Programa de Pós-Graduação em Engenharia Elétrica e de Computação
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Doctoral Thesis Sensor UHF elíptico para detecção de descargas parciais(Universidade Federal do Rio Grande do Norte, 2022-12-15) Lira, Ruann Víctor de Andrade; Campos, Antônio Luiz Pereira de Siqueira; http://lattes.cnpq.br/1982228057731254; http://lattes.cnpq.br/4745923073908650; Serres, Alexandre Jean Rene; Gomes Neto, Alfredo; Mendonça, Laercio Martins de; https://orcid.org/0000-0001-7861-3761; http://lattes.cnpq.br/1853488415531363; Silva Neto, Valdemir Praxedes daIn this work, simplified geometries for microstrip antennas were evaluated and optimized, to select one appropriate geometry, aiming for its application of partial discharge (PD) detection, as a UHF sensor. To improve the performance of the proposed antenna, cascaded frequency selective surfaces (FSS), using double square loops as a unit cell element, were designed and evaluated. Antenna reflection coefficient measurements without and with the integrated FSS were performed and compared with simulated results. The results show that the insertion of the FSSs did not impact the operational bandwidth of the antenna, which comprises 100% of the characteristic frequency range, of the PD activity (300 – 1500 MHz). The insertion of the FSSs resulted in an average gain of 4 dBi, concerning the isolated antenna, increasing the sensitivity for PD detection, within the proposed frequency range. We evaluated the PD detection of the structure through measurements in three devices, a bar of a hydro generator, an oil tank with electrodes in the flat-tip configuration, and a potential transformer (PT). The proposed UHF sensor for PD detection could detect PD activity in all three scenarios and for levels lower than 10 mV.Master Thesis Análise de antenas planares para aplicações médicas nas bandas ISM de 435 MHz, 915 MHz e 2,45 GHz(Universidade Federal do Rio Grande do Norte, 2020-01-10) Nogueira, Jurgen Klinsmann Azevedo; D'Assunção, Adaildo Gomes; Silva Neto, Valdemir Praxedes da; ; ; ; http://lattes.cnpq.br/3159722016018256; Mendonça, Laercio Martins de; ; Lins, Hertz Wilton de Castro; ; Oliveira, João Bosco Lucena de; ; Oliveira, José de Ribamar Silva;Wireless devices are presented, in the most recent researches, as alternatives for monitoring various medical parameters, with applications in the frequency bands designated for Medical Device Radiocommunications Service - MedRadio (401 - 405 MHz), Medical Implant Communication Services - MICS (402 - 405 MHz) and Industrial, Scientific and Medical - ISM (433 - 435.8 MHz; 902 - 928 MHz; 2.4 - 2.5 GHz), with the possibility of performing invasive and non-invasive analyzes on human tissue or equivalent samples, replacing human tissue. In this dissertation, a parametric analysis of three rectangular antennas is performed, with slits positioned close to the edges of the patch, for sensing. Frequency responses of planar microstrip antennas with medical applications in the ISM band are presented in the three frequency bands (433 - 435.8 MHz; 902 - 928 MHz; 2.4 - 2.5 GHz). The results of the simulations were obtained by the Ansoft HFSS software for resonance frequency, bandwidth, reflection coefficient, specific absorption rate and sensitivity. The measurements were performed with solid samples of pork. A mathematical model was created to characterize the relative permittivity of the samples. The simulated and measured results showed excellent agreement and confirm the possibility of use in medical applications for monitoring and transmitting information, in addition to measurements of meat properties, replacing human tissue.Master Thesis Antenas de microfita multibanda e reconfigurável para aplicações em sistemas de comunicação sem fio, padrões IEEE 802.11ah, IEEE 802.11ax e CBRS(2019-06-27) Bandeira, Kaio Márcio da Costa; Silva Neto, Valdemir Praxedes da; Sousa Júnior, Vicente Ângelo de; ; ; ; Vasconcelos, Cristhianne de Fátima Linhares de; ; Rodrigues, Márcio Eduardo da Costa; ; Brito Filho, Francisco de Assis;In view of the evolution of the standards of wireless communication systems, where there is a need for performance in several frequency bands, it is indispensable to design devices capable of meeting the requirements that this progress demands. The antennas are elements that play a fundamental role in these systems, in which planar microstrip antennas have been in high evidence due to their low profile, miniaturized devices, low manufacturing cost and are easily integrated with the devices. With the objective of optimizing the occupation of physical space in the transceivers and in the end devices of the users, this work presents the proposal of a microstrip antenna based on a planar monopole with ground plane with slits for operation in multiple bands to meet new systems of wireless communications such as IEEE 802.11ah, IEEE 802.11ax and CBRS. After that, it will be implemented reconfiguration frequency by using PIN diodes. The process of design formation and design of the structure will be presented, considering the most recent research in the specialized