Development of High-Efficiency Piezoelectric-Based Energy-Harvesting Power Sources Using Motion-Doubling Mechanisms

Piezoelectric-based energy harvesting power sources that employ spring-mass vibrating systems have been employed with great success to harvest energy from various shock loading and/or vibration and oscillatory motions in numerous systems. In these systems, the external stimuli is used to store mechanical energy in the spring of a mass-spring unit which is attached to a piezoelectric element or a magnet and coil generator, and generate electrical energy as the vibrating mass-spring unit undergoes vibration and applies a cyclic load to the piezoelectric element. In this paper, the implementation of such energy harvesting power sources with a novel motion-doubling mechanism is presented. This novel force transmission method has two key advantages. Firstly, it provides the means to amplify the force applied to the piezoelectric element. Secondly, it provides the means of doubling the number of cycles of compressive forces applied to the piezoelectric elements during each cycle of vibration as compared to the direct mass-spring-piezoelectric generators that have been developed to date. The motion doubling and the resulting halving of the required number of cycles of vibration of the mass-spring unit for generating a certain amount of electrical energy has the effect of significantly increasing the mechanical to electrical energy conversion efficiency of the power source by significantly reducing structural damping losses in the spring element and by the increase in the level of force that is applied to the energy harvesting piezoelectric elements. The design and prototype fabrication of such an energy harvesting power sources is discussed.