A ferrofluid-based energy harvester: An experimental investigation involving internally-resonant sloshing modes

The conformable nature of liquid-state transduction materials offers unprecedented opportunities for designing complex-shaped vibratory energy harvesters that are, otherwise, hard to realize using solid-state transduction elements. To achieve this goal, we propose an electromagnetic energy harvester which exploits the sloshing of a magnetized ferrofluid column in a base-excited container to transform vibratory energy into electricity. The sloshing of the magnetized ferrofluid column generates a change in magnetic flux which, in turn, induces a current in an adjacent closed-loop conductor. In this study, we specifically choose the dimensions of the container and the height of the fluid column such that the modal frequencies of the sloshing ferrofluid are nearly commensurate. It is shown that this choice of parameters activates a two-to-one internal energy pump between the commensurate modes resulting in two response peaks and large-amplitude voltages over a wide range of frequencies, thereby improving the steady-state bandwidth of the harvester. Influence of several of the key design parameters on the harvester's performance is also discussed.