| Summary: | 碩士 === 義守大學 === 電機工程學系 === 91 === This work investigates the advanced properties of an improved surface acoustic wave (SAW) ammonia gas sensor. The sensor was based upon a dual delay line SAW configuration. The chemical interface was L-Glutamic acid hydrochloride deposited on the surface of SAW sensor. The frequency shift of SAW devices took in real-time measurement to analyze the detection for low ammonia concentration. The perturbation mechanism is proved in this work, and the optimal sensing conditions and properties are studied.
The SAW sensor based on L-Glutamic acid hydrochloride presented excellent sensitivity, reversibility, repeatability and selectivity to ammonia. Rising the operating temperature could improve the performance of sensors. The curve of frequency shift versus ammonia concentration showed the linearity and sensitivity at high temperature, especially at 50oC. The sensitivity was 0.05 ppm/ppm at 50oC, and it could estimate the limitation of detection (LOD) to be 0.08 ppm (=80 ppb). The water vapor in air significantly influenced the detection of ammonia. Therefore, SAW sensors based on L-Glutamic acid hydrochloride are suitable for operating at 50oC in dry air.
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