Piezoelectric energy harvesting from ambient vibrations

Converting the mechanical power of ambient environmental vibrations into electrical form allows us to avoid batteries for remote sensors. Understanding and describing the properties of ambient vibration is the first, often-missed step towards efficient power conversion. We consider examples of machinery and vehicle vibrations to demonstrate how their properties can be characterised and to illustrate the key features of ambient vibrations. Another step is to design the corresponding harvester. A piezoelectric harvester consisting of a cantilever that converts ambient vibration into cantilever oscillations and a piezoelectric layer that converts the oscillations into electric charge is considered. The importance of the cantilever's nonlinearity to harvester performance is discussed. Then, by considering several signals representing ambient vibration, it is shown that the interaction between ambient vibrational features and the harvester's nonlinearity affects harvester performance. This interaction can degrade or improve the harvester's conversion efficiency. Some open questions related to exploring the nonlinearity for maximising harvester efficiency and to developing adequate models of ambient vibration are outlined.