FCT: DCM - Dissertações de Mestrado
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- Design and 3D printing of bonelike materialsPublication . Pacheco, Clara Fernandes; Ferreira, IsabelMaxillofacial injuries often require customized implants that mimic natural bone in terms of their mechanical properties and degradation behaviour. This study investigates the effectiveness and durability of 3D printed parts made of calcium phosphate and zirconia-based pastes. Various composi- tions and mixing procedures were tested on samples produced using extrusion-based 3D printing. The mechanical properties were assessed through compression and tensile tests, the degradation behaviour was analysed evaluating the composition of samples after being pressurised in an autoclave. Raman spectroscopy provided information on the structural characteristics of the materials. The results indicate that composition and mixing time significantly influence mechanical performance and degradation rate of the samples. The samples with the highest calcium carbonate content exhibited improved mechanical prop- erties and higher degradation rates. Raman analysis also indicates calcium phosphate phases and yttria- stabilized tetragonal zirconia phases. These findings suggest that 3D printing can produce implants with good mechanical strength, contributing to the advancement of patient-specific maxillofacial reconstruction.
- Characterization of MEMS Piezoresistive Pressure SensorsPublication . Piçarra, João Pedro NunesMEMS (Microelectromechanical Systems) piezoresistive pressure sensors are widely used in industries such as automotive, biomedical, and industrial automation, where high sensitivity, compactness, and low power consumption are essential. This dissertation focuses on the characterization of MEMS piezoresistive pressure sensors fabricated by Melexis, aiming to evaluate their behaviour under mechanical stress. The main challenge addressed is the accurate measurement of resistance variation in piezoresistors under strain, a key parameter for evaluating sensor performance. The problem is particularly relevant due to the adoption of a common node configuration, designed to mitigate thermal drift and packaging stress, unlike the traditional Wheatstone bridge. This configuration presents advantages in automotive applications but requires rigorous validation. The approach involved current-voltage (I-V) characterization of the sensors, four-point bending tests to induce mechanical strain, and the design of both manual and automatic interface circuits for resistance measurement. Resistance changes and gauge factors were extracted and compared against theoretical expectations for silicon-based piezoresistors. Baseline resistance values ranged from 5.21 kΩ to 5.37 kΩ with less than 2% variation. Under applied strain, longitudinal piezoresistors A2 and B2 exhibited experimental gauge factors of 67.9 and 17.4, respectively, which is substantially lower than the theoretical value of 130 for p-type silicon in the <110> direction. The results revealed significant inconsistencies, including unexpected resistance behaviour, high relative errors, and limited sensitivity to mechanical stress. After systematic testing of all components, a design error in the manual switch PCB, specifically, an incorrect FPC pin mapping, was identified as the likely cause of measurement anomalies. This work highlights the importance of reliable measurement infrastructure in sensor characterization. Despite deviations from expected behaviour, the developed methodology and analysis provide a solid foundation for future improvements in MEMS sensor testing and validation.
- Cellulose Materials for Water Supply and Management – Water Collection from DewPublication . Silva, Mariana Cristina Malanho da; Almeida, AnaFog harvesting meshes are typically made from synthetic materials. In this work, we propose the use of lignin and cellulose acetate biopolymers as a sustainable and cost-effective alternative. Lignin is the most abundant aromatic biopolymer, and cellulose acetate is a derivative of cellulose - the most abundant biopolymer on the planet. Nature has long inspired researchers in the development of fog collectors. In this study, we draw inspiration from the water-harvesting capabilities of Namib desert beetles and spider webs. The dual- wettability morphology on the backs of Namib desert beetles, along with the periodic spindle-knots and joints in the spider webs, enables efficient capture of water droplets from fog. Using the electrospinning technique, we fabricated multiple non-woven membranes composed of lignin and cellulose acetate. Electrospinning is a simple yet effective method for producing such membranes under controlled conditions. The morphology of our electrospun membranes, featuring beads-in-fiber structures, mimics spider webs, while their dual wettability characteristics resemble those of the Namib desert beetle. This combination has been shown to enhance water collection efficiency compared to surfaces that are exclusively hydrophobic or hydrophilic. In this study, two different types of membranes were developed and tested: hydrophilic lignin-CA membranes and hydrophobic lignin-CA membranes. Our CA membranes are hydrophobic, and the addition of hydrophilic lignin turns them slightly more hydrophilic. In contrast, our hydrophobic lignin-CA membranes are hydrophilic. Their water collection capacity from moist air was evaluated under controlled conditions inside a humidity chamber. The first group of membranes are sturdier and more efficient in capturing water. The most efficient membranes were CA+(2CA : 1L - 4h) and CA+(2CA : 1L - 5h) membranes.
