In this paper, we propose a piezoelectric energy harvester to scavenge the impact energy from human footsteps at low input frequencies. The device consists of an amplification mechanism and piezoelectric bimorphs. When a human foot strikes the proposed harvester, the amplification mechanism deforms the piezoelectric bimorphs in the 31-mode to produce a large mechanical strain, meaning that the output power can be generated with high efficiency. A maximum output power of 27.5 mW was generated by the proposed harvester at an input frequency of 1.5 Hz (representing fast walking), while 18.6 mW was generated at 1.0 Hz (representing slow walking). Comparison experiments also showed that the proposed harvester can produce much a higher output power than that the same harvester operating in the 33-mode under the same working conditions.

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The development of wearable electronics and sensors is constrained by the limited capacity of their batteries. Therefore, energy harvesting from human motion is explored to provide a promising embedded sustainable power supply for wearable devices. Herein, the principles, development, and applications of human motion excited energy harvesters are reviewed. The energy harvesters are classified based on the human motions with distinguished characteristics: center of mass motion (COM), joint motion, foot strike, and limb swing motion. According to the motion characteristics, the principles, features, and limitations of different energy harvesters are discussed, and the power generation performances are compared. Finally, various self-powered applications enabled by embedded energy harvesters are introduced, so as to show the great potential of embedded energy harvesting systems in boosting the development of the wearables.

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