate is investigated in high frequency ultrasonic transducers for non destructive testing or medical imaging. In this view, a recursive transmission / reflection model is presented. The influence of the constitutive layer properties of a Bragg cell is studied for two compatible sets of materials (Au/PZT or Pt/Al2O3). This model is then used in order to highlight the interest of a periodic structure loaded with a substrate. Finally, experimental results on a Bragg cell are reported and discussed.

In previous work on acoustical lens effect, a model based on the annular decomposition of an axis... more In previous work on acoustical lens effect, a model based on the annular decomposition of an axisymmetric focused piezoelectric transducer was described and found to be in agreement with FEM and experimental results. The design of a focused transducer must take into account both radiation and transduction properties. These complex models such as FEM, FDTD and PSTD methods take into account radial modes, but their influence is not significant compared to the thickness mode when the radius to thickness ratio of the piezoelectric source is high enough. This assumption was verified since the mean error was evaluated lower than 2% for the chosen lens materials and geometries. Therefore, an efficient transfer function to model the lens was proposed. This annular decomposition allows to determine the input acoustical impedance of the lens and it is shown that the lens can be considered as a semi-infinite propagation medium. For an experimental comparison, a transducer structure based on a 1-3 piezocomposite is chosen for its high thickness coupling factor kt = 64% and low acoustical impedance Z = 14 MRa. This piezoelectric source is damped by an epoxy backing and matched to the propagation medium with two quarter wavelength matching layers. Based on this structure, different types of focusing techniques are investigated: geometrical, concave lens with high velocity material and convex lens with low velocity material. Experimental results obtained on the manufactured transducers are finally compared to simulated ones and the performance of the different focusing strategies is discussed.

Electromechanical impedance monitoring is investigated to quantify changes in physical and mechan... more Electromechanical impedance monitoring is investigated to quantify changes in physical and mechanical properties during the ageing of composite plates. In this context, an experimental measurement protocol is proposed, on the basis of a broadband 1 MHz center frequency piezoelectric transducer. After a preliminary characterization of the parameters of the transducer itself, the acoustical impedance of the front medium is deduced. More particularly, the acoustical properties such as longitudinal wave velocity and attenuation are identified in the studied composite carbon/epoxy plates. From the electrical measurement results in the MHz frequency range, the acoustical impedance of the plate is plotted in the complex plane, showing characteristic signatures corresponding to the actually monitored composite plate. The ageing is quantified, showing the effectiveness of this non-destructive evaluation method. First, the acoustical parameters of an carbon/epoxy composite plate are modeled in order to study their sensitivity. During the ageing, those acoustical properties are known to evolve significantly, i.e. a decrease of the wave velocity and an increase of the attenuation, which can both be related to the increase of the porosity level in the plate. Secondly, these acoustical properties are evaluated on a set of samples which were submitted to a range of ageing duration from 500 to 5000 h performed at a thermostated temperature of 180°C. The feasibility of the evaluation of the ageing is demonstrated, and the precision of this measurement is discussed both in terms of temperature dependency and reproducibility.

Le suivi ultrasonore de proprietes durant la fabrication de materiaux composites permet d’effectu... more Le suivi ultrasonore de proprietes durant la fabrication de materiaux composites permet d’effectuer un contrôle sante de pièces composites en cours de fabrication. Ce thème de recherche se situe dans le contexte du suivi en temps reel des proprietes, tant au niveau de la detection de defauts qu’au niveau de la qualite du produit fini. Un dispositif experimental à ete mis au point, visant à contrôler un pli de fibres de carbones, avec des defauts integres, à l’interieur d’un moule en aluminium. Un transducteur multi-element lineaire haute resolution est utilise pour obtenir une resolution optimale. Une première approche consiste à suivre le deplacement des fibres avec des C-scan en deux dimension (x, y). Une deuxième approche a ete proposee, avec des C-scan en profondeur (x, y, z), afin de localiser les defauts internes et de visualiser le profil des plis. Enfin, une cartographie des plaques composites permet d’obtenir un C-scan des proprietes ultrasonores: vitesse et attenuation.

