Investigating the advantages of internal impact in high-performance lightweight ultra-low-frequency rotational energy harvesters

Piezoelectric energy harvesters are promising for collecting energy from ultra-low-frequency rotational machines due to their small-scale and lightweight characteristics. However, the power output for the reported rotational piezoelectric energy harvesters can hardly reach the milliwatt level, limiting their applications in sensor systems with high power consumption. To overcome this challenge, this Letter proposes an approach of using the internal impact mechanism to achieve high-performance lightweight ultra-low-frequency rotational energy harvesters. The internal impact is achieved by utilizing the velocity difference between a sliding mass and a tube on a piezoelectric beam. Through mathematical modeling and experimental validation, it is demonstrated that the velocity difference exists at ultra-low-rotational frequencies without a defined frequency lower limit, thus increasing the vibration amplitude of beam and enhancing the power output. The results show that the impact system achieves up to 136 times increase in power output compared to the non-impact system. With a maximum power output of 2.97 mW and a power density of 169.19 μW/g, the proposed energy harvester significantly outperforms the previously reported lightweight ultra-low-frequency rotational energy harvesters and shows great potential in self-powered sensing and monitoring of ultra-low-frequency rotational machines.