A vibration energy harvesting device with bidirectional resonance frequency tunability

Abstract

Vibration energy harvesting is an attractive technique for potential powering of wirelesssensors and low power devices. While the technique can be employed to harvest energyfrom vibrations and vibrating structures, a general requirement independent ofthe energy transfer mechanism is that the vibration energy harvesting deviceoperate in resonance at the excitation frequency. Most energy harvesting devicesdeveloped to date are single resonance frequency based, and while recent efforts havebeen made to broaden the frequency range of energy harvesting devices, what islacking is a robust tunable energy harvesting technique. In this paper, the designand testing of a resonance frequency tunable energy harvesting device using amagnetic force technique is presented. This technique enabled resonance tuning to ± 20% of the untuned resonant frequency. In particular, this magnetic-based approach enableseither an increase or decrease in the tuned resonant frequency. A piezoelectric cantileverbeam with a natural frequency of 26 Hz is used as the energy harvesting cantilever, which issuccessfully tuned over a frequency range of 22–32 Hz to enable a continuous power output240–280 µW over the entire frequency range tested. A theoretical model using variable damping ispresented, whose results agree closely with the experimental results. The magnetic forceapplied for resonance frequency tuning and its effect on damping and load resistance havebeen experimentally determined.