Flexible and stretchable electrodes for dielectric elastomer actuators
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I N V I T E D PA P E R
Flexible and stretchable electrodes for dielectric elastomer actuators Samuel Rosset · Herbert R. Shea
Received: 23 September 2012 / Accepted: 24 October 2012 / Published online: 7 November 2012 © Springer-Verlag Berlin Heidelberg 2012
Abstract Dielectric elastomer actuators (DEAs) are flexible lightweight actuators that can generate strains of over 100 %. They are used in applications ranging from haptic feedback (mm-sized devices), to cm-scale soft robots, to meter-long blimps. DEAs consist of an electrode-elastomerelectrode stack, placed on a frame. Applying a voltage between the electrodes electrostatically compresses the elastomer, which deforms in-plane or out-of plane depending on design. Since the electrodes are bonded to the elastomer, they must reliably sustain repeated very large deformations while remaining conductive, and without significantly adding to the stiffness of the soft elastomer. The electrodes are required for electrostatic actuation, but also enable resistive and capacitive sensing of the strain, leading to self-sensing actuators. This review compares the different technologies used to make compliant electrodes for DEAs in terms of: impact on DEA device performance (speed, efficiency, maximum strain), manufacturability, miniaturization, the integration of self-sensing and self-switching, and compatibility with low-voltage operation. While graphite and carbon black have been the most widely used technique in research environments, alternative methods are emerging which combine compliance, conduction at over 100 % strain with better conductivity and/or ease of patternability, including microfabrication-based approaches for compliant metal thin-films, metal-polymer nano-composites, nanoparticle implantation, and reel-to-reel production of µm-scale patterned thin films on elastomers. Such electrodes are key to miniaturization, low-voltage operation, and widespread commercialization of DEAs. S. Rosset () · H.R. Shea Ecole Polytechnique Fédérale de Lausanne (EPFL), Jaquet-Droz 1, 2002 Neuchâtel, Switzerland e-mail: [email protected]
Keywords Dielectric elastomer actuators · Compliant electrodes · Carbon · Metal thin-films
1 Introduction Dielectric Elastomer Actuators (DEAs), also known as artificial muscles, are a new type of soft transducer consisting of a thin elastomer membrane sandwiched between two compliant electrodes. When a voltage is applied between the electrodes, the opposite charges on each electrode give rise to an electrostatic force (Maxwell stress) which squeezes the dielectric layer and causes deformation of the device. The thickness strain sz caused by the Maxwell stress is defined by [1]: sz = −
r 0 V 2 , Y z2
(1)
where r and 0 are, respectively, the relative and vacuum permittivity, Y is the Young modulus of the elastomer, and z the thickness of the membrane. Driving voltages are in the order of a few kilovolts, for an elastomer membrane thickness of around 50 µm and with a Young modulus of about 1 MPa, leading to typical compression st
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