Self-sustainable flow-velocity detection via electromagnetic/triboelectric hybrid generator aiming at IoT-based environment monitoring

Highlights: • A rotation sensor with three TENG-EMG modules is presented to harvest the energy as well as sense the fluid velocity. • The device can detect the rotation speed and direction based on the voltage sequence generated by TENG-EMG modules. • With gear pairs, it can sense a broadband rotation speed (0–10 Hz) and the output can be boosted by several times. Harvesting energy from the environment has aroused widespread interest and it can supply renewable power to achieve sustainable environment monitoring for the Internet of things (IoT). In this paper, a tri-cylinder-like hybrid generator composed of triboelectric nanogenerator (TENG) and electromagnetic generator (EMG) is presented to harvest the mechanical energy produced by various fluids as well as sense the real-time flow velocity ecofriendly. This generator can be driven to rotate through a windmill or waterwheel, leading to the reciprocating sliding of the internal spring-magnet structure. By arranging coil and foldable TENG structure, it can generate hybrid signals along with the rotation while gear pairs are further utilized for both boosting the output and expanding the sensing range. The experimental result shows more than twice and six times output can be realized by gear pairs for TENG and EMG, respectively, and the recognizable rotational frequency reaches 10 Hz with a transmission ratio of 5:1. The rotation speed and direction detection are realized based on the output voltage frequency and value of TENG caused by the difference of triboelectric layer number. Combined with two hybrid generators in a vertical layout, the wind directions are also investigated to be distinguished by computing the signal characteristics. Based on these sensing mechanisms, this hybrid generator is able to achieve wireless sensing as EMG boosted by gear pairs is sufficient to supply the energy for wireless transmission. This self-sustained sensory system shows its great potential for unmanned environment monitoring, disaster warning as well as the meteorological record in IoT applications.