Energy harvesting from flows using piezoelectric patches

The highly nonlinear phenomenon of fluid-structure interaction is discussed, including examples drawn from nature and early work on aircraft flutter. Recent work on extracting the energy in a fluid stream by piezoelectric elements is reviewed, including some of the underlying physics. Whilst the energy extracted from fluttering elements is low, it is a subject of interest for powering Ultra- Low Power (ULP) devices and systems since this method of energy extraction is thought to offer a quiet alternative to conventional wind turbines. Researchers have investigated the use of thin piezoelectric patches coupled to a geometrically shaped, polymeric membrane (via a revolute hinge) which can amplify the bending, strain and hence power. Such systems respond via flutter induced by resonant bending instability of the system, or by the utilisation of time-varying external pressure gradients formed around the system. Key factors that influence performance are examined, such as critical flutter speed, mass ratio, position of revolute hinge, aspect ratio and type of piezoelectric material. The chapter concludes with a discussion of the practical implications of such systems in the future