Navegando por Autor "D´Assunção, Adaildo Gomes"

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Compact and high-performance band stop filter on textile substrate
(Institution of Engineering and Technology (IET), 2015-03) D´Assunção, Adaildo Gomes; Cavalcante, Gustavo Araújo; Minervino, Diego Ramalho; D’Assunção Junior, Adaildo Gomes
A band stop filter developed on a denim textile substrate is presented. The filter geometry is composed of interconnected half-wave-length parallel coupled resonators, in a novel microstrip filter configuration. Simulated results were obtained through the wave concept iterative method and Ansoft Designer software, for comparison purposes. In addition, prototypes were fabricated and measured for validating the simulation results. Good agreement is reported between simulated and measured results
CSRR-Based microwave sensor for dielectric materials characterization applied to soil water content determination
(MDPI, 2020-01-01) D´Assunção, Adaildo Gomes; Oliveira, João Guilherme Domingos de; Pinto, Erica Natasche de Medeiros Gurgel; Silva Neto, Valdemir Praxedes da
A new and compact sensor based on the complementary split-ring resonator (CSRR) structure is proposed to characterize the relative permittivity of various dielectric materials, enabling the determination of soil water content (SWC). The proposed sensor consists of a circular microstrip patch antenna supporting a 3D-printed small cylindrical container made out of Acrylonitrile-Butadiene-Styrene (ABS) filament. The principle of operation is based on the shifting of two of the antenna resonant frequencies caused by changing the relative permittivity of the material under test (MUT). Simulations are performed enabling the development of an empirical model of analysis. The sensitivity of the sensor is investigated and its effectiveness is analyzed by characterizing typical dielectric materials. The proposed sensor, which can be applied to characterize different types of dielectric materials, is used to determine the percentage of water contained in different soil types. Prototypes are fabricated and measured and the obtained results are compared with results from other research works, to validate the proposed sensor effectiveness. Moreover, the sensor was used to determine the percentage of water concentration in quartz sand and red clay samples
Dielectric resonator antenna based in ZrTiO with high dielectric constant
(SBMO/SBMag, 2015-09) D´Assunção, Adaildo Gomes; Oliveira, Elder Eldervitch Carneiro de; Vieira, Marcelo da Silva; Silva, Paulo Henrique da F.; Oliveira, Maciel Alves de
A novel cylindrical DRA antenna based on chemical compound Zr0.25Ti0.75O2 (zirconia titanate) with a high dielectric constant is proposed for the first time for wireless communication systems in high frequency. Numerical and experimental results are presented, as well as a discussion for the proposed antenna and its frequency response. Results of return loss, radiation pattern and input impedance are illustrated and discussed. Numerical results are obtained using Ansoft HFSS based on the element finite method and compared with experimental results, producing a broadband response. A good agreement among results were verified and discussed
Effects of an FSS reflector on a microstrip line fed bow-tie slot antenna
(Scielo, 2020-09-16) D´Assunção, Adaildo Gomes; Peixeiro, Custódio; Brito, Augusto César Rebouças de; Abreu, Antonio Salvio de
This paper describes the analysis of the effects of a frequency selective surface (FSS) on the characteristics of a microstripline fed antenna with a bow-tie slot in the ground plane for operation in the frequency range 1 to 10 GHz. The use of the FSS is proposed to miniaturize the antenna structure and increase the number of resonance frequencies and the gain. Air gaps can be inserted between the antenna and the FSS to allow for the adjustment of the resonance frequencies and increase the bandwidth. To prove the concept, antenna prototypes printed on a 30×30 mm2 FR4 low-cost substrate are designed, fabricated and tested. Good agreement is obtained between numerical simulations and experimental results, thus validating the proposed design procedure. The obtained miniaturization and multiband effects can be most convenient for multiservice wireless system applications such as WLAN, WiMAX, 4G, and 5G mobile communication systems
Efficiency estimative and characterization of nickel ferrite nanoparticles produced by sol-gel modified by ICR cross-linked technique
(Elsevier, 2019-11-01) D´Assunção, Adaildo Gomes; Silva, Isaac Barros Tavares da; Oliveira, João Bosco Lucena de; Holanda, Samanta Mesquita de
This paper describes nickel ferrite (NiFe2O4) synthesis by sol-gel modified by Ionic Coordination Reaction (ICR) cross-linked technique according to nitrate concentration on organic based solution, aiming a reduction in losses associated to production process. Chitosan is used to increase the coordination between the ions along with chelate agent glutaraldehyde, used to form the gel in sol-gel technique. Calcination process was also applied, with temperature of 1100 C, 10 C/min step for 10 h, to eliminate organic composes and obtain NiFe2O4 with particles over 300 nm diameter. The obtained efficiency results show that A03 (120 g/L) sample has better final efficiency between the proposed concentrations, reaching a 57.39% value with 95.86% purity, estimated by XRD and EDS. SEM was also performed, and confirmed size distribution based on XRD results, presenting homogeneous morphology along with narrow particle size distribution
Full-Wave analysis of stable cross fractal frequency selective surfaces using an iterative procedure based on wave concept
(Hindawi, 2015-08) D´Assunção, Adaildo Gomes; Silva Neto, V. P.; Duarte, M. J.
