1,134 research outputs found

    Development of a Miniature Electrostatic Accelerometer /MESA/ for low g applications Summary report

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    Design, fabrication, and testing of miniature digital electrostatic accelerometer for low gravity measurements in spac

    Synthesis of the System Modeling and Signal Detecting Circuit of a Novel Vacuum Microelectronic Accelerometer

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    A novel high-precision vacuum microelectronic accelerometer has been successfully fabricated and tested in our laboratory. This accelerometer has unique advantages of high sensitivity, fast response, and anti-radiation stability. It is a prototype intended for navigation applications and is required to feature micro-g resolution. This paper briefly describes the structure and working principle of our vacuum microelectronic accelerometer, and the mathematical model is also established. The performances of the accelerometer system are discussed after Matlab modeling. The results show that, the dynamic response of the accelerometer system is significantly improved by choosing appropriate parameters of signal detecting circuit, and the signal detecting circuit is designed. In order to attain good linearity and performance, the closed-loop control mode is adopted. Weak current detection technology is studied, and integral T-style feedback network is used in I/V conversion, which will eliminate high-frequency noise at the front of the circuit. According to the modeling parameters, the low-pass filter is designed. This circuit is simple, reliable, and has high precision. Experiments are done and the results show that the vacuum microelectronic accelerometer exhibits good linearity over -1 g to +1 g, an output sensitivity of 543 mV/g, and a nonlinearity of 0.94 %

    Capacitive Microaccelerometers And Fabrication Methods

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    Disclosed are moveable microstructures comprising in-plane capacitive microaccelerometers, with submicro-gravity resolution (17 pF/g). Themicrostructures are fabricated in thick(> 100 µm) siliconon-insulator (SOI) substrates or silicon substrates using a two-mask fully-dry release process that provides large seismic mass (> 10 milli-g), reduced capacitive gaps, and reduced in-plane stiffness. Fabricated devices may be interfaced to a high resolution switched-capacitor CMOS IC that eliminates the need for area-consuming reference capacitors. The measured sensitivity is 83 mV/mg (17 pF/g) and the output noise floor is -91 dBm/Hz at 10 Hz (corresponding to an acceleration resolution of 170 ng/√Hz). The IC consumes 6 mW power and measures 0.65 mm2 core area.Georgia Tech Research Corporatio

    Force feedback linearization for higher-order electromechanical sigma-delta modulators.

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    Abstract A higher-order electromechanical sigma–delta modulator can greatly improve the signal-to-noise ratio compared with a second-order loop that only uses the sensing element as a loop filter. However, the electrostatic force feedback on the proof mass is inherently nonlinear, which will produce harmonics in the output spectrum and limits the total signal-to-noise and distortion ratio. High performance inertial sensors, which use sigma–delta modulators as a closed-loop control system, have strict requirements on the output signal distortion. In this paper, nonlinear effects from the force feedback and pick-off circuits are analysed and a strategy for force feedback linearization is put forward which can considerably improve the signal-to-noise and distortion ratio. A PCB prototype of a fifth-order electromechanical modulator with a bulk micromachined accelerometer was used to demonstrate the concept

    A sigma-delta interface built-in self-test and calibration for microelectromechanical system accelerometer's utilizing interpolation method

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    This work presents the capacitive micromechanical accelerometer with a completely differential high-order switched capacitor sigma-delta modulator interface. Such modulation interface circuit generates one-bit output data using a third sigma-delta modulator low-noise front-end, doing away with the requirement for a second enhanced converter of resolution to encode the feedback route analog signal. A capacitive micromechanical sensor unit with just a greater quality factor has been specifically employed to give greater resolution. The closed-loop and electrical correction control are used to dampen the high-Q values to get the system's stability with high-order. This microelectromechanical system (MEMS) capacitive accelerometer was calibrated using a lookup table and Akima interpolation to find manufacturing flaws by recalculating voltage levels for the test electrodes. To determine the proper electrode voltages for fault compensation, COMSOL software simulates a number of defects upon that spring as well as the fingers of the sensor system. When it comes time for the feedback phase of a proof mass displacement correction, these values are subsequently placed in the lookup table

