A High Precision Nanomaterial Based Surface Acoustic Wave Humidity Sensor

近年來，對於發展一個量測濕度的系統有著龐大的需求，不僅可應用在產業需求上，也可監控環境之舒適度。截至當今，在諸多種類的濕度感測元件中，皆是以高分子濕度感測膜做為感測材料。因此，發展一種能在室溫下，穩定且容易合成的感測材料，以做為高精確、即時的濕度感測是迫切需要的。一個良好的濕度感測器，需具備以下之條件：高靈敏度、寬廣的動態範圍、快速響應、良好的重製性、簡易的介面電路、微型化、低成本。現存的感測器中，鮮少能在單一系統上滿足上述之需求。由於表面聲波式感測器所具備的許多良好特質，俾雀屏中選為此篇論文的感測裝置。 本論文中，首先製作了一組頻率為145 MHz 以 為基底的表面聲波共振器，並結合了自製的BJT放大器，構成雷利波震盪器。為了要形成一高靈敏之濕度感測器，鹽酸與樟腦磺酸為掺雜之聚苯胺奈米纖維俾滴附在共振器的感測區域以吸附待測氣體。此外，對於環境中干擾之雜訊諸如溫度及壓力效應，也使用了雙震盪器結構予以消除。最後，將製作之表面聲波式感測器，置於架設好之量測腔體中，並曝露於不同的相對溼度以探討感測器的響應，對於不同之兩種奈米纖維也做了量測與分析。實驗結果顯示，結合奈米感測材料與震盪器之表面聲波感測器，對於不同濕度下，皆能擁有良好的線性度與靈敏度。There is a growing demand for developing a sensing system to measure relative humidity not only for human comfort but also for industry applications. Up to date, various sensitive materials with good sensing characteristics are mainly polymers. Thus, development of the real-time and precise humidity sensor which utilizes easy synthesis and stable sensing materials at room temperature is highly needed. A good sensor should be characterized by high sensitivity, wide dynamic range, fast response, good reproducibility, easy interface electronics, small size, and minimum cost. Existing sensors with single sensing system are hard for matching all these criterions. However, surface acoustic wave (SAW) sensing devices are promising candidates to pursue the above goals. In this thesis, a 145 MHz based SAW resonator was fabricated and integrated with the amplifier to form an oscillator. To function as a humidity sensor, HCL-doped and CSA-doped polyaniline nanofibers were coated on the delay line of the resonator as the sensing film. Moreover, dual channel configuration was constructed for reducing environmental influences such as temperature and pressure, etc. Then, the sensing devices were exposed to various relative humidity to investigate the performances and compared the efficiency between different materials on room temperature. Good linearity and high sensitivity were acquired toward various relative humidity sensing.Acknowledgements I Chinese Abstract II Abstract III Lists of Notations IV Table of Contents VII List of Figures IX List of Tables XII Chapter 1 Introduction 1 1-1 Motivation 1 1-2 Category of Humidity Sensors 2 1-3 Literature Review 4 1-4 Contents of the Chapters 5 Chapter 2 Theories and Principles of SAW Sensor 8 2-1 Coupling-of- Modes Model 8 2-1.1 First Order Wave Equations 8 2-1.2 Propagation Loss 10 2-1.3 Reflectivity Coupling 11 2-1.4 Transduction Coupling 14 2-1.5 [P] Matrix 17 2-1.6 Simulation of Two-Port SAW Filter 21 2-2 Principles of Coating-Analyte Interactions 24 2-2.1 Physical and Chemical Interaction 25 2-2.2 Acoustoelectric Effect 26 2-2.3 Nano effect 28 Chapter 3 Design of SAW Sensor System 35 3-1 Configuration of SAW-based Oscillators 35 3-1.1 Fabrication of the SAW Resonator 36 3-1.2 Amplifier Design 39 3-2 Dual channel Configuration 40 3-3 Growth of nanomaterials 41 3-3.1 Selection of sensing material 42 3-3.2 Casting of HCL-doped and CSA-doped polyaniline nanofiber 43 3-4 Gas Flow System for Various Relative Humidity 44 Chapter 4 Realization of SAW Sensor System and Humidity Measurements 56 4-1 Measurements of SAW sensors 56 4-1.1 Measurements of SAW Oscillator 56 4-1.2 Measurements of Dual Channel Configuration 57 4-2 Polymerization of HCL-doped and CSA-doped polyaniline nanofiber 58 4-3 Data Acquisition and Real-time Visualization 59 4-4 Temperature Effect 60 4-5 Measurement Results of Sensors toward Various Relative Humidity 61 4-5.1 Repeatability 61 4-5.2 Sensitivity 63 4-5.3 Limit of Detection 64 Chapter 5 Conclusions and Future Work 79 5-1 Conclusions 79 5-2 Future perspectives 80 References 8