Piezoelectric vibration energy harvesterwith movable tip mass

This thesis presents a novel smart vibration energy harvester that is able to automatically adjust its natural frequency. The proposed harvester preserves the electrical power generating element in a resonance with ambient vibration in order to maximize power yield. The structure consists of two piezoelectric cantilever beams, a miniature piezomotor with a movable mass connected to one of the beams, a control unit and electronics. The piezomotor does not require energy to fix its movable mass as a result of its self-locking feature. At each predefined interval, the control unit performs voltage comparisons where each level crossing provides timings to calculate the phase difference between two beams. When necessary, it actuates the piezomotor to move its mass in the appropriate direction. After completing its tasks, the control unit switches to the power-saving sleep mode. It is shown that the proposed tuning algorithm successfully increases the fractional bandwidth of the harvester from 4% to 10%. A piezomotor having longer range of motion will improve this value. The system is able to deliver 66.8% of the total harvested power into usable electrical power while the piezomotor actuation uses only 3.6% of the harvested power. The presented efficient, auto-tunable and self-sufficient harvester is built using off-the shelf components and it can be easily modified for wide range of applications.