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Quantum Dynamics Effects On Amplitude-Frequency Response Of Superharmonic Resonance Of Second-Order Of Electrostatically Actuated Nems Circular Plates, Dumitru Caruntu, Julio S. Beatriz

Mechanical Engineering Faculty Publications and Presentations

This work deals with the effects of Casimir and/or van der Waals forces (quantum dynamics phenomena) on the amplitude-frequency response of the superharmonic resonance of second-order of axisymmetric vibrations of electrostatically actuated nanoelectromechanical systems (NEMS) clamped circular plates. Electrostatic actuation consists of alternating current (AC) voltage of magnitude to produce hardexcitationsandoffrequencynearonefourththenaturalfrequencyoftheclamped circular plate. The intermolecular forces Casimir and van der Waals, damping force, and electrostatic force are the forces acting on the NEMS plate. Six Reduced Order Models (ROMs) with one and up to 6 modes of vibration are used. The ROM with one mode of vibration is solved using …

Open-Loop Control Of Electrostatic Levitation Actuators To Enhance The Travel-Range Of Optical Switches, Mohammad Mousavi, Mohammad Alzgool, Daniel Lopez, Shahrzad Towfighian

Mechanical Engineering Faculty Scholarship

Command shaping is a driving technique for handling the large settling time of the high-Q-MEMS actuators. The strong nonlinearity due to the electrostatic actuation limits the linear operation range in cantilevered or torsional micro-mirrors where command shaping techniques can be applied for positioning. Experimental and simulation results of this research demonstrate the effectiveness of using electrostatic levitation to overcome the actuation nonlinearities and a significant increase in the operation range. The motivation for this research is that applying the nonlinear command shaping causes complexity in command manipulation and requires an accurate knowledge of the nonlinear terms involved in the system …

Surface Acoustic Wave (Saw) Sensors: Physics, Materials, And Applications, Debdyuti Mandal, Sourav Banerjee

Faculty Publications

Surface acoustic waves (SAWs) are the guided waves that propagate along the top surface of a material with wave vectors orthogonal to the normal direction to the surface. Based on these waves, SAW sensors are conceptualized by employing piezoelectric crystals where the guided elastodynamic waves are generated through an electromechanical coupling. Electromechanical coupling in both active and passive modes is achieved by integrating interdigitated electrode transducers (IDT) with the piezoelectric crystals. Innovative meta-designs of the periodic IDTs define the functionality and application of SAW sensors. This review article presents the physics of guided surface acoustic waves and the piezoelectric materials …

A Mems Pressure Sensor Using Electrostatic Levitation, Mohammad Mousavi, Mohammad Alzgool, Shahrzad Towfighian

Mechanical Engineering Faculty Scholarship

Applying electrostatic levitation force to the initially-closed gap-closing electrodes of our micro-electro- mechanical system (MEMS) creates multi actuation mechanisms, and opens a new world to the MEMS applications.

Electrostatic levitation allows us to measure physical quantities, such as air pressure, by exploiting pull-in instability and releasing. The beam starts from a pulled-in position by applying a voltage difference between two gap-closing electrodes. When enough voltage is applied to the side electrodes, the cantilever beam is released. At the release instant, electrostatic forces, restoring force, and surface force are applied to the cantilever. According to the experimental results of this work, …

Electrostatic Levitation: An Elegant Method To Control Mems Switching Operation, Mohammad Mousavi, Mohammad Alzgool, Shahrzad Towfighian

Mechanical Engineering Faculty Scholarship

This paper investigates the characteristics of a micro-switch that uses two side electrodes to open a normally closed switch. The side electrodes surround the xed electrode in the well-known gap-closing electrode configuration. The side electrodes can open a closed switch and be tuned to respond appropriately to outside forces. The combined electrode system dramatically improves the control of a standard gap-closing electrode configuration. In conventional switches, a DC voltage above a certain value closes the switch. To re-open the switch, the voltage difference is reduced to peel o the moving electrode. Currently the contact area is carefully designed to avoid …

Autonomous Shock Sensing Using Bi-Stable Triboelectric Generators And Mems Electrostatic Levitation Actuators, Mohammad Mousavi, Mohammad Alzgool, Shahrzad Towfighian

