Papers by Rodrigo Melo Oliveira
Energies, Oct 3, 2023
We present a synergistic investigation into ozone production dynamics within a highvoltage reacti... more We present a synergistic investigation into ozone production dynamics within a highvoltage reaction chamber operating from 1.75 kV to 10 kV, at 60 Hz. The output ozone concentration dependence on a 60 Hz root mean square high-voltage for an air input pressure of 0.1 bar was measured using an ultraviolet-based sensor. A finite-element numerical model of the reaction chamber was developed and used for obtaining the reaction rate for the generated ozone for each level of input voltage and the internal distribution of the gas vector velocity field and ozone concentration. An expression to estimate the ozone reaction rates from the measured ozone concentrations was also derived. It was then compared and validated using the developed computational model. Therefore, in this work, a formula is proposed to estimate the ozone production by providing the experimental reaction rates. The other objective is to analyze the hysteresis phenomena observed in the partial discharges' levels in the reaction chamber and in the output ozone concentration. Finally, we establish a connection between the total power of partial discharges and the consequent ozone production, clarifying the role of cumulative partial discharges' power levels in governing the resultant output ozone concentration.
The FDTD method in General Coordinates (LN-FDTD) was implemented for analyzing structures not coi... more The FDTD method in General Coordinates (LN-FDTD) was implemented for analyzing structures not coincident to the Cartesian coordinate system. The method solves the Maxwell's equations in time domain, allowing the calculation of data concerning the transitory and steady-state responses of such structures. The method is applied to analyze of special grounding electrodes. A new formulation for the truncating technique UPML, for conductive media, referred here as LN-UPML, was developed and implemented in order to make the simulations viable. A new methodology for locating grounding grid faults using two Artificial Neural Networks is presented. The LN-FDTD software was tested and validated though simulations of various grounding systems. A graphical user interface, named LANE SAGS, was implemented to simplify the use and to automate the data processing.
Journal of Microwaves, Optoelectronics and Electromagnetic Applications, 2022
Semi-analytical equations are developed for aiding the process of designing terahertz graphene-ba... more Semi-analytical equations are developed for aiding the process of designing terahertz graphene-based rectangular dipole antennas lying on glass substrates. It directly provides the dipole length required for obtaining resonance at a desired frequency since antenna width and graphene chemical potential are known. By using the finite-difference time-domain (FDTD) method, a large number of computational simulations were performed considering several combinations of antenna dimensions and chemical potential values. The simulation results were used along with graphene electrostatic scaling law combined with the least squares method to optimize the formulation coefficients. With the optimized coefficients, we obtain very satisfying accuracy levels. In the frequency range from 0.5 THz to 3.0 THz, the average relative absolute error is 1.50%, with maximum relative absolute error of 6.77%.
Energies, 2022
In this study, a methodology for automatic recognition of multiple simultaneous types of partial ... more In this study, a methodology for automatic recognition of multiple simultaneous types of partial discharges (PDs) in hydro-generator stator windings was proposed. All the seven PD sources typical in rotating machines were considered, and up to three simultaneous sources could be identified. The functionality of identifying samples with no valid PDs was also incorporated using a new technique. The data set was composed of phase-resolved partial discharge (PRPD) patterns obtained from on-line measurements of hydro-generators. From an input PRPD, noise and interference were removed with an improved version of an image-based denoising algorithm previously proposed by the authors. Then, a novel image-based algorithm that separates partially superposed PD clouds was proposed, by decomposing the input pattern into two sub-PRPDs containing discharges of different natures. From the sub-PRPDs, one extracts features quantifying the PD distribution over amplitudes and the contour of PD clouds. ...
Journal of Microwaves, Optoelectronics and Electromagnetic Applications, 2019
In this paper, a finite-difference time-domain (FDTD) formulation, based on the exponential matri... more In this paper, a finite-difference time-domain (FDTD) formulation, based on the exponential matrix and on thin material sheet methods is developed for modeling subcellular thin graphene sheets. This formulation is validated by reproducing graphene frequency selective surfaces (FSS) known from literature. Then, we propose in this work a smart graphene FSS device. Smartness is obtained by means of a unity cell formed by a graphene ring with a graphene sheet placed in its aperture. By properly regulating the chemical potentials of the graphene elements, two frequencytunable modus operandi are obtained: single-or dual-band rejection modes. When the device operates in its dual-band rejection mode, either of the rejection bands can be shifted individually in the frequency spectrum. Additionally, both rejection bands can also be reconfigured simultaneously.
