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[ES] La cantidad de servicios de telecomunicación se ha incrementado signiticativamente en las últimas décadas. El uso de teléfonos inteligentes, así como el Internet de las Cosas, está generando una saturación del espectro electromágnetico. Por tanto, los requisitos de los sistemas de microondas han cambiado para adaptarse a estos nuevos avances. Para satisfacer estas necesidades, se busca el desarrollo de dispositivos de bajo coste, volumen, peso y consumo. Además, interesa que sean espectralmente eficientes y fácilmente integrables con otros dispositivos. Entre todos los dispostivos de microondas, los filtros son elementos clave dentro de los sistemas de comunicaciones móviles e inalámbricas. Es por ello que el diseño de filtros que cumplan con los requisitos mencionados se ha convertido en un tema de gran interés. Para dar respuesta a este problema ha surgido la tecnología de Guía de Onda Integrada en Sustrato (Substrate Integrated Waveguide (SIW)), que permite la implementación de filtros con un reducido tamaño y fácilmente integrables con otros dispositivos en tecnología planar. Dicha tecnología presenta unas prestaciones en cuanto a manejo de potencia y pérdidas mejores que la tecnología de circuito impreso (Printed Circuit Board (PCB)), aunque no llegan a ser iguales que las de la guía de onda clásica. Por otro lado, la saturación espectral también lleva al estudio de filtros con respuestas variables en frecuencia, es decir, que puedan cambiar su frecuencia central y ancho de banda con el fin de adaptarse a las necesidades del sistema. Por ello, el objetivo general de esta Tesis es el análisis y diseño de nuevos filtros reconfigurables en tecnología integrada. El trabajo empieza con el estudio de los fundamentos de los filtros de microondas hasta llegar al diseño de resonadores reconfigurables en tecnología SIW usando el cristal líquido como material de reconfiguración. En primer lugar, se ha estudiado la influencia que los cambios en el valor de la permitividad dieléctrica en el interior de las estructuras filtrantes pueden tener en la respuesta de las mismos. En particular, se desarrollan filtros alternando secciones de línea con y sin dieléctrico dentro de una SIW vacía, Empty Substrate Integrated Waveguide (ESIW). Una vez hecho esto, se procede al estudio de materiales que tengan un valor de permitividad dieléctrica variable de alguna forma. En concreto, se ha realizado la caracterización de diferentes mezclas de cristal líquido a la frecuencia de microondas. Dicho material cambia su valor de permitividad cuando se le aplica un campo eléctrico o magnético. Dado que para la reconfiguración de la respuesta de los filtros se requiere de una estructura desacoplada en baja frecuencia, es decir, con más de un conductor, se ha desarrollado una estrategia para el desacoplo de la estructuras ESIW, la tecnología Decoupled Empty Substrate Integrated Waveguide (DESIW). Por último, se han diseñado resonadores en dicha tecnología DESIW, que se han llenado de cristal líquido y aplicado unos campos de polarización, consiguiendo variar su respuesta en frecuencia. Dichos resonadores constituyen el elemento básico para el desarrollo de filtros de microondas. Es por ello que el conocimiento obtenido en la Tesis es una buena base para futuros trabajos esta tecnología que permitan conseguir filtros de altas prestaciones. / [CA] La quantitat de serveis de telecomunicació s'ha incrementat significativament en les últimes dècades. L'ús de telèfons intel$\cdot$ligents, així com la internet de les coses, està generant una saturació de l'espectre electromagnètic. Per tant, els requisits dels sistemes de microones han canviat per a adaptar-se a aquests nous avanços. Per a satisfer aquestes necessitats, se cerca el desenvolupament de dispositius de baix cost, volum, pes i consum. A més, interessa que siguen espectralment eficients i fàcilment integrables amb altres dispositius. Entre tots els dispositius de microones, els filtres són elements clau dins dels sistemes de comunicacions mòbils i sense fil. És per això que el disseny de filtres que complisquen els requisits esmentats s'ha convertit en un tema de gran interès. Per a donar resposta a aquest problema ha sorgit la tecnologia de Guia d'Ona Integrada en Substrat (Substrate Integrated Waveguide (SIW)), que permet la implementació de filtres amb una reduïda grandària i fàcilment integrables amb altres dispositius en tecnologia planar. Aquesta tecnologia presenta unes prestacions quant a maneig de potència i pèrdues millors que la tecnologia de circuit imprès (Printed Circuit Board (PCB)), encara que no arriben a ser iguals que les de la guia d'ona clàssica. D'altra banda, la saturació espectral també porta a l'estudi de filtres amb respostes variables en freqüència, és a dir, que puguen canviar la seua freqüència central i l'amplada de banda amb la finalitat d'adaptar-se a les necessitats del sistema. Per això, l'objectiu general d'aquesta tesi és l'anàlisi i el disseny de nous filtres reconfigurables en tecnologia integrada. El treball comença amb l'estudi dels fonaments dels filtres de microones, fins a arribar al disseny de ressonadors reconfigurables en tecnologia SIW usant el cristall líquid com a material de reconfiguració. En primer lloc, s'ha estudiat la influència que els canvis en el valor