Fundamental study of mechanical energy harvesting using piezoelectric nanostructures

This paper numerically estimates the potential, the output power and the energy conversion efficiency of piezoelectric nanostructures, including rectangular nanowires (NWs), hexagonal NWs, and two-dimensional vertical thin films (the nanofins). Static analysis studies the maximum piezoelectric potential that can be produced by a BaTiO₃ NW, a ZnO NW, and a ZnO nanofin when they are subjected to a constant external force. Dynamic analysis is performed to study the power generation ability via the vibration of these nanostructures agitated by ambient vibration energy. ZnO NW and nanofin are selected as two representative nanogenerator elements. Their dynamic responses are modeled using a single-degree of freedom system with a series of damping ratios. Combining the transfer functions of mechanical vibration and piezoelectric charge generation, we define the output power and efficiencies as functions of the vibration frequency and the sizes. The optimal size for constructing a high efficiency and high-power nanogenerator is suggested. The material dependence of a dynamic system is also studied based on different piezoelectric and ferroelectric material systems, including ZnO, BaTiO₃, and (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃. This research reveals a comprehensive relationship between the mechanical energy harvesting ability and the nanomaterials’ morphologies, dimensions, and properties. It provides a guideline for the design of high-power nanogenerators and the development of piezoelectric nanodevices in general.