A passive wireless surface acoustic wave (SAW) sensor system for detecting warfare agents based on fluoroalcohol polysiloxane film

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Abstract
Long-term monitoring of environmental warfare agengts is a challenge for chemical gas sensors. To address this issue, we developed a 433 MHz passive wireless surface acoustic wave (WSAW) gas sensor for dimethyl methylphosphonate (DMMP) detection. This WSAW gas sensor includes a YZ lithium niobate (LiNbO3) substrate with metallic interdigital transducers (IDTs) etched on it, and an antenna was placed near the IDT. A DMMP-sensitive viscoelastic polymer fluoroalcoholpolysiloxane (SXFA) film was prepared on a LiNbO3 substrate, and mode modeling coupling was used to optimize the design parameters. The sensor can function properly in an environments between −30 °C and 100 °C with humidity less than 60% RH. When the wireless transmission distance was within the range of 0–90 cm, the sensor noise increased with distance, and the stability was less than 32°/h. While optimizing the film thickness of SXFA, a relationship was observed between sensor sensitivity and film thickness. When the film thickness of SXFA reached 450 nm, the optimal value was reached. At a distance of 20 cm between the transmitting and receiving antennas, DMMP was detected at different concentrations with the developed WSAW gas sensor. The lower detection limit of DMMP was 0.48 mg/m3, the sensitivity of the sensor was 4.63°/(mg/m3), and repeatable performance of the sensor was confirmed.

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