No description available.

Recent developments in the area of microfabrication technologies, has enabled the fabrication of many radio frequency/microwave components with better performance and lower cost than possible with semiconductor based fabrication technology. Many of these microfabricated RF components such as switches and phase shifters, popularly known as RF MEMS, are aimed at reducing the insertion loss and improving other performance parameters such as linearity. For these devices size miniaturization is not necessarily important, as in practical subsystems, these components are integrated with RF front-ends on a laminate. This thesis deals with concepts of a low cost passive phase shifter fabricated in-situ on a microwave laminate. The operation of this Mesoscale Electrostatically actuated Phase shifter on microwave Laminate (MEPL) is similar to that of a micromachined distributed MEMS transmission line (DMTL) phase shifter. In spite of advantages of low losses, wide bandwidth, low DC power consumption and high linearity over semiconductor/MMIC technology, microfabricated phase shifters are often not used in field because of issues related to fabrication reliability, packaging and integration. On the other hand, the proposed MEPL will have all the advantages of conventional MEMS phase shifters with additional benefit of lower cost. Furthermore, these are integrable to form a monolithic phased array. A MEPL phase shifter of 50-bridges periodically distributed on the co-planar waveguide (CPW) transmission line is demonstrated in this thesis. MEMS air bridges are electrostatically actuated to vary the capacitance of the transmission line, which changes the phase velocity of the propagation RF signal, consequently phase at the output port. The realized MEPL is characterized for electromagnetic as well as electromechanical performance. The electromechanical characterization of this device is performed using a Laser Doppler Vibrometer (LDV). The measured data showed good agreement with the analytical data.. Major application of a phase shifter is in a phased array antenna system. MEPL is particularly suited for a monolithic phase array antenna. The proposed monolithic phased array antenna system fabrication approach utilizes extremely simple and economical modern printed circuit board technology to pattern the conventional microwave laminate and copper foil. A complete monolithic phased array antenna system is fabricated on a microwave laminate using an embedded phase shifter operating with electrostatic principles. Other components such as DC block and bias tee are integrated into the CPW-microstrip transitions to optimize the space and performance. Integrated phased array antenna is fabricated and tested to demonstrate the beam steering capability. Measured S11 is better than -15dB at the operating frequency of 9.8GHz. The beam steering capability is shown as proof of concept by showing the beam scan angle of 10deg with bias voltage of 125V. The mesoscale phase shifter demonstrated in this thesis has several advantages compared to micromachined phase shifters. The proposed fabrication approach does not use metal deposition/patterning process, which removes the need of high cost clean room and sophisticated films deposition equipments. Secondly, as there are no thin films used, stiction is not expected on phase shifters fabricated with this approach. Since this approach uses thicker metal films, the power handling capability is expected to be significantly higher than micromachined phase shifters. Since conventional phased array antenna system components are fabricated on a microwave laminate, micro machined phase shifters realized on semiconductor substrates are required to be packaged separately before integrating with such phased array circuits. Packaging of the micro-machined RF-MEMS/MEMS devices is still a major issue and contributes to a substantial part of the total cost. Unlike micromachined phase shifters which are required to be packaged and then embedded in phased array applications, device presented in this thesis is packaged in-situ. Compared to similar monolithic phased array antenna reported on silicon substrate which are limited by wafer size, these arrays can be easily extended for larger arrays on microwave laminate as these are available in large size. To summarize, the proposed fabrication approach for phase shifters overcomes many limitations of micromachined components for microwave applications while retaining most of their advantages compared to other existing approaches based on ferrites or semiconductor technologies.

É descrita a modelagem, para controle, da dinâmica de uma plataforma semisubmersível com seis graus de liberdade. O modelo inclui os efeitos dos tanques de lastro como forças e momentos, assim como a dinâmica da plataforma. Os parâmetros do sistema foram obtidos das características da plataforma e de resultados experimentais obtidos com uma plataforma semisubmersível de dimensões reduzidas. O desenvolvimento de uma metodologia e de um software capazes de determinar o volume submerso e o centro de empuxo de uma estrutura com geometria complexa foram pontos determinantes nessa Dissertação, tendo em vista a complexidade do processo e as importâncias desses parâmetros para o desenvolvimento do modelo. A linearização do modelo permitiu a elaboração de uma estratégia de controle capaz de estabilizar a plataforma mesmo em condições iniciais distantes do equilíbrio. As equações que descrevem o movimento da plataforma nos graus de liberdade vertical, jogo e arfagem foram desenvolvidas. A realocação dos polos e um observador de estado foram utilizados com o objetivo de melhorar o controle do sistema. / A six degrees of freedom dynamic model for the development of ballast control systems for semisubmersible platforms is described. The model includes the effects os the ballast tanks such as weights, moments ans inertias as well as the platform dynamic. System parameters are computed from physical characteristics of the platform and from experimental results obtained with a small semisubmersible platform. The development of a methodology and software capable of determining the immersed volume and center of buoyancy of a structure with complex geometry are points, wich in this M. Sc. Dissertation, in view of the complexity of the process and importance of these parameters for model development. The linearization of the model allowed the development of a control strategy capable of stabilizing the semisubmersible platform in initial conditions far from the balance. The equations describing the motion of the platform in the vertical, roll and pitch degrees of freedom have been developed. The relocation of the poles and an observer of state were used in order to improve the control system.

