A Magnetically Coupled Electromagnetic Energy Harvester with Low Operating Frequency for Human Body Kinetic Energy

In this paper, a magnetically coupled electromagnetic energy harvester (MCEEH) is proposed for harvesting human body kinetic energy. The proposed MCEEH mainly consists of a pair of spring-connected magnets, coils, and a free-moving magnet. Specifically, the interaction force between the magnets is repulsive. The main feature of this structure is the use of a magnetic-spring structure to weaken the hardening response caused by the repulsive force. The magnetic coupling method enables the energy harvester system to harvest energy efficiently at low frequency. The MCEEH is experimentally investigated for improving energy harvesting efficiency. Under harmonic excitation with an acceleration of 0.5 g, the MCEEH reaches resonance frequency at 8.8 Hz and the maximum output power of the three coils are 5.2 mW, 2.8 mW, and 2.5 mW, respectively. In the case of hand-shaking excitation, the generator can obtain the maximum voltage of 0.6 V under the excitation acceleration of 0.2 g and the excitation frequency of 3.4 Hz. Additionally, a maximum instantaneous power can be obtained of about 26 mW from the human body's kinetic energy.