Array piezoelectric energy harvester with frequency up-conversion in rotational motions: theoretical analyses and experimental validations

Piezoelectric energy harvesters (PEHs) have attracted great attention to solve the power supply issue of wireless sensors in rotational motions. PEHs based on smart structures and physical principles have been widely investigated. Currently, the frequency bandwidth and the energy harvesting efficiency are two urgent issues to be solved in practical applications. Benefiting from the advantages of magnet-induced nonlinearity and frequency up-conversion, this paper proposes array PEHs for rotational energy harvesting. To reveal their broadband mechanisms, the corresponding theoretical model is established according to Lagrange equations. Then, effects of the gap distances, frequency up-conversion and installation configurations on the dynamic characteristics of PEHs are theoretically analyzed. In addition, experimental validations are conducted to investigate these effects under different rotational speeds. Experimental results demonstrate that the gap distance of 8 mm leading to a large driving force is better for improving energy harvesting performance than other gap distances. Furthermore, the frequency up-conversion phenomena are validated to widen the effective frequency bandwidth. The gravity effect on the PEHs for the forward and headstand configurations is noticed, simultaneously qualitatively verifying the gravity coefficient in the derived mathematical model. In summary, this paper presents a high-efficiency array PEHs for rotational energy harvesting with in-depth theoretical analyses, providing insights into the broadband PEH design in rotational motions.