Mechanical Engineering
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Item DIRECT LASER WRITE PROCESSES FOR SPIDER INSPIRED MICROHYDRAULICS AND MULTI-SCALE LIQUID METAL DEVICES(2023) Smith, Gabriel Lewis; Bergbreiter, Sarah; Sochol, Ryan; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Direct Laser Write (DLW) through two-photon polymerization (2PP) empowers us to delveinto the realm of genuine three-dimensional design complexity for microsystems, enabling features smaller than a single micrometer. This dissertation develops two novel fabrication processes that leverage DLW for functional fluidic microsystems. In the first process, we are inspired by arachnids that use internal hemolymph pressure to actuate extension in one or more of their leg joints. The inherent large foot displacement-to-body length ratio that arachnids can achieve through hydraulics relative to muscle-based actuators is both energy and volumetrically efficient. Until recent advances in nano/microscale 3-D printing with 2PP, the physical realization of synthetic complex ‘soft’ joints would have been impossible to replicate and fill with a hydraulic fluid into a sealed sub-millimeter system. This dissertation demonstrates the smallest scale 3D-printed hydraulic actuator 4.9 × 10^−4 mm^3 by more than an order of magnitude. The use of stiff 2PP polymers with micron-scale dimensions enable compliant membranes similar to exoskeletons seen in nature without the requirement for low-modulus materials. The bio-inspired system is designed to mimic similar hydraulic pressure-activated mechanisms in arachnid joints utilized for large displacement motions relative to body length. Using variations on this actuator design, we demonstrate the ability to transmit forces with relatively large magnitudes (milliNewtons) in 3D space, as well as the ability to direct motion that is useful towards microrobotics and medical applications. Microscale hydraulic actuation provides a promising approach to the transmission of large forces and 3D motions at small scales, previously unattainable in wafer-level 2D microelecromechanical systems (MEMS). The second fabrication process focuses on incorporating functionality through the use of liquid metals in 3D DLW structures. Room temperature eutectic Gallium Indium (eGaIn)- based liquid metal devices with stretchable, conductive, and reconfigurable behavior show great promise across many areas of technology, including robotics, communications, and medicine. Microfluidics provide one means of creating eGaIn devices and circuits, but these devices are typically limited to larger feature sizes. Developments in 3D printing via DLW have enabled sub-100 µm complex microfluidic devices, though interfacing microfluidic devices manufactured with DLW to larger millimeter-scale systems is difficult. The reduced channel diameter creates challenges for removing resist from the channels, filling microchannels with eGaIn, and electrically integrating them to larger channels or other circuitry. These challenges have prevented microscale liquid metal devices from being used more widely. In this dissertation, we demonstrate a facile, low-cost multiscale process for printing DLW microchannels and devices onto centimeter-scale custom fluidic channel substrates fabricated via stereolithography (SLA). This work demonstrates a robust interface between the two independently printed materials and greatly simplifies the filling of eGaIn microfluidic channels down to 50 µm in diameter, with the potential to achieve even smaller feature sizes of liquid metals. This work also demonstrates eGaIn coils with resistance of 43-770 mΩ and inductance of 2-4 nH. As a result, this process empowers us to manufacture interfaces that are not only low-temperature but also conductive and flexible. These interfaces find their application in connecting with sensors, actuators, and integrated circuits, thereby opening new avenues in the field of 3D electronics. Furthermore, our approach extends the lower limits of size-dependent properties for passive electronic components like resistors, capacitors, and inductors crafted from liquid metal, expanding the frontiers of possibilities in miniature electronic design.Item PERFORMANCE ENHANCEMENTS OF MICRO CORIOLIS VIBRATORY GYROSCOPES THROUGH LINEARIZED TRANSDUCTION AND TUNING MECHANISMS(2023) Knight, Ryan; DeVoe, Don L; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A quadruple mass Microelectromechanical System (MEMS) Coriolis vibratory gyroscope has been re-engineered with the singular focus of minimizing nonlinear transduction mechanisms, thereby allowing for angle random walk (ARW) noise reduction when operating at amplitudes