Piezoelectric Eels for Energy Harvesting in the Ocean

To perform long endurance military missions, small, unattended sensor packages must generate and harvest power from their surroundings. The experiments described extend our previous studies on the possibility of using piezoelectric polymers as power generation devices. Thin flexible piezoelectric membranes, or "eels, " are mounted aft of a rectangular bluff body and are excited by vortex shedding in the wake of the body. This flapping motion generates strain energy in the material that can be converted to electric power and stored in a battery to power small sensors and an acoustic modem. Here we report new experiments on the behavior of multiple eels, stacked vertically behind a single bluff body. Experiments show a range of flow regimes, ranging from poorly coupled motions, where three-dimensionality in the vortex shedding is important, to an optimally coupled state, where the membranes oscillate at the natural frequency of the undisturbed wake. The effects of membrane length are also studied.