Realisation and characterisation of metallic particulate composites used as backs of ultrasonics transducers high temperature

Dans le domaine du contrôle non-destructif par ultrasons l’utilisation de sondes ultrasonores pouvant fonctionner en continue à des températures à minima de 300°C serait d’un grand intérêt. Par exemple, cela pourrait concerner le contrôle de santé de structures de l’industrie nucléaire ou pétrolière. Plus fondamentalement, de telles sondes pourraient être également utilisées pour caractériser le comportement mécanique d’une large gamme de matériaux soumis à des stress thermiques et réaliser par exemple le suivi de l’endommagement et de vieillissement de ces matériaux. Or, commercialement il n’existe pas de sondes ultrasonores pouvant fonctionner à de telles températures, cela reste du domaine de la recherche.Une sonde ultrasonore est constituée de 3 éléments principaux : le dos, l’élément actif et la face avant. Des éléments actifs pouvant fonctionner à des températures très élevées existent, citons à titre d’exemple le LiNb03 (température de curie de 1350°C). Toutefois dans l’objectif d’obtenir des sondes ultrasonores performantes à hautes températures il est nécessaire d’optimiser les propriétés et également le couplage acoustique de chacun des trois constituants de la sonde. Le dos est un élément important qui, par atténuation de l’onde émise en face arrière de l’élément actif, permet de contrôler la bande passante et la sensibilité des sondes.Le présent travail de thèse concerne la réalisation et la caractérisation de composites particulaires métalliques utilisés comme dos de sondes ultrasonores destinées à fonctionner à hautes températures. Les composites sont réalisés par pressage uni-axial d’une poudre servant de matrice et d’une deuxième de diffuseur. Durant ce travail exploratoire nous avons mis au point un protocole de fabrication qui nous a permis de réaliser des composites d’étain/sn ayant des propriétés acoustiques intéressantes (atténuation et impédance). Pour caractériser nos échantillons un banc de spectroscopie ultrasonore a été spécifiquement mis en œuvreIn the field of ultrasonic non-destructive testing, the use of ultrasonic transducer which can operate continuously at temperatures of at least 300 ° C. would be of great interest. For example, this could concern the health control of structures in the nuclear or petroleum industry. More fundamentally, such probes could also be used to characterize the mechanical behavior of a wide range of materials subjected to thermal stresses and, for example, to monitor the damage and aging of these materials. However, commercially, there are no ultrasonic probes that can operate at such temperatures, but this is still a research area.An ultrasonic probe consists of 3 main elements: the back, the active element and the front face. Active elements which can operate at very high temperatures exist, for example LiNbO 3 (curie temperature of 1350 ° C.). However, in order to obtain high-performance ultrasonic probes at high temperatures, it is necessary to optimize the properties and also the acoustic coupling of each of the three components of the probe. The back is an important element which, by attenuation of the wave emitted on the back of the active elements, allows to control the bandwidth and the sensitivity of the probes.The present thesis deals with the realization and characterization of metallic particulate composites used as backs of ultrasonic probes intended to operate at high temperatures. The composites are produced by uni-axial pressing of a matrix powder and a second diffuser. During this exploratory work, we developed a manufacturing protocol that allowed us to produce tin / sn composites with interesting acoustic properties (attenuation and impedance). To characterize our samples a bench of ultrasonic spectroscopy has been specifically implemente

Piezoelectrics generators based on piezo-semiconducting nanowires : modelling, fabrication and characterization

