Voltage coefficient of a piezoelectric nanocomposite energy harvester Modeling and experimental verification

Piezoelectric nanocomposites composed of piezoelectric nanowires and flexible polymer have emerged as outstanding applications for flexible energy harvester. Although piezoelectric materials in their bulk form have high electromechanical coupling coefficient and can convert mechanical energy to electrical energy efficiently, they usually have low fracture toughness and are limited in applications due to difficulty in machining and casting it on to curve surfaces. Recently, additive manufacturing process (direct write) have been developed to incorporate piezoelectric nanowires into a polymer matrix with controlled alignment. It is shown that not only direct writing method can solve these issues but also it can improve the performance of the nanocomposite energy harvester significantly. In this paper, an experimentally verified finite element (FE) and micromechanics models are developed for calculation and optimization of g(31) voltage coefficient of a piezoelectric energy harvester nanocomposite. It is shown that, by using high aspect ratio nanowires with controlled alignment the g(31) coefficient can be enhanced more than five times compared to bulk form. Moreover, it is demonstrated that to achieve highest possible g(31) coefficient only a small volume fraction of nanowires is needed and further increase in volume fraction result in the reduction of g(31) coefficient.