Passive Wireless Detection for Ammonia Based on 2.4 GHz Square Carbon Nanotube-Loaded Chipless RFID-Inspired Tag.

High concentrations of ammonia (NH3) pose a potential threat to human and animal/plant health. Active detection methods such as semiconductor, electrochemical, and optical methods have been used for NH3 detection. These methods increase energy consumption and heat accumulation, which may affect the performance of detection systems. Therefore, the research on passive NH(3 )detection methods is of great significance. In our study, a passive wireless sensor for NH3 detection based on carbon nanotube (CNT)-loaded chipless radio frequency identification (CRFID) was considered, which have the advantages of low cost, passive wireless ability, miniaturization, universality, and long life. However, path loss, tag position, and actual environmental interference can affect detection efficiency. In order to better improve the robustness of NH3 detection, the principle of CNT-loaded RFID-inspired NH3 detection was introduced in our study. High-frequency simulator structure (HFSS) simulation and fabrication for RFID-inspired sensors based on metal ink material printing is proposed, which operated at the central frequency of 2.4 GHz. The resistance value changes when the NH3 concentration is 0-200 mg/L, which shows a negative growth coefficient after absorbing NH3. Furthermore, detection and analysis in real and simulated environments were derived, such as power reflection coefficient, tag angle, path loss, identification distances, and phase. The measurement comparison outside the laboratory environment and cross-sensitivity of CO2 was also carried out. The result provides a reliable theoretical and practical basis for passive wireless NH3 detection and is of great significance for environmental quality assessment and food safety traceability information disclosure.