Boosting the efficiency of a footstep piezoelectric-stack energy harvester using the synchronized switch technology

In this article, the self-supported power conditioning circuits are studied for a footstep energy harvester, which consists of a monolithic multilayer piezoelectric stack with a force amplification frame to extract electricity from human walking locomotion. Based on the synchronized switch harvesting on inductance (SSHI) technology, the power conditioning circuits are designed to optimize the power flow from the piezoelectric stack to the energy storage device under real-time human walking excitation instead of a simple sine waveform input, as reported in most literatures. The unique properties of human walking locomotion and multilayer piezoelectric stack both impose complications for circuit design. Three common interface circuits, for example, standard energy harvesting circuit, series-SSHI, and parallel-SSHI, are compared in terms of their output power to find the best candidate for the real-time-footstep energy harvester. Experimental results show that the use of parallel-SSHI circuit interface produces 74% more power than the standard energy harvesting counterpart, while the use of series-SSHI circuit demonstrates a similar performance in comparison to the standard energy harvesting interface. The reasons for such a huge efficiency improvement using the parallel-SSHI interface are detailed in this article.