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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Multimode Optomechanical Systems and Phononic Networks

Kuzyk, Mark 11 January 2019 (has links)
An optomechanical system consists of an optical cavity mode coupled to a mode of a mechanical oscillator. Depending on the configuration of the system, the optomechanical interaction can be used to drive or cool the mechanical mode, coherently swap the optical and mechanical states, or create entanglement. A multimode optomechanical system consists of many optical (mechanical) modes coupled to a mechanical (optical) mode. With the tools of the optomechanical interaction, multimode optomechanical systems provide a rich platform to study new physics and technologies. A central challenge in optomechanical systems is to mitigate the effects of the thermal environment, which remains significant even at cryogenic temperatures, for mechanical oscillators typically used in optomechanical systems. The central theme of this thesis is to study how the properties of multimode optomechanical systems can be used for such mitigation of thermal noise. The most straightforward extension of an optomechanical system to a multimode system is to have a single optical mode couple to two mechanical modes, or a single mechanical mode couple to two optical modes. In this thesis, we study both types of multimode system. In each case, we study the formation of a dark mode, an eigenstate of the three-mode system that is of particular interest. When the system is in a dark state, the two modes of similar character (optical or mechanical) interact with each other through the mode of dissimilar character, but due to interference, the interaction becomes decoupled from the properties of the dissimilar mode. Another interesting application of the three-mode system is two-mode optical entanglement, generated through mechanical motion. Such entanglement tends to be sensitive to thermal noise. We propose a new method for generating two-mode optical entanglement in the three-mode system that is robust against the thermal environment of the mechanical mode. Finally, we propose a novel, scalable architecture for a quantum computer. The architecture makes use of the concepts developed earlier in the thesis, and applies them to a system that on the surface looks quite different from the standard optomechanical system, but is formally equivalent. This dissertation includes previously published and unpublished coauthored material.

Investigation de la dispersion des ondes élastiques dans les milieux micro-structurés : applications aux poutres phononiques / Investigation of elastic wave dispersion in micro-structured media with a focus on phononic strip applications

Coffy, Etienne 13 December 2017 (has links)
La micro-structuration périodique d’un milieu influence fortement la propagation des ondes élastiques. Ces structures, nommées cristaux phononiques, permettent de manipuler les ondes en les ralentissant, voire en interdisant leurs propagations pour certaines gammes de fréquences appelées bandes interdites. Au cours de la thèse, la dispersion des ondes élastiques dans des structures composées de piliers résonants périodiquement attachés à des poutre structurées a été numériquement et expérimentalement étudiée. Basées sur la combinaison de résonances locales avec des réflexions multiples de Bragg, des poutres phononiques avec de larges bandes interdites ont été obtenues. En particulier, une poutre phononique avec une bande interdite présentant une largeur relative de 94% autour du mégahertz a été fabriquée et caractérisée.Les poutres phononiques ont été utilisées pour améliorer les facteurs de qualité des résonances de défauts insérés en fin, ou entre les poutres. Une amélioration d’un facteur 8 d’une résonance d’un défaut encastrée-libre accroché à une poutre phononique a été démontrée. Cette amélioration est attribuée au confinement de l’énergie mécanique par la poutre phononique dont la bande interdite recouvre la fréquence de résonance du défaut. En parallèle de ces activités, une plateforme pompe sonde hétérodyne femtoseconde a été utilisée pour caractériser la propagation des ondes élastiques à la surface de films minces microstructurés. Une forte anisotropie ainsi qu’une réduction des vitesses des ondes a été mis en évidence. Ces observations ont été reliées aux micro-structurations particulières des films, avec des simulations en éléments finis. / Periodic microstructures in media strongly influences the propagation of elastic waves. These structures, known as phononic crystals, allow the manipulation of waves such as their slowdown, or their prohibition for frequency ranges called band gaps.During the thesis, the dispersion of elastic waves propagating through structures composed of resonant pillars periodically attached to tailored strips was studied. Based on the combination of Bragg scattering and local resonances, phononic strips with large band gaps were achieved. Notably, a phononic strip with a band gap displaying a relative width of 94% in the megahertz range was demonstrated.Phononic strips were then used to ameliorate the resonances’ quality factors for defects inserted at the end, or within the strips. An improvement by a factor of 8 of the resonance quality factor of a beam clamped to a phononic strip was achieved. This improvement was assigned to the mechanical energy confinement linked with the phononic strip, as its band gap overlaps the resonance frequency of the defect.In parrallel to these studies, a femtosecond heterodyne pump probe setup was used to characterize the waves propagation on the surface of microstructured thin films. A strong anisotropy as well as a speed reduction were observed. These observations were linked to the particular microstructures of the films, using numerical simulations performed with the Finite Element Method.

