135 research outputs found

    Electrostatic micro actuators for mirror and other applications

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    Micro-electro-mechanical systems (MEMS) based electrostatic micro actuators are becoming important building blocks for innovations in optical signal processing and computing systems due to their inherently small size, high density, high speed and low power consumption. Generally, the principle of operation in these systems can be described as: an electrostatic attractive force causes a mechanical rotation, translation or deformation of a mirror plate, controlling the power, phase or direction of a light beam while it propagates through some medium or through free space. The fast paced, competitive research and development efforts widely being undertaken, both in academia and industry, are demanding simple, fast methods for the design of quasi-static Mirror systems, with a large, stable, analog range of operation. In addition fast prototyping methods are in demand for the proof of concept fabrication of these mirror designs. This dissertation addresses these research topics by presenting 1) a general capacitance-based quasi-static design theory and methodology for electrostatic micro actuators, 2) a study of electrostatic travel range extension methods to minimize the pull in effect, and 3) a fast prototyping approach for electrostatic mirror devices using ultra thin silicon wafer bonding and deep reactive etching technologies. In the first topic, two fundamental capacitance-based differential equations are developed for the quasi-static description of electrostatic micro actuator systems. A structural equation is developed to represent the coupled electromechanical response of the system under applied voltage bias, and a pull in equation is determined to identify the intrinsic collapse point beyond which an actuator system no longer has a stable equilibrium, the so-called pull in point. These equations are applied to various complex electrostatic micro actuator systems to predict specific quasi-static behavior. A unitless equation is introduced for each actuator category, and based on it, a design method is proposed to quickly provide specifications for a particular desired performance of an electrostatically actuated micro-mirror system. In the second topic, and as an application of the proposed design methodology, the travel range extension issue is addressed leading to two new methods to increase travel range by sacrificing driving voltage. Both methods are applied directly in the electrostatic domain. The first method utilizes a series capacitor to modulate the effective actuation voltage across the variable capacitor micro mirror. The second method utilizes negative feedback due to the coulombic repulsive interaction between charge layers inserted between the micro mirror electrodes. An analytical study of representative mirror devices is presented, and verification of the travel range extension models is provided via finite element analysis (FEA) simulation. As a further application of the design methodology developed as part of the first research topic, three state-of-the-art micro actuator systems are designed and studied: 1) a variable optical attenuator (VOA), 2) an optical cross connect device (OXC) and 3) an electrostatically tunable, wavelength selecting device. FEA simulations are used to confirm design specifications. In the third research topic, VOA and electrostatically tunable, wavelength selecting devices are fabricated using fast prototyping via ultra thin wafer bonding and deep reactive etching (DRIIE) technologies. Both silicon wet-etching and SU-8 patterning are investigated for the formation of mirror gaps. Testing in the mechanical domain and partial device characterization in the optical domain is provided for these devices. Finally, as a demonstration that the actuator design approach developed in this thesis can be applied to systems other than micro mirrors, we use the approach to design an innovative true mass flow sensor using an electrostatic resonant beam as the sensing element

    Design and Simulation of a Novel Magnetic Microactuator for Microrobots in Lab-On-a-Chip Applications

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    This article presents the design of a magnetic microactuator comprising soft magnetic material blocks and flexible beams. The modular layout of the proposed microactuator promotes scalability towards different microrobotic applications using low magnetic fields.  The presented microactuator consists of three soft magnetic material (Ni-Fe 4750) blocks connected together via two Polydimethylsiloxane (PDMS) semi-circular beams. A detailed design approach is highlighted giving considerations toward compactness, range of motion and force characteristics of the actuator. The actuator displacement and force characteristics are approximately linear in the magnetic field strength range of 80-160 kA/m. It can achieve maximum displacements of 111.6 µm (at 160 kA/m) during extension and 10.7 µm (at 80 kA/m) during contraction under no-load condition. The maximum force output of the microactuator, computed through a contact simulation, was 404.3 nN at a magnetic field strength of 160 kA/m. The microactuator achieved stroke angles up to 18.4 in a study where the microactuator was integrated with a swimming microrobot executing rowing motion using an artificial appendage, providing insight into the capabilities of actuating untethered microrobots

    AN EFFICIENT NUMERICAL SCHEME TO DETERMINE THE PULL-IN PARAMETERS OF AN ELECTROSTATIC MICRO-ACTUATOR WITH CONTACT TYPE NONLINEARITY

