A self-powered wind speed and humidity sensor based on paired flap-type triboelectric nanogenerators with differential humidity responses

This study reports a self-powered sensor that simultaneously measures wind speed and relative humidity using two triboelectric nanogenerators. The output of conventional triboelectric nanogenerators decreases with increasing ambient humidity. In previous wind sensors, this dependence has been treated as an error to be eliminated. Herein, we used the humidity dependence as a measurement signal. One device used a spin-coated polyvinyl alcohol–lithium chloride film, whose output proved far less sensitive to humidity; this behavior is consistent with reported spectroscopic evidence that lithium chloride retains the absorbed water within the film matrix rather than as a free surface layer. The other used a commercial nylon film, whose output steadily decreases with increasing humidity. Each film forms the fixed bottom layer of a device, with an identical polyethylene terephthalate film fluttering above it in the wind, making the bottom material the only material difference between the two devices. Therefore, both outputs vary with wind speed but exhibit markedly different responses to humidity, enabling wind speed and relative humidity to be determined from the paired signals over 3–5 m/s and 40–70% RH. A separately powered readout system based on a commercial microcontroller output both quantities in real time, and the values agreed with those from a commercial anemometer and hygrometer placed at the wind-tunnel outlet.