We present studies on squeeze film effects in dynamic MEMS devices with a special emphasis on the development of compact analytical models. First, the efficacy of lumped parameter modelling of dynamic MEMS devices is illustrated in MATLAB/SIMULINK software environment using a MEMS gyroscope and a MEMS microphone as examples. This is followed by a comparative study of equivalent electrical circuit models for a MEMS microphone wherein the importance of accurate extraction of lumped mass, stiffness and damping is brought into focus. In this context, a need for an in depth study of squeeze film behaviour in MEMS structures is highlighted and a strong motivation is drawn for the development of compact squeeze film models. A 2D analytical model for estimating squeeze film damping and spring force in perforated MEMS structures is presented. The governing equations based on isothermal compressible Reynolds equation are derived by considering an approximate circular pressure cell around a hole which is representative of the spatially invariant pressure pattern over the interior of the flow domain. The advantages and limitations of the solution are discussed with relevance to MEMS structures. Next, a comprehensive analytical model for 3D MEMS structures that includes effects of compressibility, inertia, and rarefaction in the flow between two parallel plates forming the squeeze region as well as the flow through perforations is developed. A modified Reynolds equation that includes the unsteady inertial term is derived from the Navier-Stokes equation to model the flow in the circular cell and the losses through the holes are modelled using Poiseuille flow. Rarefaction effects in the flow through the air-gap as well as the holes are accounted for by considering the slip boundary conditions. The analytical results are compared with extensive numerical simulations carried out using full 3-D Navier-Stokes equation solver in a commercial simulation package (ANSYS-CFX). We show that the analytical solution performs very well in tracking the net force up to the first resonant frequency of the entrapped air.

Biossensores que empregam dispositivos de efeitos de campo podem ser obtidos em diversas arquiteturas, incluindo dispositivos Eletrólito-Isolante-Semicondutor (EIS), que são capacitores em que o eletrodo metálico é substituído por um filme e uma solução. Medindo-se a capacitância em função do potencial aplicado, é possível detectar variações de pH oriundas de reações ou interações entre o filme e o analito. Nesta dissertação, sensores foram produzidos com a adsorção de filmes automontados de dendrímero (PAMAM) e nanotubos de carbono (SWNT) num chip. Medidas de espectroscopia de impedância foram realizadas para investigar o crescimento de cada bicamada do filme automontado, e os dados foram analisados com circuitos equivalentes que continham uma capacitância de dupla camada, um elemento de fase constante e uma capacitância para a região de depleção. Para o chip, os melhores ajustes foram obtidos na frequência de 2 kHz, em que a concentração de dopantes foi 6,6x1020 m-3 para o chip com isolante de SiO2 e de 1,1x1021 m-3 para o chip com isolante de SiO2/Ta2O5. O potencial de banda plana foi -0,2 V e -0,06V, respectivamente. Para os chips recobertos com os filmes de PAMAM/SWNT, observamos que a região de depleção é causada pelas cargas positivas do PAMAM. Com relação às implicações para biossensores, verificamos que o desempenho ótimo deve ser obtido com 3 bicamadas de PAMAM/SWNT. Isso pode explicar a observação empírica na literatura de que existe uma espessura ideal dos filmes para um desempenho otimizado. / Biosensors based on field effect devices can be produced with several architectures, including Electrolyte-Insulator-Semiconductor (EIS) devices, which are capacitors where conventional metal electrodes are replaced by a sensing layer and an electrolyte solution. By measuring the capacitance as a function of the bias voltage, it is possible to detect pH changes that may originate from reactions or interactions between the film in the sensing unit and the analyte. In this study sensors were obtained by adsorbing layer-by-layer (LbL) films made with dendrimers (PAMAM) and carbon nanotubes (SWNT) on a semiconductor chip. Impedance spectroscopy measurements were performed to monitor the growth of each bilayer in the LbL film, whose data were analyzed with equivalent circuits containing a double-layer capacitance, a constant phase element and a capacitance for the depletion region. The results for the semiconductor chip could be best fitted for a frequency of 2 kHz, where the doping concentration was 6.6 x1020 m-3 for the insulating SiO2 layer and 1.1 x1021 m-3 for the SiO2/Ta2O5 layer. The flat band voltage was -0.2 V and -0.06 V, respectively. In the analysis of the chip coated with different numbers of PAMAM/SWNT bilayers, we found that the depletion region appears as a contribution from the positive charges in the PAMAM layer. With regard to implications for biosensors, we found that optimized performance should be reached with three PAMAM/SWNT bilayers, which may explain the empirical finding in the literature that an ideal thickness exists for enhanced performance.

