Application of dual-frequency resonant RFID gas sensor based on ZnO/MoS₂/WO₃/rGO for indoor formaldehyde and ammonia detection.

A dual-frequency passive radio frequency identification (RFID) gas sensor based on zinc oxide (ZnO)/molybdenum disulfide (MoS2)/tungsten trioxide (WO3)/reduced graphene (rGO) is proposed for indoor detection of formaldehyde and ammonia concentrations. The antenna model is designed on the antenna simulation software, and then, the antenna is made by the engraving mechanism. Nano-sensitive materials are prepared by the hydrothermal method to characterize the materials, and then, different combinations of materials are coated on both sides of the antenna to produce gas-sensitive sensors. The experimental results show that one frequency point of the sensor works in the range of formaldehyde concentration of 0.08-1.14 ppm, amplitude variation is 17.11 dB, linearity R2 = 0.97. The sensor operates at another frequency in the ammonia concentration range of 5-100 ppm, the amplitude changes to 12.7 dB, and the linearity R2 = 0.99. Compared with the previous gas sensors, the sensor has wide measuring range, high sensitivity, good selectivity, is lightweight and portable, and provides high anti-interference ability.