Browsing by Subject "piezoelectric"

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    Mechanical Design and Testing of a High-Performance Piezoelectric Stack-Style Pneumatic Valve
    (2022-08) Gallagher, Matthew
    This thesis presents new modeling and design techniques for small displacement proportional pneumatic valves. There are two main contributions of this thesis work. The first is the design and testing of a novel piezoelectric stack-style valve design that increases mass flow capacity compared to prior art. The valve comprises a piezoelectric stack-actuated metallic seat that is capable of metering air at rates greater than 1 g/s while having a leak rate of less than 0.01% of full-scale flow. The second contribution is the development and validation of a piecewise analytical mass flow model for hard planar valve seats and seals. The model provides an accurate continuous solution that transitions from subsonic, rarified, viscous flow at small displacements to sonic, choked, compressible flow at high displacements. The analytical flow models are validated by both numerical computational fluid dynamics and experimental testing.
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    Synthesis of peptide microstructures for nanogenerators
    (2017-05) Nguyen, Vu
    Electromechanical energy conversion at the small scale utilizing micro/nanomaterials can have significant technological impacts in various areas such as mechanical energy harvesting, tissue engineering, and sensing/actuation. The breakthrough discoveries over the last decade in piezoelectric micro/nanostructures, which converts minute material deformation directly into electrical signal, has spurred intense research in micro/nano scale mechanical energy harvester, also called nanogenerator. Although a variety of advanced inorganic piezoelectric micro/nanostructures have been fabricated, little progress has been made for bioinspired piezoelectric materials, which can enable biocompatible and biodegradable energy harvesting. Meanwhile, piezoelectricity has been widely observed in biological materials such as bone, collagen, viruses and other protein-based materials. Diphenylalanine (FF) peptide, which consists of two naturally occurring phenylalanine amino acids, has attracted significant research interest due to its exceptional mechanical and piezoelectric properties as well as rich biological properties. Thus FF is promising to become one of the most technologically important bioinspired materials for piezoelectric devices, such as mechanical energy harvester. However, many challenges exist in realizing the potential of piezoelectric FF peptide, such as the lack of scalable structural alignment, lack of controllability of polarizations and lack of prototyped device. This thesis aims to address those challenges to advance the applications of FF peptide towards piezoelectric nanogenerator (PENG) and beyond. As an alternative to PENG, which converts minute material deformation into electricity, triboelectric nanogenerator (TENG) has also been proposed recently to harvest energy from large motion through a combination of triboelectric effect and electrostatic induction. Since tiny material deformation and large motion are usually available together, advances in nanogenerator are needed to harvest them effectively. Due to the apparent complementary energy conversion mechanisms of piezoelectric and triboelectric effects, performance of TENG in various environmental conditions will be studied, and hybridization of PENG and TENG into one device will also be explored as an approach to enhance the outputs of the mechanical energy harvester. In overview, first this thesis will develop a novel low-temperature epitaxial growth process to address the challenge of synthesizing aligned piezoelectric FF peptide structures in a scalable and controllable manner. Second, the random orientation and unswitchability of its polarization will be addressed by modifying the growth parameters and including an applied external electric field during the growth. The improved FF microstructures will be used to demonstrate the first peptide PENG. Third, a standalone TENG will be studied for its operation in various environmental conditions, verifying its wide applicability. Finally, a hybrid nanogenerator structure will be proposed to constructively combine the outputs of FF peptide PENG with a TENG, and the hybrid energy conversion process will be experimentally verified.