Its elastic design allows the proximity sensor to be applied flexibly to large surfaces.
Rainer Bez | Fraunhofer IPA
Researchers at Fraunhofer IPA have recently developed a proximity sensor capable of locating people or objects. The sensor consists of a thin elastic silicone layer on which numerous microscopic carbon nanotubes (CNT) are printed. "The proximity sensor can detect anything which is electroconductive. When an object approaches, the electric field changes", says IPA scientist Florian Bodny. When the surface is composed of several sensor elements, the sensor can detect both the object itself and its position.
The scientists have combined silicone and CNT in their sensor, which is composed of alternating layers of silicone and a silicone-CNT mixture. Both materials are elastic and flexible, with a high degree of environmental stability, allowing the sensor to be applied across large surface areas as well. The researchers opted for screen printing as the production process. This process is fast and involves no expensive or cumbersome preparations, Bodny explains, adding that it is possible to print large surfaces and produce the sensors in large quantities: "The sensor is easy to apply, is extremely versatile and is cheap to produce." In a series of experiments, the experts discovered that the concentration of the active material influenced the detection accuracy the most, followed by the thickness of the layers, and then the area of the sensor. To detect an object that is 8 millimetres away, three printed layers, a concentration of 1.5 percentage by mass and an area of 36 cm² are required.
The proximity sensor is an example of printed electronics with a broad range of possible applications. Surfaces with such sensors act as a human-machine interface and could be used as artificial skin in robots, for example. Also in the “smart home”, the sensor could be used, for example, to open a door as soon as the presence of a person in front of the door is detected. The sensor’s elasticity also makes it well suited for accident prevention, such as on workwear and protective clothing. Partners in industry and research are invited to test and develop the sensor further.