[pt] O surgimento do fenômeno de estabilidade de tensão na operação dos sistemas elétricos motivou centenas de pesquisadores a desenvolverem métodos que permitam detectar a proximidade à instabilidade de tensão, com eficiência computacional, e tomar medidas acertadas para garantir a operação confiável e segura. Neste trabalho são analisados diferentes métodos que permitem transformar sistemas de grande porte em circuitos simples: o circuito equivalente entre geradores e cargas, baseado no cálculo de correntes de curto-circuito, na técnica de redução de rede pela eliminação de barras intermediárias e no equivalente de Thévenin. É analisada a utilização destes equivalentes na avaliação das condições de estabilidade de tensão com sistemas-testes de 3 e 4 barras. Através de diferentes testes verificou-se que o circuito equivalente entre geradores e cargas e a técnica de redução de rede não podem ser usados para o cálculo de índices de avaliação das condições de estabilidade de tensão, enquanto que, usando circuito equivalente de Thévenin encontrou-se um método que funciona corretamente para barra de carga terminal, barra não-terminal e barra de tensão controlada por gerador. / [en] The emergence of voltage stability phenomenon in the operation of power systems has motivated hundreds of researchers to develop methods to detect the proximity to voltage instability, with computational efficiency and to take all necessary and appropriate measures to ensure reliable and safe operation. In this work, different methods that allow transforming large systems into simple circuits were analyzed, such as the equivalent circuit between generators and loads, based on the calculation of short-circuit currents; the network reduction technique for eliminating intermediate buses; and the Thévenin equivalent. The application of these equivalents on voltage stability assessment of 3 and 4 bus testing systems were extensively tested. At the end, it was verified that that the equivalent circuit between the generator and load, and the network reduction technique, cannot be used for calculating the voltage stability conditions evaluation indexes. However, using Thévenin equivalent circuit, it was found a proper method, which works correctly for terminal buses, transit buses and voltage-controlled buses.

No / A novel multi-standard dual-wide band filter with a compact size of only 8.8 mm by 16.8mm is designed and developed for transceiver devices. The proposed filter has a fundamental bandwidth of 1.6GHz with fractional bandwidth (FBW) of 29.7% centered at the 5.4GHz band, and second bandwidth of 300.0MHz with FBW of 3.6% centered at the 8.15GHz band. The basic dual-wide bandwidth is attributed to the interaction of the novel modified polygon pair and upper stub loaded stepped impedance resonator. Moreover, the added down stub loaded stepped impedance resonator (SLSIR) further enhances the pass band performance by widening the bandwidth and optimizing reflection coefficient performance considerably. To validate the proposed ideas, the multi-standard filter is designed and simulated by Ansoft HFSS software. The simulated results agree well with the theory predictions. The featured broad bandwidths over two frequency bands and the miniaturized size of the proposed filter make it very promising for applications in future multi-standard wireless communication.

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The master thesis provides a brief introduction to the lead-acid batteries. The thesis describes an internal construction, electrochemical reactions inside the batery, the area of application and possible degradation effects. The next part deals with an analytic method of the measurement called electrochemical impedance spectroscopy. The thesis describes the principle of measurement, alternative equivalent circuits, the impedance of electrochemical cell and the analyse of recorded datas. In the practical part was assembled the functional lead-acid cell. After that, experimental measurement was passed on the lead-acid cell in discharge and in a different concentration of electrolyte. In the last part was created the simulation of treatment of an electrochemical cell in the development solution Agilent VEE and after that all the measurement results were compared with the simulation.

After decades of routine operation, the hydropower industry faces new challenges. Large-scale integration of other renewable sources of generation in the power system accentuates the role of hydropower as a regulating resource. At the same time, an extensive reinvestment programme has commenced where many old components and apparatus are being refurbished or replaced. Introduction of new technical solutions in existing power plants requires good systems knowledge and careful consideration. Important tools for research, development and analysis are suitable mathematical models, numerical simulation methods and laboratory equipment. This doctoral thesis is devoted to studies of the electromechanical interaction between hydropower units and the power system. The work encompasses development of mathematical models, empirical methods for system identification, as well as numerical and experimental studies of hydropower generator and power system interaction. Two generator modelling approaches are explored: one based on electromagnetic field theory and the finite element method, and one based on equivalent electric circuits. The finite element model is adapted for single-machine infinite-bus simulations by the addition of a network equivalent, a mechanical equation and a voltage regulator. Transient simulations using both finite element and equivalent circuit models indicate that the finite element model typically overestimates the synchronising and damping properties of the machine. Identification of model parameters is performed both numerically and experimentally. A complete set of equivalent circuit parameters is identified through finite element simulation of standard empirical test methods. Another machine model is identified experimentally through frequency response analysis. An extension to the well-known standstill frequency response (SSFR) test is explored, which involves measurement and analysis of damper winding quantities. The test is found to produce models that are suitable for transient power system analysis. Both experimental and numerical studies show that low resistance of the damper winding interpole connections are vital to achieve high attenuation of rotor angle oscillations. Hydropower generator and power system interaction is also studied experimentally during a full-scale startup test of the Nordic power system, where multiple synchronised data acquisition devices are used for measurement of both electrical and mechanical quantities. Observation of a subsynchronous power oscillation leads to an investigation of the torsional stability of hydropower units. In accordance with previous studies, hydropower units are found to be mechanically resilient to subsynchronous power oscillations. However, like any other generating unit, they are dependent on sufficient electrical and mechanical damping. Two experimentally obtained hydraulic damping coefficients for a large Francis turbine runner are presented in the thesis.