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.
References
[1]
Bryant, A.; Lee, D.F.; Vetelino, J.F. A surface acoustic wave gas detector. Proceedings of the 36th Annual Symposium on Frequency Control, Philadelphia, PA, USA, 2–4 June 1982; pp. 171–174.
[2]
Wohltjen, H.; Snow, A.W.; Barger, W.R. Trace chemical vapor detection using SAW delay line oscillator. IEEE Trans. Soni. Ultr 1987, 34, 172–178.
[3]
Wang, W.; He, S.; Li, S. Advances in SXFA-coated SAW chemical sensors for organophosphorous compound detection. Sensors 2011, 11, 1526–1541.
[4]
Mcgill, R.A.; Nguyen, V.K.; Chung, R. The ‘NRL-SAWRHINO’: A nose for toxic gases. Sens. Actuat. B 2000, 65, 10–13.
[5]
Sadek, A.Z.; Wlodarski, W.; Shin, K.; Kaner, R.B.; Kalantar-zadeh, K. A Polyaniline/WO3 nanofiber composite based ZnO/64° YX LiNbO3 SAW hydrogen gas sensor. Synth. Metals 2008, 158, 29–32.
[6]
Sadek, A.Z.; Wlodarski, W.; Li, Y.X.; Yu, W.; Li, X.; Yu, X.; Kalantar-zadeh, K. A ZnO nanorod based layered ZnO/64° YX LiNbO3 SAW hydrogen gas sensor. Thin Solid Films 2007, 515, 8705–8708.
[7]
Penza, M.; Aversa, P.; Cassano, G.; Wlodarski, W.; Kalantar-zadeh, K. Layered SAW gas sensor with single-walled carbon nanotube-based nanocomposite coating. Sens. Actuat. B 2007, 127, 168–178.
[8]
Sadek, A.Z.; Baker, C.O.; Powell, D.A.; Kaner, R.B.; Wlodarski, W.; Kalantar-zadeh, K. Polyaniline nanofiber based surface acoustic wave gas sensors—Effect of nanofiber diameter on H2 response. IEEE Sens. J 2007, 7, 213–218.
[9]
Powell, D.A.; Kalantar-zadeh, K.; Wlodarski, W. Numerical calculation of SAW sensitivity: Application to ZnO/LiTaO3 transducers. Sens. Actuat. A 2004, 115, 456–461.
[10]
Staples, E.; Viswanathan, S. Ultra-high speed chromatography and virtual chemical sensors for detecting explosives and chemical warfare agents. IEEE Sens. J 2005, 5, 622–631.
[11]
Watson, G.; Staples, E.; Viswanathan, S. Development of a surface acoustic wave (SAW) analyzer for measurement of volatile organic compounds. Environ. Progress 2003, 22, 215–226.
[12]
Watson, G.W.; Staples, E.J. SAW resonators as vapor sensors. Proceedings of the IEEE Ultrasonics Symposium, Honolulu, HI, USA, 4–7 December 1990; pp. 311–314.
[13]
Staples, E.J. Dioxin/Furan detection and analysis using a SAW based electronic nose. Proceedings of the IEEE Ultrasonics Symposium, Orlando, FL, USA, 18–21 October 1998; pp. 521–524.
[14]
Watson, G.; Staples, E.; Viswanathan, S. Real time odor and VOC emission measurements associated with environmental remediation sites using a GC/SAW. Proceedings of the Annual Air and Waste Management Annual Conference, San Diego, CA, USA, 22–26 June 2003.
[15]
Staples, E.J. Real time characterization of food & beverages using an electronic nose with 500 orthogonal sensors and VaporPrintTM imaging. Proceedings of the Sensors Expo Convention, Lake Tahoe, CA, USA, May 2000.
[16]
Watson, G.W.; Staples, E.J. Real time chemical process measurements using a multi-port GC/SAW system. Proceedings of the American Institute of Chemical Engineers Annual Conference, San Francisco, CA, USA, 17–21 November 2003.
[17]
Schlichting, H. Boundary-Layer Theory; MCGRAW-HILL Book Company: New York, NY, USA, 1979; pp. 25–30.
[18]
Farnell, G.W. Symmetry considerations for elastic layer modes propagating in anisotropic piezoelectric crystals. IEEE Trans. Soni. Ultr 1970, 17, 229–238.
[19]
Tiersten, H.F. Linear Piezoelectric Plate Vibrations; Plenum: New York, NY, USA, 1969.
[20]
Auld, B.A. Acoustic Fields and Waves in Solids, 2nd ed ed.; John Wiley & Sons, Inc: New York, NY, USA, 1973; Volume 1, pp. 265–348.
[21]
Batchelor, G.K. An Introduction to Fluid Dynamics; Cambridge University Press: Cambridge, UK, 1973.
[22]
Milson, R.F.; Reilly, N.H.C.; Redwood, R. Analysis of generation and detection of surface and bulk acoustic waves by interdigital transducers. IEEE Trans. Soni. Ultr 1977, 24, 147–166.
[23]
Shen, C.; Shen, Y.; Wu, I. Viscoelastic properties of polymer films on surface acoustic wave organophosphorous vapor sensors. J. Mater. Sci 2002, 37, 295–301.
[24]
Lewis, M.F. The surface acoustic wave oscillator—A natural and timely development of the quartz crystal oscillator. Proceedings of the 28th Annual Symposium on Frequency Control Symposium, Atlantic, NJ, USA, 29–31 May 1974; pp. 304–314.
[25]
Lewis, M.F. Some aspects of SAW oscillators. Proceedings of the 1973 Ultrasonics Symposium, Monterey, CA, USA, 5–7 November 1973.
[26]
Schickfus, M.V.; Stanzel, R.; Kanmereck, T. Improving the SAW gas sensor: Device, electronics, and sensor layer. Sens. Actuat. B 1994, 18, 443–447.
