Some aspects of large strain actuation in dielectric elastomers

In the search for artificial muscles, a special contender appears to be standing out. The electric field-actuated dielectric elastomer actuators (DEA) display strains well above 100%, with actuation stresses in the MPa region. A DEA is best described as a capacitor made entirely of compliant materials: both the dielectric and the electrodes may stretch. When the capacitor is charged, the attraction between the charged electrodes applies a pressure on the dielectric, known as the Maxwell pressure, p = εε_oE².The dielectric constant and the dielectric breakdown strength are both important. Further, because large strains are desirable, the compliance of the electrodes, as well as of the dielectric material, are crucial. Elastomers are an obvious choice for the dielectric material, and they can be made conducting through the use of conducting fillers. Also, since the strains are so large, the theory describing such actuation is highly non-linear. This article intends to review the theory of DEA, with introductions to a nonlinear high-strain model.