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    ABSTRACT In this article, we present an efficient numerical scheme based on the Rayleigh-Ritz method to determine the pull-in parameters of electrostatically actuated microbeams exploiting contact type nonlinearity. A case of an electrostatically actuated cantilevered microbeam is first analyzed using the RayleighRitz energy technique. The deflection of the microbeam is approximated by a polynomial trial function. The principle of the stationary potential energy leads to a highly nonlinear algebraic equation, which is solved to determine the deflected shape of the microbeam. A novel voltage iteration algorithm is implemented to determine the critical voltage at which the pullin occurs. The analysis is then extended to the case of cantilever beam making use of the contact type nonlinearity to exhibit an extended travel range. The present case consists of a compression spring getting engaged at the cantilever tip at the critical point where the pull-in occurs. An increase in both travel range and pull-in voltage is observed with the introduction of the compression spring. A performance index is suggested, which combines the gain in the travel range together with the concomitant increase in the pull-in voltage. This index is used to determine the critical bound for the choice of the stiffness of the newly introduced compression member

    New Formulation for Finite Element Modeling Electrostatically DrivenMicroelectromechanical Systems

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    The increased complexity and precision requirements of microelectromechanical systems(MEMS) have brought about the need to develop more reliable and accurate MEMS simulation tools. To better capture the physical behavior encountered, several finite elementanalysis techniques for modeling electrostatic and structural coupling in MEMS devices havebeen developed in this project. Using the principle of virtual work and an approximationfor capacitance, a new 2-D lumped transducer element for the static analysis of MEMS hasbeen developed. This new transducer element is compatible to 2-D structural and beamelements. A novel strongly coupled 3-D transducer formulation has also been developed tomodel MEMS devices with dominant fringing electrostatic fields. The transducer is compatible with both structural and electrostatic solid elements, which allows for modeling complexdevices. Through innovative internal morphing capabilities and exact element integrationthe 3-D transducer element is one of the most powerful coupled field FE analysis tools available. To verify the accuracy and effectiveness of both the 2-D and 3-D transducer elements a series of benchmark analyses were conducted. More specifically, the numerically predicted results for the misalignment of lateral combdrive fingers were compared to available analytical and modeling techniques. Electrostatic uncoupled 2-D and 3-D finite element models werealso used to perform energy computations during misalignment. Finally, a stability analysisof misaligned combdrive was performed using a coupled 2-D finite element approach. Theanalytical and numerical results were compared and found to vary due to fringing fields

    Linear-Quadratic Control of a MEMS Micromirror Using Kalman Filtering

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    The deflection limitations of electrostatic flexure-beam actuators are well known. Specifically, as the beam is actuated and the gap traversed, the restoring force necessary for equilibrium increases proportionally with the displacement to first order, while the electrostatic actuating force increases with the inverse square of the gap. Equilibrium, and thus stable open-loop voltage control, ceases at one-third the total gap distance, leading to actuator snap-in. A Kalman Filter is designed with an appropriately complex state dynamics model to accurately estimate actuator deflection given voltage input and capacitance measurements, which are then used by a Linear Quadratic controller to generate a closed-loop voltage control signal. The constraints of the latter are designed to maximize stable control over the entire gap. The design and simulation of the Kalman Filter and controller are presented and discussed, with static and dynamic responses analyzed, as applied to basic, 100 micrometer by 100 micrometer square, flexure-beam-actuated micromirrors fabricated by PolyMUMPs. Successful application of these techniques enables demonstration of smooth, stable deflections of 50% and 75% of the gap

    Stepper microactuators driven by ultrasonic power transfer

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    Advances in miniature devices for biomedical applications are creating ever-increasing requirements for their continuous, long lasting, and reliable energy supply, particularly for implanted devices. As an alternative to bulky and cost inefficient batteries that require occasional recharging and replacement, energy harvesting and wireless power delivery are receiving increased attention. While the former is generally only suited for low-power diagnostic microdevices, the latter has greater potential to extend the functionality to include more energy demanding therapeutic actuation such as drug release, implant mechanical adjustment or microsurgery. This thesis presents a novel approach to delivering wireless power to remote medical microdevices with the aim of satisfying higher energy budgets required for therapeutic functions. The method is based on ultrasonic power delivery, the novelty being that actuation is powered by ultrasound directly rather than via piezoelectric conversion. The thesis describes a coupled mechanical system remotely excited by ultrasound and providing conversion of acoustic energy into motion of a MEMS mechanism using a receiving membrane coupled to a discrete oscillator. This motion is then converted into useful stepwise actuation through oblique mechanical impact. The problem of acoustic and mechanical impedance mismatch is addressed. Several analytical and numerical models of ultrasonic power delivery into the human body are developed. Major design challenges that have to be solved in order to obtain acceptable performance under specified operating conditions and with minimum wave reflections are discussed. A novel microfabrication process is described, and the resulting proof-of-concept devices are successfully characterized.Open Acces

