Master of Science in Mechanical Engineering, Cleveland State University, 2021, Washkewicz College of Engineering

Throughout this thesis, evidence is shown that suggests the existence of subharmonic frequencies in the Classical Spanish Acoustic Guitar and Fender Squier Electric Guitar spectra. The classic subharmonic undertone series mimics that of the harmonic overtone series, except that the fundamental frequency is divided by integer values instead of multiplied by integer values. Subharmonics that do not fit the classic subharmonic undertone series criteria are still classified as subharmonics, although subharmonics that do fit the criteria are emphasized. Throughout this manuscript, the author's original experimental procedures and results are presented. Individual tones were recorded on both guitars on every string from frets zero to twelve and were analyzed for subharmonics via Audacity software. The fundamental and subharmonic frequencies were recorded on Excel and the fundamental frequencies were divided by the subharmonic frequencies, thus yielding ratios. These ratios were used in two different charts that were color-coded based on value and if the ratios were within ten percent of an integer value. These charts suggest the frequent presence of the first and second subharmonics in both guitars, which is especially observed in the higher strings (G, B and high E strings).

Committee: Majid Rashidi (Advisor); Majid Rashidi (Committee Chair); Asuquo Ebiana (Committee Member); Michael Gallagher (Committee Member) Subjects: Acoustics; Mechanical Engineering; Physics

Master of Science, The Ohio State University, 2021, Mechanical Engineering

Nonlinear dynamic behavior of a spur gear pair has been a major topic in both gear dynamics and nonlinear vibration fields. A spur gear pair can exhibit a wide range of nonlinear behavior primarily due to its backlash and periodically time-varying mesh stiffness. While a number of theoretical studies pointed to the possibility of severe subharmonic resonances at integer multiples of the primary resonance of the gear pair, past experimental investigations focused overwhelmingly on the behavior within the speed ranges where primary and super-harmonic resonance peaks occur. There has been very little experimental evidence of such subharmonic resonances, perhaps because such investigations require very high-speed experiments pushing the limits of test machine and measurement system capabilities. In this study, a test gear pair design is implemented to reduce the primary resonance frequency significantly such that the first three subharmonic resonances can be studied using an existing test machine and a conventional gear transmission error measurement method. Transient and steady-state data are collected at different transmitted torque values to show softening type of nonlinear behavior at super-harmonic and primary resonance peaks along with a well-defined first subharmonic resonance peak dictated by period-2 motions. Other subharmonic motions up to period-4 are also demonstrated experimentally. At the end, two different dynamic models, a discrete torsional model and a deformable-body model, are employed to simulate the experiments, focusing on the subharmonic resonance regions. Both models are shown to be effective in correlating to experiments.

Committee: Ahmet Kahraman (Advisor); David Talbot (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2016, Electrical and Computer Engineering

This dissertation presents a fully-passive wireless neurorecording system for moni- toring very low level neuropotential. The subject new recording device has no battery, power harvester or regulator. As a result, it addresses concerns related to: (1) exter- nal wired connection (causing lack of mobility and risk of infection in patients), and (2) heat generation that may impact neural functioning. The developed sensor also exhibits large bandwidth and extremely high sensitivity down to 20 µVpp. Specifi- cally, this minimum detectable voltage is 25 times lower than previous fully-passive wireless neurorecorder. Further, for the first time, it allows detection of signals up to 5000 Hz. As a result, it can detect all neural signals of interest. A key aspect of the proposed sensor's increased sensitivity is the introduction of an anti-parallel diode pair (APDP) to greatly reduce the second harmonic mixing conversion loss in the implant. Also, a smaller size antenna allows for a less intrusive implant. The implant is excited by an external interrogator possibly integrated within a baseball cap, to power the implanted recorder and reading the neurosignal.

Committee: John Volakis (Advisor); Asimina Kiourti (Advisor); Waleed Khalil (Committee Member); Andrea Serrani (Committee Member) Subjects: Electrical Engineering; Electromagnetics