88 research outputs found
Meshing methods and adaptive algorithms in two and three dimensions for solving closed electromagnetic problems by means of the finite element method
[SPA] La primera parte de esta tesis, desarrollada en los capítulos 1, 2, 3 y 4, está dedicada al diseño de nuevos métodos de mallado bidimensional, superficial y volumétrico que sigan estas premisas. Aunque esos métodos han sido desarrollados en el contexto del análisis de guiado de ondas y el diseño de cavidades resonantes de microondas, su aplicación puede abarcar cualquier campo de la física, pues la fase de discretización del MEF presenta una clara independencia del
problema tratado.
La segunda parte de esta tesis, presentada en el capítulo 5, está dedicada al estudio de
este tipo de métodos. En ella se describen los distintos indicadores de error y estrategias de refinamiento h desarrolladas, y se presentan y analizan los resultados obtenidos con ellos en distintas estructuras de guiado de ondas.[ENG] In its first part, the dissertation develops a multiblock methodology of surface and volumetric mesh generation from the discretization of the problem boundary, in order to apply the finite element method. Different structured and unstructured meshing techniques in 2D (interpolation and generalized fast advancing front), 3D surface and volumetric (advancing front) domains are presented. Moreover, some a posteriori techniques for improvement of quality mesh are described. The second part of this dissertation deals with adaptive meshing within an adaptive finite element method. This technique is an iterative variant of the finite element method where, in a first step, an initial mesh with few and low order elements is generated, the corresponding algebraic problem is solved and the error in the solution is estimated in order to add degrees of freedom in those regions of the domain with the biggest error estimation. This process is repeated until an ending condition is reached. The two basic stages in this method are the error indication and the mesh enrichment. In this dissertation, within the analysis of waveguiding structures, three kinds of error indicator have been developed: (1) Error indicators based on the residual of the vector wave equation and the boundary conditions at the edges of each element. (2) Error indicators based on the comparison of the solution curl with a smoothed or recovered curl, obtained from the solution curl. (3) Error indicators based on the flux (electric or magnetic) continuity through the inner edges in the mesh. In addition, an overview on refinement techniques is presented, and the h-refinement employed in this work is in depth described. Results obtained with the different error indicators and refinement strategies are discussed and compared with the classical, non-adaptive finite element method.Universidad Politécnica de ValenciaPrograma de doctorado de Telecomunicació
Uniform electric field distribution in microwave heating applicators by means of genetic algorithms optimization of dielectric multilayer structures
In this paper, the design of a dielectric multilayer
around a clay sample is presented to achieve a uniform electric
field distribution over that sample. This structure is located within
a multimode microwave-heating oven and is designed by means
of genetic algorithms. The permittivity and geometric values for
the sample surrounding layers are the selected parameters to
be optimized in order to minimize the ratio between the typical
deviation and the absolute value of the electric field. The results
demonstrate the improvement of the electric field uniformity over
the sample using dielectric layers.This work was supported
in part by the Fundación Séneca under Project 00700/PPC/0
ETC antenna (easy to configure): a new approach to smart management of cellular networks
The ETC antenna is presented as an intermediate approach between the current radio cellular systems and the future cellular system with the smart antennas. The goal is to get a flexible and asynchronous way to optimize the coverage following the schedule traffic changes and the requirements of the cell using the current mobile operator measurements and making the beam changes by a programmatic and remote technique.La antena ETC se presenta como una aproximación intermedia entre los actuales sistemas radio celulares y el futuro sistema celular con las antenas inteligentes. El objetivo es obtener una forma flexible y asincrónica de optimizar la cobertura siguiendo los cambios de tráfico programado y los requisitos de la celda utilizando las mediciones actuales del operador móvil y realizando los cambios de haz mediante una técnica programática y remota
Optimisation of electric field uniformity in microwave heating systems by means of multi-feeding and genetic algorithms
In most of microwave heating applications obtaining uniform heating patterns
