| Summary: | 碩士 === 國立清華大學 === 動力機械工程學系 === 102 === The detection results for mixture gas (ammonia/methane) by polymer deposited on 128° YX-LiNbO3 surface acoustic wave (SAW) delay lines are studied in this work. The adsorption of mixture gas by sensitive coating material modulates the phase velocity of the acoustic wave due to the mass loading and acoustoelectric effect. Thus, the targeted mixture gas can be evaluated by recording the frequency shift of the SAW device.
In this research, we used the SAW sensor to detect chemical compounds such as ammonia, methane, and ammonia-methane mixture gases. To enhance the sensitivity and accuracy of the surface acoustic wave sensors, the sensing chamber and polymer films was improved. Miniature cover with fluidic channels (200 μl) has replaced 1L 4-neck bottle chamber as a sensing chamber of the system. PNVP with mesoporous carbon hollow nanosphere has replaced PNVP with platelet mesoporous carbon as a sensing film of the system. Very low concentration of ammonia (≈ 250 ppb) and methane (≈ 9 ppm) can be detected by our SAW devices. From the ammonia gas and methane gas database, we can find that the frequency shift of ammonia/methane mixtures equal to the sum of frequency shift of ammonia and methane. Besides, the signal loss of ammonia is much stronger than methane in high relative humidity conditions. By quantitative measurement results of ammonia/methane mixture gas, we can use synergistic effects of the gas mixture to predict the signal intensity of different concentrations. The SAW sensor can also be applied to other industrial and environmental detection, and hope the gas sensor can be widely used in the daily life.
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