Printable sensors to detect fingers without touching

Paul Boughton

Researchers form the Fraunhofer Institute are working as part of the EU 3Plast research consortium to develop sensors that can be printed onto plastic film and attached to objects so that, for example, electronic devices can be controlled just by pointing a finger. Rather than responding to a directly applied force or acceleration, the sensors react to tiny fluctuations in temperature and differences in pressure, thereby recognising a finger as it approaches.

3Plast, which stands for Printable pyroelectrical and piezoelectrical large area sensor technology, is a consortium that comprises companies and institutes from industry and research with the goal of mass-producing pressure and temperature sensors that can be cheaply printed onto plastic film and flexibly affixed to a wide range of everyday objects. The 2.2million euro project is co-ordinated by the Fraunhofer Institute for Silicate Research (ISC) in Würzburg, Germany. Gerhard Domann, who leads the project, says: "The sensor consists of pyroelectrical and piezoelectrical polymers which can now be processed in high volumes by screen printing, for example. The sensor is combined with an organic transistor, which strengthens the sensor signal. It is strongest where the finger is. The special thing about our sensor is that the transistor can also be printed."

The production of polymer sensors still poses a number of challenges. To produce printable transistors, the insulation materials have to be very thin. The experts at the ISC have, however, succeeded in producing an insulator that is only 100nm thick; the first sensors have already been printed onto film. Currently the researchers are working on optimised transistors that can amplify rapid changes in temperature and pressure.

Domann continues: "By providing everyday objects with information about their environment – for example whether a person is approaching – by means of pressure and temperature sensors, we can create and market new devices that can be controlled just by pointing a finger." The research scientist envisions further applications for the technology in the automotive and construction industries as well as in robotics: "The project comes to an end in January 2011, but we think it will take a few more years before sensors can be printed on large surfaces."

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