Mechanical Engineering Faculty Scholarship

This work presents an automatic threshold shock-sensing trigger system that consists of a bi-stable triboelectric transducer and a levitation-based electrostatic mechanism. The bi-stable mechanism is sensitive to mechanical shocks and releases impact energy when the shock is strong enough. A triboelectric generator produces voltage when it receives a mechanical shock. The voltage is proportional to the mechanical shock. When the voltage exceed a certain level, the initially pulled-in Microelectromechanical system (MEMS) switch is opened and can disconnect the current in a safety electronic system. The MEMS switch combines two mechanisms of gap-closing (parallel-plate electrodes) with electrostatic levitation (side electrodes) to …

Machine Learning Augmentation Micro-Sensors For Smart Device Applications, Mohammad H. Hasan

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Novel smart technologies such as wearable devices and unconventional robotics have been enabled by advancements in semiconductor technologies, which have miniaturized the sizes of transistors and sensors. These technologies promise great improvements to public health. However, current computational paradigms are ill-suited for use in novel smart technologies as they fail to meet their strict power and size requirements. In this dissertation, we present two bio-inspired colocalized sensing-and-computing schemes performed at the sensor level: continuous-time recurrent neural networks (CTRNNs) and reservoir computers (RCs). These schemes arise from the nonlinear dynamics of micro-electro-mechanical systems (MEMS), which facilitates computing, and the inherent ability …

Feasibility Study Of A Mems Threshold-Pressure Sensor Based On Parametric Resonance: Experimental And Theoretical Investigations, Mark Pallay, Meysam Daeichin, Shahrzad Towfighian

Mechanical Engineering Faculty Scholarship

A tunable threshold pressure sensor based on para- metric resonance of a microbeam subjected to electrostatic levitation is proposed. Parametric excitation can trigger a large amplitude vibration at twice the natural frequency if the mag- nitude of the driving force is large enough to overcome energy loss mechanisms in the system such as squeeze film damping. This causes a temporarily unstable response with a significant gain in oscillation amplitude over time until it is eventually capped by nonlinearities in the force or material or geometric properties. The instability divides the frequency region into two regions: distinct responses bounded by the …

Towards A High Bias Voltage Mems Filter Using Electrostatic Levitation, Mark Pallay, Ronald Miles, Shahrzad Towfighian

Mechanical Engineering Faculty Scholarship

Traditional MEMS filters use a comb drive structure that suffers from the pull- in instability, which places a significant limitation on the achievable signal-to- noise ration of the sensor. Because the output signal from a capacitive sensor

is linearly related to the applied voltage, it is desirable to use a capacitive sensor that can withstand large voltages upwards of 100V. However, the pull-in instability causes high voltages to destroy the device and a trade-off between performance and reliability must be made. Electrostatic levitation, which works by pulling electrodes apart instead of together, eliminates the pull-in instability and allows for very …

Porous Silica Nanotube Thin Films As Thermally Insulating Barrier Coatings, Derric B. Syme, Jason M. Lund, Brian D. Jensen, Robert C. Davis, Richard R. Vanfleet, Brian D. Iverson

Faculty Publications

The fabrication and examination of a porous silica thin film, potentially for use as an insulating thin film, were investigated. A vertically aligned carbon nanotube (CNT) forest, created by chemical vapor deposition (CVD), was used as scaffolding to construct the porous film. Silicon was deposited on the CNT forest using low-pressure CVD (LPCVD) and then oxidized to remove the CNTs and convert the silicon to silica for electrical or thermal passivation (e.g., thermal barrier). Thermal conductivity was determined using a 1D heat-transfer analysis that equated radiative heat loss in a vacuum with conduction through the substrate and thin film stack. …

Experimental Characterization Of The Electrostatic Levitation Force In Mems Transducers, Meysam Daeichin, Ronald Miles, Shahrzad Towfighian

Mechanical Engineering Faculty Scholarship

In this study, a two-step experimental procedure is described to determine the electrostatic levitation force in MEMS transducers. In these two steps, the microstructure is excited quasi-statically and dynamically and its response is used to derive the electrostatic force. The experimental results are obtained for a 1 by 1 plate that employs 112 levitation units. The experimentally obtained force is used in a lumped parameter model to find the microstructure response when it is subjected to different dynamical loads. The natural frequency and the damping ratios in the model are identified from the experimental results. The results show this procedure …

Lateral Pull-In Instability Of Electrostatic Mems Transducers Employing Repulsive Force, Meysam Daeichin, Ronald Miles, Shahrzad Towfighian

