| Summary: | 碩士 === 中原大學 === 電子工程研究所 === 93 === SAW (Surface Acoustic Wave) device is an important-key component for communication system. Because it has excellent characteristic of high wave-velocity, high electrical coupling coefficient, low transmission loss and high temperature stability. So SAW device’s the performance of high frequency filter in communication is hard to be replaceable. Due to SAW device’s specific material characteristic and wave proceeding mechanism, it had already well-used in sensor application. SAW device owns high performance, small scale size, low cost and high repeatable production benefits; it also could measure physics signals of temperature, humidity, pressure, distance & the kinds of gas by different external circuits & surface treatment.
In this paper, we adopted Quartz as piezoelectric material and we manufacture inter-digital transducer on its surface. SAW device will have specific frequency wave proceeding feature base on finger width & surface wave passing velocity. When the particle attached to the surface of SAW device, it will cause the change of wave proceeding velocity & frequency. We use two-port SAW device with simulated amplifier circuit & equal-circuit model in this paper and matching with Pierce feedback structure, accomplishing SAW oscillator. The SAW oscillator would be spread with organic thin film and this could be used as gas sensor by recognizing different mass loading effect. The SAW device center frequency is 156.9MHz, loss is -19.855db: Our SAW oscillator center frequency is 157.070MHz, output power equal to 16.35dBm, and its phase noise margin less than -96dBc/Hz@100KHz.
As above, we provide complete theory, model setup, circuit design, experiment and application about SAW oscillator. First establishing a theory of SAW device analysis, including material wave proceeding and frequency response counting of finger electrode. Then using relative high frequency simulation software to try the design and production for sensor circuit. Final we combine SAW device with sensing circuit as a fully integrated system and becoming a SAW sensor and using as gas detection.
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