Mechanical properties of dielectric elastomer actuators with smart metallic compliant electrodes

Dielectric elastomer actuator technology is based on electric field induced deformation. From the viewpoint of materials technology, many points must be addressed, among which are material dielectric properties, breakdown voltage, viscoelastic losses and elastomer spring mechanical properties. From the viewpoint of actuator manufacturing, we will mention elastomer thin film and fiber processing as well as compliant electrode design. However, among all the previously mentioned key-points, compliant electrode design remains the major problem to solve, as electrodes required to distribute the electric field in the material need to be at least as compliant as the active elastomer material. In this paper, we present the analysis of dielectric elastomer-based actuators made with metallic compliant electrodes that show a relatively good overall mechanical performance. Large displacements, force densities and low creep, as well as fast response and million cycles are achieved using micro-structuring and thin-film techniques. We have succeeded in making smart anisotropic compliant metallic electrodes that can maintain conductivity up to 33% expansion before breaking and loosing electrical connectivity. Actuators are made with a silicone elastomer as the active material and silver as coating electrodes. The spring constant of a 3-layer actuator consisting of silver electrodes with a thickness up to 1100 A and elastomer film with a thickness up to 50 micrometers is typically 2 times larger than that of the elastomer film taken alone. Force-displacement and constant load measurements are used as a basis to analyze the mechanical properties of the artificial muscle. Capacity measurements at high frequency in the kilohertz range are carried out to study the built-in sensor properties for feedback control of the actuator.