Energy harvesting with dielectric elastomers

Dielectric elastomer membranes are interesting for energy harvesting, because they are lightweight and cheap. Dielectric elastomer generators promise very high values of harvesting energy per mass and therefore seem economically interesting for applications on large and small scales. Currently the full potential of elastomer generators has not yet been exploited. Based on available material data for the commonly used acrylic elastomer 3MVHB4910, an energy of conversion per mass of 1.7 J/g has been predicted by Zhigang Suo and co-workers from Harvard University. Dielectric elastomer generators use variable deformable parallel plate capacitors, where the capacity can be changed mechanically by applying forces, or electrically by applying electric fields. In work conjugate force displacement and voltage charge planes limit states define shaded regions of allowable states for elastomer generators. Thermodynamic working cycles are ascribed into these shaded areas to maximize energy of conversion. In an elastomer generator charges are harvested at a low voltage and stored by electromechanical energy conversion at a higher voltage level. Though it seems natural to follow such a thermodynamic analysis of elastomer generators, there are only few studies attempting to investigate the full potential of dielectric elastomer generators. In this project we intend to study dielectric elastomer generators in a fully computer controlled, laboratory scale generator set-up. All necessary mechanical and electrical parameters are continuously recorded to allow for the construction of work conjugate plots with limit states. We extend to explore the full potential of the acrylic elastomer 3MVHB4910 and of natural rubber for elastomer energy harvesting. Also alternative harvesting cycles and novel materials, like interpenetrating networks will be analyzed for elastomer based generators. It is expected that the project helps in improving the basics of energy harvesting with soft, compliant capacitors. The project is carried out in close co-operation with the Mechanics of Materials and Structures group of Zhigang Suo at Harvard University. The Soft Matter Physics team provides experimental data to be analyzed by the Harvard group. Close synergies between the two complementary groups are expected as a result of the project. In summary we intend to explore the full potential of dielectric elastomer generators, based on model materials, like acrylic elastomers and natural rubber, as well as on new materials, like interpenetrating networks. We intend to develop work conjugate plots with limit states and thermodynamic working cycles with maximum energy of conversion, to provide guidelines to application engineers for generator design and optimization.

Elastomers, in everyday language rubber, show significant potential in high technology applications. Elastomers may be used in future for the conversion of the mechanical energy of water waves into electrical energy. Elastomers are used as mechanically deformable capacitors, able to convert mechanical into electrical energy in a cycle, similar to the Carnot cycle in thermodynamics. The potential of the proposed technology is huge; the worldwide electricity generation may be met by converting the mechanical energy of water waves into electrical energy. However, due to the lack of a suitable technology this potential energy source is largely untapped. Following theoretical investigations of Zhigang Suos team at Harvard University, we showed in close cooperation with the team at Harvard University the huge potential of elastomer energy generators based on calculations with realistic mechanical models of the elastomers. In the project we first developed an experimental approach to characterize elastomers for electromechanical energy generation, in order to identify the best suitable rubbers. In analogy to thermodynamics we used an electrical Carnot cycle with mechanically deformable capacitors to determine the efficiency of the electromechanical energy conversion. Our results were immediately used in two European Community financed projects, with experiments conducted in wave tanks under realistic conditions. Since we achieved the project goals faster than expected, we decided to extend project work towards novel research in stretchable electronics, promising far-reaching applications in mobile electronics and healthcare.