According to the Saarland researchers, the sensors make it possible – for the first time – to capture touches on the body precisely, even from multiple fingers, and they have managed to successfully test their prototypes in four different applications.
“The human body offers a large surface that is easy to access, even without eye contact,” says Professor Jürgen Steimle of Saarland University.
Steimle explains that there has been much interest in a literal human-computer interface, but because the necessary sensors couldn’t measure touch precisely enough or capture them from multiple fingertips simultaneously, it has, until now, been an unobtainable vision.
The sensor, named Multi-Touch Skin, looks similar in structure to the touch displays used in smartphones. Two electrode layers, each arrayed in rows and columns, when stacked on top of each other, form a kind of coordinate system, at whose intersections the electrical capacitance is constantly measured. This is lowered at the point where fingers touch the sensor, because the fingers conduct electricity and therefore, allow the charge to drain away. These changes are captured at each point, meaning touch from multiple fingers can be detected.
In order to find the optimal balance between conductivity, mechanical robustness and flexibility, the researchers say they evaluated different materials. They discovered that if silver is chosen as the conductor, PVC plastic for the insulating material between the electrodes, and PET plastic for the substrate, then the sensor can be printed using a household inkjet printer in less than a minute.
The team freed the sensors from their rectangular shape so they were able to use the sensors on all parts of the body. To achieve this, they developed a software for designers, which enabled them to create their own desired sensor shape.
In the computer program, the designer first draws the outer shape of the sensor, then outlines the area within this outer shape that is to be touch-sensitive. A special algorithm then calculates the layout that will optimally cover this defined area with touch-sensitive electrodes. Finally, the sensor is printed.
In one of the tests, the sensor was placed behind the right ear. The participant was then able to swipe upward or downward on it, in order to use it as a volume control. Swiping right or left changed the song being played, while touching with a flat finger stopped the song.
In the future, the researchers say they want to focus on providing more advanced sensor design programs, and develop sensors that capture multiple sensory modalities.
