https://repositorio.ufba.br/handle/ri/9683 2026-05-04T07:32:05Z https://repositorio.ufba.br/handle/ri/44369 Título: Técnicas de modulação vetorial baseadas na distribuição da energia de modo comum para atenuação da corrente de fuga em inversores fotovoltaicos de três níveis Autor(es): Mendonça, Luan Aleixo Canário Primeiro Orientador: Bahia, Filipe Antônio da Costa Abstract: Transformerless photovoltaic inverters are susceptible to leakage current, predominantly caused by the common-mode voltage. Modulation strategies typically focus on reducing the amplitude of this voltage, while its frequency spectrum is often neglected. Since the leakage current flows through an RLC loop formed by the output filter and the parasitic capacitance of the photovoltaic modules, the distribution of the common-mode voltage frequency spectrum relative to the circuit resonance frequency has a direct impact on its magnitude. Therefore, shifting the energy of its frequency components away from the resonance region constitutes an effective leakage current mitigation strategy. Based on this premise, this work introduces a modulation approach grounded in the spectral distribution of common-mode energy. To validate this approach, two modulation techniques are proposed. The first concentrates most of the energy around the switching frequency, making it more suitable when the resonance frequency is significantly higher. The second redistributes part of the energy to higher-order harmonics, making it more advantageous when the resonance frequency is close to or lower than the switching frequency. The proposed techniques operate over the entire modulation index range, enable DC-link capacitor voltage balancing, and exhibit low harmonic distortion and switching losses, as confirmed by both simulation and experimental results. In addition, the analysis of leakage current as a function of the modulation index reveals an optimal operating region in which the leakage current is minimized. Editora / Evento / Instituição: Universidade Federal da Bahia Tipo: Tese 2026-04-10T00:00:00Z https://repositorio.ufba.br/handle/ri/44267 Título: Soluções inovadoras em hardware reconfigurável para processamento online em um detector com alta taxa de eventos Autor(es): Luz, Igo Amaurí dos Santos Primeiro Orientador: Simas Filho, Eduardo Furtado de Abstract: The Large Hadron Collider (LHC) at CERN, the world's largest operational particle accelerator, will undergo an upgrade to the HL-LHC (High Luminosity LHC) phase, increasing the luminosity and energy of proton-proton collisions. For the ATLAS experiment, the accelerator upgrade process impacts, among other things, the energy measurement system (calorimeter) and the event selection and data acquisition system (Trigger and Data Acquisition - TDAQ). The changes proposed by this upgrade process may cause the superposition of signals measured by the TileCal sensors, affecting the particle characterization process. To mitigate the effects caused by signal distortion, it becomes necessary to perform the estimation of the original signal in an online manner. Another challenge for the HL-LHC operation is the new hardware component, the Global Trigger. It will implement the computing and selection algorithms, and one of these algorithms is the NeuralRinger, a method that combines a ring-shaped representation of electromagnetic showers and machine learning to efficiently select electrons. In this context, the main objective of this work is to develop online processing solutions in FPGA for the problems generated for the ATLAS experiment due to the LHC operation scenario in HL-LHC. This work proposes a hardware solution for energy estimation and also the implementation of the NeuralRinger in the Global Trigger. For energy estimation, two different techniques were implemented and evaluated: one based on the FIR filter, and the other on the Positive Gradient Descent algorithm. The NeuralRinger was designed and implemented as a component integrated into the Global Event Processor (GEP), which is the core of the Global Trigger. The error results from the implementations of the energy estimation and electron selection algorithms indicated the efficiency of the hardware implementation. The implemented circuits were also synthesized for the FPGAs defined in the ATLAS electronics upgrade project: the Xilinx XC7VX485T for the TileCal electronics, used in the design of the energy estimation algorithms, and the Xilinx Virtex UltraScale+ VCU118 for the Global Trigger, used in the NeuralRinger design. The circuit synthesis results for energy estimation, using the deterministic approach, reported a utilization of approximately 0.8% of Registers, LUTs, and DSPs, and, for the iterative approach, approximately 11% for LUTs, 9% for Registers, and 17% for DSPs. For the NeuralRinger, the synthesis tool reported a utilization of 1.42% of LookUp Tables and 0.96% of Flip-Flops for the ring construction circuit, and 0.12% of LookUp Tables and 0.26% of Flip-Flops for the neural network. These results indicated the viability of deploying both solutions on the respective FPGAs boards. Editora / Evento / Instituição: Universidade Federal da Bahia Tipo: Tese 2025-12-17T00:00:00Z https://repositorio.ufba.br/handle/ri/44214 Título: Simulador fenomenológico-aprendizado de máquina de ruído acústico submarino para aplicações em SONAR passivo Autor(es): Santos, Anderson Damacena Primeiro Orientador: Simas Filho, Eduardo Furtado de Abstract: Underwater SONAR systems play a fundamental role in various civil and military applications. However, the development