Researchers have discovered a new resonance phenomenon in a dielectric elastomer rotary joint that can make the artificial joint bend up and down, like a flapping wing. The new phenomenon makes the dielectric elastomer joint a good candidate for creating a soft and lightweight flapping wing for robotic birds, which would be more efficient than bird wings based on electrical motors due to the higher energy conversion efficiency of the dielectric elastomer.

(Left) The structure of the rotary joint. (Right) The system to measure the joint rotation. (Jianwen Zhao/Harbin Institute of Technology Weihai, University of California-Los Angeles)

Soft robotics provides many advantages compared to traditional robotics based on rigid materials, including safer physical human-robot interactions, more efficient/stable locomotion, and adaptive morphologies. Dielectric elastomers, due to their soft and lightweight inherent properties and superior electromechanical performances, are considered as a kind of material close to human muscles, attracting wide attention among soft-technology scientists.

Made by sandwiching a soft insulating elastomer film between two compliant electrodes, dielectric elastomers can be squeezed and expanded in a plane when a voltage is applied between electrodes. In contrast to actuators based on rigid materials such as silicon, dielectric elastomers can reach a very large extent of stretch, often exceeding 100 percent elongation while not breaking, enabling new possibilities in many fields including soft robotics, tunable optics, and cell manipulation.