Table 5 A summary of soft actuations used in robotic fish

FEA (Fluidic Elastomer Actuators)

Pressure input leads to bending constrained by an inextensible layer;

Stress < 5 MPa, strain < 15%, typical frequency ≈ 2 Hz, efficiency < 20%, work density ≈ 0.5 J/kg

See Figure 10

DEA (Dielectric Elastomer Actuators)

Maxwell stress results in compression in one side and extension in the other;

Stress < 7.2 MPa, strain < 380% (area), typical frequency ≈ 1−10 Hz, efficiency < 90%, work density < 3.5 J/kg

SMA (shape memory alloy)

Deformed at low temperatures and recovered to original shape at high temperatures; long time delays;

Stress > 300 MPa, strain > 4%, efficiency > 3.8%

IPMC (ionic polymer-metal composite)

When an electric field is applied, swelling on the cathode side and shrinking on the anode side cause bending;

Stress < 5 MPa, typical frequency ≈ 5 Hz, efficiency < 3%, work density < 4 J/kg