Orientador: Luis Vicente de Andrade Scalvi / Resumo: Este trabalho visa apresentar o desenvolvimento e as principais conclusões referentes à combinação de heterojunções a base de GaAs com óxidos semicondutores, para aplicações em dispositivos optoeletrônicos. O texto foi dividido em duas partes principais, sendo a primeira parte voltada para a síntese e produção do SnO2, relacionada com a formação da heteroestrutura GaAs/SnO2; e a segunda parte é focada na produção dos ressonadores de onda acústicas de bulk,na ordem de GHz, a base de GaAs/ZnO. Na primeira parte, priorizou-se filmes de SnO2, que foram depositados por duas técnicas: sol-gel dip-coating e evaporação resistiva. Os filmes foram depositados sobre substratos de vidro soda-lime, e sobre substratos de GaAs, de quartzo e de a-SiO2. SnO2 foi também depositado sobre filme de GaAs depositado por sputtering. No caso da evaporação resistiva, a rota sol-gel é utilizada também para a preparação do pó que é utilizado como precursor para a evaporação resistiva de filmes de SnO2, combinando essas duas técnicas. Foram investigadas as propriedades ópticas e elétricas de filmes finos de SnO2 dopado com 1% de Er3+ e estruturas hibridas de GaAs/SnO2: Er3+. Entre os principais resultados, verificou-se: 1) espectros de luminescência diferentes do íon Er3+ ao se depositar SnO2 sobre substrato de vidro ou GaAs; 2) Microscopia eletrônica de varredura (MEV) e espectroscopia de energia dispersiva de raios-x (EDX) para filmes de SnO2, depositados por evaporação resistiva, atestaram uma relação... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work aims to present the development and the main conclusions obtained so far regarding the combination of GaAs-based heterojunctions with semiconductor oxides, for applications in optoelectronic devices. The text has been divided in two main parts, where the first one is related to the synthesis and production of SnO2, associated with the formation of the heterostructure GaAs/SnO2; and the second one if focused on the production of bulk acoustic wave resonators, with frequencies in GHz range, based on GaAs/ZnO. In the first part, attention was given to SnO2 films, deposited by two techniques: sol-gel dipcoating and resistive evaporation, on soda-lime glass substrates, and on GaAs, quartz and a-SiO2 substrates. SnO2 was also deposited on GaAs film deposited by sputtering. In the case of resistive evaporation, the sol-gel route is also used to prepare the powder which is used as a precursor for resistive evaporation of SnO2 films, then, by combining these two techniques. Optical and electrical properties of Er3+ -doped SnO2 thin films were investigated as well as the hybrid structure GaAs/SnO2 .Among the main results were: 1) different luminescence spectra of Er3+ ion when depositing SnO2 on glass or GaAs substrate; 2) scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) for SnO2 films deposited by resistive evaporation show a relationship of the thermal annealing temperature with the concentration of Er ions in the surface layers; 3) this con... (Complete abstract click electronic access below) / Doutor

Récemment, beaucoup d'efforts ont été consacrés au contrôle de l'aimantation dans les nanostructures par d'autres moyens qu'un champ magnétique externe. En effet, le but est de miniaturiser les dispositifs et il est difficile d'imposer un champ magnétique présentant de faibles dimensions latérales. D'autre part, les ondes de spin ouvrent actuellement de nouvelles perspectives dans le traitement de l'information. Les avantages qu'elles présentent sont les suivants: longueurs d'onde nanométriques, à comparer à celles des ondes électromagnétiques dans la même gamme de fréquences (GHz-THz), et absence de chauffage par effet Joule. Une possibilité de contrôle réside dans l'utilisation d'ondes acoustiques de surface pour induire la dynamique de l'aimantation ou pour contrôler les ondes de spin. En d'autres termes le contrôle de l'aimantation s’exerce alors via une déformation dynamique. Ceci est rendu possible grâce à une propriété fondamentale des corps magnétiques, le couplage magnéto-élastique, c'est-à-dire le couplage entre aimantation et déformation. Cette thèse porte sur la phénoménologie de l'interaction magnéto-élastique dans les couches minces épitaxiées magnétostrictives de Fe0.8Ga0.2. Nous avons effectué une étude expérimentale systématique des interactions magnéto-élastiques dans des films minces de différentes épaisseurs et structures magnétiques. Nous avons aussi développé deux modèles phénoménologiques, pour interpréter nos expériences. Nous obtenons le résultat important suivant: il est possible d'extraire, d'une étude acoustique, les constantes magnéto-élastiques ainsi que les constantes d'anisotropie magnétique. La thèse a aussi une forte composante technologique. Un des buts était d'exciter efficacement des ondes acoustiques de surface dans la gamme de fréquences de quelques GHz (1-5 GHz) sur substrat piézoélectrique de GaAs dans le but d'observer l'interaction résonante avec les ondes de spin thermiques. Nous avons aussi cherché à exciter des ondes de spin, dans des couches minces épitaxiées, avec des antennes RF afin d'observer l'interaction résonante. Nous présentons des expériences préliminaires sur cette interaction, qui