higher than 2 μm. The redesign involved six primary steps: (i) the creation of an aspect-ratio independent deep reactive ion etch with minimal notching on 100 μm thick silicon-on-insulator device layer, (ii) the creation of micro-torr vacuum packaging capability, enabling operation at the thermoelastic dissipation limit of silicon, (iii) the redesign of Coriolis mass folded flexures and shuttle springs, (iv) the linearization of the antiphase coupler spring rate while maintaining parasitic modal separation, (v) the substitution of parallel plate transducers with linear combs, and (vi) the implementation of dedicated force-balanced electrostatic frequency tuners. Cross-axis stiffness is also reduced through folded-flexure moment balancing to further reduce ARW. By balancing positive and negative Duffing frequency contributions, net fractional frequency nonlinearity was reduced to -20 ppm. The gyroscope presented in this research has achieved, a first reported of its kind, an ARW of 0.0005 °/√hr, with an uncompensated bias instability of 0.08 °/hr. These advancements hold promise for enhancing navigation and North-finding applications. In tandem with gyroscope performance enhancements, vacuum packaging of ceramic chip carrier physics packages has achieved pressure levels below 1 micro-torr, a first in the field and remains state-of-the-art. Besides high-performance MEMS inertial sensors, ultrahigh vacuum packaging proves beneficial for chip scale atomic clocks, which require micro-torr vacuum levels to maintain fractional frequencies less than 10^-12. Finally, an approach to tuning the quality factor mismatch between degenerate modes in as-fabricated gyroscopes has demonstrated a reduction in gyroscope bias instability. This tuning can be achieved by incorporating lead zirconate titanate into regions where the trade-off between mechanical Q, tuning Q, and bias instability reduction is balanced. Both modeling and empirical frequency data justify this approach, suggesting, for typical MEMS foundry Q mismatch of 7%, a 70× reduction in bias instability.Item Fabrication and Characterization of Nanoscale Shape Memory Alloy MEMS Actuators(2020) Knick, Cory R.; Bruck, Hugh; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The miniaturization of engineering devices has created interest in new actuation methods capable of large displacements and high frequency responses. Shape memory alloy (SMA) thin films have exhibited one of the highest power densities of any material used in these actuation schemes with thermally recovery strains of up to 10%. With the use of a biasing force, such as from a passive layer in a “bimorph” structure, homogenous SMA films can experience reversible shape memory effect provided they are thick enough that the crystal structure is capable of transforming. However, thick films exhibit lower actuation displacements and speeds because of the larger inertial resistance. Therefore, there is a need to find a way to process thinner SMA films with grain structures that are capable of transformation in order to realize larger actuation displacements at higher speeds. In this work, a near-equiatomic NiTi magnetron co-sputtering process was developed to create nanoscale thick SMA films as thin as 120 nm. By using a metallic seed layer, it was possible to induce the crystallization of epitaxial, columnar grains exhibiting the shape memory effects in nanoscale films ranging from 120 – 400 nm. It was also possible to crystalize these SMA films at lower processing temperatures (as low as 325 °C) compared to directly sputtering thicker films onto Si wafers. The transformation behavior associated with the SME in these films were characterized using x-ray diffraction (XRD), differential scanning calorimetry (DSC), and stress-temperature measurements at wafer level. After quantifying the shape memory effects at wafer-level, the SMA films were used to fabricate various microscale MEMS actuators. The SMA films were mated in several “bimorph” configurations to induce out of plane curvature in the low-temperature Martensite phase. The curvature radius vs. temperature was characterized on MEMS cantilever structures to elucidate a relationship between residual stress, recovery stress, radius of curvature, and degree of unfolding. SMA MEMS actuators were fabricated and tested using joule heating to demonstrate rapid electrical actuation of NiTi MEMS devices at some of the lowest powers (5-15 mW) and operating frequencies (1-3 kHz) ever reported for SMA or thermal actuators. By developing a process to create nanoscale thickness NiTi SMA film, we enabled the fabrication of MEMS devices with full, reversible, actuation as low as 0.5 V. This