This research program addresses the grand challenge of extracting usable energy from small-scale aquatic systems. This program envisions establishing a fundamental understanding of the spectrum of energy scavenging modalities in marine environments towards the development of self-sustained multifunctional marine microsensors. This project seeks to exploit ambient mechanical vibrations and coherent fluid flow structures for energy harvesting. Mechanical vibrations in aquatic environments occur in a vast array of both man-made and natural structures, as well as in animal swimming. Coherent fluid structures, such as Karman vortex streets and turbulent eddies, are generally present in aquatic environments and are due to a variety of mechanisms, including flow separation from fixed immersed bodies, thermal and pressure gradients, and momentum transfer from swimming animals. Practicality dictates that harvesters for underwater applications be lightweight, require small forces and low frequencies to elicit motion, produce sufficient electrical power to run a set of microdevices, and operate in wet conditions. Ionic Polymer Metal Composites (IPMCs) meet all of these requirements and are thus selected for this study.
In this project, we have studied energy harvesting devices in aquatic environments towards the development of self-sustained multifunctional underwater microsensors. We have sought to exploit ubiquitous natural and man-made ambient mechanical vibrations and little eddies in a flow as energy sources. Fish swimming is one example that offers both mechanical vibrations from the tail undulations and small eddies shed from the fins. To transform mechanical energy into useful electrical energy, we have employed Ionic Polymer Metal Composites (IPMCs), a novel class of smart materials that are well suited for operation in aquatic environments. These soft materials consist of a sandwich structure with a thin polymer coated on both sides by metal electrodes. We have studied energy transduction in IPMCs in a wide range of experimental conditions and established predictive models for estimating energy harvesting. We have ultimately established an array of fundamental methodologies and technical devices that incorporate IPMCs for scavenging energy underwater. Specifically, we have studied the possibility of energy harvesting from: IPMCs that vibrate in response to the motion of their base; fluttering flapping flags that host IPMCs; vortex rings impacting IPMCs; experimental models of fish swimming with IPMCs attached to the beating tail; hull slamming of flexible wedges with IPMCs; vibrations of arrays of IPMCs; and turbines hosting IPMCs. The project also contributed to an improved understanding of underwater vibrations in general, as well as experimental techniques to measure fluid flows in the laboratory and beyond. Several graduate and undergraduate students have been trained in interdisciplinary research on sensors and sensing systems, publishing their findings in international journals and presenting at technical conferences. High school students and teachers have been extensively involved in experimental research. Research findings have been heavily disseminated to the general public through outreach events in New York City and Washington DC, in which participants interacted with IPMCs and learnt about underwater sensing and energy harvesting.
