594 research outputs found

    Detailed Study of Amplitude Nonlinearity in Piezoresistive Force Sensors

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    This article upgrades the RC linear model presented for piezoresistive force sensors. Amplitude nonlinearity is found in sensor conductance, and a characteristic equation is formulated for modeling its response under DC-driving voltages below 1 V. The feasibility of such equation is tested on four FlexiForce model A201-100 piezoresistive sensors by varying the sourcing voltage and the applied forces. Since the characteristic equation proves to be valid, a method is presented for obtaining a specific sensitivity in sensor response by calculating the appropriate sourcing voltage and feedback resistor in the driving circuit; this provides plug-and-play capabilities to the device and reduces the start-up time of new applications where piezoresistive devices are to be used. Finally, a method for bypassing the amplitude nonlinearity is presented with the aim of reading sensor capacitance

    Modelado de sensores piezoresistivos y uso de una interfaz basada en guantes de datos para el control de impedancia de manipuladores robóticos

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    Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Arquitectura de Computadores y Automática, leída el 21-02-2014Sección Deptal. de Arquitectura de Computadores y Automática (Físicas)Fac. de Ciencias FísicasTRUEunpu

    Device modelling for bendable piezoelectric FET-based touch sensing system

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    Flexible electronics is rapidly evolving towards devices and circuits to enable numerous new applications. The high-performance, in terms of response speed, uniformity and reliability, remains a sticking point. The potential solutions for high-performance related challenges bring us back to the timetested silicon based electronics. However, the changes in the response of silicon based devices due to bending related stresses is a concern, especially because there are no suitable models to predict this behavior. This also makes the circuit design a difficult task. This paper reports advances in this direction, through our research on bendable Piezoelectric Oxide Semiconductor Field Effect Transistor (POSFET) based touch sensors. The analytical model of POSFET, complimented with Verilog-A model, is presented to describe the device behavior under normal force in planar and stressed conditions. Further, dynamic readout circuit compensation of POSFET devices have been analyzed and compared with similar arrangement to reduce the piezoresistive effect under tensile and compressive stresses. This approach introduces a first step towards the systematic modeling of stress induced changes in device response. This systematic study will help realize high-performance bendable microsystems with integrated sensors and readout circuitry on ultra-thin chips (UTCs) needed in various applications, in particular, the electronic skin (e-skin)

    Dynamic Force/Position Modeling of a one-DOF Smart Piezoelectric Micro-Finger with Sensorized End-Effector.

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    International audienceIn this paper, a generic microscale system is studied where a smart microsystem composed of an active based material actuator, sensorized structure and transformation system is studied. This problem is important at the microscale because it offers a force measurement of the applied force by the actuator to a flexible environment which enables to understand the interaction between the complete smart microsystem and the environment and to design and control the interaction between the system and the environment. A special case where a sensorized end-effector is fixed on the tip of a piezoelectric actuator is detailed. Integrating a sensorized end-effector influences the behavior of the smart microfinger and is not studied in recent works. The complete finger, which is called in this paper smart finger, consists of a piezoelectric actuator, an end-effector and a novel piezoresistive force sensor. A complete model is developed for generating both force and displacement at the finger's tip while interaction with a flexible environment. A nonlinear model of the piezoelectric actuator is considered and a complete model is developed taking into account the frequency dependent hysteresis of the piezoelectric actuator. The model of the hysteresis is based on the Bouc-Wen method which simplifies the parameter estimation. The complete dynamic force/position model of the finger is validated experimentally with small errors (less than 10%)

