Le développement des énergies renouvelables peut non seulement compenser le manque d'énergie fossile à l'avenir, mais aussi sauver notre planète en réduisant la pollution par les émissions de CO2. Les matériaux piézoélectriques ont la capacité de convertir les mouvements mécaniques environnementaux en énergie électrique. Dans le cadre de cette thèse, deux types de matériaux piézoélectriques ont été étudiés pour la récupération d’énergie : les nanofils de ZnO et les microfibres de PVDF-TrFE. L’objectif ultime de cette thèse est de réaliser les dispositifs de la récupération d’énergie à faible coût pour rendre les capteurs autonomes.Au cours de la dernière décennie, les nanofils de ZnO ont suscité un grand intérêt dans le domaine de la recherche en raison de leurs multifonctionnalités avec un grand potentiel d’applications dans les différents domaines (récupération d’énergie par effet piézoélectrique et photovoltaïque, capteurs biologiques & chimiques, dépollution de l’eau & de l’air par effet photocatalytique, …). Le PVDF-TrFE est un polymère attrayant dans les applications de la récupération d'énergie en raison de ses propriétés piézoélectriques, son faible coût et sa grande flexibilité mécanique.Dans ce travail, deux méthodes de synthèse ont été employées pour obtenir les micro- & nanomatériaux piézoélectriques : Hydrothermale pour les réseaux verticaux des nanofils de ZnO et Electrospinning pour les microfibres de PVDF-TrFE. Les conditions de synthèse ont été optimisées afin d’obtenir les échantillons adéquats aux applications envisagées. Ensuite, deux types de dispositifs de la récupération d’énergie ont été fabriqués. Dans un premier temps, nous avons conçu des microgénérateurs (MGs) à base des microfibres de PVDF-TrFE déposées sur le substrat Kapton. Ces MGs flexibles basés sur l’effet piézoélectrique direct permettant la conversion de l’énergie mécanique en énergie électrique à basse fréquence de l’ordre d’hertz. Le second type de nanogénérateurs (NGs) est basé sur des nanofils verticaux de ZnO sur le substrat en silicium. Les tests de la récupération d’énergie ont été réalisés dans une gamme de fréquences de quelques centaines d’hertz pour l’application aéronautique / Development of renewable energy can not only compensate for the lack of fossil energy in the future, but also save our planet by reducing CO2 emission pollution. Piezoelectric materials have the ability to convert environmental mechanical movements into electrical energy. In this thesis, two types of piezoelectric materials have been studied for energy harvesting: ZnO nanowires and PVDF-TrFE microfibers. The ultimate goal of this thesis is to realize the low cost energy harvesting devices for self-powered sensors.Over the past decade, ZnO nanowires had attracted a great interest in the research field due to their multifunctionality with a great potential in the various applications (energy harvesting by piezoelectric and photovoltaic effect, bio & chemical sensors, water & air purification by photocatalytic effect ...). PVDF-TrFE is also an attractive polymer in energy harvesting due to its piezoelectric properties, high mechanical flexibility, and also for its low cost.In this work, two synthesis methods have been used to obtain the piezoelectric micro- & nanomaterials: Hydrothermal for the ZnO nanowire arrays and Electrospinning for the PVDF-TrFE microfibers. The synthesis conditions have been optimized in order to obtain the suitable samples for the applications. Then, two types of energy harvesting devices were manufactured. First, we realized the microgenerators (MGs) based on the PVDF-TrFE microfibers deposited on the Kapton substrate. These flexible MGs based on the direct piezoelectric effect allowing the conversion of mechanical energy into electrical energy at low frequency of the order of hertz. The second type of nanogenerators (NGs) is based on ZnO nanowire array on the silicon substrate. The energy harvesting tests were carried out in a frequency range of a few hundred hertz for the aeronautical application