Mechanical Engineering Faculty Scholarship

We report on the lateral pull-in in capacitive MEMS transducers that employ a repulsive electrostatic force. The moving element in this system undergoes motion in two dimensions. A two degree-offreedom mathematical model is developed to investigate the pull-in quantitatively. The nonlinear electrostatic force, which is a vector function of two spatial coordinates, is determined by calculating the potential energy of the system using a boundary element approach. The equilibrium points are found by numerically solving the nonlinear coupled static equations. A stability analysis reveals that depending on the values of the lateral and transverse stiness, the system undergoes dierent bifurcations …

Pairing Electrostatic Levitation With Triboelectric Transduction For High-Performance Self-Powered Mems Sensors And Actuators, Mark Pallay, Alwathiqbellah I. Ibrahim, Ronald N. Miles, Shahrzad Towfighian

Mechanical Engineering Faculty Scholarship

We demonstrate that an electrostatic levitation MEMS switch can be operated by applying mechanical pres- sure to a triboelectric generator. The toggling mechanism of the switch draws no current but requires a high actuating voltage, while the generator can supply a high voltage but only produces microwatts of power. The synergistic combination results in an entirely self-powered sensor and switch; the normally-closed MEMS switch can be toggled open by applying a threshold force to the generator without the need for any outside power or supplementary circuitry. A model of the MEMS switch and electrostatic force is validated with experimental data. …

A Tunable Electrostatic Mems Pressure Switch, Mark Pallay, Ronald N. Miles, Shahrzad Towfighian

Mechanical Engineering Faculty Scholarship

We demonstrate a tunable air pressure switch. The switch detects when the ambient pressure drops below a threshold value and automatically triggers without the need for any computational overhead to read the pressure or trigger the switch. The switch exploits the significant fluid interaction of a MEMS beam undergoing a large oscillation from electrostatic levitation to detect changes in ambient pressure. If the oscillation amplitude near the resonant frequency is above a threshold level, dynamic pullin is triggered and the switch is closed. The pressure at which the switch closes can be tuned by adjusting the voltage applied to the …

A Parametric Electrostatic Resonator Using Repulsive Force, Mark Pallay, Shahrzad Towfighian

Mechanical Engineering Faculty Scholarship

In this paper, parametric excitation of a repulsive force electrostatic resonator is studied. A theoretical model is developed and validated by experimental data. A correspondence of the model to Mathieu's Equation is made to prove the existence and location of parametric resonance. The repulsive force creates a combined response that shows parametric and subharmonic resonance when driven at twice its natural frequency. The resonator can achieve large amplitudes of almost 24 μm and can remain dynamically stable while tapping on the electrode. Because the pull-in instability is eliminated, the beam bounces off after impact instead of sticking to the electrode. …

Near-Field Thermal Radiation For Solar Thermophotovoltaics And High Temperature Thermal Logic And Memory Applications, Mahmoud Elzouka

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

This dissertation investigates Near-Field Thermal Radiation (NFTR) applied to MEMS-based concentrated solar thermophotovoltaics (STPV) energy conversion and thermal memory and logics. NFTR is the exchange of thermal radiation energy at nano/microscale; when separation between the hot and cold objects is less than dominant radiation wavelength (~1 μm). NFTR is particularly of interest to the above applications due to its high rate of energy transfer, exceeding the blackbody limit by orders of magnitude, and its strong dependence on separation gap size, surface nano/microstructure and material properties.

Concentrated STPV system converts solar radiation to electricity using heat as an intermediary through a …

Improved Sensitivity Mems Cantilever Sensor For Terahertz Photoacoustic Spectroscopy, Ronald A. Coutu Jr., Ivan R. Medvedev, Douglas T. Petkie

Faculty Publications

In this paper, a microelectromechanical system (MEMS) cantilever sensor was designed, modeled and fabricated to measure the terahertz (THz) radiation induced photoacoustic (PA) response of gases under low vacuum conditions. This work vastly improves cantilever sensitivity over previous efforts, by reducing internal beam stresses, minimizing out of plane beam curvature and optimizing beam damping. In addition, fabrication yield was improved by approximately 50% by filleting the cantilever’s anchor and free end to help reduce high stress areas that occurred during device fabrication and processing. All of the cantilever sensors were fabricated using silicon-on-insulator (SOI) wafers and tested in a custom …

Mems Fabrication Process Base On Su-8 Masking Layers, Scott A. Ostrow, Ronald A. Coutu Jr.

