Efficient swimming through electroactive polymer hydrodynamic sensing

Abstract

For long-range swimming fish, low cost of transportation is a critical requirement. This also applies to autonomous fishlike robots (AFR). As with their biological cohorts, AFR require sensory input that characterizes the flow of the water surrounding them. Thus, there is a need for low power hydrodynamic sensors that can be deployed on a fish-like robot, and which can provide flow information from open water conditions. Electroactive polymers offer opportunities for flow sensing on soft and flexible AFR. We developed and evaluated an approach for capacitive electroactive polymer flow sensing. This uses dielectric elastomer sensor membranes mounted on a liquid-filled cavity protruding into the flow. Flow speed and incident angle on a hydrofoil standing in for the fish are registered through electrical capacitance changes resulting from deformation of its 350μm thick membrane. Through its triple-electrode design, measurements are largely shielded against the influence of the surrounding water on the capacitor. Differences in flow speed along the sensor can be detected with high reproducibility for extended durations of time. The developed sensors were assessed regarding accuracy, reliability, and durability. For performance and long-term testing, an automated tabletop water tunnel test rig was created. This setup enables sensor testing for flows up to 1 m/s with automated incident angle control and data logging. We are thus presenting further steps towards robust ocean-faring hydrodynamic sensory systems by demonstrating advances in electroactive sensory technology and testing facilities.