Shape-Shifting Robotic Wing Cuts Underwater Turbulence Jolt by 87% Using Liquid Metal Nerves
A fish navigating a river full of obstacles does not fight the current. It reads it. Receptors distributed along the fish's lateral line detect minute pressure changes in the water flowing around its body, and its fins and musculature respond in milliseconds, making continuous small adjustments that keep it on course without wasting energy on brute resistance. Birds do something analogous in air, sensing changes in airflow through feathers and adjusting wing shape in real time.
Autonomous underwater vehicles - the robots used for ocean surveying, pipeline inspection, and environmental monitoring - cannot do this. Their rigid bodies and fixed wings absorb the energy of sudden currents as jolts, and their onboard systems must actively counteract these forces, consuming power and reducing efficiency. A research team led by the University of Southampton, in collaboration with the University of Edinburgh and Delft University of Technology in the Netherlands, set out to close this gap by transplanting the principles of biological proprioception into a robotic wing.
Liquid Metal Wires as Artificial Nerves
The central innovation is an electronic skin - an e-skin - made from flexible liquid metal wires encased in silicone. When the wing bends in response to water flow changes, the metal wires deform, changing their electrical resistance. Those resistance changes are the signal. The wing reads them as it would nerve impulses, translating the deformation pattern into information about the nature and magnitude of the disturbance.
Two hydraulic tubes run through the wing's body, pressurized to control the wing's stiffness and curvature - its camber. When the sensors detect a disturbance, the system adjusts the hydraulic pressure to change the wing's shape, reducing the force of the impact. The entire loop - sense, interpret, respond - operates without external control inputs. The wing governs its own behavior.
The results, published in npj Robotics, show this system reduces unwanted uplift impulse - the vertical jolt caused by a sudden underwater current - by 87% compared to the rigid wings currently used on autonomous underwater vehicles. The proprioceptive wing also responds up to four times faster than comparable soft wings without sensing capability, and consumes five times less energy than thermally actuated shape-changing wings, which use heat to trigger material deformation.
Comparing to Biology
Lead author Leo Micklem, who carried out the work at the University of Southampton and is now at Portland State University, noted that the wing's stability improvement is roughly double that of a barn owl during glide - a striking comparison, though one the authors flag should be interpreted cautiously. Biological flight and underwater vehicle dynamics involve different physical regimes, and the comparison is informative rather than strictly quantitative. What it illustrates is that the performance gap between biological adaptive systems and engineered ones is narrowing.
Practical Obstacles Still Ahead
The research team is candid about what stands between this laboratory demonstration and deployment on operational vehicles. Scaling the e-skin and hydraulic actuation systems to full-size autonomous underwater vehicles introduces integration challenges with the rigid structural components those vehicles require. Long-term robustness in real ocean conditions - salt water, biofouling, pressure at depth, temperature variation - has not yet been tested. The tests conducted involved disturbances of defined shapes and magnitudes under controlled conditions; the ocean produces a more varied and unpredictable disturbance environment.
The team also suggests that more powerful actuators could extend the stability improvements further, and that the e-skin sensing principle could potentially be adapted for other applications where sensitive environmental perception and adaptive response would benefit robotic systems operating in unstructured natural environments.
Professor Blair Thornton of the University of Southampton, a coauthor on the paper, framed the goal: ocean robots must continuously sense what is happening around them and respond accordingly. This wing represents a step toward machines that work with the water rather than against it.