A novel soft encapsulated multi-directional and multi-modal piezoelectric vibration energy harvester

Advances in the design of various piezoelectric vibration-based energy harvesters (PVEHs), as a kind of power devices that can convert ambient energy to useable electrical energy, have become a hot topic in recent years due to their potential perspectives in wireless sensor networks, wearable electronics and low-power microelectronics. Unfortunately, conventional PVEHs modelled by beam- or plate-type planar structures are mainly restricted to harness kinetic energy in a single direction only. However, ambient vibration sources often work in multiple directions and broadband frequencies. To address this challenging problem, a mechanically-guided three-dimensional (3D) assembly structure is strategically designed to construct a soft cruciform-encapsulated PVEH in this work. Meanwhile, a reliable soft encapsulation technology is introduced to maintain the 3D configuration, which not only can avoid the collapse problem and also improve the dynamical performance. The entire system consists of a compressive buckling cruciform structure with a proof mass, PVDF thin film, and soft encapsulation. The dynamic characteristics of the system can be adjusted by changing the structural parameters, such as the pre-stressing force of the pre-stretched elastic substrate and the quality of the additional mass block. Finite element analysis and experimental studies are conducted to investigate the modal characteristics of system. A comparison of the vibration energy harvesting performance between the encapsulated and unencapsulated piezoelectric harvesters is presented. The results demonstrate that the encapsulated one can work well under multi-directional, multi-modal and low-frequency conditions. A maximum power output of 9.8 mW in the frequency range of 1e20 0 Hz can be achieved, which is almost 560 times more than that of the unencapsulated one. The proposed methodology also offers a new perspective for the fabrication design of soft-type PVEHs with higher working performance.(c) 2022 Elsevier Ltd. All rights reserved.