Anais de XXXVII Simpósio Brasileiro de Telecomunicações e Processamento de Sinais, 2019
Resumo-O método das Diferenças Finitas no Domínio do Tempo está consolidado na literatura para a ... more Resumo-O método das Diferenças Finitas no Domínio do Tempo está consolidado na literatura para a predição de sinais eletromagnéticos. Em duas dimensões (FDTD-2D), é simples de implementar e não requer grande esforço computacional em termos de memória e tempo de processamento. Porém, com métodos bidimensionais, tal como FDTD-2D, calcula-se a atenuação do sinal eletromagnético com baixa concordância com experimentos. Neste trabalho, é proposto um fator de correção aplicado à curva de Perda de Percurso. A ideia é aumentar a precisão do método FDTD-2D para que forneça resultados adequados na análise do sinal eletromagnético em ambientes interiores. No desenvolvimento dos resultados foram utilizados dados experimentais de uma campanha de medição e dados preditos com a versão em três dimensões do método Traçado de Raios.
Sensors
A novel graphene antenna composed of a graphene dipole and four auxiliary graphene sheets oriente... more A novel graphene antenna composed of a graphene dipole and four auxiliary graphene sheets oriented at 90∘ to each other is proposed and analyzed. The sheets play the role of reflectors. A detailed group-theoretical analysis of symmetry properties of the discussed antennas has been completed. Through electric field control of the chemical potentials of the graphene elements, the antenna can provide a quasi-omnidirectional diagram, a one- or two-directional beam regime, dynamic control of the beam width and, due to the vertical orientation of the dipole with respect to the base substrate, a 360∘ beam steering in the azimuth plane. An additional graphene layer on the base permits control of the radiation pattern in the θ-direction. Radiation patterns in different working states of the antenna are considered using symmetry arguments. We discuss the antenna parameters such as input reflection coefficient, total efficiency, front-to-back ratio, and gain. An equivalent circuit of the anten...
Energies
In this paper, we propose a mitigation method for reducing lightning-induced insulator voltages b... more In this paper, we propose a mitigation method for reducing lightning-induced insulator voltages based on the installation of low-voltage surge arresters aligned parallelly to the insulator. The three-dimensional finite-difference time-domain (FDTD) method is applied to numerically model a real surge arrester residual voltage evaluation system. The application of a transient current pulse, typical of lightning discharges, is considered in our numerical model. We considered cases with one or two surge arresters installed per phase, in three different geometric and parametric configurations for installing distribution surge arresters. In addition to the Kirchhoff current division, which reduces both the absorbed energy and the thermal stress, the results associated with the installation of two surge arresters parallelly aligned to the insulator show that the interaction of magnetic fields generated by the surge arresters’ currents can produce an additional strong reduction in lightning...
Revista Principia - Divulgação Científica e Tecnológica do IFPB
As técnicas numéricas são ferramentas extremamente poderosas utilizadas na solução de diversos pr... more As técnicas numéricas são ferramentas extremamente poderosas utilizadas na solução de diversos problemas, pois são capazes de manipular grandes quantidades de dados, com complicadas geometrias, que são tão comuns na prática de simulações empregadas nas Engenharias. [...]
Journal of Microwaves, Optoelectronics and Electromagnetic Applications, 2016
A methodology based on spectral analysis for localization of multiple partial discharges in diele... more A methodology based on spectral analysis for localization of multiple partial discharges in dielectric region of hydro-generator coils is proposed. This pinpointing of multiple discharges aims to provide means for performing diagnosis of insulating regions of the coil. A numerical model of the structure was developed by using the finite-difference time-domain method (FDTD-3D) to solve Maxwell's equations. Transient voltage associated with partial discharges that occurs at different positions of the coil is calculated at specific point and its spectrum is used to perform the diagnosis. In 90% of simulations, accurate estimates of simultaneous discharges location were obtained. Physical phenomena allowing the development of the methodology are assessed numerically and experimentally. Finally, a localized artificial PD injection schema is proposed and used for validating our numerical results and physical analysis.
Lecture Notes in Computer Science, 2004
A computational code has been developed for analyzing 3-D radiation problems in curved geometries... more A computational code has been developed for analyzing 3-D radiation problems in curved geometries. To accomplish this, a suitable formulation is developed considering Maxwell equations in a general coordinate system and numerically solved by the use of a parallel curvilinear finite-difference time-domain (FDTD) method. In order to validate the computational code, the method analyzes a microstrip antenna mounted on a curved surface. The results obtained by the developed code are then compared to those generated by the conventional (orthogonal) FDTD method and by experimental measurements.
