Electrical & Computer Engineering
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Item Novel Integrated System Architecture for an Autonomous Jumping Micro-Robot(2010) Churaman, Wayne Anthony; Goldsman, Neil; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As the capability and complexity of robotic platforms continue to evolve from the macro to micro-scale, innovation of such systems is driven by the notion that a robot must be able to sense, think, and act [1]. The traditional architecture of a robotic platform consists of a structural layer upon which, actuators, controls, power, and communication modules are integrated for optimal system performance. The structural layer, for many micro-scale platforms, has commonly been implemented using a silicon die, thus leading to robotic platforms referred to as "walking chips" [2]. In this thesis, the first-ever jumping microrobotic platform is demonstrated using a hybrid integration approach to assemble on-board sensing and power directly onto a polymer chassis. The microrobot detects a change in light intensity and ignites 0.21mg of integrated nanoporous energetic silicon, resulting in 246µJ of kinetic energy and a vertical jump height of 8cm.Item IMPLEMENTATION OF KALMAN FILTER TO TRACKING CUSTOM FOUR-WHEEL DRIVE FOUR-WHEEL-STEERING ROBOTIC PLATFORM(2010) Stanley, Michael Patrick; Davis, Christopher C; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Vehicle tracking is an important component of autonomy in the robotics field, requiring integration of hardware and software, and the application of advanced algorithms. Sensors are often plagued with noise and require filtering. Additionally, no single sensor is sufficient for effective tracking. Data from multiple sensors is needed in order to perform effective tracking. The Kalman Filter provides a convenient and efficient solution for filtering and fusing sensor data as well as estimating noise error covariances. Consequently, it has been essential in tracking algorithms since its introduction in 1960. This thesis presents an application of the Kalman filter to tracking of a custom four-wheel-drive four-wheel-steering vehicle using a limited sensor suite. Sensor selection is discussed, along with the characteristics of the sensor noise as related to meeting the requirements of the Kalman filter for guaranteeing optimality. The filter requires the development of a dynamical model, which is derived using empirical data methods and evaluated. Tracking results are presented and compared to unfiltered data.Item An MRI-based articulatory and acoustic study of American English liquid sounds /r/ and /l/(2009) Zhou, Xinhui; Espy-Wilson, Carol Y; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In American English, the liquid sounds /r/ and /l/ are the most articulatorily variable and complex sounds. They can be produced by several distinct types of tongue configurations and are the most troublesome sounds for children and nonnative English-speakers to learn. Better understanding of this many-to-one mapping between articulation and acoustics would be beneficial to other areas such as speech pathology, speaker verification, speech recognition and speech synthesis. In this dissertation, two articulatory configurations for each liquid sound were studied (a "retroflex" /r/ vs. a "bunched" /r/, and a light /l/ vs. a dark /l/). Different from previous work on liquids, finite element analysis has been performed to obtain the acoustic responses of the three-dimensional (3-D) vocal tract models, which are based on volumetric magnetic resonance (MR) imaging. Area function models were derived based on the wave propagation property inside the vocal tract. The retroflex /r/ and the bunched /r/ show similar patterns of F1-F3 but very different spacing between F4 and F5. The results from the formant acoustic sensitivity functions and simple-tube vocal tract models suggested that this F4/F5 difference can be explained largely by differences in whether the long cavity behind the palatal constriction acts as a half- or a quarter-wavelength resonator. For both the retroflex /r/ and the bunched /r/, F4 and F5 (along with F3 for the particular speakers studied in this research) come from the long back cavity. However, these formants are half wavelength resonances for the retroflex /r/, but quarter wavelength resonances for the bunched /r/. While both the dark /l/ and the light /l/ have a linguo-alveolar contact and two lateral channels, they differ in the length of the linguo-alveolar contact and in the presence of the linguopalatal contacts caused by raising the sides of the tongue. Both have similar patterns in F1-F3, but differ in the number and locations of zeros in spectrum. For the dark /l/, only one zero occurs below 6 kHz and it is produced by the cross mode posterior to the linguo-alveolar contact. For the light /l/, three zeros below 6 kHz are produced by the asymmetrical channels, the supralingual cavity and the cross mode posterior to the linguo-alveolar contact. The results from two simple vocal tract models show that the lateral channels have to be asymmetrical with an effective length between 3-6 cm to get a zero in the region of F3-F5. Based on the Buckeye database, the acoustic variability and discriminative power of liquids were studied with the mel-frequency band energy coefficients as acoustic parameter. Analysis of variance shows that the inter-speaker variability of /r/ is larger than any other phonemes except /sh/, /s/ and /zh/. On average, /r/ and /l/ have larger inter-speaker variability