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26 April 2011 A practical application of using tree movement to power a wireless sensor node
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A novel energy harvester based around capturing the motion of trees has been built and tested. The device consists of an electromagnetic generator located close to ground level, attached via an inelastic cord to a point on the trunk of a 5-6 meter tall eucalypt tree. The device uses the movement of the tree to drive the generator in one direction, rotationally, and a mass to keep the cord taught when the tree returns to its resting position. The electrical output is sent to electrical circuitry that rectifies, stores and switches the electrical power to supply a wireless sensor node. The initial configuration stored energy in a super-capacitor, the voltage of which indicates storage charge level. Once there was sufficient power to operate the sensor node it transmits local information such as temperature, and energy state, in terms of capacitor voltage, to a base node located approximately 80m away. Results show that there is sufficient energy in this method to power a wireless sensor node continuously in wind as low as 3-4m/s. In order to allow continuous operation in lower wind speeds a number of alterations have been investigated. These are reported here and include: operation with a secondary battery in place of the storage capacitor, increasing the electrical storage capacity and varying the connection point on the tree and the electronic duty cycle.
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Scott A. McGarry and Christopher G. Knight "A practical application of using tree movement to power a wireless sensor node", Proc. SPIE 7977, Active and Passive Smart Structures and Integrated Systems 2011, 797704 (26 April 2011);


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