Eigenfrequency Tuning of a Non-Linear Bi-Stable Piezoelectric Vibration Energy Harvester

Abstract

Piezoelectric vibration energy harvesters (PVEHs) represent a promising power source for low-energy wireless sensors. However, their performance degrades significantly when ambient vibration frequencies deviate from the harvester resonance. Bi-stable concepts can broaden the operational bandwidth through nonlinear dynamics, yet a quantitative understanding of how boundary condition variations affect resonance tuning in post-buckled harvesters remains limited. This thesis investigates the use of controllable boundary conditions to tune the eigenfrequency of a nonlinear, bi-stable piezoelectric vibrational harvester, with particular focus on the symmetric clamp angle and axial pre-tension.
A combined numerical-experimental methodology is developed. A parameterised multiphysics finite-element model implemented in COMSOL captures the post buckled equilibrium configuration, piezoelectric coupling, and the linearised frequency response under base excitation. In parallel, a dedicated experimental platform, referred to as the Green Gobbling device, enables repeatable adjustment of the clamp angle and axial pre-tension. This experimental setup is supported by a comprehensive validation study to ensure that the measured resonance shifts are reliable.
Both numerical simulations and experimental results demonstrate substantial and nonlinear tuning capability. Numerically, increasing the clamp angle from 3◦ to 8◦ shifts the primary resonance from 75.44 Hz to 49.28 Hz, corresponding to a reduction of approximately 35%. Similarly, increasing the axial pre-tension from 0.25% to 0.50% raises the resonance frequency from 58.93 Hz to 69.94 Hz, representing an increase of approximately 19%. Experimental results confirm the same qualitative trends, with even larger relative shifts observed. For instance, the base well resonance decreases from 80 Hz to 35 Hz, approximately −56%, across the clamp angle sweep and increases from 42.7 Hz to 68.5 Hz, approximately 61% across the pre-tension sweep. In all cases, the top well configuration consistently exhibits lower resonance frequencies than the base well configuration.
Overall, this work provides experimentally supported insight into boundary condition driven resonance tuning in bi-stable PVEHs and establishes a foundation for future adaptive tuning strategies aimed at robust energy harvesting under variable excitation conditions.