    A Large-Stroke Electrostatic Micro-Actuator

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    Voltage-driven parallel-plate electrostatic actuators suffer from an operation range limit of 30% of the electrostatic gap; this has restrained their application in microelectromechanical systems. In this paper, the travel range of an electrostatic actuator made of a micro-cantilever beam above a fixed electrode is extended quasi-statically to 90% of the capacitor gap by introducing a voltage regulator (controller) circuit designed for low-frequency actuation. The voltage regulator reduces the actuator input voltage, and therefore the electrostatic force, as the beam approaches the fixed electrode so that balance is maintained between the mechanical restoring force and the electrostatic force. The low-frequency actuator also shows evidence of high-order superharmonic resonances that are observed here for the first time in electrostatic actuators

    Laminated chemical and physical micro-jet actuators based on conductive media

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    This dissertation presents the development of electrically-powered, lamination-based microactuators for the realization of large arrays of high impulse and short duration micro-jets with potential applications in the field of micro-electro-mechanical systems (MEMS). Microactuators offer unique control opportunities by converting the input electrical or chemical energy stored in a propellant into useful mechanical energy. This small and precise control obtained can potentially be applied towards aerodynamic control and transdermal drug delivery applications. This thesis discusses the development of both chemical and physical microactuators and characterizes their performance with focus towards the feasibility of using them for a specific application. The development of electrically powered microactuators starts by fabricating an array of radially firing microactuators using lamination-based micro fabrication techniques that potentially enable batch fabrication at low cost. The microactuators developed in this thesis consist of three main parts: a micro chamber in which the propellant is stored; two electrode structures through which electrical energy is supplied to the propellant; and a micro nozzle through which the propellant or released gases from the propellant are expanded as a jet. The fabricated actuators are then integrated with MEMS-process-compatible propellants and optimized to produce rapid ignition of the propellant and generate a fluidic jet. This rapid ignition is achieved either by making the propellant itself conductive, thus, passing an electric current directly through the propellant; or by discharging an arc across the propellant by placing it between two closely spaced electrodes. The first concept is demonstrated with chemical microactuators for the application of projectile maneuvering and the second concept is demonstrated with physical microactuators for transdermal drug delivery application. For both the actuators, the propellant integrated microactuators are characterized for performance in terms of impulse delivered, thrust generated and duration of the jet. The experimentally achieved results are validated by comparing with results from theoretical modeling. Finally, the feasibility of using chemical microactuators for maneuvering the path of a 25 mm projectile spinning at 500 Hz is discussed and the feasibility of applying the physical microactuators for increasing skin's permeability to drug analog molecules is studied.Ph.D.Committee Chair: Allen, Mark; Committee Member: Allen, Sue; Committee Member: Glezer, Ari; Committee Member: Koros, Williams; Committee Member: Prausnitz, Mar

    Microelectromechanical Systems and Devices

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    The advances of microelectromechanical systems (MEMS) and devices have been instrumental in the demonstration of new devices and applications, and even in the creation of new fields of research and development: bioMEMS, actuators, microfluidic devices, RF and optical MEMS. Experience indicates a need for MEMS book covering these materials as well as the most important process steps in bulk micro-machining and modeling. We are very pleased to present this book that contains 18 chapters, written by the experts in the field of MEMS. These chapters are groups into four broad sections of BioMEMS Devices, MEMS characterization and micromachining, RF and Optical MEMS, and MEMS based Actuators. The book starts with the emerging field of bioMEMS, including MEMS coil for retinal prostheses, DNA extraction by micro/bio-fluidics devices and acoustic biosensors. MEMS characterization, micromachining, macromodels, RF and Optical MEMS switches are discussed in next sections. The book concludes with the emphasis on MEMS based actuators

    Fundamental design principles of novel MEMS based Landau switches, sensors, and actuators : Role of electrode geometry and operation regime

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    Microelectromechanical systems (MEMS) are considered as potential candidates for More-Moore and More-than-Moore applications due to their versatile use as sensors, switches, and actuators. Examples include accelerometers for sensing, RF-MEMS capacitive switches in communication, suspended-gate (SG) FETs in computation, and deformable mirrors in optics. In spite of the wide range of applications of MEMS in diverse fields, one of the major challenges for MEMS is their instability. Instability divides the operation into stable and unstable regimes and poses fundamental challenges for several applications. For example: Tuning range of deformable mirrors is fundamentally limited by pull-in instability, RF-MEMS capacitive switches suffer from the problem of hard landing, and intrinsic hysteresis of SG-FETs puts a lower bound on the minimum power dissipation. ^ In this thesis, we provide solutions to the application specific problems of MEMS and utilize operation in or close to unstable regime for performance enhancement in several novel applications. Specifically, we propose the following: (i) novel device concepts with nanostructured electrodes to address the aforementioned problems of instability, (ii) a switch with hysteresis-free ideal switching characteristics based on the operation in unstable regime, and (iii) a Flexure biosensor that operates at the boundary of the stable and unstable regimes to achieve improved sensitivity and signal-to-noise ratio. In general, we have advocated electrode geometry as a design variable for MEMS, and used MEMS as an illustrative example of Landau systems to advocate operation regime as a new design variabl
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