than any other broad phonetic class. The F-ratio averages of liquids are larger than glides, fricatives, affricates and stops, but smaller than nasals. The speaker identification experiments show that the ranking of the average discriminative power for liquids and other broad phonetic classes is: /r/ > Glides > /l/ > Affricates > Fricatives > Stops > Nasals > Vowels.Item Microturbopump Utilizing Microball Bearings(2008-08-05) Waits, Christopher Michael; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation presents the development of a microfabricated turbopump capable of delivering fuel with the flow rates and pressures required for portable power generation. The device is composed of a spiral-groove viscous pump that is driven by a radial in-flow air turbine and supported using a novel encapsulated microball bearing. First, the encapsulated microball bearing and methods to investigate the wear and friction behaviors were developed. Two primary raceway designs, point-contact and planar-contact designs, were developed with the key design factor being wearing of the raceway. A modification to the planar-contact design was made for the final turbopump that reduced both wear and debris generation. Second, two air turbine platforms were developed using the encapsulated microball bearings to characterize both the bearing and the turbine drive mechanism. A tangential air turbine platform was first developed and characterized using the point-contact bearing mechanism. Rotational speeds >37,000 rpm were demonstrated and long-term operation (>24 hours) using this platform, but with large driving pressures (tens of psi) and large raceway wear (tens of microns). Furthermore, the circumferential asymmetry of the turbine design led to difficulty in measuring pressure distribution and sealing for pump applications. Results from the tangential air turbine platform led to an axisymmetric radial in-flow air turbine platform using a planar-contact bearing design. Rotational speeds greater than 85,000 rpm with turbine pressure differentials in the range of 1 psi were demonstrated using this platform. The wear of the raceway was observed to be on the order of single microns (a 10x improvement). The radial in-flow air turbine platform allowed an empirical model to be developed relating the friction torque to the rotational speed and load for the planar-contact bearing. This enabled calculation of the power balance for pumping and a method to characterize future bearing designs and materials. Lastly, a microfabricated turbopump was demonstrated based on a spiral-groove viscous pump and the radial in-flow turbine platform using the planar-contact bearing. Pumping operation was demonstrated with a differential pressure up to +0.3 psi and flow rates ranging from 35 mL/hour to 70 mL/hour, within the range relevant to portable power generation.Item Indium Phosphide MEMS Cantilever Waveguides with Integrated Readout for Chemical Sensing(2007-11-26) Siwak, Nathan Paul; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis presents the development towards an integrated, monolithic, micro-electro-mechanical system (MEMS) cantilever waveguide resonator chemical sensor using the III-V semiconductor indium phosphide (InP). Waveguide cantilevers with resonant frequencies as high as 5.78 MHz, a quality factor of 340, and a sensitivity of 4.4x10^16 Hz/g are shown for the first time in this system. The first demonstration of vapor detection using the sensor platform is performed utilizing an organic semiconductor Pentacene absorbing layer. Vapors are measured from mass shifts of 6.56x10^-14 and 7.28x10^-14 g exhibiting a mass detection threshold of 5.09x10^-15 g. The design, fabrication, and testing of an integrated waveguide PIN photodetector with an In0.53Ga0.47As absorbing layer is reported. Dark currents as low as 8.7 nA are measured for these devices. The first demonstration of a resonating cantilever waveguide measurement is also performed using the monolithically integrated waveguide photodiodes with uncertainty of less than ± 35 Hz. Finally, a future outlook is presented for this monolithic InP sensor system.Item Benzocyclobutene-based Electric Micromachines Supported on Microball Bearings: Design, Fabrication, and Characterization(2007-11-21) Modafe, Alireza; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation summarizes the research activities that led to the development of the first microball-bearing-supported linear electrostatic micromotor with benzocyclobutene (BCB) low-k polymer insulating layers. The primary application of this device is long-range, high-speed linear micropositioning. The future generations of this device include rotary electrostatic micromotors and microgenerators. The development of the first generation of microball-bearing-supported micromachines, including device theory, design, and modeling, material characterization, process development, device fabrication, and device test and characterization is presented. The first generation of these devices is based on a 6-phase, bottom-drive, linear, variable-capacitance micromotor (B-LVCM). The design of the electrical and mechanical components of the micromotor, lumped-circuit modeling of the device and electromechanical characteristics, including variable capacitance, force, power, and speed are presented. Electrical characterization of BCB polymers, characterization of BCB chemical mechanical planarization (CMP), development of embedded BCB in silicon (EBiS) process, and integration of device components using microfabrication techniques