Programa de Pós-Graduação em Engenharia Elétrica e de Computação
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Doctoral Thesis Análise de um sistema de micro-ondas na medição de umidade em blocos de concreto(Universidade Federal do Rio Grande do Norte, 2024-09-27) Monteiro Sobrinho, Francisco Magno; Campos, Antônio Luiz Pereira de Siqueira; http://lattes.cnpq.br/1982228057731254; https://orcid.org/0000-0003-3715-4065; http://lattes.cnpq.br/2442187033698346; Gomes Neto, Alfredo; Andrade, Humberto Dionísio de; Silva, José Patrocínio da; Mendonça, Laercio Martins deThis work presents the development and analysis of a sensor based on frequency selective surfaces (FSS) for the indirect measurement of moisture in concrete blocks. The proposed sensor utilizes the variation in the resonance frequency of the FSS to detect changes in the relative humidity of the blocks, offering a non-destructive and efficient approach for monitoring construction materials. Experiments were conducted to compare simulated and measured results, demonstrating good agreement between them. The analysis revealed a strong negative correlation (r = −0.981) between the resonance frequency and relative humidity, indicating that the frequency decreases as the moisture increases. Comparison between the proposed sensor and a reference sensor showed significant improvements in sensitivity and accuracy. The results indicate that the proposed sensor is effective in detecting moisture variations and surpasses existing sensors in the literature in terms of sensitivity and precision. This non-destructive approach provides an innovative solution for moisture monitoring in concrete blocks, contributing to the evaluation and maintenance of construction structures with greater efficiency and reliability.Doctoral Thesis Antena bow-tie integrada a uma FSS refletora para aplicações em sistemas 5G(Universidade Federal do Rio Grande do Norte, 2021-02-02) Brito, Augusto César Rebouças de; D'Assunção, Adaildo Gomes; ; http://lattes.cnpq.br/4159638862269940; ; http://lattes.cnpq.br/4336431068613473; Mendonça, Laercio Martins de; ; http://lattes.cnpq.br/1853488415531363; Vasconcelos, Cristhianne de Fátima Linhares de; ; http://lattes.cnpq.br/3140725798737102; D'Assunção Júnior, Adaildo Gomes; ; http://lattes.cnpq.br/7359899329008024; Peixeiro, Custódio José Oliveira; ; Oliveira, José de Ribamar Silva; ; http://lattes.cnpq.br/4002176927695547In recent years, the advances observed in wireless communication systems and the growth in the number of their applications have made the use of compact multiband and broadband antennas attractive, both for applications in commercial and military communications systems. The most common examples are found in the variety of portable wireless communication devices, such as: smartphones, headsets and portable computers, among others. The emergence of different wireless technologies, such as GSM (Global System for Mobile Communications), RFID (Radio Frequency Identification), Bluetooth, Wi-Fi and WiMAX, has served as a motivation to boost research in the telecommunications area. In this way, the search for lighter, more compact and low-cost devices, to be used in several areas, such as biomedical, military and security, has been increasingly greater. In addition, the constant search for increasingly lighter and more flexible antennas, which can be molded to the contact surface of devices, has boosted research in the area. In this respect, the microwaveable antennas stand out, as they have the ability to communicate with various devices, they are simple, inexpensive, light, with a thin profile and depending on the application they have a large bandwidth. The development of antennas with these characteristics is still a challenge to current research. This work aims to study, design, manufacture and measure new geometries of planar antennas, with openings in the ground plane and use of FSS (Frequency Selective Surface), aiming to reduce its dimensions, volume and weight as well as an increase in the gain of the antennas, to meet the demands of the services offered by the 5G Mobile Systems, for example. The analysis of a microwaveable antenna with a bow-tie slit in its ground plane is highlighted, with results for loss of return, bandwidth, current distribution and radiation diagram for a frequency range between 1 and 10 GHz. The insertion of air layers between the antenna and the FSS structure was also used aiming at a greater degree of freedom to adjust the resonance frequencies. Computer simulations in order to predict the values of the parameters that characterize the proposed structures were performed mainly using the HFSS 13.0 software and results in the laboratory showed excellent agreement.Doctoral Thesis Aplicação de EBG (Electromagnetic Band Gap) em superfícies seletivas em