ont été réalisées en diffusion Brillouin (BLS) et en diffusion micro Brillouin, en collaboration avec le laboratoire GHOST à Pérouse, en Italie. / Recently, lot of efforts have been devoted to control the magnetization in nanostructures by means other than external magnetic field to achieve device miniaturization, as it is difficult to handle the magnetic field at low lateral dimensions. On the other hand, a new road emerged towards the wave based computing by employing spin waves (SWs). The advantages, that SWs offer for the data processing are nm wavelength as compared to the electromagnetic waves in the same frequency range (GHz-THz) and the absence of Joule heating. A possibility exists to use Surface Acoustic Waves (SAWs), in other words, dynamic strain, to induce magnetization dynamics or to control spin waves. This is possible due to a very fundamental property of magnetic bodies, the magneto-elastic coupling, that is when magnetization orientation and strain are coupled. This thesis focuses on the phenomenology of the magneto-elastic interaction in thin epitaxied films of magnetostrictive Fe0.8Ga0.2. We performed a systematic experimental study of the magneto-elastic interactions in thin films of different thicknesses and magnetic structures. We also developed two phenomenological models in order to interpret our results. An important result of this study is that we are able to extract the magneto-elastic and the magnetic anisotropy constants by acoustic means. The thesis has also a strong technological component. One aim was to efficiently excite surface acoustic waves in GHz frequency range (1-5 GHz) on GaAs piezoelectric substrates in order to observe the resonant interaction with thermal spin waves. We also managed to excite spin waves in thin epitaxied magnetostrictive layers, using RF antennas. We report preliminary measurements on this interaction that were performed with Brillouin light scattering (BLS) and micro BLS techniques in collaboration with the GHOST laboratory in Perugia, Italy.

Die vorliegende Dissertation beschäftigt sich mit der Verbesserung der Leistungsbeständigkeit von Interdigitalwandlern für zukünftige SAW-Bauelemente durch die Verwendung von kupferbasierten Fingerelektroden. In Bezug auf die Akustomigration, d.h. der Elektrodenschädigung infolge hochzyklischer SAW-Belastung, besitzt Kupfer im Vergleich zu standardmäßig eingesetztem polykristallinem Aluminium eine erhöhte Beständigkeit. Diese lässt sich weiter verbessern, indem die Grenzflächen der Fingerelektroden gegen die durch SAW-Belastung auftretende Loch- und Hügelbildung stabilisiert werden. Das Ziel bestand deshalb darin, die Aktivierungsenergie für den Materialtransport an den Elektrodengrenzflächen zu erhöhen. Zu diesem Zweck wurden in dieser Arbeit Metallisierungen in Form von Kupfer Aluminium-Schichtstapeln und -Legierungen mit jeweils geringem Aluminiumanteil hergestellt. Es konnte gezeigt werden, dass Fingerelektroden aus wärmebehandelten Kupfer-Aluminium-Schichtstapeln eine signifikant erhöhte Leistungsbeständigkeit aufweisen, wobei der elektrische Widerstand im Vergleich zu vollständig legierten Kupfer-Aluminium-Metallisierungen deutlich reduziert ist. Insbesondere kann dieses Schichtsystem durch Elektronenstrahlverdampfung und Lift-Off-Technologie auch kostengünstig hergestellt werden. Der Einfluss von thermischer- und SAW-Belastung auf den mechanischen Spannungszustand in einer Fingerelektrode wurde mittels einer Finiten-Elemente-Simulation untersucht. Darüber hinaus wird der Schädigungsmechanismus für die Akustomigration anhand eines erweiterten Eyringmodells diskutiert.:Inhaltsverzeichnis Kurzfassung 1 Abkürzungen und Symbole 5 1 Einleitung und Stand der Literatur 9 1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.2 Physikalische Grundlagen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.2.1 Wirkungsprinzip von SAW Bauelementen . . . . . . . . . . . . . . . 10 1.2.2 Mathematische Beschreibung von Oberflächenwellen . . . . . . . . . 11 1.2.3 Rayleighwellen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1.2.4 Scherwellen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1.2.5 Interdigitalwandler (IDT) . . . . . . . . . . . . . . . . . . . . . . . . . 15 1.2.6 Deltafunktionsmodell und Messgrößen . . . . . . . . . . . . . . . . . 16 1.3 Materialien für SAW-Bauelemente . . . . . . . . . . . . . . . . . . . . . . . . 23 1.3.1 Substratmaterialien . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 1.3.2 Metallisierungen für Fingerelektroden . . . . . . . . . . . . . . . . . . 25 1.3.3 Diffusionsbarrieren . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 1.4 Modellierung der Lebensdauer von SAW-Filtern . . . . . . . . . . . . . . . . 33 1.4.1 Ursachen der Frequenzverschiebung . . . . . . . . . . . . . . . . . . 33 1.4.2 Allgemeines Eyringmodell und Näherungen . . . . . . . . . . . . . . 35 1.4.3 Berechnung von akustischer Energie- und mechanischer Spannungsverteilung . . . . . . . . . . . . . . . . . . . 38 1.5 Zielstellung und Gliederung der Arbeit . . . . . . . . . . . . . . . . . . . . . 40 2 Experimentelles 43 2.1 Herstellung der SAW-Proben . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.1.1 Lift-Off-Technologie und Elektronenstrahlverdampfung . . . . . . . 