This master's thesis deals with application design and implementation of secured communication between smartphones. Analyses issues of cross-platform portability between operating systems, its differences and common features. It shows an overview of Android OS architecture and its individual layers. Thesis describes basic principles of secured communication in the modern cryptography and implementation of application for mobile platforms. Also shows an overview of modern mobile technologies such as NFC (Near Field Communication) and Bluetooth. This thesis reveals basic architecture and the way how it fits into concept of secured communication. It also describes the architecture of application and concept of secured communication, which is then implemented. In conclusion is summarization of achieved results and possible extensions of implemented application.

Ma thèse a été centrée sur l’étude par luminescence à deux photons (TPL) de nanostructures d’or uniques, éventuellement couplées, dans le but d’en déterminer les propriétés de nano-antennes optiques. Les différentes expériences réalisées ont permis de mettre en évidence les paramètres clés à l’origine de la luminescence à deux photons (TPL) permettant de mettre en évidence le rôle du plasmon transverse. Ce résultat a été confirmé par l’étude de nanobipyramides présentant des caractéristiques plasmoniques légèrement différentes. Ce modèle a été approfondi via l’étude des propriétés TPL de nanobâtonnets présentant des volumes différents mais des résonances plasmoniques identiques. Enfin, en confrontant les résultats expérimentaux à des simulations obtenues par BEM (Boundary Element Method), nous avons montré que le signal provenait a priori des atomes du volume de la NP. Des problèmes de photo-dégradations ont par ailleurs été constatés et analysés. Au-delà des nano-bâtonnets, nous avons quantifié les effets dits de pointes de nanobipyramides présentant des caractéristiques plasmoniques proches de celles des bâtonnets. Nous avons également pu mettre en évidence de très fortes intensités TPL sur les points chauds issus d’échantillons d’or semi-continu. Un second volet de mes travaux a concerné la mise en œuvre et la caractérisation des propriétés optiques linéaires et non-linéaires de nano-émetteurs hybrides individuels couplant une nano-antenne à des fluorophores. Différentes techniques ont été testées : la mise en œuvre de dépôts multicouches (méthode dite « layer-by-layer »), ou la nanophotopolymérisation localisée. Dans les deux cas, outre la complexité de mise en œuvre de ces techniques, nous avons été confrontés à la difficulté d’extraire le signal des molécules du très fort signal de luminescence à deux photons des nanostructures d’or. / My PhD work has been dealing with the two-photon luminescence (TPL) study of single gold nanostructures, possibly coupled in order to determine their nano-antenna optical properties. Key parameters to explain the origin of the TPL were provided from the two-photon luminescence study of single small 10 nm x 40 nm colloidal gold nanorods (GNR) which highlight the transverse plasmon influence. This origin was confirmed by the results obtained after the characterization of nanobipyramid exhibiting plasmonic properties closed to nanorods. A deeper insight in this model was further developed after investigating the properties of gold nanorods having closed aspect ratio and plasmonic resonances but increasing volume. Experimental data were correlated with BEM (Boundary Elements Method) simulations. It was shown that the TPL signal was coming from the bulk atoms. Photodegradations problems have moreover been observed and analyzed. Above the analysis of gold nanorods, the lightning rod effect of nanobipyramid was also investigated. Finally very high TPL intensity spots were recorded in semi-continuous gold films close to percolation. A second part of my study was related to the fabrication and the characterization of the optical properties of hybrid nano-emitters. They were fabricated by coupling a nano-antenna with fluorophores. Two different techniques were tested: the so-called layer-by-layer method and localized nanophotopolymerization. In both cases, together with the difficulty to accurately control both methods, retrieving the molecules signal from the huge TPL signal of the gold nanostructures was shown to be rather difficult.