de la permitivitat dielèctrica a l'interior de les estructures filtrants poden tenir en la resposta d'aquestes. En particular, es desenvolupen filtres que alternen seccions de línia amb dielèctric i sense dins d'una SIW buida, Empty Substrate Integrated Waveguide (ESIW). Una vegada fet això, es procedeix a l'estudi de materials que tinguen un valor de permitivitat dielèctrica variable d'alguna forma. En concret, s'ha realitzat la caracterització de diferents mescles de cristall líquid a la freqüència de microones. Aquest material canvia el seu valor de permitivitat quan se li aplica un camp elèctric o magnètic. Atès que per a la reconfiguració de la resposta dels filtres es requereix una estructura desacoblada en baixa freqüència, és a dir, amb més d'un conductor, s'ha desenvolupat una estratègia per al desacoblament d'estructures ESIW, la tecnologia Decoupled Empty Substrate Integrated Waveguide (DESIW). Finalment, s'han dissenyat ressonadors en aquesta tecnologia DESIW, que s'han omplit de cristall líquid i aplicat uns camps de polarització, i s'ha aconseguit variar la seua resposta en freqüència. Aquests ressonadors constitueixen l'element bàsic per al desenvolupament de filtres de microones. És per això que el coneixement obtingut en la tesi és una bona base per a futurs treballs d'aquesta tecnologia que permeten aconseguir filtres d'altes prestacions. / [EN] The number of telecommunication services has increased significantly in recent decades. The use of smartphones, as well as the Internet of Things, is generating a saturation of the electromagnetic spectrum. Therefore, the requirements of microwave systems have changed to adapt to these new developments and related challenges. For achieving these needs, the development of devices with low cost, volume, weight and power consumption is sought. In addition, it interests to be spectrally efficient, to offer high performance, and to be easily integrated with other devices. Among all microwave devices, filters are key elements within mobile and wireless communication systems. In this context, the design of filters that meet the aforementioned requirements has become a topic of great interest. For solving this problem, Substrate Integrated Waveguide (SIW) technology has emerged, which allows the implementation of filters with a small size and to be easily integrated with other devices in planar technology. This technology has better power handling and loss performance than Printed Circuit Board (PCB) technology, although they do not have the performance of the classic waveguide counterpart. On the other hand, the spectral saturation also leads to the study of filters with tunable frequency response, that is, they can change their central frequency and bandwidth, in order to fulfil the changing system requirements. Therefore, the general objective of this PhD Thesis work is the analysis and design of new reconfigurable filters in integrated technology. The work begins with the study of the basics of microwave filters until the design of reconfigurable resonators in SIW technology, using Liquid Crystal (LC) as reconfiguration material. Firstly, the influence that the change of the dielectric permittivity value inside the filtering structures have on the frequency response has been studied. Particularly, filters have been obtained by alternating line sections with and without dielectric material inside an empty SIW (Empty Substrate Integrated Waveguide (ESIW)). Once this is done, it is proceed to the study of materials that have a variable dielectric permittivity value. Specifically, the characterization of different LC mixtures at microwave frequencies has been carried out. This material changes its permittivity value when an electric or magnetic bias field is applied. A low-frequency decoupled structure is required for the reconfiguration of filters, that is, structures with more than one conductor. For that, a strategy for decoupling ESIW structures has been developed, i.e, the Decoupled Empty Substrate Integrated Waveguide (DESIW) technology. Finally, some resonators have been designed in DESIW technology, which have been filled with LC. The use of LC allows to tune their frequency response. These resonators are basic elements for the development of microwave filters. So that, the knowledge obtained in this Thesis work is a good basis for future works in this technology that allow for achieving high performance filters. / Sánchez Marín, JR. (2019). Reconfigurable Devices using Liquid Crystal at Microwave Frequencies in Substrate Integrated Waveguide [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/132183

