吳政忠臺灣大學：應用力學研究所湯和泰Tang, He-TaiHe-TaiTang2007-11-292018-06-292007-11-292018-06-292004http://ntur.lib.ntu.edu.tw//handle/246246/62528無　　Focused interdigital transducers (FIDTs) can generate SAW sources with high intensity and high beam width compression ratios. Owing to these features, they are very suitable for being the sources of micro channels or waveguides in the near future. But most of savants, who had researched on focused transducers, didn’t discuss how to design a FIDT in detail. They just used “curved” transducers and applied different numerical methods to simulate the amplitude fields of FIDTs. Actually, the shapes of FIDTs will dominate their performances. With different designs, the focusing properties of FIDTs will be quite different. Due to the reason, the amplitude fields of FIDTs predicted by some savants were discordant. In this thesis, we use the exact angular spectrum of plane wave theory (ASoW) to analyze the amplitude fields of FIDTs and then provide a design concept according to what kinds of SAW sources we need. In addition, even though FIDTs had been used for a long time, no one had concerned about their frequency responses. In this thesis, we introduce Visintini’s 2-D SAW filter model, which is based on ASoW, and then use it to simulate the frequency responses of focused type SAW devices with different designs. Good agreements between experimental and simulated results are obtained. Later, we summarize the features of the frequency responses of focused type SAW devices and provide a design concept for future applications. Finally, we note that the conclusions of this thesis may served as an important reference for designing a focused type SAW device, including the analysis of its amplitude field and frequency response.Table of Contents Acknowledgements I Abstract II List of Notations III Table of Contents VII List of Figures IX List of Tables XII Chapter 1 Introduction1 1 1-1 Research Motivation………………………………………………………….1 1-2 Literature Review 2 1-3 Contents of the Chapters 3 Chapter 2 Angular Spectrum of Plane Wave Theory 6 2-1 Angular Spectrum of Plane Wave Theory 6 2-2 Amplitude Field of a Straight Interdigital Transducer 8 2-3 Construct a 2-D SAW Filter Model 9 2-3.1 2-D Charge Distribution 9 2-3.2 Surface Potential 11 2-3.3 Admittance Matrix and Scattering Parameters 18 2-3.4 Verify the 2-D SAW Filter Model with Experiment 24 Chapter 3 Design and analysis of a Focused Interdigital Transducer 38 3-1 A Focused Interdigital Transducer Based on Concentric Circles 38 3-2 A Focused Interdigital Transducer Based on Concentric Wave Surfaces 42 3-3 Focusing Properties in Different Substrates 45 3-4 Design and Analysis of a Focused Interdigital Transducer 46 Chapter 4 Frequency Response of a Focused Type SAW Device 63 4-1 Simulation Model 63 4-2 Simulation Results 67 4-3 Fabrication of a Focused Type SAW Device 68 4-4 Comparison of Experimental and Simulation Results 71 Chapter 5 Conclusions 86 5-1 Conclusions of this Thesis 86 5-2 Future Work 87 References 89en-US聚焦式表面聲波元件微機電表面聲波聚焦表面聲波元件頻率響應聚焦式交指叉電極角頻譜法MEMSFIDTAngular spectrum of plane waveASoWfocusing SAWSAW deviceFrequency responseFocused Interdigital transducerthesis