VIDEO: Nanogenerators from simple movements will revolutionize the future of electronics 12/14/2013 - 00:00 With one stomp of his foot, Zhong Lin Wang illuminates a thousand LED bulbs – with no batteries or power cord. The current comes from essentially the same source as that tiny spark that jumps from a fingertip to a doorknob when you walk across carpet on a cold, dry day. Wang and his research team have learned to harvest this power and put it to work.A professor at the Georgia Institute of Technology, Wang is using what’s technically known as the triboelectric effect to create surprising amounts of electric power by rubbing or touching two different materials together. He believes the discovery can provide a new way to power mobile devices such as sensors and smartphones by capturing the otherwise wasted mechanical energy from such sources as walking, the wind blowing, vibration, ocean waves or even cars driving by.Beyond generating power, the technology could also provide a new type of self-powered sensor, allowing detection of vibrations, motion, water leaks, explosions – or even rain falling. The research has been supported by a variety of sponsors, including the National Science Foundation; U.S. Department of Energy; MANA, part of the National Institute for Materials in Japan; Korean corporation Samsung and the Chinese Academy of Sciences. The research has been reported in journals including ACS Nano,Advanced Materials, Angewandte Chemie, Energy and Environmental Sciences, Nano Energy and Nano Letters.“We are able to deliver small amounts of portable power for today’s mobile and sensor applications,” saidWang, a Regents professor in Georgia Tech’s School of Materials Science and Engineering. “This opens up a source of energy by harvesting power from activities of all kinds.”In its simplest form, the triboelectric generator uses two sheets of dissimilar materials, one an electron donor, the other an electron acceptor. When the materials are in contact, electrons flow from one material to the other. If the sheets are then separated, one sheet holds an electrical charge isolated by the gap between them. If an electrical load is then connected to two electrodes placed at the outer edges of the two surfaces, a small current will flow to equalize the charges.By continuously repeating the process, an alternating current can be produced. In a variation of the technique, the materials – most commonly inexpensive flexible polymers – produce current if they are rubbed together before being separated. Generators producing DC current have also been built.“The fact that an electric charge can be produced through triboelectrification is well known,” Wang explained. “What we have introduced is a gap separation technique that produces a voltage drop, which leads to a current flow in the external load, allowing the charge to be used. This generator can convert random mechanical energy from our environment into electric energy.”Since their first publication on the research, Wang and his research team have increased the power output density of their triboelectric generator by a factor of 100,000 – reporting that a square meter of single-layer material can now produce as much as 300 watts. They have found that the volume power density reaches more than 400 kilowatts per cubic meter at an efficiency of more than 50 percent. The researchers have expanded the range of energy-gathering techniques from “power shirts” containing pockets of the generating material to shoe inserts, whistles, foot pedals, floor mats, backpacks and floats bobbing on ocean waves.
