Comparative Study of a 2-DoF Hybrid Piezoelectric-Electromagnetic Energy Harvester and a Standalone Piezoelectric Harvester

This study investigates the effect of incorporating an electromagnetic harvester inside the bluff body of a 2-DoF hybrid harvester in comparison to a standalone piezoelectric harvester for various external loads. The design consists of an electromagnetic harvester embedded inside a cylindrical bluff body, which is attached to the free end of a composite PZT cantilever beam. The harvester is excited through a vortex-induced vibration owing to the resultant wake vortices created behind the bluff body. The coupled equations of motion of the harvester are derived using the lumped-mass equivalent representation and Lagrange formulation. Numerical results show that at high operating flow speed and large electrical load, the standalone piezoelectric harvester outperforms the hybrid harvester. Nevertheless, for small electrical loads and at low-speed flow, the hybrid harvester outperforms the standalone ones for a wider range of the flow speed. In these operating conditions, numerical simulations also showed that an optimum spring stiffness of the electromagnetic harvester exists at a certain flow speed for a maximized harvested output power. In general, such hybrid energy harvester showed to be more effective at low-speed fluid flow and small electrical loads.