Resonance Properties of Surface Acoustic Wave Resonator in Supercritical CO2

概要

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A supercritical fluid is a fluid at a temperature and pressure above its critical point. Supercritical CO2 functions as a moderate solvent, has zero surface tension, and has high permeability in fine structures. These properties are regarded as ideal for the processing of nano- and microscale substances. A problem of applying supercritical fluids is fluctuations in their density. By utilizing a surface acoustic wave (SAW), it may be possible to realize a sensor for measuring the density fluctuation. In this study, the resonance property of a shear-horizontal-type SAW resonator fabricated on a 36° Y--X LiTaO3 substrate and the impedance of an interdigitated electrode (IDE) fabricated on a nonpiezoelectric substrate were measured in high-pressure CO2. Abrupt changes in the resonance property owing to discontinuous changes in the density and viscosity were observed at a certain CO2 pressure between gas and liquid phases. The impedance change of the IDE owing to discontinuous changes in the permittivity was also observed.
2012-07-25