| Summary: | 碩士 === 國立成功大學 === 微機電系統工程研究所 === 92 === Surface Acoustic Wave (SAW) sensors have many applications including Rayleigh wave mode chemical adsorption vapor sensors, Lamb wave mode accelerators and mass-loading Love wave mode liquid viscosity sensors for sensing and detection. Among them, Love wave mode liquid viscosity sensors use a pair of interdigital transducers (IDT) to excite and receive shear-horizontal type of surface wave propagating in a guiding solid layer on top of a half-space piezoelectric substrates. These modes are known best for liquid sensing applications. In general, Love wave sensors are used with a network analyzer to measure the inserting loss and frequency shift, which display velocity change and wave attenuation. However, the technology of frequency shift detection is difficult and insensitive. Besides, the measurement instruments are heavy and expensive, and therefore limit the applications.
In this project, a stand-alone and a convenient electronic system is designed and developed to incorporate the 4.89mm x 4.89mm Love wave liquid viscosity sensors. Three types of guiding layers, Polymethyl methacrylate (PMMA), SiO2 and ZnO, have been tested and compared, and best fabrication parameters have been evaluated. We also propose a detection way for Love wave sensors, which is the phase information about wave propagation, along with the liquid/solid interface for determining the liquid viscosity. A stand-alone measurement unit is made with integrated circuits and printed-circuit boards, including AD8302 (Analog Device) for phase/gain detector, Texas Instrument product THS3201 (Taxas Instrument) for 80MHz and 156MHz oscillators, OPA690 for an all pass filter, OPA355 for subtraction circuits, and L-type matching network. The all pass filter and the subtraction circuits are used to compensate the phase loss and the AD8302 output level offset respectively. L-type matching network are used to transform the available power from oscillators to Love wave sensors. This new circuit unit is to replace the inconvenient and heavy instruments and to construct a complete, compact, and inexpensive sensor system for liquid viscosity measurement. Potential applications in mechanical, chemical, and biomedical fields of this sensor system will be discussed.
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