Macroscopic theory of surface acoustic wave gas microsensors

Lec, R.M.; Vetelino, J.F.; Falconer, R.S.; Xu, and Honghua

doi:10.1109/ultsym.1988.49444

Cited by 31 publications

(9 citation statements)

References 5 publications

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“…The interaction between the surface wave and the resistive overlayer causes both attenuation and a change in velocity [44]. The effect of a resistive layer on the velocity has been calculated [45,46]; neglecting the mechanical effect of the sensing layer it can be shown that:

\frac{Δ ν}{ν_{0}} = \frac{K^{2}}{2} \frac{{σ_{s}}^{2}}{{σ_{s}}^{2} + {(ν_{0} ɛ_{eff})}^{2}}

where Δ ν is the change in velocity, v 0 the velocity without a surface layer, K 2 (≈0.0038 for the (0°, 138°, 27°) direction [47]) the electromechanical coupling coefficient, σ s the sheet conductivity of the sensing layer, and ε eff the effective dielectric permittivity.…”

Section: Saw Gas Sensing—sensing Layer Considerationsmentioning

confidence: 99%

Surface Acoustic Wave Devices for Harsh Environment Wireless Sensing

Greve

Chin

Zheng

et al. 2013

Sensors

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Langasite surface acoustic wave devices can be used to implement harsh-environment wireless sensing of gas concentration and temperature. This paper reviews prior work on the development of langasite surface acoustic wave devices, followed by a report of recent progress toward the implementation of oxygen gas sensors. Resistive metal oxide films can be used as the oxygen sensing film, although development of an adherent barrier layer will be necessary with the sensing layers studied here to prevent interaction with the langasite substrate. Experimental results are presented for the performance of a langasite surface acoustic wave oxygen sensor with tin oxide sensing layer, and these experimental results are correlated with direct measurements of the sensing layer resistivity.

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\frac{Δ ν}{ν_{0}} = \frac{K^{2}}{2} \frac{{σ_{s}}^{2}}{{σ_{s}}^{2} + {(ν_{0} ɛ_{eff})}^{2}}

Section: Saw Gas Sensing—sensing Layer Considerationsmentioning

confidence: 99%

Surface Acoustic Wave Devices for Harsh Environment Wireless Sensing

Greve

Chin

Zheng

et al. 2013

Sensors

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“…We consider here a SAW device with a gas sensing layer [10,11,12]. SAW gas sensing can be accomplished using either gas-induced conductivity [11] or mass changes to the sensing layer covering the acoustic path [12].…”

Section: Saw Sensor Modelingmentioning

confidence: 99%

“…SAW gas sensing can be accomplished using either gas-induced conductivity [11] or mass changes to the sensing layer covering the acoustic path [12]. Changes in the electrical conductivity or the mass density change the velocity of the surface acoustic wave, which can be detected in transient or steadystate measurements.…”

Section: Saw Sensor Modelingmentioning

confidence: 99%

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Langasite surface acoustic wave gas sensors: modeling and verification

Zheng

Greve

Oppenheim

2013

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

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We report finite element simulations of the effect of conductive sensing layers on the surface wave velocity of langasite substrates. The simulations include both the mechanical and electrical influences of the conducting sensing layer. We show that three-dimensional simulations are necessary because of the out-of-plane displacements of the commonly used (0, 138.5, 26.7) Euler angle. Measurements of the transducer input admittance in reflective delay-line devices yield a value for the electromechanical coupling coefficient that is in good agreement with the threedimensional simulations on bare langasite substrate. The input admittance measurements also show evidence of excitation of an additional wave mode and excess loss due to the finger resistance. The results of these simulations and measurements will be useful in the design of surface acoustic wave gas sensors.

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“…2(b). Physically absorbed organics on the crystal surface change the frequency of the resonator by slowing down the surface waves [14], [15]. The change in frequency is proportional to the adsorbed mass on the crystal surface.…”

Section: B Surface Acoustic Wave (Saw) Gc Detectormentioning

confidence: 99%

Ultrahigh-speed chromatography and virtual chemical sensors for detecting explosives and chemical warfare agents

Staples

Viswanathan

2005

IEEE Sensors J.

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Chromatographic separation of organic compounds is a well-known method of producing time-resolved chemical spectra or chromatograms. Whereas conventional chromatography using 10-100-m columns is slow, often requiring minutes to hours, ultrahigh-speed chromatography with short resistively heated metal columns requires only seconds. The performance of an ultrahigh-speed gas chromatograph using a surface acoustic wave (SAW) resonator to measure the mass of eluted chemical compounds is described. Closed-loop temperature programming of a resistively heated 1-m capillary column at rates as high as 20 C/s produces near real-time, 10-s chromatograms with chemical spectra peak widths measured in milliseconds. Eluted chemicals are physically adsorbed on an uncoated SAW resonator and frequency deviation versus time produces an eluted mass versus time chromatogram. The derivative of frequency versus time produces a mass/unit time chromatogram of column flux, which is used to measure the retention times of eluted compounds. This paper describes the instrument and process where independent database of chemical spectra are produced by indexing the retention time of specific target chemicals (e.g., explosives and chemical warfare agents) to the retention times of n-alkane standards. It is also shown that assigning time windows centered about specific indices can be used to create arrays of nonoverlapping virtual sensors for specific compounds. Repeated high-speed chromatographic measurements enable virtual sensor readings to be updated in near real time. This work clearly proves that arrays of virtual chemical sensors specific to explosive and chemical warfare agents can detect part per trillion levels of these compounds with high probability of detection and low probability of false alarm.Index Terms-Chemical spectra, explosives and chemical weapon detection, surface acoustic wave (SAW) sensor, zNose.

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Macroscopic theory of surface acoustic wave gas microsensors

Cited by 31 publications

References 5 publications

Surface Acoustic Wave Devices for Harsh Environment Wireless Sensing

Surface Acoustic Wave Devices for Harsh Environment Wireless Sensing

Langasite surface acoustic wave gas sensors: modeling and verification

Ultrahigh-speed chromatography and virtual chemical sensors for detecting explosives and chemical warfare agents

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