Adaptive liquid-crystal phase-only passive devices

This PhD work is focused on liquid crystal based tunable phase devices with special emphasis on their design and manufacturing. In the course of the work a number of new manufacturing technologies have been implemented in the UPM clean room facilities, leading to an important improvement in the range of devices being manufactured in the laboratory. Furthermore, a number of novel phase devices have been developed, all of them including novel electrodes, and/or alignment layers. The most important manufacturing progress has been the introduction of reactive ion etching as a tool for achieving high resolution photolithography on indium-tin-oxide (ITO) coated glass and quartz substrates. Another important manufacturing result is the successful elaboration of a binding protocol of anisotropic conduction adhesives. These have been employed in high density interconnections between ITO-glass and flexible printed circuits. Regarding material characterization, the comparative study of nonstoichiometric silicon oxide (SiOx) and silica (SiO2) inorganic alignment layers, as well as the relationship between surface layer deposition, layer morphology and liquid crystal electrooptical response must be highlighted, together with the characterization of the degradation of liquid crystal devices in simulated space mission environment. A wide variety of phase devices have been developed, with special emphasis on beam steerers. One of these was developed within the framework of an ESA project, and consisted of a high density reconfigurable 1D blaze grating, with a spatial separation of the controlling microelectronics and the active, radiation exposed, area. The developed devices confirmed the assumption that liquid crystal devices with such a separation of components, are radiation hard, and can be designed to be both vibration and temperature sturdy. In parallel to the above, an evenly variable analog beam steering device was designed, manufactured and characterized, providing a narrow cone diffraction free beam steering. This steering device is characterized by a very limited number of electrodes necessary for the redirection of a light beam. As few as 4 different voltage levels were needed in order to redirect a light beam. Finally at the Wojskowa Akademia Techniczna (Military University of Technology) in Warsaw, Poland, a wedged analog tunable beam steering device was designed, manufactured and characterized. This beam steerer, like the former one, was designed to resist the harsh conditions both in space and in the context of the shuttle launch. Apart from the beam steering devices, reconfigurable vortices and modal lens devices have been manufactured and characterized. In summary, during this work a large number of liquid crystal devices and liquid crystal device manufacturing technologies have been developed. Besides their relevance in scientific publications and technical achievements, most of these new devices have demonstrated their usefulness in the actual work of the research group where this PhD has been completed. El presente trabajo de Tesis se ha centrado en el diseño, fabricación y caracterización de nuevos dispositivos de fase basados en cristal líquido. Actualmente se están desarrollando dispositivos basados en cristal líquido para aplicaciones diferentes a su uso habitual como displays. Poseen la ventaja de que los dispositivos pueden ser controlados por bajas tensiones y no necesitan elementos mecánicos para su funcionamiento. La fabricación de todos los dispositivos del presente trabajo se ha realizado en la cámara limpia del grupo. La cámara limpia ha sido diseñada