Using the static electricity from human skin to generate enough energy for electronic devices which require little power – a group of researchers from National University of Singapore (NUS) presented this idea during the IEEE MEMS 2015 conference with a small, stamp-sized, flexible generator that can be strapped to the skin, which converts the friction it creates with the skin into electricity. Such device can open the gates for wearable sensors that will utilize body movements to power itself, instead of using batteries.
For many years, there have been studies on how to harvest electricity from human body movement to power up mobile electronic devices and sensors such as the implants used in medicine as personal health tracker. One common technology was the nanogenerator, where mechanical or thermal energy is used to produce electricity. Studies on nanogenerators typically revolve on three methods: piezoelectricity, pyroelectricity, and triboelectricity. Piezoelectricity is the energy accumulated from mechanical stress. Temperature change, on the other hand, can also create electrical energy called pyroelectricity. Lastly, triboelectricity is the type of energy produce by contact electrification. It occurs when the layers of two different materials gain electrical charge through friction
A study about triboelectric effect took advantage of the static electricity induced by friction to generate electrical energy. Since human skin is a natural triboelectric material, the National University of Singapore researchers were only required to develop the other half of the layer where the human skin will be put in contact. They constructed a flexible rubber patch made from silicone and bonded it with gold film of 50 nm thickness. The gold film served as the generator’s electrode, where the resulting electricity is accumulated. Thousands of tiny pillar-like structures were attached beneath the silicone rubber layer to increase the surface area of the device that gets in contact with the skin. This increases friction, which means generates more current.
Lokesh Dhakar, one of the researchers that presented this human patch nanogenerator, has described the skin as the most abundant surface on the human body and a natural choice for one of the triboelectric layers. He further explained that skin as a triboelectric material has a high tendency to donate electrons or get positively charged, which is important in improving the performance of the device if the other triboelectric layer intentionally chosen as the one with a tendency to get negatively charged.
A simple finger-tap on the device has produced 90 V at 0.8 mW, generating enough power to light up 12 commercial LEDs. The device was also tried by strapping it to a human forearm, where fist-clenching was able to create 7.3 V. Moreover, with the device attached to the throat, speaking generated about 7.5 V.
Though Georgia Tech researchers had an earlier study on skin-based triboelectric effect generator, whose results were reported to generate as much as 1 kV in ACS NANO last 2013, this device has two main distinctions from the human patch presented by National University of Singapore: flexibility and wearability. For one, Georgia Tech’s triboelectric effect generator is much larger than the human patch. Moreover, the material used by Georgia Tech was not as flexible as the one used by the human patch. Dhakar explained that their human patch was aimed to provide wearable options by means of a more flexible material for the nanogenerator. They wanted their device to fit any possible shape of the human body, in any size required.