indicated the potential of these devices to be used for high frequency, low power, and large displacement applications in power constrained environments (i.e. on chip).Item ENHANCING THE COMBUSTION CHARACTERISTICS OF ENERGETIC NANOCOMPOSITES THROUGH CONTROLLED MICROSTRUCTURES(2018) Jacob, Rohit; Zachariah, Michael R; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Metastable Intermolecular Composites (MIC’s) are a relatively new class of reactive materials which, through the incorporation of nanoscale metallic fuel and oxidizer, have exhibited multiple orders of magnitude improvement in reactivity. Although considerable research has been undertaken, their reaction mechanism is still poorly understood, primarily due to the complex interplay between chemical, fluid mechanic and thermodynamic processes that happen rapidly at nanoscale. For my dissertation, I have attempted to tackle this problem by employing controlled nanomaterial synthesis routes and optical diagnostics to identify the dominant underlying mechanisms. I begin my investigation by examining the nature of metal nanoparticle combustion wherein, I employed laser ablation to generate size- controlled aggregates of titanium and zirconium nanoparticles and studied their combustion behavior in a hot oxidizing environment. The experiments revealed the dominant role of rapid nanoparticle coalescence, before significant reaction could occur, resulting in a drastic loss of nanostructure. The large-scale effects of sintering on MIC combustion was explored through a forensic analysis of reaction products. Electron microscopy was employed to evaluate the product particle size distributions and focused ion beam milling was used to expose the interior composition of the product particles. The experiments established the predominance of condensed phase reaction at nanoscale and the interior composition revealed the poor extent of reaction due to rapid reactant coalescence before attaining completion. In light of such limitations, the final part of my dissertation proposes a solution to counteract rapid, premature coalescence through the synthesis of smart nanocomposites containing gas generating (GG) polymers. The GG acts as a binder as well as a dispersant, which disintegrates the composite into smaller clusters prior to ignition, thereby avoiding large scale loss of nanostructure. High speed optical diagnostics including an emission spectrometer and a high-speed color camera pyrometer were developed to quantify the enhanced combustion characteristics which indicate an order of magnitude improvement in reactivity over counterparts using commercial nanomaterials. Moreover, thermal pretreatment as a possible bulk processing strategy to improve nanoaluminum reactivity in a MIC is examined, where a 1000% increase in reactivity was observed compared to the untreated case. Finally, composites of nanoaluminum and reactive fluoropolymers (PVDF) are examined as a possible candidate for energetic material additive manufacturing (EMAM) and its viability is demonstrated by 3D printing and characterizing reactive multilayer films.Item INVESTIGATION OF THERMO-OPTIC EFFECTS IN SILICON MICRORING RESONATORS FOR SENSING AND INTERROGATION(2017) Kim, Hyun-Tae; Yu, Miao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Integrated photonics technology has great potential for enhancing the performance and reducing the volume and cost of optical sensing systems. Among many integrated photonic structures, silicon microring resonators have received much attention for both sensing and interrogation. Particularly, the high quality-factor of the microring resonators and the large thermo-optic coefficient and high thermal conductivity of silicon make them attractive for temperature sensing and thermally-tunable-filter-based interrogation. In this dissertation work, the thermo-optic effects in silicon microring resonators is studied and used in the silicon-ring-resonator-based temperature sensing and interrogation. The first objective of this dissertation work is to develop a highly sensitive photonic temperature sensor, which can be potentially used for achieving portable, compact temperature sensing systems employing a low-resolution on-chip spectrometer. However, the sensitivity of conventional silicon-ring-resonator-based temperature sensors is relatively low (less than ~80 pm/°C). These sensors often require the use of a bulky and expensive fine-resolution interrogator for high resolution temperature monitoring, since the sensor resolution is determined by the sensitivity. In this work, a novel photonic temperature sensor based on cascaded-ring-resonators with the Vernier effect is developed to