This work presents a full-wave analysis of stable frequency selective surfaces (FSSs) composed of periodic arrays of cross fractal patch elements.The shapes of these patch elements are defined conforming to a fractal concept, where the generator fractal geometry is successively subdivided into parts which are smaller copies of the previous ones (defined as fractal levels). The main objective of this work is to investigate the performance of FSSs with cross fractal patch element geometries including their frequency response and stability in relation to both the angle of incidence and polarization of the plane wave. The frequency response of FSS structures is obtained using the wave concept iterative procedure (WCIP). This method is based on a wave concept formulation and the boundary conditions for the FSS structure. Prototypes were manufactured and measured to verify the WCIP model accuracy. A good agreement between WCIP and measured results was observed for the proposed cross fractal FSSs. In addition, these FSSs exhibited good angular stability
A Hybrid path loss prediction model based on artificial neural networks using empirical models for LTE and LTE-A at 800 MHz and 2600 MHz
(Scielo, 2017-09) D´Assunção, Adaildo Gomes; Cavalcanti, Bruno J.; Cavalcante, Gustavo A.; Mendonça, Laércio M. de; Cantanhede, Gabriel Moura; Oliveira, Marcelo M.M.de
This article presents the analysis of a hybrid, error correction-based, neural network model to predict the path loss for suburban areas at 800 MHz and 2600 MHz, obtained by combining empirical propagation models, ECC-33, Ericsson 9999, Okumura Hata, and 3GPP’s TR 36.942, with a feedforward Artificial Neural Network (ANN). The performance of the hybrid model was compared against regular versions of the empirical models and a simple neural network fed with input parameters commonly used in related works. Results were compared with data obtained by measurements performed in the vicinity of the Federal University of Rio Grande do Norte (UFRN), in the city of Natal, Brazil. In the end, the hybrid neural network obtained the lowest RMSE indexes, besides almost equalizing the distribution of simulated and experimental data, indicating greater similarity with measurements
Iterative full-wave analysis of mandelbrot-inspired fractal patch antenna on textile substrate for UWB applications
(Hindawi, 2017-11) D´Assunção, Adaildo Gomes; Silva Neto, Valdemir Praxedes da
This work presents the analysis of monopole microstrip antennas with truncated ground plane and patch geometry inspired on the Mandelbrot fractal curve for applications in UWB systems. The proposed antenna geometry is analyzed using the Wave Concept Iterative Procedure (WCIP), a full-wave method. Results for the proposed antenna operating frequency, bandwidth, VSWR, gain, and radiation pattern are obtained and discussed. The WCIP results are compared with simulation results provided by HFSS software, for validation purpose. In addition, a prototype antenna is built and measured. A good match between WCIP theoretical and simulation, HFSS simulation, and measurement results is observed for the antenna frequency response
Miniaturization of a microstrip patch antenna with a koch fractal contour using a social spider algorithm to optimize shorting post position and inset feeding
(Hindawi, 2019-05-02) D´Assunção, Adaildo Gomes; Souza, Eduardo A. M.; Oliveira, Phelipe Sena; Mendonça, Laércio Martins de; Peixeiro, Custódio
This paper presents a social spider optimization (SSO) design of a small-size microstrip antenna. Two antenna miniaturization techniques, based on the use of a Koch fractal contour and a shorting post (connecting the patch to the ground plane), are combined to enable a major size reduction. The antenna is inset fed by a microstrip line. The developed SSO algorithm is used to find out the best radius and position of the shorting post and the length of the inset feed, to achieve the desired resonant frequency with good impedance matching. Antenna prototypes have been fabricated and measured. The good agreement obtained between numerical simulation and experimental results has validated the design procedure. Compared with a conventional rectangular patch, the antenna resonance frequency is reduced from 2.45 GHz to 730 MHz, which corresponds to a remarkable miniaturization of about 70%. The proposed antenna is suitable for applications in the 700-800 MHz frequency range, such as 4G mobile communication systems
