Doctor of Philosophy, The Ohio State University, 2024, Nuclear Engineering

The nuclear industry continues evolving towards more reliable and powerful operations, and instrumentation technology must keep pace to ensure safety and consistency throughout the next generation of nuclear reactor designs. Sensor technology in extreme environments continues developing to meet these and other developing needs. These devices must tolerate very high temperatures, high irradiation dose, and related microstructural transformation. Piezoelectric surface acoustic wave (SAW) resonators are a class of microelectromechanical systems (MEMS) that utilize the modulation of surface acoustic waves as a physical sensing mechanism. A distributed network of small, lightweight, inexpensive sensors would allow improved characterization of reactor operating conditions and assist in the development and benchmarking of related models. Irradiation response of SAW devices must be thoroughly characterized. Device response is a result of competing mechanisms including defect generation, diffusion, recombination, and absorption. These mechanisms impact material properties including elastic constant, piezoelectric constant, and dielectric constant. This research utilizes in-situ observation of SAW resonators to characterize material behavior in a high-temperature neutron irradiation. Lithium niobate (LiNbO3), bulk aluminum nitride (AlN), and thin-film aluminum nitride (AlN/Al2O3) devices were tested up to 500oC temperature and 1.9 x 1012 n/cm2s neutron flux. Device resonant frequency, which is related to ultrasonic wave velocity, shifts in response to temperature and neutron flux. The dominant mechanism responsible for the altered wave velocity is determined by applying analytical models and identifying the best fit via correlation coefficient. Trends of the fitted parameters with temperature and neutron flux describe the characterization captured in this analysis. In SAW devices, elastic constants have been shown to be the primary mechanis (open full item for complete abstract)

Doctor of Philosophy (Ph.D.), University of Dayton, 2023, Electrical Engineering

Doping of metal oxide semiconductors with other metal oxides or metal ions is an effective way to improve the sensing performance of gas sensors. In this dissertation, In-doped SnO2 thin film is used in different gas sensing platforms, such as surface acoustic wave (SAW) transducers and impedance spectroscopy, for the detection of volatile organic vapors at room temperature. The properties of the piezoelectric materials play a critical role in determining the sensing response of the SAW based gas sensors. Recently, various ferroelectric materials have been used as piezoelectric materials in the manufacturing of SAW based gas sensors. Among them, Ba0.6Sr0.4TiO3 (BST) has emerged as a potential candidate due to its high acoustic velocity and electromechanical coupling coefficient. In the development of gas sensors, noble metals are extensively used as electrode or transducer materials. However, noble metals are expensive and scarce. On the basis of their favorable electrical conductivity, 2D metallic transition-metal dichalcogenides (VTe2, NbTe2, and TaTe2) are emerging as promising candidates for use in 2D electronic devices. In this dissertation, the design, fabrication, and validation of BST-based SAW and NbTe2- based impedance spectroscopy sensor platforms with the In-doped SnO2 sensing film were demonstrated. Different deposition and photolithography techniques were applied to fabricate the sensors. The morphology, structural, elemental compositions, and electrical properties of the as-deposited samples were characterized by HRSEM, XRD, EDS, and the four-point probe sheet resistance method. The samples exhibited excellent film adhesion. Furthermore, the sensing performances of the SAW and impedance spectroscopy-based gas sensors towards ethanol and humidity were evaluated at room temperature. The SAW sensors exhibited a significant negative frequency shift, which can be attributed to the mass and electric loading effects o (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2018, Materials Science and Engineering

Elastic constants Cij are one of the essential properties to understand mechanical behaviors of materials. They are indispensable inputs for physics-based models of microstructural evolution and constitutive/micro-mechanistic simulations of properties. Young's modulus, bulk modulus, shear modulus and Poisson's ratio are just different combinations of elastic constant components and they only describe mechanical behavior under specific conditions. Elastic constants Cij are the intrinsic parameters fully describing the elastic mechanical behavior under any given condition. Several experimental methods have been developed to measure elastic constants of materials but most of them require single-crystal samples, which are time-consuming to grow. Many compounds are not even possible to grow single crystals. As a result, only about 1% (roughly 1500 out of 160,000 kinds) of distinct solid compounds have experimental values of the elastic constants. To change this scenario, an innovative experimental method has been developed to measure single-crystal elastic constants directly from polycrystalline samples, without the need of growing single crystals. The new method is based on measuring and modeling femtosecond laser-generated surface acoustic waves (SAWs) that only propagate on the sample surface and decay with the distance from the surface into the sample exponentially. An elastodynamic model has been developed to predict the SAW phase velocities along any general direction at given full elastic constants and density. A femtosecond laser-based experimental set-up was applied to generate and detect SAW velocities along any specific direction. To enable measuring narrow-band SAW velocities along a single direction without any interference from multiple modes, an organic PDMS (polydimethylsiloxane) film of 1-D grating was placed on top of the sample surface to guarantee only one SAW mode survives to be detected. With modeling predictions and experimental measurements (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 1984, Graduate School

