Efficiency of energy conversion for devices containing a piezoelectric component

Recent developments in miniaturized sensors, digital processors and wireless communication systems have many desirable applications. The realization of these applications however, is limited by the lack of a similarly sized power source. Micro-scale concepts to generate electrical power include devices which use the stored energy in fuels to those which harvest energy from the environment. Many proposed power generation systems employ a piezoelectric component to convert the mechanical energy to electrical energy. Of primary importance is the efficiency of power conversion. In this paper, an exact formula is developed that predicts the power conversion efficiency for a device that contains a piezoelectric component. This formula transparently and quantitatively reveals a trade-off effect on efficiency caused by the quality factor and electromechanical coupling factor of the device. In particular, decreasing the structural stiffness leads to the largest gains in efficiency, followed by decreasing the mechanical damping and increasing the effective mass.