Micro Kinetic Energy Harvesting for Autonomous Wearable Devices

For wearable devices, the availability of energy is one of the main limiting factors of performance and lifetime. To overcome this issue, micro-energy harvesting circuits, which extract energy from the environment, are very promising. Among other environmental sources, kinetic energy could significantly improve the energy availability in wearable applications. However, the majority of kinetic energy harvesting circuits do not perform well with the low-frequency patterns found in human motion and are therefore not suited for wearable devices. This paper aims to overcome this limitation by developing a high-efficiency energy harvesting system, which is optimized for frequencies occurring in human motion. A Micro Generator System (MGS) 26.4, by Kinetron, has been exploited as a kinetic transducer to generate energy. The implemented kinetic harvesting system has been designed to maximize the energy conversion efficiency and supply and recharge wearable devices. The final design has been implemented and field-tested in different positions on the human body. Experimental measurements demonstrate the end-to-end efficiency of up to 84%, and an average power of up to $\mathbf{624\mu W}$, which is superior to the state-of-art for the type of MGS. Moreover, a preliminary evaluation of the correlation between acceleration and power harvested is presented. Using the values obtained from experimental data, we estimate that two hours of walking and 30 minutes of running per day can provide 1.4 joules of electrical energy.