A multidirectional ultralow-frequency rotational energy harvester: Modeling and characterization

Energy harvesting under ultralow-frequency rotation is challenging, especially for frequencies below 1 Hz. This paper proposes a highly robust multidirectional ultralow-frequency rotational energy harvester (MUREH). The impact force generated by periodic gravity provides double excitation for the harvester at ultralow frequencies. The piezoelectric cantilever beam resonates at the intrinsic frequency under ultralow-frequency excitation, achieving frequency up-conversion and energy harvesting abilities under 1 Hz. An electromechanical coupling model is developed to analyze the influence of crucial parameters. Uniaxial and triaxial rotation measurements characterize the performance of the MUREH. At optimum conditions, the MUREH's root mean square voltage is 4.995 V at 0.8 Hz. The adaptability of attitude randomness is verified by triaxial rotation experiments, with an output of not less than 77 % when tilted less than 45 degrees. Under frequent disturbances, 66 % power is maintained, demonstrating high robustness.