Progress in the application of triboelectric nanogenerators in modern agriculture

This review aimed to examine the application potential of triboelectric nanogenerators (TENGs) in agricultural micro-energy (ME) harvesting and self-powered sensing. An emphasis was focused on whether weak, low-frequency, and distributed energy sources under agricultural environments were converted into usable electrical energy, and whether TENG-based devices were supported battery-free monitoring of key environmental and biochemical parameters. Technical challenges were also identified using field deployment. A summary was finally given for the directions on TENG energy harvesting and sensing in smart agriculture. A comparison was made on contact electrification and electrostatic induction, in terms of device structures, materials, and hybrid configurations. ME harvesting was classified into wind, raindrops, and water flow, whereas self-powered sensing was for wind speed, wind direction, flow behavior, and nutrient concentration. A systematic evaluation was conducted on output and sensing performance, stability, as well as system integration. The results showed that TENGs provided an effective technical route to collect irregular agricultural energy and then convert mechanical interaction into electrical signals. Low-speed startup, airflow adaptability, and output stability were improved in wind energy harvesting using rotary devices with swing and blade structure in adaptive direction. Direction-adaptive hybrid devices exhibited stable output under variable wind conditions and were capable of powering multiple wireless sensors, indicating their adaptability to open farmland and greenhouse ventilation environments. For raindrop and water-flow energy harvesting, liquid-solid TENGs, droplet-based generators, water-tube structures, and waterwheel hybrid systems have been developed to utilize rainfall, irrigation flow, and dynamic liquid-solid interfaces. Their performance was improved after surface modification, hydrophobic materials, optimal electrode structures, and coupling with electromagnetic generators. Electrical output was used to support low-power sensing, wireless transmission, and liquid-state monitoring. In self-powered sensing, TENGs directly converted external mechanical or liquid disturbances into measurable electrical signals. Reported sensing targets included wind speed, wind direction, liquid flow rate, droplet behavior, leakage, blockage, and nutrient concentration. Wind sensors were used to monitor airflow in the range of 3-5 m/s, while biochemical sensing devices were to detect urea concentrations from 0-5 m/L. Microfluidic and droplet-based devices also showed sensitivity to bubble state, liquid motion, bacterial targets, and chemical composition. Therefore, TENG-based sensors shared the simple structure, active signal generation, low power demand, and compatibility with distributed monitoring nodes. Their output was still dominated by humidity, surface contamination, material wear, environmental disturbance, and load matching. Key challenges remained on output fluctuation, long-term durability, packaging reliability, and power application. TENGs can be expected for agricultural ME harvesting and self-powered sensing, especially in scenarios where conventional batteries difficult to replace or maintain. Future studies should improve structural robustness, material stability, environmental resistance, and consistent output. TENG devices can also integrate with power circuits, energy storage modules, and low-power wireless communication units. Full sensing is often required to combine energy harvesting, signal processing, data transmission, and field calibration in smart agriculture