Master of Science, The Ohio State University, 2008, Electrical and Computer Engineering

A wireless strain sensing system utilizing passive, wireless, physically small and light weight sensors is desirable for measuring strain in harsh environments such as jet engine compressor and turbine blades. A cluttered and time varying environment results in high loss, blockage, multipath and modulation of the electromagnetic wave. Also, temperature changes affect the sensitivity of the strain measurement. Isolating the information signal from the reverberations in the environment requires time delays in the order of 100s of ns for jet engine environment. Therefore, a wireless strain gauge system that utilizes surface acoustic wave (SAW) strain sensors was studied and tested.SAW strain sensors are designed to operate at 2.45GHz. Electron beam lithography is used to achieve minimum required feature size at this frequency. The fabrication process is outlined and scanning electron microscope images of some results are given. A transceiver circuit is designed and constructed. The circuit is tested in free space, in the presence of signal blockage and a time varying channel. Measurements are shown to be in good agreement with predicted data. Sources of errors in the setup are identified to be leakage from transceiver circuit switches and bounce waveforms from the transceiver antenna. A General Electric J85 jet engine compressor section is analyzed for signal propagation characteristics. Minimum frequency that can propagate through the compressor section is determined to be 5.2GHz. Measurements are done to show that circumferential polarization propagates stronger than radial inside the compressor section. An analytical approximation for the compressor section is generated by modeling compressor section blades as rectangular waveguides. Good agreement on cutoff frequency is achieved for circumferential polarization with the analytical predictions and measurement. SAW temperature and strain sensors are measured in comparison to traditional gauges. This concept can be ge (open full item for complete abstract)

Master of Science, University of Akron, 2012, Mechanical Engineering

Manipulation of microscale particles and fluid liquid droplets is an important task for lab-on-a-chip devices for numerous biological researches and applications, such as cell detection and tissue engineering. Particle manipulation techniques based on surface acoustic waves (SAW) appear effective for lab-on-a-chip devices because they are non-invasive, compatible with soft lithography micromachining, have high energy density, and can work for nearly any type of microscale particles. In this thesis, a new two-stage particle separation device based on standing surface acoustic waves was developed. The different sizes of particles were firstly focused in a line at the first stage and then separated at the second stage. This device only utilizes standing surface acoustic force in both stages, does not require sheath flow, avoiding any risk of contamination of sample and simplifying the stature of the device. The electrode was patterned and etched on a golden coated LiNbO3 wafer by photolithography. The PDMS microchannel was fabricated by curing it on a mold that was fabricated on glass substrate also by photolithography. Then we bonded the electrode and PDMS channel together under a microscope with designed align marks. The device was tested using two kinds of micro particles with different sizes, 20 ¿¿¿¿m polystyrene beads and 5 ¿¿¿¿m polystyrene beads, which were separated in a short time. Experimental conditions including applied voltage, frequency and flow velocity were optimized to increase efficiency and throughput. A high throughput of 50 ¿¿¿¿L/hour was achieved by this device, which is a few time higher than that of existing similar micro devices (typically have a throughput less than 20 ¿¿¿¿L/hour). A SSAW separation device with a wide separation channel was also tested to increase the throughput dramatically. The throughput of this wide channel device can reach up to 300 ¿¿¿¿L/hour. The feasibility of separating blood was studied and confirmed by calculat (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2013, Physics

Ultrafast laser optics is becoming a powerful tool in materials research. The interaction between femtosecond laser pulses with electrons and the subsequent relaxation process is an active research topic in recent years. In the time scale of femtoseconds to nanoseconds, several interesting physics take place. The laser pulses are short that they can be used to probe these very short time scale interactions, for example, the spin precession in GHz range. The laser can be easily focused using an objective lens, thus providing a micron-scale spatial resolution. In this dissertation, I will start by discussing the dynamics of electron, lattice and spin after a sample absorbs focused femtosecond laser pulses and the information can be used for measurement of elastic constants and saturation magnetization. The micron-scale spatial resolution and picosecond temporal resolution of our ultrafast laser pump-probe system allows us to measure elastic, magnetic and thermal properties of materials locally. By performing such measurements on diffusion couple/multiple samples with composition gradients, we can more effectively establish composition dependent property databases than conventional ways of making single uniform alloys and measuring them one at a time. Absorption of low power focused femtosecond laser pulses by sample surface leads to localized thermal expansion, which launches Surface Acoustic Waves (SAW) that can be used to measure elastic modulus. Such measurements must be supplemented by theoretical calculations since there are complications related to pseudo-SAWs and skimming longitudinal waves in addition to regular SAWs. It is a bit surprising that a mathematical solution to the surface response induced by a thermally expansion source on an arbitrary bulk surface (half space) of an isotropic crystal/solid is not available in the literature. By convolving the strain Green's function with the thermal stress field created by an ultrafast Gaussian laser illuminat (open full item for complete abstract)