| Summary: | 碩士 === 義守大學 === 電機工程學系 === 88 === Propagation characteristics of surface acoustic wave (SAW) generated by interdigital transducers (IDTs) depend on both acoustoelectric properties of piezoelectric substrate and its surface loading. A measurement system, which consists of a vector network analyzer, has been developed for determining characteristics of SAWs. The measured transmission coefficients were employed to calculate phase velocity and attenuation constant of SAWs. However, these two measured data are not sufficient to invert six acoustoelectric properties of the fluid medium. Hence, for further investigation a multivariate analysis method is utilized for identifying the fluid medium.
In this study, a measurement system is proposed for determining electric properties of the fluid medium using measured transmission coefficients. The measurement system consists of a vector network analyzer, personal computer and a dual delay-line SAW device. By directly solving the Christoffel's equations subjected to appropriate boundary conditions, characteristics of SAW were analyzed numerically. Simulation results indicate that the effects of the electrical property of the fluid medium on characteristics of SAWs can be realized using a dual delay-line SAW device with a small amount of error. The phase velocity and attenuation constant of the fluid medium with different conductivity and dielectric constant were measured and then were employed to invert conductivity and dielectric constant of the fluid medium. In this study, the effects of temperature, humidity and other environmental parameters were not taken into account. These may result in errors for the measured conductivity and dielectric constant of the sample liquids. These errors, we believe, can be corrected by modifying the proposed measurement system. The electric properties of the fluid medium then can be characterized accurately in the future based upon the results obtained in this study.
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