Abstract
This paper presents a piezostack-based frequency up-converting generator for scavenging ultra-low frequency (lower than 5 Hz) vibration energy associated with human motion. The generator, consisting of a force amplifier, a piezoelectric stack, a spring-mass system, and a spring limiter, realizes ultra-low frequency conversion mainly through the impact-induced frequency conversion effect. To estimate the output voltage of the generator numerically, we built a two-degree-of-freedom (2DOF) equivalent model based on the mechanical structure of the harvester. Moreover, we conducted five series of experiments to investigate the output performance of a fabricated prototype. The prototype generates an instantaneous peak-peak output power of 5.56 W (averaged power of 0.93 mW) excited by human running motions. A 'SHU' LED array was lighted up in real-time successfully. We then tested the performance of the prototype in a real-time self-powered system. The generator is able to power a watch and a thermometer in real-time. More importantly, when the excitation stops, they are powered by redundant charges for approximately 50 minutes and 1 minute, respectively. This research can make an essential contribution to ultra-low frequency vibration energy harvesting and the realization of real-time self-powered wearable devices.
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