[pt] Alguns óleos crus brasileiros formam emulsões estáveis, mesmo contendo baixo teor de asfaltenos, os quais são reconhecidos como os principais surfactantes naturais do petróleo. Este trabalho visou compreender os fatores que contribuem na formação e estabilização dessas emulsões através da caracterização de frações com atividade interfacial: os materiais interfaciais (IM) e os ácidos naftênicos (NA). Para isso, tais frações foram extraídas de três óleos crus brasileiros com API entre 21 e 30 graus, permitindo a caracterização da sua composição química e estrutura coloidal. Além disso, estas frações e os óleos residuais de suas extrações foram usados para preparar emulsões água-em-óleo (A/O). A caracterização química realizada por análise elementar, espectroscopia de infravermelho, ressonância magnética nuclear e espectrometria de massas, mostrou que os IM podem ser compostos por saturados, aromáticos, resinas e asfaltenos e NA por saturados e aromáticos. Porém, são enriquecidos em compostos aromáticos e com grupos polares, como ácidos carboxílicos, aminas, sulfóxidos e sulfônicos, em relação aos seus óleos de origem. Ainda assim, a fração de NA não apresentou um papel relevante nas emulsões. Já os compostos anfifílicos presentes nos IM são capazes de formar agregados coloidais caracterizados pela técnica de espalhamento de raios X a baixos ângulos (SAXS) e promover a formação de emulsões, mas não são suficientes para garantir sua estabilização. A remoção dos IM aumentou a auto-organização dos agregados no óleo cru residual e a estabilidade das emulsões, o que parece ter mais relação com propriedades reológicas do que com a atividade interfacial dos compostos. / [en] Some Brazilian crude oils form stable emulsions, even containing alow content of asphaltenes, recognized as the main natural surfactants in petroleum. This work aimed to understand the factors contributing to theformation and stabilization of these emulsions through the characterization of fractions with possible interfacial activity: interfacial materials (IM) and naphthenic acids (NA). For this, these fractions were extracted from three Brazilian crude oils with API between 21 and 30 degrees, allowing the characterization of their chemical composition and colloidal structure. Furthermore, these fractions and the residual oils from their extractions were used to prepare water-in-oil (W/O) emulsions. Chemical characterization carried out by elemental analysis, infrared spectroscopy, nuclear magnetic resonance, and mass spectrometry, showed that IM can be composed of saturates, aromatics, resins, and asphaltenes and NA by saturates and aromatics. However, they are enriched in aromatic compounds and polar groups, such as carboxylic acids, amines, sulfoxides,and sulfonic acids, concerning their original oils. Nevertheless, the NAfraction did not play a relevant role in emulsions. The amphiphilic compounds present in IM can form colloidal aggregates characterized by the small-angle X-ray scattering (SAXS) technique and promote the formation of emulsions. Still, they are not sufficient to guarantee their stabilization. The removal of IM increased the self-organization of aggregates in the residual crude oil and the stability of emulsions, which seems to be more related to rheological properties than to the interfacial activity of the compounds.

The thesis concerns the mathematical study of the calculus of variations and its application to liquid crystals. In the first chapter we examine vectorial problems in the calculus of variations with an additional pointwise constraint so that any admissible function <strong>n</strong> ε W^1,1(ΩM), and M is a manifold of suitable regularity. We formulate necessary and sufficient conditions for any given state <strong>n</strong> to be a strong or weak local minimiser of I. This is achieved using a nearest point projection mapping in order to use the more classical results which apply in the absence of a constraint. In the subsequent chapters we study various static continuum theories of liquid crystals. More specifically we look to explain a particular cholesteric fingerprint pattern observed by HP Labs. We begin in Chapter 2 by focusing on a specific cholesteric liquid crystal problem using the theory originally derived by Oseen and Frank. We find the global minimisers for general elastic constants amongst admissible functions which only depend on a single variable. Using the one-constant approximation for the Oseen-Frank free energy, we then show that these states are global minimisers of the three-dimensional problem if the pitch of the cholesteric liquid crystal is sufficiently long. Chapter 3 concerns the application of the results from the first chapter to the situations investigated in the second. The local stability of the one-dimensional states are quantified, analytically and numerically, and in doing so we unearth potential shortcomings of the classical Oseen-Frank theory. In Chapter 4, we ascertain some equivalence results between the continuum theories of Oseen and Frank, Ericksen, and Landau and de Gennes. We do so by proving lifting results, building on the work of Ball and Zarnescu, which relate the regularity of line and vector fields. The results prove to be interesting as they show that for a director theory to respect the head to tail symmetry of the liquid crystal molecules, the appropriate function space for the director field is S BV² (Ω,S<sup>2,/sup>). We take this idea and in the final chapter we propose a mathematical model of liquid crystals based upon the Oseen-Frank free energy but using special functions of bounded variation. We establish the existence of a minimiser, forms of the Euler-Lagrange equation, and find solutions of the Euler-Lagrange equation in some simple cases. Finally we use our proposed model to re-examine the same problems from Chapter 2. By doing so we extend the analysis we were able to achieve using Sobolev spaces and predict the existence of multi-dimensional minimisers consistent with the known experimental properties of high-chirality cholesteric liquid crystals.

