Fraunhofer Researchers Develop Sensor from Silicone for Stepless Device Controlling

Given that silicone is extremely soft and flexible, it easily gets deformed by the pressure of a finger. The research team at Fraunhofer has recently developed sensors made from this flexible material, making it a whole lot simpler and easier to steplessly control devices. At the Hannover Messe, the team is presenting a glove that can gauge pressure and a steering wheel that enables the driver to control light, music and ventilation at the touch of a finger.

Nowadays, multifunction steering wheels come as standard in most automobiles, and drivers can also smoothly manipulate the cruise control and stereo without the need to take their hands off the wheel. However, the buttons are inflexible and the driver can often just switch something “on” and “off” or can just select the “next” or “previous” song. According to Dr. Holger Böse, technical and scientific manager of the Center Smart Materials (CeSMa) at the Fraunhofer Institute for Silicate Research ISC in Würzburg, Germany, this is because they are made of inflexible materials such as metal, hard plastic or ceramics. In his work, Böse focuses on smart materials with mechanical features that can be controlled either magnetically or electrically.

These new sensors invented at ISC are capable of sending out electrical impulses to control things. Hence, they have been designed like an electrical capacitor: two electrode layers comprised of a conductive silicone above and below and one insulating film layer in between. However, when the capacitor is pressed, nothing happens at first.

Explaining the concept, Böse says: “The electrical capacitance – the electrical charge pided by the voltage applied – is the decisive factor. However, in a conventional capacitor structure the pressure effect is so small that it can barely be measured let alone be used for control purposes.”

For the pressure to have an effect, the research team applied extra silicone layers on the film. Hence, for instance, two more films press from above and below to put extra pressure on the film in the middle. The two films are not smooth but feature a special pattern that was added by the team. Through their special capacitor design, the team were able to utilize a physical property of silicone, which has only been observed when stretching a silicone film coated with electrode layers—its geometry changes; the surface gets bigger and the silicone layer becomes thinner. As a result, there is an increase in electrical capacitance. “We transferred it from tensile forces to compression forces,” Böse adds.

The strength of the compression force depends on how the pattern is applied to the film and how the electrodes are attached. The electrical capacitance of the sensor is different in each case. The research team can use these differences and embrace the design of the sensors inpidually to various sensitivities and geometries. They apply industrial intermediate silicone products or use their own formula.

Böse adds that their chemical department can come up with customized silicone for the sensors based on the customers’ needs. “We can vary the chemical composition and technical shape of the sensors depending on the properties required.”

The research team’s project is now in its seventh year and is anticipated to be completed by the end of the year. Since the sensors are soft and flexible, they can be suitably integrated into all kinds of environments. In cars, they are applicable for central consoles, steering wheels, seats or window openers.