43 2.1.2 Atomlagenabscheidung . . . . . . . . . . . . . . . . . . . . . . . . . . 44 2.2 Analyse- und Charakterisierungsmethoden . . . . . . . . . . . . . . . . . . . 45 2.2.1 Elektrischer Widerstand . . . . . . . . . . . . . . . . . . . . . . . . . . 45 2.2.2 Chemische Zusammensetzung . . . . . . . . . . . . . . . . . . . . . . 46 2.2.3 Probenpräparation und Schichtquerschnitt . . . . . . . . . . . . . . . 48 2.3 Lebensdauermessungen an Teststrukturen . . . . . . . . . . . . . . . . . . . 50 2.3.1 Lebensdauermessungen an Power-SAW-Strukturen . . . . . . . . . . 50 2.3.2 Lebensdauermessungen an 2-GHz Reaktanzfilter . . . . . . . . . . . 58 3 Ergebnisse und Diskussion 61 3.1 Voruntersuchungen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 3.1.1 elektrischer Widerstand und thermische Stabilität von Cu/Al-Metallisierungssystemen . . . . . . . . . . . . . . . . . . 62 3.1.2 Cu(Al)-Legierungsverdampfung . . . . . . . . . . . . . . . . . . . . . 64 3.1.3 Cu/Al-Multischicht . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.1.4 Auswahl des Metallisierungssystems . . . . . . . . . . . . . . . . . . 69 3.2 TTF-Messungen an 2-GHz-Filtern mit Al/Cu/Al-Multischichten . . . . . . 71 3.3 Ergebnisse am Al 2nm/Cu 100nm/Al 2nm/Ti 5nm - Multischichtsystem . . 75 3.3.1 Thermische Stabilität der Mikrostruktur . . . . . . . . . . . . . . . . . 75 3.3.2 Einfluss von TiOx und AlOx auf die Grenzflächen und Lebensdauern 75 3.4 Vergleichende Akustomigrationsexperimente an PSAW-Strukturen . . . . . 80 3.4.1 Erwärmung der Metallisierung durch HF-Leistungseintrag . . . . . 80 3.4.2 Frequenzverschiebung durch Temperaturänderung . . . . . . . . . . 81 3.4.3 TTF-Bestimmung: Cu/Al-Metallisierung vs. Referenzsysteme . . . . 82 3.4.4 Mikrostrukturelle Änderungen nach Leistungsbelastung . . . . . . . 89 3.4.5 Zusammenfassung der experimentellen Ergebnisse . . . . . . . . . . 91 4 Simulation der mechanischen Spannungen in den Fingerelektroden 93 4.1 Geometrisches Simulationsmodell (2D) . . . . . . . . . . . . . . . . . . . . . 94 4.2 Randbedingungen, Materialparameter und Vorgehensweise . . . . . . . . . 95 4.3 Thermische Spannungen in Cu-Fingerelektroden ohne äußere Belastung . . 97 4.4 Cu-Fingerelektroden unter SAW-Belastung . . . . . . . . . . . . . . . . . . . 99 5 Schädigungshypothese 101 5.1 Erweitertes Lebensdauermodell . . . . . . . . . . . . . . . . . . . . . . . . . . 101 5.2 Mikroskopische Beschreibung durch Schädigungsmodelle . . . . . . . . . . 103 5.2.1 Elektrodenschädigung bei Scherwellenbelastung . . . . . . . . . . . 103 5.2.2 Elektrodenschädigung bei Rayleighwellenbelastung . . . . . . . . . 104 6 Zusammenfassung und Ausblick 107 Literaturverzeichnis 109 Abbildungsverzeichnis 121 Tabellenverzeichnis 123 Eidesstattliche Erkl¨arung 125 Danksagung 127 Anhang 129 / The aim of this dissertation is the improvement of the power durability of interdigital transducers for future SAW devices using copper based finger electrode materials. Compared to polycrystalline aluminum, which is typically used as electrode material, copper shows a higher durability with respect to acoustomigration, which can be further increased by a stabilization of the electrode interfaces against material transport. For that purpose, copper based metallizations with a small aluminum content were developed as layer stacks or alloys. It could be shown that heat-treated copper-alumininum layer stacks have a significantly higher power durability while the electrical resistivity is reduced in comparison to completely alloyed copper-aluminium metallizations. Additionally, the thin film layer system can be produced by using economical techniques such as electron beam evapouration and lift-off-technology. The influence of thermal and mechanical load on the stress distribution in the finger electrodes was investigated by a finite elements method. The damage mechanism of acoustomigration will be discussed based on an extended Eyring model.:Inhaltsverzeichnis Kurzfassung 1 Abkürzungen und Symbole 5 1 Einleitung und Stand der Literatur 9 1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.2 Physikalische Grundlagen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.2.1 Wirkungsprinzip von SAW Bauelementen . . . . . . . . . . . . . . . 10 1.2.2 Mathematische Beschreibung von Oberflächenwellen . . . . . . . . . 11 1.2.3 Rayleighwellen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1.2.4 Scherwellen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1.2.5 Interdigitalwandler (IDT) . . . . . . . . . . . . . . . . . . . . . . . . . 15 1.2.6 Deltafunktionsmodell und Messgrößen . . . . . . . . . . . . . . . . . 16 1.3 Materialien für SAW-Bauelemente . . . . . . . . . . . . . . . . . . . . . . . . 23 1.3.1 Substratmaterialien . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 1.3.2 Metallisierungen für Fingerelektroden . . . . . . . . . . . . . . . . . . 25 1.3.3 Diffusionsbarrieren . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 1.4 Modellierung der Lebensdauer von SAW-Filtern . . . . . . . . . . . . . . . . 33 1.4.1 Ursachen der Frequenzverschiebung . . . . . . . . . . . . . . . . . . 33 1.4.2 Allgemeines Eyringmodell und Näherungen . . . . . . . . . . . . . . 35 1.4.3 Berechnung von akustischer Energie- und mechanischer Spannungsverteilung . . . . . . . . . . . . . . . . . . . 