The cutting edge: Sensors stretch and remain flexible

May 12, 2011

Though still in the research stage, a development at the Fraunhofer Institute for Silicate Research ISC in Würzburg, Germany could, one day, find use in plastics processing applications. Those researchers have developed sensors capable of expanding up to twice their original length and so flexible as to go virtually unnoticed if worn inside clothing.

sensors that stretch
Fraunhofer scientists are working on polymeric sensors that stretch.

The first public showing of these sensors will be at the Sensor+Test trade fair in Nuremberg from June 7 - 9, 2011. Potential applications could include in car seats, so that an air bag recognizes not only that someone is in a seat but also at which angle he is sitting.

"The sensor films can measure stretch, as well as pressure," says Holger Böse, scientific and technical manager of the ISC's Smart Materials center. He explains that the sensors are made form "a highly stretchable elastomeric film, coated on both sides with flexible electrodes."

When the sensor is stretched, the sensor's thickness and, as a result, its electrical capacitance also change, and this change can be measured. In contrast to conventional strain gauge strips, the new dielectric elastomeric sensors can stretch by up to 100% in some cases.

Depending on the application in which the materials are applied, it might be necessary to coat the elastomer film with multiple electrode pairs. This is the case, for example, when measuring the distribution of body pressure to determine a person's posture in a seat. Each pair of electrodes serves, in effect, as an independent sensor, measuring the local strain. "This is how we can say precisely where and to what degree the pressure has changed," explains Böse.

The elastomeric film consists of a polymer in which the individual molecules are chemically bonded with one another. The better the network of molecules, the sturdier the material. The scientists can control the degree of bonding in the polymer. "If the sensor is being used to measure high pressures, we produce a sturdier elastomer film as substrate; for measuring lower pressures, we use more pliant films," says Böse.

Though still a few years-at least-from commercial use, the development seems to hold promise for many applications in which plastics and plastic processors play a part.


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