E-skin detects both temperature and force with one sensor

To create the skin, Pohang University of Science and Technology (Postech) teamed up with Stanford University.

“Human skin is freely stretchable yet unbreakable because it is full of electrolytes, so the joint research team made the sensor using them,” according to the Korean university. “They also took advantage of the fact that the ion conductor material containing electrolyte can have different measurable properties according to its measurement frequency. On the basis of the finding, a multi-functional artificial receptor was created that can measure a tactile sensation and temperature at the same time.”

The skin has a simple electrode-electrolyte-electrode structure and measures temperature as well as the direction of force stimuli in complex touch like squeezing, pinching, spreading or twisting.

Measuring sensing points on the skin at two frequencies allowed two clearly separated variables to be derived:

• charge relaxation time – how long polarisation of the ions takes to disappear – is dependent on temperature and does not respond to movements
• normalised capacitance can measure movements without responding to temperature

“When an index finger touches an electronic skin, the electronic skin detects contact as a temperature change, and when a finger pushes the skin, the back part of the contact area stretches and recognises it as movement,” said Postech researcher Insang You. “I suspect that this mechanism is one of the ways that the actual human skin recognises different stimuli like temperature and movement.”

In a demonstration of how sensitive temperature measurement can be, without being upset by movement, proof-of-concept sensors were attached to the cheek and neck of a volunteer who was also monitored by infra-red camera as the person both moved and, as a way of altering body temperature, drank alcohol (results left).