La demande de nouvelles technologies de conversion d'énergie augmente considérablement. Elle a pour but d’offrir une durée de vie augmentée aux microsystèmes et garantir ainsi leur autonomie sans aucune intervention humaine. Dans cette thèse, nous exploitons les nanotechnologies pour le développement d’une nouvelle génération de récupérateurs d’énergie mécanique flexibles et robustes, à partir des matériaux piézoélectriques. Des études expérimentales et des simulations numériques ont été effectuées afin d’améliorer les performances des NanoGénérateurs PiézoElectriques (PENG). Le dispositif piézoélectrique actif choisi est à base de nanofils de ZnO, synthétisé via une voie de synthèse hydrothermale à faible coût et basse température, compatible avec l’utilisation de substrats souples. Des études ont été effectuées dans le but d’optimiser les propriétés des nanostructures piézoélectriques, tels que la densité de charge libre dans le semi-conducteur, mais aussi la densité surfacique et la morphologie des nanofils. Des PENGs flexibles sur substrat de polydiméthylsiloxane, ont également été fabriqués et soumis à une force de compression à basse fréquence, montrant une bonne reproductibilité des performances, avec une puissance moyenne de 0,25 µW sur une charge de 56 MΩ, pour une force de 6 N appliquée à la fréquence de 5 Hz. Cette thèse ouvre d’intéressantes perspectives de développement des systèmes de récupération d'énergie mécanique totalement flexibles pour un développement de microsystèmes autonomes.The demand for new technologies of energy conversion is dramatically increasing that can offer increased life to the micro-systems and also ensures their energy autonomy without any human intervention. By exploiting nanotechnologies, the present thesis focuses on the development of new generation of flexible and robust piezoelectric mechanical energy harvesters, from piezoelectric materials. Both experiment and theoretical simulation studies are performed to improve the performance of PiezoElectric NanoGenerators (PENGs). The active piezoelectric material, ZnO nanowires, are synthesized via cost-effective and low-temperature hydrothermal synthesis route, compatible with different types of flexible substrates. Studies have been carried out in order to optimize the properties of piezoelectric material properties such as effect of free charge density in semiconductor, density and morphology of nanowires. Flexible PENGs on a polydimethylsiloxane substrate are also manufactured and subjected to a low frequency compression force, showing good performance reproducibility, with an average power of 0,25 µW on a load of 56 MΩ, for an applied force of 6 N at the frequency of 5 Hz. This thesis can open up interesting opportunities to develop fully flexible mechanical energy recovery systems for the development of autonomous micro system

Réalisation et caractérisation de composites particulaires métalliques utilisés comme dos de sondes ultrasonores hautes températures

In the field of ultrasonic non-destructive testing, the use of ultrasonic transducer which can operate continuously at temperatures of at least 300 ° C. would be of great interest. For example, this could concern the health control of structures in the nuclear or petroleum industry. More fundamentally, such probes could also be used to characterize the mechanical behavior of a wide range of materials subjected to thermal stresses and, for example, to monitor the damage and aging of these materials. However, commercially, there are no ultrasonic probes that can operate at such temperatures, but this is still a research area.An ultrasonic probe consists of 3 main elements: the back, the active element and the front face. Active elements which can operate at very high temperatures exist, for example LiNbO 3 (curie temperature of 1350 ° C.). However, in order to obtain high-performance ultrasonic probes at high temperatures, it is necessary to optimize the properties and also the acoustic coupling of each of the three components of the probe. The back is an important element which, by attenuation of the wave emitted on the back of the active elements, allows to control the bandwidth and the sensitivity of the probes.The present thesis deals with the realization and characterization of metallic particulate composites used as backs of ultrasonic probes intended to operate at high temperatures. The composites are produced by uni-axial pressing of a matrix powder and a second diffuser. During this exploratory work, we developed a manufacturing protocol that allowed us to produce tin / sn composites with interesting acoustic properties (attenuation and impedance). To characterize our samples a bench of ultrasonic spectroscopy has been specifically implementedDans le domaine du contrôle non-destructif par ultrasons l’utilisation de sondes ultrasonores pouvant fonctionner en continue à des températures à minima de 300°C serait d’un grand intérêt. Par exemple, cela pourrait concerner le contrôle de santé de structures de l’industrie nucléaire ou pétrolière. Plus fondamentalement, de telles sondes pourraient être également utilisées pour caractériser le comportement mécanique d’une large gamme de matériaux soumis à des stress thermiques et réaliser par exemple le suivi de l’endommagement et de vieillissement de ces matériaux. Or, commercialement il n’existe pas de sondes ultrasonores pouvant fonctionner à de telles températures, cela reste du domaine de la recherche.Une sonde ultrasonore est constituée de 3 éléments principaux : le dos, l’élément actif et la face avant. Des éléments actifs pouvant fonctionner à des températures très élevées existent, citons à titre d’exemple le LiNb03 (température de curie de 1350°C). Toutefois dans l’objectif d’obtenir des sondes ultrasonores performantes à hautes températures il est nécessaire d’optimiser les propriétés et également le couplage acoustique de chacun des trois constituants de la sonde. Le dos est un élément important qui, par atténuation de l’onde émise en face arrière de l’élément actif, permet de contrôler la bande passante et la sensibilité des sondes.Le présent travail de thèse concerne la réalisation et la caractérisation de composites particulaires métalliques utilisés comme dos de sondes ultrasonores destinées à fonctionner à hautes températures. Les composites sont réalisés par pressage uni-axial d’une poudre servant de matrice et d’une deuxième de diffuseur. Durant ce travail exploratoire nous avons mis au point un protocole de fabrication qui nous a permis de réaliser des composites d’étain/sn ayant des propriétés acoustiques intéressantes (atténuation et impédance). Pour caractériser nos échantillons un banc de spectroscopie ultrasonore a été spécifiquement mis en œuvr

