Walter Carpes Jr

This paper presents a methodology for determining the values of magnetic induction and current density in the design of transformers and inductors based on planar magnetic elements. From experimental values, datasheet parameters and through an optimization tool based on genetic algorithms, we obtain curves of magnetic induction and current density corresponding to operation with minimal magnetic losses. Hence, from the obtained results, it is possible to design a planar magnetic device operating with minimal losses.

El análisis paramétrico usado en la determinación de los efectos de los parámetros geométricos y los asociados al dieléctrico en Superficies Selectivas en Frecuencia (SSF), es una herramienta de uso generalizado debido a la ausencia de formulaciones que permitan evaluar este tipo de efectos. El objetivo de esta clase de análisis es determinar la influencia en la frecuencia de resonancia de un parámetro en particular, bien sea asociado al soporte dieléctrico o a los parámetros geométricos de la superficie selectiva, con la finalidad de orientar el proceso de diseño de la superficie. En este artículo se presenta la aplicación del Modelo de Circuito Equivalente (MCE) actuando en conjunto con una novedosa formulación de la permitividad efectiva del dieléctrico en SSF tipo bucle cuadrado, el cual permite determinar los efectos de los parámetros geométricos y los asociados al dieléctrico en la frecuencia de resonancia de la superficie selectiva, haciendo innecesario el uso de análisis de ...

Purpose The purpose of this paper is to present the results of a particle swarm optimization (PSO) method applied in the design of a square-loop frequency selective surface (FSS) via the equivalent circuit model (ECM), considering the dielectric effective permittivity as a variable in the optimization problem. Design/methodology/approach In the optimization process considered, besides the FSS square loop geometric parameters, the thickness and relative permittivity of dielectric material used as support are included as variables in the search space, using for this a model of dielectric effective permittivity introduced by the authors in a previous work. Findings Square loops were designed and the obtained results were compared with designs reported in literature for applications in wireless local area network and long-term evolution 4G systems. The low computational cost is remarkable as well as the acceptable accuracy obtained with the proposed approach. The PSO method results were...

ABSTRACT This paper presents a methodology for determining the values of magnetic induction and current density for the design of transformers and inductors using planar magnetic elements. From experimental values as well as datasheet parameters and by using an optimization tool based on genetic algorithms, we obtained curves of magnetic induction and current density corresponding to operation with minimal magnetic losses. From the obtained results, it is possible to design a planar magnetic device operating with minimal losses.

This work presents the modeling of the frequency response of a transformer using equivalent networks and Genetic Algorithms (GA). The transformer is modeled by an equivalent impedance at its terminals representing resonances occurring in the analyzed frequency response. Initially, the electric parameters of this impedance are coarsely estimated using the theory of band-pass filters. Afterward, these parameters are optimized using GA technique by fitting the frequency response curves acquired by an impedance analyzer to those of the developed model.

This paper aims at presenting several parameters for the determination of magnetic losses in planar magnetic devices. All the figures, equations, and graphics presented were obtained by analytical studies, simulations using finite-element analysis, and mainly through the measurements taken on a magnetic device built for this purpose. From the obtained results, it is possible to design a planar transformer or

Due to the growing demand for traffic communication, the requirement for reconfigurable antennas for future generation of satellites is growing steadily. This article presents designs examples of reconfigurable satellite contour beam reflector antennas via multi-objective evolutionary optimization. One configuration is composed of shaped reflector illuminated by a single feed horn. To explore the concept, we consider the case of a satellite that can be placed in three orbital positions to provide different coverage: Europe, North America and South America. A second example considers a single shaped reflector illuminated by two feed horns to simultaneously provide dual coverage with frequency reuse.

This paper presents a numerical method based on finite elements
in both frequency and time domain for modeling the coupling of an
incident wave with a conducting wire placed inside a metallic cavity having a small aperture. The method uses edge elements on tetrahedra for the electric field representation. The formulation can take into account thin wires as well as lumped elements. In the time-domain approach, the time derivatives are discretized by the Newmark method, which allows obtaining an unconditionally-stable scheme with second-order accuracy. Numerical results are provided to validate the presented method.

This paper presents a comparison of mass lumping techniques for the time-domain solution of the 3D Maxwell's equations through edge elements. These techniques allow obtaining a fully explicit time integration procedure. We present two different techniques: the so-called classical method and the Lacoste method as well as a modified scheme to avoid numerical problems due to the shape of mesh elements. Numerical results are presented and compared with those obtained with a consistent method (without lumping).

