Skin sensors can seamlessly transmit information about a person's glucose concentration, blood pressure, heart rate and activity level from the sensor to the smartphone for further analysis. Most now communicate via embedded Bluetooth chips, which in turn are powered by small batteries. But these conventional chips and power sources are likely to be too bulky for next-generation sensors.

Now MIT engineers have developed a new kind of wearable sensor that communicates wirelessly - without needing embedded chips or batteries.

Flexible and ultra-thin "E-Skin"

This is a kind of electronic skin or "e-skin" - a flexible, semi-conductive film that hugs the skin like electronic tape. At its heart is an ultra-thin film of gallium nitride that can both generate an electrical signal in response to mechanical stress and vibrate mechanically in response to an electrical impulse.

The researchers found that they could take advantage of these properties of gallium nitride and use the material for sensing and wireless communication at the same time.

Reinforced with a conductive gold layer, the developed device became sensitive enough to vibrate in response to a person's heartbeat as well as the salt in their sweat. In addition, the vibrations of the material produced an electrical signal that could be read by a nearby receiver. "You could wear it on your body like a bandage and, in conjunction with a mobile phone, wirelessly monitor your pulse, sweat and other biological signals," said MIT professor Jeehwan Kim.