A new conductive Ink for microstrip antenna and bioinspired FSS designs on glass and fiberglass substrates
(Scielo, 2019-06-19) D´Assunção, Adaildo Gomes; Oliveira, João Bosco Lucena; Mesquita, Marcelo David Silva de; Batista, Yuri Max Vieira
This paper describes an investigation of the possibility of using a new conductive ink, instead of copper clad laminates, in the manufacturing of microstrip patch antennas on glass and fiberglass substrates and of bioinspired frequency selective surfaces (FSSs) on fiberglass substrates for wireless communication systems. The new conductive ink is developed using synthesized nitrocellulose which, in ethyl acetate solution, works as a bonding agent and carrier for the formation of a conductive film. The load used in the fabrication process is silver metallic powder. Simulation and analysis are performed using Ansoft Designer and HFSS softwares. Microstrip antenna and FSS prototypes are fabricated and measured for comparison purpose. An agreement is observed between simulation and measurements results
A new technique using axially slotted microstrip line for antenna impedance matching designs
(Journal of Microwaves, Optoelectronics and Electromagnetic Applications - Scielo, 2019-06-19) D´Assunção, Adaildo Gomes; Silva, André N. da; Carvalho, Rafaela Gomes Gonçalves de; D’Assunção Júnior, Adaildo Gomes; D’Assunção, Adaildo Gomes
A new technique is presented for designing microstrip patch antennas with very good input impedance matching. The analysis is carried out for 1.78 GHz, 2.42 GHz and 3.46 GHz rectangular patch antennas printed on low-cost fiberglass substrates (FR-4), mounted on a ground plane and fed by a microstrip line. The antenna impedance matching is obtained using a slotted microstrip line feeder. The use of the proposed impedance matching technique showed considerable improvement from the reflection coefficient point of view, with reduction of about 20 dB at the resonant frequency, without modifying the original dimensions of the antenna patch elements or the width of the feeding microstrip line. Numerical characterization is carried out using Ansoft Designer software and iterative method WCIP. Prototypes are fabricated and measured, for validation purpose, showing good agreement when compared to simulated results
Simple, compact, and multiband frequency selective surfaces using dissimilar sierpinski fractal flements
(Hindawi, 2015-11) D´Assunção, Adaildo Gomes; Nóbrega, Clarissa de Lucena; Silva, Marcelo Ribeiro da; Silva, Paulo Henrique da Fonseca; Siqueira, Gláucio Lima
This paper presents a design methodology for frequency selective surfaces (FSSs) using metallic patches with dissimilar Sierpinski fractal elements. The transmission properties of the spatial filters are investigated for FSS structures composed of two alternately integrated dissimilar Sierpinski fractal elements, corresponding to fractal levels k=1, 2, and 3. Two FSS prototypes are fabricated and measured in the range from 2 to 12 GHz to validate the proposed fractal designs. The FSSs with dissimilar Sierpinski fractal patch elements are printed on RT/Duroid 6202 high frequency laminate. The experimental characterization of the FSS prototypes is accomplished through two different measurement setups composed of commercial horns and elliptical monopole microstrip antennas. The obtained results confirm the compactness and multiband performance of the proposed FSS geometries, caused by the integration of dissimilar fractal element. In addition, the proposed FSSs exhibited frequency tuning ability on the multiband frequency responses. Agreement between simulated and measured results is reported
Simulation and design of a bandpass filter based on substrate integrated E-Plane waveguide
(Scielo, 2019-09-12) D´Assunção, Adaildo Gomes; Costa, Claudio P.; Nascimento, Hélder C.; D’Assunção Junior, Adaildo Gomes