In this study, the real time ultrasonic monitoring is investigated to quantify changes in physica... more In this study, the real time ultrasonic monitoring is investigated to quantify changes in physical and mechanical properties during the manufacture of composite structures. In this context, an experimental transmission was developed with the aim of characterizing a high temperature polymerization reaction and post-curing properties using an ultrasonic method. First, the monitoring of ultrasonic parameters of a thermosetting resin is carried out in a device reproducing the experimental conditions for manufacturing a composite material with a process known as RTM, that is to say an isothermal polymerization at T = 160°C. During this curing, the resin is changing from its initial viscous liquid state to its final viscous solid state. Between those states, a glassy transition stage is observed, during which the physical properties are strongly changing, i.e. an increase of the ultrasonic velocity up to its steady value and a transient increase of the ultrasonic attenuation. Second, the ultrasonic inspection of the thermosetting resin is performed during a heating and cooling process to study the temperature sensitivity after curing. This type of characterization leads to identifying the ultrasonic properties dependence before, during and after the glassy transition temperature Tg . Eventually, this study is composed of two complementary parts: the first is useful for the curing optimization, while the second one is fruitful for the post-processing characterization in a temperature range including the glassy transition temperature Tg .

Abstract A one dimensional Phononic Crystals (PC) composed of a periodic stack including piezoele... more Abstract A one dimensional Phononic Crystals (PC) composed of a periodic stack including piezoelectric plates is studied. When the size of the pattern is a multiple of the wavelength, Bragg gaps appear based on interference mechanisms. In addition to this property, it is shown in this paper that the use of active piezoelectric plates allows opening hybridization gaps. These gaps are due to a coupling of an electrical resonance with the propagation of the acoustic waves. The electrical resonance is obtained by connecting inductances on the piezoelectric plates. Both experimental and analytical studies are conducted in this paper in order to study this phenomenon.

This work deals with the control of the propagation of ultrasonic waves in a piezoelectric phonon... more This work deals with the control of the propagation of ultrasonic waves in a piezoelectric phononic crystal (PC) by mean of electrical negative capacitance charges. In a first step, a theoretical and experimental study of a unit block of the PC constituted by a piezoelectric plate connected to a negative capacitance is performed in the MHz frequency range. An electrical circuit based on the current feedback operational amplifiers is proposed in order to achieve experimentally the negative capacitance. In a second step, the experimental transmission of waves through a PC constituted by a stack of piezoelectric layers connected to negative capacitance is studied and compared to the theoretical band structure of the piezoelectric PC.

We consider a one dimensional Phononic Crystal (PC) based on a stack of plates including piezoele... more We consider a one dimensional Phononic Crystal (PC) based on a stack of plates including piezoelectric layers. The model takes into account electrical external circuit connected to the piezoelectric layers with the exception of the layer for which the impedance is evaluated. Only longitudinal waves propagation (thickness modes) through the PC is taken into account. Experimentally, a finite periodic structure based on a PMMA/Pz26 elementary stack is studied in the MHz frequency range. Different types of external electrical load are investigated. The electrical impedance of an active layer is affected by the electrical boundary conditions and is related to changes in the band structure of the acoustic transmission through the PC.

PhD Thesis, 2012

Les etudes experimentales menees au LOMC sur le procede de fabrication des materiaux composites R... more Les etudes experimentales menees au LOMC sur le procede de fabrication des materiaux composites RTM (Resin Transfer Moulding), montrent l'apparition de bulles, à differentes echelles, au cours de la diffusion de la resine dans le reseau fibreux. Elles se deplacent pendant le processus, certaines se resorbent, d'autres persistent et diminuent ainsi la qualite globale du produit fini. Le sujet de cette thèse consiste à etudier l'apparition des bulles le long de fibres enfermees dans un canal de production. L'utilisation de mesures ultrasonores permet de suivre le front de liquide lors de son deplacement. Au moyen de ces mesures, l'apparition et l'evolution des bulles sont reliees aux processus qui les genèrent pour tenter de trouver des ameliorations à la technique de mise en forme. Par traitement des signaux, des bulles sont detectees et leur evolution est suivie sur le trajet d'ecoulement de la resine. Trois parties principales sont abordees au cours de cette thèse. Dans la première partie le comportement des ondes ultrasonores interagissant avec la resine en cours de polymerisation a ete etudie. La deuxième partie consiste à etudier les conditions de detections de bulles en utilisant un transducteur multielements au sein de la resine. Dans la dernière partie, le suivi d'evolution des bulles dans le materiau composite en cours de fabrication a egalement ete realise. Le but est de quantifier les concentrations de bulles relativement au taux de fibres et de resine. En perspective, des techniques d'imagerie ultrasonore utilisant l'effet Doppler ou encore des proprietes de l'acoustique non lineaire pourraient être envisagees. Le developpement des techniques de contrôles d'END (Evaluation Non Destructive) lors de la realisation de materiaux composites vise à permettre une meilleure comprehension des phenomènes et à completer les bases de donnees utilisees lors des simulations numeriques.