Générateurs piézoélectriques à base de nanofils piézo -semiconducteurs: modélisation, fabrication et caractérisation

The demand for new technologies of energy conversion is dramatically increasing that can offer increased life to the micro-systems and also ensures their energy autonomy without any human intervention. By exploiting nanotechnologies, the present thesis focuses on the development of new generation of flexible and robust piezoelectric mechanical energy harvesters, from piezoelectric materials. Both experiment and theoretical simulation studies are performed to improve the performance of PiezoElectric NanoGenerators (PENGs). The active piezoelectric material, ZnO nanowires, are synthesized via cost-effective and low-temperature hydrothermal synthesis route, compatible with different types of flexible substrates. Studies have been carried out in order to optimize the properties of piezoelectric material properties such as effect of free charge density in semiconductor, density and morphology of nanowires. Flexible PENGs on a polydimethylsiloxane substrate are also manufactured and subjected to a low frequency compression force, showing good performance reproducibility, with an average power of 0,25 μW on a load of 56 MΩ, for an applied force of 6 N at the frequency of 5 Hz. This thesis can open up interesting opportunities to develop fully flexible mechanical energy recovery systems for the development of autonomous micro systems.La demande de nouvelles technologies de conversion d'énergie augmente considérablement. Elle a pour but d’offrir une durée de vie augmentée aux microsystèmes et garantir ainsi leur autonomie sans aucune intervention humaine. Dans cette thèse, nous exploitons les nanotechnologies pour le développement d’une nouvelle génération de récupérateurs d’énergie mécanique flexibles et robustes, à partir des matériaux piézoélectriques. Des études expérimentales et des simulations numériques ont été effectuées afin d’améliorer les performances des NanoGénérateurs PiézoElectriques (PENG). Le dispositif piézoélectrique actif choisi est à base de nanofils de ZnO, synthétisé via une voie de synthèse hydrothermale à faible coût et basse température, compatible avec l’utilisation de substrats souples. Des études ont été effectuées dans le but d’optimiser les propriétés des nanostructures piézoélectriques, tels que la densité de charge libre dans le semi-conducteur, mais aussi la densité surfacique et la morphologie des nanofils. Des PENGs flexibles sur substrat de polydiméthylsiloxane, ont également été fabriqués et soumis à une force de compression à basse fréquence, montrant une bonne reproductibilité des performances, avec une puissance moyenne de 0,25 μW sur une charge de 56 MΩ, pour une force de 6 N appliquée à la fréquence de 5 Hz. Cette thèse ouvre d’intéressantes perspectives de développement des systèmes de récupération d'énergie mécanique totalement flexibles pour un développement de microsystèmes autonomes