- Next Gen BMS Materials: Selection Of Coatings For High Voltage ApplicationsPublication . Silva, António Pedro Machado; Igreja, Rui; Sarmento, Joana; Águas, HugoThe high complexity and increasing reliability requirements of the systems that manage batteries (Battery Management Systems) in automotive applications have highlighted the critical role of Printed Circuit Boards (PCBs) and their protection mechanisms. One of the key problems covered in this dissertation is the degradation and failure of PCBs, with special attention to the viability of conformal coatings as a protective solution. This problem is particularly challenging due to the need to guarantee the durability and physical and electrical performance of PCBs in aggressive environments, where factors such as humidity, micro-particles, and thermal variations can compromise the integrity of the systems. The diversity of protective technologies and the lack of standardized evaluation methods make their analysis even more complex. To respond to this challenge, a tool was developed that includes all the relevant coatings on the market and a table summarizing the different standards, taking reference data for each parameter studied. A detailed experimental approach was also implemented, including surface characterization (surface tension, FTIR, roughness), coating deposition, and curing methods. Functional and characterization tests, such as visual inspection, adhesion tests, electrical performance, aging, and thickness measure-ment, were carried out to evaluate the performance of the different coatings selected in this study. The results demonstrate that the type of surface and the coating selected have a significant influ-ence on the adhesion and the physical properties of the coating. These results contribute to the bench-marking of this product, widely used in automotive electronics, providing guidelines for optimizing the protection of PCBs.
- Piezoresistive sensing systems for predictive maintenance of automobile bumpersPublication . Alves, David Alexandre Figueiredo; Pinheiro, Tomás; Barquinha, PedroRoad safety remains a major global concern as the number of vehicles continues to rise. This increase leads to a higher risk of traffic accidents, often resulting in serious human, financial, and structural consequences. While automotive engineering has made significant progress in enhancing crashworthiness improving how vehicles absorb and dissipate impact energy one key challenge persists: detecting hidden internal damage after a collision. Such damage may not be visible externally but can weaken the vehicle’s structural integrity over time, posing safety risks. Addressing this issue requires the development of intelligent systems capable of monitoring structural health in real time. These systems are essential for enabling predictive maintenance and enhancing vehicle safety. In this context, the current study, part of the Be.Neutral project, focuses on designing and testing a novel bumper monitoring system using piezoresistive sensors made from laser-induced graphene (LIG) on polyimide (PI) substrates. These materials were selected for their flexibility, thermal stability, and environmental durability. The sensors detect mechanical strain by converting it into measurable changes in electrical resistance, enabling continuous monitoring of structural integrity. To assess sensor performance, mechanical tests were conducted using a universal testing machine. Two approaches were used for electrical characterization: a high precision potentiostat and a Wheatstone bridge circuit connected to an Arduino, supporting real-time, multi-channel data collection. The sensors achieved consistent quality, with an average sheet resistance of 4.54 ± 0.29 Ω/sq. They could detect strain as low as 0.01%, with optimal performance at 0.5% strain, showing a mean gauge factor of 4.11 ± 1.47. Environmental testing confirmed their robustness under different temperature and humidity conditions. These findings highlight the promise of LIG-based sensors for smart, lightweight, and scalable vehicle monitoring systems, contributing to safer and more sustainable transportation.
- Smart Materials for Pathogen InactivationPublication . Silva, Mariana Gonçalves; Almeida, Henrique; Carlos, EmanuelAntimicrobial resistance (AMR) poses a significant global health challenge, driven by the wide- spread use of antibiotics and the increasing incidence of infections caused by resistant microorganisms. This problem is particularly concerning in healthcare settings, where the effectiveness of conventional treatments is compromised. The urgent need for novel strategies to combat AMR has sparked interest in the development of alternative antimicrobial agents on surfaces, including biopolymer-based membranes that leverage natural materials' inherent antibacterial properties. This work aims to develop a membrane that combines the antibacterial properties of biopolymers such as chitosan and alginate, glycerol and spinel ferrite nanoparticles, to prevent bacterial contamination on surfaces without the use of antibiotics or other chemical agents. This approach addresses the growing concern over antibiotic resistance by providing a sustainable, non-chemical alternative for bacterial control in healthcare, research and industrial settings. Chitosan and alginate membranes were chosen for their biocompatibility and biodegradability and were incorporated with zinc spinel ferrite (ZnFe₂O₄) and copper spinel ferrite (CuFe₂O₄) nanoparticles, known for their antibacterial properties and low toxicity. Glycerol was added as a plasticizer and for its inherent antibacterial activity. Preliminary findings indicate that chitosan membranes formulated with glycerol and spinel ferrite nanoparticles exhibit significant antibacterial activity and improved mechanical properties, suggesting potential application is antibacterial settings. The results of this study show the potential of these membranes as an eco-friendly and effective solution for controlling bacterial contamination. Ultimately, this research could lead to the development of effective, sustainable antimicrobial surfaces that mitigate the risks associated with antibiotic resistance, thereby contributing to public health and safety.
