Experimental Analysis of Nonlinear Piezoelectric Systems for Vibration Energy Harvesting

Nonlinear piezoelectric vibration energy harvesting (VEH) offers distinct advantages over conventional linear harvesters, particularly in addressing the narrowband limitation inherent in resonance-based systems. By intentionally introducing nonlinear mechanisms, these devices can achieve improved energy conversion efficiency, broader operational bandwidth, and greater adaptability to environmental variability. Among nonlinear approaches, stopper-based configurations—also referred to as motion limiters—provide a practical method to generate piecewise nonlinear stiffness. In theory, properly designed stoppers induce hardening effects, suppress excessive displacements, and enable energy harvesting across multiple frequency bands. However, practical realization remains challenging, as stopper dynamics themselves may contribute unintended resonances and energy exchanges not accounted for in simplified models. This thesis investigates stopper-integrated cantilever piezoelectric systems through numerical modelling and experimental testing. Initially, a nonlinear lumped-parameter model is established and solved using state-space and Newmark-ß integration methods, with the stopper represented as a high-stiffness element. Simulations predicted clear hardening behavior and bandwidth enhancement. Experimental results, however, revealed discrepancies. The 3D-printed stoppers are significantly more flexible than predicted by SolidWorks simulations, introducing their own resonance frequencies close to the cantilever’s first mode. This unexpected interaction suppressed the anticipated hardening effect and instead caused energy exchange between beam and stopper. These findings highlight the limitations of simplified stopper models and the need to account for the dynamic behavior of flexible limiter structures. Building on this analysis, the thesis proposes directions for a redesigned test setup, including more rigid stopper geometries, alternative mounting orientations, and potential horizontal shaker implementation. The outcomes contribute both practical insight into stopper realization and theoretical refinement of nonlinear VEH modelling strategies.