Les couches minces de LiNbO3 (LN) avec des orientations du single cristallographique en dehors-du-plan et dans-le-plan sont nécessaires pour les dispositifs optiques et acoustiques. La technique PIMOCVD est adapté pour la déposition de couches minces de LN avec des orientations cristallographiques différentes sur des substrats monocristallins. Pour obtenir des couches avec une surface lisse et composé une phase pure de LN avec une concentration contrôlé de Li, les paramètres de déposition ont été ajustés.Un effort particulier a été mis dans la croissance de couches avec une orientation unique dans-le-plan. La qualité cristalline, la qualité de l’épitaxie, Li2O nonstoichiometrique, l’orientation dans-le-plan, le stress résiduel et le twinning ont été étudiés avec la diffraction des rayons X et la spectroscopie Raman. Couches de LN avec composition presque stoichiometrique on été obtenues. Les couches épaisses ont tendance à se fracturer et à former twins pour détendre les grands stress thermique. Les différences dans les mécanismes de relaxation et dans la capacité de supporter des stress dans les couches de X-, Y- et Z-LN sont discutés. Dans le cas des couches Z-LN le stress thermique sont equi-biaxial quand le stress dans les couches X- et Y- sont anisotropies. On a étudié aussi la structure des domaines ferroélectriques et la réponse piézoélectrique des couches. L’énergie de bande et l’indice de réfraction des couches de LN, mesuré pas elipsometrie spectrale, sont très proche de ceux du LN monocristallin. On démontre expérimentalement la présence d’une résonance à 5.5 GHz dans un résonateur à un seul port réalisé dans une couche de Z-LN/saphir de 150 nm d’épaisseur. / LiNbO3 (LN) thin films are attracting interest due to possibility to miniaturize, to integrate and to ameliorate the performance of acoustical and optical devices. These applications require LN films with single crystallographic out-of-plane and in-plane orientations. PIMOCVD technique was used for deposition of high quality of different crystallographic orientations LN thin films, offering a possibility to obtain films with various different cut on single crystalline substrates.In order to obtain films with smooth surface and consisting of pure LN phase with controlled Li concentration, the deposition parameters were tuned.A particular effort was done to obtain films with single in-plane orientation. The crystallinity, epitaxial quality, Li2O nonstoichiometry, in-plane orientation, residual stresses and twinning were studied by means of X-ray diffraction and Raman spectroscopy. The LN films with nearly stoichiometric composition were obtained. The thick films tend to crack and to form the twins in order to relax the high thermal stresses. The differences in relaxation mechanisms and in ability to withstand high stresses of X-, Y- and Z-LN films were discussed. In the case of Z-LN films the thermal stresses are equibiaxial, while the stresses in X- and Y- films are anisotropic. The ferroelectric domain structure and piezoelectric response of grown films were investigated. Energy gap and refractive indexes of LN films, measured by spectroscopic ellipsometry, were similar to those of single crystal. Acoustic resonance at 5.5 GHz in single-port resonators based on as-grown 150 nm thick Z-LN film on sapphire films was demonstrated experimentally.

