Soft Electrohydraulic Actuators

Abstract

Soft electrohydraulic actuators (SEHAs) represent a novel class of electrostatic-driven soft actuators sharing a common working principle: the coupling of electrostatic actuation with dielectric liquid transmission or hydrodynamic actuation. As a result, SEHAs inherit the combined advantages of both actuation mechanisms, including high response speed, high force density, diverse actuation modes, silent operation, low power consumption, and minimal heat emission—attributes that have attracted much attention and applications in soft robotics and human-machine interaction recently. This review provides the first holistic overview of SEHAs, with a primary focus on three categories classified according to the different coupling methods between electrostatic actuation and dielectric liquids: hydraulically amplified self-healing electrostatic (HASEL), electro-ribbon (ER), and electrohydrodynamic (EHD) actuators. We then compare and contrast their similarities and differences, while elaborating on their actuation mechanisms, structural designs tailored to different actuation modes, material selection strategies, fabrication techniques, and potential application scenarios. Finally, we discuss the key challenges and prospective research directions, including reducing operating voltage, enhancing actuation performance, and advancing integration and intelligent technologies for practical applications. This review is expected to provide guidance and inspiration for the high-performance soft actuators, while continuously stimulating the innovation and application of SEHAs in next-generation flexible electromechanical systems.