Sistema el��ctrico y de control de potencia de un tunel aerodin��mico = Design of the power distributation and control system for a wind tunnel facility

La utilizaci��n de t��neles aerodin��micos en ingenier��a civil est�� cada vez m��s demandada debido al actual desarrollo urban��stico, esto es, la necesidad de edificios cada vez m��s altos en los que concentrar mayor cantidad de poblaci��n, puentes y estructuras que faciliten el paso de medios de transporte alternativos, la importancia de los aspectos art��sticos en la construcci��n (adem��s de los funcionales), etc. Son muchos los factores que pueden hacer necesario el ensayo de alguna de esas estructuras en un t��nel aerodin��mico, y no existe un criterio universal a la hora de decidir si conviene o no hacerlo.

Development of Shape-Optimization Tools for the Aerodynamic Design of Turbomachinery Blades

The aim of this work is to develop an automated tool for the optimization of turbomachinery blades founded on an evolutionary strategy. This optimization scheme will serve to deal with supersonic blades cascades for application to Organic Rankine Cycle (ORC) turbines. The blade geometry is defined using parameterization techniques based on B-Splines curves, that allow to have a local control of the shape. The location in space of the control points of the B-Spline curve define the design variables of the optimization problem. In the present work, the performance of the blade shape is assessed by means of fully-turbulent flow simulations performed with a CFD package, in which a look-up table method is applied to ensure an accurate thermodynamic treatment. The solver is set along with the optimization tool to determine the optimal shape of the blade. As only blade-to-blade effects are of interest in this study, quasi-3D calculations are performed, and a single-objective evolutionary strategy is applied to the optimization. As a result, a non-intrusive tool, with no need for gradients definition, is developed. The computational cost is reduced by the use of surrogate models. A Gaussian interpolation scheme (Kriging model) is applied for the estimated n-dimensional function, and a surrogate-based local optimization strategy is proved to yield an accurate way for optimization. In particular, the present optimization scheme has been applied to the re-design of a supersonic stator cascade of an axial-flow turbine. In this design exercise very strong shock waves are generated in the rear blade suction side and shock-boundary layer interaction mechanisms occur. A significant efficiency improvement as a consequence of a more uniform flow at the blade outlet section of the stator is achieved. This is also expected to provide beneficial effects on the design of a subsequent downstream rotor. The method provides an improvement to gradient-based methods and an optimized blade geometry is easily achieved using the genetic algorithm.

Optimized design of the prestress in continuous bridge decks

In this paper a method for automatic design of the prestress in continuous bridge decks is presented. In a first step of the procedure the optimal prestressed force for a completely geometrically defined and feasible prestress layout is obtained by means of linear programming techniques. Further on, in a second step the prestress geometry and minimum force are automatically found by steepest descent optimization techniques. Finally this methodology is applied to two-span continuous bridge decks and from the obtained results some preliminary design rules can be drawn.

Preliminary design of symmetric arch-gravity dams

In this paper, a set of design parameters, such as the slopes of upstream and downstream faces of the dam, radius of the upper arch, width of the dam at the top level and height of the vertical upper part of the dam, are given as function of the valley characteristics when the dam is situated, such as its geometry and its geotechnical properties. These tables have been obtained using a regression of the design parameters of an arch-gravity dam with a minimum concrete volume, placed in a large number of valleys with different characteristics and properties. Elasticites for these design parameters are also discussed.

Simplified serviceability design of jointless structures. Experimental verification and application to typical bridge and building structures

In this article an experimental campaign aimed at validating a previously published simplified serviceability design method of the columns of long jointless structures is presented. The proposed method is also extended to include tension stiffening effects which proved to be significant in structures with small amount of reinforcement subjected to small axial loading. This extension allows significant improvement of predictions for this type of element. The campaign involved columns with different reinforcement and squashing load ratios, given that these parameters had been identified as crucial when designing columns subjected to imposed displacements. Experimental results are presented and discussed, with particular regard to cracking behaviour and structural stiffness. Considerations on tension stiffening effects are also made. Finally, the application of the method to typical bridge and building cases is presented, showing the feasibility of jointless construction, and the limits which should be respected.

Design of Reinforcement in Concrete Shells: a unified Approach

The problem of design/verification of reinforcement in concrete shells is reviewed. Methods of analysis are classified, and the elastic-plastic approach is described in detail in the general case of shells subjected to both bending and membrane action. The procedure is then reduced to membrane shells (applicable also to concrete walls) and to pure bending, as in the case of plates. The procedure, which is based on previous research,generally requires the use of a desk-top computer.

Design of a Two-Phase buck converter with fourth-order output filter for envelope amplifiers of limited bandwidth

The use of techniques such as envelope tracking (ET) and envelope elimination and restoration (EER) can improve the efficiency of radio frequency power amplifiers (RFPA). In both cases, high-bandwidth DC/DC converters called envelope amplifiers (EA) are used to modulate the supply voltage of the RFPA. This paper addresses the analysis and design of a modified two-phase Buck converter optimized to operate as EA. The effects of multiphase operation on the tracking capabilities are analyzed. The use of a fourth-order output filter is proposed to increase the attenuation of the harmonics generated by the PWM operation, thus allowing a reduction of the ratio between the switching frequency and the converter bandwidth. The design of the output filter is addressed considering envelope tracking accuracy and distortion caused by the side bands arising from the nonlinear modulation process. Finally, the proposed analysis and design methods are supported by simulation results, as well as demonstrated by experiments obtained using two 100-W, 10-MHz, two-phase Buck EAs capable of accurately tracking a 1.5-MHz bandwidth OFDM signal.

Conceptual design of offshore platform supply vessel based on hybrid diesel generator-fuel cell power plant

Nowadays increasing fuel prices and upcoming pollutant emission regulations are becoming a growing concern for the shipping industry worldwide. While fuel prices will keep rising in future years, the new International Convention for the Prevention of Pollution from Ships (MARPOL) and Sulphur Emissions Control Areas (SECA) regulations will forbid ships to use heavy fuel oils at certain situations. To fulfil with these regulations, the next step in the marine shipping business will comprise the use of cleaner fuels on board as well as developing new propulsion concept. In this work a new conceptual marine propulsion system is developed, based on the integration of diesel generators with fuel cells in a 2850 metric tonne of deadweight platform supply vessel. The efficiency of the two 250 kW methanol-fed Solid Oxide Fuel Cell (SOFC) system installed on board combined with the hydro dynamically optimized design of the hull of the ship will allow the ship to successfully operate at certain modes of operation while notably reduce the pollutant emissions to the atmosphere. Besides the cogeneration heat obtained from the fuel cell system will be used to answer different heating needs on board the vessel

Mixed-criticality design of a satellite software system

The continuous increment of processors computational power and the requirements on additional functionality and services are motivating a change in the way embedded systems are built. Components with different criticality level are allocated in the same processor, which give rise to mixed-criticality systems. The use of partitioned systems is a way of preventing undesirable interferences between components with different criticality level. An hypervisor provides these partitions or virtual machines, ensuring spatial, temporal and fault isolation between them. The purpose of this paper is to illustrate the development of a mixed-critical system. The attitude control subsystem is used for showing the different steps, which are supported by a toolset developed in the context of the MultiPARTES research project.

