“…Pursuing progress in clean, renewable and sustainable energy has become a critical issue to replace conventional energy sources [ 1 ]. In the meantime, the widespread application of high-performance devices in wireless sensor networks (WSNs) and the Internet of Things (IoT), e.g., wearable electronics, sensors, tags, data transmitters and microprocessors, has extended their appearance in building monitoring, climate information acquisition, smart factories/traffic/homes, personal healthcare and environmental monitoring, which is greatly excited by advances in material science, manufacturing techniques and ecofriendly concepts [ 2 , 3 , 4 , 5 , 6 , 7 ]. However, the power supply for WSNs/IoT is still dominated by conventional electrochemical batteries, whose periodic replacement inevitably brings great environmental problems and maintenance challenges, whereas the low-power feature of these devices also provides great feasibility in taking advantage of ambient mechanical energy to sustainably power these systems.…”