Performance evaluation of suspended energy harvesting backpack using half-wave mechanical rectification

Human beings are becoming more and more dependent on electronic devices, such as smart phones, smart watches, GPS, etc. This paper presents the design, modeling and testing of a novel suspended energy harvesting backpack using half-wave mechanical rectification. The proposed half-wave rectification mechanism can convert bidirectional linear vibration into unidirectional rotation with nonlinear inertia. Compared with full-wave mechanical rectification, the proposed half-wave rectification is designed only to convert the motion in one of the vibration directions while remaining idle in the other direction. Numerical simulation shows the proposed half-wave rectification based suspended energy harvesting backpack can obtain about two times of the average output power as the previous full-wave rectification design while also maintaining larger output power in the wideband frequency range. Bench test results indicate that the proposed half-wave rectification-based energy harvesting backpack can harvest 6.7 W (peak)/2.1 W (average) under 2 Hz and 6 mm excitation with a 31.8 kg payload, which is a significant improvement compared with 1.9 W(peak)/0.9 W (average) for the counterpart of full-wave rectification system. In addition, bench test results also validate the energy harvesting in wideband frequency range. Treadmill tests demonstrate an average power range of 1.2-11.0 W under walking speeds of 3.2-6.4 km/h with a 13.6 kg payload.