Near-field optical microscopy has attracted remarkable attention, as it is the only technique that allows the investigation of local optical properties with a resolution far below the diffraction limit. Especially, the scattering-type near-field optical microscopy allows the nondestructive examination of surfaces without restrictions to the applicable wavelengths. However, its usability is limited by the availability of appropriate light sources. In the context of this work, this limit was overcome by the development of a scattering-type near-field microscope that uses a widely tunable free-electron laser as primary light source. In the theoretical part, it is shown that an optical near-field contrast can be expected when materials with different dielectric functions are combined. It is derived that these differences yield different scattering cross-sections for the coupled system of the probe and the sample. Those cross-sections define the strength of the near-field signal that can be measured for different materials. Hence, an optical contrast can be expected, when different scattering cross-sections are probed. This principle also applies to vertically stacked or even buried materials, as shown in this thesis experimentally for two sample systems. In the first example, the different dielectric functions were obtained by locally changing the carrier concentration in silicon by the implantation of boron. It is shown that the concentration of free charge-carriers can be deduced from the near-field contrast between implanted and pure silicon. For this purpose, two different experimental approaches were used, a non-interferometric one by using variable wavelengths and an interferometric one with a fixed wavelength. As those techniques yield complementary information, they can be used to quantitatively determine the effective carrier concentration. Both approaches yield consistent results for the carrier concentration, which excellently agrees with predictions from literature. While the structures of the first system were in the micrometer regime, the capability to probe buried nanostructures is demonstrated at a sample of indium arsenide quantum dots. Those dots are covered by a thick layer of gallium arsenide. For the first time ever, it is shown experimentally that transitions between electron states in single quantum dots can be investigated by near-field microscopy. By monitoring the near-field response of these quantum dots while scanning the wavelength of the incident light beam, it was possible to obtain characteristic near-field signatures of single dots. Near-field contrasts up to 30 % could be measured for resonant excitation of electrons in the conduction band of the indium arsenide dots.

The sound produced by military aircraft is dominated by noise generated by the turbulent mixing of the jetted exhaust with the ambient air. This jet noise has the potential to annoy the community and pose a hearing loss risk for military personnel. The goal of this dissertation is to characterize spatiospectral features in the field produced by full-scale military aircraft that are not traditionally seen at the laboratory scale and identify potential noise mechanisms for these features. Measurements of two military aircraft jet noise fields are found to be best described as a superposition of spatiospectral lobes, whose relative amplitudes dictate the overall directivity at each engine power. Near-field acoustical holography techniques are applied to one of the military aircraft measurements to characterize the behavior of the lobes as a function of engine power. The simulated jet noise of a highly heated laboratory-scale jet is then analyzed to compare with the military aircraft measurement and is found to only partially contain the spatiospectral lobe phenomenon. Application of near to far field coherence tracing and near-field acoustical holography to the simulations provides validation of the methods used on the military aircraft and illuminate potential source mechanisms that may explain the presence of the spatiospectral lobes.

The noise emissions of jets from full-scale engines installed on military aircraft pose a significant hearing loss risk to military personnel. Noise reduction technologies and the development of operational procedures that minimize noise exposure to personnel are enhanced by the accurate characterization of noise sources within a jet. Hence, more than six decades of research have gone into jet noise measurement and prediction. In the past decade, the noise-source visualization tool near-field acoustical holography (NAH) has been applied to jets. NAH fits a weighted set of expansion wave functions, typically planar, cylindrical, or spherical, to measured sound pressures in the field. NAH measurements were made of a jet from an installed engine on a military aircraft. In the present study, the algorithm of statistically optimized NAH (SONAH) is modified to account for the presence of acoustic reflections from the concrete surface over which the jet was measured. The three dimensional field in the jet vicinity is reconstructed, and information about sources is inferred from reconstructions at the boundary of the turbulent jet flow. Then, a partial field decomposition (PFD) is performed, which represents the total field as the superposition of multiple, independent partial fields. This is the most direct attempt to equate partial fields with independent sources in a jet to date.

