A Self-Propelled Mechanism to Increase Range of Bistable Operation of a Piezoelectric Cantilever-Based Vibration Energy Harvester.

In our previous works, we presented a method to increase the harvested energy from vibrations using a piezoelectric cantilever and to increase the frequency range of operation by introducing bistability with the use of magnetic repulsion. However, for small excitations, the cantilever may not be able to overcome the magnetic repulsive force but vibrate at one of its two equilibrium positions with reduced amplitude. This work introduces a method of increasing the range of excitations over which the operation remains bistable. This is achieved by spring loading one of the magnets, previously on a fixed support, allowing motion in one dimension only, toward and away from the cantilever in the horizontal plane. Configured so, as the cantilever moves toward this magnet, the repulsion due to the cantilever-mounted magnet pushes the spring-loaded magnet away, increasing distance, and thus, reducing magnetic force between them, required to be overcome by external excitations for bistable operation. Similarly, as the cantilever moves away, the spring pushes the magnet closer to the cantilever-mounted magnet, increasing vibration amplitude. Thus, the spring introduces a negative feedback which favors bistable operation over an increased range of excitations. This completely mechanical method requires no additional energy cost. Peak power gains of up to 90 and a decrease in excitation voltage of up to 60% were observed over the fixed magnet.