Control of Nanoscale Thermal Transport for Thermoelectric Energy Conversion and Thermal Rectification

Pal, Souvik 18 December 2013 (has links)
Materials at the nanoscale show properties uniquely different from the bulk scale which when controlled can be utilized for variety of thermal management applications. Different applications require reduction, increase or directional control of thermal conductivity. This thesis focuses on investigating thermal transport in two such application areas, viz., 1) thermoelectric energy conversion and 2) thermal rectification. Using molecular dynamics simulations, several methods for reducing of thermal conductivity in polyaniline and polyacetylene are investigated. The reduction in thermal conductivity leads to improvement in thermoelectric figure of merit. Thermal diodes allow heat transfer in one direction and prevents in the opposite direction. These materials have potential application in phononics, i.e., for performing logic calculations with phonons. Rectification obtained with existing material systems is either too small or too difficult to implement. In this thesis, a more useful scheme is presented that provides higher rectification using a single wall carbon nanotube (SWCNT) that is covalently functionalized near one end with polyacetylene (PA). Although several thermal diodes are discussed in literature, more complex phononic devices like thermal logic gates and thermal transistors have been sparingly investigated. This thesis presents a first design of a thermal AND gate using asymmetric graphene nanoribbon (GNR) and characterizes its performance. / Ph. D.


aryana, kiumars 22 June 2018 (has links)
No description available.

Theoretical and Experimental Investigations to Improve the Performance of Surface Acoustic Wave (SAW) Biosensors

Richardson, Mandek 01 January 2014 (has links)
The objective of this dissertation is to improve the performance of surface acoustic wave (SAW) biosensors for use in point-of-care-testing (POCT) applications. SAW biosensors have the ability to perform fast, accurate detection of an analyte in real time without the use of labels. However, the technology suffers from the inability to differentiate between specific and non-specific binding. Due to this limitation, direct testing of bodily fluids using SAW sensors to accurately determine an analyte's concentration is difficult. In addition, these sensors are challenged by the need to detect small concentrations of a biomarker that are typically required to give a clinical diagnosis. Sensitivity, selectivity and reliability are three critical aspects for any sensing platform. To improve sensitivity the delay path of a SAW sensor has been modified with microcavities filled with various materials. These filled cavities increased sensitivity by confining wave energy to the surface by way of constructive interference and waveguiding. Thus, the improved sensitivity will result in a lower limit of detection. In addition, insertion loss is decreased as a consequence of increased wave confinement to the surface. Sensor selectivity and reliability are adversely affected by non-specific binding of unwanted species present in a sample. To address this issue a multifunctional SAW sensor is presented. The sensor consists of two SAW delay lines oriented orthogonal to each on ST-quartz in order to generate two distinct wave modes. One wave mode is used for sensing while the other is used to remove loosely bound material. By using the same transduction mechanism for both removal and sensing, the sensor chip is simplified and complex electronics are avoided. The findings of this research involve the technological advances for SAW biosensors that make their use in POCT possible.

Electromagnetically Modulated Sonic Structures

Walker, Ezekiel Lee 05 1900 (has links)
Phononic crystals are structures composed of periodically arranged scatterers in a background medium that affect the transmission of elastic waves. They have garnered much interest in recent years for their macro-scale properties that can be modulated by the micro-scale components. The elastic properties of the composite materials, the contrast in the elastic properties of the composite materials, and the material arrangement all directly affect how an elastic wave will behave as it propagates through the sonic structure. The behavior of an elastic wave in a periodic structure is revealed in its transmission bandstructure, and modification of any the elastic parameters will result in tuning of the band structure. In this dissertation, a phononic crystal with properties that can be modulated using electromagnetic radiation, and more specifically, radio-frequency (RF) light will be presented.

Remotely Controlled Magneto-Phononic Devices Achieving Nonreciprocity and Anderson Localization in Ferrofluid

Jin, Yuqi 12 1900 (has links)
Motivated by previous relevant research on phononics including both active and passive phononics, the interest of faster turnability and more functions of the active phononics of further study led to this proposing research topic: magnetic field tunable active functional phononics. The first design of magnetic field tunable reciprocal--non-reciprocal transmission acoustic device was established, material was characterized, and numerical simulation has been performed. The simulation results show clear T-symmetric breaking non-reciprocity due to energy level splitting effect with Doppler effect – an acoustic Zeeman effect. Inspired by this preliminary work, further experiments were planned to demonstrate this effective Zeeman effect in phononics and effectively charged phonons in water based ferro-fluid. The objectives of this work as the next series of tasks were to illustrate acoustic Zeeman effect and acoustic Landau levels in various strength of magnetic field to investigate a design non-reciprocal sound device with magnetic field switching, which could be controlled on the amount of non-reciprocity with the strength of magnetic field. Once this new field first discovered by the proposed study tasks, more active tunable magnetic field phononics devices could be designed and exemplified in terms of both simulations and experiments. Faster and more controllable active phononic devices could be designed and made based on this study. The experimental maximum non-reciprocity was measured as 22 dB difference and the amount of the non-reciprocity can be further controlled by adjusting the strength of the external magnetic field. The remote pumping system in the device worked as expected and did not introduce any impact of the cavity properties.

