Tuning and widening the bandwidth of vibration energy harvesters using a ferrofluid embedded mass

Widening the bandwidth and tunability are two of the major challenges associated with vibrational energy harvesting devices. This paper demonstrates a novel method involving embedding liquid into the mass which can be used to either widen the bandwidth or tune the frequency without significant decrease in power output. The paper builds upon previous research on using movable masses to widen the bandwidth. Various liquids including magnetic ferrofluid and Gallium-based liquid metal embedded masses were investigated. Ferrofluid location within the mass can be controlled using integrated hard magnet materials to tune and widen the bandwidth. Frequency tunability of 13.5% is demonstrated using ferrofluid with magnetic actuation. Bandwidth increase from 2.15 (non-movable mass) to 10.15 Hz with ferrofluid, and 17 Hz with liquid metal embedded mass was demonstrated without significant decrease in power output. Fill volume and applied acceleration significantly influence the bandwidth as they affect the percentage of movable mass as well as the force required to displace the liquid.