MIT's tree-powered wireless network

MIT researchers and a Massachusetts company are devising a forest fire-sensing network that draws its power from the minute amounts of electricity created by trees. The idea is to seed large areas of forest with temperature and humidity sensors, linked via a ZigBee 802.15.4 wireless mesh to a satellite node and powered by rechargeable batteries. The batteries can slowly be recharged by the electric current found in a tree. In a striking analogy one fo the researchers likened this trickle charge to a "dripping faucet [that] can fill a bucket over time." The system produces enough power to allow the sensors to upload data 4 times daily, or in case of a fire, immediately. The mesh passes the signal from node to node until it reaches a U.S. Forest Service remote automated weather station, equipped with a satellite data link. The information then funnels inot a command center in Boise, Idaho. One challenge the researchers had to overcome was figuring out exactly how trees generated the miniscule voltage. They eliminated several possibilities, including one well-known phenomenon: the simple electrochemical redox reactions, the kind that power potatoe or lemon "batteries" in high school science projects. The conclusion, reported recently in "Public Library of Science ONE," is that the current is created by a pH imbalance between the tree and the soil it grows in. The tests were run with a potted Ficus benjamina in a Faraday cage. The actual sensor network is being developed by Voltree Power, a bioenergy startup in Canton, Mass. The goal is a vast, very low-cost-per-acre network that doesn't require manual replacement of batteries, and as a result can generate real-time temperature and humidity data. (Two of the MIT researchers, Christopher Love and Andreas Meshin, are executives in Voltree.) According to the MIT release, testing of the network will beginin in Spring 2009 on a 10-acre Forest Service site.