    Optimal and Robust Design Method for Two-Chip Out-of-Plane Microaccelerometers

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    In this paper, an optimal and robust design method to implement a two-chip out-of-plane microaccelerometer system is presented. The two-chip microsystem consists of a MEMS chip for sensing the external acceleration and a CMOS chip for signal processing. An optimized design method to determine the device thickness, the sacrificial gap, and the vertical gap length of the M EMS sensing element is applied to minimize the fundamental noise level and also to achieve the robustness to the fabrication variations. In order to cancel out the offset and gain variations due to parasitic capacitances and process variations, a digitally trimmable architecture consisting of an 11 bit capacitor array is adopted in the analog front-end of the CMOS capacitive readout circuit. The out-of-plane microaccelerometer has the scale factor of 372 mV/g∼389 mV/g, the output nonlinearity of 0.43% FSO∼0.60% FSO, the input range of ±2 g and a bias instability of 122 μg∼229 μg. The signal-to-noise ratio and the noise equivalent resolution are measured to be 74.00 dB∼75.23 dB and 180 μg/rtHz∼190 μg/rtHz, respectively. The in-plane cross-axis sensitivities are measured to be 1.1%∼1.9% and 0.3%∼0.7% of the out-of-plane sensitivity, respectively. The results show that the optimal and robust design method for the MEMS sensing element and the highly trimmable capacity of the CMOS capacitive readout circuit are suitable to enhance the die-to-die uniformity of the packaged microsystem, without compromising the performance characteristics

    Silicon micromachined resonant accelerometer with CMOS interface circuits

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    Ph.DDOCTOR OF PHILOSOPH

    CAPACITIVE BASED CMOS-MEMS MICROACTUATOR FOR BIOMEDICAL APPLICATION

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    The purpose of this project is to design electrostatic microacluator for biomedical application using CMOS and MEMS. The technology of microelectromechanical system (MEMS) is widely used in many daily applications such as aerospace Microsystems, biomedical applications, consumer electronic devices and so on. Specifically in biomedical applications, the experimentation always related to a macro meter objects manipulation. Due to that constraint, the tools that being used are also in macro meter-sized. Therefore, basically this project implements a micro actuator with an integrated capacitive force sensor which can be used in biomedical applications in handling cells and micron-size objects. An actuator for macro-size objects is already in market and it is not suitable to be used to the small cells like micron-cells. In my research, I had determined that there are several actuation principles of different types of gripper which are eleclmstatic, electromagnetic, electro thermal and electro osmotic. The problem where the procedure of handling the active cells must be taken seriously now can be solved with the invention of the grippers. Tn order to design the structure of this device, certain requirements should be taken into considerations. This project will improve the design for microactuator by applying electrostatic principles. The device then simulated in fvlATLAB to find other parameters needed for the microgripper. The performance of this device will be determined by its sensitivity for gripping the Hela cells. The device can be operated with 58V of actuator voltage supply and produced 9.9238 J.lN to have displacement of 1 J.lm. The results show that the device can be used with low voltage and able to be used for cell manipulations