- Conductive Nature-Derived Materials for BioelectronicsPublication . Monteiro, Gerson Daniel Rodrigues Lima; Almeida, Henrique; Pinheiro, TomásThe development of sustainable and electrically conductive biohybrid substrates was achieved by integrating laser-induced graphene (LIG) into agarose-lignin membranes via UV laser irradiation, addressing the need for biocompatible, flexible, and conductive materials for muscle tissue engineering. Two agarose-lignin formulations, AGL1 and AGL2, were produced and converted into LIG in a single-step UV laser process. Structural and chemical analyses confirmed the transformation: Raman spectroscopy showed the characteristic D, G, and 2D peaks, XPS indicated conversion of sp³ to sp² carbon, and EDS mapping revealed a homogeneous carbon-rich network. Electrical characterization identified AGL1, with 3 wt.% agarose and 0.25 wt.% lignin, under laser condition A4, as the best performing substrate, with thinner LIG layers (19.83 ± 3.10 μm), lowest sheet resistance (93.87 ± 7.92 Ω/sq), and higher electrical conductivity (537.74 S·m⁻¹). SEM imaging associated reduced thickness to higher porosity and enhanced conductivity. Biological assays confirmed cytocompatibility, with C2C12 myoblasts showing higher viability on AGL1 than AGL2. Electrical stimulation promoted a significant increase in cell survival and favored the early alignment of myotubes when compared to non-stimulated substrates. Additionally, APTES functionalization was one of the parameters evaluated, which showed no cytotoxicity and enabled the comparative evaluation of different experimental conditions. PBS stability tests validated the robustness of AGL1 membranes. Agarose-lignin LIG membranes (especially AGL1 under condition A4) are promising platforms for bioelectronics, highlighting the importance of balancing surface functionalization with the preservation of electrical integrity to optimize electroresponsive cell applications.
- Design and Analysis of Comparator/Slicer Architectures for DFE in FinFET TechnologyPublication . Ferreira, Rafael Estevens da Costa; Oliveira , Luís; Boyapati , SubrahmanyamEsta dissertação de mestrado apresenta duas novas arquiteturas de StrongARM latch (SAL) desenvolvidas para otimizar o desempenho de comparadores em aplicações de alta velocidade, sem comprometer a eficiência energética nem o desempenho em termos de ruído. O primeiro design proposto introduz um transistor adicional na parte inferior do latch, mitigando de forma eficaz o problema de clock feedthrough e permitindo que o comparador entre na fase de amplificação imediatamente após a transição do sinal de relógio para o nível alto. Este mecanismo de descarga antecipada conduz a um pequeno aumento de energia, de aproximadamente 3% em relação ao SAL convencional. No entanto, a melhoria obtida é significativa, com o design proposto a alcançar um tempo de decisão 35% mais rápido e uma redução de 13% no ruído de entrada, resultando numa figura de mérito (FoM) de 33 fJ·ps·µV². O segundo design proposto baseia-se no primeiro, incorporando uma técnica de body-biasing aplicada ao par diferencial de entrada. Este método reduz dinamicamente a tensão de limiar dos transístores e aumenta a sua transcondutância, melhorando ainda mais o atraso e o consumo de energia. Como resultado, esta versão alcança uma melhoria adicional de cerca de 3% em ambos os parâmetros relativamente ao primeiro latch proposto. Ambos os comparadores foram implementados e simulados na tecnologia TSMC FinFET CMOS de 16 nm e comparados com soluções recentes do estado da arte. Os resultados demonstram que as arquiteturas propostas alcançam um funcionamento significativamente mais rápido, mantendo um desempenho energético e de ruído equivalente, confirmando a sua eficácia para aplicações modernas de baixo consumo e alta velocidade.