This paper presents a bandpass filter based on a substrate integrated E-plane waveguide (SIEW) structure for wireless applications, at X-band. The SIEW geometry allows the development of new horizontally polarized filter topologies, unlike filter structures based on substrate integrated waveguide (SIW), which present vertical polarization (perpendicular to the ground plane). The simulation of the proposed SIEW filter is carried out using Ansoft HFSS software. To evaluate the performance of the proposed structure, the frequency behaviors of the scattering parameters are obtained for a horizontally polarized excitation. In the simulation, analyses are performed for the lossless and lossy (dielectric and metallic) cases, in order to compare the obtained results. The SIEW filter is fabricated and measured using a vector network analyzer (VNA). Measurement results are in agreement with simulation ones, validating the proposed filter design and topology. The fabricated prototype resonates at 10.54 GHz, with a bandwidth of 1.20 GHz, defined for a -3 dB transmission coefficient reference level. The SIEW filter structure is easy to design and manufacture and can be used in wireless communications systems that require components with ease integration into other planar structures
Software for project and analysis of frequency selective surfaces
(SBMO/SBMag, 2012-06) D´Assunção, Adaildo Gomes; Campos, Antonio L. P. S.; Maniçoba, Robson Hebraico Cipriano; Araújo, Lincoln Machado
In this paper, a software for design and analysis of frequency selective surfaces (FSS) based on the equivalent circuit model is presented, with emphasis on teaching students in the interaction between FSS parameters. Tools to design FSSs and a tutorial with theoretical elements of the equivalent circuit method, applied to FSS, compose this software. The software can be used at FSS analysis and design course to consolidate the first theoretical and illustrated concepts
Synthesis and mechanical reconfiguration of ground plane tilted microstrip antennas based on tetra-circle fractals
(Scielo, 2020-06-08) D´Assunção, Adaildo Gomes; Duarte, Mychael Jales; Silva Neto, Valdemir Praxedes da
A synthesis procedure of a mechanically reconfigurable antenna based on tetra-circle fractal patch elements is presented, enabling to change both resonant frequencies and radiation pattern performance. The antenna geometry reconfiguration is implemented by tilting the ground plane of the microstrip antenna with respect to the fractal patch and substrate layer. The tilt angle is defined as the angle between the back of the dielectric substrate and the tilted ground plane and is electromechanically varied using a thin rod of dielectric material sliding up and down, in a simple geometry. Simulation results for the proposed antenna parameters are obtained using Ansoft HFSS software. In addition to promoting frequency and pattern reconfiguration, the tilting of the ground plane has proven to be an alternative to increase the antenna gain and enable single-band or dual-band operation. Prototypes were fabricated and measured for comparison purpose showing a good agreement between simulation and measurement results
Synthesis of new reconfigurable limited size FSS structures using an improved hybrid particle swarm optimization
(Scielo, 2019-06) D´Assunção, Adaildo Gomes; Lacouth, Patric; Gomes Neto, Alfrêdo
This paper describes a new design methodology for reconfigurable printed circuits with limited size, using an improved hybrid particle swarm optimization (HPSO) algorithm, reducing the search space by the definition of negative zones (NZ), regions where the swarm of particles should not travel. The proposed design methodology (HPSO-NZ) is used in the development of reconfigurable frequency selective surfaces (RFSSs), restricted to a limited overall size, resulting in entirely new frequency selective surface (FSS) geometries. Two FSS prototypes are designed, fabricated, and measured for comparison purpose. A good agreement is observed between simulation and measurements results, confirming the efficiency and accuracy of the HPSO-NZ algorithm. Also, the performance of the HPSO-NZ algorithm is compared to the ones of genetic algorithm (GA) and particle swarm optimization (PSO) algorithm, showing good consistency results

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Navegando por Autor "D´Assunção, Adaildo Gomes"