23 July 2014

Smart Sensors Offer Haptic Feedback

Fraunhofer ISC's Centre for Smart Materials (CeSMa) has demonstrated smart materials that can be used to create intelligent sensors with haptic feedback. Intelligent and adaptive materials possess properties that react to external factors such as magnetic or electrostatic fields. For instance, consistency, flow properties, expansion behaviour, or pressure sensibility can change under influence of these external factors. These properties can be used to make these materials act as sensors or actuators. The CeSMa, an entity of the Fraunhofer Institute for Silicate Research (ISR) in Würzburg, Germany, uses such materials to develop prototypes for many industry branches. Switches and pressure sensors based on highly sensitive piezoelectric layers or dielectric elastomer sensors (DES) -- which are extremely stretchy -- can adapt to a variety of haptic requirements and mechanical sensor functions. While DES are more suitable for soft surfaces, piezoelectric sensors can be utilized more easily with hard materials such as steel. DES represented a new category of mechanical sensors that can be used to measure strain, forces, and pressure. It can be integrated into structures that are subject to significant deformation and strain. An example would be seat occupancy sensors that provide additional information on load distribution. CeSMa researchers succeeded in developing innovative sensor mats that react very sensitively to pressure. Car seats equipped with these intelligent DES sensor mats can sense the position of the passenger and help to reduce the risk of injury during an accident. Other potential applications could be in the field of geriatric care.

Thin piezoelectric layers on steel foil carriers offer great design freedom with respect to size, shape, and curvature. In addition, this technology can be used to implement "invisible" switches and sensors in car interiors, for instance on the instrument panel. Insensitive to dust and dirt, they enable implementing functional surfaces even in rough environments. In addition, electrostatic fields can be integrated into the foils, which can serve as proximity sensors. Thus, the control panels generate a proximity signal and at the same time provide a haptic feedback when activated. The combination of proximity and pressure sensor with haptic feedback offers new options in the design of human-machine interfaces (HMIs). The sensor concepts developed by the CeSMa also make it possible to monitor safety relevant components, enabling continuous or periodic monitoring. Another technique developed by the CeSMa is suited to detecting structural damage in glass, carbon fibre, or steel structures. The Würzburg scientists developed ultrasound transducers based on piezoelectric materials that transform mechanical strain into electric signals or electric control voltages into movement. This principle can also be applied to carrier materials with high operating temperatures. Towards this end, the Würzburg researchers developed high-temperature signal transducers based on novel monocrystal materials that can be used for permanent structural monitoring in high-temperature environments. An application example for these transducers is monitoring hot pipelines operating at temperatures of up to 600°C in chemical and power plants.

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