Guidelines for the design of an environmental flow regime program at the regional scale: Application of the ELOHA framework in the Ebro River basin

La gesti��n de los recursos h��dricos se convierte en un reto del presente y del futuro frente a un panorama de continuo incremento de la demanda de agua debido al crecimiento de la poblaci��n, el crecimiento del desarrollo econ��mico y los posibles efectos del calentamiento global. La pol��tica hidr��ulica desde los a��os 60 en Espa��a se ha centrado en la construcci��n de infraestructuras que han producido graves alteraciones en el r��gimen natural de los r��os. Estas alteraciones han provocado y acrecentado los impactos sobre los ecosistemas fluviales y ribere��os. Desde los a��os 90, sin embargo, ha aumentado el inter��s de la sociedad para conservar estos ecosistemas. El concepto de caudales ambientales consiste en un r��gimen de caudales que simula las caracter��sticas principales del r��gimen natural. Los caudales ambientales est��n dise��ados para conservar la estructura y funcionalidad de los ecosistemas asociados al r��gimen fluvial, bajo la hip��tesis de que los elementos que conforman estos ecosistemas est��n profundamente adaptados al r��gimen natural de caudales, y que cualquier alteraci��n del r��gimen natural puede provocar graves da��os a todo el sistema. El m��todo ELOHA (Ecological Limits of Hydrological Alteration) tiene como finalidad identificar las componentes del r��gimen natural de caudales que son clave para mantener el equilibrio de los ecosistemas asociados, y estimar los l��mites m��ximos de alteraci��n de estas componentes para garantizar su buen estado. Esta tesis presenta la aplicaci��n del m��todo ELOHA en la cuenca del Ebro. La cuenca del Ebro est�� profundamente regulada e intervenida por el hombre, y s��lo las cabeceras de los principales afluentes del Ebro gozan todav��a de un r��gimen total o cuasi natural. La tesis se estructura en seis cap��tulos que desarrollan las diferentes partes del m��todo. El primer cap��tulo explica c��mo se origin�� el concepto ���caudales ambientales��� y en qu�� consiste el m��todo ELOHA. El segundo cap��tulo describe el ��rea de estudio. El tercer cap��tulo realiza una clasificaci��n de los reg��menes naturales de la cuenca (RNC) del Ebro, basada en series de datos de caudal m��nimamente alterado y usando exclusivamente par��metros hidrol��gicos. Se identificaron seis tipos diferentes de r��gimen natural: pluvial mediterr��neo, nivo-pluvial, pluvial mediterr��aneo con una fuerte componente del caudal base, pluvial oce��nico, pluvio-nival oce��nico y Mediterr��neo. En el cuarto cap��tulo se realiza una regionalizaci��n a toda la cuenca del Ebro de los seis RNC encontrados en la cueca. Mediante par��metros clim��ticos y fisiogr��ficos se extrapola la informaci��n del tipo de RNC a puntos donde no existen datos de caudal inalterado. El patr��n geogr��fico de los tipos de r��gimen fluvial obtenido con la regionalizaci��n result�� ser coincidente con el patr��n obtenido a trav��s de la clasificaci��n hidrol��gica. El quinto cap��tulo presenta la validaci��n biol��gica de los procesos de clasificaci��n anteriores: clasificaci��n hidrol��gica y regionalizaci��n. La validaci��n biol��gica de los tipos de reg��menes fluviales es imprescindible, puesto que los diferentes tipos de r��gimen fluvial van a servir de unidades de gesti��n para favorecer el mantenimiento de los ecosistemas fluviales. Se encontraron diferencias significativas entre comunidades biol��gicas en cinco de los seis tipos de RNC encontrados en la cuenca. Finalmente, en el sexto cap��tulo se estudian las relaciones hidro-ecol��gicas existentes en tres de los seis tipos de r��gimen fluvial encontrados en la cuenca del Ebro. Mediante la construcci��n de curvas hidro-ecol��gicas a lo largo de un gradiente de alteraci��n hidrol��gica, se pueden sugerir los l��mites de alteraci��n hidrol��gica (ELOHAs) para garantizar el buen estado ecol��gico en cada uno de los tipos fluviales estudiados. Se establecieron ELOHAs en tres de los seis tipos de RNC de la cuenca del Ebro Esta tesis, adem��s, pone en evidencia la falta de datos biol��gicos asociados a registros de caudal. Para llevar a cabo la implantaci��n de un r��gimen de caudales ambientales en la cuenca, la ubicaci��n de los puntos de muestreo biol��gico cercanos a estaciones de aforo es imprescindible para poder extraer relaciones causa-efecto de la gesti��n hidrol��gica sobre los ecosistemas dependientes. ABSTRACT In view of a growing freshwater demand because of population raising, improvement of economies and the potential effects of climate change, water resources management has become a challenge for present and future societies. Water policies in Spain have been focused from the 60���s on constructing hydraulic infrastructures, in order to dampen flow variability and granting water availability along the year. Consequently, natural flow regimes have been deeply altered and so the depending habitats and its ecosystems. However, an increasing acknowledgment of societies for preserving healthy freshwater ecosystems started in the 90���s and agreed that to maintain healthy freshwater ecosystems, it was necessary to set environmental flow regimes based on the natural flow variability. The Natural Flow Regime paradigm (Richter et al. 1996, Poff et al. 1997) bases on the hypothesis that freshwater ecosystems are made up by elements adapted to natural flow conditions, and any change on these conditions can provoke deep impacts on the whole system. Environmental flow regime concept consists in designing a flow regime that emulates natural flow characteristics, so that ecosystem structure, functions and services are maintained. ELOHA framework (Ecological Limits of Hydrological Alteration) aims to identify key features of the natural flow regime (NFR) that are needed to maintain and preserve healthy freshwater and riparian ecosystems. Moreover, ELOHA framework aims to quantify thresholds of alteration of these flow features according to ecological impacts. This thesis describes the application of the ELOHA framework in the Ebro River Basin. The Ebro River basin is the second largest basin in Spain and it is highly regulated for human demands. Only the Ebro headwaters tributaries still have completely unimpaired flow regime. The thesis has six chapters and the process is described step by step. The first chapter makes an introduction to the origin of the environmental flow concept and the necessity to come up. The second chapter shows a description of the study area. The third chapter develops a classification of NFRs in the basin based on natural flow data and using exclusively hydrological parameters. Six NFRs were found in the basin: continental Mediterranean-pluvial, nivo-pluvial, continental Mediterranean pluvial (with groundwater-dominated flow pattern), pluvio-oceanic, pluvio-nival-oceanic and Mediterranean. The fourth chapter develops a regionalization of the six NFR types across the basin by using climatic and physiographic variables. The geographical pattern obtained from the regionalization process was consistent with the pattern obtained with the hydrologic classification. The fifth chapter performs a biological validation of both classifications, obtained from the hydrologic classification and the posterior extrapolation. When the aim of flow classification is managing water resources according to ecosystem requirements, a validation based on biological data is compulsory. We found significant differences in reference macroinvertebrate communities between five over the six NFR types identified in the Ebro River basin. Finally, in the sixth chapter we explored the existence of significant and explicative flow alteration-ecological response relationships (FA-E curves) within NFR types in the Ebro River basin. The aim of these curves is to find out thresholds of hydrological alteration (ELOHAs), in order to preserve healthy freshwater ecosystem. We set ELOHA values in three NFR types identified in the Ebro River basin. During the development of this thesis, an inadequate biological monitoring in the Ebro River basin was identified. The design and establishment of appropriate monitoring arrangements is a critical final step in the assessment and implementation of environmental flows. Cause-effect relationships between hydrology and macroinvertebrate community condition are the principal data that sustain FA-E curves. Therefore, both data sites must be closely located, so that the effects of external factors are minimized. The scarce hydro-biological pairs of data available in the basin prevented us to apply the ELOHA method at all NFR types.

