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.
Browse
3 results
Search Results
Item Characterizing the combined effect of electrostatics and polymer adhesion for elastomer-based electroadhesives(2019) Chen, Simpson Abraham; Bergbreiter, Sarah; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation presents work done in the fabrication and characterization of polymer-based electroadhesives to understand the underlying mechanisms of electroadhesion with the inclusion of soft polymers as the functional surface material. Electrostatic models for parallel plate and interdigitated electrodes provide insight into the effect of design parameters on electric fields. However, little work has been done to model how electrostatic force affect adhesion in soft electroadhesives while accounting for their mechanical and material properties. To this end, a basic friction model is presented to describe the critical shear force for a single electrode electroadhesive. The effect of voltage, contact area, dielectric thickness, and bulk thickness on shear adhesion is explored. It was shown that within a range of design parameters the basic friction model could accurately predict the critical shear force and with stiff dielectric layers higher compliance improved adhesion. However, improved models are required to cover behavior over a larger parameter space. To move beyond friction-based modeling, the combined effect of polymer adhesion and electrostatic force on conductive polymer layers is explored through performing JKR tack tests. Tack tests can measure the intrinsic adhesive property of a polymer, called the critical energy release rate. By performing JKR tack tests with two different tack systems, a rigid probe contacting a soft elastic surface and a soft probe contacting a rigid surface, it was shown that the combination of the two adhesion mechanisms can be described as a superposition of the critical energy release rate of the polymer and electrostatic force. Using these findings, a design framework is developed to combine gecko adhesives with electrostatics to increase the controllable adhesion range. Textured electroadhesives with arrays of spherical bumps were fabricated and showed an increase in adhesion up to 20x. The textured electroadhesives were also mounted onto 3D printed mounts to pick up various objects weighing from 2g to 60g. The work presented here provides a theoretical and design framework for future soft electroadhesives to build upon for applications from climbing robots to pick and place manufacturing.Item DEVELOPMENT OF A SIMPLIFIED, MASS PRODUCIBLE HYBRIDIZED AMBIENT, LOW FREQUENCY, LOW INTENSITY VIBRATION ENERGY SCAVENGER (HALF-LIVES)(2010) Khbeis, Michael Tawfik; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Scavenging energy from environmental sources is an active area of research to enable remote sensing and microsystems applications. Furthermore, as energy demands soar, there is a significant need to explore new sources and curb waste. Vibration energy scavenging is one environmental source for remote applications and a candidate for recouping energy wasted by mechanical sources that can be harnessed to monitor and optimize operation of critical infrastructure (e.g. Smart Grid). Current vibration scavengers are limited by volume and ancillary requirements for operation such as control circuitry overhead and battery sources. This dissertation, for the first time, reports a mass producible hybrid energy scavenger system that employs both piezoelectric and electrostatic transduction on a common MEMS device. The piezoelectric component provides an inherent feedback signal and pre-charge source that enables electrostatic scavenging operation while the electrostatic device provides the proof mass that enables low frequency operation. The piezoelectric beam forms the spring of the resonant mass-spring transducer for converting vibration excitation into an AC electrical output. A serially poled, composite shim, piezoelectric bimorph produces the highest output rectified voltage of over 3.3V and power output of 145uW using ¼ g vibration acceleration at 120Hz. Considering solely the volume of the piezoelectric beam and tungsten proof mass, the volume is 0.054cm3, resulting in a power density of 2.68mW/cm3. Incorporation of a simple parallel plate structure that provides the proof mass for low frequency resonant operation in addition to cogeneration via electrostatic energy scavenging provides a 19.82 to 35.29 percent increase in voltage beyond the piezoelectric generated DC rails. This corresponds to approximately 2.1nW additional power from the electrostatic scavenger component and demonstrates the first instance of hybrid energy scavenging using both piezoelectric and synchronous electrostatic transduction. Furthermore, it provides a complete system architecture and development platform for additional enhancements that will enable in excess of 100uW additional power from the electrostatic scavenger.Item Electrostatic Gas-Liquid Separation from High Speed Streams--Application to Advanced On-Line/On- Demand Separation Techniques(2009) Alshehhi, Mohamed Saeed; Ohadi, Michael M; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The separation of suspended droplets from gases has been one of the basic scientific and technical problems of the industrial era and this interest continues. Various industrial applications, such as refrigeration and HVAC systems, require control of fine droplets concentrations in moving gaseous mediums to maintain system functionality and efficiency. Separating of such fine droplets can be achieved using electrostatic charging as implemented in electrostatic precipitators (ESPs). They use electrostatic force to charge and collect solid particles. The objective of the present work was to study the feasibility of using wiretube electrostatic separator on the removal of fine water and oil droplets from air stream based on corona discharge ionization process. A parametric study was conducted to find key parameters affecting the separation process. This goal was approached by simulating the charging and separation phenomena numerically, and then verifying the modeling findings through experiments. The numerical methodology simulated the highly complex interaction between droplets suspended in the flow and electrical field. Two test rigs were constructed, one for air-water separation and the other for air-oil separation. A wiretube electrostatic separator was used as the test section for both test rigs. The separation performance was evaluated under different electric field and flow conditions. Finally, based on the results, a novel air-water separator prototype was designed, fabricated and tested. The numerical modeling results qualitatively showed acceptable agreement with the experimental data in terms of the trend of grade efficiency based on droplets size. Both numerical modeling results and experimental data showed that with a proper separator design, high separation efficiency is achievable for water and oil droplets. Based on the experimental data, at flow velocity of 5 m/s and applied voltage of 7.0 kV, the maximum separation efficiency for water and oil was 99.999 % and 96.267 %, respectively. The pressure drop was as low as 100 Pa and maximum power consumption was 12.0 W.