The capability of using a linear kinetic energy harvester-A cantilever structured piezoelectric energy harvesterto harvest human motions in the real-life activities is investigated. The whole loop of the design, simulation, fabrication and test of the energy harvester is presented. With the smart wristband/watch sized energy harvester, a root mean square of the output power of 50 μW is obtained from the real-life hand-arm motion in human's daily life. Such a power is enough to make some low power consumption sensors to be self-powered. This paper provides a good and reliable comparison to those with nonlinear structures. It also helps the designers to consider whether to choose a nonlinear structure or not in a particular energy harvester based on different application scenarios.

This paper presents a novel design of a nonlinear kinetic energy harvester for very low excitation frequencies below 10 Hz. The design is based on a proof mass, rolling in a circular cavity in a Tusi couple configuration. This allows for an unconstrained displacement of the proof mass while maintaining the option of keeping the energy transduction element engaged during the whole cycle and thus reducing the required number of transduction elements. Both the presented model and the fabricated prototype of the device employ electromagnetic induction to harvest energy from low frequency and low magnitude vibrations that are typically associated with human movements. The prototype demonstrated an average power of 5.1 mW from a 1.3 g periodic acceleration waveform at 2.78 Hz. The highest simulated normalized power density reaches up to 230 μW/g 2 /cm 3 , but this depends heavily on the excitation conditions.

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