Comprehensive investigation of a broadband wearable energy harvester using adaptive kinetic energy reallocation mechanism

Energy harvesting technology has become a crucial way to accomplish battery-free wireless sensor networks. Although the output power of the wearable energy harvester has been significantly improved, the bandwidth of the energy harvester is still a key issue that hinders the applications of the energy harvester since the output power could dramatically fluctuate within a small excitation range. In this paper, adaptive kinetic energy reallocation (AKER) mechanism is proposed to stabilize the output power of the wearable energy harvester. In contrast to potential energy-based method, the AKER utilizes a pre-programmable and variable frequency-up converter to manipulate the kinetic energy transfer. Thus, the kinetic energy is adaptively controlled to enhance system response such that the output power can be stabilized. A mathematical model is built to predict the system performance and assess the feasibility of AKER mechanism. To validate the AKER, a prototype is fabricated and tested under single pendulum and simulated limb swinging excitations. Both the theoretical and experimental results show that the AKER can effectively stabilize the output power for all the excitation conditions. Compared with conventional energy harvester, the AKER can reduce the power ratio by up to 42 % and generate maximum power of 1.48 mW under single pendulum excitation. Moreover, under simulated limb swinging excitation, the AKER cuts down the power ratio decrease by 46 % and the maximum power reaches 1.47 mW. Based on these results, the AKER demonstrates great advantage in improving the output power stability and provides a novel method to enhance the bandwidth of the energy harvester.