The use of piezoelectric materials for actuation, and vibration suppression of thin beams, is the subject of study in this doctoral thesis. The initial focus is set on reducing beam vibrations with resistively shunted piezoelectric patches, where the converted electrical energy is dissipated by the resistor to give an additional damping. The amount of additional damping achieved depends on the value of shunted resistor, the dimensions of the piezoelectric, and its location on the substructure. Hence, the resistively shunted piezoelectric-beam was modelled to determine the optimal values, and to examine its dynamics. A multi-modal model was derived based on the Euler-Bernoulli beam theory, and a reduced non-dimensionalized transfer function was obtained from the multi-modal model. The presented model was derived from assumptions which aptly describe the dynamics of the resistively shunted piezoelectric-beam. The aptness of the presented model in representing the system, over the existing models, was evident from the comparison of the analytical predictions with the existing experimental data. With the model derived, the second part of the work deals with determining the value of resistance which would yield maximum amplitude attenuation (referred as the optimal resistance value). A method for obtaining the optimal resistance value from the analytical model, based on the presence of a fixed-point in the amplitude response, exists in the literature. But, this method cannot be used on the presented analytical model, as it includes the base-damping of the structure. Hence, a different approach was adopted to determine the optimal resistance from the analytical model. Analytical results were also validated with experimental results from a cantilever piezoelectric-beam. The amplitude plots of the first, second, and third modes of the piezoelectric-beam exhibited a softening e ect, indicating a non-linear behaviour of the piezoelectric patches. Hence, a non-linear constitutive equation was required to describe the behaviour of the piezoelectric patches. In the third part of the work, a two-step experimental procedure was devised to construct the non-linear constitutive equation of the piezoelectric actuators. In the first step, the piezoelectric patches were short circuited and a family of displacement curves were obtained for the first, second and third modes of the piezoelectric-beam by base excitation. The pro le of backbone curves from these plots were used to identify the type of non-linear terms required to describe the mechanical domain. In the second step, voltage excitation was used to obtain a similar set of displacement curves. A comparison of the profile of the backbone curves, of the displacement frequency response plot, from the voltage excited data with those from the base excited data, lead to the identification of the non-linear electromechanical coupling term. The constitutive equation, which accounts for the non-linear nature, of the piezoelectric actuator contains (apart from the linear terms) a quadratic strain term, a cubic strain term, and a term with the product of cubic strain and electric field.

Les matériaux ferroélectriques sont de bons candidats pour réaliser des microdispositifs photostrictifs, capables de se déformer mécaniquement sous éclairement. En effet, lorsqu’ils sont soumis à un rayonnement d’énergie supérieure à leur bande interdite, les charges photoinduites sont séparées par le champ électrique interne du matériau qui dépend de sa polarisation rémanente. Cette séparation de charges génère alors une modification photoinduite du champ électrique et par conséquent une déformation puisque le matériau ferroélectrique est aussi piézoélectrique. Dans cette thèse, le matériau ferroélectrique Pb(ZrₓTi₁₋ₓ)O₃ (PZT) a été choisi pour son coefficient piézoélectrique important. Des couches minces de PZT de haute qualité cristalline ont été déposées par ablation laser pulsé (PLD), et intégrées dans une géométrie capacitive, entre deux électrodes afin de contrôler électriquement les propriétés du matériau. Dans un premier temps, les propriétés piézoélectriques, diélectriques, ferroélectriques et de conduction électrique des couches minces de PZT ont été étudiées et ont montré l’influence des interfaces électrode/ferroélectrique. Les propriétés photovoltaïques des couches minces ont ensuite été étudiées, en fonction de la longueur d’onde d’excitation et de l’état de polarisation, et les résultats obtenus ont démontré l’importance de l’ingénierie sur les réponses photoinduites dans le PZT, notamment le choix de l’électrode supérieure et de la longueur d’onde d’excitation. Le choix de l’électrode supérieure s’est en effet révélé très important pour contrôler le signe des courants et tensions photoinduites ainsi que leur stabilité temporelle. Finalement, les déformations photoinduites dans des films minces de PZT après une impulsion UV ont été étudiées par diffraction des rayons X résolue en temps. L’une des avancées les plus importante de ces travaux réside dans le contrôle in situ de la photostriction (à la fois du signe et de l’amplitude des déformations photoinduites) en faisant varier l’état de polarisation. En considérant les différentes contributions intervenant dans le champ électrique total dans la couche mince, un modèle a été proposé pour expliquer le rôle de la polarisation dans la photostriction. Pour aller plus loin dans l’étude et le contrôle de la photostriction et son optimisation, plusieurs approches ont été explorées, comme la modification de la polarisation rémanente, de la longueur de pénétration des UV, de la fréquence d’excitation UV ou de l’interface électrode/PZT, qui ont montré des effets plus ou moins forts sur la dynamique et l’amplitude de la réponse photostrictive. / Ferroelectric materials are good candidates for photostrictive actuators that deform under illumination. When illuminated above the bandgap energy, photoinduced charges will be separated by the internal electric field of the material, which depends on its remnant polarization. This separation leads to both a photoinduced modification of the electric field and a deformation since a ferroelectric material is also piezoelectric. In this thesis, the ferroelectric material Pb(ZrₓTi₁₋ₓ)O₃ (PZT) was chosen for its high piezoelectric coefficient. PZT thin films of high crystalline quality were grown by pulsed laser deposition (PLD), and integrated in a capacitance geometry between two metallic electrodes to enable the control of the material properties. First, the ferroelectric, dielectric and transport properties were studied to determine the influence of the electrode/ferroelectric interface. The photovoltaic behavior of PZT thin films was subsequently investigated, specifically its dependence on the incident wavelength and the polarization state. The results show that photoinduced response in PZT can be engineered. The choice of the electrodes and the incident energy were found to be particularly important in controlling the sign of the photoinduced current and voltage as well as the temporal stability of the device. Finally, the photoinduced deformation of a PZT thin film after a UV was studied by time-resolved X-ray diffraction. The novelty of this work comes from the in-situ control of the photostriction (both in sign and amplitude) by manipulating the polarization state. By considering the competition between the different components of the total electric field present in the sample, a model was proposed to determine the polarization’s contribution on the photostriction. In order to further control and optimize the photoinduced strain in devices, various approaches were studied, such as tuning the remnant polarization, the UV depth penetration and UV pulses frequency, and developing asymmetric electrodes, and all these approaches were found to affect dynamics and amplitude of photostriction.