38 1.5 Zielstellung und Gliederung der Arbeit . . . . . . . . . . . . . . . . . . . . . 40 2 Experimentelles 43 2.1 Herstellung der SAW-Proben . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.1.1 Lift-Off-Technologie und Elektronenstrahlverdampfung . . . . . . . 43 2.1.2 Atomlagenabscheidung . . . . . . . . . . . . . . . . . . . . . . . . . . 44 2.2 Analyse- und Charakterisierungsmethoden . . . . . . . . . . . . . . . . . . . 45 2.2.1 Elektrischer Widerstand . . . . . . . . . . . . . . . . . . . . . . . . . . 45 2.2.2 Chemische Zusammensetzung . . . . . . . . . . . . . . . . . . . . . . 46 2.2.3 Probenpräparation und Schichtquerschnitt . . . . . . . . . . . . . . . 48 2.3 Lebensdauermessungen an Teststrukturen . . . . . . . . . . . . . . . . . . . 50 2.3.1 Lebensdauermessungen an Power-SAW-Strukturen . . . . . . . . . . 50 2.3.2 Lebensdauermessungen an 2-GHz Reaktanzfilter . . . . . . . . . . . 58 3 Ergebnisse und Diskussion 61 3.1 Voruntersuchungen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 3.1.1 elektrischer Widerstand und thermische Stabilität von Cu/Al-Metallisierungssystemen . . . . . . . . . . . . . . . . . . 62 3.1.2 Cu(Al)-Legierungsverdampfung . . . . . . . . . . . . . . . . . . . . . 64 3.1.3 Cu/Al-Multischicht . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.1.4 Auswahl des Metallisierungssystems . . . . . . . . . . . . . . . . . . 69 3.2 TTF-Messungen an 2-GHz-Filtern mit Al/Cu/Al-Multischichten . . . . . . 71 3.3 Ergebnisse am Al 2nm/Cu 100nm/Al 2nm/Ti 5nm - Multischichtsystem . . 75 3.3.1 Thermische Stabilität der Mikrostruktur . . . . . . . . . . . . . . . . . 75 3.3.2 Einfluss von TiOx und AlOx auf die Grenzflächen und Lebensdauern 75 3.4 Vergleichende Akustomigrationsexperimente an PSAW-Strukturen . . . . . 80 3.4.1 Erwärmung der Metallisierung durch HF-Leistungseintrag . . . . . 80 3.4.2 Frequenzverschiebung durch Temperaturänderung . . . . . . . . . . 81 3.4.3 TTF-Bestimmung: Cu/Al-Metallisierung vs. Referenzsysteme . . . . 82 3.4.4 Mikrostrukturelle Änderungen nach Leistungsbelastung . . . . . . . 89 3.4.5 Zusammenfassung der experimentellen Ergebnisse . . . . . . . . . . 91 4 Simulation der mechanischen Spannungen in den Fingerelektroden 93 4.1 Geometrisches Simulationsmodell (2D) . . . . . . . . . . . . . . . . . . . . . 94 4.2 Randbedingungen, Materialparameter und Vorgehensweise . . . . . . . . . 95 4.3 Thermische Spannungen in Cu-Fingerelektroden ohne äußere Belastung . . 97 4.4 Cu-Fingerelektroden unter SAW-Belastung . . . . . . . . . . . . . . . . . . . 99 5 Schädigungshypothese 101 5.1 Erweitertes Lebensdauermodell . . . . . . . . . . . . . . . . . . . . . . . . . . 101 5.2 Mikroskopische Beschreibung durch Schädigungsmodelle . . . . . . . . . . 103 5.2.1 Elektrodenschädigung bei Scherwellenbelastung . . . . . . . . . . . 103 5.2.2 Elektrodenschädigung bei Rayleighwellenbelastung . . . . . . . . . 104 6 Zusammenfassung und Ausblick 107 Literaturverzeichnis 109 Abbildungsverzeichnis 121 Tabellenverzeichnis 123 Eidesstattliche Erkl¨arung 125 Danksagung 127 Anhang 129

On étudie l'évolution d'une solution initialement homogène constituée de deux espèces soumises à un gradient thermique qui génère un transfert de matière, ce qui peut conduire à la séparation des espèces du fluide binaire. La configuration choisie pour étudier la séparation est une cellule rectangulaire (ou parallélépipédique), horizontale et placée dans le champ de pesanteur. La présence d'une source piézo-électrique, sur l'une des parois verticales de la cavité, permet de générer un écoulement stationnaire à grande échelle. L'écoulement est induit par la propagation d'ondes ultrasonores au sein du fluide visqueux : la dissipation de l'énergie acoustique de l'onde au sein du fluide porte le nom d'Eckart streaming. On cherche à optimiser la séparation en combinant gradient thermique et source acoustique. La première partie consiste en l'étude de l'écoulement isotherme généré par l'onde ultrasonore dans un fluide mono-constituant. Après avoir calculé le champ d'intensité acoustique avec l'intégrale de Rayleigh, le profil est implémenté dans un code aux éléments finis Comsol Multiphysics. Les résultats numériques sont comparés avec des résultats expérimentaux antérieurs. Dans une seconde partie, on considère une cavité contenant un fluide binaire. On détermine analytiquement, à l'aide du logiciel Maple, la séparation (différence de fraction massique entre les deux extrémités de la cellule) en fonction des paramètres de contrôle du problème. Des simulations numériques 2D et 3D ont montré un bon accord entre les résultats analytiques et numériques, pour un paramètre acoustique constant et un chauffage par le bas ou par le haut de la cellule. Le problème considéré dépend alors de huit paramètres adimensionnels. Trois d'entre eux sont propres à la nature du fluide binaire : le nombre de Lewis Le, de Prandtl Pr et le facteur de séparation ψ. Il y a ensuite deux paramètres de contrôle, le nombre de Rayleigh thermique Ra et la force acoustique adimensionnelle A. Enfin, les autres paramètres adimensionnels sont les deux rapports d'aspect de la cavité, ainsi que l'épaisseur relative du faisceau acoustique / The evolution of an initially homogeneous solution consisting of two species subjected to a thermal