A continuous spiral-spring triboelectric nanogenerator for energy harvesting and self-sensing under ultra-low-frequency rotation

Self-powered monitoring of slowly rotating components is hindered by the small relative speed and limited installation space available to conventional rotary triboelectric nanogenerators (TENGs). Here, a continuously driven unidirectional rotary TENG (CDUR-TENG) is developed by integrating a multilayer spiral-spring electrode with a ratchet-triggered energy-storage/release mechanism. During winding, the spring stores elastic energy while its adjacent triboelectric interfaces progressively separate; ratchet disengagement then initiates rapid elastic recoil and concentrated charge transfer. The device therefore decouples the electrical pulse from the slow external rotation. At 0.2 Hz, the CDUR-TENG provides a peak-to-peak open-circuit voltage of approximately 130 V and a maximum short-circuit current of 55 μA; it transfers 0.165 μC per cycle and reaches a maximum instantaneous power of 2.182 mW at 1 Hz and 1.1 MΩ. The resulting normalized power density reaches 191.4 W m−3Hz−1, at least 8.57 times that of the compared rotary harvesters. Voltage signatures further distinguish operating angle, angular overshoot, and reverse rotation, demonstrating a compact route toward self-powered condition monitoring under ultra-low-frequency rotation.