Design of equalized ROADMs devices with flexible bandwidth based on LCoS technology

This paper describes the theory, design, applications and performance of a new Reconfigurable Add-drop Multiplexer (ROADM) with flexible bandwidth allocation. The device can address several wavelengths at the input to four output fibers, according to the holograms stored in a SLM (Spatial Light Modulator), where all the outputs are equalized in power. All combinations of the input wavelengths are possible at the different output fibers. Each fiber has assigned all the signals with the same bandwidth; the possible bandwidths are 12.5GHz, 25GHz, 50GHz and 100GHz, according to ITU-T 694.1 Recommendation. It is possible to route several signals with different bandwidth in real time thanks to Liquid Crystal over Silicon (LCoS) technology.

Simulation and geometrical design of multi-section tapered semiconductor optical amplifiers at 1.57 ��m

Fully integrated semiconductor master-oscillator power-amplifiers (MOPA) with a tapered power amplifier are attractive sources for applications requiring high brightness. The geometrical design of the tapered amplifier is crucial to achieve the required power and beam quality. In this work we investigate by numerical simulation the role of the geometrical design in the beam quality and in the maximum achievable power. The simulations were performed with a Quasi-3D model which solves the complete steady-state semiconductor and thermal equations combined with a beam propagation method. The results indicate that large devices with wide taper angles produce higher power with better beam quality than smaller area designs, but at expenses of a higher injection current and lower conversion efficiency.

Design of a Semi-analytical Method to Describe Plasma-Wall Interactions

Electric probes are objects immersed in the plasma with sharp boundaries which collect of emit charged particles. Consequently, the nearby plasma evolves under abrupt imposed and/or naturally emerging conditions. There could be localized currents, different time scales for plasma species evolution, charge separation and absorbing-emitting walls. The traditional numerical schemes based on differences often transform these disparate boundary conditions into computational singularities. This is the case of models using advection-diffusion differential equations with source-sink terms (also called Fokker-Planck equations). These equations are used in both, fluid and kinetic descriptions, to obtain the distribution functions or the density for each plasma species close to the boundaries. We present a resolution method grounded on an integral advancing scheme by using approximate Green's functions, also called short-time propagators. All the integrals, as a path integration process, are numerically calculated, what states a robust grid-free computational integral method, which is unconditionally stable for any time step. Hence, the sharp boundary conditions, as the current emission from a wall, can be treated during the short-time regime providing solutions that works as if they were known for each time step analytically. The form of the propagator (typically a multivariate Gaussian) is not unique and it can be adjusted during the advancing scheme to preserve the conserved quantities of the problem. The effects of the electric or magnetic fields can be incorporated into the iterative algorithm. The method allows smooth transitions of the evolving solutions even when abrupt discontinuities are present. In this work it is proposed a procedure to incorporate, for the very first time, the boundary conditions in the numerical integral scheme. This numerical scheme is applied to model the plasma bulk interaction with a charge-emitting electrode, dealing with fluid diffusion equations combined with Poisson equation self-consistently. It has been checked the stability of this computational method under any number of iterations, even for advancing in time electrons and ions having different time scales. This work establishes the basis to deal in future work with problems related to plasma thrusters or emissive probes in electromagnetic fields.