Carbone dioxide capture and utilization in gas turbine plants via the integration of power to gas

International audienceRecent studies have shown that the concentration of greenhouse gases such as carbon dioxide in the atmosphere is growing rapidly over recent years and this can lead to major dangers for the planet. This growth is mainly due to the emissions from fossil power source such as diesel plants and gas turbines. The purpose of the present paper is to study the feasibility of integrating a technique based on power to gas concept in fossil power plants such as gas turbine. This work is based on the reduction of pollutant gas emissions produced from a gas turbine plant, especially the carbon dioxide. This captured gas (CO2CO2) can be converted once again into energy via the technique of power to gas concept. This concept starts by extracting CO2CO2 from exhaust gases which is carried out by multiple chemical process. On the other side, H2H2 is produced from water electrolysis using the excess electricity which is produced but not consumed by the existing loads. finally the production of Methane (CH4CH4) can be achieved by combination of the captured CO2CO2 and the extracted H2H2 via a reactor known as a reactor of Sabatier, this operation is called methanation or hydrogenation of carbon dioxide. Simulation results are presented for the validation of the proposed technique based on real data obtained on site from a gas turbine plant

Numerical approach to design efficient mechanical energy harvesting system based on piezo-semiconducting nanowires

International audienceNanoscale mechanical energy harvesting using PiezoElectric NanoGenerators (PENGs) has been highlightedas a potential candidate for the realization of self-powered biomedical devices such as pacemakers andwearable communication devices. A PENG can be described as a stack of five layers (Figure 1) : a rigid orflexible substrate, a bottom electrode, an electroactive layer (piezoelectric semiconducting nanowires (NWs)surrounded by an insulating polymer), a top layer of insulating material and a top electrode [1]. For thecontinual performance improvement of PENG devices, optimization of the piezoelectric semiconductingnanomaterial, including morphology, density and quality, is of great interest and crucial. For example, it hasbeen theoretically shown that the output potential and efficiency of PENGs strongly depend on the electricalquality of the nanomaterial [2]. Among several nanomaterials, zinc oxide (ZnO) NWs can be synthesized byhydrothermal method, which is low temperature, industrially scalable and compatible with flexible substrates[3]. Different approaches have been used to model ZnO NW based PENGs including analytical models andnumerical models using finite element method (FEM) [1].In the present work, COMSOL software is used to model ZnO NW based PENGs. First, the piezoelectricpotential distribution in ZnO NWs is studied for different intrinsic doping concentrations. In terms ofpiezopotential magnitude, cylindrical shaped NWs with low doping completely outperformed their homologueNWs being highly doped leading to significant piezoelectric potential screening effect. Figure 2 shows that, atthe applied static pressure of 6.25 MPa, a cylindrical NW with a 1010 (/cm3) charge density presents amaximum piezoelectric potential of 2.9 V compared to 0.25 V reached by a 1015 (/cm3) doped NW. Moreover,in order to predict the complete PENG electrical characteristics and to reduce computation time, a newapproach using FEM simulation and analytical modelling has been developed [1]. This method combines FEMsimulation of a PENG unit cell (including one NW) in order to estimate the open-circuit voltage (without anyexternal electrical circuit), and an analytical model of the full PENG in order to predict the maximum powerand the corresponding optimal load. Further works will consist in studying the effect of the geometricalcharacteristics and electromechanical properties of the nanowire-polymer composite on the complete PENGperformance.References[1] Doumit N and Poulin-Vittrant G 2018 A new simulation approach for performance prediction ofvertically integrated nanogenerators Adv. Theory Simul. 1800033 1–8[2] Gao Y and Wang Z L 2009 Equilibrium potential of free charge carriers in a bent piezoelectricsemiconductive nanowire Nano Lett. 9 1103–10[3] Dahiya A S, Morini F, Boubenia S, Nadaud K, Alquier D, Poulin-Vittrant G 2017 Organic / inorganichybrid stretchable piezoelectric nanogenerators for self-powered wearable electronics AdvancedMaterials Technologies 1700249 11 pp