This paper presents the application of genetic algorithms in the optimization of an offset reflector antenna. The antenna shape is designed in order to obtain a uniform radiation pattern on the Brazilian territory. Modified genetic operators are proposed with the aim to increase the efficiency of the real coded genetic algorithms used here.

In this paper, we use the transmission line matrix (TLM) method to calculate the specific absorption rate (SAR) in an inhomogeneous model of human head exposed to the near fields irradiated by a mobile phone very close to metallic walls. The cellular phone is modeled as a 4 monopole antenna above a rectangular metal box. For computations, two operation frequencies with different radiated powers were selected: a phone model at 835 MHz and 0.6 W, and a phone model at 1800 MHz and 0.125 W. We accomplish a systematic investigation of the change in SAR due to the presence of metallic walls at different orientations and at different distances from the head. The TLM simulation showed that, in some cases, the walls cause significant increases of SAR over the values corresponding to the free-space. Index Terms—Cellular telephone, electromagnetic propagation in biological media, specific absorption rate, transmission line matrix method.

This paper presents the application of two numerical methods in the analysis of the coupling of an incident wave with a conducting wire inside a metallic cavity having a small aperture. The Finite Element Method in the frequency domain and the Transmission-line Modeling Method are the numerical methods used in the analysis. Earlier published experimental results are used in order to evaluate the obtained numerical results.

This paper presents a 3D body-conforming finite element solution of the time-dependent vector wave equation. The method uses edge elements on tetrahedra for the electric field interpolation. This kind of element is suited to model Maxwell's equations since it only enforces tangential continuity of vector fields. For the discretization of time derivatives we use the Newmark method, which allows obtaining an unconditionally stable scheme with second-order accuracy. The Silver-Müller absorbing boundary condition is employed for the domain truncation in unbounded problems. Numerical results for some examples are provided to validate the presented method.

This paper presents a new model for prediction of wave propagation in indoor and outdoor environments. The method is based on two-dimensional ray-tracing techniques using image theory to determine all valid paths. The computation of fields is based on geometrical optics and uniform theory of diffraction. A new approach for transmitted rays through the walls is proposed and validated by comparison with results obtained via the finite-difference time-domain method. Results for a practical indoor environment are presented by mapping the received power.

This paper presents a coverage prediction model using the 2-D ray-tracing technique associated to a real-coded mono-objective Genetic Algorithm for optimizing the base station antenna location in an indoor environment. The model was applied in two examples of indoor scenarios to find the best location of the base station antenna by maximizing the lower electric field in the coverage area.

The parameters set of the Jiles–Atherton hysteresis model is identified by using a real coded genetic algorithm. The parameters identification is performed by minimizing the mean squared error between experimental and simulated magnetic field curves. The procedure is validated by comparing experimental and simulated results.

This paper presents a model, obtained through numerical simulation and curve fitting, for the dielectric effective permittivity of frequency selective surfaces (FSSs). The numerical model is based on the permittivity and thickness of the dielectric layer supporting the FSS metallic elements, as well as on the period and on a factor dependent on the FSS geometry. The model is developed for square-loop FSS, using a given geometry reported in literature as a reference case. The results from electromagnetic simulations with the finite-element method are used for developing the numerical model. Index Terms— Effective permittivity, equivalent circuit model (ECM), frequency selective surfaces (FSSs), square loop.

This paper presents a methodology for determining the values of magnetic induction and current density in the design of transformers and inductors based on planar magnetic elements. From experimental values, datasheet parameters and through an optimization tool based on genetic algorithms, we obtain curves of magnetic induction and current density corresponding to operation with minimal magnetic losses. Hence, from the obtained results, it is possible to design a planar magnetic device operating with minimal losses.

This paper presents the association of a particle swarm optimization (PSO) optimization tool with a quasi-3D ray-tracing propagation model for both mono and multi-criterion antenna positioning in indoor environments. The association was applied for a typical wireless indoor system and showed to be an efficient tool to solve typical design antenna positioning problems.

This paper presents an indoor propagation model that uses image-based ray-tracing with a quasi-3D approach. A fast 2D algorithm finds the most relevant rays lying in the horizontal plan of the indoor environment. Then, every path is converted into five rays that lie in the vertical plane. As a consequence, the third-dimension effect is considered in the field computation. Comparisons were made with measurements for a typical indoor scenario and the quasi-3D approach results showed to be as good as the results obtained by a full 3D ray-tracing tool. With this approach, it is possible to have a computational cost comparable to that of a 2D algorithm, without significant impairment in the accuracy compared to results obtained with a 3D tool.

