Optimization of a piezoelectric unimorph for shock and impact energy harvesting

Piezoelectric bending structures can be designed to act as an electrical generator for converting ambient mechanical energy into useful electrical energy. The produced electrical energy is stored or dissipated into an electrical load. Most of the analyses on piezoelectric generators proposed in the literature are limited to a steady-state approach to the problem. These analyses fail to give clear insights when the dynamical behaviour of the piezoelectric bender is governed by its transient characteristics, for example in the case of a shock or impact excitation, and we analyse such a situation in this paper. It is first pointed out that the rate of transfer of energy towards the electrical load is optimized by maximizing the figure of merit of the structure and by choosing an appropriate value of the load. According to this consideration, a method to design piezoelectric benders for impact or shock energy harvesting in terms of their geometry and material properties is then proposed.