in certain regions of the applicator is a key issue. In this paper, the proposed solution for
achieving electric field uniformity consists of designing the configuration of the feeding
system in a multimode cavity by means of Genetic Algorithms. The feeding system is
constituted by waveguides or slots arrays. The electric field pattern inside the cavity
depends on the location of these sources and an improvement in the electric field
uniformity on the product can be obtained by means of a proper design of this feeding
system. Results for the curing of epoxy resin over a marble slab are presented and they
show a significant improvement in the electric field uniformity over the epoxy resin.This work was supported in part by the CICYT, Spain, under project reference TIC 2004-
05037-C02-02 and Consejería de Economía, Industria e Innovación, Región de Murcia,
Spain, under the project reference 2I04SU063
Combined use of genetic algorithms and gradient descent optimization methods for accurate inverse permittivity measurement
A novel inverse transmission-line method for the
complex permittivity determination of arbitrary shaped materials
is presented. Complex permittivity is inferred by using an inverse
calculation procedure, which is based on a combined optimization
strategy of both genetic algorithms and the gradient descent
method. The optimization procedure matches the measured and
simulated complex scattering parameters’ frequency behavior
of materials within a WR340 waveguide. High accuracy and
practical suitability are validated through experimental tests.
The dielectric properties of PTFE and epoxy resin mixed with
iron–oxide-doped fiberglass have been measured for different
shapes and positions. Dielectric multilayer structures have been
used to demonstrate that this technique is able to measure the
individual permittivity of each element of the structure. Both twoand
three-dimensional approaches have been carried out and their
advantages and drawbacks discussed
Multimode cavity efficiency optimization by optimum load location-experimental approach
In this paper, a novel load-matching procedure for
microwave-heating applicators is presented and tested. In order to
accomplish the optimization procedure, an optimization method
based on the use of the Lebenverg–Marquardt technique has
been specifically developed and tested on two different microwave
ovens. The proposed procedure allows an efficient optimization of
three-dimensional microwave applicators by means of the dielectric
sample relocation as a function of its complex permittivity,
size, and operating frequency. Experimental measurements of
the reflection coefficient are presented and analyzed over several
samples and multimode cavities. Results indicate that high power
efficiencies can be obtained provided that operating frequency
is not just below TM-mode cutoff frequencies for the transverse
dimensions of the oven.This work
was supported in part by the Spanish Science and Technology Ministry under
Project TIC2001-2778-CO2-02
Benefits of using conductive plastics in shielding configurations to reduce radiated electromagnetic interference
Conductive plastic cabinets have become an alternative to traditional metallic enclosures to shield electronic equipment from electromagnetic interference. These materials allow a wide range of conductivities that can satisfy any particular design. In this paper the benefits of using conductive plastics in enclosure configurations have been evaluated. A design with an outer metallic layer and an inner layer of conductive dielectric can provide advantages from both materials since a conductive plastic box is lighter and its shielding properties may have advantages over metallic materials. An optimum for resonance suppression has been obtained for the hybrid structure. These shielding structures have been evaluated with the help of measurements and simulations. Shielding effectiveness and Q-factor have been used to compare the capabilities of these enclosures with the metallic ones showing their benefits and possibilities. Resonance suppression and shielding levels provided by conductive plastics are discussed.This work was funded by Fundación Séneca, Agencia Regional de Ciencia y Tecnología, through the project 00700/PPC/04 and partly done during a research stay funded by the “Programa de formación y movilidad del personal docente e investigador de la Universidad Politécnica de Cartagena (PMPDI-UPCT-2007)” at the Physical Layer Group, Department of Electronics, University of York
A novel technique for sterilization using a power self-regulated single-mode microwave cavity
