Mechanical Engineering
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Item MEMS Conveyance: Piezoelectric Actuator Arrays for Reconfigurable RF Circuits(2015) Tellers, Mary; Bergbreiter, Sarah E; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An array of piezoelectric cantilevers was designed, fabricated, and characterized for use as a micromanipulation surface in a reconfigurable RF circuit micro-factory. The project, known as RFactory, is an effort by the U.S. Army Research Laboratory to create environmentally adaptable, rapidly upgradeable RF systems. The RFactory actuator surface uses unimorph lead zirconate titanate cantilevers with metal posts at the tip that exaggerate the horizontal deflection produced by out-of-plane bending. The motion of a circuit component on the surface has been modeled and observed experimentally. By varying the waveform, voltage amplitude, and frequency of the drive signal, as well as the actuator length and width, the speed and precision of the motion can be controlled. From these characterization efforts, operating conditions that create speeds above 1 mm/s and low positional error (<200 microns after 5 mm translation) have been identified. Finally, full system RF reconfigurability has been demonstrated.Item Piezoelectric Vibration Energy Harvesting From Coupled Structural-Acoustic Systems(2013) ALADWANI, ABDULAZIZ EBRAHIM; Baz, Amr; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A comprehensive theoretical and experimental study of the fundamentals and the underlying phenomena governing the operation of piezoelectric vibration energy harvesting from coupled structural-acoustic systems is presented. Analytical and finite element models are developed based on variational formulations to describe the energy harvesting from uncoupled structural elements as well as structural elements coupled with acoustic cavities. The models enable the predictions of the structural displacement, output electric voltage, and fluid pressure for various loading conditions on the energy harvesting system. The developed models also include dynamic magnification means to enhance the energy harvesting capabilities and enable harnessing of the vibration energy over a broader operating frequency range. The predictions of all the models are experimentally validated by using structural elements varying from beams to plates. Close agreements are demonstrated between the theoretical predictions and the obtained experimental results. The theoretical and experimental tools developed, in this dissertation, provide invaluable means for designing a wide variety of efficient energy harvesters for harnessing the vibrational energy inside automobiles, helicopters, aircrafts, and other types of structures that interact internally or externally with a fluid medium. With such harnessed energy, a slew of on-board sensors can be powered to enable the continuous monitoring of the condition and health of these structures without the need for external power sources.Item Traveling Wave Thermoacoustic-Piezoelectric Energy Harvester: Theory and Experiment(2011) Roshwalb, Andrew Zvi; Baz, Amr; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis presents a theoretical and experimental investigation of a piezoelec- tric energy harvester coupled to a traveling wave thermoacoustic engine (TWTAE). By simplifying the engine using a lumped-parameter model, the performance pa- rameters such as pressure oscillation frequency and amplitude, regenerator hot end temperature, and piezoelectric output voltage are predicted. Also, an axisymmetric finite element model of the piezoelectric energy harvester is developed, resulting in a two-part reduced-order model of the electromechanical impedance of the harvester. The predictions of the finite element model are compared with those of ANSYS finite element analysis and validated experimentally. The two-part model is utilized in a numerical analysis of the TWTAE using DeltaEC (Design Environment for Low- Amplitude ThermoAcoustic Energy Conversion). Results from pressure transducers and the piezoelectric disc attached to a physical realization of the TWTAE are com- pared with theoretical predictions of the lumped-parameter models and DeltaEC analysis. The developed theoretical techniques and experimental validation provide invaluable tools for effective design of the thermoacoustic-piezoelectric harvester.Item LEAD ZIRCONATE TITANATE THIN FILMS FOR PIEZOELECTRIC ACTUATION AND SENSING OF MEMS RESONATORS(2005-12-07) Piekarski, Brett; DeVoe, Donald; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This research is focused on examining the potential benefits and limitations of applying sol-gel lead zirconate titanate (PZT) piezoelectric thin films to on-chip piezoelectrically driven RF microelectromechanical system (MEMS) resonators in the low frequency (LF) to very high frequency (VHF) frequency range. MEMS fabrication methods are presented for fabricating PZT-based MEMS resonator structures along with investigations into the resultant thin film residual stresses and material properties, and their impact on resonator frequency, beam curvature, and resonant mode shape. The PZT, silicon dioxide (SiO2), platinum (Pt), and silicon nitride (Si3N4) thin film material properties are characterized and validated by wafer bow, cantilever resonance, cantilever thermal-induced tip deflection and finite element modeling (FEM) techniques. The performance of the fabricated PZT-based MEMS resonators are presented and compared to previously demonstrated zinc oxide (ZnO) based resonators as well as to electrostatically based MEMS resonator designs. Resonators with frequency response peaks of greater than 25 dB, quality factors up to 4700, and resonant frequencies up to 10 MHz are demonstrated along with a discussion of their advantages and disadvantages for use as MEMS resonators. Nonlinear resonator response is also investigated in relation to the onset of classic Duffing behavior, beam buckling and mode coupling. Fabrication techniques, operating conditions, and design rules are presented to minimize or eliminate nonlinear resonator response.