and validation of signal-processing techniques for such systems face significant challenges, mainly due to the limited availability of experimental acoustic data, especially under different environmental conditions. In this work, we present a Submarine Acoustic Signal simulator (SAS) that integrates phenomenological models of environmental noise (sea state and rain) and radiated noise (cavitation and machinery). To enhance the realism of the synthetic signals, a recurrent neural network of the NARX (Nonlinear Autoregressive Exogenous) type is incorporated, designed to learn and reproduce nonlinear characteristics observed in experimental measurements. The proposed hybrid approach enables the generation of signals that more precisely represent the complex structure of real underwater acoustic environments, especially regarding spectral energy distribution and harmonic content. The applicability and scalability of the SAS are expanded, allowing, from a reference experimental signal, the generation of extended temporal scenarios (simulated signals of the same vessel with longer duration and under different ambient-noise conditions), fleet modeling (generating signals for distinct vessels of the same class by leveraging the NARX network’s extrapolation capability), and operational-dynamics simulation (simulating propeller-speed variations during operation). Validation performed with real data indicates that the simulated signals preserve high similarity to experimental ones, both in broadband characteristics and narrowband components associated with vessel activity. The integration of phenomenological modeling with NARX networks resulted in a hybrid method that significantly improves the correspondence between the phenomenological and experimental signals. The analysis of machinery noise illustrates this improvement: the Mean Absolute Error between amplitudes decreased from 992.06\% (phenomenological model) to 10.33\% (hybrid model), and the Wasserstein Distance was reduced from 30.51 to 2.42. For cavitation, the NARX network achieved a Wasserstein Distance of 0.88~dB, outperforming the phenomenological model’s value of 2.43~dB. Consequently, the proposed method stands as an effective solution to support the design, validation, and evaluation of signal-processing algorithms applied to passive SONAR systems. Its main advantage lies in the ability to create a reproducible and controllable test environment, which drastically reduces the need for field data-collection campaigns, traditionally costly and time-consuming. Editora / Evento / Instituição: Universidade Federal da Bahia Tipo: Tese 2025-12-19T00:00:00Z https://repositorio.ufba.br/handle/ri/44097 Título: Projeto e análise óptica de estruturas de filtro-absorvedor reconfiguráveis integradas com materiais de mudança de fase Autor(es): Oliveira, Israel Alves Primeiro Orientador: Rodriguez-Esquerre, Vitaly Felix Abstract: Phase‐change materials (PCMs) based on chalcogenides have emerged as promising functional platforms due to their unique ability to combine state retention, an essential feature for non-volatile memory applications, with pronounced contrasts in electrical and optical properties between the amorphous and crystalline phases. Over the past decade, these materials have been extensively explored in optics and photonics, driven by their high refractive-index contrast, non-volatility, and compatibility with integration processes on established photonic platforms. This thesis presents the development, modeling, and analysis of reconfigurable photonic devices based on PCMs. The proposed work investigates the use of GeTe, In3SbTe2 (IST), and Sb2S3 in active and tunable optical applications, taking advantage of their distinctive optical properties that enable dynamic spectral modulation through reversible phase transitions. Such transitions allow active control over the absorption, reflection, and transmission of electromagnetic radiation. The developed architectures include planar and multilayer nanoscale configurations, with emphasis on ultrathin optical absorbers and filters. The analyses were performed through numerical simulations based on the Finite Element Method (FEM), incorporating realistic, wavelength-dependent dispersive models. For Sb2S3 in particular, experimental studies were also carried out, involving the nanofabrication of thin films via physical vapor deposition (PVD) and spectroscopic ellipsometry characterization conducted at École Centrale de Lyon (France). From these measurements, complex optical parameters were extracted for both phase states, showing excellent agreement with the simulated results, thereby validating both the developed optical model and the suitability of Sb2S3 for actively controlled photonic devices. The results demonstrate the strong potential of PCMs for enabling reconfigurable photonic architectures aimed at spectral modulation, optical sensing, and communication applications. The proposed devices were designed to operate from the visible to the mid-infrared spectral ranges, exploiting different physical mechanisms associated with electromagnetic field interaction and confinement, including resonance effects, interference, and optical coupling. Finally, the influences of geometric and material parameters on device performance are analyzed, along with the feasibility of nanoscale fabrication. These findings highlight the relevance of PCMs for next-generation integrated photonics and programmable optoelectronic technologies. Editora / Evento / Instituição: UNIVERSIDADE FEDERAL DA BAHIA Tipo: Tese 2025-12-29T00:00:00Z