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
5 results
Search Results
Item Force Sensing by Electrical Contact Resistance in SOI-DRIE MEMS(2018) Rauscher, Scott Gibson; Bruck, Hugh; DeVoe, Don; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)MEMS force sensors employ microfabricated elements to convert applied external forces to electrical signals, typically by piezoelectric, piezoresistive, or capacitive transduction. While existing force sensors based on these sensing principles have commercial success, system dynamics inherent to displacement and strain-based sensing can limit force and frequency ranges. This work explores an alternative force-sensing principle in silicon-based MEMS devices that exploits changes in electrical contact resistance (ECR) during loading between two silicon surfaces, with the aim to determine if ECR can be used to sense force in SOI-DRIE microsystems containing only Silicon and bond pads. While several analytic models were combined to create an ECR-force model for predicting ECR-force sensitivity in systems containing differing contact geometry, topology, and electrical properties, experimental testing is the focal point of this work. The feasibility of using ECR to sense force in bare DRIE silicon contacts is initially evaluated using force applied by simple thermal actuation, which indicated that ECR behavior during applied cyclic loading was erratic and occasionally nonmonotonic with increasing load, while absolute contact resistance varied significantly chip-to-chip (200 Ω – 15 kΩ) and increased asymptotically as contact was removed. Results from further investigation using manual spring elongation show a consistent pre-load of at least 5 mN is critical to obtaining repeatable ECR-force curves, “break-in” cycling is required prior to consistent ECR-force behavior, and sidewall fracture occurs in 100 µm line contacts with radii less than 50 µm. Results from testing of packaged chips through inertial acceleration of embedded proof masses show that minimizing contact area during line contact loading reduces relative standard deviation (RSD) and increases sidewall fracture. When normalized to initial contact resistance, chips subjected to inertial loading exhibited linearized sensitivities of 2.0 %/mN and 2.1% hysteresis, with 1.6% RSD. The use of DRIE, as opposed to additive poly-Silicon-based fabrication, allows a tailorable force range through proof mass sizing and aspect ratio changes, adjustable pre-load through simple design, and integration of an ECR force sensor into existing systems. The successful use of a proof mass to apply force by acceleration indicates ECR between SOI-DRIE interfaces is a viable method to measure acceleration in the future. As with piezo-sensors, calibration of ECR force sensors is expected to improve chip-to-chip repeatability. Compared to commercially available force sensors, the realized ECR force sensor has several advantages (smaller size, lower force range, and simpler fabrication) that may be further leveraged in future development.Item 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.Item DESIGN, MODELING, AND FABRICATION OF MICROROBOT LEGS(2016) Vogtmann, Dana Elise; Bergbreiter, Sarah; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation presents work done in the design, modeling, and fabrication of magnetically actuated microrobot legs. Novel fabrication processes for manufacturing multi-material compliant mechanisms have been used to fabricate effective legged robots at both the meso and micro scales, where the meso scale refers to the transition between macro and micro scales. This work discusses the development of a novel mesoscale manufacturing process, Laser Cut Elastomer Refill (LaCER), for prototyping millimeter-scale multi-material compliant mechanisms with elastomer hinges. Additionally discussed is an extension of previous work on the development of a microscale manufacturing process for fabricating micrometer-sale multi-material compliant mechanisms with elastomer hinges, with the added contribution of a method for incorporating magnetic materials for mechanism actuation using externally applied fields. As both of the fabrication processes outlined make significant use of highly compliant elastomer hinges, a fast, accurate modeling method for these hinges was desired for mechanism characterization and design. An analytical model was developed for this purpose, making use of the pseudo rigid-body (PRB) model and extending its utility to hinges with significant stretch component, such as those fabricated from elastomer materials. This model includes 3 springs with stiffnesses relating to material stiffness and hinge geometry, with additional correction factors for aspects particular to common multi-material hinge geometry. This model has been verified against a finite element analysis model (FEA), which in turn was matched to experimental data on mesoscale hinges manufactured using LaCER. These modeling methods have additionally been verified against experimental data from microscale hinges manufactured using the Si/elastomer/magnetics MEMS process. The development of several mechanisms is also discussed: including a mesoscale LaCER-fabricated hexapedal millirobot capable of walking at 2.4 body lengths per second; prototyped mesoscale LaCER-fabricated underactuated legs with asymmetrical features for improved performance; 1 centimeter cubed LaCER-fabricated magnetically-actuated hexapods which use the best-performing underactuated