Cette thèse porte sur l’evaluation et la caracterisation non destructives (END/CND) par ultrasons... more Cette thèse porte sur l’evaluation et la caracterisation non destructives (END/CND) par ultrasons de materiaux composites contribuant en partie au concept de contrôle sante structural (SHM). Plus particulièrement, les phenomènes d’adhesion et de vieillissement de structures sandwichs composites à âme en nid d’abeille sont d’un interêt determinant pour l’aeronautique. Les proprietes liees à ces deux phenomènes ont ete etudiees à l’aide de modèles theoriques, de simulations numeriques et de resultats experimentaux. Sur la base de travaux anterieurs, les ondes de Lamb ont permis de caracteriser l’adhesion et le vieillissement. Des simulations complementaires par elements finis ont ete menees avec le logiciel Comsol Multiphysics©.Des defauts d’adhesion tels que les delaminages ou decohesions ont pu être detectes et localises au moyen de la transformee de Fourier à fenêtre glissante, par simulation et par l’experience. Dans la perspective de cadences d’END industrielles, les transducteurs multielements permettent une inspection et une caracterisation locales du collage. À titre de comparaison, la Mod{\'{e}}lisation par serie de Debye (DSM) a permis de resoudre localement le problème inverse sur un plan de coupe d’un composite à nid d’abeille.Le vieillissement de structures sandwichs a ete etudie dans un premier temps par ondes de Lamb dans l’air et dans un second temps par mesure d’impedance electromecanique via un transducteur en contact avec les echantillons. Les resultats de Mod{\'{e}}lisation et experimentaux montrent que les frequences et largeurs de resonances varient suivant le taux de porosites, illustrant la sensibilite de ces methodes au vieillissement.

Le cadre general de ce memoire de thèse est l’etude de cristaux phononiques unidimensionnels. L’o... more Le cadre general de ce memoire de thèse est l’etude de cristaux phononiques unidimensionnels. L’objet principal porte sur l’etude de la diffusion acoustique à travers des milieux multicouches periodiques plans. Ces structures ont un grand interêt industriel notamment la realisation de guides d’ondes et des filtres acoustiques. Les trois premières parties de ce manuscrit ont ete consacrees globalement à l’etude theorique de multicouches periodiques. Trois methodes de calcul des coefficients de reflexion et de transmission ont ete detaillees. Une etude portant sur la determination et la resolution des equations de dispersion qui donnent les modes propres de vibration d’une structure N-periodique dans le vide où 2<N<10 est realisee. Deux familles de modes ont ete mises en evidence, modes de periode et modes de structure. Les premiers sont fortement attenues et dependent des proprietes physiques et geometriques de la periode et apparaissent dans les bandes d’arrêts ou à leurs limites. Les seconds sont propagatifs et apparaissent dans les bandes passantes. Dans la gamme des basses frequences les modes propagatifs sont appeles modes verticaux. Nous avons developpe une methode analytique approchee qui donne les frequences de coupure de ces modes. Une etude basee sur la comparaison des courbes de dispersion dans le vide et les zeros du coefficient de reflexion d’une structure periodique dans l’eau a ete presentee. L’influence de l’insertion de defauts sur l’evolution des bandes passantes et interdites du module du coefficient de reflexion |R|² a ete analysee. La deperiodisation par insertion d’un defaut d’epaisseur ou d’une couche mince constituent respectivement le premier et le deuxième type de defauts etudies. La dernière partie de ce travail a ete consacree à l’etude experimentale d’une structure periodique stratifiee fluide/solide. L’etude theorique du modèle a ete realisee. La comparaison des resultats theoriques et experimentaux ont montre une très bonne concordance.

