Analysis and design principles for shear-mode piezoelectric energy harvesting with ZnO nanoribbons

A comprehensive theory addresses the potential for nanoscale energy harvesting with an array of vertically aligned zinc oxide (ZnO) nanoribbons. Through shear-mode piezoelectric coupling, the nanoribbons are capable of generating electricity from elastic deformations induced by sliding friction or mechanical vibration. In contrast to current ZnO nanowire generators, nanoribbons exhibit a unique combination of geometry and poling orientation that eliminates the need for a nanostructured cathode and allows electrodes to be permanently bonded to the array. The theory incorporates principles and design constraints from solid mechanics, electrostatics, piezoelectricity, vibration dynamics, circuit theory, and tribology. The accuracy of the approximate algebraic solutions is evaluated with finite element modeling. For geometries and operation modes of interest, the electrical power output and conversion ratio from mechanical power input are limited to ∼10 nW mm−3 and 1000:1, respectively. While modest, such numbers provide a proper perspective on the potential for nanopiezoelectric energy harvesting. (Some figures in this article are in colour only in the electronic version)