por el grupo de investigación, es de dimensiones reducidas pero muy versátil. Está dividida en distintas áreas de trabajo dependiendo del tipo de proceso que se lleva a cabo. La cámara limpia está completamente cubierta de un material libre de polvo. Todas las entradas de suministro de gas y agua están selladas. El aire filtrado es constantemente bombeado dentro de la zona limpia, a fin de crear una sobrepresión evitando así la entrada de aire sin filtrar. Las personas que trabajan en esta zona siempre deben de estar protegidas con un traje especial. Se utilizan trajes especiales que constan de: mono, máscara, guantes de látex, gorro, patucos y gafas de protección UV, cuando sea necesario. Para introducir material dentro de la cámara limpia se debe limpiar con alcohol y paños especiales y posteriormente secarlos con nitrógeno a presión. La fabricación debe seguir estrictamente unos pasos determinados, que pueden cambiar dependiendo de los requerimientos de cada dispositivo. Por ello, la fabricación de dispositivos requiere la formulación de varios protocolos de fabricación. Estos protocolos deben ser estrictamente respetados a fin de obtener repetitividad en los experimentos, lo que lleva siempre asociado un proceso de fabricación fiable. Una célula de cristal líquido está compuesta (de forma general) por dos vidrios ensamblados (sándwich) y colocados a una distancia determinada. Los vidrios se han sometido a una serie de procesos para acondicionar las superficies internas. La célula se llena con cristal líquido. De forma resumida, el proceso de fabricación general es el siguiente: inicialmente, se cortan los vidrios (cuya cara interna es conductora) y se limpian. Después se imprimen las pistas sobre el vidrio formando los píxeles. Estas pistas conductoras provienen del vidrio con la capa conductora de ITO (óxido de indio y estaño). Esto se hace a través de un proceso de fotolitografía con una resina fotosensible, y un desarrollo y ataque posterior del ITO sin protección. Más tarde, las caras internas de los vidrios se acondicionan depositando una capa, que puede ser orgánica o inorgánica (un polímero o un óxido). Esta etapa es crucial para el funcionamiento del dispositivo: induce la orientación de las moléculas de cristal líquido. Una vez que las superficies están acondicionadas, se depositan espaciadores en las mismas: son pequeñas esferas o cilindros de tamaño calibrado (pocos micrómetros) para garantizar un espesor homogéneo del dispositivo. Después en uno de los sustratos se deposita un adhesivo (gasket). A continuación, los sustratos se ensamblan teniendo en cuenta que el gasket debe dejar una boca libre para que el cristal líquido se introduzca posteriormente dentro de la célula. El llenado de la célula se realiza en una cámara de vacío y después la boca se sella. Por último, la conexión de los cables a la célula y el montaje de los polarizadores se realizan fuera de la sala limpia (Figura 1). Dependiendo de la aplicación, el cristal líquido empleado y los demás componentes de la célula tendrán unas características particulares. Para el diseño de los dispositivos de este trabajo se ha realizado un estudio de superficies inorgánicas de alineamiento del cristal líquido, que será de gran importancia para la preparación de los dispositivos de fase, dependiendo de las condiciones ambientales en las que vayan a trabajar. Los materiales inorgánicos que se han estudiado han sido en este caso SiOx y SiO2. El estudio ha comprendido tanto los factores de preparación influyentes en el alineamiento, el comportamiento del cristal líquido al variar estos factores y un estudio de la morfología de las superficies obtenidas.

