Figure 4. Verification on a robotic fin and a fabric-based finger. a The robotic fin swings in water to produce propulsion force where \(p_{low}\)= 10 kPa, \(\Delta p\)=10 kPa. b The robotic fin comprises two Double Bellows and a PVC sheet with a thickness of 0.5 mm. c Propulsion force in real-time when \(p_{high}\)=50, 75, 100 kPa, respectively. d Swinging frequency of the robotic fin. e Average propulsion force produced by the robotic fin. f Energy consumption per cycle of the robotic fin. g The fabric-based actuator is composed of a flexing chamber and an extending chamber. The actuator is worn on a silicone model hand to assist the finger. h Steady-state actuation frequency of the actuator. i Steady-state energy consumption per cycle of the actuator.