Put a special kind of plastic called an electro active polymer (EAP) between two electrodes and you can apply an electric field to change the plastic's shape. This idea has been used for many years to make up sensors that react to stretching or straining. But Danfoss PolyPower A/S in Europe is investigating ways of employing this kind of material as a way of harvesting energy in situations characterized by physical movement in one direction.
The Dielectric EAP that Danfoss has devised is basically a capacitor that changes its capacitance when a voltage is applied. The silicone film is coated on both sides with metal electrodes. The polymer grows thinner and expands under influence of the electric field (usually in the range of several thousand volts) but with a very low electric power consumption.
Charging a stretched DEAP film with a voltage and then allowing it to relax will boost the voltage significantly, thus converting mechanical energy to electrical energy and allowing the device to function as a generation. Danfoss created a special configuration with this in mind that puts a special corrugated surface on the silicone which is then coated with the metallic electrode . The resulting PolyPower elastomer film is stiff in the direction along the corrugations so it only elongates in one direction.
Right now Danfoss says it is focusing on sensing applications for the material. But it is working with a research group that includes seven Danish companies and three Danish universities with the idea of developing and improving DEAP technology for applications as an actuation method and for energy harvesting.