Gauges that determine the amount of strain on an object are commonly used in mechanical engineering research and development to measure the stresses generated by machinery and to test structural elements like aircraft components. The most common type of strain gauge consists of an insulating flexible backing material that supports a metallic foil pattern whose electrical resistance changes as the foil is deformed, which allows the amount of strain to be measured. However, the relatively low elastic limits of the foil restrict the possible applications for such gauges. Now researchers at the Fraunhofer Institute of Silicate Research have developed a sensor that can be stretched to twice its size, dramatically increasing its possible applications.
The Fraunhofer-developed sensors work in a similar way to conventional strain gauges – measuring the change in electrical capacitance as the sensor is stretched – but they are made of a highly stretchable elastomeric polymer film that is coated on both sides with flexible electrodes. By controlling the degree of chemical bonding within the elastomer film, the researchers are also able to tailor the sensors for specific applications.
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"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 Dr. Holger Böse, Scientific and Technical Manager of the ISC's Center Smart Materials.
The researchers say the flexibility of the new dielectric elastomeric sensors makes them suitable for a wide variety of applications. For example, they could be integrated into car seats to detect not only if the seat is occupied, but also the position of the occupant. This would allow the force of the airbag to be lessened if the occupant is leaning forward in the event of an accident.
According to the researchers, the sensors are even supple enough to go virtually unnoticed when sewn into clothing where they could be used to analyze movements to help athletes optimize their training.
Possible industrial applications include measuring the pressure of gases by stretching the elastomer film across a ring to detect any deformation caused by gas exerting pressure on the sensor membrane. They could also be used to detect if someone is coming too close to hazardous machinery by embedding the sensors in the floor.
Fraunhofer researchers will be demonstrating the new sensor at the Sensor+Test trade fair being held in Nuremburg, Germany from June 7 to 9, 2011.