frequência para supressão de modos de ordem superior(Universidade Federal do Rio Grande do Norte, 2020-11-06) Bezerra, Tiago dos Santos; Campos, Antônio Luiz Pereira de Siqueira; ; ; http://lattes.cnpq.br/4584698860634661; Braz, Erico Cadineli; ; Silva, José Patrocínio da; ; Mendonça, Laercio Martins de; ; Silva, Mauricio Weber Benjó da;We propose an application of EBG (Electromagnetic Band Gap) for suppression or reduction of higher order resonant modes in FSS (Frequency Selective Surfaces), not yet studied in the literature. The study consists of the application of a rectangular periodic array of circular air holes in an FSS dielectric substrate to create rejection bands and to suppress or reduce specific resonant frequency modes. Another type of unconventional air hole used was the square shaped hole, aiming to reduce the computational effort during the simulations. To obtain the diameter of the holes and the dimensions of the rectangular patch, an optimization algorithm based on Genetic Algorithms (AG) was used. This procedure was necessary in order to suppress or reduction spurious modes in the frequency of interest of the project. In order to prove that the prohibited bands occurred in the desired frequency bands, a Brillouin dispersion diagram was constructed verifying that the structures acted as EBG. Seven prototypes were manufactured and the measured results were compared with the simulated results obtained in Ansoft HFSS ®. A good agreement between the results is observed. Simulations and measurements show suppression levels of up to 6 dB. The simulation time of FSS with EBG of square holes showed a reduction of 70% in relation to the simulation time of FSS with EBG of cylindrical holes.Doctoral Thesis Novas configurações de antenas, filtros e FSS com fractais de fuga no tempo para aplicações em microondas e ondas milimétricas(2017-12-14) Minervino, Diego Ramalho; D'Assunção, Adaildo Gomes; ; ; Mendonça, Laercio Martins de; ; D'Assunção Júnior, Adaildo Gomes; ; Gomes Neto, Alfredo; ; Peixeiro, Custódio José Oliveira;In this work, new configurations of devices and circuits of millimeter waves and microwaves with fracturing configurations of escape-time are investigated and proposed, such as the Julia and Mandelbrot sets, which are structures defined by a recurrence relation of each point in space. Specifically, it will be investigated the distribution of currents on the surfaces of filter conductors, planar antennas and frequency selective surfaces (FSS) with the considered fractal geometries, for applications in both wireless communication systems and systems in millimeter waves, in the frequency range between 0.7 and 30 (GHz). Transmission planar structures such as the microstrip lines and the coplanar waveguide (CPW) were considered in the development of filters and antennas with Euclidean and fractal geometries for microwave and millimeter wave applications. The choice of microstrip line structures for the development of new antenna and filter configurations is justified by the wide application of these transmission lines, always resulting in the manufacture of flat circuits with small structures, low cost, easy to construct and especially easy to integrate with other microwave and millimeter wave circuits. The great interest in applications in the millimeter wave range is associated to the growth of the use in the L and S bands, the speed of transmission between circuits, wireless communications systems and the reduction of components for use in wavelengths and millimeter waves. Initially, the study of time-fracturing fracturing was focused on microwave applications in antennas fed by coaxial cable and CPW. Finally, simulations, measurements and constructions of prototypes of antennas, filters and FSSs were carried out to validate the work done in this doctoral thesis.Doctoral Thesis Análise de novas topologias de filtros CPS, SIEW e FSS-EBG para sistemas de comunicação sem fio(2019-07-30) Costa, Cláudio Pereira da; D'Assunção, Adaildo Gomes; ; ; D'Assunção Júnior, Adaildo Gomes; ; Vasconcelos, Cristhianne de Fátima Linhares de; ; Cavalcante, Gervásio Protásio dos Santos; ; Carvalho, Joabson Nogueira de; ; Silva Neto, Valdemir Praxedes da;The objective of this thesis is to present the analysis of new topologies of coplanar stripline (CPS) filters, substrate integrated E-plane waveguide (SIEW) filter, and frequency selective surface electromagnetic bandgap (FSS-EBG) for applications in wireless systems. The CPS configuration consists of two conducting strips carried by two split ring resonator (SRR) cells forming a CPS filter. The SIEW filter is based on the substrate integrated E-plane waveguide technology, being composed of several dielectric layers stacked with two resonant elements inside, enabling selectivity with horizontal polarization. The