Bubble-like dielectric elastomer actuator with hydrostatic coupling for tactile displays

To improve versatility and safety of electroactive polymer actuators made of dielectric elastomers, so-called hydrostatically coupled dielectric elastomer actuators (HCDEAs) have recently been shown to offer new design opportunities. HCDEAs are based on an incompressible fluid that mechanically couples a DE-based active part to a passive part interfaced to the load, so as to enable hydrostatic transmission. In this paper, we present ongoing development of bubble-like HCDEAs. The device includes the following parts: 1) an electromechanically active membrane, made of a dielectric elastomer film coated with compliant electrodes; 2) an electromechanically passive membrane, working as end effector in contact with the user; 3) an incompressible fluid contained between the two membranes. Actuation of the active membrane through a voltage difference applied between its electrodes exerts onto the fluid a pressure, which is hydrostatically transmitted to the passive membrane. The active membrane buckles outwards (owing to its pre-curvature), while the passive membrane follows inwards. This principle allows safe transmission and delivery of actuation from the active membrane to the user. The paper describes performance of prototype samples of millimeter-sized bubble-like HCDEAs made of silicone and oil, used to develop soft, light-weight, acoustically silent and cheap tactile displays.