This thesis presents a piezoelectric energy-harvesting push-button that applies stiffness compensation to reduce input work and improve mechanical-to-electrical efficiency. The design combines a compliant compressive force amplifier with two negative-stiffness flexure shuttles mounted in parallel at the input.

An analytical model and finite element (FE) simulation were developed to predict the performance of a machined and 3D-printed prototype. The results show good agreement in trends between the models and experiments. The force amplifier achieves an amplification factor of approximately 9 with an input stiffness of 29 N/mm, while adding the negative-stiffness mechanisms reduces the effective stiffness to about 21.5 N/mm. Under equal mechanical input, the harvested electrical energy doubles from roughly 0.11 mJ to 0.22 mJ, demonstrating the effectiveness of stiffness compensation.

These findings confirm that integrating negative stiffness can enhance the efficiency of piezoelectric energy harvesters. Although the prototype is not yet at normal button dimensions, the principle is scalable and shows potential for compact, self-powered devices such as switches and sensors.

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.

This research investigates a novel approach to vibration energy harvesting (VEH) using a statically balanced lever mechanism to compress piezoelectric stacks. Current state-of-the-art VEH methods struggle with scaling and harvesting energy efficiently, this proposed prototype addresses these limitations by utilizing the piezoelectric charge constant more efficiently. A prototype was developed and tested, showing a maximal stiffness reduction of 95% and demonstrating the principle's improvement in increasing power output by at most a factor of 116. A model is introduced to predict power output from the response and to estimate the generated power of an unbalanced mechanism. The scalability and improved performance highlight the potential of this approach for future VEH applications.

The thesis investigates the feasibility of using stencil printing to fabricate piezoelectric vibrational energy harvesters. The primary goal was to develop and improve techniques for applying a piezoelectric composite material directly onto a stainless steel substrate. The research encompassed theoretical background, fabrication processes, and experimental validations. Stencil printing, known for its scalability, allows efficient production of large systems and offers flexibility in optimizing the piezoelectric layers' shape, location, and thickness. The study demonstrated that thinner layers (up to 0.25 mm) generated significantly more power than thicker layers. However, challenges like porosity and cracks limit the power output, necessitating further refinement in the fabrication process

This study focuses on enhancing the performance and reliability of piezoelectric bistable vibration energy harvesters. The research systematically classifies and evaluates different design strategies, aiming to maximize power density through strategic stress manipulation. Five designs are selected for optimization using a finite element model and are evaluated based on a proposed performance metric. The study introduces a method for effectively placing piezoelectric material to enhance power density. Experimental validation shows significant performance improvements, with the best design demonstrating a 71% increase in performance over conventional designs. The findings underscore the importance of addressing performance and durability in developing practical energy harvesters.