# Ultralight soft electrostatic actuators based on solid-liquid-gas architectures

## TL;DR

This paper introduces ultralight soft electrostatic actuators that use a solid-liquid-gas design to significantly improve power-to-weight ratio and actuation speed for agile robots.

## Contribution

The novel use of gaseous dielectrics in electrostatic actuators to enhance performance and reduce mass.

## Key findings

- A gas mixture of C4F7N and CO2 achieved a specific energy of 51.4 J kg-1, a nine-fold improvement.
- Using ambient air as a dielectric still achieved a power-to-weight ratio of 1600 W kg-1.
- A jumping robot demonstrated a 60% increase in jump height with the new actuators.

## Abstract

Soft actuators enable versatile and adaptable robots capable of operating in unstructured environments and close to humans. Soft electrostatic actuators utilizing electrohydraulic principles are particularly promising, combining all-around actuation performance with portable driving electronics. These electrohydraulic actuators harness liquid dielectrics enclosed in solid dielectric shells to sustain high electric fields; the liquid dielectric however constitutes most of the actuator mass, limiting power-to-weight ratio. Here, we present ultralight soft electrostatic actuators based on solid-liquid-gas architectures: the introduction of gaseous dielectrics as a third phase substantially improves power-to-weight ratio by reducing actuator mass and increasing actuation speed. Through theoretical and experimental analyses, we pinpoint the fundamental performance limit as the electrical breakdown in the gas, governed by Paschen’s law, thereby providing a guideline for selection of gaseous dielectrics. Using the Peano-HASEL (hydraulically amplified self-healing electrostatic) actuator as a model system, we identify a gas mixture of C4F7N and CO2 that enables outstanding specific energy of 51.4 J kg-1 (a nine-fold improvement over conventional Peano-HASELs); using ambient air as gaseous dielectric we still achieve 33.5 J kg-1 and a power-to-weight ratio of 1600 W kg-1 (a five- and eleven-fold improvement). We illustrate these enhanced performance metrics in a jumping robot, showing a 60% increase in jump height, highlighting the wide potential of ultralight soft electrostatic actuators for adaptable and agile robotic systems.

Soft electrostatic actuators are crucial for advancing robotic systems that require adaptability and safety in unstructured environments. This study introduces ultralight soft electrostatic actuators utilizing solid-liquid-gas architectures, achieving significant improvements in power-to-weight ratio and actuation speed, exemplified by a 60% increase in jump height in a jumping robot compared to traditional designs.