simultaneously enhance the sensitivity and sensing range. With a proof-of-concept device, sensitivity enhancement of 6.3 times and sensing range enhancement of 5.3 times are demonstrated. On-chip optical interrogators employing a silicon-ring-resonator-based thermally tunable filter (SRRTF) offer a promising solution for realizing portable, compact optical sensing systems. However, the slow interrogation speed of conventional SRRTF-based interrogators (less than a few Hz) has hindered their application for dynamic sensing. The second objective of this dissertation work is to develop a high-speed SRRTF-based interrogator, which can be used to interrogate optical sensors monitoring dynamic parameters. In this work, an SRRTF-based system utilizing the nonlinear transient thermal response of the SRRTF is developed for the speed enhancement. High speed interrogation (100 kHz of interrogation speed) of a fiber Bragg grating (FBG) sensor is successfully demonstrated with this system. The third objective of the dissertation work is to further enhance the tuning speed and range of the previously developed SRRTF and to use it for simultaneous interrogation of multiplexed FBG sensors. Performance of SRRTF-based interrogators is primarily determined by thermal and optical characteristics of the SRRTF. However, conventional SRRTF structures with a metallic heater on the top oxide cladding have limitations on interrogation speed and range. In this dissertation work, a novel SRRTF employing an interior-ridge-ring resonator and thermal through-cladding-vias is developed, which can realize enhanced tuning speed and range. With this SRRTF, interrogation of multiplexed FBG sensors at 125 kHz speed is demonstrated.Item NANOTUBE-MATRIX INTERPLAY AND TUNABILITY IN ULTRAHIGH VOLUME-FRACTION ALIGNED CARBON NANOTUBE POLY(URETHANE-UREA) NANOCOMPOSITES(2017) Gair, Jeffrey Lynn; Bruck, Hugh A.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The present dissertation seeks to better understand the nature of biphasic poly(urethane-urea) (PUU) interactions in materials with densely packed, aligned carbon nanotubes (CNTs). Of particular interest are the CNT-matrix interactions with in-situ polymerized PUU of various stoichiometric ratios. A novel synthesis method for PUU which permits fabrication of PUU-based polymer nanocomposites (PNCs) has been developed. Study of the thermal and multiscale mechanical behavior of stoichiometrically varied PUU materials has been conducted to demonstrate significant interaction between the matrix and CNTs, both in terms of morphology and mechanical reinforcement. PNCs with CNT Vf up to 30% have been achieved with excellent wetting confirmed via Micro-CT. TGA and DSC have revealed that CNTs stabilize thermal degradation of PUU by inducing crystallinity and reducing phase-mixing. AFM confirmed this by visualizing the crystals present in the matrix materials. CNT-induced crystallinity and phase-separation are attributed to the binding of CNTs to hard segments, which limit chain mobility during polymerization. Higher CNT Vf PNCs were found to increase soft-segment crystallinity, though with diminishing returns. Extreme crystallinity was found at 10% Vf CNTs which is though to arise due to an optimized spacing to permit ordered crystal formation of the PUU. Enhancements to indentation modulus of up to 1600% in the transverse orientation and 3500% in the axial orientation have been recorded via quasi-static nanoindentation. Greater CNT Vf and greater hard-segment composition lead to reduced chain mobility, and in some instances, can reduce CNT effectiveness in mechanical enhancement. The 10% CNT Vf exhibits greater indentation and storage moduli arising which is thought to arise from an optimized balance of inter-CNT spacing and chain mobility. Furthermore, PUU with higher hard-segment content is highly anisotropic and highly rate-sensitive, indicating significant morphological interactions with inter-CNT spacing of ~18nm. Degradation and increased loss modulus are seen in similar PUU with 20% loading, pointing to weak chain interactions and reduced hydrogen, likely do to confinement and reduced mobility. A model has also been developed which sheds light on the evolution of CNT-matrix interactions across a wide range of CNT volume-fractions.Item SYSTEM MODELING AND MATERIAL DEVELOPMENT FOR STANDALONE THERMOELECTRIC POWER GENERATORS(2014) Huang, Dale Hsien-Yi; Yang, Bao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation addresses the need to develop a scalable and standalone power generator for personal, commercial, and military transportation and communication systems. The standalone thermoelectric power generator (TPG) converts