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 gener