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8332004 
Journal Article 
PLATE-MODE ULTRASONIC OSCILLATOR SENSORS 
White, RM; Wicher, PJ; Wenzel, SW; Zellers, ET 
1987 
1 
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control
ISSN: 0885-3010
EISSN: 1525-8955 
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC 
PISCATAWAY 
UFFC-34 
2 
163-172 
English 
18290105 
WOS:A1987G693400008 
The characteristics of sensors that employ propagation of the lowest order symmetric and antisymmetric (S0 and A0) Lamb waves on composite Si-ZnO membranes were examined. A comparison of calculated results for a PVC-coated ZnO-on-Si surface acoustic wave (SAW) oscillator (7. 5- mu m ZnO, 1- mu m PVC) and PVC-coated Lamb wave devices (2- or 3- mu m Si, 01- or 0. 3- mu m ZnO, 1- mu m PVC), for operation at the same wavelength, shows the phase velocity for the latter to be five to ten times more sensitive than that of the SAW device to small changes of PVC thickness and density, as might be produced by sorption of a vapor. The fractional frequency shift of a thin A0-mode feedback oscillator should be twice its fractional velocity change, owing to dispersion. Practical A0-mode devices may have phase velocities low enough to permit their use while in contact with a liquid and could operate for a given wavelength at frequencies more than an order of magnitude lower than the corresponding SAW device. Test results are given for a 30-MHz ST-quartz SAW oscillator vapor sensor, coated with approximately 3 mu m of poly(dimethylsiloxane), when exposed to airborne vapors of pentane, hexane, iso-octane, toluene, and three fuels (premium unleaded gasoline, Jet A, and diesel).