To perform long endurance military missions, small, unattended sensors must generate and harvest power from their surroundings. Experiments have shown that a flexible membrane, made from piezoelectric material, can be excited in a flag-like fashion by the von Karman vortex street forming behind a bluff body to produce power to trickle charge a battery. The image shows the vortical structures exciting the membrane.

Reference:

Allen, J. J. & Smits, A. J. Energy Harvesting Eel. Journal of Fluids and Structures, 15, 2001, 629-640.

*Mexico State University