Surface acoustic wave gas monitor for ppm ammonia detection

A shear horizontal surface acoustic wave (SH-SAW) sensor coated with polyaniline (PANI) film was investigated in this study. The frequency shift of SH-SAW was measured to detect the presence of ammonia. In addition, an analysis of humidity interference with the ammonia was performed. The SH-SAW sensor in this study responded to the ammonia gas and could be recovered using dry nitrogen. Detecting at an ammonia concentration of 20.45 ppm, the frequency shift was 1.79 ppm and the signal-to-noise ratio was 25.06 dB. This sensor had a response time of less than 150 s. Also, the frequency shift increased as the humidity increased. The cross-sensitivity varied nonlinearly with the ammonia concentration.