- Avaliação do comprometimento das propriedades mecânicas e térmicas do abs sob ciclos de reprocessamento repetitivosPublication . Divino, Arthur Fernandes; Santos, Miguel; Lança, Maria do CarmoA crescente preocupação ambiental e a necessidade de atender à procura por materiais mais sustentáveis têm impulsionado a busca por soluções que minimizem o desperdício e o consumo de recursos naturais. Nesse contexto, o reaproveitamento de polímeros surge como uma alternativa promissora, especialmente em indústrias onde o uso de materiais termoplásticos é predominante. Um polímero amplamente utilizado é o ABS (Acrilonitrilo Butadieno Estireno), conhecido pela sua versatilidade e propriedades mecânicas excecionais. O ABS é produzido por meio de processos de copolimerização, que combinam três monómeros principais: acrilonitrilo, butadieno e estireno. Cada um desses monómeros contribui para características específicas do polímero final, esta composição confere ao material uma combinação equilibrada de resistência mecânica, rigidez e tenacidade ao impacto, além de boas características térmicas e facilidade de processamento. O processamento do ABS inclui a moldagem por injeção, extrusão e termoformagem, o que o torna ideal para uma ampla gama de aplicações industriais e comerciais. Neste trabalho, foi utilizado ABS de alto impacto fornecido pela LyondellBasell (França), um dos principais fornecedores globais de polímeros. O material em questão, comercializado sob o nome Polyman E/HI, é conhecido pela sua elevada resistência ao impacto e excelente processabilidade em moldagem por injeção. Este estudo tem como objetivo principal analisar o impacto do reprocessamento de rejeitos de produção, considerando formulações de polímero reprocessado e virgem em diferentes proporções. A análise foca-se nas propriedades mecânicas e térmicas das formulações de polímero, avaliando a sua viabilidade como uma alternativa sustentável para reduzir o desperdício e o consumo de matéria-prima, sem comprometer significativamente a qualidade final do produto/componente produzido com as referidas formulações. Os resultados obtidos demonstram que o ABS reprocessado mantém propriedades térmicas e mecânicas comparáveis ao material virgem, mesmo após três ciclos de reprocessamento. O ensaio de DSC revelou uma diferença de apenas 1,6 °C na temperatura de transição vítrea entre as formulações 100% virgem e 100% reprocessado, com um desvio máximo de 2,0 °C em relação à média. O FTIR confirmou a estabilidade da estrutura química. Os ensaios de tração apresentaram um módulo de Young médio de 2026 MPa para o ABS virgem e 1971 MPa para o ABS 100% reprocessado, sem comprometer a integridade mecânica do material. Os valores experimentais de MFR e MVR registaram uma variação de até 17% face aos teóricos, mantendo-se, contudo, dentro dos limites aceitáveis de qualidade.
- ULTRA-LOW VOLTAGE SELF-CLOCKED CHOPPER DIGOTA FOR OFFSET REDUCTIONPublication . Matos, Alexandra Gondar; Toledo, Pedro; Oliveira, JoãoEm aplicações de ultra-baixo consumo o Digital Operational Transconductance Amplifier (DIGOTA) é frequentemente utilizado como front-end analógico (AFE) pela sua implementação com células padrão, e operação a baixas tensões. Contudo, em aplicações de baixa largura de banda, surgem erros de baixa frequência como offset DC e ruído 1/f, gerados na cadeia de deteção. A estabilização via chopper é uma solução fiável, mas a exige a utilização de um relógio externo, introduzindo custos geração, distribuição e compromete a sua simplicidade. Esta dissertação estuda três arquiteturas. Uma referência com inversores simples (DIGOTA), outra com inversores Schmitt-Trigger (ST-DIGOTA) e, um novo ST-DIGOTA com estabilização por chopper sem clock externo (Chopper DIGOTA). As três arquiteturas foram validadas em configuração de ganho unitário e avaliadas em corners de Processo, Tensão e Temperatura (PVT). O Chopper DIGOTA explora a auto-oscilação da malha interna, para excitar um FlipFlop D configurado como divisor de frequência gerando as fases complementares para a modulação à entrada e desmodulação sincrona do à saída, eliminando a necessidade de relógio externo. Verificou-se um consumo de potência de 20 nW, ganho DC de 58 dB, produto ganho-largura de banda de 1.9 kHz e margem de fase de 135.4º, ocupando uma area de 161.2 𝜇m2 . O offset referido à entrada reduz de 9mv para 2.4 mV em comparação com a mesma arquitetura sem estabilização por chopper (ST-DIGOTA) correspondendo a uma redução de 73%. Estes resultados demonstram a translação eficaz de erros de baixa frequênica para a banda de chopping com uma sobrecarga de area de apenas 23% (161 vs 130 𝜇m2 ). Este trabalho quantifica os compromissos entre ganho, largura de banda, margem de fase, potência, área e offset, ilustrando a viabilidade do Chopper DIGOTA para circuitos de ultra baixo tensão e potência.