<p>In this thesis a multilayer actuator structure is developed for the I-SWARM project. In order to build an energy efficient and low voltage actuator system for the 3x3x3 mm3 robot, the resonance drive mode in combination with a ten layer multilayer structure build upon the most suitable substrate material was used. Two different sizes of the locomotion module were built. The first one is five times larger than the small version. It has five active layers and is simpler to work with and to test. The small module has three 2x0.4 mm can-tilevers on a 3x3mm body and ten active layers.</p><p>The multilayer process involve easily defined flexible printed circuit (FPC) board as substrate material, spin coating piezoelectric poly(vinylidenefluoride- tetrafluoroethylene) P(VDF-TrFE) as active stack material, and evaporated aluminum electrodes on each active polymer layer. By using different shadow masks for each electrode layer, special inter con-tact areas can be contacted from above after the polymer has been removed by an Inductively Coupled Plasma (ICP) etch. The contours of the locomo-tion module was etched in a Reactive Ion Etch (RIE) equipment. Both the cupper layer in the FPC and the electrode layers of the active stack, were used as etch mask.</p><p>The deflections of the cantilevers were measured at low voltages to ensure as realistic drive voltage as possible for the I-SWARM robot. The large struc-ture showed a 250 µm deflection at 4 V and 170 Hz resulting in a Q-value of 19. The deflection of the small structure was 8 µm at 3.3 V and 5000 Hz and the measured Q-value was 31.</p>

L'objectif de ce travail est l'élaboration de nouveaux matériaux nanocomposites hybrides à propriétés spécifiques (piézoélectricité, optique non-linéaire). Dans un premier temps, des modèles numériques simples portant sur les propriétés mécaniques des nanocomposites sont présentées, ainsi que des simulations de déformation réalisées sur les nanocomposites à nanoparticules piézoélectriques. Les résultats expérimentaux de caractérisation mécanique (par spectrométrie Brillouin) et tribologique de différents nanocomposites sont exposés, y compris de nanocomposites réalisés au sein du laboratoire. L'influence des nanoparticules et de leur fonctionnalisation sur la matrice polymère y est discutée, et en particulier leur incidence sur les volumes libres dans les nanocomposites. Plusieurs procédés de synthèse de nanoparticules aux propriétés piézoélectriques ont parallèlement été étudiées. En particulier, un protocole de synthèse de nanoparticules de LiNbO3 a été mis au point. Ces nanoparticules ont été caractérisées par des techniques structurales, chimiques et d'imagerie. Enfin, ces travaux ont conduit à l'élaboration de films nanocomposites à matrice PVDF-TrFE incorporant des nanoparticules produites en laboratoire ou d'origine commerciale. Les méthodes de polarisation des films sont décrites, et les propriétés piézoélectriques de ces films nanocomposites ont été mesurées. Plus particulièrement, des films nanocomposites PVDF-TrFE/Al2O3 polarisés présentant une bonne réponse piézoélectrique ont été élaborés. / This work aims at the elaboration of new hybrid nanocomposites with specific properties (piezoelectricity, non-linear optic). First, simple numeric modelings on mechanical properties of nanocomposites are presented, as well as simulation of deformation in nanocomposites with piezoelectric nanoparticles. Experimental results on tribological and mechanical (performed by Brillouin Spectroscopy) characterization of different nanocomposites are exposed. The influence of nanoparticles and their fonctionalization on the polymer matrix is discussed, and in particular the incidence on free volume in nanocomposites. Several piezoelectric nanoparticles synthesis processes have been also studied. In particular, a LiNbO3 nanoparticles synthesis protocol has been worked out. These nanoparticles were characterized by structural, chemical and imaging techniques. Finally, these works leads to the elaboration of PVDF-TrFE matrix thin films nanocomposites filled with commercial or produced in laboratory nanoparticles. The methods used to polarize the films are described. The piezoelectric properties of the nanocomposites have been measured. More particularly, PVDF-TrFE/Al2O3 nanocomposites thin films with a good piezoelectric response have been elaborated.