<p>Understanding of thermal transport in small scales gains more importance with increasing demand in microelectronics and advancing fabrication technologies. In addition, scarce in energy sources adds more pressure with increasing expectations on research in energy conversion devices and renewable energies. In parallel to these, new phenomena observable only in small scales are discovered with the research, bringing more opportunities for engineers to solve real-world problems by applying the discoveries and more questions to answer. Thermal radiation as a thermal transport phenomenon is the epicenter of this research. Recent developments such as near-field radiative heat transfer exceeding blackbody radiation or control of radiative cooling via biasing grows the attraction on thermal radiation because these examples challenge our long-lasting understanding of nature. Exploring nature further in the small scale may help us meet the expectations mentioned above.</p> <p> </p> <p>In this thesis work, first, we carry out analyses on radiative heat transfer of natural hyperbolic material, calcite, and compare to that of a polar material SiC. Our study reveals that the high- modes within the hyperbolic bands are responsible for the substantial enhancement in near field radiation. Comparison of calcite with SiC illustrates the significance of the high- modes in calcite vs. surface polariton modes in SiC in their contributions to near-field radiation enhancement, for temperature differences ranging from 1 K to 400 K. We also noticed that the contributions of high- modes in calcite to near-field radiation is comparable to that of surface polaritons in SiC. The results of these analyses will be helpful in the search of hyperbolic materials that can enhance near field radiative transfer.</p> <p> </p> <p>Second, we demonstrate an experimental technique to measure near-field radiative heat transfer between two parallel plates at gap distances ranging from a few nanometers to far-field. A differential measurement circuit based on resistive thermometry to measure the defined temperatures are explained. To predict the defined temperatures, a computational method is utilized. We also detail an alignment technique that consists of a coarse and fine alignment in the relevant gap regions. This technique presents a method with high precision for gap measurement, dynamic gap control, and reliable sensitivity for extreme near-field measurements. Finally, we report experimental results that shows 18,000 times enhancement in radiative heat transfer between two parallel plates.</p> <p> </p> <p>Third, we analyze near-field radiative transfer due to hyperbolic phonon polaritons, driven by temperature gradient inside the bulk materials. We develop a mesoscale many-body scattering approach to account for the role of hyperbolic phonon polaritons in radiative transfer in the bulk and across a vacuum gap. Our study points out the equivalency between the bulk-generated mode and the surface mode in the absence of a temperature gradient in the material, and hence provide a unified framework for near-field radiative transfer by hyperbolic phonon polaritons. The results also elucidate contributions of the bulk-generated mode and the bulk temperature profile in the enhanced near-field radiative transfer.</p> <p> </p> <p>Forth, we study radiative heat transfer in hyperbolic material, hyperbolic boron nitride (hBN), and show a major contribution to energy transport arising from phonon polaritons supported in Reststrahlen bands. This contribution increases spectral radiative transfer by six orders of magnitude inside Reststrahlen bands compared to that outside Reststrahlen bands. The equivalent radiative thermal conductivity increases with temperature increase, and the radiative thermal conductivity can be of the same order of the phonon thermal conductivity. Experimental measurements are discussed. We showed the radiative contribution can account for as much as 27 % of the total thermal transport at 600 K. Hence, in hBN the radiative thermal transport can be comparable to thermal conduction by phonons. We also demonstrate contribution of polaritons to thermal transport in MoO₃. To calculate radiative heat transfer in three principal coordinates separately, we modify and apply the derived many-body model. Our analysis shows that radiative thermal conductivity in both in- and out-of-plane directions increases with temperature and contribution to energy transport by polaritons exceeds that by phonons.</p> <p> </p> Fifth, we build an experimental setup to examine near-field properties of materials using an external thermal source. The nanospectroscopy setup combines near-field microscopy technique, near-field scanning optical microscopy (NSOM), and Fourier-transform infrared (FTIR) spectroscopy. We further explain challenges in building a nanospectroscopy setup using a weak thermal source and coupling two techniques. This method enables us to investigate spectral thermal radiation and local dielectric properties in nanoscale.