gradient which generates a mass transfer, which can lead to the separation species from the binary fluid, is studied. The configuration chosen to study the separation is a rectangular (or parallelepipedic) cell, horizontal and placed in the gravitational field. The presence of a piezoelectric source on one of the vertical walls of the cavity makes it possible to generate a stationary flow on a large scale. The flow is induced by the propagation of ultra-sonic waves within the viscous fluid : the dissipation of the acoustic energy of the wave within the fluid is called Eckart streaming. We seek to optimize the separation by combining thermal gradient and acoustic source. The first part consists of the study of the isothermal flow generated by the ultrasonic wave in a monoconstituent fluid. After calculating the acoustic intensity field with the Rayleigh integral, the profile is implemented in a Comsol Multiphysics finite element code. The numerical results are compared with previous experimental results. In a second part, we consider a cavity containing a binary fluid. A configuration heated from the top is privilegied to allow the insertion of an acoustic source. The separation (difference of mass fraction between the two ends of the cell) is determined analytically using the Maple software as a function of the control parameters of the problem. 2D and 3D numerical simulations showed a good agreement between the analytical and numerical results, for a constant acoustic parameter. The problem considered depends on eight dimensionless parameters. Three of them are specific to the nature of the binary fluid : the Lewis number Le, the Prandtl number Pr and the separation factor ψ. There are then two control parameters, the thermal Rayleigh number Ra and the adimensional acoustic force A. Finally, the other dimensionless parameters are the two aspect ratios of the cavity, as well as the relative thickness of the beam.

Cette thèse est consacrée à l'étude du problème de la diffraction d'une onde acoustique par un ensemble de petites hétérogénéités pénétrables ainsi qu'au développement de méthodes de simulation numérique dédiées à la résolution efficace de ce type de problèmes. La principale nouveauté de ces travaux provient du fait que nous traitons ce problème dans le domaine temporel.La première partie de ce manuscrit est consacrée à l'analyse asymptotique du problème de diffraction, menée à bien grâce à la méthode des développements asymptotiques raccordés, le petit paramètre étant la taille caractéristique des défauts $varepsilon$. Ceci nous permet d'obtenir un développement du champ acoustique comme perturbation du problème sans défauts. Nous prouvons un résultat de consistance entre le champ exact et son développement asymptotique en $varepsilon$.Dans la seconde partie, en s'appuyant sur les résultats de l'analyse asymptotique, nous proposons deux modèles approchés pour le problème de diffraction. Ces deux modèles sont bien-posés et leur solution sont chacune des approximations précises du champ total. La principale caractéristique de ces modèles approchés est qu'ils s'appuient tous deux sur une équation d'onde dans le milieu ambiant (sans défauts), couplée à des termes sources auxiliaires permettant de rendre compte de la présence des défauts. Il est ainsi envisageable, pour traiter ces problèmes approchés, d'utiliser une méthode de discrétisation par éléments finis présentant des performances de temps de calcul similaires au cas de la propagation d'une onde dans l'espace libre, puisque l'opérateur des ondes sous-jacent s'appuie sur une géomètrie indépendante des petits défauts. Nous présentons un certain nombre de résultats numériques permettant de valider les deux modèles proposés ainsi qu'une analyse d'erreur numérique. / This work is dedicated to the study of the diffraction of acoustic waves by a set of small inclusions, as well as to the development of numerical methods for the simulation of such phenomenons. The main novelty of this work is that we deal with time-domain waves.The first part of this manuscript deals with the asymptotic analysis of the diffraction problem, which is carried out by matched asymptotics, the small parameter being the characteristic size of the defects $varepsilon$. This furnishes an asymptotic expansion of the acoustic field as a perturbation of the defect-free problem. We prove a consistency result between the total field and its $varepsilon$-asymptotic expansion.In the second part, using the results of the asymptotic analysis, we introduce two approximate models for the diffraction problem. These models are well-posed and their solution are precise approximations of the total acoustic field. One of the main features of these approximate models is that they both lie on a wave equation in the surrounding medium (without defects), coupled to auxiliary source terms which account for the presence of the inclusions. It is then possible to discretize these approximate models using a finite element method, leading to a numerical method which performs as fast as in the defect-free case, since the underlying wave operator is independent of the defects. We present several numerical results which validate both approximate models as well as some insights about numerical error analysis.