É descrita a modelagem, para controle, da dinâmica de uma plataforma semisubmersível com seis graus de liberdade. O modelo inclui os efeitos dos tanques de lastro como forças e momentos, assim como a dinâmica da plataforma. Os parâmetros do sistema foram obtidos das características da plataforma e de resultados experimentais obtidos com uma plataforma semisubmersível de dimensões reduzidas. O desenvolvimento de uma metodologia e de um software capazes de determinar o volume submerso e o centro de empuxo de uma estrutura com geometria complexa foram pontos determinantes nessa Dissertação, tendo em vista a complexidade do processo e as importâncias desses parâmetros para o desenvolvimento do modelo. A linearização do modelo permitiu a elaboração de uma estratégia de controle capaz de estabilizar a plataforma mesmo em condições iniciais distantes do equilíbrio. As equações que descrevem o movimento da plataforma nos graus de liberdade vertical, jogo e arfagem foram desenvolvidas. A realocação dos polos e um observador de estado foram utilizados com o objetivo de melhorar o controle do sistema. / A six degrees of freedom dynamic model for the development of ballast control systems for semisubmersible platforms is described. The model includes the effects os the ballast tanks such as weights, moments ans inertias as well as the platform dynamic. System parameters are computed from physical characteristics of the platform and from experimental results obtained with a small semisubmersible platform. The development of a methodology and software capable of determining the immersed volume and center of buoyancy of a structure with complex geometry are points, wich in this M. Sc. Dissertation, in view of the complexity of the process and importance of these parameters for model development. The linearization of the model allowed the development of a control strategy capable of stabilizing the semisubmersible platform in initial conditions far from the balance. The equations describing the motion of the platform in the vertical, roll and pitch degrees of freedom have been developed. The relocation of the poles and an observer of state were used in order to improve the control system.

