A 2-degree-of-freedom cubic nonlinear piezoelectric harvester intended for practical low-frequency vibration

In the field of piezoelectric energy harvesting from ambient low-frequency vibrations, frequency up-converting effect is a classical approach to improve the efficiencies of energy conversion and extraction. However, most of the frequency up-converting harvesters are implemented by either mechanical impacts or non-contact impulse-like accelerations, which needs high-level excitations and usually leads to reduced longevity or considerable noise. To address these limitations, this paper introduces and demonstrates a novel frequency up-converting energy harvester based on 1:3 internal resonance. The nonlinear harvester mainly consists of two asymmetric cantilever beams in which the ratio of their resonant frequencies is 1:3. The harvester features two vibrational degrees-of-freedom (DOFs) corresponding to the two cantilevers: The primary DOF picks up the ambient low-frequency vibrations and excites the secondary one to vibrate drastically at its resonant frequency. Because the secondary resonance is three times higher than the excited frequency, the harvester realizes the frequency up-conversion. The underlying mechanisms of this design are thoroughly analyzed in the numerical simulation and experiment.