Les transducteurs ultrasonores font l'objet de nombreux developpements en contrôle non-destructif... more Les transducteurs ultrasonores font l'objet de nombreux developpements en contrôle non-destructif (CND) industriel. Utilise ponctuellement et periodiquement, le CND ultrasonore permet d'etablir des diagnostics sur la sante des materiaux. La caracterisation ultrasonore en temps reel constitue un outil de surveillance de l'evolution des proprietes physiques lors de la fabrication des materiaux composites. Dans ce contexte, des etudes sont menees au LOMC pour optimiser le procede de fabrication des materiaux composites par RTM (Resin Transfer Molding) afin d’ameliorer la qualite du produit. Ce travail de thèse consiste à developper des methodes ultrasonores pour le suivi des proprietes viscoelastiques d’un composite pendant la phase de production. Les proprietes viscoelastiques sont etudiees à l’aide de modèles theoriques, de simulations numeriques et de resultats experimentaux. Des etudes de calibration ont ete menees afin d’etudier les facteurs d’influence sur le suivi de proprietes ultrasonores lors de la mise en oeuvre d’un procede RTM. Le suivi des paramètres viscoelastiques de resines epoxy est effectue dans un premier temps à basse temperature au cours d'une polymerisation isotherme et d’une post-cuisson. Ensuite, une approche basee sur la methode de caracterisation en emission/transmission a ete developpee afin d’etudier le comportement à haute temperature. La Mod{\'{e}}lisation de la reponse electroacoustique par serie de Debye (DSM) a ete effectuee en se basant sur des approches analytiques. L’utilisation des transducteurs multielements permet la localisation et le dimensionnement de defauts lors du deplacement de fibres de carbone dans une resine liquide, entre des moules

We consider a one dimensional Phononic Crystal (PC) based on a stack of plates including piezoele... more We consider a one dimensional Phononic Crystal (PC) based on a stack of plates including piezoelectric layers. The model takes into account electrical external circuit connected to the piezoelectric layers with the exception of the layer for which the impedance is evaluated. Only longitudinal waves propagation (thickness modes) through the PC is taken into account. Experimentally, a finite periodic structure based on a PMMA/Pz26 elementary stack is studied in the MHz frequency range. Different types of external electrical load are investigated. The electrical impedance of an active layer is affected by the electrical boundary conditions and is related to changes in the band structure of the acoustic transmission through the PC.

We consider a one dimensional Phononic Crystal (PC) based on a stack of plates including piezoele... more We consider a one dimensional Phononic Crystal (PC) based on a stack of plates including piezoelectric layers. The model takes into account electrical external circuit connected to the piezoelectric layers with the exception of the layer for which the impedance is evaluated. Only longitudinal waves propagation (thickness modes) through the PC is taken into account. Experimentally, a finite periodic structure based on a PMMA/Pz26 elementary stack is studied in the MHz frequency range. Different types of external electrical load are investigated. The electrical impedance of an active layer is affected by the electrical boundary conditions and is related to changes in the band structure of the acoustic transmission through the PC.

We consider a one dimensional Phononic Crystal (PC) based on a stack of plates including piezoele... more We consider a one dimensional Phononic Crystal (PC) based on a stack of plates including piezoelectric layers. The model takes into account electrical external circuit connected to the piezoelectric layers with the exception of the layer for which the impedance is evaluated. Only longitudinal waves propagation (thickness modes) through the PC is taken into account. Experimentally, a finite periodic structure based on a PMMA/Pz26 elementary stack is studied in the MHz frequency range. Different types of external electrical load are investigated. The electrical impedance of an active layer is affected by the electrical boundary conditions and is related to changes in the band structure of the acoustic transmission through the PC.