Maximizing the energy density of dielectric elastomer generators using equi-biaxial loading

Dielectric elastomer generators (DEGs) for harvesting electrical energy from mechanical work have been demonstrated but the energy densities achieved are still small compared with theoretical predictions. In this study, significant improvements in energy density (560 J/kg with a power density of 280 W/kg and an efficiency of 27%) are achieved using equi-biaxial stretching, a mechanical loading configuration that maximizes the capacitance changes. The capacitance of dielectric elastomers subjected to equi-biaxial stretches is demonstrated to be proportional to the fourth power of the stretch. Quantification of the individual energy contributions indicates that attaining higher conversion efficiencies is limited by viscous losses within the acrylic elastomer, suggesting that still higher conversion efficiencies with other elastomers should be attainable with our novel mechanical loading design. A thin sheet of acrylic elastomer, coated with black carbon conductive grease on both sides, is equi-biaxially stretched by applying radial forces to its circumference. In its unstretched state, the elastomer thickness is 0.5 mm, and the electroded radius is 2.0 cm corresponding to a mass of dielectric elastomer of 0.60 g.