Ces travaux de recherche proposent une approche expérimentale pour étudier les capacités de l'imagerie radar basse fréquence pour la détection des zones humides dans le sous-sol des régions arides terrestres et martiennes et la cartographie géologique de leur proche subsurface. En particulier, l'analyse phasimétrique d'images SAR (bande L) de la Dune du Pyla nous a permis de mettre en évidence un comportement particulier de la différence de phase copolaire, lié à la présence d'une zone humide dans la subsurface. Afin d'interpréter et de modéliser ce phénomène, nous avons développé un modèle analytique de diffusion simple, de type IEM, complété par une expression analytique du terme de diffusion par réflexion multiple. Simulant avec succès le phénomène observé, notre modèle confirme que le signal de phase est généré par le profil d'humidité des structures enfouies occasionnant une composante de diffusion par réflexion multiple. Il a également été montré que ce signal de phase copolaire permet la détection d'interfaces humides à des profondeurs plus importantes que celles autorisées par l'analyse des indicateurs radiométriques classiques. Participant au programme Terrestrial Analog to Mars de la NASA, nous avons également travaillé à la définition des performances d'un système SAR orbital en bande P pour la détection d'humidité dans la proche subsurface de la planète Mars, au moyen de la phase radar. Incluant un terme de diffusion de volume, notre précédent modèle IEM montre que la présence d'hétérogénéités dans les premiers mètres de la croûte martienne pourrait altérer les performances de la différence de phase copolaire pour la détection d'humidité en terme de profondeur d'investigation. Néanmoins, nos résultats de simulations indiquent qu'un tel système SAR, exploitant la phase copolaire, autoriserait la détection de l'humidité et son suivi à l'échelle saisonnière jusqu'à des profondeurs de 3 mètres dans les régions présentant un contexte géologique favorable i.e. une faible concentration de diffuseurs de surface et de proche subsurface. Au-delà de la détection d'humidité des sols, nous avons également cherché à mettre en évidence l'apport de l'imagerie radar pour les applications de cartographie d'interfaces géologiques à grande échelle au moyen de systèmes radar orbitaux. L'analyse polarimétrique de données SIR-C/XSAR pour la Mauritanie a permis de montrer le potentiel de l'imagerie radar basse fréquence pour la détection de structures géologiques de surface ainsi que pour la cartographie de la paléo-hydrologie de la proche subsurface en contexte aride. En particulier, nos résultats ont montré que les données polarimétriques fournissent non seulement des éléments d'information sur les mécanismes de diffusion mis en jeu, mais permettent également de différencier les structures de surface par la rugosité qu'elles occasionnent, des structures de subsurface par la diffusion de volume qu'elles génèrent.

Ces travaux de recherche proposent une approche expérimentale pour étudier les capacités de l'imagerie radar basse fréquence pour la détection des zones humides dans le sous-sol des régions arides terrestres et martiennes et la cartographie géologique de leur proche subsurface. En particulier, l'analyse phasimétrique d'images SAR (bande L) de la Dune du Pyla nous a permis de mettre en évidence un comportement particulier de la différence de phase copolaire, lié à la présence d'une zone humide dans la subsurface. Afin d'interpréter et de modéliser ce phénomène, nous avons développé un modèle analytique de diffusion simple, de type IEM, complété par une expression analytique du terme de diffusion par réflexion multiple. Simulant avec succès le phénomène observé, notre modèle confirme que le signal de phase est généré par le profil d'humidité des structures enfouies occasionnant une composante de diffusion par réflexion multiple. Il a également été montré que ce signal de phase copolaire permet la détection d'interfaces humides à des profondeurs plus importantes que celles autorisées par l'analyse des indicateurs radiométriques classiques. Participant au programme Terrestrial Analog to Mars de la NASA, nous avons également travaillé à la définition des performances d'un système SAR orbital en bande P pour la détection d'humidité dans la proche subsurface de la planète Mars, au moyen de la phase radar. Incluant un terme de diffusion de volume, notre précédent modèle IEM montre que la présence d'hétérogénéités dans les premiers mètres de la croûte martienne pourrait altérer les performances de la différence de phase copolaire pour la détection d'humidité en terme de profondeur d'investigation. Néanmoins, nos résultats de simulations indiquent qu'un tel système SAR, exploitant la phase copolaire, autoriserait la détection de l'humidité et son suivi à l'échelle saisonnière jusqu'à des profondeurs de 3 mètres dans les régions présentant un contexte géologique favorable i.e. une faible concentration de diffuseurs de surface et de proche subsurface. Au-delà de la détection d'humidité des sols, nous avons également cherché à mettre en évidence l'apport de l'imagerie radar pour les applications de cartographie d'interfaces géologiques à grande échelle au moyen de systèmes radar orbitaux. L'analyse polarimétrique de données SIR-C/XSAR pour la Mauritanie a permis de montrer le potentiel de l'imagerie radar basse fréquence pour la détection de structures géologiques de surface ainsi que pour la cartographie de la paléo-hydrologie de la proche subsurface en contexte aride. En particulier, nos résultats ont montré que les données polarimétriques fournissent non seulement des éléments d'information sur les mécanismes de diffusion mis en jeu, mais permettent également de différencier les structures de surface par la rugosité qu'elles occasionnent, des structures de subsurface par la diffusion de volume qu'elles génèrent.

