Effect of hydrodynamic interaction on energy harvesting in arrays of ionic polymer metal composites vibrating in a viscous fluid

In this paper, we investigate underwater energy harvesting of a parallel array of nominally identical ionic polymer metal composites (IPMCs) subjected to low frequency base excitation in water. The IPMCs are connected in parallel and shunted with a varying resistor. We model the IPMCs as slender beams with uniform cross section undergoing small oscillations in an otherwise quiescent viscous fluid. We utilize a boundary element approach to compute the hydrodynamic loading on each structure, which is due to the oscillations of the whole array. Leveraging recent findings on sensing in ionic polymer metal composites, we propose a coupled electromechanical model for predicting energy harvesting as a function of the IPMCs' impedance and the base excitation. To validate our theoretical predictions, we perform experiments on an in-house-fabricated array of five centimeter-size composites, which we characterize on a dedicated test rig. We experimentally determine the power harvested by varying the excitation frequency in the broad range 2-35 Hz and the shunting resistance from 1 to 1000 Ω.