leg design to locomote at up to 10.6 body lengths per second; five microfabricated magnetically actuated single-hinge mechanisms; a 14-hinge, 11-link microfabricated gripper mechanism; a microfabricated robot leg mechansim demonstrated clearing a step height of 100 micrometers; and a 4 mm x 4 mm x 5 mm, 25 mg microfabricated magnetically-actuated hexapod, demonstrated walking at up to 2.25 body lengths per second.Item Polymer Based Miniature Fabry-Perot Pressure Sensors with Temperature Compensation: Modeling, Fabrication, and Experimental studies(2013) Bae, Hyungdae; Yu, Miao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Miniature Fabry-Perot (FP) pressure sensors have been of great interest because of their advantages of small sizes, high performance, and immunity to electromagnetic interference. Most of these sensors are built with silicon/silica materials that have good mechanical, chemical, and thermal stabilities. However, due to the large Young's modulus of silica/silicon, developing a high sensitivity miniature sensor becomes difficult. In addition, fabrication of these sensors often involves high temperature fusion bonding and harsh acid etching. On the other hand, a polymer material becomes an attractive choice for high sensitive and miniature pressure sensors due to its small Young's modulus relative to that of silicon/glass. Moreover, polymer processes can be performed under ambient pressure and temperature without hazardous chemicals. However, a polymer-based sensor suffers from high temperature sensitivity, which must be compensated to obtain accurate pressure measurements. In this dissertation, three types of polymer based FP miniature sensors for static or quasi-static pressure measurements are investigated through modeling, microfabrication, and experiments. First, co-axial and cross-axial FP sensors with a built-in fiber Bragg grating (FBG) for temperature measurement and compensation are studied. In both sensors, the FP cavity is precisely self-aligned with the optical axis by using the fiber as a natural mask, which eliminates the need for a photo mask and tedious optical alignments. Second, a FP sensor composed of a UV-molded optical cavity with a pre-written FBG is developed. For the first time, a UV molding process with an optical fiber based mold is developed for fabrication of miniature FP sensors. This process enables high accuracy optical alignment for UV molding. Taking advantage of the UV molding process, the third type of sensor features a hybrid dual FP cavity for simultaneous temperature and pressure measurements. A novel signal processing method is developed to retrieve the multiple cavity lengths with an improved speed, resolution, and noise resistance. Experimental studies show that these polymer based sensors have good pressure and temperature sensing performance as well as temperature compensation capabilities. In addition, blood pressure and intradiscal pressure measurements of a swine are performed, which demonstrates the feasibility of these sensors for biomedical applications.Item A Refrigerant Expansion Control Device Fabricated Through Nickel Deposition Within SU8 Micromolds(2006-03-29) Yashar, David Anthony; DeVoe, Donald; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Control of refrigerant expansion offers improved system efficiency and reduced noise among other benefits. The cost of traditional active expansion devices, however, has limited their use to large HVAC&R systems. The design, fabrication and testing of a thermopneumatic microfabricated valve for controlling refrigerant mass flow rate during expansion is presented in this dissertation. This device was fabricated through nickel electroplating within very thick SU-8 molds, thereby realizing expansion devices useful for small HVAC&R applications through an inexpensive modified UV-LIGA process. This work begins with process development to make meso-scale nickel electroplating within SU8 micromolds a feasible option. Then, two test apparatuses were constructed and used to benchmark the performance of a prototype; one to control the flow of compressed air, one to control refrigerant expansion. Next, three dimensional CFD simulations were performed on the flowfield within the device at various levels of actuation to predict the device's ability to control compressed air flow. A numerical code was also developed to predict the device's temporal response and relationship between actuation level and power input. The assembled prototype was demonstrated on the air flow test bench. The prototype was able to reduce the mass flow rate of the compressed air by 22 % at the conditions used in the CFD analysis. The performance was then demonstrated in a 1.5-2 kW R134a vapor compression system. Both steady state and transient response were characterized. Steady state data showed that the mass flow rate of refrigerant could be effectively controlled using the valve. The level of refrigerant subcooling defined the magnitude of the response. Steady state data taken at 750 kPa inlet pressure shows the mass flow rate was reduced by 4.2 % at 1 ºC subcooling and up to 10.8 % at 5 ºC subcooling for a given level of actuation. Transient system response was characterized using cyclic actuation of the device in the HVAC system. The change in capacity was approximately 5 %, at the conditions used during these tests. Data from the transient response tests showed the device's time constant to be within 11 % of the value predicted in the simulations.