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Selective gas detection using uncoated SAW delay lines

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1. Selective gas detection using uncoated SAW delay lines. 2. Introduction ... The sensing properties are dependent on the test gas ... Results and discussion ... – PowerPoint PPT presentation

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Title: Selective gas detection using uncoated SAW delay lines


1
Selective gas detection using uncoated SAW delay
lines
2
Introduction
  • The attractive properties of acoustic wave
    sensing
  • The principle of acoustic wave sensing
  • The sensing properties are dependent on the test
    gas and material of the film
  • The detection principle of the uncoated SAW gas
    sensor
  • The limitation of the uncoated SAW gas sensor

3
Experimental
  • Substrates (001),lt110gtBi12SiO20 and AT, X-SiO2
  • Untuned insertion loss 20 dB
  • Operation frequency 20 MHz(Bi12SiO20) and 156
    MHz(SiO2)

4
  • Operating temperature 25-100oC
  • Test cell 250 ml
  • Flow rate 500 ml min-1
  • The flow of the gases injected into the cell was
    perpendicular to the SAW substrate
  • Reference gas Ar and N2
  • Reference gas (at least two hours)?test gas (20
    min)?reference gas
  • Noise level ???? 2 ppm

5
Results and discussion
  • Selective operation of the sensor is suggested by
    vanishing ?? or TCD for a given gas of two test
    gases
  • When ?? or TCD are zero, the SAW response is zero

6
The vanishing of ??(T)
  • The large ?? , the higher is the sensor response
    and lower is the minimal detectable level
  • ?? n?rg(T)-?tg(T)

7
  • The vanishing ?? for EtOH is achieved at a given
    temperature without the vanishing of ?? for CH4
    at the same temperature
  • The SAW responses accord with behaviour of ??(T)

8
  • The SAW response for EtOH vanishes at 73oC, while
    the SAW response for CH4 reaches 1800ppm at the
    same temperature
  • It confirms the selective operation towards EtOH

9
Vanishing of TCD(T)
  • The crossing zero is at 77oC
  • The SAW response is increased or decreased by the
    proper selection of the operation temperature

10
  • Vanishing of the SAW Ar response achieved at 73oC
  • The sign change of the response to Ar is related
    to the sign change of the TCD

11
  • For the optimum temperature, The SAW response
    towards He is higher than that for Ar

12
  • The injection of He(??lt0) decreases the
    temperature of substrate
  • The injection of Ar(??gt0) increases the
    temperature of substrate
  • The sensor working around the turnover
    temperature is able to distinguish between Ar and
    He
  • The uncoated SAW sensors have not the problems of
    film stability and aging
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