No description available.

Microelectromechanical Systems are ubiquitous in modern technology, with applications ranging from accelerometers in smartphones to ultra-high precision motion stages used for atomically-precise positioning. With the appropriate selection of materials and device design, MEMS resonators with ultra-high quality factors can be fabricated at minimal cost. As the sizes of such resonators decrease, however, their mechanical, electrical, and material properties can no longer be treated as linear, as can be done for larger-scale devices. Unfortunately, adding nonlinear effects to a system changes its dynamics from exactly-solvable to only solvable in specific cases, if at all. Despite (and because of) these added complications, nonlinear effects open up an entirely new world of behaviors that can be measured or taken advantage of to create even more advanced technologies. In our resonators, oscillations are induced and measured using aluminum nitride transducers. I used this mechanism for several separate highly-sensitive experiments. In the first, I demonstrate the incredible sensitivity of these resonators by actuating a mechanical resonant mode using only the force generated by the radiation pressure of a laser at room temperature. In the following three experiments, which use similar mechanisms, I demonstrate information transfer and force measurements by taking advantage of the nonlinear behavior of the resonators. When nonlinear resonators are strongly driven, they exhibit sum and difference frequency generation, in which a large carrier signal can be mixed with a much smaller modulation to produce signals at sum and difference frequencies of the two signals. These sum and difference signals are used to detect information encoded in the modulation signal using optical radiation pressure and acoustic pressure waves. Finally, in my experiments, I probe the nonlinear nature of the piezoelectric material rather than take advantage of the nonlinear resonator behavior. The relative sizes of the linear and nonlinear portions of the piezoelectric constant can be determined because the force applied to the resonator by a transducer is independent of the dielectric constant. This method allowed me to quantify the nonlinear constants.

