A smart device for harnessing energy from aerodynamic flow fields

In this work, inspired by music playing harmonicas, we conduct a conceptual investigation of a coupled aero-electromechanical system for wind energy harvesting. The system consists of a piezoelectric cantilever unimorph structure embedded within an air chamber to mimic the vibration of the reeds in a harmonica when subjected to air flow. In principle, when wind blows into the air chamber, the air pressure in the chamber increases and bends the cantilever beam opening an air path between the chamber and the environment. When the volumetric flow rate of air past the cantilever is large enough, the energy pumped into the structure via the nonlinear pressure forces offset the intrinsic damping in the system setting the beam into self-sustained limit-cycle oscillations. These oscillations induce a periodic strain in the piezoelectric layer which produces a voltage difference that can be channeled into an electric load. Unlike traditional vibratory energy harvesters where the excitation frequency needs to match the resonant frequency of the device for efficient energy extraction, the nonlinearly coupled aero-elasto dynamics of this device guarantees autonomous vibration of the cantilever beam near its natural frequency as long as the volumetric flow rate is larger than a certain threshold. Experimental results are presented to demonstrate the ability of this device to harvest wind energy under normal wind conditions.