Fiber micro-architected Electro–Elasto-Kinematic muscles

Abstract

Electro-active polymers (EAP) such as dielectric elastomers can reproduce biomimetic functions requiring micro-scale actuation such as color and texture change, or tunable wetting and adhesion. For these applications, large actuation strains and energy density are required. Recent studies with fiber reinforced elastomers demonstrated the ability to obtain anisotropic in- and out-of-plane actuation in macro-scale elastomer membranes. We design a new class of fiber micro-architected elastomers capable of anisotropic actuation in the two orthogonal in-plane directions under uniform electrostatic field. We reinforce the two sides of a pre-stretched VHB film with parallel arrays of stiff ultra-high molecular weight polyethylene fibers. By controlling the spacing and bias angle between the fibers, we create diamond shaped unit cells of 100–300 um size, and demonstrate a wide range of kinematics showing maximum extension of 26% at 45° and maximum contraction of −6.3% at 65° at maximum efficiency of 15%. We call these devices Micro-architected Electro–Elasto-Kinematic muscles (MEEKs). We use analytical modeling and finite element analysis to explain the observed actuation kinematics and the associated non-homogeneous strain distribution. We expect this principle to be suitable for micro-actuation and smart skins where anisotropy can be advantageous.