third configuration consists of two periodic arrays formed by an FSS and an EBG, composing an integrated structure. The investigation of these structures was carried out by numerical analysis of the frequency response due to the variation of the physical parameters of the geometries, highlighting the attractive potentialities for several applications in the microwave range. The simulated results were obtained with the commercial software Ansoft HFSS and exhibited attractive characteristics, such as: reconfiguration, wide bandwidth, dual band, simple design, light weight and easy manufacturing on a large scale. Prototypes of the proposed filters were manufactured and measured. A good agreement is observed between measured and simulated results.Doctoral Thesis Síntese de uma nova tinta condutiva para circuitos de micro-ondas impressos sobre substrato de vidro e fibra de vidro(2019-05-31) Mesquita, Marcelo David Silva de; D'Assunção, Adaildo Gomes; ; ; D'Assunção Júnior, Adaildo Gomes; ; Silva, Jefferson Costa e; ; Oliveira, João Bosco Lucena de; ; Mendonça, Laercio Martins de; ; Giraldi, Maria Thereza Miranda Rocco;This thesis describes the work carried out for the synthesis of new conductive ink, with a high concentration of silver particles, and its use is proposed as an alternative to the use of conventional techniques of manufacturing microwave integrated circuits. The importance of the use of conductive ink is associated with the ease, efficiency, versatility, and reduction of manufacturing costs of the integrated circuits, by using small brushes for the application on various dielectric materials. Research on the use of conductive ink has carried out in the development of microstrip antennas, bioinspired frequency selective surfaces (FSS), direct current blockers (DC blockers) and directional couplers. The simulation and the design of these circuits were performed with the software Ansys Designer and Ansys HFSS. The investigation of the behavior of frequency scattering parameters these circuits, which allowed the evaluation of aspects related to transmission, reflection, coupling, radiation and electromagnetic wave filtering. In order to validate the results of the simulations and to compare the experimental results, prototypes of these circuits with copper laminates and with surfaces painted were fabricated and measured. The good agreement observed between the simulated and measured results for the prototypes of microwave integrated circuits painted with silver ink confirms the efficiency and versatility of the printing procedure with the use of the synthesized conductive ink.Master Thesis Análise de antenas CPW e CPS e de FSS com geometrias fractais para sistemas de comunicação sem fio(2018-07-13) Costa, Luis Felipe de Vasconcelos Torres da; D'Assunção, Adaildo Gomes; ; ; D'Assunção Júnior, Adaildo Gomes; ; Carvalho, Joabson Nogueira de; ; Mendonça, Laércio Martins de;The main objective of this work is the simulation of CPW and CPS structures for the design of new CPW and CPS antennas with fractal elements for operation in the 1 GHz to 14 GHz band, aiming at applications in multiband, wide band and ultra-wideband (UWB). In addition, the characteristics of radiation, gain and polarization of the antennas are observed. Computational simulations are performed and several conFigurations of CPW and CPS antennas and FSS are designed using Ansoft HFSS software. For purpose of comparison with the simulated results, several prototypes of CPW and CPS antennas are manufactured and measured. FSS structures are also designed, simulated and measured. The experimental results show a good agreement with the results of the numerical simulations performed for both antennas and FSS.Master Thesis Superfícies Seletivas em frequência Complementares (CFSS): conceito e projeto(2018-01-24) Silva, Bruno Sátiro da; Campos, Antonio Luiz Pereira de Siqueira; ; ; Gomes Neto, Alfredo; ; Rodrigues, Marcio Eduardo da Costa;Wireless communications are an integral part of modern society, with fundamental role in the process of globalization and technological progress. Therefore, several researches are carried out in order to achieve constant optimization in this area. Frequency Selective Surfaces (FSS) have been approached for decades because of its telecommunications functionalities. Due to evolution of technology, new demands arise every day, each one with specific responses for each application, thus, the FSS need to be modeled to meet the most diverse requirements. In this context, the present work aims to show a specific model of FSS. The Complementary Frequency Selective Surfaces (CFSS) have very interesting characteristics for modern communication systems, such as multi-band frequency behavior, high selectivity in transmission bands, narrow null bands and great angular stability, being