TEDE Communidade:

Controle Fuzzy T–S Tipo-2 intervalar por modos deslizantes adaptativo acionado por eventos e com garantia de passividade robusta para sistemas com atraso de tempo

2026-08-17T18:54:00Z

Título: Controle Fuzzy T–S Tipo-2 intervalar por modos deslizantes adaptativo acionado por eventos e com garantia de passividade robusta para sistemas com atraso de tempo Autor: NORONHA, Rodrigo Possidônio Primeiro orientador: SERRA, Ginalber Luiz de Oliveira Abstract: This thesis addresses the design of event-triggered adaptive sliding mode control for interval type 2 Takagi–Sugeno (T–S) fuzzy nonlinear systems with time-varying delay, subject to matched perturbations with unknown upper bound and unmatched perturbations, with distinct input matrices among the local linear subsystems. Two control methods are proposed, denoted control method 1 and control method 2, which share the same practical stabilization and robust passivity framework while differing in the adaptive law governing the switching gain. In both methods, practical stabilization and robust passivity within the practical sliding mode region are obtained from the robust passivity inequality, with the storage function defined by a fuzzy Lyapunov Krasovskii functional, from which conditions in the form of delay-dependent linear matrix inequalities are derived, dependent on the maximum delay, the upper bounds on the rates of variation of the delay and of the membership degrees, and the robust passivity coefficient. The feasibility of these conditions determines the sliding variable matrix and provides the decision variables required to derive the practical stabilization conditions, whose practical stability region radius, for both methods, is determined independently of the estimate of the upper bound of the matched perturbation, as is the upper bound of the practical sliding mode region. Control method 1 employs an adaptive law based on monotonic growth, which dispenses with knowledge of this bound and forces the gain to converge once the practical sliding mode region is reached. Control method 2 employs an adaptive law based on a barrier function, which relaxes the dominance of the gain over the matched and unmatched perturbations through a relaxation region, allowing the gain to both increase and decrease and yielding a less aggressive control action than the monotonic strategy. For both methods, the positive invariance of the practical sliding mode region is established under the simultaneous presence of time-varying delay, matched and unmatched perturbations, and event-triggered control, with reaching instants independent of the estimate of the upper bound of the matched perturbation. The event-triggering mechanism is formulated with an analytical guarantee of the absence of Zeno behavior, and certification of the maximum admissible delay is carried out via bisection decoupled from the control design. An upper bound for the triggering threshold is further derived, for each method, as a function of the robust passivity coefficient, establishing an energy-based link between the triggering mechanism and the closed-loop dissipativity, while this same coefficient bounds the impact of the unmatched perturbation on the output. The results are validated through computational simulations that demonstrate the effectiveness and comparative advantages of the proposed methods over existing approaches in the literature. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese

Desenvolvimento de um absorvedor eletromagnético têxtil aplicado às bandas 4G E 5G

2026-08-17T18:31:48Z

Título: Desenvolvimento de um absorvedor eletromagnético têxtil aplicado às bandas 4G E 5G Autor: CARVALHO, Paulo Henrique Bezerra de Primeiro orientador: SANTANA, Ewaldo Eder Carvalho Abstract: Absorbing materials are developed to attenuate electromagnetic radiation and ensure the compatibility of electronic equipment in environments subject to interference. Although microwave frequency transmissions are essential for communication systems, absorber solutions are required to reduce the intensity of unwanted signals. This Thesis presents a flexible and low cost textile electromagnetic absorber designed for 4G and 5G technologies, operating at 2.5 GHz and 3.5 GHz. The developed material consists of a natural graphite and poly(vinyl alcohol) (PVA) composite applied onto a denim substrate. The electromagnetic losses of the device are based on the interaction of the incident wave with the conductivity and permittivity of the material, characterizing it as a resistive-type absorber. To verify the device efficiency, four samples were fabricated and tested, with thicknesses ranging from 0.96 mm to 1.05 mm, whose electromagnetic characterizations were performed using a Vector Network Analyzer (VNA) in the 2 GHz to 4 GHz frequency range. The electrical properties were analyzed to demonstrate its resistive behavior through conductivity and permittivity measurements, using the four-point probe and coaxial probe methods, respectively. To identify the structural and morphological properties of the composite, characterizations were performed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). In the frequency band of interest, the results revealed significant attenuation between 2 GHz and 3.5 GHz, with values ranging from -11.89 dB (at 3.5 GHz) to -20.83 dB (at 2.14 GHz). The average attenuation was -16.96 dB in the 2 GHz to 2.5 GHz range; -16.93 dB between 2.5 GHz and 3 GHz; and -14.58 dB between 3 GHz and 3.5 GHz. The sample with the best absorption performance presented a direct current (DC) conductivity of 1.36 S/m, associated with an imaginary permittivity in the range of 1 < 𝜀′′ < 1.2 and a dielectric loss tangent between 0.1 < tan𝛿 < 0.15. These results demonstrated the efficiency of the absorber, which is characterized by electromagnetic losses predominantly driven by Joule heating. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese

