The energy harvesting bracelet (EHB) is based on two permanent magents that move in opposite directions to capture energy through the natural motions of the wearer’s wrist.
The EHB developed by Zhiyi Wu of the Engineering Research Center for Mechanical Testing Technology and Equipment of Ministry of Education at Chongqing University of Technology transforms motion in any orientation except the axial to drive four coil transducers and induces significant electro-motive forces across the coils. The prototype can charge a capacitor with 470 μF to more than 0.81 V in 132 ms from a single excitations.
The double-repulsion configuration of the moving magnets provided the best displacement and velocity for the best output voltage. The two magnets have a 60° circle arc, 29.5 mm inner radius, and 40.5 mm outer radius and are located in a tube with a 57 mm inner diameter with four wound coils of approximately 800 turns and a resistance of 85 Ω, and are contained in a £D printed shell.
The power management circuit simply consists of a rectification circuit and a capacitor. The EHB with four coils connected in parallel after using the rectification circuit has been used to charge a 470 μF 25 V capacitor. and the energy stored in the capacitor exceeds 0.15 mJ, giving an effective average power of over 1.17 mW.