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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    Electroosmotic Soft Actuators
    (2017) Sritharan, Deepa; Smela, Elisabeth; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation details the research involved in creating the first paper-based soft actuator driven by electroosmosis. To accomplish this, research breakthroughs were made in the fields of electrokinetic pumping and device manufacturing using soft materials. Electroosmosis is an electrically induced microfluidic flow phenomenon. When an electric field is applied to the fluid, across the microchannels, electroosmotic flow occurs in the direction of the applied electric field. In this work, liquid was electroosmotically displaced within a flexible microfluidic device to actuate an elastomeric membrane. The goal of this work was to create a fully sealed fluidic actuator. It was therefore necessary to encapsulate the pumping fluid within the device, and to maximize pressure it was necessary to eliminate compliance caused by trapped gases. Electrolytic gas formation is well known to disrupt pumping in DC electroosmotic systems that use water as the pumping liquid. In this work, electrolysis was eliminated by replacing water with propylene carbonate (PC): PC was determined to be electrochemically stable up to at least 10 kV, in the absence of moisture or salt contaminants. Bubble-free electroosmotic pumping with PC was achieved within sealed miniature actuators, which could be continuously operated for at least one hour. Benchtop fabrication techniques were developed to build encapsulated fluidic actuators composed entirely of soft, flexible materials. Stretchable electrochemically stable electrodes were made using a conductive paint made by mixing carbon nanoparticles into a silicone base. High-density microchannel networks were incorporated by using paper and other flexible porous materials, instead of conventional planar replica-molded microchannels. The device was filled with pumping fluid without the use of external tubing, and then encapsulated by casting a film of elastomer over the filled reservoir to form the actuating membrane. The resulting actuators were flexible and stretchable, demonstrating significant membrane deformations (hundreds of micrometers) within seconds of applying the electric field and ability to lift large loads (tens of grams). These polymeric electroosmotic actuators are unique among electroactive polymer actuators because they are able to simultaneously generate high force as well as large stroke. It is envisioned that this research will pave the way for the creation of artificial muscles and smart shape-changing materials that can be actuated by electroosmosis.
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    Silicon and Polymer Components for Microrobots
    (2013) Gerratt, Aaron; Bergbreiter, Sarah; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation presents the characterization and implementation of the first microfabrication process to incorporate high aspect ratio compliant polymer structures in-plane with traditional silicon microelectromechanical systems (MEMS). This discussion begins with in situ mechanical characterization of microscale polymer springs using silicon-on-insulator-MEMS (SOI-MEMS). The analysis compares microscale samples that were tested on-chip with macroscale samples tested using a dynamic mechanical analyzer. The results describe the effect of the processing steps on the polymer during fabrication and help to guide the design of mechanisms using polymers. Characterization of the dielectric breakdown of polymer thin films with thicknesses from 2 to 14 μm between silicon electrodes was also performed. The results demonstrate that there is a strong dependence of the breakdown field on both the electrode gap and shape. The breakdown fields ranged from 250 V/μm to 635 V/μm, depending on the electrode geometry and gap, approaching 10x the breakdown fields for air gaps of the same size. These materials were then used to create compliant all-polymer thermal and electrostatic microactuators. All-polymer thermal actuators demonstrated displacements as large at 100 μm and forces as high as 55 μN. A 1 mm long electrostatic dielectric elastomer actuator demonstrated a tip displacement as high as 350 μm at 1.1 kV with a electrical power consumption of 11μW. The actuators are fabricated with elastomeric materials, so they are very robust and can undergo large strains in both tension and bending and still operate once released. Finally, the compliant polymer and silicon actuators were combined in an actuated bio-inspired system. Small insects and other animals use a multitude of materials to realize specific functions, including locomotion. By incorporating compliant elastomer structures in-plane with traditional silicon actuators, compact energy storage systems based on elastomer springs for small jumping robots were demonstrated. Results include a 4 mm x 4 mm jumping mechanism that has reached heights of 32 cm, 80x its own height, and an on-chip actuated mechanism that has been used to propel a 1.4mg projectile over 7 cm.