Bionic dragonfly staggered flapping hydrofoils triboelectric-electromagnetic hybrid generator for low-speed water flow energy harvesting

Water flow energy harvesting with triboelectric nanogenerators (TENGs) is in the spotlight. However, existing front-end energy harvesting structures have drawbacks, such as traditional turbines requiring higher flow speed to start-up, and devices based on vortex-induced vibration exhibiting a lock-in phenomenon, which severely limits the performance of the TENGs in low-speed water environments. Here, a bionic dragonfly flapping hydrofoils-driven triboelectric-electromagnetic hybrid generator (BDFH-TEHG) is reported. The dragonfly-wing-like staggered tandem hydrofoil configuration enables the BDFH-TEHG continuous energy harvesting in the entire time domain. Meanwhile, the power generation part and front-end structure parameters are optimized to enhance the electrical output of the harvester. As a result, the BDFH-TEHG exhibits a low starting flow speed, and efficient power generation at different flow speeds. At the flow speed of 0.21 m/s, the triboelectric nanogenerator (TENG) and electromagnetic generator (EMG) achieve peak powers of 4.19 mW and 8.01 mW, respectively. Furthermore, the BDFH-TEHG can power the wireless water quality sensor and provide early warning successfully for agricultural activities. This work provides a valid method for low-speed water flow energy harvesting, toward practical applications of water environment monitoring in smart agriculture.