This thesis presents three distinct methodologies aimed at exploring pivotal aspects within the domain of fiber optics and piezoelectric materials. The first approach offers a comprehensive exploration of three pivotal aspects within the realm of fiber optics and piezoelectric materials. The study delves into the influence of voltage variation on piezoelectric displacement, examines the effects of bending multimode fiber (MMF) on data transmission, and scrutinizes the performance of an Autoencoder in MMF image reconstruction with and without additional noise. To assess the impact of voltage variation on piezoelectric displacement, experiments were conducted by applying varying voltages to a piezoelectric material, meticulously measuring its radial displacement. The results revealed a notable increase in displacement with higher voltage, presenting implications for fiber stability and overall performance. Additionally, the investigation into the effects of bending MMF on data transmission highlighted that the bending process causes the fiber to become leaky and radiate power radially, potentially affecting data transmission. This crucial insight emphasizes the necessity for further research to optimize data transmission in practical fiber systems. Furthermore, the performance of an Autoencoder model was evaluated using a dataset of MMF images, in diverse scenarios. The Autoencoder exhibited impressive accuracy in reconstructing MMF images with high fidelity. The results underscore the significance of ongoing research in these domains, propelling advancements in fiber optic technology.The second approach of this thesis entails a comparative investigation involving three distinct neural network models to assess their efficacy in improving image quality within optical transmissions through multimode fibers, with a specific focus on mitigating speckle patterns. Our proposed methodology integrates multimode fibers with a piezoelectric source, deliberately introducing noise into transmitted images to evaluate their performance using an autoencoder neural network. The autoencoder, trained on a dataset augmented with noise and speckle patterns, adeptly eliminates noise and reconstructs images with enhanced fidelity. Comparative analyses conducted with alternative neural network architectures, namely a single hidden layer (SHL) model and a U-Net architecture, reveal that while U-Net demonstrates superior performance in terms of image reconstruction fidelity, the autoencoder exhibits notable advantages in training efficiency. Notably, the autoencoder achieves saturation SSIM in 450 epochs and 24 minutes, surpassing the training durations of both U-Net (210 epochs, 1 hour) and SHL (160 epochs, 3 hours and 25 minutes) models. Impressively, the autoencoder's training time per epoch is six times faster than U-Net and fourteen times faster than SHL. The experimental setup involves the application of varying voltages via a piezoelectric source to induce noise, facilitating adaptation to real-world conditions. Furthermore, the study not only demonstrates the efficacy of the proposed methodology but also conducts comparative analyses with prior works, revealing significant improvements. Compared to Li et al.'s study, our methodology, particularly when utilizing the pre-trained autoencoder, demonstrates an average improvement of 15% for SSIM and 9% for PSNR in the worst-case scenario. Additionally, when compared to Lai et al.'s study employing a generative adversarial network for image reconstruction, our methodology achieves slightly superior SSIM outcomes in certain scenarios, reaching 96%. The versatility of the proposed method is underscored by its consistent performance across varying voltage scenarios, showcasing its potential applications in medical procedures and industrial inspections. This research not only presents a comprehensive and innovative approach to addressing challenges in optical image reconstruction but also signifies significant advancements compared to prior works. The final approach of this study entails employing Hermit Gaussian Functions with varying orders as activation functions within a U-Net model architecture, aiming to evaluate its effectiveness in image reconstruction. The performance of the model is rigorously assessed across five distinct voltage scenarios, and a supplementary evaluation is conducted with digit 5 excluded from the training set to gauge its generalization capability. The outcomes offer promising insights into the efficacy of the proposed methodologies, showcasing significant advancements in optical image reconstruction. Particularly noteworthy is the robust accuracy demonstrated by the higher orders of the Hermit Gaussian Function in reconstructing MMF images, even amidst the presence of noise introduced by the voltage source. However, a decline in accuracy is noted in the presence of voltage-induced noise, underscoring the imperative need for further research to bolster the model's resilience in real-world scenarios, especially in comparison to the utilization of the Rectified Linear Unit (ReLU) function.

