Scientists harvest energy from beam's self induced, self sustaining vibrations in airflow

In an attempt to harvest the kinetic energy of airflow, researchers have demonstrated the ability to harvest energy directly from the vibrations of a flexible, piezoelectric beam placed in a wind tunnel. While the general approach to harvesting energy from these "aeroelastic" vibrations is to attach the beam to a secondary vibrating structure, such as a wing section, the new design eliminates the need for the secondary vibrating structure because the beam is designed so that it produces self-induced and self-sustaining vibrations. As a result, the new system can be made very small, which increases its efficiency and makes it more practical for applications, such as self-powered sensors.

The researchers, Mohamed Y. Zakaria, Mohammad Y. Al-Haik, and Muhammad R. Hajj from the Center for Energy Harvesting Materials and Systems at Virginia Tech, have published a paper on the new energy-harvesting method in a recent issue of Applied Physics Letters.

"The greatest significance of the work is the reduction of the volume of the harvester, which translates to an increase in the power density, by eliminating the need for a secondary structure to be attached to the beam," Zakaria said. "This reduction is important in the design of very small harvesters that can be used to develop self-powered sensors."

The research shows that subjecting a flexible beam to wind at the right angle of attack can cause the beam to bend so much that the beam's "flutter speed" is significantly reduced. A large degree of bending also induces a change in the beam's natural frequencies that basically results in a synchronization of the beam's bending and twisting frequencies. Specifically, the beam's second bending frequency and torsional frequency coalesce, resulting in "self-induced flutter" of the beam. Complex aerodynamic effects ensure that the vibrations are self-sustaining, allowing for continuous energy harvesting.
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