The wireless industry is such that suppliers of antennas have to adapt their designs to requirement changes over a period of just a few months. In these short design cycles time is crucial. Radiation pattern testing of the antennas at various points in this design cycle are nowadays mostly done using spherical near-field techniques, where the tangential electric field is acquired over an imaginary sphere close to, and surrounding, the antenna under test, and this data then transformed into a far-zone radiation pattern. There are some applications where acquisition over a rotationally symmetric surface other than a spherical one would not only reduce test times, but allow equipment cost reductions as well. However, near-field to far-field transformations for finite non-spherical measurement surface shapes are not available. Such a transformation is proposed, implemented and validated in this thesis. It uses the method of moments, customized to a rotationally symmetric surface (body of revolution) to effect this transformation.

Les nanocristaux semi-conducteurs colloïdaux possèdent des propriétés photo-physiques qui en font des objets de choix pour des applications variées, comme le marquage biologique, le photovoltaïque ou encore l’optique quantique. Leur interaction avec une structure photonique peut modifier leurs propriétés d’émission (durée de vie, intensité…). Le microscope optique de champ proche est un outil privilégié pour venir sonder ces modifications à l’échelle nanométrique.Cette thèse porte sur la réalisation d’une sonde active de champ proche réalisée à partir d’un nanocristal cœur/coquille CdSe/CdS greffé à l’apex d’une fibre optique amincie. Cette sonde est utilisée pour cartographier, dans les 3 dimensions de l’espace et à l’échelle nanométrique, les variations de durée de vie de l’émetteur. Elle permet de rendre compte des variations des modes photoniques sur la surface.Une partie de cette thèse porte sur la réalisation de la sonde active elle-même. Grâce à cette sonde les études sont alors développées sur un réseau de trous dans un film mince d’or. Des simulations FDTD ont été réalisées dans le but de déterminer les paramètres pertinents du réseau et d’analyser leur réponse en champ proche.Les résultats expérimentaux des durées de vie en divers points de différents réseaux, obtenus avec la sonde active, sont confrontés aux résultats numériques. / Colloidal semiconductor nanocrystals have photo-physical properties that make them objects of choice for various applications, such as biological marking, photovoltaics or quantum optics. Their interaction with a photonic structure can modify their emission properties (lifetime, intensity, etc.). The near-field optical microscope is a privileged tool to probe these changes at the nanoscale.This thesis deals with the realization of an active near-field probe made from a CdSe / CdS core / shell nanocrystal grafted to the apex of a thinned optical fiber. This probe is used to map, in the 3 dimensions of the space and on the nanometric scale, the variations in the lifetime of the emitter. It makes it possible to account for variations in photonic modes on the surface.A part of this thesis concerns the realization of the active probe itself. Thanks to this probe the studies are then developed on a hole grating made in a thin film of gold. FDTD simulations were performed to determine relevant grating parameters and to analyze their near field response.The experimental results of the lifetimes at various points of different gratings, obtained with the active probe, are compared with the numerical results.

abstract: Near-field thermal radiation occurs when the distance between two surfaces at different temperatures is less than the characteristic wavelength of thermal radiation. While theoretical studies predict that the near-field radiative heat transfer could exceed Planck’s blackbody limit in the far-field by orders of magnitudes depending on the materials and gap distance, experimental measurement of super-Planckian near-field radiative heat flux is extremely challenging in particular at sub-100-nm vacuum gaps and few has been demonstrated. The objective of this thesis is to develop a novel thermal metrology based on AFM bi-material cantilever and experimentally measure near-field thermal radiation. The experiment setup is completed and validated by measuring the near-field radiative heat transfer between a silica microsphere and a silica substrate and comparing with theoretical calculations. The bi-material AFM cantilever made of SiNi and Au bends with temperature changes, whose deflection is monitored by the position-sensitive diode. After careful calibration, the bi-material cantilever works as a thermal sensor, from which the near-field radiative conductance and tip temperature can be deduced when the silica substrate approaches the silica sphere attached to the cantilever by a piezo stage with a resolution of 1 nm from a few micrometers away till physical contact. The developed novel near-field thermal metrology will be used to measure the near-field radiative heat transfer between the silica microsphere and planar SiC surface as well as nanostructured SiC metasurface. This research aims to enhance the fundamental understandings of radiative heat transfer in the near-field which could lead to advances in microelectronics, optical data storage and thermal systems for energy conversion and thermal management. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2019

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