Contribution to the analysis and design of reflectarray antennas for reconfigurable beam applications at frequencies above 100 GHz using liquid crystal technology

El trabajo contenido en esta tesis doctoral est�� encuadrado en el desarrollo de antenas reconfigurables electr��nicamente capaces de proporcionar prestaciones competitivas a las aplicaciones cada vez m��s comunes que operan a frecuencias superiores a 60 GHz. En concreto, esta tesis se centra en el estudio, dise��o, e implementaci��n de las antenas reflectarray, a las que se introduce la tecnolog��a de cristal l��quido como elemento caracter��stico con el que se consigue reconfigurabilidad de haz de forma electr��nica. Desde un punto de vista muy general, se puede describir un cristal l��quido como un material cuya permitividad el��ctrica es variable y controlada por una excitaci��n externa, que generalmente suele corresponderse con un campo el��ctrico quasi-est��tico (AC). Las antenas reflectarray de cristal l��quido se han escogido como objeto de estudio por varias razones. La primera de ellas tiene que ver con las ventajas que los reflectarrays, y en especial aquellos realizados en configuraci��n planar, proporcionan con respecto a otras antenas de alta ganancia como los reflectores o los ���phased-arrays���. En los reflectarrays, la alimentaci��n a trav��s de una fuente primaria com��n (caracter��stica de reflectores) y el elevado n��mero de grados de libertad de las celdas que los componen (caracter��stica de arrays) hacen que estas antenas puedan proporcionar prestaciones el��ctricas iguales o mejores que las anteriores, a un coste m��s reducido y con estructuras de antena m��s compactas. La segunda raz��n radica en la flexibilidad que ofrece el cristal l��quido a ser confinado y polarizado en recintos de geometr��a variada, como consecuencia de su fluidez (propiedad de los l��quidos). Por ello, la tecnolog��a de cristal l��quido permite que el propio elemento reconfigurable en las celdas de reflectarray se adapte a la configuraci��n planar de manera que en s�� mismo, el cristal l��quido sea una o varias de las capas caracter��sticas de esta configuraci��n. Esto simplifica de forma dr��stica la estructura y la fabricaci��n de este tipo de antenas, incluso si se comparan con reflectarrays reconfigurables basados en otras tecnolog��as como diodos, MEMS, etc. Por tanto, su coste y desarrollo es muy reducido, lo que hace que se puedan fabricar reflectarrays reconfigurables el��ctricamente grandes, a bajo coste, y en producci��n elevada. Un ejemplo claro de una estructura similar, y que ha tenido ��xito comercial, son las pantallas de cristal l��quido. La tercera raz��n reside en el hecho de que el cristal l��quido es, hasta la fecha, de las pocas tecnolog��as capaces de ofrecer reconfigurabilidad del haz a frecuencias superiores a 60 GHz. De hecho, el cristal l��quido permite reconfigurabilidad en un amplio margen de frecuencias, que va desde DC a frecuencias del espectro visible, incluyendo las microondas y los THz. Otras tecnolog��as, como los materiales ferroel��ctricos, el grafeno o la tecnolog��a CMOS ���on chip��� permiten tambi��n conmutar el haz en estas frecuencias. Sin embargo, la tecnolog��a CMOS tiene un elevado coste y actualmente est�� limitada a frecuencias inferiores a 150 GHz, y aunque los materiales ferroel��ctricos o el grafeno puedan conmutar a frecuencias m��s altas y en un rango m��s amplio, tienen serias dificultades que los hacen a��n inmaduros. En el caso de los materiales ferroel��ctricos, los elevados voltajes para conmutar el material los hacen poco atractivos, mientras que en el caso del grafeno, su modelado a��n est�� en discusi��n, y todav��a no se han arrojado resultados experimentales que validen su idoneidad. Estas tres razones hacen que los reflectarrays basados en cristal l��quido sean atractivos para multitud de aplicaciones de haz reconfigurable a frecuencias superiores a 60 GHz. Aplicaciones como radar de escaneo de im��genes de alta resoluci��n, espectroscopia molecular, radi��metros para observaci��n atmosf��rica, o comunicaciones inal��mbricas de alta frecuencia (WiGig) son algunas de ellas. La tesis est�� estructurada en tres partes. En la primera de ellas se describen las caracter��sticas m��s comunes de los cristales l��quidos, centr��ndonos en detalle en aquellas propiedades ofrecidas por este material en fase nem��tica. En concreto, se estudiar�� la anisotrop��a diel��ctrica (Ae) de los cristales l��quidos uniaxiales, que son los que se emplean en esta tesis, definida como la diferencia entre la permitividad paralela (��//) y la perpendicular (e��): Ae = e,, - e��. Tambi��n se estudiar�� la variaci��n de este par��metro (Ae) con la frecuencia, y el modelado electromagn��tico macrosc��pico m��s general que, extra��do a partir de aquella, permite describir el cristal l��quido para cada tensi��n de polarizaci��n en celdas de geometr��a planar. Este modelo es de suma importancia para garantizar precisi��n en el desfasaje proporcionado por las diferentes celdas reconfigurables para reflectarrays que se describir��n en la siguiente parte de la tesis. La segunda parte de la tesis se centra en el dise��o de celdas reflectarray resonantes basadas en cristal l��quido. La raz��n por la que se escogen estos tipos de celdas reside en el hecho de que son las ��nicas capaces de proporcionar rangos de fase elevados ante la reducida anisotrop��a diel��ctrica que ofrecen los cristales l��quidos. El objetivo de esta parte trata, por tanto, de obtener estructuras de celdas reflectarray que sean capaces de proporcionar buenas prestaciones el��ctricas a nivel de antena, mejorando sustancialmente las prestaciones de las celdas reportadas en el estado del arte, as�� como de desarrollar una herramienta de dise��o general para aquellas. Para ello, se estudian las prestaciones el��ctricas de diferentes tipos de elementos resonantes de cristal l��quido que van, desde el m��s sencillo, que ha limitado el estado de la t��cnica hasta el desarrollo de esta tesis y que est�� formado por un s��lo resonador, a elementos que constan de varios resonadores (multi-resonantes) y que pueden ser monocapa o multicapa. En un primer paso, el procedimiento de dise��o de estas estructuras hace uso de un modelo convencional de cristal l��quido que ha venido siendo usado en el estado del arte para este tipo de celdas, y que considera el cristal l��quido como un material homog��neo e is��tropo cuya permitividad var��a entre (e/7) y (e��). Sin embargo, en esta parte de la tesis se demuestra que dicho modelado no es suficiente para describir de forma gen��rica el comportamiento del cristal l��quido en las celdas tipo reflectarray. En la tesis se proponen procedimientos m��s exactos para el an��lisis y dise��o basados en un modelo m��s general que define el cristal l��quido como un material anis��tropo e inhomogeneo en tres dimensiones, y se ha implementado una t��cnica que permite optimizar celdas multi-resonantes de forma eficiente para conseguir elevadas prestaciones en cuanto a ancho de banda, rango de fase, p��rdidas, o sensibilidad al ��ngulo de incidencia. Los errores cometidos en el uso del modelado convencional a nivel de celda (amplitud y fase) se han analizado