A two-degree-of-freedom pendulum-based piezoelectric-triboelectric hybrid energy harvester with vibro-impact and bistable mechanism

A novel two-degree-of-freedom hybrid piezoelectric-triboelectric energy harvester is proposed in this work, which consists of a pendulum oscillator whose ‘tip mass’ houses a piezoelectric cantilever beam that also forms two triboelectric sub-harvesters working in contact-separation mode. To broaden the bandwidth of the harvester, magnets are introduced to the system, bringing about bistability to both the pendulum and the cantilever beam. An electromechanical coupled theoretical model is established, based on which the vibro-impact dynamic behaviours of the energy harvester are investigated under various working conditions. Both experimental and numerical results indicate that, through this pendulum-based design, the energy harvester can achieve large-amplitude oscillation in a broad low-frequency band, which overcomes the difficulties of traditional bistable energy harvesters that interwell motion can't be achieved under low-frequency and weak excitations. It is found that the maximum outputs of the sub piezoelectric energy harvester and the sub triboelectric energy harvester are 0.93 mW and 0.053 mW, respectively, when the excitation frequency is 4 Hz and the excitation amplitude is 15 mm, which are 23 times and 38 times larger than the configuration without pendulum swinging. This research has provided a new effective solution to scavenge vibration energy from low-frequency and weak excitations.