High output, lightweight and small-scale rotational piezoelectric energy harvester utilizing internal impact effect

It is in great need to achieve continuous battery-free wireless sensing and monitoring of an amount of ultra-low-frequency large-scale rotational machines in transportation, civil engineering, manufacturing, and energy industry. Rotational piezoelectric energy harvesters are promising candidates to power sensors for their high energy densities and ease of integration. However, meeting the sufficient and continuous power supply needs of long-distance sensors for the Internet of Things (IoT) while maintaining the small volume and mass of harvesters remains a challenging task. To overcome this challenge, this work firstly implements the internal impact mechanism to a rotational centrifugal softening piezoelectric energy harvester to achieve its high output, lightweight and small-scale characteristics. On one hand, the internal impact effect utilizes the velocity difference between the piezoelectric beam and sliding mass to enlarge the deflection of piezoelectric material and boost the energy output. On the other hand, the centrifugal softening effect reduces the resonant frequency of harvester, leading to the harvester suitably used for the ultra-low-frequency rotation environment. Theoretical and experimental results demonstrate that the proposed harvester can achieve the normalized energy densities of 17.39 $\mu$W/(g Hz) and 1800.97 $\mu$W/(cm${}^3$ Hz) that stand out among the previously reported rotational piezoelectric energy harvesting devices. Additionally, it is proven experimentally that the energy harvester can achieve the self-powered LoRa system under ultra-low-frequency rotations. The proposed harvester demonstrates significant potential for future battery-free sensors in large-scale rotational machinery monitoring.