A vibration energy harvesting device with bidirectional resonance frequency tunability

TLDR

Vibration energy harvesting is promising for powering wireless sensors, yet most devices rely on a single resonance frequency, underscoring the need for a robust tunable technique. The study designs and tests a magnetic‑force based device that tunes its resonance frequency. The device uses magnetic forces to adjust resonance frequency, supported by a variable‑damping model and experimental characterization of damping and load effects. The device achieves ±20 % tuning, shifting a 26 Hz cantilever to 22–32 Hz and delivering 240–280 µW continuously across that range.

Abstract

Vibration energy harvesting is an attractive technique for potential powering of wireless sensors and low power devices. While the technique can be employed to harvest energy from vibrations and vibrating structures, a general requirement independent of the energy transfer mechanism is that the vibration energy harvesting device operate in resonance at the excitation frequency. Most energy harvesting devices developed to date are single resonance frequency based, and while recent efforts have been made to broaden the frequency range of energy harvesting devices, what is lacking is a robust tunable energy harvesting technique. In this paper, the design and testing of a resonance frequency tunable energy harvesting device using a magnetic force technique is presented. This technique enabled resonance tuning to ± 20% of the untuned resonant frequency. In particular, this magnetic-based approach enables either an increase or decrease in the tuned resonant frequency. A piezoelectric cantilever beam with a natural frequency of 26 Hz is used as the energy harvesting cantilever, which is successfully tuned over a frequency range of 22–32 Hz to enable a continuous power output 240–280 µW over the entire frequency range tested. A theoretical model using variable damping is presented, whose results agree closely with the experimental results. The magnetic force applied for resonance frequency tuning and its effect on damping and load resistance have been experimentally determined.