Wireless surface acoustic wave chemical sensor for simultaneous measurement of CO 2 and humidity

A 440-MHz wireless and passive surface acoustic wave SAW microsensor was developed for simultaneous measurement of CO2 and relative humidity RH. The developed SAW microsensor was composed of SAW reflective delay lines structured by an interdigital transducer IDT and several shorted grating reflectors, CO2, and water vapor-sensitive films. A theoretical model was established to predict the response mechanism of the polymer-coated SAW gas sensor. Infusion of CO2 into the chamber and humidity changes induced large phase shifts in the reflection peaks. Good linearity and repeatability were observed in the CO2 concentration of 0400 ppm and 2080% RH. The obtained sensitivity was 2° ppm 1 for CO2 detection and 7.45°/%RH for humid- ity sensing. Temperature and humidity effects were also investigated dur- ing the sensitivity evaluation process. © 2009 Society of Photo-Optical Instrumen-

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