Purpose – The purpose of this paper is to present the results of a particle swarm optimization (PSO) method applied in the design of a square-loop frequency selective surface (FSS) via the equivalent circuit model (ECM), considering the dielectric effective permittivity as a variable in the optimization problem. Design/methodology/approach – In the optimization process considered, besides the FSS square loop geometric parameters, the thickness and relative permittivity of dielectric material used as support are included as variables in the search space, using for this a model of dielectric effective permittivity introduced by the authors in a previous work. Findings – Square loops were designed and the obtained results were compared with designs reported in literature for applications in wireless local area network and long-term evolution 4G systems. The low computational cost is remarkable as well as the acceptable accuracy obtained with the proposed approach. The PSO method results were implemented with the ECM and compared with those obtained via Ansys – high frequency structure simulator commercial software simulations. Originality/value – The lack of a model of dielectric effective permittivity for the ECM causes a restricted search space in the stochastic FSS design process limited to only geometric parameters, as it is reported in the available literature. The proposed approach simplifies and makes more flexible the design process, and allows guiding the FSS design to unit cell surface and/or dielectric thickness of small dimensions.

The purpose of this article is based on analyzing the use of RTQ3D ("quasi-3D" ray tracing technique) to produce the value of the initial electromagnetic fields or fitness for a hundred and sixty receivers according to the possible positions of two antennas to be distributed in a closed environment. The problem variables consist of the values of the magnetic fields for one hundred and sixty receptors depending on the positions of the antennas to the base stations, which serve as input data for the algorithm to the RMLP (Artificial Neural Network, multilayer perceptron with Real backpropagation learning algorithm). The values of the magnetic fields associated with the positions of the antennas are the values to be learned by the network, the teacher of RMLP. This study aims to develop efficient techniques for optimization of electromagnetic problems. We use the PSO (Particle Swarm Optimization) algorithm associated with a metamodel based on an ANN (Artificial Neural Network). Specifically, we use the MLP (Multilayer Perceptron) with the backpropagation algorithm in order to evaluate objective functions in an efficient way. The ANN will be used to assist the technique of "quasi 3D" ray-tracing in order to reduce the high computational cost of this technique in PSO optimization.

This paper presents a 3D body-conforming finite element solution of the time-dependent vector wave equation. The method uses edge elements on tetrahedra for the electric field interpolation. This kind of element is suited to model Maxwell's equations since it only enforces tangential continuity of vector fields. For the discretization of time derivatives we use the Newmark method, which allows obtaining an unconditionally stable scheme with second-order accuracy. The Silver–Müller absorbing boundary condition is employed for the domain truncation in unbounded problems. Numerical results for some examples are provided to validate the presented method. Copyright © 2000 John Wiley & Sons, Ltd.

The result of a multiobjective evolutionary optimization is an efficient solution set surrounded by other candidate solution points. To choose a final solution, we can perform a sensitivity study. Applying this methodology, disturbances that occur in real-world design problems are not neglected. This paper presents an easy way to perform the sensitivity analysis directly from the data generated from a multiobjective stochastic optimization process. No additional function evaluation is required. As an example, we have solved some optimization problems concerning electromagnetic devices

In this paper, we use the transmission line matrix (TLM) method to calculate the specific absorption rate (SAR) in an inhomogeneous model of human head exposed to the near fields irradiated by a mobile phone very close to metallic walls. The cellular phone is modeled as a λ/4 monopole antenna above a rectangular metal box. For computations, two operation frequencies with different radiated powers were selected: a phone model at 835 MHz and 0.6 W, and a phone model at 1800 MHz and 0.125 W. We accomplish a systematic investigation of the change in SAR due to the presence of metallic walls at different orientations and at different distances from the head. The TLM simulation showed that, in some cases, the walls cause significant increases of SAR over the values corresponding to the free-space

A modelagem analítica de um sistema de cabos tripolares é um grande desafio devido à configuração não concêntrica dos elementos envolvidos. Face a essas limitações, uma modelagem numérica de elementos finitos 2D foi desenvolvida no intuito de se obter o valor da impedância série do referido cabo para a gama de frequências entre 20 Hz e 20 kHz. Para isso usou-se uma formulação magnetodinâmica em potencial vetor magnético no domínio da frequência. A metodologia foi aplicada em um cabo típico de 300 mm2 - 18/30 kV. Os resultados numéricos foram comparados com os resultados analíticos para um cabo monopolar, validando a modelagem numérica. Em seguida, aplicou-se a modelagem numérica para um cabo tripolar na formação trifólio.