In this thesis, we have designed and optimized strip waveguide based micro-ring and micro-ring and micro-racetrack resonators for biosensing applications. Silicon-On-Insulator (SOI) platform which offers several advantages over other materials such as Lithium Niobate, Silica on Silicon and Silicon nitride is considered here. High index contrast enables us to miniaturize the biosensor devices and monolithic integration of source and detectors on the same chip. We have considered the dispersive nature of the waveguide and proceeded towards optimization. Finite difference schemes and Finite Difference Time Domain (FDTD) methods are the primary tools used to model the biosensor. Various structures such as channel waveguides and beam structures are analyzed on the basis of their suitability for sensing applications. Strip and Rib waveguides are the two geometries considered in our studies. In an optical guiding structure, effective index of the propagating optical mode can be induced by two different phenomena: i. Homogeneous Sensing In this category, effective index of a propagating optical mode changes with uniformly distributed analytes extending over a distance well exceeding the evanescent field penetration depth. The sample serves as the waveguide cover. ii. Surface Sensing In the case of surface sensing, analytes bound to the surface of the waveguide. The effective index of an optical mode changes with the refractive index as well as the thickness of an adlayer. A thin layer of adsorbed or bound molecules transported from liquid or gaseous medium serving as waveguide cover is referred as an adlayer. Both homogeneous and surface sensing schemes are addresses in this work. By bulk sensing method, the characteristics of bioclad covering the device are studied. Optimization of the resonator structure involves the analysis of following parameters: • Gap between the ring and bus waveguides • Free spectral range • Extinction ratio • Quality factor We have achieved a maximum bulk sensitivity of 115 nm / RIU with ring waveguide width of 450 nm and bus width of 350 nm which is better than an earlier reported value of 70 nm/ RIU. We have proposed a novel detection scheme consisting of a micro-racetrack resonator formed over a cantilever structure. The devoice works on the principle of opto-mechanical coupling to detect conformational changes due to biomolecular adherence. BSA (Bovine Serum Albumin) and IgG ( Immuno Globulin G) are the two proteins considered in the work. Mechanical analysis of the beam for tensile and compressive stresses and corresponding spectral responses of the racetrack resonators are analyzed both by semi-analytical and method and numerical analyzes. We compared various aspects of rib and strip waveguide racetrack resonators. We have proved by numerical simulation, that the device is capable of distinguishing tensile and compressive stress. Two strip waveguides of dimensions : 450 nm X 220 nm and 400 nm X 180 nm, former supporting both Quasi-TE and Quasi-TM modes where as the second configuration allows only Quasi-TE mode alone. Sensitivity of the cantilever sensor is : 0.3196 x 10-3 nm/ µɛ at 1550 nm wavelength.

