Abstract
Dielectric elastomer actuators (DEAs) are soft, electrically powered actuators that have no discrete moving parts, yet can exhibit large strains (10%–50%) and moderate stress (∼100 kPa). This Tutorial describes the physical basis underlying the operation of DEA's, starting with a simple linear analysis, followed by nonlinear Newtonian and energy approaches necessary to describe large strain characteristics of actuators. These lead to theoretical limits on actuation strains and useful non-dimensional parameters, such as the normalized electric breakdown field. The analyses guide the selection of elastomer materials and compliant electrodes for DEAs. As DEAs operate at high electric fields, this Tutorial describes some of the factors affecting the Weibull distribution of dielectric breakdown, geometrical effects, distinguishing between permanent and “soft” breakdown, as well as “self-clearing” and its relation to proof testing to increase device reliability. New evidence for molecular alignment under an electric field is also presented. In the discussion of compliant electrodes, the rationale for carbon nanotube (CNT) electrodes is presented based on their compliance and ability to maintain their percolative conductivity even when stretched. A procedure for making complaint CNT electrodes is included for those who wish to fabricate their own. Percolative electrodes inevitably give rise to only partial surface coverage and the consequences on actuator performance are introduced. Developments in actuator geometry, including recent 3D printing, are described. The physical basis of versatile and reconfigurable shape-changing actuators, together with their analysis, is presented and illustrated with examples. Finally, prospects for achieving even higher performance DEAs will be discussed.
Highlights
The goal of creating artificial muscles with performances comparable to mammalian muscles has proven to be a rallying call to scientists and engineers, in the soft robotics community
In the discussion of compliant electrodes, the rationale for carbon nanotube (CNT) electrodes is presented based on their compliance and ability to maintain their percolative conductivity even when stretched
Several different active polymer approaches have been proposed1 for reaching this goal, but in this Tutorial, we focus on dielectric elastomer actuators (DEAs)
Summary
The goal of creating artificial muscles with performances comparable to mammalian muscles has proven to be a rallying call to scientists and engineers, in the soft robotics community. It was increasingly recognized that devices require elastomer/electrode multilayer configurations in order to generate sufficiently large forces at moderate applied voltages [Fig. 1(c)] Since those early studies, considerable advances have been made toward the goal of producing dielectric elastomer artificial muscles. Considerable advances have been made toward the goal of producing dielectric elastomer artificial muscles These include elastomer materials engineered to show optimum strain-stiffening behaviors; electrodes optimized for high compliance, electrical conductivity, and self-clearing; new functionalities such as self-sensing have been added; a variety of different configurations proposed; and numerous novel devices based on DEAs have been demonstrated. II, the physical basis for DEA is first described in terms of the “compliant capacitor model” in which the deformation of a soft material by electrostatic forces in a parallel plate configuration is considered This is useful conceptually even though the equations usually reported in the literature are based on the linear elastic behavior. VII describes shape-changing actuators, a different path in the evolution of electrically driven and reversible actuators
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