Dans ce travail nous étudions l’élaboration, la caractérisation et les applications de différents matériaux poreux. L’étude est organisée en trois parties majeures: la synthèse de zéolithes micro/mesoporeux et leur application potentielle dans l’industrie pétrochimique, l’étude théorique de mécanismes réactionnels sur des zeolites microporeux, et le design de métaux mesoporeux avec une chiralité intrinsèque de leur surface interne. Ces matériaux poreux montrent des propriétés excellentes, notamment pour des applications potentielles en catalyse et comme interfaces chirales. / In the present work, the elaboration, characterisation and applications of differentporous materials have been studied. Porous materials are divided into three categoriesdepending on the porous cavity size, namely microporous materials (pore diameter < 2nm), mesoporous materials (2 nm < pore diameter < 50 nm) and macroporous materials(pore diameter > 50 nm). The thesis work is organized in three major parts: the synthesisof hierarchical micro/mesoporous zeolites and their potential application for thepetrochemical industry, the theoretical study of reaction mechanisms on microporouszeolite and the design of mesoporous metals with intrinsic chirality at their inner surface.The hierarchical micro/mesoporous zeolite, composed of microporous andmesoporous features, has been prepared using carbon-silica (C/SiO2) composites derivedfrom a pyrolysis of hydrocarbon gas on silica gel. Our findings demonstrate that not onlythe presence of a high surface area and porosity, but also an improved efficiency of thesematerials for many petrochemical processes such as n-butene isomerization, nhexadecanecatalytic cracking and hydrocracking. The novel synthetic method is expectedto be generalized for other types of zeolites, and is considered to be a promising methodfor creating hierarchical micro/mesoporous zeolites for potential catalytic applications,especially in the petrochemical industry.In addition to the study of practical catalytic aspects, a theoretical approach hasbeen used to investigate potential reaction mechanisms such as the selective isomerizationof 1-butene into isobutene. More specifically, the monomolecular skeletal isomerizationof 1-butene into isobutene on H-FER zeolite was theoretically studied by using theONIOM approach. This process was found to involve the transformation of adsorbed 1-butene through 2-butoxide, isobutoxide, and tert-butyl cation intermediates. The ratedeterminingstep is the conversion of isobutoxide into isobutene, in which the reactionhas to proceed through the primary isobutyl cation transition state. The shape selectivitydue to the “nano-confinement” effect of the zeolite framework strongly affects theadsorption, the stability of alkoxide species and carbenium ion, as well as the skeletalisomerization mechanism of 1-butene.Moreover, the microporous and mesoporous zeolite, the generation of chiralmesoporous metal and its enantioselective recognition properties have been studied.Molecular imprinting (MI) is a major approach for generating materials withenantioselective properties. In this work, a chiral imprinted mesoporous platinum hasbeen obtained by the electrochemical reduction of platinum salts in the simultaneouspresence of a lyotropic liquid crystal phase and chiral template molecules. The resultingmaterials exhibit not only a dramatic increase in active surface area due to theirmesoporosity, but also a significant discrimination between two enantiomers of a chiralprobe, confirmed by both electrochemical and enantioselective adsorption experiments.Most importantly the porous platinum retains its chiral character even after removal of thechiral template molecule. Our findings could lead to the development of new materials,which are of potential interest for applications in areas such as chiral synthesis, sensors,separation, purification and drug development.