Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    COMPARATIVE ANALYSIS OF MINIATURE INTERNAL COMBUSTION ENGINE AND ELECTRIC MOTOR FOR UAV PROPULSION
    (2017) Chiclana, Branden; Cadou, Christopher; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This thesis compares the performance of an engine/fuel tank based propulsion system to a motor/battery based propulsion system of equal total mass. The results show that the endurance of the engine/fuel system at the same thrust output is approximately 5 times greater than that of the motor/battery system. This is a direct result of the fact that the specific energy of the fuel is 20 times that of the lithium-polymer batteries used to power the motor. A method is also developed to account for the additional benefits of fuel consumption (and hence weight reduction) over the course of the flight. Accounting for this effect can increase endurance exponentially. Taken together, the results also demonstrate the dramatic performance improvements that are possible simply by replacing motor/battery systems with engine/fuel systems on small unmanned air vehicles.
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    MICROFABRICATION OF BULK PZT TRANSDUCERS AND DEVELOPMENT OF A MINIATURIZED TRAVELING WAVE MOTOR
    (2017) Hareesh, Prakruthi; DeVoe, Don L; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Diverse applications including consumer electronics, robotic systems, and medical devices require compact, high-torque motors capable of operating at speeds in the range of 10s to a 1000 rpm. Traveling wave ultrasonic motors are a perfect fit for these specifications as they generate higher torques for a given size-scale compared to electrostatic and electromagnetic motors. Furthermore, the electrostatic and electromagnetic motors require an additional gearing mechanism to operate at low speeds, which adds more complexity to the system. The miniaturization of ultrasonic rotary traveling wave motor has had limited success due to lack of high-resolution, high-precision fabrication techniques. This dissertation describes the development of a novel microfabrication technique for the manufacture of bulk lead zirconate titanate (PZT) microsystems involving only two lithography steps that enables the realization of bending-mode piezoelectric microsystems from a single homogeneous layer of bulk piezoceramic, requiring a few hours to fabricate. This novel fabrication process and device design concept is applied to the development of a new class of bulk PZT rotary traveling wave micromotor fabricated using a single sheet of commercially available bulk PZT. For the microfabrication of bulk PZT microsystems, relationships between micro powder blasting process parameters and PZT etching characteristics are presented, including key process parameters such as particle size, nozzle pressure and nozzle-to-substrate distance, with etch rate and etch anisotropy evaluated as a function of these parameters and space resolution. Furthermore, the photolithographic masking of bulk PZT using dry film photoresist, yielding a facile method for achieving precise and high-resolution features in PZT is presented. The work on the development of a new class of homogeneous bulk PZT unimorphs, which eliminates the need of additional elastic layers found in traditional piezoelectric bimorphs, is also reported. The developed fabrication and actuation process are key parameters to developing miniaturized bulk PZT traveling wave motor. The challenges of generating traveling waves are described in detail, followed by the successful demonstration of bi-directional traveling waves and rotor motion. The stator and rotor performance under varying stator/rotor preload forces and actuation conditions have been characterized.