Splitting of neutral mechanical plane of conformal, multilayer piezoelectric mechanical energy harvester

Flexible piezoelectric mechanical energy harvesters (MEHs) are of recent interest as an important emerging variant of traditional piezoelectric devices. The design of stacking multilayer MEHs with adhesive in between is an effective way to enhance the magnitude of power generation. Here, we present an analytic model to study the mechanical behavior of the multilayer MEHs based on lead zirconate titanate (PZT) subjected to Euler buckling. Being different from the hypothesis of the plane section for the entire stack, it is found that each polyimide (PI) layer holds plane section of its own, while soft adhesives serve as shear lags. Accordingly, the neutral mechanical plane is split into multiple ones. The deformation is almost the same for each PI layer, as well as PZT arrays, which is very beneficial to avoid the premature failure of devices. The extreme cases and the transition of these cases are all captured quantitatively with a unified analytic model which is verified by the finite element method. A dimensionless parameter is obtained to characterize the degree of the splitting of neutral mechanical plane, which is significant for the design of the multilayer PZT MEHs.