Granularly Coupled Dielectric Elastomer Actuators

Dielectric elastomer actuators (DEAs) have been demonstrated to represent today a high-performance technology for electroactive polymer mechatronics. As a means to improve versatility and safety of DEAs, so-called "hydrostatically coupled" DEAs (HC-DEAs) have recently been shown to offer new opportunities. HC-DEAs 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. Drawing inspiration from this concept, this paper presents a new kind of actuators, analogous to HC-DEAs, except for the fact that the fluid is replaced by fine powder. The related technology, here referred to as "granularly coupled" DEAs (GC-DEAs), relies entirely on solid-state materials. This permits to avoid drawbacks (such as handling and leakage) inherent to usage of fluids, especially those in liquid phase. This paper presents functionality and actuation performance of bubble-like GC-DEAs, in direct comparison with HC-DEAs. For this purpose, prototype actuators made of two prestretched membranes (2-cm wide and less than 2-mm high) of acrylic elastomer, coupled via talcum powder (for GC-DEA) or silicone grease (for HC-DEA), were manufactured and comparatively tested. As compared to HC-DEAs, GC-DEAs showed a higher maximum stress (2.1 kPa), the same maximum relative displacement (-100%), the same -3 dB bandwidth (3 Hz), and a higher resonance frequency (200 Hz). Advantages and drawbacks of GC-DEAs, in comparison with HC-DEAs, are preliminarily identified and discussed.