Calibration proposal for new antenna array architectures and technologies for space communications

In large antenna arrays with a large number of antenna elements, the required number of measurements for the characterization of the antenna array is very demanding in cost and time. This letter presents a new offline calibration process for active antenna arrays that reduces the number of measurements by subarray-level characterization. This letter embraces measurements, characterization, and calibration as a global procedure assessing about the most adequate calibration technique and computing of compensation matrices. The procedure has been fully validated with measurements of a 45-element triangular panel array designed for Low Earth Orbit (LEO) satellite tracking that compensates the degradation due to gain and phase imbalances and mutual coupling.

Phase transition in the countdown problem

We present a combinatorial decision problem, inspired by the celebrated quiz show called Countdown, that involves the computation of a given target number T from a set of k randomly chosen integers along with a set of arithmetic operations. We find that the probability of winning the game evidences a threshold phenomenon that can be understood in the terms of an algorithmic phase transition as a function of the set size k. Numerical simulations show that such probability sharply transitions from zero to one at some critical value of the control parameter, hence separating the algorithm's parameter space in different phases. We also find that the system is maximally efficient close to the critical point. We derive analytical expressions that match the numerical results for finite size and permit us to extrapolate the behavior in the thermodynamic limit.

Air Mines. Urban Space Station

Air Mines The sky over the city's port was the color of a faulty screen, only partly lit up. As the silhouette of nearby buildings became darker, but more clearly visible against the fading blur-filter of a background, the realization came about how persistent a change had been taking place. Slowly, old wooden water reservoirs and rattling HVAC systems stopped being the only inhabitants of roofs. Slightly trembling, milkish jellyfish-translucent air volumes had joined the show in multiples. A few years ago artists and architects seized upon the death of buildings as their life-saving media. Equipped with constructive atlases and instruments they started disemboweling their subjects, poking about their systems, dumping out on the street the battered ugliness of their embarrassing bits and pieces, so rightly hidden by facades and height from everyday view. But, would you believe it? Even ?old ladies?, investment bankers or small children failed to get upset. Of course, old ladies are not what they used to be. It was old ladies themselves that made it happen after years of fights with the town hall, imaginative proposals and factual arguments. An industry with little financial gains but lots of welcome externalities was not, in fact, the ground for investment bankers. But they too had to admit that having otherwise stately buildings make fine particulate pencils with their facades was not the worse that could happen. Yes, making soot pencils had been found an interesting and visible end product of the endeavor, a sort of mining the air for vintage writing tools one can actually touch. The new view from the street did not seem as solid or dignified as that of old, and they hated that the market for Fine Particulates Extraction (FPE, read efpee) had to be applied on a matrix of blocks and streets that prevented undue concentration of the best or worse solutions. It had to be an evenly distributed city policy in order for the city to apply for cleaning casino money. Once the first prototypes had been deployed in buildings siding Garden Avenue or Bulwark Street even fast movers appreciated the sidekick of flower and plant smell dripping down the Urban Space Stations (USS, read use; USSs, read uses) as air and walls cooled off for a few hours after sunset. Enough. It was all nice to remember, but it was now time to go up and start the lightweight afternoon maintenance of their USS. Coop discussions had taken place all through the planning and continued through the construction phase as to how maintenance was going to be organized. Fasters had voted for a pro, pay a small amount and let them use it for rent and produce. In the end some neighbors decided they were slow enough to take care and it was now the turn. Regret came periodically, sometimes a week before, and lasted until work actually started. But lately it had been replaced by anxiety when it needed to be passed over to the next caretaker. It did not look their shift was good enough and couldn?t wait to fix it. Today small preparations needed to be made for a class visit next day from a nearby cook school. They were frequenters. It had not been easy, but it shouldn?t have been that hard. In the end, even the easiest things are hard if they involve a city, buildings and neighbors. On the face of the data, the technicalities and the way final designs had been worked out for adaptation to the different settings, the decision of where to go was self evident, but organization issues and the ever-growing politics of taste in a city of already-gentrified-rodents almost put the project in the frozen orbit of timeless beautiful future possibilities. This is how it was. A series of designs by XClinic and OSS had made it possible to adapt to different building structures, leave in most cases the roof untouched and adapted a new technology of flexing fiberglass tubes that dissipated wind pressure in smooth bending.......

State space models for multi-setup operational modal analysis

Operational Modal Analysis consists on estimate the modal parameters of a structure (natural frequencies, damping ratios and modal vectors) from output-only vibration measurements. The modal vectors can be only estimated where a sensor is placed, so when the number of available sensors is lower than the number of tested points, it is usual to perform several tests changing the position of the sensors from one test to the following (multiple setups of sensors): some sensors stay at the same position from setup to setup, and the other sensors change the position until all the tested points are covered. The permanent sensors are then used to merge the mode shape estimated at each setup (or partial modal vectors) into global modal vectors. Traditionally, the partial modal vectors are estimated independently setup by setup, and the global modal vectors are obtained in a postprocess phase. In this work we present two state space models that can be used to process all the recorded setups at the same time, and we also present how these models can be estimated using the maximum likelihood method. The result is that the global mode shape of each mode is obtained automatically, and subsequently, a single value for the natural frequency and damping ratio of the mode is computed. Finally, both models are compared using real measured data.