    Micro-g MEMS accelerometer based on time measurement

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    Programa Doutoral em Engenharia Electrónica e de ComputadoresThe MEMS sensor market has experienced an amazing growth on the last decades, with accelerometers being one of the pioneers pushing the technology into widespread use with its applications on automotive industry. Since then, accelerometers have been gradually replacing conventional sensors due mainly to its lower cost. As the performance of MEMS accelerometers improves, the applications range where they replace conventional accelerometers increases. Nowadays, there is still a large range of applications for which suitable MEMS accelerometers are yet to be developed. This work focuses on the development of a high performance accelerometer taking advantage of the high sensitivity of a non-linear phenomenon that occurs in electrostatically actuated movable capacitive microdevices: electrostatic pull-in. Although the pull-in effect has been known for more than 40 years, it is usually avoided when dealing with movable microstructures as it leads to a region of instability, where the position of movable parts cannot be fully controlled. In the last decade, the pull-in displacement profile of 1-DOF parallel-plates devices has been the subject of research that revealed the presence of a so-called meta-stability. This meta-stability occurs in specific damping and voltage actuation conditions and translates as a non-linear displacement profile, rather than simple time-of-flight. This feature makes the pull-in time duration significantly longer, and it happens to be extremely sensitive to intervenient forces, such as external acceleration. Basically, measuring the pull-in time of specifically designed microstructures (while maintaining the other parameters constant) allows the measurement of the external acceleration that acts on the system. Using a pull-in time measurement rather than direct capacitance/displacement/acceleration transduction presents several advantages. The most important is the fact that time can be measured very accurately with technology readily available. For instance, if one uses a 100MHz clock on the time counting mechanism, which corresponds to a time measurement resolution of 100 ns, given the 0.26 μs/μg sensitivity of the accelerometer developed in this work, an acceleration resolution of 0.38 μg could be achieved. One of the main challenges of the time based accelerometer development is the damper design, as damping is of outmost importance in defining the accelerometer performance parameters, namely sensitivity and noise. A new squeeze-film damper geometry design has been presented and studied. It consists of flow channels implemented on the parallel-plates that relieve the squeeze-film damping pressures generated when the device is moving. This geometry has proved to be very effective in increasing the capacitance/damping ratio in parallel-plates, which was up to now a great challenge of in-plane parallel-plates design. This work reports the development of an open-loop accelerometer with 0.26 μs/μg sensitivity and 2.7 μg /√Hz noise performance. The MEMS structures used for its experimental implementation were fabricated using a commercially available SOI micromachining process. The main drawbacks of this accelerometer were the low system bandwidth and non-linearity. Closed-loop approaches using electrostatic feedback were explored in this work in order to overcome these limitations, and the dynamic range was successfully extended to 109 dB along with improvements on the linearity. From the thorough damping study performed in this work, a new application for the pullin time using the same microstructures was developed. It consists of a gas viscosity sensing application. At the low frequencies operated, damping is directly proportional to the viscosity of the gas medium. The experimental results obtained with gases with viscosities ranging from 8 μP to 18 μP have shown a sensitivity of 2 ms/μP, making the pull-in time viscosity sensor a very promising approach.Nas últimas décadas assistiu-se a um imenso crescimento no mercado de sensors MEMS, tendo os acelerómetros sido uma das maiores forças impulsionadoras desse crescimento devido às suas aplicações na indústria automóvel. Desde então, a gama de aplicações destes sensores expandiu-se multidirecionalmente, novas aplicações emergiram e acelerómetros convencionais em aplicações já existentes foram substituídos por acelerómetros MEMS. Isto deve-se essencialmente ao seu baixo custo e pequenas dimensões. Há no entanto, aplicações para as quais o desempenho dos acelerómetros MEMS ainda não é suficiente. O objectivo deste trabalho é desenvolver um acelerómetro de elevado desempenho tirando partido da elevada sensibilidade do efeito de pull-in a forças externas tais como a aceleração. O efeito de pull-in, descrito pela primeira vez há mais de 40 anos, ocorre em dispositivos capacitivos com partes móveis. Este é um efeito não-linear geralmente evitado/indesejado, uma vez que se traduz numa instabilidade que dificulta o controlo da posição das partes móveis. Na última década foi dedicada alguma investigaçao científica a este fenómeno, tendo sido descoberta a existência de um perfil de deslocamento particular, denominado meta-estabilidade, em determinadas condições de amortecimento e de actuação electrostática. Esta característica do pull-in torna a sua duração extremamente sensível a variações nas forças intervenientes, incluindo aceleração externa. Assim sendo, a medição do tempo de pull-in de micro-estruturas especificamente concebidas para o efeito pode ser utilizada para medir aceleração. Esta abordagem apresenta vantagens significativas em comparação com a transdução direta de capacidade para aceleração (caso da generalidade dos acelerómetros capacitivos). Nomeadamente, a variável tempo pode ser medida com elevada precisão com relativa facilidade e sem necessidade de desenvolvimentos tecnológicos (o que não é o caso da medição de capacidade). Por exemplo, o uso de uma frequência de relógio de 100 MHz no mecanismo de contagem de tempo permite uma resolução de 100 ns na medição de tempo, o que corresponde, considerando a sensibilidade de 0.26 μs/μg do acelerómetro desenvolvido neste trabalho, a uma resolução na medição de acceleração de 0.38μg. Um dos maiores desafios do desenvolvimento de um acelerómetro baseado no tempo de pull-in é o desenho do amortecedor, pois a sensibilidade e o ruído/resolução do sensor final dependem do nível de amortecimento. Uma nova geometria para o amortecedor (estabelecido por um mecanismo de squeeze-film) é apresentada e estudada neste trabalho. Esta consiste em abrir canais nas placas paralelas facilitando assim o fluxo de ar quando as placas se movem. Ficou provado que esta geometria é eficaz na redução da razão capacidade/amortecimento, o que constituía um problema recorrente no desenho de dispositivos de placas paralelas in-plane. Neste trabalho é descrito o desenvolvimento de um acelerómetro em malha aberta com uma sensibilidade de 0.26 μs/μg e 2.7 μg /√Hz de ruído. As estruturas MEMS utilizadas na sua implementação foram fabricadas num processo de microfabrico SOI comercial. As principais desvantagens desta abordagem são pequena gama dinâmica devido à não-linearidade da resposta. Neste trabalho foram exploradas abordagens em malha fechada, usando feedback electrostático, de modo a ultrapassar estas limitações, tendo sido alcançado um aumento da gama dinâmica para 109 dB, com grandes melhoria na linearidade. Uma nova aplicação para o tempo de pull-in foi também desenvolvida: medição de viscosidade de gases. Uma vez que as microstruturas utilizadas são operadas a baixas frequências, o amortecimento é proporcional à viscosidade. O estudo efectuado mostra que o tempo de pull-in é muito sensível ao amortecimento e portanto a variações de viscosidade. Os resultados experimentais obtidos com gases e misturas de gases com viscosidades entre 8 μP e 18 μP mostraram uma sensibilidade de 2 ms/μP, confirmando o potencial da utilização de tempo de pull-in na medição de viscosidade.The author, Rosana Maria Alves Dias, was supported by Portuguese Foundation for Science and Technology (SFRH/BD/46030/2008)
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