The goal of this work is to investigate the piezoelectricity of composite laminates embedded with layers of zinc oxide (ZnO) nanowires. ZnO nanowire embedded composites have the potential to sense and actuate giving the potential for these smart composites to serve the function of being load bearing structures and monitoring the integrity of the structure. This work examines the piezoelectric characteristics of composite beams by investigating their electromechanical coupling in the form of vibration under the presence of electrical excitation. With the help of a mathematical model, piezoelectric constants are estimated for these samples. A layer of ZnO nanowires were grown on plane woven fiberglass fabric that was incorporated into a carbon fiber epoxy composite. The beam deflection velocity was measured as a varying voltage was applied to the composite. Using Hamilton's Principle and Galerkin's method of weighted residuals, a mathematical model was derived to estimate piezoelectric constants for the composites from the experimental data. Piezoelectric properties were determined using vibrational testing and a mathematical model. Piezoelectric constants h31, g31, and d31 were estimated to be 9.138 E7 V/m, 6.092 E-4 Vm/N, and 2.46 E-14 respectively. To demonstrate the electromechanical coupling, ZnO nanowire composites were bonded to Al beams that were progressively damaged to determine if a change in electrical impedance could be observed to correspond to the change in structural impedance of the host beam. Changes in impedance were detected by a change in root mean squared deviation damage metric M. A significant correlation was shown between increasing damage in the host beam and an increase in damage metric M. / Master of Science / A major problem facing both commercial and military aircraft fleets is aircraft grounded time due to inspection. Inspection times tend to be lengthy since visual inspection cannot detect all types of incurred damage an aircraft may face. In the case of composite aircraft structures, a special type of damage known as delamination (when layers of the composite structure become un-bonded) can occur. Since delamination is not always visible from the surface, and composite structures cannot be taken apart since they are made in one piece; additional damage detection methods are necessary. Impedance-based structural health monitoring (IBSHM) is one technique of nondestructive evaluation (NDE) that examines changes in vibrational response of the structure in order to detect damage. A novel approach to IBSHM is incorporating zinc oxide, a type of piezoelectric material, inside the composites due to its ability to deform in the presence of an electric field or generate a voltage when stressed. The goal of this research is to determine piezoelectric properties of composites with ZnO nanowires grown on inner layers of the laminates. Piezoelectric properties were determined using vibrational testing and a mathematical model. To demonstrate the electromechanical coupling, ZnO nanowire composites were bonded to Al beams that were progressively damaged to determine if a change in electrical impedance could be observed to correspond to the change in structural impedance of the host beam. Changes in impedance were detected by a change in root mean squared deviation damage metric M. A significant correlation was shown between increasing damage in the host beam and an increase in damage metric M.

The aim of this thesis was to improve the understanding of microstructure in single crystal ferroelectrics. This was achieved through macroscopic testing of Lead Magnesium Niobate – Lead Titanate (PMN-PT) and microscopic observations of Barium Titanate (BT) single crystals. Multi-axial polarization rotation tests on PMN-PT showed a gradual increase in the change in dielectric displacement due to ferroelectric switching as the electric field is applied at increasing angles to the initial polarization direction. A relatively high remnant polarization for loading angle near to 90° suggested that PMN-PT is more polarizable in certain directions. Strains measured in two directions, parallel to the electric field and perpendicular to the electric field, showed a noticeable variation on two opposite faces of the specimen suggesting an effect of local domain configurations on macroscopic behaviour. A micromechanical model gave an insight into the switching systems operating in the crystal during the polarization rotation test. Domain structure in BT was mapped using synchrotron X-ray reflection topography. By making use of the angular separation of the diffracted reflections and specimen rocking, different domain types could be unambiguously identified, along with the relative tilts between adjacent domains. Fine needle domains (width ≈ 10μm) were successfully mapped providing a composite topograph directly comparable with optical micrograph. The domain structure was confirmed using other techniques such as piezoresponse force microscopy and atomic force microscopy/scanning electron microscopy and optical observations on the etched crystal. Results show that combined use of multiple techniques is necessary to gain a consistent interpretation of the microstructure. Finally, domain evolution in BT under compressive mechanical loading was observed in-situ using optical and X-ray diffraction techniques providing a series of images that show ferroelastic transition. The domain configurations influence the switching behaviour and constitutive models that can account for such effects need to be developed. Quantitative and qualitative data presented in this thesis can assist model development and validation.

Vibration measurements conducted in three vehicles windshields are used to determine frequency content in the windshield of moving vehicles. A piezoelectric energy harvester is modeled, and used in simulations to determine output voltage and power with measured acceleration signal as input.

No description available.