A self-tuning resonator for vibration energy harvesting

This work is concerned with developing a vibration-based energy harvester with a tunable natural frequency. The harvester is designed to automatically adjust its own natural frequency to match that of the imposed base excitation. The proposed device consists of a cantilever beam carrying a tip mass in the form of a magnet which is placed in close proximity to another magnet with opposite polarity that can move axially thereby adjusting the beam's natural frequency by mechanical straining. The system is designed to autonomously adjust the gap between the two magnets so as to achieve a harvester whose natural frequency matches that of the excitation. As such, the movable magnet is mounted on a motor-driven tray that undergoes linear motion and adjusts its position in accordance with the frequency of the support motion. The base motion frequency is detected by an electromagnetic means, wherein another magnet, fixed to the base, moves past a stationary coil generating an electric signal. The signal is conditioned through a microprocessor to detect its frequency and is then used to determine the favorable gap between the tuning magnets to achieve resonance from a lookup table. Based on the findings of this work, the natural frequency of the harvester is successfully tuned from 4.7 Hz to 9.0 Hz generating voltage per acceleration from 6.3 V/m/s2 to 1.1 V/m/s2, respectively.