heat to electrical power in a unique way that does not draw on conventional power sources like batteries. A TPG is comprised of four main components: a heat source, thermoelectric modules, a heat sink, and thermal insulation. For system modeling and materials development purposes, the dissertation invented the first pyrophoric heated standalone TPG, solid-state renewable heat source, and two-component nanocomposite thermoelectric power generation material. In this work, the first pyrophoric heated standalone thermoelectric power generator was designed, fabricated, and tested. The bases of the system were four porous silicon carbide combustors for the exothermic reaction of pyrophoric iron powder with oxygen. These combustors provided a heat source of 2,800 to 5,600 W to the heat sinks (through TE modules) at conditions suitable for a standalone, pyrophoric iron fueled TE power generator. The system integrated with 16 commercial bismuth telluride thermoelectric modules to produce 140 to 280 W of electrical power with a TE power conversion efficiency of ~5%. This demonstration represents an order-of-magnitude improvement in portable electrical power from thermoelectrics and hydrocarbon fuel, and a notable increase in the conversion efficiency compared with other published works. To optimize the TE heat-to-power conversion performance of the TPG, numerical simulations were performed with computational fluid dynamics (CFD) using FLUENT. The temperature dependent material properties of bismuth telluride, effects of air flow rate (6 – 14 m/s) at 300 K, and effects of thermoelectric element thickness (4 – 8 mm) on temperature gradient generated across the module are investigated under constant power input (7.5 W). The obtained results reveal that all geometric parameters have important effect on the thermal performance of thermoelectric power generation module. The optimized single TE element thickness is 7 mm for electrical power generation of 0.47 W at temperature difference of 138 K. The TE heat-to-power conversion efficiency is 6.3%. The first solid-state renewable heat source (without the use of hydrocarbons) were created with porous silicon carbide combustors coated with pyrophoric 1-3 micron-sized iron particles mixture. The thermal behavior and ignition characteristics of iron particles and mixtures were investigated. The mixture include activate carbon and sodium chloride, in which iron is the main ingredient used as fuel. The final mixture composition is determined to consist of iron powder, activate carbon, and sodium chloride with a weight ratio of approximately 5/1/1. The mixture generated two-peak DSC curves featured higher ignition temperatures of 431.53°C and 554.85°C with a higher heat generation of 9366 J/g than single iron particles. The enhancement of figure-of-merit ZT or efficiency of thermoelectric materials is dependent on reducing the thermal conductivity. This dissertation synthesized and characterized the advanced two-component Si-Ge nanocomposites with a focus on lowering the thermal conductivity. The ball-milled two-component Si-Ge material demonstrated 50% reduction in thermal conductivity than the single component material used in the radioisotope thermoelectric generators and 10% reduction than the p-type SiGe alloy.Item Design of three degrees-of-freedom motion stage for micro manipulation(2014) Kim, Yong-Sik; Gupta, Satyandra K; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A miniaturized translational motion stage has potentials to provide not only performances equivalent to conventional motion stages, but also additional features from its small form factor and low cost. These properties can be utilized in applications requiring a small space such as a vacuum chamber in a scanning electron microscopy (SEM), where hidden surface can decrease by manipulating objects to measure. However, existing miniaturized motion stages still have several cm3 level volumes and provide simple operations. In this dissertation, Micro-electro-mechanical systems (MEMS)-based motion stages are utilized to replace a miniaturized motion stage for micro-scale manipulation and possible applications. However, most MEMS fabrication methods remain in monolithic fabrication methods and a lot of MEMS based multiple degrees-of-freedom (DOFs) motion stage also remain for in-plane motions. In this dissertation, a nested structure based on a serial kinematic mechanism is implemented in order to overcome these constraints and implement out-of-plane motion, where one independent stage is embedded into the other individual stage with additional features for structurally and electrically isolations among the engaged stages. MEMS actuators and displacement amplifiers are also investigated for reasonable performance. 