[pt] Em poços de petróleo, uma boa cimentação é fundamental para garantir o suporte estrutural do revestimento e isolar o poço de águas subterrâneas. A alteração das propriedades e o surgimento de defeitos no cimento podem levar a vazamentos e danos ambientais. Durante a desativação e o abandono do poço em operações conhecidas como P&A (Plug & Abandonment), é necessário avaliar a condição do cimento assim como a identificação de possíveis defeitos. Desde 1950, ferramentas de perfilagem acústica capazes de analisar a condição do cimento vem sendo desenvolvidas e aprimoradas. As ferramentas mais famosas foram a Cement Bond logging Tools (CBT), baseada na técnica de operação CBL (Cement Bond Logging) e VDL (Variable Density Logging), e a Cement Evaluation Tools (CET). Contudo, essas ferramentas foram projetadas para operar somente em configurações com um único revestimento e sem a coluna de produção. Remover a coluna de produção é um processo caro, por isso, um desafio na indústria que permanece até os dias atuais é a criação de uma ferramenta capaz de operar em poços sem a necessidade de se remover a coluna de produção visando a redução dos custos do processo, ou em poços que possuem múltiplos revestimentos. Nos últimos anos muitas patentes e artigos tem sido publicados abordando esse mesmo tema. Este trabalho possui como motivação analisar a eficiência da utilização de ondas ultrassônicas guiadas em poços com multicamadas para detecção de defeitos presentes na camada de cimento. Para isso, primeiramente se realizou uma vasta pesquisa bibliográfica buscando identificar os tipos mais frequentes de defeitos existentes, o princípio de funcionamento das principais ferramentas comerciais existentes e os avanços das pesquisas na fronteira do conhecimento desse assunto. Modelou-se a partir da teoria de ondas e de suas equações analíticas o poço estudado, encontrando as equações de dispersão que regem o problema. Desenvolveu-se um código analítico-numérico capaz de resolver essas equações e de obter as curvas de dispersão. Além disso, analisou-se como os defeitos e suas variações afetam as curvas de dispersão, identificando os comportamentos característicos para cada caso. Posteriormente, a distribuição da energia, obtida a partir do vetor de Poynting no poço, foi usado afim de se investigar os modos que concentram a energia na camada de cimento. Para o caso sem a coluna de produção, concluiu se que os melhores modos de excitação estão em alta frequência, pois a energia se concentra no cimento. Já para o caso com a coluna de produção, encontrou-se que na frequência de 30,13 kHz a uma vagarosidade de 726,5 us/m a energia está praticamente toda concentrada no cimento o que é interessante para se analisar defeitos apenas no cimento e que em 39,17 kHz e 507 us/m a energia está distribuída entre o cimento e a coluna de produção, sendo interessante para analisar defeitos que envolvam ambos. / [en] In oil wells, a good cementation is essential to guarantee the structural support of the casing and isolate the well from groundwater. The variations in the material properties and the presence of defects in the cement can lead to leaks and environmental damage. During the deactivation and abandonment of the well in P&A operations (Plug & Abandonment), it is necessary to evaluate the cement condition as well as investigate possible defects. Since 50 s, cement bond logging tools capable of analyzing the cement condition have been developed and improved. The most famous tools were Cement Bond Logging Tools (CBT), based on CBL (Cement Bond Logging) and VDL (Variable Density Logging) operation technique and the Cement Evaluation Tools (CET). However, these tools were designed to operate only in single-casing set, without the tubing. Remove the tubing is an expensive process, so a challenge in the industry that remains open is the creation of a tool capable of operating in wells with tubing in order to reduce process costs or in wells that have multiple casings. In recent years, many patents and scientific paper have been published on the same topic. This work analyzes the effectiveness of the use of guided ultrasonic waves in multilayer wells to detect defects present in the cement layer. To this end, a vast bibliographic search was first carried out in order to identify the most frequent types of existing defects, the principle of operation of the main commercial tools and the advances in research on this subject. The well studied was modelled from analytical equations of the elastic wave theory, aiming at the dispersion equations that govern the problem. An analytical-numerical code was developed capable of solving these equations and obtaining the dispersion curves. Furthermore, it was analyzed how the defects and their variations affect the dispersion curves, identifying the characteristic behaviours for each case. Subsequently, the energy distribution, obtained by the Poynting vector, in the well was used in order to investigate the modes that concentrate the energy in the cement layer. For the single-casing, it was concluded that the best excitation modes were those with high frequency, because the energy is concentrated in cement. For through-tubing case, it was found that at a frequency of 30.13 kHz and a slowness of 726.5 us/m, the energy is virtually completely concentrated in cement, which is interesting to analyze defects present only in cement layer and that at 39.17 kHz and 507 us/m the energy is distributed between cement and tubing, being interesting to analyze defects that involve both layers.

