An innovative energy harvesting backpack strategy through a flexible mechanical motion rectifier

This paper reports a fundamentally different strategy for realizing high-performance energy harvesting backpacks to effectively scavenge ultralow-frequency human body motions. The proposed backpack strategy is based on an innovative flexible mechanical motion rectifier (MMR) that consists of an inelastic strap, an elastic strap, a shaft with a double-layered plectrum, and a rotor. The flexible MMR first converts the human motion induced vibrations to the alternating spin of a shaft, and then enables the mono-directional spin of a rotor by a shaft through the stiffness self-adaptive plectrum. To examine the feasibility of the proposed strategy, an energy harvesting backpack was constructed with an array of the flexible MMR-based harvesters, and an electromechanical model of the backpack was also established and verified. Both simulations and experiments reveal the high output power of the backpack under various human travel velocities. Experiments show that, under a running velocity of 9 km/h, the backpack with a small payload of 3.6 kg can deliver high output power of 1.284 W. Under a walking velocity of 6 km/h, the electric energy generated by only one harvester of the backpack with a payload of 1.7 kg is sufficiently large for charging both a smart bracelet and a smart phone. This study demonstrates the feasibility of achieving high-performance energy harvesting backpacks with the flexible MMR for portable and wearable electronics.