| Summary: | This work is centered on low-frequency and high-frequency multiphysics problems of piezoelectric structures submerged in a quiescent fluid domain for the applications of vibration energy harvesting, biomimetic actuation, and contactless acoustic energy transfer. In the first part of this research, Macro-Fiber Composite (MFC)-based piezoelectric structures are employed for underwater mechanical base excitation and electrical biomimetic actuation in bending mode at low frequencies (the fundamental underwater bending resonance being in the infrasonic frequency range). The MFC technology (fiber-based piezoelectric composites with interdigitated electrodes) exploits the effective 33-mode of piezoelectricity, and strikes a balance between structural deformation and force levels for actuation to use in underwater locomotion, in addition to offering high power density for energy harvesting to enable battery-less aquatic sensors. Following in-air electroelastic composite model development, the fundamental research problem is to establish semi-analytical models that can predict the underwater dynamics of thin MFC cantilevers for different length-to-width aspect ratios. In-air analytical electroelastic dynamics of MFCs is therefore coupled with added mass and nonlinear hydrodynamic damping effects of fluid to describe the underwater electrohydroelastic dynamics in harvesting and actuation. To this end, passive plates of different aspect ratios are tested to extract and explore the repeatability of the inertia and drag coefficients in Morison’s equation. The focus is placed on the first two bending modes in this semi-empirical approach. In particular, electrode segmentation is studied for performance enhancement in the second bending mode. Additionally, nonlinear dependence of the output power density to aspect ratio is characterized theoretically and experimentally in the underwater base excitation problem. In the second part of this work, Ultrasonic Acoustic Energy Transfer via piezoelectric transduction is investigated theoretically and experimentally. Contactless energy transfer using acoustic excitation offers larger distances of power transmission as compared to well-studied inductive method. Various transmitter configurations (e.g. spherical, cylindrical, and focused) are explored for energy transfer to a piezoelectric receiver bar (operating in the longitudinal/thickness mode) that is shunted to a generalized resistive-reactive circuit. Fixed-free and free-free mechanical boundary conditions of the receiver are explored in detail. The resulting multiphysics analytical model framework is compared with finite-element simulations and experiments conducted in fluid (water and oil). Optimal piezoelectric receiver material and electrical loading conditions are sought for performance and bandwidth enhancement.
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