Fast and Dexterous Locomotion in a Soft Robotic Fish Enabled by Liquid Metal Electromagnetic Actuation

Pulsed-jet propulsion is a common loco-motion mode among marine animals. Inspired by the jet propulsion mechanism of cephalopods, this paper proposes a fast-moving, agile, and quiet soft robotic jet fish based on an electromagnetic liquid metal actuator. The interaction between the powered liquid metal coils and the magnetic field drives the robotic fish's body to contract and expand periodically, generating pulsed jets and thus obtaining propulsive force. We systematically investigate the influence of different design parameters and driving currents on the swimming speed and turning ability of the robotic fish. This paper describes in detail the design and control methods of the soft robotic fish and validates its locomotion performance through water tank experiments. With an optimal parameter combination-square wave current with +1.5 A for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.4\ s$</tex> followed by −1.5 A for 0.3 s in each cycle, and a nozzle diameter of 6.5 mm-the robotic fish can achieve a straight-line swimming speed of 1.7 BL/s (8.9 cm/s), exhibiting excellent propulsive performance. Furthermore, by incorporating a deflection angle on the nozzle, we enhance the robotic fish's turning capabilities. Experimental results show that it achieves a maximum turning speed of 47.4 deg/s and a minimum turning radius of 0.4 BL. With programmed control, the robotic fish can execute complex motions, demonstrating its potential applications in fields such as environmental monitoring, marine exploration, and search and rescue operations.