Neste trabalho foram realizadas otimizações no processo de fabricação de micro cavidades na superfície do aço DIN 16MnCr5, com o objetivo de reduzir o coeficiente de atrito dinâmico entre duas superfícies. Para a confecção das micro cavidades (dimples) foi utilizado um laser com pulsos ultracurtos, de largura temporal de algumas dezenas de femtossegundos. Além de estudos de variação de fluência do laser, também foi analisado o resultado da utilização de diferentes perfis de energia do feixe. Para a caracterização das micro cavidades, foram utilizadas técnicas como a microscopia eletrônica de varredura, para análise morfológica, interferometria de luz branca e microscopia confocal para análise topográfica, dimensional e perfilométrica. Foram realizados ensaios de desgaste, em tribômetro para análise da variação do coeficiente de atrito após a texturização. Após os ensaios, percebeu-se que a texturização com pulsos ultracurtos apresenta grande vantagem na confecção de micro cavidades devido a precisão e ausência de interação térmica entre o laser e o material. Em relação ao atrito, as amostras texturizadas apresentaram redução da força e do coeficiente de atrito, porém, foram observados sinais de aumento da pressão de contato entre as superfícies. / In this work, optimizations were realized in the dimples manufacturing process on DIN 16MnCr5 steel surface, the target were to reduce the coefficient of dynamic friction between two surfaces. A laser with ultrashort pulses, temporal width of a few tens of femtoseconds, was used to manufacture dimples. In addition to studies of variation of laser beam fluency, the results of the use of different beam energy profiles were also analyzed. For analysis of dimples, techniques such as scanning electron microscopy (SEM), for morphological analysis, white light interferometry and confocal surface microscopy were used for topographic, dimensional and perfilometry. Wear tests were performed to analyze the variation of the friction coefficient in texturing surface. After the tests, it was observed that the texturing with ultrashort pulses presents a great advantage in manufacturing of dimples, due to the precision and absence of thermal interaction between the laser beam and the material. In relation to the friction coefficient, the textured samples presented a reduction of the friction force and consequently of the friction coefficient, but an increase in the contact pressure between the studied surfaces was observed.

Neste trabalho foram realizadas otimizações no processo de fabricação de micro cavidades na superfície do aço DIN 16MnCr5, com o objetivo de reduzir o coeficiente de atrito dinâmico entre duas superfícies. Para a confecção das micro cavidades (dimples) foi utilizado um laser com pulsos ultracurtos, de largura temporal de algumas dezenas de femtossegundos. Além de estudos de variação de fluência do laser, também foi analisado o resultado da utilização de diferentes perfis de energia do feixe. Para a caracterização das micro cavidades, foram utilizadas técnicas como a microscopia eletrônica de varredura, para análise morfológica, interferometria de luz branca e microscopia confocal para análise topográfica, dimensional e perfilométrica. Foram realizados ensaios de desgaste, em tribômetro para análise da variação do coeficiente de atrito após a texturização. Após os ensaios, percebeu-se que a texturização com pulsos ultracurtos apresenta grande vantagem na confecção de micro cavidades devido a precisão e ausência de interação térmica entre o laser e o material. Em relação ao atrito, as amostras texturizadas apresentaram redução da força e do coeficiente de atrito, porém, foram observados sinais de aumento da pressão de contato entre as superfícies. / In this work, optimizations were realized in the dimples manufacturing process on DIN 16MnCr5 steel surface, the target were to reduce the coefficient of dynamic friction between two surfaces. A laser with ultrashort pulses, temporal width of a few tens of femtoseconds, was used to manufacture dimples. In addition to studies of variation of laser beam fluency, the results of the use of different beam energy profiles were also analyzed. For analysis of dimples, techniques such as scanning electron microscopy (SEM), for morphological analysis, white light interferometry and confocal surface microscopy were used for topographic, dimensional and perfilometry. Wear tests were performed to analyze the variation of the friction coefficient in texturing surface. After the tests, it was observed that the texturing with ultrashort pulses presents a great advantage in manufacturing of dimples, due to the precision and absence of thermal interaction between the laser beam and the material. In relation to the friction coefficient, the textured samples presented a reduction of the friction force and consequently of the friction coefficient, but an increase in the contact pressure between the studied surfaces was observed.

The need for miniaturized, and high performance microwave devices has focused significant attention onto new fabrication technologies that can simultaneously achieve high performance and low manufacturing complexity. Additive manufacturing (AM) has proven its capability in fabricating high performance, compact and light weight microwave circuits and antennas, as well as the ability to achieve designs that are complicated to fabricate using other manufacturing approaches. Direct print additive manufacturing (DPAM) is an emerging AM process that combines the fused deposition modeling (FDM) of thermoplastics with micro-dispensing of conductive and insulating pastes. DPAM has the potential to jointly combine high performance and low manufacturing complexity, along with the possibility of real-time tuning. This dissertation aims to leverage the powerful capabilities of DPAM to come-up with new designs and solutions that meet the requirements of rapidly evolving wireless systems and applications. Furthermore, the work in this dissertation provides new techniques and approaches to alleviate the drawbacks and limitations of DPAM fabrication technology. Firstly, the development of 3D packaged antenna, and antenna array are presented along with an analysis of the inherent roughness of 3D printed structures to provide a deeper understanding of the antenna RF performance. The single element presents a new volumetric approach to realizing a 3D half-wave dipole in a packaged format, where it provides the ability to keep a signal distribution network in close proximity to the ground plane, facilitating the implementation of ground connections (e.g. for an active device), mitigating potential surface wave losses, as well as achieving a modest (10.6%) length reduction. In addition, a new approach of implementing conformal antennas using DPAM is presented by printing thin and flexible substrate that can be adhered to 3D structures to facilitate the fabrication and reduce the surface roughness. The array design leverages direct digital manufacturing (DDM) technology to realize a shaped substrate structure that is used to control the array beamwidth. The non-planar substrate allows the element spacing to be changed without affecting the length of the feed network or the distance to the underlying ground plane. The second part describes the first high-Q capacitively-loaded cavity resonator and filter that is compatible with direct print additive manufacturing. The presented design is a compromise between quality factor, cost and manufacturing complexity and to the best of our knowledge is the highest Q-factor resonator demonstrated to date using DPAM compatible materials and processes. The final version of the single resonator achieves a measured unloaded quality factor of 200-325 over the frequency range from 2.0 to 6.5 GHz. The two pole filter is designed using a coupled-resonator approach to operate at 2.44 GHz with 1.9% fractional bandwidth. The presented design approach simplifies evanescent-mode filter fabrication, eliminating the need for micromachining and vias, and achieving a total weight of 1.97 g. The design is fabricated to provide a proof-of-principle for the high-Q resonator and filter that compromises between performance, cost, size, and complexity. A stacked version of the two-pole filter is presented to provide a novel design for multi-layer embedded applications. The fabrication is performed using an nScrypt Tabletop 3Dn printer. Acrylonitrile Butadiene Styrene (ABS) (relative permittivity of 2.7 and loss tangent of 0.008) is deposited using fused deposition modeling to form the antenna, array, resonator, and filter structures, and Dupont CB028 silver paste is used to form the conductive traces conductive regions (the paste is dried at 90 °C for 60 minutes, achieving a bulk DC conductivity of 1.5×106 S/m.). A 1064 nm pulsed picosecond Nd:YAG laser is used to laser machine the resonator and filter input and output feedlines.

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