The widespread adoption of photonic circuits requires the economics of volume manufacturing offered by integration technology. A Complementary Metal-Oxide Semiconductor compatible silicon material platform is particularly attractive because it leverages the huge investment that has been made in silicon electronics and its high index contrast enables tight confinement of light which decreases component footprint and energy consumption. Nevertheless, there remain challenges to the development of photonic integrated circuits. Although the density of integration is advancing steady and the integration of the principal components – waveguides, optical sources and amplifiers, modulators, and photodetectors – have all been demonstrated, the integration density is low and the device library far from complete. The integration density is low primarily because of the difficulty of confining light in structures small compared to the wavelength which measured in micrometers. The device library is incomplete because of the immaturity of hybridisation on silicon of other materials required by active devices such as III-V semiconductor alloys and ferroelectric oxides and the difficulty of controlling the coupling of light between disparate material platforms. Metamaterials are nanocomposite materials which have optical properties not readily found in Nature that are defined as much by their geometry as their constituent materials. This offers the prospect of the engineering of materials to achieve integrated components with enhanced functionality. Metamaterials are a class of photonic crystals includes subwavelength grating waveguides, which have already provided breakthroughs in component performance yet require a simpler fabrication process compatible with current minimum feature size limitations. The research reported in this PhD thesis advances our understanding of the structure-property relations of key planar light circuit components and the metamaterial engineering of these properties. The analysis and simulation of components featuring structures that are only just subwavelength is complicated and consumes large computer resources especially when a three dimensional analysis of components structured over a scale larger than the wavelength is desired. This obstructs the iterative design-simulate cycle. An abstraction is required that summarises the properties of the metamaterial pertinent to the larger scale while neglecting the microscopic detail. That abstraction is known as homogenisation. It is possible to extend homogenisation from the long-wavelength limit up to the Bragg resonance (band edge). It is found that a metamaterial waveguide is accurately modeled as a continuous medium waveguide provided proper account is taken of the emergent properties of the homogenised metamaterial. A homogenised subwavelength grating waveguide structure behaves as a strongly anisotropic and spatially dispersive material with a c-axis normal to the layers of a one dimensional multi-layer structure (Kronig-Penney) or along the axis of uniformity for a two dimensional photonic crystal in three dimensional structure. Issues with boundary effects in the near Bragg resonance subwavelength are avoided either by ensuring the averaging is over an extensive path parallel to boundary or the sharp boundary is removed by graded structures. A procedure is described that enables the local homogenised index of a graded structure to be determined. These finding are confirmed by simulations and experiments on test circuits composed of Mach-Zehnder interferometers and individual components composed of regular nanostructured waveguide segments with different lengths and widths; and graded adiabatic waveguide tapers. The test chip included Lüneburg micro-lenses, which have application to Fourier optics on a chip. The measured loss of each lens is 0.72 dB. Photonic integrated circuits featuring a network of waveguides, modulators and couplers are important to applications in RF photonics, optical communications and quantum optics. Modal phase error is one of the significant limitations to the scaling of multimode interference coupler port dimension. Multimode interference couplers rely on the Talbot effect and offer the best in-class performance. Anisotropy helps reduce the Talbot length but temporal and spatial dispersion is necessary to control the modal phase error and wavelength dependence of the Talbot length. The Talbot effect in a Kronig-Penny metamaterial is analysed. It is shown that the metamaterial may be engineered to provide a close approximation to the parabolic dispersion relation required by the Talbot effect for perfect imaging. These findings are then applied to the multimode region and access waveguide tapers of a multi-slotted waveguide multimode interference coupler with slots either in the transverse direction or longitudinal direction. A novel polarisation beam splitter exploiting the anisotropy provided by a longitudinally slotted structure is demonstrated by simulation. The thesis describes the design, verification by simulation and layout of a photonic integrated circuit containing metamaterial waveguide test structures. The test and measurement of the fabricated chip and the analysis of the data is described in detail. The experimental results show good agreement with the theory, with the expected errors due to fabrication process limitations. From the Scanning Electron Microscope images and the measurements, it is clear that at the boundary of the minimum feature size limit, the error increases but still the devices can function.