The ability to sense gas such as methane can provide an early warning system to protect human lives. High demand for the ability to sense the world around us has provided an extensive area of research for sensor technology. In particular, current sensor technology, specifically for methane, has provided sensors that require a heated environment to function. The majority of current methane sensors function at temperatures between 150°C and 450°C [1-3]. This thesis will explore an approach to produce a room temperature methane sensor.

Acoustic simulation of sound propagation inside the vocal tract is a key element of speech research, especially for articulatory synthesis, which allows one to relate the physics of speech production to other fields of speech science, such as speech perception. Usual methods, such as the transmission line method, have a very low computational cost and perform relatively good up to 4-5 kHz, but are not satisfying above. Fully numerical 3D methods such as finite elements achieve the best accuracy, but have a very high computational cost. Better performances are achieved with the state of the art semi-analytical methods, but they cannot describe the vocal tract geometry as accurately as fully numerical methods (e.g. no possibility to take into account the curvature). This work proposes a new semi-analytical method that achieves a better description of the three-dimensional vocal-tract geometry while keeping the computational cost substantially lower than the fully numerical methods. It is a multimodal method which relies on two-dimensional finite elements to compute transverse modes and takes into account the curvature and the variations of crosssectional area. The comparison with finite element simulations shows that the same degree of accuracy (about 1% of difference in the resonance frequencies) is achieved with a computational cost about 10 times lower.

In both, cell secretome analysis and bacteria evolution, controlled handling of particles with a few to sub-micrometers in size and media exchange are inevitable in order to investigate body fluid’s proteins or change the surrounding culture conditions for pivoted evolution. Typically, nanofiltration and ultra-centrifugation are employed which can lead to cell damage, need large sample volumes and have a high sample loss. Using contactless and label-free acoustic cell manipulation, disadvantages of other magnetic, dielectric or hydrodynamic methods can be avoided. Here, a novel design using acoustic forces for small particle trapping and media exchange is thoroughly numerically investigated including first- and second-order acoustic effects. The device comprises parallel aligned medium and air channels separated by a thin wall. Particle trapping occurs at this thin wall. The medium channel dimensions (height and width) and thin wall thickness are optimized with respect to trapping forces. Thinnest walls are preferable and an aspect ratio of 0.8. First preliminary experimental variation with polystyrene particles showed good agreement with the simulations. Thereby the particle trapping efficiency is evaluated under quiescent flow conditions. For particle trapping, a device with a channel height of 290μm and an aspect ratio of 0.7 is superior which supports the numerical results. Finally, medium exchange of E. coli bacteria is demonstrated with best results for a device with a channel height of 450μm and an aspect ratio of 0.8 showing that 13.4% of the initial bacteria were released after medium exchange which can be used for further processing.

Καθώς η εξέλιξη της βιοϊατρικής επιστήμης και τεχνολογίας είναι συνεχής και ραγδαία, η έρευνα επικεντρώνεται τόσο στη βελτίωση των κλινικών τεχνικών όσο και στην ανάπτυξη νέων με κυριότερο σκοπό την ακριβέστερη και ασφαλέστερη διάγνωση και θεραπεία. Στην παρούσα διατριβή, μελετάται η χρήση δύο περιοχών του φάσματος, που ανήκουν στο πεδίο των μη ιοντιζουσών ακτινοβολιών, των μικροκυματικών και των ακουστικών συχνοτήτων, για διαγνωστικές λειτουργικές εφαρμογές εγκεφάλου. Παρόλο που η χρήση των υπερήχων έχει αξιοποιηθεί στην κλινική εφαρμογή, οι αναφορές για τη χρήση των ακουστικών κυμάτων στις βιοϊατρικές εφαρμογές είναι περιορισμένες στη διεθνή βιβλιογραφία. Στην παρούσα διδακτορική διατριβή μελετάται η ανάπτυξη ενός συστήματος για διαγνωστικές εφαρμογές εγκεφάλου στις ακουστικές συχνότητες. Στα δύο πρώτα κεφάλαια περιγράφονται οι βασικές αρχές που διέπουν την επιστήμη του ήχου (ακουστική) αλλά και οι φυσικές αρχές αλληλεπίδρασης των ακουστικών κυμάτων με τους βιολογικούς ιστούς (δημιουργία και εξέλιξη των φυσικών φαινομένων ανάκλασης, διάθλασης, μετάδοσης και απορρόφησης της ηχητικής δέσμης). Πιο συγκεκριμένα, μοντελοποιείται και μελετάται θεωρητικά το πρόβλημα της αλληλεπίδρασης των ακουστικών κυμάτων με τον ανθρώπινο εγκέφαλο ενώ τέλος παρουσιάζονται βασικές και σύγχρονες εφαρμογές ακουστικής στην ιατρική. Στο τρίτο κεφάλαιο παρατίθεται η θεωρητική ανάλυση και οι βασικές αρχές της προτεινόμενης