Microdispositivos piezelétricos tem uma vasta aplicação em mecânica de precisão, como, por exemplo, manipulação de células, microcirurgias, equipamentos de nanotecnologia e principalmente em microeletromecanismos (MEMS). Os microdispositivos piezelétricos considerados nesta tese essencialmente consistem de uma estrutura multi-flexível atuada por duas ou mais piezocerâmicas, que geram deslocamentos e forças em direções e regiões pré-determinadas do domínio, ou seja, a estrutura multi-flexível atua como um transformador mecânico amplificando e alterando os deslocamentos gerados pelas piezocerâmicas nos movimentos de atuação. O desenvolvimento destes microdispositivos piezelétricos em sua grande maioria não utiliza ferramentas sistemáticas e genéricas. A complexidade dos movimentos de atuação torna o desenvolvimento dos microdispositivos piezelétricos complexo, principalmente devido ao surgimento de movimentos indesejados ou acoplados durante a sua atuação. Portanto, é necessário um método sistemático e eficiente como o método de otimização topológica (MOT), que incorpore na sua formulação as principais exigências de projeto dos microdispositivos, como apresentado nesse trabalho. O MOT implementado é baseado na abordagem CAMD (Distribuição Contínua da Distribuição de Material), onde as pseudo-densidades são interpoladas nos nós de cada elemento finito, resultando numa distribuição contínua de material no domínio. Um método adjunto foi implementado para o cálculo das sensibilidades. São consideradas três formulações. A primeira denominada de MAPs (Multi-Atuadores Piezelétricos) considera as regiões piezocerâmicas fixas, otimizando apenas a estrutura multi-flexível no domínio de projeto. Nesta formulação materiais não-piezelétricos (como, por exemplo, Alumínio) e vazio são distribuídos no domínio de projeto, mantendo as regiões piezocerâmicas fixas e homogêneas. Para validar os resultados obtidos com essa formulação foram fabricados protótipos de nanoposicionadores $XY$, que foram caracterizados experimentalmente utilizando técnicas de interferometria laser, considerando excitação quasi-estática. No entanto, essa primeira formulação impõe restrições no problema, limitando a optimalidade da solução obtida pela otimização topológica. Assim, surgiu a necessidade de desenvolver uma segunda formulação, que permite distribuir simultaneamente material não-piezelétrico, piezelétrico e vazio no domínio de projeto, denominada de LOMPs (Localização Ótima do Material Piezelétrico). A formulação dos LOMPs obtém simultaneamente a localização do material piezelétrico na estrutura flexível otimizada pela OT, e inclui também uma variável de projeto para determinar o ângulo ótimo entre as direções de polarização e do campo elétrico. Nesta formulação como as posições dos eletrodos não são conhecidas, ``a priori\'\', é utilizado como abordagem aplicar um campo elétrico constante para determinar a localização do material piezelétrico e conseqüentemente dos eletrodos. Finalmente, foi explorado o conceito de materiais com gradação funcional (MGFs) no projeto dos MAPs. Os MGFs apresentam uma distribuição contínua de materiais na sua microestrutura, não possuindo interface entre os materiais distribuídos, o que possibilita aumentar a vida útil do dispositivo piezelétrico. Assim, foi implementado uma terceira formulação denominada de MAPs MGFs, que permite obter a gradação ótima de materiais piezelétricos e não-piezelétricos no domínio piezocerâmico dos MAPs, conjuntamente com a topologia da estrutura multi-flexível. Essa formulação foi estendida para projetar atuadores bilaminares MGFs. Todas as formulações desenvolvidas utilizam uma função multi-objetivo, que permite controlar a rigidez e a flexibilidade minimizando o movimento acoplado, de cada movimento de atuação. Os exemplos numéricos são limitados a modelos bi-dimensionais, utilizando o estado plano de tensões e deformações mecânicas e elétricas, uma vez que a grande maioria das aplicações dos microdispositivos piezelétricos são bi-dimensionais. / Microtools offer significant promise in a wide range of applications such as cell manipulation, microsurgery, nanotechnology processes, and many other fields. The microtools considered in this doctoral thesis essentially consist of a multi-flexible structure actuated by two or more piezoceramic devices that when each piezoceramic is actuated, it generates an output displacement and force at a specified point of the domain and direction. The multi-flexible structure acts as a mechanical transformer by amplifying and changing the direction of the piezoceramic output displacements. Thus, the development of microtools requires the design of actuated flexible structures that can perform complex movements. The development of these microtools is still in the beginning and it can be strongly enhanced by using design tools. In addition, when multiple piezoceramic devices are involved, coupling effects in their movements become critical, especially the appearance of undesired movements, which makes the design task very complex. One way to avoid such undesirable effects is the use of a systematic design method, such as topology optimization, with appropriate formulation of the optimization problem. The topology optimization method implemented is based on the CAMD (Continuous Approximation of Material Distribution) approach where fictitious densities are interpolated at each finite element, providing a continuum material distribution in the domain. The corresponding sensitivity analysis is presented using the adjoint method. Three formulations are considered. The first formulation, called Piezoelectric Multi-Actuators (PMAs), keeps fixed piezoceramic positions in the design domain and only the flexible structure is designed by distributing some non-piezoelectric material (Aluminum, for example). $XY$ Piezoelectric Nanopositioner are manufactured and experimentally analyzed to validate the results of the topology optimization obtained using this formulation. Experimental analyses are conducted using laser interferometry to measure displacement, while considering a quasi-static excitation. However, this first formulation imposes a constraint to the position of piezoelectric material in the optimization problem limiting the optimality of the solution. Thus, the second formulation presented, called LOMPs, allows the simultaneous distribution of non-piezoelectric and piezoelectric material in the design domain, to achieve certain specified actuation movements. The optimization problem is posed as the simultaneous search for an optimal topology of a flexible structure as well as the optimal position of piezoceramics in the design domain and optimal rotation angle of piezoceramic material axes that maximize output displacements or output forces at a specified point of the domain and direction. When the distribution of a non-piezoelectric conductor material and a piezoceramic material is considered in the design domain, the electrode positions are not known ``a priori\'\'. To circumvent this problem, an electric field is applied as electrical excitation. Finally, the concept of functionally graded materials (FGM) is applied to PMAs design. FGMs are special materials that possess continuously graded properties without interfaces which can increase lifetime of piezoelectric devices. Thus, a third formulation is implemented to find the optimum gradation and polarization sign variation of piezoceramic FGMs, while simultaneously optimizing the multi-flexible structural configuration. This formulation is extended to design bimorph type FGM actuators. For all developed formulations, a multi-objective function is defined that controls the stiffness and flexibility, minimizing the coupling movement of each actuated movement. The present examples are limited to two-dimensional models because most part of the applications for such micro-tools are planar devices.