AFIT Patents

A novel fabrication process uses a combination of negative and positive photoresists with positive tone photomasks, resulting in masking layers suitable for bulk micromachining high-aspect ratio microelectromechanical systems (MEMS) devices. This technique allows the use of positive photomasks with negative resists, opening the door to an ability to create complementary mechanical structures without the fabrication delays and costs associated with having to obtain a negative photomask. In addition, whereas an SU-8 mask would normally be left in place after processing, a technique utilizing a positive photoresist as a release layer has been developed so that the SU-8 masking material can …

Piezoresistive Feedback Control Of A Mems Thermal Actuator, Robert K. Messenger, Quentin Theodore Aten, Timothy W. Mclain, Larry L. Howell

Faculty Publications

Feedback control of MEMS devices has the potential to significantly improve device performance and reliability. One of the main obstacles to its broader use is the small number of on-chip sensing options available to MEMS designers. A method of using integrated piezoresistive sensing is proposed and demonstrated as another option. Integrated piezoresistive sensing utilizes the inherent piezoresistive property of polycrystalline silicon from which many MEMS devices are fabricated. As compliant MEMS structure’s flex to perform their functions, their resistance changes. That resistance change can be used to transduce the structures’ deflection into an electrical signal. The piezoresistive microdisplacement transducer (PMT) …

Observations Of Piezoresistivity For Polysilicon In Bending That Are Unexplained By Linear Models, Tyler L. Waterfall, Gary K. Johns, Robert K. Messenger, Brian D. Jensen, Timothy W. Mclain, Larry L. Howell

Faculty Publications

Compliant piezoresistive MEMS sensors exhibit great promise for improved on-chip sensing. As compliant sensors may experience complex loads, their design and implementation require a greater understanding of the piezoresistive effect of polysilicon in bending and combined loads. This paper presents experimental results showing the piezoresistive effect for these complex loads. Several n-type polysilicon test structures, fabricated in MUMPs and SUMMiT processes, were tested. Results show that, while tensile stresses cause a linear decrease in resistance, bending stresses induce a nonlinear rise in resistance, contrary to the effect predicted by linear models. In addition, tensile, compressive, and bending loads combine in …

Performance Comparison Of Pb(Zr0.52Ti0.48)O3-Only And Pb(Zr0.52Ti0.48)O3-On-Silicon Resonators, Hengky Chandrahalim, Sunil A. Bhave, Ronald G. Polcawich, Jeff Pulskamp, Dan Judy, Roger Kaul, Madan Dubey

Faculty Publications

This paper provides a quantitative comparison and explores the design space of lead zirconium titanate (PZT)–only and PZT-on-silicon length-extensional mode resonators for incorporation into radio frequency microelectromechanical system filters and oscillators. We experimentally measured the correlation of motional impedance (R_X) and quality factor (Q) with the resonators’ silicon layer thickness (t_Si). For identical lateral dimensions and PZT-layer thicknesses (t_PZT), the PZT-on-silicon resonator has higher resonant frequency (f_C), higher Q (5100 versus 140), lower R_X (51 Ω versus 205 Ω), and better linearity [third-order input intercept …

Piezoresistive Feedback For Decreased Response Time Of Mems Thermal Actuators, Robert K. Messenger, Timothy W. Mclain, Larry L. Howell

Faculty Publications

Feedback control is commonly used in positioning systems to improve dynamic response, disturbance rejection, accuracy, and repeatability. Similar benefits can be expected for microelectromechanical systems (MEMS) that are used for positioning applications. Sensing at the micro level poses significant challenges. Most of these challenges are associated with the small size of the devices and the small motions and forces which are of interest. In many situations, applying the macro system paradigm, where the sensor is a component that is added to the system, leads to unacceptable results. At the macro level, sensors are typically small relative to the systems they …

Techniques In The Design Of Thermomechanical Microactuators, Larry L. Howell, Timothy W. Mclain, Michael S. Baker, Christian D. Lott

Faculty Publications

The purpose of this chapter is to provide fundamental background for the design of thermomechanical microactuators. Actuation has been a particularly challenging aspect of microsystem development. Many actuation approaches used at the macro level, such as hydraulics, pneumatics, electric motors, internal combustion engines and turbines, are either too difficult to fabricate at the micro level or do not work well at that scale. Electrostatic attraction is one approach that has been widely used for actuation of microsystems; however, electrostatic actuators tend to have high voltage requirements and low output force capabilities. While electrostatic actuation is suitable for many applications, some …