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. 2011;11(12):11871-84.
doi: 10.3390/s111211871. Epub 2011 Dec 20.

Advances in SAW gas sensors based on the condensate-adsorption effect

Jiuling Liu  1 , Wen Wang, Shunzhou Li, Minghua Liu, Shitang He
Affiliations

Advances in SAW gas sensors based on the condensate-adsorption effect

Jiuling Liu et al. Sensors (Basel). 2011.

Abstract

A surface-acoustic-wave (SAW) gas sensor with a low detection limit and fast response for volatile organic compounds (VOCs) based on the condensate-adsorption effect detection is developed. In this sensor a gas chromatography (GC) column acts as the separator element and a dual-resonator oscillator acts as the detector element. Regarding the surface effective permittivity method, the response mechanism analysis, which relates the condensate-adsorption effect, is performed, leading to the sensor performance prediction prior to fabrication. New designs of SAW resonators, which act as feedback of the oscillator, are devised in order to decrease the insertion loss and to achieve single-mode control, resulting in superior frequency stability of the oscillator. Based on the new phase modulation approach, excellent short-term frequency stability (±3 Hz/s) is achieved with the SAW oscillator by using the 500 MHz dual-port resonator as feedback element. In a sensor experiment investigating formaldehyde detection, the implemented SAW gas sensor exhibits an excellent threshold detection limit as low as 0.38 pg.

Keywords: gas chromatography (GC); gas sensor; surface acoustic wave (SAW); threshold detection limit.

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Figures

Figure 1.
Figure 1.
The schematic of the SAW gas sensor based on condensate-adsorption effect.
Figure 2.
Figure 2.
The coordinate system in this study.
Figure 3.
Figure 3.
The surface effective dielectric constant εs(s) on ST-X quartz.
Figure 4.
Figure 4.
(a) Velocity shift from frequency effect and viscosity (b) Velocity shift from normalized thickness of condensate.
Figure 5.
Figure 5.
(a) The structure of the SAW device, and (b) the frequency response of the fabricated device.
Figure 6.
Figure 6.
(a) Schematic and principle of the SAW oscillator, (b) the PCB with the SAW sensor.
Figure 7.
Figure 7.
Frequency stability testing of oscillator modulated at the frequency point of (a) central frequency point, and (b) at the lowest insertion loss point.
Figure 8.
Figure 8.
Sensor responses to different inputs (a) no input, (b) 0.1 ng derived formaldehyde.
See this image and copyright information in PMC

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