Passive Ammonia Detection Sensor Based on Zinc Stannate Loaded Dual-Frequency Chipless RFID-Inspired Technique

Ammonia is a toxic and flammable gas, and chemical resistance sensors have great potential in practical ammonia monitoring applications. For scenarios where there is a lack of circuit wired connection, it is important to explore a passive wireless, low-cost, and universal means of detecting ammonia. However, due to the limitations of single-frequency operation and interference from environmental factors (e.g., temperature, humidity, and interfere gas), research in this area is still ongoing. In this article, a dual-band patch antenna-based passive ammonia sensor utilizing chipless radio frequency identification (RFID)-inspired technology was designed. Meanwhile, the antenna’s performance parameters, including return loss, voltage standing wave ratio (VSWR), and normalized impedance, were optimized. Porous zinc stannate (Zn2SnO4) was selected as the sensing material, Zn2SnO4 material was characterized using energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The cross-shaped recess in the center of the antenna was coated with Zn2SnO4 to create the sensing unit. The passive sensor was operated at two distinct frequency bands, centered around 2.3 and 4.5 GHz and exhibited advantageous characteristics such as a simple structure, mechanical flexibility, and high gain. The sensor demonstrated excellent stability and sensitivity at daily operating temperatures ( $25~^{\circ }$ C). The limit of detection (LOD) method reveals that the detectable ammonia concentration is 40 ppm at the low-frequency point and 30 ppm at the high-frequency point. The reaction process between surface adsorbed oxygen species and ammonia is described to verify the passive sensing mechanism. This work presented chipless RFID-inspired technology with a specific emphasis on passive ammonia detection, offering potential applications in environmental monitoring and industrial safety.