para varias geometr��as, usando medidas de varios prototipos de antena que usan un cristal l��quido real a frecuencias superiores a 100 GHz. Las medidas se han realizado en entorno peri��dico mediante un banco cuasi-��ptico, que ha sido dise��ado especialmente para este fin. Uno de estos prototipos se ha optimizado a 100 GHz para conseguir un ancho de banda relativamente elevado (10%), p��rdidas reducidas, un rango de fase mayor de 360��, baja sensibilidad al ��ngulo de incidencia, y baja influencia de la inhomogeneidad transversal del cristal l��quido en la celda. Estas prestaciones a nivel de celda superan de forma clara aquellas conseguidas por otros elementos que se han reportado en la literatura, de manera que dicho prototipo se ha usado en la ��ltima parte de la tesis para realizar diversas antenas de barrido. Finalmente, en esta parte se presenta una estrategia de caracterizaci��n de la anisotrop��a macrosc��pica a partir de medidas de los elementos de reflectarray dise��ados en banco cuasi-��ptico, obteniendo resultados tanto en las frecuencias de inter��s en RF como en AC, y compar��ndolas con aquellas obtenidas mediante otros m��todos. La tercera parte de la tesis consiste en el estudio, dise��o, fabricaci��n y medida de antenas reconfigurables basadas en cristal l��quido en configuraciones complejas. En reflectarrays pasivos, el procedimiento de dise��o de la antena se limita ��nicamente al ajuste en cada celda de la antena de las dimensiones de las metalizaciones que se emplean para el control de fase, mediante procesos de optimizaci��n bien conocidos. Sin embargo, en el caso de reflectarrays reconfigurables basados en cristal l��quido, resulta necesario un paso adicional, que consiste en calcular de forma adecuada las tensiones de control en cada celda del reflectarray para configurar la fase requerida en cada una de ellas, as�� como dise��ar la estructura y los circuitos de control que permitan direccionar a cada elemento su tensi��n correspondiente. La s��ntesis de tensiones es por tanto igual o m��s importante que el dise��o de la geometr��a de las celdas, puesto que ��stas son las que est��n directamente relacionadas con la fase. En el estado del arte, existen varias estrategias de s��ntesis de tensiones que se basan en la caracterizaci��n experimental de la curva de fase respecto al voltaje. Sin embargo, esta caracterizaci��n s��lo puede hacerse a un solo ��ngulo de incidencia y para unas determinadas dimensiones de celda, lo que produce que las tensiones sintetizadas sean diferentes de las adecuadas, y en definitiva que se alcancen errores de fase mayores de 70��. De esta forma, hasta la fecha, las prestaciones a nivel de antena que se han conseguido son reducidas en cuanto a ancho de banda, rango de escaneo o nivel de l��bulos secundarios. En esta ��ltima parte de la tesis, se introduce una nueva estrategia de s��ntesis de tensiones que es capaz de predecir mediante simulaciones, y con alta precisi��n, las tensiones que deben introducirse en cada celda teniendo en cuenta su ��ngulo de incidencia, sus dimensiones, la frecuencia, as�� como la se��al de polarizaci��n definida por su frecuencia y forma de onda AC. Esta estrategia se basa en modelar cada uno de los estados de permitividad del cristal l��quido como un sustrato anis��tropo con inhomogeneidad longitudinal (1D), o en ciertos casos, como un tensor equivalente homog��neo. La precisi��n de ambos modelos electromagn��ticos tambi��n se discute. Con el objetivo de obtener una herramienta eficiente de c��lculo de tensiones, tambi��n se ha escrito e implementado una herramienta de an��lisis basada en el M��todo de los Momentos en el Dominio Espectral (SD-MoM) para sustratos estratificados anis��tropos, que se usa en cada iteraci��n del procedimiento de s��ntesis para analizar cada una de las celdas de la antena. La s��ntesis de tensiones se ha dise��ado adem��s para reducir al m��ximo el efecto del rizado de amplitud en el diagrama de radiaci��n, que es caracter��stico en los reflectarrays que est��n formados por celdas con p��rdidas elevadas, lo que en s��, supone un avance adicional para la obtenci��n de mejores prestaciones de antena. Para el c��lculo de los diagramas de radiaci��n empleados en el procedimiento de s��ntesis, se asume un an��lisis elemento a elemento considerando periodicidad local, y se propone el uso de un m��todo capaz de modelar el campo incidente de forma que se elimine la limitaci��n de la periodicidad local en la excitaci��n. Una vez definida la estrategia adecuada de c��lculo de las tensiones a aplicar al cristal l��quido en cada celda, la estructura de direccionamiento de las mismas en la antena, y dise��ados los circuitos de control, se dise��an, fabrican y miden dos prototipos diferentes de antena de barrido electr��nico a 100 GHz usando las celdas anteriormente presentadas. El primero de estos prototipos es un reflectarray en configuraci��n ���single offset��� con capacidad de escaneo en un plano (elevaci��n o azimut). Aunque previamente se realizan dise��os de antenas de barrido en 2D a varias frecuencias en el rango de milim��tricas y sub-milim��tricas, y se proponen ciertas estrategias de direccionamiento que permiten conseguir este objetivo, se desarrolla el prototipo con direccionamiento en una dimensi��n con el fin de reducir el n��mero de controles y posibles errores de fabricaci��n, y as�� tambi��n validar la herramienta de dise��o. Para un tama��o medio de apertura (con un numero de filas y columnas entre 30 y 50 elementos, lo que significa un reflectarray con un n��mero de elementos superior a 900), la configuraci��n ���single offset��� proporciona rangos de escaneo elevados, y ganancias que pueden oscilar entre los 20 y 30 dBi. En concreto, el prototipo medido proporciona un haz de barrido en un rango angular de 55��, en el que el nivel de l��bulos secundarios (SLL) permanece mejor de -13 dB en un ancho de banda de un 8%. La ganancia m��xima es de 19.4 dBi. Estas prestaciones superan de forma clara aquellas conseguidas por otros autores. El segundo prototipo se corresponde con una antena de doble reflector que usa el reflectarray de cristal l��quido como sub-reflector para escanear el haz en un plano (elevaci��n o azimut). El objetivo b��sico de esta geometr��a es obtener mayores ganancias que en el reflectarray ���single offset��� con una estructura m��s compacta, aunque a expensas de reducir el rango de barrido. En concreto, se obtiene una ganancia m��xima de 35 dBi, y un rango de barrido de 12��. Los procedimientos de s��ntesis de tensiones y de dise��o de las estructuras de las celdas forman, en su conjunto, una herramienta completa de dise��o precisa y eficiente de antenas reflectarray reconfigurables basados en cristales l��quidos. Dicha herramienta se ha validado mediante el dise��o, la fabricaci��n y la medida de los prototipos anteriormente citados a 100 GHz, que consiguen algo nunca alcanzado anteriormente en la investigaci��n de este tipo de antenas: unas prestaciones competitivas y una predicci��n excelente de los resultados. El procedimiento es general, y por tanto se puede usar a cualquier frecuencia en la que el cristal l��quido ofrezca anisotrop��a diel��ctrica, incluidos los THz. Los prototipos