Analysis of Focused Type SAW Devices and Their Frequency Responses

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　　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.