表面聲波元件振盪器的物理模型於氣體感測之應用

Physical Model of Surface Acoustic Wave Device Oscillators for Vapor Sensing

陳志傑(Chih-Chieh Chen)

指導教授 ： 鄭湘原

中原大學/工學院/電子工程研究所/碩士(2006年)

https://doi.org/10.6840/CYCU.2008.00401

摘要

表面聲波元件 ( SAW device ) 最早使用於國防及軍事用途， 例如軍事雷達中的頻譜分析濾波器。然而隨著1990年代全球通訊及電信產業的蓬葧發展，表面聲波元件便開始大量使用於無線通訊方面 ，尤其以行動電話的需求量最大。正因為表面聲波濾波器具有體積微小、成本低廉、IC製程相容性高、高濾波特性、頻率範圍廣泛（主要涵蓋在10MHz至3GHz）及高訊號/雜訊比等優點，使得其在射頻訊號發射、接收及訊號處理的領域使用特別的多。最重要的是它可以針對不同的需求，選用不同的壓電材料，設計成適合不同波段的濾波器。所以成為無線通訊系統及行動電話的關鍵零組件。
除了應用於電子及通訊方面外，表面聲波元件亦是極佳的感測器材料。主要是因為它具有高靈敏度。尤其對於表面上極微小的質量變化依然可以精確量測。其應用原理為在表面聲波元件塗上一層具有反應或吸附能力的有機物或無機物薄膜，當此薄膜與待測物反應時，會使元件表面質量改變，進而改變其元件的頻率特性。根據此種特性，我們選擇一種表面聲波元件，它的中心頻率為156.8 MHz、插入損耗為19.75dB。 接著我們設計一個表面聲波振盪器，做為酒精感測之用。因為質量負載效應，表面聲波振盪器會產生頻率飄移。我們會用理論証明此現象。最後我們會建立一個表面聲波等效模型來模擬氣體感測的行為。

關鍵字

物理模型 ； 表面聲波元件振盪器 ； 氣體感測

並列摘要

SAW (Surface Acoustic Wave) devices are and important components in wireless communication and mobile phones because they provide excellent characteristic of high wave velocity, high electrical coupling coefficient, high temperature stability and low transmission loss. Moreover, they also show wide frequency range (major in 10MHz to 3GHz) and high signal/noise ratio. In addition to electronic and communication domains, SAW devices are also excellent for sensing purpose because of their good thermal and chemical sensibility. The sensing mechanism of SAW devices is to add organic-molecule thin films on them. Because the organic film on SAW device can selectively absorb gas molecules, the propagation velocity and resultant resonance frequency of SAW devices can be changed due to the mass loading effect. A little variation of these factors could be measured accurately by mean of electronic circuits. Therefore, SAW devices with ST-Cut Quartz as SAW sensors are chosen in this work for their near-zero temperature coefficient. The SAW devices with center frequency of 156.8 MHz and insertion loss of 19.75dB are designed and fabricated. A SAW oscillator is designed base on Pierce oscillator scheme as two-port SAW resonance cavity. Following this oscillator, for alcohol gas sensing, was performed to verify its mass loading effect. These phenomena were then interpreted into physical parameters theoretically. Finally the two-port SAW model is obtained to fit with the measured gas sensing results.

並列關鍵字

surface acoustic wave device oscillators ； physical model ； vapor sensing

參考文獻

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