desarrollados en esta tesis doctoral suponen tambi��n unas de las primeras antenas de barrido real a frecuencias superiores a 100 GHz. En concreto, la antena de doble reflector para escaneo de haz es la primera antena reconfigurable electr��nicamente a frecuencias superiores a 60 GHz que superan los 25 dBi de ganancia, siendo a su vez la primera antena de doble reflector que contiene un reflectarray reconfigurable como sub-reflector. Finalmente, se proponen ciertas mejoras que a��n deben se deben realizar para hacer que estas antenas puedan ser un producto completamente desarrollado y competitivo en el mercado. ABSTRACT The work presented in this thesis is focused on the development of electronically reconfigurable antennas that are able to provide competitive electrical performance to the increasingly common applications operating at frequencies above 60 GHz. Specifically, this thesis presents the study, design, and implementation of reflectarray antennas, which incorporate liquid crystal (LC) materials to scan or reconfigure the beam electronically. From a general point of view, a liquid crystal can be defined as a material whose dielectric permittivity is variable and can be controlled with an external excitation, which usually corresponds with a quasi-static electric field (AC). By changing the dielectric permittivity at each cell that makes up the reflectarray, the phase shift on the aperture is controlled, so that a prescribed radiation pattern can be configured. Liquid Crystal-based reflectarrays have been chosen for several reasons. The first has to do with the advantages provided by the reflectarray antenna with respect to other high gain antennas, such as reflectors or phased arrays. The RF feeding in reflectarrays is achieved by using a common primary source (as in reflectors). This arrangement and the large number of degrees of freedom provided by the cells that make up the reflectarray (as in arrays), allow these antennas to provide a similar or even better electrical performance than other low profile antennas (reflectors and arrays), but assuming a more reduced cost and compactness. The second reason is the flexibility of the liquid crystal to be confined in an arbitrary geometry due to its fluidity (property of liquids). Therefore, the liquid crystal is able to adapt to a planar geometry so that it is one or more of the typical layers of this configuration. This simplifies drastically both the structure and manufacture of this type of antenna, even when compared with reconfigurable reflectarrays based on other technologies, such as diodes MEMS, etc. Therefore, the cost of developing this type of antenna is very small, which means that electrically large reconfigurable reflectarrays could be manufactured assuming low cost and greater productions. A paradigmatic example of a similar structure is the liquid crystal panel, which has already been commercialized successfully. The third reason lies in the fact that, at present, the liquid crystal is one of the few technologies capable of providing switching capabilities at frequencies above 60 GHz. In fact, the liquid crystal allows its permittivity to be switched in a wide range of frequencies, which are from DC to the visible spectrum, including microwaves and THz. Other technologies, such as ferroelectric materials, graphene or CMOS "on chip" technology also allow the beam to be switched at these frequencies. However, CMOS technology is expensive and is currently limited to frequencies below 150 GHz, and although ferroelectric materials or graphene can switch at higher frequencies and in a wider range, they have serious difficulties that make them immature. Ferroelectric materials involve the use of very high voltages to switch the material, making them unattractive, whereas the electromagnetic modelling of the graphene is still under discussion, so that the experimental results of devices based on this latter technology have not been reported yet. These three reasons make LC-based reflectarrays attractive for many applications that involve the use of electronically reconfigurable beams at frequencies beyond 60 GHz. Applications such as high resolution imaging radars, molecular spectroscopy, radiometers for atmospheric observation, or high frequency wireless communications (WiGig) are just some of them. This thesis is divided into three parts. In the first part, the most common properties of the liquid crystal materials are described, especially those exhibited in the nematic phase. The study is focused on the dielectric anisotropy (Ac) of uniaxial liquid crystals, which is defined as the difference between the parallel (e/7) and perpendicular (e��) permittivities: Ae = e,, - e��. This parameter allows the permittivity of a LC confined in an arbitrary volume at a certain biasing voltage to be described by solving a variational problem that involves both the electrostatic and elastic energies. Thus, the frequency dependence of (Ae) is also described and characterised. Note that an appropriate LC modelling is quite important to ensure enough accuracy in the phase shift provided by each cell that makes up the reflectarray, and therefore to achieve a good electrical performance at the antenna level. The second part of the thesis is focused on the design of resonant reflectarray cells based on liquid crystal. The reason why resonant cells have been chosen lies in the fact that they are able to provide enough phase range using the values of the dielectric anisotropy of the liquid crystals, which are typically small. Thus, the aim of this part is to investigate several reflectarray cell architectures capable of providing good electrical performance at the antenna level, which significantly improve the electrical performance of the cells reported in the literature. Similarly, another of the objectives is to develop a general tool to design these cells. To fulfill these objectives, the electrical yields of different types of resonant reflectarray elements are investigated, beginning from the simplest, which is made up of a single resonator and limits the state of the art. To overcome the electrical limitations of the single resonant cell, several elements consisting of multiple resonators are considered, which can be single-layer or multilayer. In a first step, the design procedure of these structures makes use of a conventional electromagnetic model which has been used in the literature, which considers that the liquid crystal behaves as homogeneous and isotropic materials whose permittivity varies between (e/7) y (e��). However, in this part of the thesis it is shown that the conventional modelling is not enough to describe the physical behaviour of the liquid crystal in reflectarray cells accurately. Therefore, a more accurate analysis and design procedure based on a more general model is proposed and developed, which defines the liquid crystal as an anisotropic three-dimensional inhomogeneous material. The design procedure is able to optimize multi-resonant cells efficiently to achieve good electrical performance in terms of bandwidth, phase range, losses, or sensitivity to the angle of incidence. The errors made when the conventional modelling (amplitude and phase) is considered