Design of Electro-Magnetic Energy Harvester (EMEH) From Knee’s Muscle Work During Walking

Energy harvesting from human motions can extend battery lifespan and enhance mobile device convenience, with promising applications in military and medical fields. Knee motion is an excellent candidate for energy harvesting due to its significant recoverable negative work. This paper aims to design an Electro-Magnetic Energy Harvester (EMEH) that captures power from knee muscle work during walking. We used 2D motion capture techniques to obtain input data, including knee angular rotation and muscle work during walking. Position vectors were extracted with a motion tracker, angular positions were formulated, and the data were imported into MATLAB® Simscape MultibodyTM to develop a walking-leg model. The model obtained angular velocity, torque, and power, revealing an angular displacement within −60-0°, a maximum angular velocity of 5.42 rad/s, a maximum torque of 30 Nm, and an average power of 15.9 W. These results indicated both positive and negative work phases in one gait cycle, consistent with reference data, helping determine the energy harvester’s operating range. The EMEH model in MATLAB/Simulink® predicted the system’s output voltage and power, guiding prototype construction. Performance tests of the prototype showed a peak power output of about 8 W, with cumulative energy harvested at 5.5 J per gait cycle. With a prototype mass of 1.35 kg, the design achieved an average power density of 3.12 W/kg. Thus, our compact and lightweight EMEH prototype successfully converted the motion of the human knee into electricity while walking, achieving a power output suitable for practical applications.