Plastic-film sensor may double as energy harvesting device

March 22, 2013
A special silicone-based material normally used to sense movement could double as an energy harvesting device in situations characterized by relatively large strain and relatively low forces.

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.

DEAP material forms a sensor on this arm brace that detects the angle of the wearer's elbow.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.  

The corrogated surface on the DEAP lets it stretch and contract mainly in one direction.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. Where DEAP fits in with out energy harvesting materials.

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.Danfoss president Michael Hamann demonstrates the DEAIn a typical stretch and compression cycle, the DEAP generates power as it relaxes.P mateerial undergoing a stretch test.

About the Author

Leland Teschler

Lee Teschler served as Editor-in-Chief of Machine Design until 2014. He holds a B.S. Engineering from the University of Michigan; a B.S. Electrical Engineering from the University of Michigan; and an MBA from Cleveland State University. Prior to joining Penton, Lee worked as a Communications design engineer for the U.S. Government.

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