    Nonlinearity in nanomechanical cantilevers

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    Euler-Bernoulli beam theory is widely used to successfully predict the linear dynamics of micro- and nanocantilever beams. However, its capacity to characterize the nonlinear dynamics of these devices has not yet been rigorously assessed, despite its use in nanoelectromechanical systems development. In this article, we report the first highly controlled measurements of the nonlinear response of nanomechanical cantilevers using an ultralinear detection system. This is performed for an extensive range of devices to probe the validity of Euler-Bernoulli theory in the nonlinear regime. We find that its predictions deviate strongly from our measurements for the nonlinearity of the fundamental flexural mode, which show a systematic dependence on aspect ratio (length/width) together with random scatter. This contrasts with the second mode, which is always found to be in good agreement with theory. These findings underscore the delicate balance between inertial and geometric nonlinear effects in the fundamental mode, and strongly motivate further work to develop theories beyond the Euler-Bernoulli approximation

    MEMS Accelerometers

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    Micro-electro-mechanical system (MEMS) devices are widely used for inertia, pressure, and ultrasound sensing applications. Research on integrated MEMS technology has undergone extensive development driven by the requirements of a compact footprint, low cost, and increased functionality. Accelerometers are among the most widely used sensors implemented in MEMS technology. MEMS accelerometers are showing a growing presence in almost all industries ranging from automotive to medical. A traditional MEMS accelerometer employs a proof mass suspended to springs, which displaces in response to an external acceleration. A single proof mass can be used for one- or multi-axis sensing. A variety of transduction mechanisms have been used to detect the displacement. They include capacitive, piezoelectric, thermal, tunneling, and optical mechanisms. Capacitive accelerometers are widely used due to their DC measurement interface, thermal stability, reliability, and low cost. However, they are sensitive to electromagnetic field interferences and have poor performance for high-end applications (e.g., precise attitude control for the satellite). Over the past three decades, steady progress has been made in the area of optical accelerometers for high-performance and high-sensitivity applications but several challenges are still to be tackled by researchers and engineers to fully realize opto-mechanical accelerometers, such as chip-scale integration, scaling, low bandwidth, etc

    Nonlinear Mode Coupling and Internal Resonances in MoS2 Nanoelectromechanical System

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    Atomically thin two dimensional (2D) layered materials have emerged as a new class of material for nanoelectromechanical systems (NEMS) due to their extraordinary mechanical properties and ultralow mass density. Among them, graphene has been the material of choice for nanomechanical resonator. However, recent interest in 2D chalcogenide compounds has also spurred research in using materials such as MoS2 for NEMS applications. As the dimensions of devices fabricated using these materials shrink down to atomically thin membrane, strain and nonlinear effects have become important. A clear understanding of nonlinear effects and the ability to manipulate them is essential for next generation sensors. Here we report on all electrical actuation and detection of few layers MoS2 resonator. The ability to electrically detect multiple modes and actuate the modes deep into nonlinear regime enables us to probe the nonlinear coupling between various vibrational modes. The modal coupling in our device is strong enough to detect three distinct internal resonances

    Modeling and analysis of a resonant nanosystem

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    The majority of investigations into nanoelectromechanical resonators focus on a single area of the resonator\u27s function. This focus varies from the development of a model for a beam\u27s vibration, to the modeling of electrostatic forces, to a qualitative explanation of experimentally-obtained currents. Despite these efforts, there remains a gap between these works, and the level of sophistication needed to truly design nanoresonant systems for efficient commercial use. Towards this end, a comprehensive system model for both a nanobeam resonator and its related experimental setup is proposed. Furthermore, a simulation arrangement is suggested as a method for facilitating the study of the system-level behavior of these devices in a variety of cases that could not be easily obtained experimentally or analytically. ^ The dynamics driving the nanoresonator\u27s motion, as well as the electrical interactions influencing the forcing and output of the system, are modeled, experimentally validated, and studied. The model seeks to develop both a simple circuit representation of the nanoresonator, and to create a mathematical system that can be used to predict and interpret the observed behavior. Due to the assumptions used to simplify the model to a point of reasonable comprehension, the model is most accurate for small beam deflections near the first eigenmode of the beam. ^ The process and results of an experimental investigation are documented, and compared with a circuit simulation modeling the full test system. The comparison qualitatively proves the functionality of the model, while a numerical analysis serves to validate the functionality and setup of the circuit simulation. The use of the simulation enables a much broader investigation of both the electrical behavior and the physical device\u27s dynamics. It is used to complement an assessment of the tuning behavior of the system\u27s linear natural frequency by demonstrating the tuning behavior of the full nonlinear response. The simulation is used to demonstrate the difficulties with the contemporary mixing approach to experimental data collection and to complete a variety of case studies investigating the use of the nanoresonator systems in practical applications, such as signal filtering. Many of these case studies would be difficult to complete analytically, but results are quickly achieved through the use of the simulation

