Novel hybrid piezoelectric harvesters based on a nonlinear x-structure for ocean wave energy harvesting

A novel hybrid ocean wave energy harvesting (WEH) system is investigated in this study based on an X-shaped structure coupled with piezoelectric harvesters of special arrangements. In this system, the X-shaped structure not only acts as a supporting structure that transfers the mechanical energy from the base excitation, but also as a master and tunable structure. This enables the resonant harvesting frequency of the harvesters to match the ambient ocean wave whose frequency is usually below 5 Hz. The piezoelectric harvesters are specially installed on the X-shaped structure to explore potential benefits that the X-shaped structure could provide. Each piezoelectric beam has two layers composed of a PVC (Polyvinyl chloride) base patch and a MFC (Micro fiber composite) patch. Two types of special mounting configurations (horizontal and vertical) of the beam harvesters are designed, and the beam harvesters are mounted on the X-shaped structure through auxiliary horizontal and vertical leverages respectively. The results indicate that, the energy harvesting performance of the piezoelectric harvesters can be enhanced especially in low-frequency range by the proposed novel arrangements, compared with simple cantilevered piezoelectric harvesters. The X-structure based generators can enable piezoelectric materials to harvest power from ocean wave energy which is at low frequency range, and the harvesting systems demonstrate beneficial nonlinear properties and/or features by employing the X-structure, without a risk of losing stability. Also, several structural parameters can be easily adjusted to achieve tunable and ultra-low resonant harvesting frequency and wider energy harvesting bandwidth. The design and results would provide an innovative solution and insight to improve the energy harvesting efficiency in small-scale ocean wave energy harvesting to power wireless sensor networks for multiple offshore applications.