Piezoelectric energy harvesting from human walking using a two-stage amplification mechanism

This paper presents the design, modeling and experimental tests of a novel piezoelectric energy harvester with a two-stage force-amplification compliant mechanism for scavenging energy from human walking. The harvester consists of four units of two-stage force amplification piezoelectric transducers sandwiched between two heel-shaped plates. The dynamic reaction force at a heel is amplified twice by the two-stage force amplification frames before applied to the 33-mode piezoelectric stacks and therefore a large power output is achieved. Experiments were performed on the prototype of the two-stage piezoelectric energy harvester over different load levels and frequencies. Numerical simulation results based on a simplified single degree-of-freedom model agreed well with the experiment results. An average power of 34.3 mW and a peak power of 110.2 mW were obtained from the simulation under the dynamic force with the amplitude of 500 N and frequency of 3 Hz. At 2 Hz and 1.0 Hz, the average power outputs of 23.9 mW and 11.0 mW, peak power outputs of 65.8 mW and 31.7 mW were experimentally achieved. Numerical simulations show that the average power output of 12.8 mW and peak power output of 204.7 mW could be obtained at the walking speed of 3.5 mph (5.6 km/h) from a male subject with the body weight of 84 kg and height of 172 cm. Comparison study demonstrated that the proposed two-stage piezoelectric harvester has a larger power output than the reported results in literature.