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Proceedings Paper

Simultaneous and wireless measurement of CO2 and humidity using a SAW reflective delay line
Author(s): Chunbae Lim; Wen Wang; Keekeun Lee; Hae-Kwan Oh; Sangsik Yang
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Paper Abstract

A 440MHz wireless and passive surface acoustic wave (SAW) based chemical sensor was developed for simultaneous measurement of CO2 gas and relative humidity (RH) using a reflective delay line pattern as the sensor element. The reflective delay line was structured by an inter-digital transducer (IDT) and several shorted grating reflectors positioned both sites of the IDTs along the SAW propagation direction. A Teflon AF 2400 film with large solubility, permeability, and selectivity towards to CO2 and a hydrophilic SiO2 layer for water vapor sensing are used as the sensitive film and deposited onto the piezoelectric substrate. A simulation on the SAW device was performed using the coupling of modes (COM). The measured reflection coefficient S11 in time domain of the fabricated SAW device shows sharp reflection peaks with high signal-to-noise (S/N) ratio, small signal attenuation, and few spurious peaks. During the CO2 and humidity testing, high sensitivity (~2o ppm-1 for CO2 detection and 7.45o/%RH for humidity sensing), good linearity and repeatability were observed in the CO2 concentration of 50~400ppm and humidity of 20~80%RH. Temperature and humidity compensations were also investigated during the sensitivity evaluation process.

Paper Details

Date Published: 23 February 2009
PDF: 9 pages
Proc. SPIE 7207, Microfluidics, BioMEMS, and Medical Microsystems VII, 72070W (23 February 2009); doi: 10.1117/12.809994
Show Author Affiliations
Chunbae Lim, Ajou Univ. (Korea, Republic of)
Wen Wang, Ajou Univ. (Korea, Republic of)
Keekeun Lee, Ajou Univ. (Korea, Republic of)
Hae-Kwan Oh, Ajou Univ. (Korea, Republic of)
Sangsik Yang, Ajou Univ. (Korea, Republic of)

Published in SPIE Proceedings Vol. 7207:
Microfluidics, BioMEMS, and Medical Microsystems VII
Wanjun Wang, Editor(s)

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