Anais do XXV Simpósio Brasileiro de Telecomunicações, 2007
Resumo-Este trabalho apresenta uma proposta de antena monopolo planar operando na faixa para sist... more Resumo-Este trabalho apresenta uma proposta de antena monopolo planar operando na faixa para sistemas de comunicação de banda ultralarga (UWB) de 3.1 a 10.6 GHz. Inicialmente, é analisada uma antena monopolo planar constituída por um condutor retangular de largura w = 12 mm e altura h = 20 mm sobre um plano de terra, a qual tem largura de banda de 3,5 GHz. Aqui, foram plotadas: a curva de perda de retorno e o diagrama de irradiação, os quais estão de acordo com os resultados da literatura. Foi projetada uma outra antena monopolo planar com altura h = 14 mm e largura w = 8 mm, a qual possui largura de banda igual a 6,2GHz. Em seguida, foram utilizados três elementos parasitas em conjunto com a antena anterior, sendo obtida uma antena de largura de banda de 6,5 GHz dentro da faixa de 3.1 a 10.6GHz. As freqüências de corte superior e inferior, utilizadas para calcular a largura de banda, foram obtidas em-10 dB. Todas as análises foram realizadas a partir de simulações utilizando o método FDTD.
Particle Swarm Optimization, 2009
Particle Swarm Optimization 184 scattering environments). The equidistant point, determined via P... more Particle Swarm Optimization 184 scattering environments). The equidistant point, determined via PSO, is the position estimative for single radar. For a radar network, which is necessary for a large area under monitoring, the transmitters should operate in TDM (Time-Division Multiplexing) mode in order to avoid interference among them. For each possible transceiver-receivers combination, an estimate is obtained and, from the set of estimations, statistical parameters are calculated and used in order to produce a unique prediction of the intruder's position. 2. The FDTD Method and its Applications The FDTD Method (Finite-Difference Time-Domain) had its first application in the solution of Maxwell's equations, in 1966, when Kane Yee used it in the analysis of spread of electromagnetic waves through bidimensional structures (Yee, 1966). This technique defines the spacial positioning of the components of the electric and magnetic fields in such a way that Ampère and Faraday laws are satisfied, and it approaches the derivates, constituents of those equations, by centered finite differences, in which the updating of the components of the electric fields is alternately verified in relation to those of the magnetic fields, by forming this way what is known as the algorithm of Yee. The method constitutes a solution of complete wave, in which the reflection, refraction, and diffraction phenomena are implicitly included. Years passed by and, along with them, several scientific advances contributed to the establishment of this method as an important tool in the analysis and synthesis of problems in electromagnetism, among them it is noted: new high speed computers and autoperformance computer networks; the expansion of the method for the solution of problems in the 3D space, with the inclusion of complex materials, and the condition of stability (Taflove & Brodwin, 1975); development of truncation techniques of the region of analysis, known as ABC´s (Absorbing Boundary Conditions), such as the operators of Bayliss-Turkel
Energies, 2021
In this paper, a novel image denoising algorithm and novel input features are proposed. The algor... more In this paper, a novel image denoising algorithm and novel input features are proposed. The algorithm is applied to phase-resolved partial discharge (PRPD) diagrams with a single dominant partial discharge (PD) source, preparing them for automatic artificial-intelligence-based classification. It was designed to mitigate several sources of distortions often observed in PRPDs obtained from fully operational hydroelectric generators. The capabilities of the denoising algorithm are the automatic removal of sparse noise and the suppression of non-dominant discharges, including those due to crosstalk. The input features are functions of PD distributions along amplitude and phase, which are calculated in a novel way to mitigate random effects inherent to PD measurements. The impact of the proposed contributions was statistically evaluated and compared to classification performance obtained using formerly published approaches. Higher recognition rates and reduced variances were obtained usi...
Journal of Microwaves, Optoelectronics and Electromagnetic Applications, 2020
In this work, a compact ultra-wide-band microstrip antenna loaded with C-shaped parasitic element... more In this work, a compact ultra-wide-band microstrip antenna loaded with C-shaped parasitic elements, for Digital Video Broadcasting -Terrestrial (DVB-T) and LTE 450 / 700 signal reception, is designed and presented. The proposed antenna is named "HI Monopole", and its geometry has been designed to be simple, lightweight, and compact. Fabrication process is inexpensive and suitable for electronic gadgets. The HI Monopole operates with ultra-wide bandwidth characteristics, encompassing Digital Video Broadcasting -Terrestrial (DVB-T) standard (470-890 MHz), LTE-450 and LTE-700 bands. This feature has been accomplished by inserting an indent in its ground plane, adjusting dimensions of the feeding line, and adding two C-shaped parasite elements onto the region posterior to the antenna's main radiating element. It was verified via electromagnetic measuring that this device is capable of covering the 429-1022 MHz range. Hence, its total bandwidth is 593 MHz. The superior and inferior cutoff frequencies have been defined using the -10 dB return loss reference level. Therefore, the proposed antenna can be employed for receiving DTV and LTE signals broadcasted in any country, independently of its adopted standard.