literature. For the purposes of analysis, simulations were performed by the Finite Element method implemented through the commercial software Ansoft HFSS. Some initial prototypes were fabricated for purposes of validation of the preliminary results of this work. The experimental characterization of these prototypes was performed through a vector network analyzer. In view of the comparisons between simulated theoretical results and the preliminary experiments, it can be affirmed that a good agreement between them is observed corroborating with the studies previously developed.Master Thesis Desenvolvimento de antenas planares reconfiguráveis em estruturas com metasuperfícies(2017-01-30) Araújo, Felipe Ferreira de; D'Assunção, Adaildo Gomes; ; ; http://lattes.cnpq.br/6573890509544616; Mendonça, Laercio Martins de; ; http://lattes.cnpq.br/1853488415531363; Silva, Gutembergue Soares da; ; http://lattes.cnpq.br/1214925346969928; D'Assunção Júnior, Adaildo Gomes; ; Oliveira, José de Ribamar Silva; ; http://lattes.cnpq.br/4002176927695547All over the world, the evolution of the technological apparatus for telecommunications systems has been increasingly required, as a clear consequence of the exponentially growth in the demand for wireless communication services. Therefore, the integration of multiple wireless standards on a single platform, like a reconfigurable antenna, also known as tunable antenna, is attracting much attention. Metasurfaces structures have been extensively used in recent years to improve the performance of planar antennas for wireless applications, including reconfiguration. A metasurface (also referred to as a metafilm) is the equivalent of a metamateriaI surface. More precisely, one metafilm is a surface with a distribution of small scatterers arranged along a region of space, to achieve desirable electromagnetic behaviors. For many applications, metasurfaces can be used in place of metamaterials because they have the advantage of taking up less physical space than the three-dimensional structures of metamaterials, offering the possibility of reduced losses, which has generated great interest. Therefore, this master thesis presents the simulation, design and implementation of planar antenna structures coupled to metasurfaces structures in order to reconfigure frequency, polarization and multiband antennas for wireless communications applications. The analysis of the antenna structures is performed with the aid of computational tools. Prototypes are fabricated and measured for experimental verification purpose. Simulations and measurements results are in good agreement.Master Thesis Antenas planares multicamadas com materiais supercondutores e fotônico para comunicações móveis(Universidade Federal do Rio Grande do Norte, 2006-08-04) Alves, George Dennes Fernandes; Fernandes, Humberto César Chaves; ; http://lattes.cnpq.br/0246709532151067; ; http://lattes.cnpq.br/7643120608586848; Silva, Paulo Henrique da Fonseca; ; http://lattes.cnpq.br/0656625630248917; Costa, José Alfredo Ferreira; ; http://lattes.cnpq.br/9745845064013172; Martins, Ronaldo de Andrade; ; http://lattes.cnpq.br/0978273656336966; Silva, Gutembergue Soares da;Recently, planar antennas have been studied due to their characteristics as well as the advantages that they offers when compared with another types of antennas. In the mobile communications area, the need for this kind of antennas have became each time bigger due to the intense increase of the mobile communications this sector. That needs of antennas which operate in multifrequency and wide bandwidth. The microstrip antennas presents narrow bandwidth due the loss in the dielectric generated by radiation. Another limitation is the radiation pattern degradation due the generation of surface waves in the substrate. In this work some used techniques to minimize the disadvantages (previously mentioned) of the use of microstrip antennas are presented, those are: substrates with PBG material - Photonic Bandgap, multilayer antennas and with stacked patches. The developed analysis in this work used the TTL - Transverse Transmission Line method in the domain of Fourier transform, that uses a component of propagation in the y direction (transverse to the direction real of propagation z), treating the general equations of electric and magnetic field as functions of Ey and Hy. One of the advantages of this method is the simplification of the field equations. therefore the amount of equations lesser must the fields in directions x and z be in function of components Ey and Hy. It will be presented an brief study of the main theories that explain the superconductivity phenomenon. The BCS theory. London Equations and Two Fluids model will be the theories that will give support the application of the superconductors in the microfita antennas. The inclusion of the superconductor patch is made using the resistive complex contour condition. This work has as objective the application of the TTL method to microstrip structures with single and multilayers of rectangular patches, to obtaining the resonance frequency and radiation pattern of each structure