3-axis motions are divided into two in-plane motions and one out-of-plane motion; an in-plane 1 DOF motion stage (called an X-stage) and one out-of-plane 1 DOF motion stage (called a Z-stage) are designed and characterized experimentally. Based on the two stages, the XY-stage is designed by merging one X-stage into the motion platform of the other X-stage with a different orientation (called an XY-stage). With this nested approach, the fabricated XY-stage demonstrated in-plane motions larger than 50 µm with ignorable coupled motion errors. Based on this nested approach, the 3-axis motion stage is also implemented by utilizing the nested structure twice; integrating the Z-stage with the motion platform of the XY-stage (called an XYZ-stage). The XYZ-stage demonstrated out-of-plane motions about 23 µm as well as the in-plane motions. Two presented motion stages have been utilized in the manipulation of micro-scale object by the cooperation of the two XY-stages inside a SEM chamber. The large motion platform of the X-stage is also utilized in a parallel plate type rheometer to measure the material properties of viscoelastic materials.Item Leveraging Porous Silicon Carbide to Create Simultaneously Low Stiffness and High Frequency AFM Microcantilevers(2014) Barkley, Sarice; Solares, Santiago; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Many operative modes of the atomic force microscope (AFM) are optimized by using cantilever probes that have both a low force constant and a high resonance frequency. Due to fabrication limitations, however, this ideal cannot be achieved without resorting to sizes incompatible with standard AFM instrumentation. This project proposes that cantilevers made from electrochemically etched porous silicon carbide (SiC) enjoy reduced force constants without significantly sacrificing frequency or size. The study includes prototype fabrication, as well as parametric experiments on the etching recipe and suggestions to improve the process. Analysis of the mechanical properties of the prototypes proves that introducing porosity to the structure greatly reduces the force constant (porous k = 0.27 bulk k) while only slightly reducing the resonance frequency (porous f0 = 0.86 bulk f0).Item THERMOPHYSICAL PROPERTIES AND BOILING HEAT TRANSFER OF SELF-ASSEMBLED NANOEMULSION FLUIDS(2013) Xu, Jiajun; YANG, BAO; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recently, society has witnessed a blossom of the development of electronics, communications, and auto-computing industries, and this trend is going to continue through this century. The power dissipation density has been increased drastically because of the continuous miniaturization and the multiplication of speed of operation and data transfer. Today, it is not unusual to see heat fluxes of 200 W/cm2 in a power module, a figure that is expected to increase up to 1000 W/cm2 in the near future. Thermal management of such high flux is quickly becoming the bottleneck to improvements in electronic and optoelectrical devices. Most efforts to improve thermal management technology in the past has been devoted to improving transport processes, such as jet impingement, and microchannels. Much less attention has been paid to the fact that the existing fluids themselves possess poor thermal transport properties. In this study, Nanoemulsion fluids have been developed to overcome barriers of state-of-the-art heat transfer fluids via forming self-assembled liquid nanodroplets in conventional heat transfer fluids to elevate their heat transfer capability. A systematic investigation on nanoemulsion fluids especially their applicability in thermal management of high heat flux devices was done on the following topics: (a) the preparation of several nanoemulsion heat transfer fluids and their inner structure characterization; (b) investigation of thermophysical and phase change heat transfer characteristics in both pool boiling and flow boiling conditions; (c) optimization of nanoemulsion fluids for better thermal performance and to identify the influence of different dispersed phase, base fluid and surfactants and their concentration, on (1) inner structure and thermophysical properties, and (2) on the phase change heat transfer characteristics; (d) analytical/numerical modeling and simulation of the nanoemulsion fluids and their enhanced thermophysical properties. Overall, nanoemulsion fluids with greatly enhanced heat transfer properties, especially, the phase change properties has been developed and demonstrated here. Potential applications and the future of nanoemulsion fluids are discussed too