A terahertz graphene antenna with dynamical control of its radiation pattern
2017 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC)
A graphene antenna that exhibits a controllable radiation pattern is proposed. The antenna is for... more A graphene antenna that exhibits a controllable radiation pattern is proposed. The antenna is formed by a graphene dipole and two parasitic elements, and operates at 1.84 THz. At this frequency, it is possible select three operation states by choosing the values of chemicals potentials applied on the graphene parasitic elements. In two of these states, due to the obtained current antiphase modes, the proposed antenna presents a directional lobe, which can be directed to — x-direction or x-direction depending on the device operation state. The third state consists of a dipole-like radiation pattern.
Journal of Microwaves, Optoelectronics and Electromagnetic Applications, 2021
The Amazon region has high lightning occurrence rates, with many lightning hot spots. Different r... more The Amazon region has high lightning occurrence rates, with many lightning hot spots. Different rivers cross the Amazon rainforests and the people that live there use these rivers as roads to go from one place to another. Every year, lightning deaths are reported in the Brazilian Amazon region. In 2018, a lightning struck a small riverboat, which killed 4 people and injured 5 in the North region of Brazil. In this study, we investigate lightning fatalities in Amazon rivers and compute electric field distribution in a small riverboat due to a lightning strike using the finite-difference time-domain (FDTD) method. The results show that the electric field produced inside the boat is large enough to cause air breakdown. Additionally, we propose a cost-effective method to improve lightning safety to people that use small boats in the Amazon region.
Journal of Microwaves, Optoelectronics and Electromagnetic Applications
It is shown that proper representation of transmitting and receiving antennas in indoor environme... more It is shown that proper representation of transmitting and receiving antennas in indoor environments are decisive for accurate prediction of electromagnetic power transfer parameters using the standard 3D-FDTD method. With the standard Yee method, it is not always possible to precisely describe all the geometrical details of electrically small antennas. A new approach for description of the discone antenna in uniform 3D-FDTD lattice is presented. The calculations are validated by comparing FDTD results with the polyhedral beam-tracing method and experimental data.
Modelling, Simulation and Identification, 2010
The present work shows the results of a R&D project carried out by ELETRONORTE and by the Federal... more The present work shows the results of a R&D project carried out by ELETRONORTE and by the Federal University of Pará (UFPA). Its core objective is the development of a computational system, called LANE-MAXWELL, for performing analysis and synthesis involving electromagnetic interference (EMI) in a power system substation environment. For the analysis stage, the numerical solution of the problem is obtained by numerically solving the Maxwell's equations written in a local non-orthogonal coordinate system by employing the Non-orthogonal Curvilinear Finite-Difference Time-Domain Method (LN-FDTD). The truncation of the analysis region is done by a new formulation called LN-UPML which involves the solution of the Maxwell Equations for lossy anisotropic media in a general coordinate system. For the synthesis stage, techniques such as neural networks, genetic algorithms and particle swarm optimization are used. The computational environment conceived has a friendly data input/output interface for the user, which permits a better understanding of the electromagnetic phenomena involved. For illustrate the versatility of the computational environment some practical applications involving complex power systems structures are presented.
Journal of Microwaves, …, 2011
In this letter, a methodology is proposed for automatically (and locally) obtaining the shape fac... more In this letter, a methodology is proposed for automatically (and locally) obtaining the shape factor c for the Gaussian basis functions, for each support domain, in order to increase numerical precision and mainly to avoid matrix inversion impossibilities. The concept of calibration function is introduced, which is used for obtaining c. The methodology developed was applied for a 2-D numerical experiment, which results are compared to analytical solution. This comparison revels that the results associated to the developed methodology are very close to the analytical solution for the entire bandwidth of the excitation pulse. The proposed methodology is called in this work Local Shape Factor Calibration Method (LSFCM). Index Terms − improved numerical precision, matrix inversion difficulties, optimum shape factor calculation, radial point interpolation method (RPIM). I. INTRODUCTION One of the most used numerical methods for solving Maxwell's equations in time domain is the finite-difference (FD) technique, on which the finite-difference time-domain method (FDTD) is based [1], [2]. Meshless methods, such as the Radial Point Interpolation Method (RPIM), have become an important alternative to solve numerically problems involving partial differential equations [3], [4], [5], [6], due to the fact it provides greater geometric flexibility [7], [8] than FD-based methods. This kind of methdology employs a set of points for representing the analysis region, instead of grids. The field components are locally interpolated by using subgroups of points, called support domains [3] (Fig. 1).
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Papers by Rodrigo Melo Oliveira