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Hydrostatically Coupled Dielectric Elastomer Actuators: New Opportunities for Haptics Federico Carpi, Gabriele Frediani and Danilo De Rossi Interdepartmental Research Centre 'E. Piaggio', University of Pisa, School of Engineering,Via Diotisalvi, 2 - 56100 Pisa, Italy. ABSTRACT Dielectric elastomer actuators (DEAs) have been demonstrated to represent today a highperformance technology for electromechanical transducers based on electroactive polymers. As a means to improve versatility and safety of DEAs for several fields of application, so-called ‘hydrostatically coupled’ DEAs (HC-DEAs) have recently been described. 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. This paper presents ongoing developments of bubble-like HC-DEAs and their promising potential application in the field of haptics. In particular, the first part of the paper describes a static and dynamic characterization of a prototype actuator made of two pre-stretched membranes (20 mm wide, 1.8 mm high, and 60 μm thick) of 3M VHB acrylic elastomer, coupled via silicone grease. The actuator exhibited a maximum stress of 1.3 kPa at 4.4 kV, a relative displacement of -80% at 4.4 kV, a -3dB bandwidth of 3 Hz, and a resonance frequency of 160 Hz. The second part of the paper presents possible applications of the tested actuator configuration for haptic interfaces. Two specific examples are considered. The first deals with a wearable tactile/haptic display used to provide users with tactile feedback during electronic navigation in virtual environments. The display consists of HC-DEAs arranged in contact with finger tips. As a second example of usage, an upscaled prototype version of an 8-dots refreshable cell for dynamic Braille displays is shown. Each Braille pin consists of a miniature HC-DEA, with a diameter lower than 2 mm. Both types of applications clearly show the potential of the new technology and the prospective opportunities for haptics. INTRODUCTION Electromechanical actuators based on ElectroActive (or Electromechanically Active) Polymers (EAPs) represent today a well established and promising scientific field of research and development [1-7]. EAPs form a broad family of smart materials capable of transducing energy from the electrical to the mechanical form, and vice versa. As such, they are studied for electromechanical actuation and mechanoelectrical sensing, as well as mechanical energy harvesting to generate electricity, thus gaining the nickname of ‘Artificial Muscles’ [1-7]. EAPs are commonly classified in two major families: ionic EAPs, activated by an electrically-induced transport of ions and/or solvent, and electronic EAPs, activated by electrostatic forces. Ionic EAPs include polymer gels, ionic polymer metal composites, conjugated polymers, and carbon nanotubes. Electronic EAPs include piezoelectric polymers, electrostrictive polymers, dielectric elastomers, liquid crystal elastomers, and carbon nanotube ae