[EN] Nature is nonlinear. The linear description of physical phenomena is useful for explain observations with the simplest mathematical models, but they are only accurate for a limited range of input values. In the case of intense acoustics waves, linear models obviate a wide range of physical phenomena that are necessary for accurately describe such high-amplitude waves, indispensable for explain other exotic acoustic waves and mandatory for developing new applied techniques based on nonlinear processes. In this Thesis we study the interactions between nonlinearity and other basic wave phenomena such as non-classical attenuation, anisotropic dispersion and periodicity, and diffraction in specific configurations. First, we present intense strain waves in a chain of cations coupled by realistic interatomic potentials. Here, the nonlinear ionic interactions and lattice dispersion lead to the formation of supersonic kinks. These intrinsically-nonlinear localized dislocations travel long distances without changing its properties and explain the formation of dark traces in mica crystals. Then, we analyze nonlinear wave processes in a system composed of multilayered acoustic media. The rich nonlinear dynamics of this system is characterized by its strong dispersion. Here, harmonic generation processes and the relation with its band structure are presented, showing that the nonlinear processes can be enhanced, strongly minimized or simply modified by tuning the layer parameters. In this way, we show how the dynamics of intense monochromatic waves and acoustic solitons can be controlled by artificial layered materials. In a second part, we include diffraction and analyze four types of singular beams. First, we study nonlinear beams in two dimensional sonic crystals. In this system, the inclusion of anisotropic dispersion is tuned for obtain simultaneous self-collimation for fundamental and second harmonic beams. The conditions for optimal second harmonic generation are presented. Secondly, we present limited diffraction beam generation using equispaced axisymmetric diffraction gratings. The obtained beams are truncated version of zero-th order Bessel beams. Third, the grating spacing can be modified to achieve focusing, where the generated nonlinear beams presents high gain, around 30 dB, with a focal width which is between the diffraction limit and the sub-wavelength regime, but with its characteristic high amplitude side lobes strongly reduced. Finally, we observe that waves diffracted by spiral-shaped gratings generate high-order Bessel beams, conforming nonlinear acoustic vortex. The conditions to obtain arbitrary-order Bessel beams by these passive elements are presented. Finally, the interplay of nonlinearity and attenuation in biological media is studied in the context of medical ultrasound. First, a numerical method is developed. The method solves the constitutive relations for nonlinear acoustics and the frequency power law attenuation of biological media is modeled as a sum of relaxation processes. A new technique for reducing numerical dispersion based on artificial relaxation is included. Second, this method is used to study the harmonic balance as a function of the power law, showing the role of weak dispersion and its impact on the efficiency of the harmonic generation in soft-tissues. Finally, the study concerns the nonlinear behavior of acoustic radiation forces in frequency power law attenuation media. We present how the interplay between nonlinearity and the specific frequency power law of biological media can modify the value for acoustic radiation forces. The relation of the nonlinear acoustic radiation force with thermal effects are also discussed. The broad range of nonlinear processes analyzed in this Thesis contributes to understanding the behavior of intense acoustic waves traveling trough complex media, while its implications for enhancing existent applied acoustics techniques are presented. / [ES] La Naturaleza es no lineal. La descripción lineal de los fenómenos físicos es de gran utilidad para explicar nuestras observaciones con modelos matemáticos simples, pero éstos sólo son precisos en un limitado rango de validez. En el caso de onda acústica de alta intensidad, los modelos lineales obvian un amplio rango de fenómenos físicos que son necesarios para describir con precisión las ondas de gran amplitud, pero además son necesarios para explicar otros procesos más exóticos e indispensables para desarrollar nuevas aplicaciones basadas en propagación no lineal. En esta Tesis, estudiamos las interacciones entre no linealidad y otros procesos complejos como atenuación no-clásica, dispersión anisotrópica y periodicidad, y difracción en configuraciones específicas. En primer lugar, presentamos ondas de deformación en una cadena de cationes acoplados por potenciales realísticas. Aquí, las interacciones no lineales entre iones, producen la conformación de kinks supersónicos. Estas dislocaciones