Characterization of circular-type actuators
The characterization process is depicted in Figure S4. The actuation strain of the actuator was measured using a laser displacement sensor (OPTEX FA, CDX-150). Up to 10 kV of voltage was applied to the actuator with 1 kV incremental. A PTFE sheet was placed on the actuator so that the laser sensor can detect the actuated displacement accurately. For characterizing the strain-voltage relationship, the actuation force was measured at a certain strain using a linear stage (Thorlabs, PT 1/M). The force generated by actuation was measured using a load cell (FUTEK, LSB 200). The load cell was placed above the actuator to identify the accurate normal force. The initial load was applied, the mass of which was identical to the PTFE sheet.