Tuning of Vibration Energy Harvesters by Means of Liquid Masses

This paper presents a piezoelectric harvester prototype with liquid tip mass for frequency tuning. The use of a liquid mass makes it possible to limit mechanical stress inside the harvester, with a resonance frequency reduction comparable to a solid mass. A mathematical model of the water sloshing in the tip container, which makes it possible to predict natural frequencies of a harvester with liquid mass, is presented. Such analytical model can be used for the harvester tuning to low-frequency vibration sources. Mathematical predictions are in good agreement with experimental results obtained from the harvester prototype. As an example of practical application is considered: energy harvesting from bicycle vibrations.