localizadas intrínsecamente no lineales viajan por la red largas distancias sin variar sus propiedades, y pueden explicar la formación de trazas en minerales como la mica. Aumentando la escala del problema, estudiamos los procesos acústicos no lineales en medios multicapa. La rica dinámica de estos medios está caracterizada por la fuerte dispersión debido a la periodicidad del sistema. Aquí, estudiamos los procesos de generación de harmónicos, mostrando como modificando la estructura podemos potenciar, minimizar, o simplemente modificar artificialmente la transferencia de energía entre las componentes espectrales, y de esta manera controlar la dinámica de las ondas y solitones en el interior de la estructura. En la segunda parte, incluimos difracción y analizamos cuatro tipos de haces singulares. En primer lugar, analizamos haces ultrasónicos no lineales en cristales de sonido bidimensionales. En este sistema, las propiedades de anisotropía del medio son ajustadas para obtener la auto-colimación simultánea del primer y segundo harmónico. Así, se obtiene la propagación no difractiva para las dos componentes. En segundo lugar, presentamos haces de difracción limitada empleando rejillas de difracción axisimétricas. Por último, demostramos la generación de haces de Bessel de orden superior mediante estructuras en espiral. En la última parte, estudiamos la competición entre no linealidad y la atenuación y dispersión observable en medios biológicos en el contexto de las aplicaciones de biomédicas de los ultrasonidos. En primer lugar desarrollamos un nuevo método computacional para la dependencia frecuencial en forma de ley de potencia de la absorción característica de los tejidos. Este método en dominio temporal es usado posteriormente para revisar los procesos básicos no lineales prestando especial interés en el paper de la dispersión del tejido. Por último, la resolución de las ecuaciones constitutivas nos permite abordar la descripción no lineal de la fuerza de radiación acústica producida en tejidos biológicos, y las implicaciones existentes con la deposición de energía y transferencia de momento para ondas ultrasónicas de alta intensidad. El amplio abanico de procesos no lineales analizados en esta tesis contribuye a una mejor comprensión de la dinámica de las ondas acústicas de alta intensidad en medios complejos, donde las implicaciones existentes en cuanto a la mejora de sus aplicaciones prácticas son puestas de manifiesto. / [CA] La Naturalesa és no lineal. La descripció lineal dels fenòmens físics és de gran utilitat per a explicar les nostres observacions amb models matemàtics simples, però aquests sol són precisos en un limitat rang de validesa. En el cas d'ona acústica d'alta intensitat, els models lineals obvien un ampli rang de fenòmens físics que són necessaris per a descriure amb precisió les ones de gran amplitud, però a més són necessaris per a explicar altres processos més exòtics i indispensables per a desenvolupar noves aplicacions basades en propagació no lineal. En aquesta Tesi, estudiem les interaccions entre no-linealitat i altres processos complexos com atenuació no-clàssica, dispersió anisotròpica i periodicitat, i difracció en configuracions específiques. En primer lloc, presentem ones de deformació en una cadena de cations acoblats per potencials realistes. Ací, les interaccions no lineals entre ions, produeixen la conformació de kinks supersònics. Aquestes dislocacions localitzades intrínsecament no lineals viatgen per la xarxa llargues distàncies sense variar les seues propietats, i poden explicar la formació de traces en minerals com la mica. Augmentant l'escala del problema, estudiem els processos acústics no lineals en mitjans multicapa. La rica dinàmica d'aquests mitjans es caracteritza per la forta dispersió a causa de la periodicitat del sistema. Ací, estudiem els processos de generació d'harmònics, mostrant com modificant l'estructura podem potenciar, minimitzar, o simplement modificar artificialment la transferència d'energia entre les components espectrals, i d'aquesta manera controlar la dinàmica de les ones i solitons a l'interior de l'estructura. En la segona part, incloem difracció i analitzem quatre tipus de feixos singulars. En primer lloc, analitzem feixos ultrasònics no lineals en cristalls de so bidimensionals. En aquest sistema, les propietats d'anisotropia del medi són ajustades per a obtenir l'acte-col·limació simultània del primer i segon harmònic. Així, s'obté la propagació no difractiva per a les dues components. En segon lloc, presentem feixos de difracció limitada emprant reixetes de difracció axisimètriques. Per últim, vam demostrar la generació de feixos de Bessel d'ordre superior mitjançant estructures en espiral. En l'última part, estudiem la competició entre no linealitat i l'atenuació i dispersió observable en medis biològics en el context de les aplicacions biomèdiques dels ultrasons. En primer lloc desenvolupem un nou mètode computacional per a la dependència