Review of electrohydraulic actuators inspired by the HASEL actuator

The muscle-like movement and speed of the electrohydraulic actuator have granted it much attention in soft robotics. Our aim is to review the advancements in electrohydraulic actuators inspired by the Hydraulically Amplified Self-healing Electrostatic (HASEL) actuator. With this paper, we focus on the performance of 21 electrohydraulic actuator designs developed across five Universities, ranging from the earliest HASEL designs to the latest electrohydraulic designs. These actuators reported up to 60 N forces and contracting strains of up to 99%. The actuators with the best overall performance so far have been the Quadrant HASEL actuator and the HEXEL actuator, developed at the University of Colorado Boulder. However, notable is also the HALVE actuator (produced by ETH Zürich, Switzerland), which, by using a 5 µm PVDF-TrFE-CTFE film with a relative permittivity of 40, produced 100 times the electrostatic force of any of the electrohydraulic actuators under review. The latter shows that there is room for improvement as low force and displacement still limit the viability of the soft actuators in real-life applications.