High-efficient internal resonance energy harvesting: Modelling and experimental study

This research investigates a U-shaped vibration-based energy harvester with broadband and bidirectional features via an internal resonance. The proposed U-shaped structure has been tailored in a way that displays a two-to-one internal resonance between the selected transverse modes. The resonant modes and mode shapes of the proposed device have been designed and validated through an analytical method, the finite-element simulations as well as experimental tests, showing good agreement. The experimental tests imply the benefits of energy transfer between two modes, as resonance phenomena in all segments have been successfully triggered to obtain large-amplitude oscillations for high-efficient energy conversion via piezoelectric effects. Under harmonic excitations, different from conventional multi-mode vibration energy harvesters, the proposed device presented broadened resonance regions for both modes, and exhibited equally effective bandwidths under forward/backward sweeps. Moreover, the device is capable of being excited in two orthogonal directions as a bi-directional energy harvester. Parametric studies on the acceleration levels are also presented to evaluate the system performance and reveal the critical excitation level for triggering the internal resonance. It has been found that even under a 0.1 g acceleration level, the internal resonance phenomenon can still be observed between the first and second modes, which implies the feasibility of the proposed device even for ambient vibration sources with low energies.