The objective of this research is to develop a new class of miniaturized sensors on-catheter technology through the integration of functional nanomaterials and flexible microsystems, with high sensitivity, fast recovery time, reduced form factor, for in situ blood pressure and flow monitoring with minimal invasiveness. Real-time endovascular pressure measurement techniques are crucial to evaluate the hemodynamics, which indicates the physiological state of the cardiovascular system. Current technology relies on fluid filled catheter coupled to remote transducers to measure endovascular pressures and gradients. The fluid filled catheters are bulky, inherently inaccurate due to the tubing mechanical resonance, and with low signal integrity due to the vibration noises from the environment. Silicon based conventional pressure sensors have complications due to issues of catheter stiffness, biocompatibility or small form factor integration. We propose a paradigm shift in designing the endovascular pressure sensing technology, through developing compact flexible sensing structures using nanoengineered piezoelectric polymers which can be integrated on catheters without consuming the internal lumen space. We focused on designing novel nanostructures using PVDF-TrFE (Polyvinyledene fluoride trifluoroethylene), with well controlled [Beta]-crystalline phase to significantly improve the resulting sensor performance. The research objectives include: (1) Thin-film structures for higher piezoelectric effect without any mechanical stretching or poling requirements, (2) High density highly-aligned electrospun nanofibers through electrospinning towards enhanced sensitivity; (3) Core-shell electrospun nanofiber for tapping the near [Beta]-crystalline phase formation and high cyrstallinity by virtue of inherent stress and stretching involved in the fabrication procedure. For pressure sensor design and characterization, we worked on two main form factors designs: thin-film, and aligned electrospun nanofiber based sensors patterned on catheter tips which are ready to be deployed in intra-vascular environment. Testing results showed promising results from PVDF based pressure sensors. The average sensitivity of the PVDF sensors was found to be four times higher than commercial pressure sensor while the PVDF sensor had five fold shorter response time than commercial pressure sensor, making the PVDF sensors highly suitable for real-time pressure measurements using catheters. / text

In this thesis a multilayer actuator structure is developed for the I-SWARM project. In order to build an energy efficient and low voltage actuator system for the 3x3x3 mm3 robot, the resonance drive mode in combination with a ten layer multilayer structure build upon the most suitable substrate material was used. Two different sizes of the locomotion module were built. The first one is five times larger than the small version. It has five active layers and is simpler to work with and to test. The small module has three 2x0.4 mm can-tilevers on a 3x3mm body and ten active layers. The multilayer process involve easily defined flexible printed circuit (FPC) board as substrate material, spin coating piezoelectric poly(vinylidenefluoride- tetrafluoroethylene) P(VDF-TrFE) as active stack material, and evaporated aluminum electrodes on each active polymer layer. By using different shadow masks for each electrode layer, special inter con-tact areas can be contacted from above after the polymer has been removed by an Inductively Coupled Plasma (ICP) etch. The contours of the locomo-tion module was etched in a Reactive Ion Etch (RIE) equipment. Both the cupper layer in the FPC and the electrode layers of the active stack, were used as etch mask. The deflections of the cantilevers were measured at low voltages to ensure as realistic drive voltage as possible for the I-SWARM robot. The large struc-ture showed a 250 µm deflection at 4 V and 170 Hz resulting in a Q-value of 19. The deflection of the small structure was 8 µm at 3.3 V and 5000 Hz and the measured Q-value was 31.

Les recherches que nous présentons dans ce mémoire s'inscrivent dans le cadre du développement de nouvelles structures et de l'étude de matériaux accordables en vue d'une intégration industrielle comme radôme actif.Plus particulièrement, ils consistent en la réalisation d'un dispositif micro-onde permettant à la fois un filtrage et une agilité fréquentiels en espace libre. Des structures basées sur des surfaces sélectives en fréquences, pour l'aspect filtrage, et sur des matériaux de type ferroélectrique, pour l'aspect accordabilité, sont développées. Des modélisations et des simulations électromagnétiques montrent que le changement de permittivité du matériau, obtenu par application d'un champ électrique externe, permet le pilotage fréquentiel de la transmission de la structure. Une mise en oeuvre expérimentale complète ces travaux, au cours de laquelle des prototypes ont été fabriqués par des techniques de photolithographie, puis caractérisés en espace libre grâce à un banc ABmm. Les mesures micro-ondes valident ainsi les résultats de simulations menées en amont et montrent les possibilités de contrôler la fréquence de transmission du radôme. / The research we present in this memory registers within the framework to develop new structures and to study tunable materials for an industrial integration as an active radome. Specifically, they consist of achieving a free space microwave device for both a filtering behaviour and a frequency agility behaviour. Structures based on frequency selective surfaces, for the filtering aspect, and on ferroelectric materials for the tuning aspect, are developed. Modeling and simulations show that the change of the material permittivity, obtained by applying an external electric field, enable piloting the transmission frequency of the structure. An experimental implementation complete this work and prototypes have been fabricated by photolithography techniques and then characterized in free space with a bench ABmm. Thus, microwave measurements validate the results of simulations and show the possibility to control the frequency transmission of the radome.

