[en] Highlights: • A TENG-based self-powered instantaneous wireless humidity sensor system is developed with the passive components only. • A precise analytical model is developed for the capacitive sensor systems, shows excellent agreement with experiments. • A high performance TENG is developed using PA66 and FEP films with an peak power density of 4.8 W/m². • The sensor system has a high sensitivity of 1.26 kHz/%RH and high linearity. Self-powered wireless sensor systems are highly sought for the forthcoming Internet of Things era. However, most of the technologies take the route of energy harvesting, storage, and power regulation to power wireless sensor systems, which has a limited operation duration due to the low energy utilization efficiency of the multiple energy conversions involved. Here, we propose a triboelectric nanogenerator (TENG) based fully self-powered, instantaneous wireless sensor system which yet does not contain electronic devices and chips, but the passive components only. By integrating a capacitive sensor and an inductor coil with TENG, the pulse voltage output of the TENG is converted into a sinusoidal signal containing the sensing information with a resonant frequency and is transmitted to the receiver in distance wirelessly and continuously. A precise analytical model is developed for the capacitive sensor system with general implication; the oscillating signal generated by the model shows excellent agreement with experimental results. A capacitive humidity sensor is then utilized for sensing demonstration, showing that the maximum transmission distance of the sensor system is 50 and 90 cm for a 1 cm diameter magnetic-core coil pair and 20 cm diameter air-core coil pair, respectively. The wireless humidity sensor exhibits a sensitivity of 1.26 kHz/%RH, fast response speed, and excellent linearity, demonstrating its great application potential of the self-powered technology.

[en] Highlights: • A triboelectric nanogenerator (TENG) based self-powered instantaneous wireless traffic monitoring system is developed which yet does not contain electronic devices, but the passive components. • The traffic recognition monitoring system can identify pedestrians on the sidewalk and illegal vehicles entering the footpath. • The traffic speed monitoring system can realize the function of electric vehicle speed measurement and driving direction judgment. The self-powered wireless sensor systems are highly sought for the information era, as they are able to link everything together, yet without the need for electric power supply. They have been exploited for applications in various fields, particularly for environment-related ones. Here, we propose a fully self-powered triboelectric nanogenerator (TENG)-based wireless traffic monitoring system for real-time monitoring of illegally entered electric motorbikes on the footpaths, and flow rates of pedestrians and motorbikes, and speed and driving direction of electric motorbikes on non-motorized lanes. The TENG was used to directly convert the energy from pedestrian’s stepping and electric motorbike’s rolling into an oscillating signal with encoded sensing information, and transmit it to the receiver wirelessly via magnetic resonance coupling. Results showed that the multi-variable traffic monitoring system can identify pedestrians and motorbikes, check the illegally entered motorbikes on the footpath, and measure speed of the motorbikes with an accuracy of over 94%, monitor driving direction of electric motorbikes on non-motorized lanes. The self-powered wireless traffic monitoring system is simple in structure, low cost, easy to install, and spontaneous response to the traffic condition, and does not contain electronic devices, microcontrollers and transmission chips but the passive components, hence it has great application potential as a green intelligent traffic monitoring system.