Compressão sem perdas de dados de telemetria satelital usando o algoritmo On+

2026-08-13T13:14:39Z

Título: Compressão sem perdas de dados de telemetria satelital usando o algoritmo On+ Autor: BARROS, José Flávio Gomes Primeiro orientador: BARROS FILHO, Allan Kardec Duailibe Abstract: Satellite data telemetry comprises the set of information required to monitor, control, and ensure the safe and efficient operation of space missions. The reduction in the volume of this data, transmitted from the satellite to ground stations, is called telemetry stream compression. Lossless compression applied to this data is essential to guarantee the integrity of the original data. This approach primarily exploits the statistical redundancy present in the data to reduce the volume of information transmitted or stored. In this context, lossless compression becomes even more relevant, given the severe bandwidth constraints on communication links and the limited on-board storage capacity of satellites. This study proposes On+, a new lossless compression algorithm for satellite telemetry data. Using real telemetry data captured by the Aldebaran-1 CubeSat satellite and the TinyGS Ground Station platform, a dataset consisting of 2500 binary files was created. The performance of the proposed algorithm was evaluated in comparison with classical methods (Huffman coding and Arithmetic coding) and various commercial compressors (.rar, .zip, .7z, .xz, and .gz). The On+ algorithm achieved an average compression ratio of 29.19% on Aldebaran-1 satellite data, with a standard deviation of 1.26% and a median of 29.09%, outperforming the evaluated methods in terms of compression ratio. For satellites on the TinyGS platform, On+ also delivered significant results, achieving a median compression ratio close to 50% in specific satellite classes, with Starlink standing out in particular. This result demonstrates the method’s ability to efficiently exploit the statistical characteristics of certain telemetry datasets, obtaining substantial compression gains. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese

Mapeamento de sedimentos da margem equatorial brasileira usando algoritmos de aprendizado de máquina

2026-08-13T13:03:29Z

Título: Mapeamento de sedimentos da margem equatorial brasileira usando algoritmos de aprendizado de máquina Autor: DANTAS, Diego de Oliveira Primeiro orientador: BARROS FILHO, Allan Kardec Duailibe Abstract: Large-scale mapping of seafloor sediments is essential for environmental management, offshore engineering, and the sustainable exploitation of resources, especially in optically complex coastal regions such as the Brazilian Equatorial Margin (BEM). Although tradi- tional acoustic surveys provide high accuracy, their application is limited by operational costs and low acquisition frequency. This thesis presents a reproducible machine learning pipeline for regional sediment classification using Sentinel-2 imagery, systematically cover- ing the shallow shelf between 0 and 30 m depth. The methodology integrates Principal Component Analysis (PCA), Multilayer Perceptron (MLP), and Synthetic Minority Over- sampling Technique (SMOTE), combined with a conservative curation protocol based on historical granulometric consistency, local spatial agreement, and independence between image patches. The final predictive scope was defined as the binary Sand vs Mud scenario, using 2,199 spatially independent samples under 25 km block-based spatial validation with five folds. Among the evaluated model families, including convolutional neural networks, MLPs, SVMs, and EfficientNet models, the MLP+PCA+SMOTE pipeline was selected as the recommended configuration because it combined competitive performance, stability, and low computational cost. The optimized configuration achieved an accuracy of 92.64% ± 1.95, macro F1 of 89.04% ± 2.40, and computational cost 6.6 times lower than that of CNN-Base. Although no statistically significant differences were observed in relation to the evaluated convolutional architectures, the cartographic agreement of 84.9% with an independent sedimentological map indicates regional cartographic consistency, without constituting contemporary in situ validation. The results demonstrate that lightweight spectral models represent a viable and scalable alternative for regional sediment mapping in complex coastal environments, provided that they are accompanied by rigorous curation, adequate spatial validation, and cautious interpretation of the temporal limitations of the data. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese