Magnetic-gear-enabled counter-rotating electromagnetic energy harvester for capturing low-speed wind energy

Wind energy is an abundant ambient power source for self-powered sensing, but conventional electromagnetic wind harvesters remain constrained under weak wind due to low rotor speed and limited magnetic flux variation. To address this issue, this paper presents a magnetic-gear-enabled Savonius-driven counter-rotating electromagnetic energy harvester (MG-SCR-EMEH) that integrates a Savonius turbine, an axial magnetic gear, and upper and lower electromagnetic power-generation modules. A non-contact magnetic speed amplification mechanism and a coaxial counter-rotating configuration triple the effective magnet-coil relative speed over direct-drive, thereby enhancing the magnetic flux variation and induction output while avoiding the wear and dissipation of contact-based frequency up-conversion. A theoretical model that combines aerodynamic drag and induced-voltage analyses, supported by finite element simulations, elucidates the mechanisms of magnetic-field modulation, torque transmission, and voltage generation. Experimental results show that the proposed MG-SCR-EMEH starts up at 3.5 m/s and, at 4.5 m/s, delivers 5.552 mW system-level equivalent charging power (27.76 mJ over 5 s into a 1 mF capacitor, 1.903 W/m 3 power density). At the same input speed of 50 RPM, increasing the magnet-coil relative speed from 50 RPM in the direct-drive configuration to 150 RPM in the magnetic-gear-coupled configuration raises the peak power from 22.78 to 166.78 mW. Furthermore, integrated with an energy-management unit, layered millimeter-wave radar nodes, and a BLE module, the MG-SCR-EMEH serves as the power source for a falling-object warning system, highlighting strong potential for low-speed wind energy harvesting and structural safety monitoring.