have been also analysed for various cell geometries, by using measured results from several antenna prototypes made up of real liquid crystals at frequencies above 100 GHz. The measurements have been performed in a periodic environment using a quasi-optical bench, which has been designed especially for this purpose. One of these prototypes has been optimized to achieve a relatively large bandwidth (10%) at 100 GHz, low losses, a phase range of more than 360��, a low sensitivity to angle of incidence, and a low influence of the transversal inhomogeneity of the liquid crystal in the cell. The electrical yields of this prototype at the cell level improve those achieved by other elements reported in the literature, so that this prototype has been used in the last part of the thesis to perform several complete antennas for beam scanning applications. Finally, in this second part of the thesis, a novel strategy to characterise the macroscopic anisotropy using reflectarray cells is presented. The results in both RF and AC frequencies are compared with those obtained by other methods. The third part of the thesis consists on the study, design, manufacture and testing of LCbased reflectarray antennas in complex configurations. Note that the design procedure of a passive reflectarray antenna just consists on finding out the dimensions of the metallisations of each cell (which are used for phase control), using well-known optimization processes. However, in the case of reconfigurable reflectarrays based on liquid crystals, an additional step must be taken into account, which consists of accurately calculating the control voltages to be applied to each cell to configure the required phase-shift distribution on the surface of the antenna. Similarly, the structure to address the voltages at each cell and the control circuitry must be also considered. Therefore, the voltage synthesis is even more important than the design of the cell geometries (dimensions), since the voltages are directly related to the phase-shift. Several voltage synthesis procedures have been proposed in the state of the art, which are based on the experimental characterization of the phase/voltage curve. However, this characterization can be only carried out at a single angle of incidence and at certain cell dimensions, so that the synthesized voltages are different from those needed, thus giving rise to phase errors of more than 70��. Thus, the electrical yields of the LCreflectarrays reported in the literature are limited in terms of bandwidth, scanning range or side lobes level. In this last part of the thesis, a new voltage synthesis procedure has been defined and developed, which allows the required voltage to be calculated at each cell using simulations that take into account the particular dimensions of the cells, their angles of incidence, the frequency, and the AC biasing signal (frequency and waveform). The strategy is based on the modelling of each one of the permittivity states of the liquid crystal as an anisotropic substrate with longitudinal inhomogeneity (1D), or in certain cases, as an equivalent homogeneous tensor. The accuracy of both electromagnetic models is also discussed. The phase errors made by using the proposed voltage synthesis are better than 7��. In order to obtain an efficient tool to analyse and design the reflectarray, an electromagnetic analysis tool based on the Method of Moments in the spectral domain (SD-MoM) has also written and developed for anisotropic stratified media, which is used at each iteration of the voltage synthesis procedure. The voltage synthesis is also designed to minimize the effect of amplitude ripple on the radiation pattern, which is typical of reflectarrays made up of cells exhibiting high losses and represents a further advance in achieving a better antenna performance. To calculate the radiation patterns used in the synthesis procedure, an element-by-element analysis is assumed, which considers the local periodicity approach. Under this consideration, the use of a novel method is proposed, which avoids the limitation that the local periodicity imposes on the excitation. Once the appropriate strategy to calculate the voltages to be applied at each cell is developed, and once it is designed and manufactured both the structure to address the voltages to the antenna and the control circuits, two complete LC-based reflectarray antennas that operate at 100 GHz have been designed, manufactured and tested using the previously presented cells. The first prototype consists of a single offset reflectarray with beam scanning capabilities on one plane (elevation and azimuth). Although several LC-reflectarray antennas that provide 2-D scanning capabilities are also designed, and certain strategies to achieve the 2-D addressing of the voltage are proposed, the manufactured prototype addresses the voltages in one dimension in order to reduce the number of controls and manufacturing errors, and thereby validating the design tool. For an average aperture size (with a number of rows and columns of between 30 and 50 elements, which means a reflectarray with more than 900 cells), the single offset configuration provides an antenna gain of between 20 and 30 dBi and a large scanning range. The prototype tested at 100 GHz exhibits an electronically scanned beam in an angular range of 55�� and 8% of bandwidth, in which the side lobe level (SLL) remains better than -13 dB. The maximum gain is 19.4 dBi. The electrical performance of the antenna is clearly an improvement on those achieved by other authors in the state of the art. The second prototype corresponds to a dual reflector antenna with a liquid crystal-based reflectarray used as a sub-reflector for beam scanning in one plane (azimuth or elevation). The main objective is to obtain a higher gain than that provided by the single offset configuration, but using a more compact architecture. In this case, a maximum gain of 35 dBi is achieved, although at the expense of reducing the scanning range to 12��, which is inherent in this type of structure. As a general statement, the voltage synthesis and the design procedure of the cells, jointly make up a complete, accurate and efficient design tool of reconfigurable reflectarray antennas based on liquid crystals. The tool has been validated by testing the previously mentioned prototypes at 100 GHz, which achieve something never reached before for this type of antenna: a competitive electrical performance, and an excellent prediction of the results. The design procedure is general and therefore can be used at any frequency for which the liquid crystal exhibits dielectric anisotropy. The two prototypes designed, manufactured and tested in this thesis are also some of the first antennas that currently operate at frequencies above 100 GHz. In fact, the dual reflector antenna is the first electronically scanned dual reflector antenna at frequencies above 60 GHz (the operation frequency is 100 GHz) with a gain greater than 25 dBi, being in turn the first dual-reflector antenna with a real reconfigurable sub-reflectarray. Finally, some improvements that should be still investigated to make these antennas commercially competitive are proposed.

