Nitrogen Dioxide Wireless Sensor Based on Carbon Nanotubes and UWB RFID Technology

This letter presents a semi-passive wireless nitrogen dioxide gas sensor based on a time-coded ultra-wideband tag. The gas is sensed by means of oxygen-plasma-treated multiwall carbon nanotubes. The reader consists of a commercial ultra-wideband radar. The signal backscattered at the tag is modulated by a single-pole double-throw switch and contains information on the gas concentration. The tag is normally in sleep mode and includes a wake-up circuit. A self-calibration circuit is also included, enabling two additional measurements used for background subtraction and calibration to be obtained. The sensor is able to detect nitrogen dioxide concentrations from 10 ppm to 100 ppm, with a mean relative error of 0.34%.