are also presented. The micromotor consists of a silicon stator, a silicon slider, and four stainless-steel microballs. The aligning force profile of the micromotor was extracted from simulated and measured capacitances of all phases. An average total aligning force of 0.27 mN with a maximum of 0.41 mN, assuming a 100 V peak-to-peak square-wave voltage, was measured. The operation of the micromotor was verified by applying square-wave voltages and characterizing the slider motion. An average slider speed of 7.32 mm/s when excited by a 40 Hz, 120 V square-wave voltage was reached without losing the synchronization. This research has a pivotal impact in the field of power microelectromechanical systems (MEMS). It establishes the foundation for the development of more reliable, efficient electrostatic micromachines with variety of applications such as micropropulsion, high-speed micropumping, microfluid delivery, and microsystem power generation.Item Design, Fabrication, and Characterization of a Rotary Variable-Capacitance Micromotor Supported on Microball Bearings(2007-07-31) Ghalichechian, Nima; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The design, fabrication, and characterization of a rotary micromotor supported on microball bearings are reported in this dissertation. This is the first demonstration of a rotary micromachine with a robust mechanical support provided by microball-bearing technology. One key challenge in the realization of a reliable micromachine, which is successfully addressed in this work, is the development of a bearing that would result in high stability, low friction, and high resistance to wear. A six-phase, rotary, bottom-drive, variable-capacitance micromotor is designed and simulated using the finite element method. The geometry of the micromotor is optimized based on the simulation results. The development of the rotary machine is based on studies of fabrication and testing of linear micromotors. The stator and rotor are fabricated separately on silicon substrates and assembled with the stainless steel microballs. Three layers of low-k benzocyclobutene (BCB) polymer, two layers of gold, and a silicon microball housing are fabricated on the stator. The BCB dielectric film, compared to conventional silicon dioxide insulating films, reduces the parasitic capacitance between electrodes and the stator substrate. The microball housing and salient structures (poles) are etched in the rotor and are coated with a silicon carbide film to reduce friction. A characterization methodology is developed to measure and extract the angular displacement, velocity, acceleration, torque, mechanical power, coefficient of friction, and frictional force through non-contact techniques. A top angular velocity of 517 rpm corresponding to the linear tip velocity of 324 mm/s is measured. This is 44 times higher than the velocity achieved for linear micromotors supported on microball bearings. Measurement of the transient response of the rotor indicated that the torque is 5.620.5 micro N-m which is comparable to finite element simulation results predicting 6.75 micro N-m. Such a robust rotary micromotor can be used in developing micropumps which are highly demanded microsystems for fuel delivery, drug delivery, cooling, and vacuum applications. Micromotors can also be employed in micro scale surgery, assembly, propulsion, and actuation.Item MEMS-Based Silicon Nitride Thin Film Materials and Devices at Cryogenic Temperatures for Space Applications(2005-04-13) Chuang, Wen-Hsien; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microshutter arrays, scheduled to be launched in 2011 as part of NASA's James Webb Space Telescope (JWST), will be the first micro-scale optical devices in outer space using MEMS technology. As the microshutter arrays consist of electrical and mechanical components and must operate in a cryogenic environment reliably over a 10 year mission lifetime, a fundamental challenge for the development of this device is to understand the mechanical behaviors of the micro-scale materials used and the possible failure mechanisms at 30 K. This thesis investigates the mechanical properties and reliability of low-stress LPCVD silicon nitride thin films, the structural materials of the microshutter arrays, at cryogenic temperatures. A helium-cooled cryogenic measurement setup installed inside a focused-ion-beam system is designed, implemented, and characterized to obtain a cryogenic environment down to 20 K. Resonating T-shaped cantilevers with different "milling masses" are used to measure the Young's modulus of silicon nitride thin films, while the fracture strength is characterized by bending tests of these beams. A passive high-sensitivity microgauge sensor based on displacement amplification is introduced to measure residual stress and coefficients of thermal expansion, which are critical for the device performance. To achieve accelerated fatigue study of the microshutter arrays, a novel mechanical-amplifier actuator is designed, fabricated, and tested to emulate their torsional operating stress. Furthermore, nano-scale tensile fatigue tests are demonstrated using similar mechanical-amplifier actuators. The research results of this thesis provide important thin film material parameters for the design, fabrication, and characterization of the microshutter arrays. Moreover, the presented test devices and experimental techniques are not limited for space applications only but can be extended for characterization of other thin film materials used in MEMS and microsystems.