In this paper, a novel technique to achieve precise temperatures in food sterilization has been proposed. An accurate temperature profile is needed in order to reach a commitment between the total removal of pathogens inside the product and the preservation of nutritional and organoleptic characteristics. The minimal variation of the target temperature in the sample by means of a monitoring and control software platform, allowing temperature stabilization over 100 °C, is the main goal of this work. A cylindrical microwave oven, under pressure conditions and continuous control of the microwave supply power as function of the final temperature inside the sample, has been designed and developed with conditions of single-mode resonance. The uniform heating in the product is achieved by means of sample movement and the self-regulated power control using the measured temperature. Finally, for testing the sterilization of food with this technology, specific biological validation based on Bacillus cereus as a biosensor of heat inactivation has been incorporated as a distribution along the sample in the experimental process to measure the colony-forming units (CFUs) for different food samples (laboratory medium, soup, or fish-based animal by-products). The obtained results allow the validation of this new technology for food sterilization with precise control of the microwave system to ensure the uniform elimination of pathogens using high temperatures.This work was supported by the Ministerio de Economía y Competitividad under the project with reference DPI2014-61857-EXP
Fast computation of shielding effectiveness of metallic enclosures with apertures and inner elements
In this study, radiated immunity and emission of a metallic box with apertures have been evaluated through a fast approach. The influence of printed circuit boards inside the enclosure has been studied and also the effect of placing conductive polymer sheets in the housing in order to characterize the behaviour of these materials used nowadays for shielding cabinets. Measurements have been carried out in anechoic chamber in order to evaluate the approximated technique showing its limitations and advantages. Since good agreement has been found between simulations and measurements, this approach can be used for design or optimization purposes with the main advantage of reduced time calculations.This work has been funded by Fundación Séneca, Agencia Regional de Ciencia y Tecnología through the project 00700/PPC/04
Microondas: líneas de transmisión, guías de onda y cavidades resonantes
Como su título indica, este libro pretende servir de apoyo al estudio de la parte de la asignatura de Microondas relacionada con la teoría de líneas de transmisión y guías de onda, así como de otros dispositivos creados a partir de éstas, como las cavidades resonantes. Aunque existen en el mercado excelentes publicaciones sobre esta materia, con esta obra se ha intentado ajustar los contenidos con el fin de que éstos puedan ser impartidos de un modo claro y sosegado en un total de ocho semanas con tres horas semanales de clase magistral y de resolución de problemas. Se pretende seguir una estructura clara y progresiva que facilite el aprendizaje por parte del alumno o lector, incorporando contenidos teóricos y prácticos para cada uno de los temas planteados. Se han incluido en el texto de un modo detallado todas las demostraciones de importantes expresiones matemáticas con el fin de que el propio alumno sea capaz de seguirlas sin necesidad de que el profesor las desarrolle en clase. A lo largo de cada capítulo se desarrollan ejemplos y se plantean ejercicios a realizar por el lector. Asimismo, al final de cada capítulo se han añadido cuestiones de repaso y problemas. El capítulo de introducción define el concepto de microondas, repasa los principales hitos históricos en esta rama de la ingeniería y presenta un breve resumen de las aplicaciones fundamentales de las microondas. El estudio de líneas de transmisión se desarrolla a lo largo de los capítulos 2, 3 y 4. En el segundo se presenta la línea de transmisión ideal, estudiando su comportamiento tanto en el dominio del tiempo (análisis de transitorios) como en el dominio de la frecuencia, donde el análisis se centra en el uso del diagrama de Smith para adaptación de cargas. En el tercer capítulo se aborda el estudio de líneas de transmisión reales, presentando los conceptos de atenuación y dispersión y analizando las principales líneas con dos conductores. Para finalizar el estudio de líneas de transmisión, el capítulo 4 aborda el análisis de guías de onda, así como de modos superiores del cable coaxial, cuya resolución electromagnética presenta una dificultad superior. Aquí se presentan los modos transversal eléctrico y transversal magnético y se analizan sus características de propagación y de potencia. Este capítulo finaliza con el análisis de cavidades resonantes rectangulares y cilíndricas a partir del estudio previamente realizado sobre guías de onda
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