This kind of epidermal electronic is relatively new technology, but thanks to its low cost, production of these devices is growing rapidly.
John Rogers, materials scientist at the University of Illinois at Urbana-Champaign, and his team presented a wearable device that transmits health data. The best of all is the fact that this electronic device is battery-free which makes it five to ten times thinner than comparable gadgets.
This stretchable, ultra-thin patch is wirelessly powered via near-field communication transmissions. Smartphones, tablets, and other consumer electronics use near-field communications with the Apple Pay and Android Pay wireless payment schemes.
Once wirelessly powered, the device's LEDs illuminate the skin. Some of the light is absorbed, while the reflected light gets picked up by the patch’s light sensors. The device then wirelessly transmits data to an external device. An ultraviolet-sensitive material embedded in the patch can also measure ultraviolet ray exposure, and an embedded heat sensor can help measure skin temperature.
Thanks to a small group of volunteers, the scientist found that this device can be used to monitor heart rate, blood oxygen level, skin temperature, ultraviolet radiation exposure, and changes in skin color.
As Roger said, the range at which these devices can be powered by a smartphone is a couple of centimeters. With long-range readers, the range is up to about 1 meter. When mounted under a mattress, such a system could provide coverage across a hospital bed, for instance.
Rogers believe that battery-free designs may open up applications in hospitals and sleep monitoring.
source - http://spectrum.ieee.org/