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

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

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

Aplicación de algoritmos genéticos en el diseño de hornos microondas: eficiencia energética y calentamiento uniforme

En este artículo se describe la aplicación de algoritmos genéticos en el diseño de hornos microondas para procesos industriales de calentamiento. Los objetivos perseguidos en estos diseños son, fundamentalmente, la eficiencia energética mediante una adecuada adaptación entre la fuente de microondas y su carga, y la obtención de un campo eléctrico sobre la muestra lo más uniforme posible, con el fin de generar un calentamiento homogéneo en todo el producto y aumentando así la calidad del producto fina

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

Patrón primario de ruido térmico de banda ancha

Número de publicación: 2 415 083 Número de solicitud: 201130156Patrón primario de ruido térmico de banda ancha. Sistema coaxial para un patrón primario empleado en la trazabilidad de fuentes de ruido térmico, que comprende una línea de transmisión coaxial y un anillo, estando una parte de la línea de transmisión coaxial sumergida en nitrógeno líquido y otra parte de la línea de transmisión coaxial rodeada por un circuito de agua donde se encuentra el anillo, comprendiendo la citada línea de transmisión coaxial un conductor exterior y un conductor interior, estando ambos conductores unidos mediante el anillo que está realizado en un material que garantiza la conductividad térmica entre el conductor exterior y el conductor interior, comprendiendo el anillo un tramo central en contacto en toda su longitud con la superficie interior del conductor exterior, y porque la relación entre el radio del conductor interior y el radio exterior del anillo es tal que en toda la longitud del anillo la impedancia es la misma que la impedancia nominal de la línea coaxial.Universidad Politécnica de CartagenaInstituto Nacional de Técnica Aeroespacial (INTA