Robotic jellyfish actuated with a shape memory alloy spring

We demonstrate a new approach to the design of a synthetic jellyfish that imitates the morphology and kinematics of the actual animal. Since jellyfish usually move at low speeds, the locomotion can be mimicked using shape memory alloy (SMA) springs as artificial muscles. Compared to previous attempts at biomimetic underwater robots, the current research aims to simplify the design, generate larger stroke, and lower the actuation cycle for propulsion. The robot consists of a soft silicone rubber disk with an embedded pre-stretched SMA spring along its circumference, which when heated contracts to initiate large shape changes in the structure. Our approach harnesses the buckling instability of the main body to create a relatively quick motion that produces a pulsed jet of water to generate thrust. The rubber disk is also equipped with several flaps that contribute to the swimming motion by displacing the surrounding water through a rowing-like mechanism. The influence of different operation parameters, including the amplitude of the input power and the actuation frequency, are investigated on the swimming motion and propulsive thrust.