Instabilities in dielectric elastomers: buckling, wrinkling, and crumpling.

Instabilities in a thin sheet are ubiquitous and can be induced by various stimuli, such as a uniaxial force, liquid-vapor surface tension, etc. This paper investigates voltage-induced instabilities in a membrane of a dielectric elastomer. Instabilities including buckling, wrinkling, and crumpling are observed in the experiments. The prestretches of the dielectric elastomer are found to play a significant role in determining its instability mode. When the prestretch is small, intermediate, or large, the membrane may undergo buckling, wrinkling, or crumpling, respectively. Finite element analysis is conducted to study these instability modes, and the simulations are well consistent with the experimental observations. We hope that this investigation of mechanical and physical properties of dielectric elastomers can enhance their extensive and significant applications in soft devices and soft robots.

An electronically tunable duct silencer using dielectric elastomer actuators.

A duct silencer with tunable acoustic characteristics is presented in this paper. Dielectric elastomer, a smart material with lightweight, high elastic energy density and large deformation under high direct current/alternating current voltages, was used to fabricate this duct silencer. The acoustic performances and tunable mechanisms of this duct silencer were experimentally investigated. It was found that all the resonance peaks of this duct silencer could be adjusted using external control signals without any additional mechanical part. The physics of the tunable mechanism is further discussed based on the electro-mechanical interactions using finite element analysis. The present promising results also provide insight into the appropriateness of the duct silencer for possible use as next generation acoustic treatment device to replace the traditional acoustic treatment.

A Lesson from Plants: High-Speed Soft Robotic Actuators.

Rapid energy-efficient movements are one of nature's greatest developments. Mechanisms like snap-buckling allow plants like the Venus flytrap to close the terminal lobes of their leaves at barely perceptible speed. Here, a soft balloon actuator is presented, which is inspired by such mechanical instabilities and creates safe, giant, and fast deformations. The basic design comprises two inflated elastomer membranes pneumatically coupled by a pressurized chamber of suitable volume. The high-speed actuation of a rubber balloon in a state close to the verge of mechanical instability is remotely triggered by a voltage-controlled dielectric elastomer membrane. This method spatially separates electrically active and passive parts, and thereby averts electrical breakdown resulting from the drastic thinning of an electroactive membrane during large expansion. Bistable operation with small and large volumes of the rubber balloon is demonstrated, achieving large volume changes of 1398% and a high-speed area change rate of 2600 cm2 s-1. The presented combination of fast response time with large deformation and safe handling are central aspects for a new generation of soft bio-inspired robots and can help pave the way for applications ranging from haptic displays to soft grippers and high-speed sorting machines.

Stretchable, transparent, ionic conductors.

Existing stretchable, transparent conductors are mostly electronic conductors. They limit the performance of interconnects, sensors, and actuators as components of stretchable electronics and soft machines. We describe a class of devices enabled by ionic conductors that are highly stretchable, fully transparent to light of all colors, and capable of operation at frequencies beyond 10 kilohertz and voltages above 10 kilovolts. We demonstrate a transparent actuator that can generate large strains and a transparent loudspeaker that produces sound over the entire audible range. The electromechanical transduction is achieved without electrochemical reaction. The ionic conductors have higher resistivity than many electronic conductors; however, when large stretchability and high transmittance are required, the ionic conductors have lower sheet resistance than all existing electronic conductors.