freqüencial en forma de llei de potència de l'absorció característica dels teixits biològics. Aquest mètode en domini temporal és usat posteriorment per a revisar els processos bàsics no lineals prestant especial interés en el paper de la dispersió del teixit. Per últim, la resolució de les equacions constitutives ens permet abordar la descripció no lineal de la força de radiació acústica produïda en teixits biològics, i les implicacions existents amb la deposició d'energia i transferència de moment per a ones ultrasòniques d'alta intensitat. L'ampli ventall de processos no lineals analitzats en aquesta tesi contribueix a una millor comprensió de la dinàmica de les ones acústiques d'alta intensitat en medis complexos, on les implicacions existents quant a la millora de les seues aplicacions practiques són posades de manifest. / Jiménez González, N. (2015). Nonlinear Acoustic Waves in Complex Media [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/53237 / TESIS / Premios Extraordinarios de tesis doctorales

The emergence of Ultra-wideband (UWB) technology application has yielded tremendous and vital impacts in the field of microwave wireless communications. These applications include military radar imaging, security screening, and tumour detection, especially for early detection of breast cancer. These indicators have stimulated and inspired many researchers to make the best use of this promising technology. UWB technology challenges such as antenna design, the problem of imaging reconstruction techniques, challenges of severe signal attenuation and dispersion in high loss material. Others are lengthy computational time demand and large computer memory requirements are prevalent constraints that need to be tackled especially in a large scale and complex computational electromagnetic analysis. In this regard, it is necessary to find out recently developed optimisation techniques that can provide solutions to these problems. In this thesis, designing, optimisation, development, measurement, and analysis of UWB antennas for near-field microwave imaging applications are considered. This technology emulates the same concept of surface penetrating radar operating in various forms of the UWB spectrum. The initial design of UWB monopole antennas, including T-slots, rectangular slots, and hexagonal slots on a circular radiating patch, was explicitly implemented for medical imaging applications to cover the UWB frequency ranging from 3.1 GHz to 10.6 GHz. Based on this concept, a new bow-tie and Vivaldi UWB antennas were designed for a through-the-wall imaging application. The new antennas were designed to cover a spectrum on a lower frequency ranging from 1 GHz - 4 GHz to ease the high wall losses that will be encountered when using a higher frequency range and to guarantee deeper penetration of the electromagnetic wave. Finally, both simulated and calculated results of the designed, optimised antennas indicate excellent agreement with improved performance in terms of return loss, gain, radiation pattern, and fidelity over the entire UWB frequency. These breakthroughs provided reduced computational time and computer memory requirement for useful, efficient, reliable, and compact sensors for imaging applications, including security and breast cancer detection, thereby saving more lives. / Tertiary Education Trust Fund (TET Fund) Supported by the Nigerian Defence Academy (NDA)

No description available.

Since the last few years, the unprecedented growth of communication systems involving the propagation of electromagnetic waves is particularly due to developments in mobile phone technology. The reverberation chamber is a reliable bench-test, enabling the study of the effects of electromagnetic waves on a specific electronic appliance. However, the operating of a reverberation chamber being rather complicated, development of numerical models are of utmost importance to determine the crucial parameters to be considered.This thesis consists in the modelling and the simulation of the operating principles of a reverberation chamber by means of the Finite-Difference Time-Domain method. After a brief study based on field and power measurements performed in a reverberation chamber, the second chapter deals with the different problems encountered during the modelling. The consideration of losses being a very important factor in the operating of the chamber, two methods of implementation of these losses are set out in this chapter. Chapter~3 consists in the analysis of the influence of the stirrer on the first eigenmodes of the chamber; the latter modes can undergo a frequency shift of several MHz. Chapter~4 shows a comparison of results issued from high frequency simulations and theoretical statistical results. The problem of an object placed in the chamber, resulting in a field disturbance is also tackled. Finally, in the fifth chapter, a comparison of statistical results for stirrers having different shapes is set out.