useful in a wide range of applications, such as aircrafts, radomes and satellite communication. As part of this work, new unit-cell geometries for CFSS were proposed and analyzed. Computational simulations, with a detailed parametric study of the proposed structures, were performed for a better understanding of the frequency response.Doctoral Thesis Desenvolvimento de uma nova técnica para otimização de circuitos planares inspirada no comportamento social das aranhas(2017-02-06) Oliveira, Phelipe Sena; D'Assunção, Adaildo Gomes; http://lattes.cnpq.br/4159638862269940; http://lattes.cnpq.br/4056707813492264; http://lattes.cnpq.br/4056707813492264; Mendonça, Laercio Martins de; https://orcid.org/0000-0001-7861-3761; http://lattes.cnpq.br/1853488415531363; D'Assunção Júnior, Adaildo Gomes; Cavalcante, Gervasio Protásio dos Santos; http://lattes.cnpq.br/2265948982068382; Fontgalland, Glauco; https://orcid.org/0000-0003-3506-3522; http://lattes.cnpq.br/4256595317953538; Oliveira, José de Ribamar Silva; http://lattes.cnpq.br/4002176927695547The new settings for devices and microwaves circuits result in an increase of complexity in the processes of development, specially in regards to the process of synthesis. Antennas and Frequency Selective Surfaces (FSS) are primordial in communication systems. Alternatively, these structures may be optimized through the usage of bio-inspired algorithms. Generally, in order for the bio-inspired algorithms to assist in the optimization of FSS structures, it is necessary to implement several numerical analysis techniques, such as the method of moments or finite elements. Because of the difficulty to model such methods, it has been turned common the usage of a point estimation function, such as artificial neural networks, to substitute the numerical analysis. Although these procedures end up encountering desirable solutions, the estimations are done after a training process conducted through a database. Additionally, every FSS antenna demands a specific database. This work proposes an optimization technique that relies on the usage of a bio-inspired algorithm and a framework (that provides the integration between the algorithm and the commercial software ANSS HFSS). The purpose of the work is to do simulations of possible solutions during the execution of the bio-inspired algorithm; therefore, avoiding the usage of the database; and so, make the technique flexible and efficient in relation to altering the antennas’ structures or FSS. Furthermore, another objective of this work is the usage of the algorithm, namely Social Spider Optimization - SSO in the search for solutions in the field of applied electromagnetism. In order to prove the efficiency of the proposed techniques, some FSS’ and antennas’ projects are optimized through the variation of their structural parameters. In conclusion, the results that were obtained through the procedures previously shown, are compared to other techniques, resulting in a satisfying agreement rate.Master Thesis Desenvolvimento de FSS mecanicamente reconfigurável para aplicações em micro-ondas(2017-01-30) Carvalho, Rafaela Gomes Gonçalves de; Silva, José Patrocinio da; D'Assunção, Adaildo Gomes; ; ; http://lattes.cnpq.br/5753289728835624; ; http://lattes.cnpq.br/0256476955529038; D'Assunção Júnior, Adaildo Gomes; ; Gomes Neto, Alfredo; ; http://lattes.cnpq.br/1403715441701958; Mendonça, Laercio Martins de; ; http://lattes.cnpq.br/1853488415531363Reconfigurability is a very important feature in modern communication systems because it allows the same structure to adapt to different scenarios of the same application, such as radomes, cognitive radio, and adaptive screens that block unwanted wireless transmissions. This characteristic can be achieved by traditional methods, such as the use of active semiconductor devices (PIN and Schottky diodes) or variable capacitors coupled to each basic element of the frequency selective surface (FSS), requiring the use of a separate circuit to feed these components. However, these methods require a high number of active elements, which increases the complexity and cost of manufacturing, opening space for the emergence of simpler and more robust techniques for selectivity, such as mechanical reconfigurability. This work consists of the development of a reconfigurable frequency selective surface (FSS), to operate in the X-band, composed of triangular patch elements printed on a dielectric layer of fiberglass (FR-4). The developed FSS allows the reconfiguration of the resonant frequency from the variation of the angle of the incident wave in the structure, in the TE polarization, and can be applied in satellite communication systems through a microcontrolled interface. The analysis of the structure of the FSS is done through Ansoft Designer software and WCIP method.