A Coaxial Wrist-Worn Energy Harvester for Self-Powered Internet of Things Sensors

Energy harvesting from human motion has great potential of sustainably powering Internet of Things (IoT) sensors and satisfying their continuous sensing requirement. In this article, we propose a high-performance wrist-worn energy harvester to efficiently capture the biomechanical energy of arm swinging to self-power wearable sensors. Based on coaxial topology, a planetary gear system serves as frequency-up converter to increase energy conversion capacity, and all the functional units are coaxially installed to achieve a highly compact structure. Thanks to improved energy conversion capacity and structure compactness, the energy harvester can efficiently capture the kinetic energy of arm swinging and achieve high average power. We derive an analytical model to predict the system dynamics and power generation performance using the Lagrangian approach and mirror image method. We fabricate a miniature prototype with different proof mass configurations, which is characterized under bench-top excitations and tested under real walking excitations. The results show that in bench-top testing, the prototype generates maximum average power of 2.73 mW and maximum power density of 535.29
$\mathbf {\mathrm {\mu }}\text{W}$
/cm3 at the excitation frequency of 1.2 Hz among different configurations. In terms of average power and power density, this energy harvester significantly overperforms its counterparts. In real walking testing, the prototype generates maximum average power of 3.13 mW at a walking frequency of 1.2 Hz among different configurations and achieves higher power output than bench-top testing. Finally, the prototype is used to simultaneously power four sensors and demonstrates great potential in self-powered IoT applications.