Low-frequency energy scavenging by a stacked tri-stable piezoelectric energy harvester

Abstract

We present a portable, stacked and tri-stable energy harvester based on the unique geometrical structure of L-shaped beams and the nonlinearity of magnetic force to harness low-frequency and low-level excitations. In this device, multiple L-shaped piezoelectric beams are connected in a head-to-tail manner. Such a special stacked structure reduces the natural frequency of the system while realizing the series connection of multiple piezoelectric sheets in a limited space, thus improving the acquisition efficiency. Additionally, magnetic coupling endows the harvester with tri-stability and consequently enhances the bandwidth responses in low-frequency environments. The mathematical model is developed, and the static behaviors are explored by the bifurcation theory. Furthermore, the complex dynamic frequency method combined with the arc length method is conducted to investigate the dynamic responses with different parameters. Sinusoidal excitation experiments on the prototype verify the rationality of the mathematical model and the low-frequency broadband capability of the harvester. In the experiments, the designed harvester can reach a maximum output power of 1.49 mW at the low excitation amplitude of 0.4 g, and the magnet coupling significantly enhanced the electrical responses. The human motion tests demonstrate that the designed harvester has the potential to convert biomechanical energy into electrical energy for continuous powering of wireless devices.