Contribution to the improvement of communication services in nanosatellite constellations using delay and disruption tolerant networking based architectures

Esta tesis se desarrolla dentro del marco de las comunicaciones satelitales en el innovador campo de los peque��os sat��lites tambi��n llamados nanosat��lites o cubesats, llamados as�� por su forma cubica. Estos nanosat��lites se caracterizan por su bajo costo debido a que usan componentes comerciales llamados COTS (commercial off-the-shelf) y su peque��o tama��o como los Cubesats 1U (10cm*10 cm*10 cm) con masa aproximada a 1 kg. Este trabajo de tesis tiene como base una iniciativa propuesta por el autor de la tesis para poner en ��rbita el primer sat��lite peruano en mi pa��s llamado chasqui I, actualmente puesto en ��rbita desde la Estaci��n Espacial Internacional. La experiencia de este trabajo de investigaci��n me llevo a proponer una constelaci��n de peque��os sat��lites llamada Waposat para dar servicio de monitoreo de sensores de calidad de agua a nivel global, escenario que es usado en esta tesis. Es ente entorno y dadas las caracter��sticas limitadas de los peque��os sat��lites, tanto en potencia como en velocidad de datos, es que propongo investigar una nueva arquitectura de comunicaciones que permita resolver en forma ��ptima la problem��tica planteada por los nanosat��lites en ��rbita LEO debido a su car��cter disruptivo en sus comunicaciones poniendo ��nfasis en las capas de enlace y aplicaci��n. Esta tesis presenta y eval��a una nueva arquitectura de comunicaciones para proveer servicio a una red de sensores terrestres usando una soluci��n basada en DTN (Delay/Disruption Tolerant Networking) para comunicaciones espaciales. Adicionalmente, propongo un nuevo protocolo de acceso m��ltiple que usa una extensi��n del protocolo ALOHA no ranurado, el cual toma en cuenta la prioridad del trafico del Gateway (ALOHAGP) con un mecanismo de contienda adaptativo. Utiliza la realimentaci��n del sat��lite para implementar el control de la congesti��n y adapta din��micamente el rendimiento efectivo del canal de una manera ��ptima. Asumimos un modelo de poblaci��n de sensores finito y una condici��n de tr��fico saturado en el que cada sensor tiene siempre tramas que transmitir. El desempe��o de la red se evalu�� en t��rminos de rendimiento efectivo, retardo y la equidad del sistema. Adem��s, se ha definido una capa de convergencia DTN (ALOHAGP-CL) como un subconjunto del est��ndar TCP-CL (Transmission Control Protocol-Convergency Layer). Esta tesis muestra que ALOHAGP/CL soporta adecuadamente el escenario DTN propuesto, sobre todo cuando se utiliza la fragmentaci��n reactiva. Finalmente, esta tesis investiga una transferencia ��ptima de mensajes DTN (Bundles) utilizando estrategias de fragmentaci��n proactivas para dar servicio a una red de sensores terrestres utilizando un enlace de comunicaciones satelitales que utiliza el mecanismo de acceso m��ltiple con prioridad en el tr��fico de enlace descendente (ALOHAGP). El rendimiento efectivo ha sido optimizado mediante la adaptaci��n de los par��metros del protocolo como una funci��n del n��mero actual de los sensores activos recibidos desde el sat��lite. Tambi��n, actualmente no existe un m��todo para advertir o negociar el tama��o m��ximo de un ���bundle��� que puede ser aceptado por un agente DTN ���bundle��� en las comunicaciones por sat��lite tanto para el almacenamiento y la entrega, por lo que los ���bundles��� que son demasiado grandes son eliminados o demasiado peque��os son ineficientes. He caracterizado este tipo de escenario obteniendo una distribuci��n de probabilidad de la llegada de tramas al nanosat��lite as�� como una distribuci��n de probabilidad del tiempo de visibilidad del nanosat��lite, los cuales proveen una fragmentaci��n proactiva ��ptima de los DTN ���bundles���. He encontrado que el rendimiento efectivo (goodput) de la fragmentaci��n proactiva alcanza un valor ligeramente inferior al de la fragmentaci��n reactiva. Esta contribuci��n permite utilizar la fragmentaci��n activa de forma ��ptima con todas sus ventajas tales como permitir implantar el modelo de seguridad de DTN y la simplicidad al implementarlo en equipos con muchas limitaciones de CPU y memoria. La implementaci��n de estas contribuciones se han contemplado inicialmente como parte de la carga ��til del nanosat��lite QBito, que forma parte de la constelaci��n de 50 nanosat��lites que se est�� llevando a cabo dentro del proyecto QB50. ABSTRACT This thesis is developed within the framework of satellite communications in the innovative field of small satellites also known as nanosatellites (<10 kg) or CubeSats, so called from their cubic form. These nanosatellites are characterized by their low cost because they use commercial components called COTS (commercial off-the-shelf), and their small size and mass, such as 1U Cubesats (10cm * 10cm * 10cm) with approximately 1 kg mass. This thesis is based on a proposal made by the author of the thesis to put into orbit the first Peruvian satellite in his country called Chasqui I, which was successfully launched into orbit from the International Space Station in 2014. The experience of this research work led me to propose a constellation of small satellites named Waposat to provide water quality monitoring sensors worldwide, scenario that is used in this thesis. In this scenario and given the limited features of nanosatellites, both power and data rate, I propose to investigate a new communications architecture that allows solving in an optimal manner the problems of nanosatellites in orbit LEO due to the disruptive nature of their communications by putting emphasis on the link and application layers. This thesis presents and evaluates a new communications architecture to provide services to terrestrial sensor networks using a space Delay/Disruption Tolerant Networking (DTN) based solution. In addition, I propose a new multiple access mechanism protocol based on extended unslotted ALOHA that takes into account the priority of gateway traffic, which we call ALOHA multiple access with gateway priority (ALOHAGP) with an adaptive contention mechanism. It uses satellite feedback to implement the congestion control, and to dynamically adapt the channel effective throughput in an optimal way. We assume a finite sensor population model and a saturated traffic condition where every sensor always has frames to transmit. The performance was evaluated in terms of effective throughput, delay and system fairness. In addition, a DTN convergence layer (ALOHAGP-CL) has been defined as a subset of the standard TCP-CL (Transmission Control Protocol-Convergence Layer). This thesis reveals that ALOHAGP/CL adequately supports the proposed DTN scenario, mainly when reactive fragmentation is used. Finally, this thesis investigates an optimal DTN message (bundles) transfer using proactive fragmentation strategies to give service to a ground sensor network using a nanosatellite communications link which uses a multi-access mechanism with priority in downlink traffic (ALOHAGP). The effective throughput has been optimized by adapting the protocol parameters as a function of the current number of active sensors received from satellite. Also, there is currently no method for advertising or negotiating the maximum size of a bundle which can be accepted by a bundle agent in satellite communications for storage and delivery, so that bundles which are too large can be dropped or which are too small are inefficient. We have characterized this kind of scenario obtaining a probability distribution for frame arrivals to nanosatellite and visibility time distribution that provide an optimal proactive fragmentation of DTN bundles. We have found that the proactive effective throughput (goodput) reaches a value slightly lower than reactive fragmentation approach. This contribution allows to use the proactive fragmentation optimally with all its advantages such as the incorporation of the security model of DTN and simplicity in protocol implementation for computers with many CPU and memory limitations. The implementation of these contributions was initially contemplated as part of the payload of the nanosatellite QBito, which is part of the constellation of 50 nanosatellites envisaged under the QB50 project.