Influence of the Cl2_2 etching on the Al2_2O3_3 /GaN metal–oxide–semiconductor interface

International audienceControlling the plasma etching step involved in metal-oxide-semiconductor high-electron-mobility-transistor (MOSHEMT) GaN fabrication is essential for device performance and reliability. In particular, understanding the impact of GaN etching conditions on dielectric/GaN interface chemical properties is critically important. In this work, we investigate the impact of the carrier wafers (Si, photoresist, SiO 2 , and Si 3 N 4 ) used during the etching of GaN in chlorine plasma on the electrical behavior of Al 2 O 3 /n-GaN metal–oxide–semiconductor (MOS) capacitors. X-ray Photoelectron spectroscopy (XPS) analyses show that the Al 2 O 3 /GaN interface layer contains contaminants from the etching process after the Al 2 O 3 deposition. Their chemical nature depends on the plasma chemistry used as well as the chemical nature of the carrier wafer. Typically, Cl and C are trapped at the interface for all substrates. In the particular case of Si carrier wafer, a significant amount of SiO x is present at the Al 2 O 3 /GaN interface. The capacitance–voltage (C–V) characteristics of the MOS capacitors indicate that the presence of Si residues at the interface shifts the flat band voltage to negative values, while the presence of Cl or C at the interface increases the hysteresis. We demonstrate that introducing an in situ plasma cleaning treatment based on N 2 /H 2 gas, before the atomic layer deposition, allows the removal of most of the residues except silicon and suppresses the hysteresis

Impacts of different carrier wafers during Cl2 Inductively Coupled Plasma etching on the GaN surface and the Al2O3/GaN interface

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CMUT-Based Sensor for Acoustic Emission Application: Experimental and Theoretical Contributions to Sensitivity Optimization

International audienceThe paper deals with a capacitive micromachined ultrasonic transducer (CMUT)-basedsensor dedicated to the detection of acoustic emissions from damaged structures. This work aims to explore different ways to improve the signal-to-noise ratio and the sensitivity of such sensors focusing on the design and packaging of the sensor, electrical connections, signal processing, coupling conditions, design of the elementary cells and operating conditions. In the first part, the CMUT-R100 sensor prototype is presented and electromechanically characterized. It is mainly composed of a CMUT-chip manufactured using the MUMPS process, including 40 circular 100 µm radius cells and covering a frequency band from 310 kHz to 420 kHz, and work on the packaging, electricalconnections and signal processing allowed the signal-to-noise ratio to be increased from 17 dB to 37 dB. In the second part, the sensitivity of the sensor is studied by considering two contributions: the acoustic-mechanical one is dependent on the coupling conditions of the layered sensor structure and the mechanical-electrical one is dependent on the conversion of the mechanical vibration to electrical charges. The acoustic-mechanical sensitivity is experimentally and numerically addressed highlighting the care to be taken in implementation of the silicon chip in the brass housing. Insertion losses of about 50% are experimentally observed on an acoustic test between unpackaged and packaged silicon chip configurations. The mechanical-electrical sensitivity is analytically describedleading to a closed-form amplitude of the detected signal under dynamic excitation. Thus, the influence of geometrical parameters, material properties and operating conditions on sensitivity enhancement is clearly established: such as smaller electrostatic air gap, and larger thickness, Young’s modulus and DC bias voltage