Hybrid Magnetic-Piezoelectric Energy Harvester for Power Generation around Waistline During Gait

The development of a novel hybrid energy harvester for scavenging power around human waistline is presented. The harvester is composed of mm-scale electromagnetic coils and piezoelectric transducers incorporated on a belt, as well as permanent magnet structures placed on wristbands. The coils and transducers are positioned on the belt such that they correspond to either sides of the waist, facing the wrists and the hipbone. This configuration leads to simultaneous power generation on the coils and transducers due to swinging arm motion and varying belt stress during gait, respectively. Moderate walking at 1 m/s resulted in a peak open circuit voltage of 2.8 V on the coils, reaching up to 4.3 V at 2 m/s fast walking. The open circuit voltage obtained from the transducers varied from 5.2 to 9 V, corresponding to moderate walking at 1 m/s and running at a speed of 3 m/s, respectively. Instantaneous AC power was characterized separately at 1 m/s walking speed, and measured to be 14 mW and 13.5 μW from the coils and piezoelectric transducers, respectively. The two harvesting mechanisms were coupled with rectifiers and DC/DC converter circuitry to store energy in an onboard 20 mAh 3 V LiPo battery. Walking for 10 min was shown to raise the battery voltage from 2.2 to 2.8 V. The results reported here demonstrate the feasibility of this MEMS-scale harvesting scheme to recharge batteries of portable electronic devices.