Modeling of piezoelectret foam in a multilayer stack configuration for energy harvesting

Piezoelectric materials have the potential to completely replace batteries for low-power electronics. This benefit especially suits inaccessible or remote, battery-powered sensor applications. Energy harvesters of this kind usually employ one of two classes of materials: either piezoceramics or piezopolymers. Piezopolymers, such as the polypropylene piezoelectret foam used here, have several benefits over the more commonly used piezoceramic materials such as lead zirconate titanate (PZT). Since piezopolymers are flexible and resilient, they can be mounted to curved or flexible surfaces and used in applications with large shocks. They may also safely be used in vivo, as they have a lead-free composition. In addition to this, piezopolymers are lighter than piezoceramics, though they generally have a smaller piezoelectric coupling coefficient than the latter. Traditional piezoceramics exhibit piezoelectricity as a result of dipole shifts that take place in the material's crystal structure. The piezoelectret foam used in this study, on the other hand, achieves its energy harvesting capability from deformation of the large, surface charged, internal gas-filled voids. This study focuses on creating and validating an electromechanical model for a piezoelectret foam stack energy harvester device. This multi-degree of freedom, lumped-parameter model predicts the energy harvesting performance of the stack at various frequencies for various stack properties and is verified by experimentally-obtained response data from a fabricated 20-layer piezofoam stack