Piezoelectric energy harvesting from extremely low-frequency vibrations via gravity induced self-excited resonance

In this paper, we originally present a gravity induced self-excited vibration generator based on a cantilever piezoelectric resonator. The configuration is composed of a sliding rod, a sleeve, a transduction unit. To estimate output voltage and investigate dynamic responses of the generator, an equivalent model based on mechanical structure was established and numerically solved. The effects of the cantilever length, tip mass and linear coupling factor on the open circuit voltage were discussed. In addition, we also conducted series of experiments to validate the theoretical responses. In a 10s cycle (namely 0.1Hz excitation frequency) scenario, the transduction unit responds with structural resonant frequency of 8.621Hz. The results of the experiments show that the open circuit voltage of the generator increases with increment of the cantilever beam length and the tip mass, which agrees well with simulation estimations. We also conducted impedance matching experiments to examine power response in the load spectrum, of which the results indicate that the prototype peak power reaches maximum 1.897 mW. We also discussed the change of gravity potential energy of the prototype and compared it with electric energy. This work provides a novel approach for piezoelectric energy harvesting from extremely low frequency excitations.