Harvesting energy by mimicking Aspen tree leavesDavid Wagman | March 18, 2019
Researchers at the University of Warwick have used the movement of trembling Aspen leaves to devise an energy harvesting mechanism.
The team investigated whether the underlying mechanisms that produce low-wind-speed quiver in Aspen leaves could efficiently and effectively generate electrical power by exploiting the wind-generated mechanical movement of a device modeled on the leaf.
The mechanism provides a mechanical means of generating power without the use of bearings, which can stop working in environments with extreme cold, heat, dust or sand. The amount of potential power that could be generated is small, but still could power autonomous electrical devices, such as those in wireless sensor networks. These networks could be used for applications such as providing automated weather sensing in remote and extreme environments.
The key to Aspen leaves' low wind but large amplitude quiver relates to the stem's essentially flat shape. The researchers used mathematical modeling to come up with a mechanical equivalent of the leaf. They then used a low-speed wind tunnel to test a device with a cantilever beam like the flat stem of the Aspen leaf, and a curved blade tip with a circular arc cross-section acting like the main leaf.
The blade was then oriented perpendicular to the flow direction. That allowed the harvester to produce self-sustained oscillations at low wind speeds like the Aspen leaf. The tests showed that the air flow becomes attached to the rear face of the blade when the blade's velocity becomes high enough.
The researchers said that in nature, the propensity of a leaf to quiver is enhanced by the thin stem's tendency to twist in two different directions. However, the modeling and testing found that the researchers did not need to replicate the additional complexity of a further degree of movement in their mechanical model. Simply replicating the basic properties of the flat stem in a cantilever beam and curved blade tip with a circular arc cross-section acting like the main leaf was enough to create sufficient mechanical movement to harvest power.
The researchers said they will next examine which mechanical movement-based power-generating technologies would best be able to exploit this device and how the device could best be deployed in arrays.