μεθόδου για μέτρηση της εγκεφαλικής δραστηριότητας στις ακουστικές συχνότητες και πραγματοποιούνται προσομοιώσεις, με τη βοήθεια του λογισμικού MATLAB, παραθέτοντας τα αντίστοιχα αριθμητικά αποτελέσματα. Ολοκληρώνοντας το πρώτο μέρος της διατριβής, στο τέταρτο κεφάλαιο παρουσιάζεται η πρακτική υλοποίηση του προτεινόμενου συστήματος, περιλαμβάνοντας ανάλυση του πιεζοηλεκτρικού φαινομένου και των αντίστοιχων αισθητήρων, εκτενής μελέτη του κάθε τμήματός του καθώς και πειραματικές μετρήσεις με ομοιώματα. Τα μικροκύματα έχουν χρησιμοποιηθεί σε πλήθος διαγνωστικών και θεραπευτικών τεχνικών τόσο σε επίπεδο έρευνας όσο και στην κλινική πράξη. Στην παρούσα διατριβή πραγματοποιείται θεωρητική μελέτη και υλοποίηση πολυσυχνοτικών κυρτών προσαρμόσιμων μικροταινιακών τυπωμένων κεραιών και χρήση τους με σύστημα ευαίσθητου δέκτη μικροκυματικής ραδιομετρίας. Στο κεφάλαιο 5 περιγράφονται η βασική τεχνολογία και οι βασικές αρχές λειτουργίας της παθητικής μεθόδου διάγνωσης με μικροκύματα, της μικροκυματικής ραδιομετρίας ενώ στο κεφάλαιο 6 μοντελοποιούνται οι προτεινόμενες κυρτές κεραίες και μελετούνται με τη βοήθεια του ηλεκτρομαγνητικού προσομοιωτικού λογισμικού πακέτου HFSS που χρησιμοποιεί τη μέθοδο των πεπερασμένων στοιχείων. Επίσης, παρουσιάζονται αναλυτικά οι ιδιότητες εστίασης των κεραιών αυτών σε δύο διαφορετικά μοντέλα κεφαλιού στο εύρος συχνοτήτων 2 – 3.3 GHz. Τέλος, οι κεραίες που μελετήθηκαν θεωρητικά, κατασκευάζονται και χρησιμοποιούνται ως κεραίες λήψης ραδιομέτρου τύπου διακόπτη Dicke (Dicke switch) για πειραματικές μετρήσεις σε ομοιώματα (κεφάλαιο 7). Ο συνδυασμός των δύο συστημάτων σε μια κοινή υλοποίηση και η πραγματοποίηση κοινών πειραματικών μετρήσεων και στις δύο περιοχές συχνοτήτων είναι μια πολύ σημαντική προοπτική που μπορεί να βελτιώσει τα πιθανά μειονεκτήματα της κάθε μεθόδου αλλά και να τις επαληθεύσει, με την παροχή και το συνδυασμό διαφορετικού είδους πληροφορίας για το ίδιο αίτιο. / As progress in the field of biomedical science and technology is continuous, the research focuses mainly on the improvement of existing clinical techniques and the development of new ones, aiming at the most accurate and safe diagnosis and treatment. In the present thesis, passive diagnosis in the non ionizing radiation regime and especially two frequency bands, microwave and acoustic frequencies, are used for diagnostic functional brain applications. Despite the fact that ultrasounds have been utilized in clinical practice, the references regarding the application of acoustic waves in medical diagnosis are restrained in international literature. In the present thesis the development of a system for diagnostic brain applications operating at acoustic frequencies is studied. In the first two chapters the basic principles of acoustics and the physical principles of the interaction of acoustic waves with biological tissue (including physical phenomena of reflection, diffraction, transmission and absorption of sound) are described. More specifically, the problem of the interaction of acoustic waves with the human brain tissues is theoretically modeled and studied. In the third chapter theoretical analysis is carried out and the basic operation principles of the suggested method for monitoring brain activity in acoustic frequencies are described. Simulations are performed using the MATLAB software and the respective numerical results are presented. Completing the first part of the thesis, the fundamentals of the system’s practical implementation are introduced in the fourth chapter. All system modules are described and the results of the implementation study through experiments using phantoms are presented. Microwaves have been used in many diagnostic and therapeutic techniques both at research level and in clinical practice. Herein, a theoretical study and implementation of various multi-frequency conformal microstrip patch antennas are performed, and finally they are used in conjunction with a sensitive microwave radiometry receiver. In chapter 5 the basic technology and the basic operation principles of the passive diagnostic method with microwaves (microwave radiometry) are described, while in chapter 6 the suggested conformal antennas are modeled and studied using the electromagnetic simulation tool HFSS that implements the finite element method (FEM). Moreover, the properties of these antennas and their focusing ability on specific brain areas are presented at 2 – 3.3 GHz in two different head models. Finally, a few are materialized in Rogers 4350B dielectric substrate and two of them are used together with a Dicke switch type radiometer for experimental measurements with phantoms (chapter 7). The combination of the aforementioned systems in a common implementation and the realization of common experimental measurements in both frequency bands is a very significant prospective which can optimize the performance of each methodology, by collecting and combining different types of information originating from the same event.