No description available.

The resonance frequency of electrostatically actuated micromachined beams can be tuned substantially by applying a DC voltage bias, first by decreasing the frequency until the onset of pull-in and then by increasing it by the virtue of contact. With the objective of modeling and designing the micromechanical structures after pull-in, a semi-analytical method was developed to determine the length of the contact between the beam and the substrate. The semi-analytical method which is validated on the straight beams is extended for the folded beam structures. This method provides a tool to the microsystem designer to quickly evaluate the deformed configuration of the folded beams after pull-in without the time-intensive contact analysis. This tool is used to design the micro‐speaker elements suitable for emitting low frequency sounds. Multiple instabilities after the pull-in were numerically observed and it was shown that the resonant frequency of an L-shaped beam can be varied in different frequency bands. The speaker element can emit any frequency in a given range, as the resonant frequency of the beam structures can be tuned both before and after pull-in. Operating the speaker element at resonance maximizes the efficiency of the speaker design because the amplitude of vibration is maximum at the resonance frequency. Furthermore, the interplay between the torsional and bending loads is used to minimize the out-of-plane deflection under self weight. A selection criterion is employed to choose a beam structure with optimum stiffness and natural frequency. Beam-based micro-speaker element designs with single and multi-layered suspended structures are proposed. Practical considerations such as volume displacement, mode shapes and dynamic coupling are discussed, on the basis of which design guidelines for a speaker element are proposed. Squeeze film effects and nonlinearity due to the midplane stretching is integrated into the transient analysis model to analyze the effect on the stroke of beam operating at resonance. A comparison between various speaker elements is presented.

This thesis presents a new mechanical design for an exoskeleton actuator to power the sagittal plane motion in the human hip. The device uses a DC motor to drive a Scotch yoke mechanism and series elasticity to take advantage of the cyclic nature of human gait and to reduce the maximum power and control requirements of the exoskeleton. The Scotch yoke actuator creates a position-dependent transmission that varies between 4:1 and infinity, with the peak transmission ratio aligned to the peak torque periods of the human gait cycle. Simulation results show that both the peak and average motor torque can be reduced using this mechanism, potentially allowing a less powerful motor to be used. Furthermore, the motor never needs to reverse direction even when the hip joint does. Preliminary testing shows the exoskeleton can provide an assistive torque and is capable of accurate position tracking at speeds covering the range of human walking. This thesis provides a detailed analysis of how the dynamic nature of human walking can be leveraged, how the hip actuator was designed, and shows how the exoskeleton performed during preliminary human trials.

The main goal of this work is to introduce new carbon structures - carbon nanotubes. The main objective of this work is to take advantage of the unique characteristic of carbon nanotubes to emit electrons at very low supply voltage.

Today in the scientific and technological world, physical and artificial processes are often described by mathematical models which can be used for simulation, optimization or control. As the mathematical models get more detailed and different coupling effects are required to include, usually the dimension of these models become very large. Such large-scale systems lead to large memory requirements and computational complexity. To handle these large models efficiently in simulation, control or optimization model order reduction (MOR) is essential. The fundamental idea of model order reduction is to approximate a large-scale model by a reduced model of lower state space dimension that has the same (to the largest possible extent) input-output behavior as the original system. Recently, the system-theoretic method Balanced Truncation (BT) which was believed to be applicable only to moderately sized problems, has been adapted to really large-scale problems. Moreover, it also has been extended to so-called descriptor systems, i.e., systems whose dynamics obey differential-algebraic equations. In this thesis, a BT algorithm is developed for MOR of index-1 descriptor systems based on several papers from the literature. It is then applied to the setting of a piezo-mechanical system. The algorithm is verified by real-world data describing micro-mechanical piezo-actuators. The whole algorithm works for sparse descriptor form of the system. The piezo-mechanical original system is a second order index-1 descriptor system, where mass, damping, stiffness, input and output matrices are highly sparse. Several techniques are introduced to reduce the system into a first order index-1 descriptor system by preserving the sparsity pattern of the original models. Several numerical experiments are used to illustrate the efficiency of the algorithm.