CO₂ Sensor using Quartz Crystal Microbalance Coated with Sensitive Membrane

Abstract

We tried to make a CO₂ sensor using a quartz crystal microbalance (QCM) coated with acrylonitrile-styrene copolymer (AS). Concentration of CO₂ gas diluted with dry N₂ gas was measured using the QCM whose output is frequency shift. Sensitivity of the QCM to Ar, O₂ and humidity was also examined because atmosphere is composed of N₂, O₂, CO₂, Ar and water vapor. Consequently it was revealed that the QCM coated with AS is sensitive to not only CO₂ but humidity and insensitive to O₂ and Ar. Next relationships between concentration of CO₂ gas diluted with damp N₂ gas and frequency shift of the QCM were examined. Consequently it was clarified that the frequency shift compensated for influence of humidity is nearly equal to the frequency shift caused by CO₂ gas diluted with dry N₂ gas. Accordingly it was shown that concentration of CO₂ gas in atmosphere can be measured using the QCM. Furthermore it was found that sensitivity to concentration of CO₂ and humidity grows higher with increasing thickness of AS membrane.