Nonlinear Ultrafast Excitation and Two-Dimensional Terahertz Spectroscopy of Solids

Knighton, Brittany E. 27 July 2021 (has links)
Ultrafast spectroscopy allows us to probe and understand material properties. With it, we can measure phonon-polaritons (optical phonons coupled with light) and the resulting dispersion curve in lithium niobate. Customizing the excitation source in ultrafast measurements can excite phonon modes to large amplitudes, allowing the experimental exploration of the Potential Energy Surface in solids. However, stronger pump fluences and bigger signal isn't always the answer in ultrafast spectroscopy. When sample signals and their nonlinear and mechanisms cannot be distinguished with 1D measurements, simple 2D THz measurements are a great place to start searching for distinct factors as was the case in cadmium tungstate. 2D measurements when paired with modeling and first principles calculations can reveal cutting edge information about exciting materials.

Establishing a Machine Learning Framework for Discovering Novel Phononic Crystal Designs

Feltner, Drew 26 August 2022 (has links)
No description available.

Contribution à l'étude des cristaux phononiques à résonance locale dans les régimes sonique et hypersonique : approches théorique et expérimentale / A contribution to study of locally resonant phononic crystals in sonic and hypersonic regimes : theory and experiments

Oudich, Mourad 04 November 2011 (has links)
Dans le cadre de cette thèse, nous nous sommes intéressés d'abord au mécanisme de résonance locale en développant différents modèles théoriques pour l'étude de nouveaux cristaux phononiques à résonance locale (CPRL) en plaque dont l'élément principal et l'élastomère (silicone rubber). Le mode opératoire de ce mécanisme a été étudié et les ouvertures des bandes interdites ont été interprétées théoriquement ainsi que les phénomènes physiques mis en jeu. La mise en évidence expérimentale de la bande interdite a été réalisée par la fabrication et la caractérisation de structures CPRL et une parfaite concordance a été constatée entre les résultats théoriques et expérimentaux. Une étude des phénomènes de guidage a permis par ailleurs de montrer la possibilité du confinement et de la transmission d'un seul mode élastique au niveau d'un CPRL. Dans un second temps, nous avons montré que les propriétés d'un CPRL peuvent être reproduites dans le régime hypersonique. En effet, par le biais de la mise en place d'un nouveau modèle théorique et en proposant un nouveau CPRL à ondes de surface à base de films de diamant, nous avons pu montrer que ce type de cristal peut faire l'objet d'applications potentielles à des fins de guidage et de démultiplexage et ainsi initier la conception de nouveaux dispositifs miniaturisés à ondes de surface destinés aux systèmes de télécommunications (>GHz). / In this PhD work, we focused our interest on the theoretical and experimental study of locally resonant phononic crystals (LRPC) operating in sonic and hypersonic regimes. We first developed numerical models to understand the dispersion behaviour of elastic waves in those plate-type LRPC in which the silicone rubber plays a key role. We showed that with such structure, we can understand clearly how the local resonance (LR) mechanism operates to give rise to opening of low frequency BG two orders of magnitude that the one allowed by Bragg diffusion. The physics behind such structures was also figured out by means of theoretical models. An experimental study was then undertaken by manufacturing a new LRPC plate which has been characterized in terms of elastic behaviour and BG investigation. A perfect concordance was demonstrated between the theoretical an experimental results by evidencing a 2kHz BG opening using a 6mm diameter rubber stub and 1cm periodicity. In addition, waveguiding phenomena was investigated in those structures and showed the possibility of guiding of only one defect mode unlike conventional PCs in which many defects modes are generated. A second part of this study was dealt with LR mechanism in hypersonic regime. Using a new numerical and theoretical approach, we were able to show the BG opening and waveguiding for surface acoustic waves (SAW) in a LRPC composed of metallic stubs arranged on a diamond semi-infinite substrate. The added value of LR in such frequency regime remains in its ability to select only one guided mode due to the longer involved wavelengths. Such structures can then be suitable for filtering and demultiplexing applications.

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