    Using the Nonlinear Duffing Effect of Piezoelectric Micro-Oscillators for Wide-Range Pressure Sensing

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    This paper investigates the resonant behaviour of silicon-based micro-oscillators with a length of 3600 µm, a width of 1800 µm and a thickness of 10 µm over a wide range of ambient gas (N2 ) pressures, extending over six orders of magnitude from 10−3 mbar to 900 mbar. The oscillators are actuated piezoelectrically by a thin-film aluminium-nitride (AlN) layer, with the cantilever coverage area being varied from 33% up to 100%. The central focus is on nonlinear Duffing effects, occurring at higher oscillation amplitudes. A theoretical background is provided. All relevant parameters describing a Duffing oscillator, such as stiffness parameters for each coverage size as well as for different bending modes and more complex modes, are extracted from the experimental data. The so-called 2nd roof-tile-shaped mode showed the highest stiffness value of −97.3·107 m−2 s −2 . Thus, it was chosen as being optimal for extended range pressure measurements. Interestingly, both a spring softening effect and a spring hardening effect were observed in this mode, depending on the percentage of the AlN coverage area. The Duffing-effect-induced frequency shift was found to be optimal for obtaining the highest pressure sensitivity, while the size of the hysteresis loop is also a very useful parameter because of the possibility of eliminating the temperature influences and long-term drift effects of the resonance frequency. An reasonable application-specific compromise between the sensitivity and the measurement range can be selected by adjusting the excitation voltage, offering much flexibility. This novel approach turns out to be very promising for compact, cost-effective, wide-range pressure measurements in the vacuum range

    On New Applications and Sensitivity Enhancement of Cantilever-based Sensing Systems

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    Cantilever-based Sensing Systems (CSS) have become a focal area for research with the rise of micro- and nanotechnology. History has led us to use cantilever beams as one of the foremost sensing devices for small scale applications, beginning with the atomic force microscopy, and then being expanded into numerous sensor devices. The CSS include such applications as accelerometers, thermal and chemical sensors which are expanding into the applications of mass sensing and material characterization. Soon, this technology may be used in \u27lab on chip\u27 biosensing applications. This study covers the experimentation into new CSS applications and sensitivity enhancement. In order to do this, an overview of CSS is presented. The history of cantilever is covered from its humble beginnings to the recent explosion of interest. Next, working principles, operational modes and microfabrication of the CSS are briefly overviewed. Experimentation into novel CSS applications for material characterization of a thermally sensitive polymer is discussed first. To accomplish this, an array of cantilevers is used to isolate effect of the polymer. The results show that static mode CSS using optical transduction can be effectively used to sense polymers lower critical solution temperature via measuring the beam deflection caused by surface stress due to the polymer instead of repeated traditional surface hydrophobicity tests. In the next part of the thesis, a new CSS design is fabricated and used for mass detection. This new design utilizes stress measurements of an integrated strain gauge with reference cantilever. The new design allows for the measurement of the frequency shift while compensating for environmental effects. The CSS design is characterized and tested utilizing the addition of Au nanoparticles as functional added mass. The final section of this study focuses on an exciting new CSS sensitivity enhancement technique. This new technique utilizes a delayed feedback to create stable limit cycles. The amplitude of these limit cycles is shown to be highly sensitive to changes in tip mass added or attached to the cantilever. The theory is presented and verified utilizing macroscale experimentation. Both theoretical and experimental results demonstrate a two-orders-of magnitude sensitivity enhancement over traditional frequency shift methods
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