Filmes de poli(fluoreto de vinilideno-co-trifluoretileno), P(VDF-IrFE), com uma razão molar 70/30 de VDF e IrFE, respectivamente, foram expostos à radiação-X sob vácuo em uma ampla faixa de doses de irradiação. Este é um copolímero estatístico e semi-cristalino que possui a especial característica de cristalizar espontaneamente numa estrutura ferroelétrica. Ele também possui uma transição de fase ferro-paraelétrica detectável, definida como a temperatura de Curie (Tc). Devido a estas características tem despertado considerável interesse, em especial na área da eletrônica como elemento transdutor. As modificações induzidas foram investigadas por espectroscopia fotoacústica no infravermelho (FT-IR/PAS), assim como FI-IR por transmitância, calorimetria exploratória diferencial (DSC), termogravimetria (IG), difração de raios-X, UV/Visível e espectroscopia Raman. As técnicas espectroscópicas vibracionais (fotoacústica no IR, Raman e absorção no IR) foram utilizadas na identificação de bandas relacionadas às regiões cristalinas e amorfas, formação e rompimento de ligações e presença de novos grupos funcionais. Nos espectros IR e Raman são observadas duas bandas que estão relacionadas às regiões cristalinas e sofrem mudanças nas suas intensidades relativas de acordo com a dose de radiação. Essas mudanças podem ser interpretadas como aumento ou diminuição do grau de cristalinidade, e também em termos de modificações de arranjos cristalinos. A difração de raio-X mostrou o aparecimento de um pico, próximo àquele da fase ferroelétrica, sob aumento da dose de radiação, devido a um processo de modificação do arranjo cristalino acima da dose de 480 kGy. Foi observado um aumento de intensidade no referido pico de difração, correspondendo a um aumento do grau de cristalinidade da amostra. As curvas de DSC mostraram picos endotérmicos correspondentes a fusão e transições de fases que, através de suas variações, possibilitam avaliar os efeitos da irradiação com raios-X. Os espectros UV/Visível mostraram absorções dos cromóforos cujas intensidades de banda aumentam com a dose de radiação e diminuem durante o envelhecimento da amostra. Os dados indicam que a radiação-X induz uma modificação no arranjo cristalino do P(VDF-TrFE). Tal modificação, é provavelmente uma mudança de estrutura ferroelétrica para outra, paraelétrica. / Poly(vinylidene fluoride-co-trifluoroethylene) films, P(VDF-TrFE), with a molar ratio 70/30 of VDF and TrFE units, respectively, were exposed to X-ray radiation under vacuum in a wide range of irradiation doses. This is a statistic semi-crystalline copolymer and displays the unique feature of a spontaneous crystallization into a ferroelectric structure. It also possesses a detectable ferro-paraelectric transition, the Curie temperature (Tc). Due to these characteristics considerable interest in such copolymer has been generated, specially in electronics as a transducer element. The induced modifications were investigated by Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) as well as transmittance FT-IR, differential scanning calorimetry (DSC), thermogravimetry (TG), X-ray diffraction, UV/Visible and Raman spectroscopies. The spectroscopic vibrational techniques (FT-IR/PAS, FT-IR and Raman) were used to identify bands related to crystalline and amorphous regions, bond formation, bond scission and presence of new functional groups. In both IR and Raman spectra were observed a couple of bands related to the crystalline regions that undergo changes of relative intensities with the radiation dose. These changes may be interpreted as an increase or decrease of the crystallinity degree, and also modifications of crystal structure. X-ray diffraction showed a new peak, close to that of the ferroelectric phase, under increasing radiation doses, due to a modification of crystal structure process above 480 kGy dose. An increase in the intensity of the former diffraction peak was observed, corresponding to an increase in the crystallinity degree. The DSC curves showed the endothermic peaks corresponding to the melting and the phase transitions, whose variations allow an evaluation of the effects of X-ray radiation. UV/Visible spectra showed chromophores absorptions whose band intensities increase by radiation dose and decrease during sample\'s aging. The data indicate that P(VDF-TrFE) under X-ray radiation exposition undergoes a crystal structure modification, probably a change of a ferroelectric structure to another one, paraelectric.

Filmes de poli(fluoreto de vinilideno-co-trifluoretileno), P(VDF-IrFE), com uma razão molar 70/30 de VDF e IrFE, respectivamente, foram expostos à radiação-X sob vácuo em uma ampla faixa de doses de irradiação. Este é um copolímero estatístico e semi-cristalino que possui a especial característica de cristalizar espontaneamente numa estrutura ferroelétrica. Ele também possui uma transição de fase ferro-paraelétrica detectável, definida como a temperatura de Curie (Tc). Devido a estas características tem despertado considerável interesse, em especial na área da eletrônica como elemento transdutor. As modificações induzidas foram investigadas por espectroscopia fotoacústica no infravermelho (FT-IR/PAS), assim como FI-IR por transmitância, calorimetria exploratória diferencial (DSC), termogravimetria (IG), difração de raios-X, UV/Visível e espectroscopia Raman. As técnicas espectroscópicas vibracionais (fotoacústica no IR, Raman e absorção no IR) foram utilizadas na identificação de bandas relacionadas às regiões cristalinas e amorfas, formação e rompimento de ligações e presença de novos grupos funcionais. Nos espectros IR e Raman são observadas duas bandas que estão relacionadas às regiões cristalinas e sofrem mudanças nas suas intensidades relativas de acordo com a dose de radiação. Essas mudanças podem ser interpretadas como aumento ou diminuição do grau de cristalinidade, e também em termos de modificações de arranjos cristalinos. A difração de raio-X mostrou o aparecimento de um pico, próximo àquele da fase ferroelétrica, sob aumento da dose de radiação, devido a um processo de modificação do arranjo cristalino acima da dose de 480 kGy. Foi observado um aumento de intensidade no referido pico de difração, correspondendo a um aumento do grau de cristalinidade da amostra. As curvas de DSC mostraram picos endotérmicos correspondentes a fusão e transições de fases que, através de suas variações, possibilitam avaliar os efeitos da irradiação com raios-X. Os espectros UV/Visível mostraram absorções dos cromóforos cujas intensidades de banda aumentam com a dose de radiação e diminuem durante o envelhecimento da amostra. Os dados indicam que a radiação-X induz uma modificação no arranjo cristalino do P(VDF-TrFE). Tal modificação, é provavelmente uma mudança de estrutura ferroelétrica para outra, paraelétrica. / Poly(vinylidene fluoride-co-trifluoroethylene) films, P(VDF-TrFE), with a molar ratio 70/30 of VDF and TrFE units, respectively, were exposed to X-ray radiation under vacuum in a wide range of irradiation doses. This is a statistic semi-crystalline copolymer and displays the unique feature of a spontaneous crystallization into a ferroelectric structure. It also possesses a detectable ferro-paraelectric transition, the Curie temperature (Tc). Due to these characteristics considerable interest in such copolymer has been generated, specially in electronics as a transducer element. The induced modifications were investigated by Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) as well as transmittance FT-IR, differential scanning calorimetry (DSC), thermogravimetry (TG), X-ray diffraction, UV/Visible and Raman spectroscopies. The spectroscopic vibrational techniques (FT-IR/PAS, FT-IR and Raman) were used to identify bands related to crystalline and amorphous regions, bond formation, bond scission and presence of new functional groups. In both IR and Raman spectra were observed a couple of bands related to the crystalline regions that undergo changes of relative intensities with the radiation dose. These changes may be interpreted as an increase or decrease of the crystallinity degree, and also modifications of crystal structure. X-ray diffraction showed a new peak, close to that of the ferroelectric phase, under increasing radiation doses, due to a modification of crystal structure process above 480 kGy dose. An increase in the intensity of the former diffraction peak was observed, corresponding to an increase in the crystallinity degree. The DSC curves showed the endothermic peaks corresponding to the melting and the phase transitions, whose variations allow an evaluation of the effects of X-ray radiation. UV/Visible spectra showed chromophores absorptions whose band intensities increase by radiation dose and decrease during sample\'s aging. The data indicate that P(VDF-TrFE) under X-ray radiation exposition undergoes a crystal structure modification, probably a change of a ferroelectric structure to another one, paraelectric.