声表面波单指无内反射叉指换能器
The IDT with high internal reflection suppression
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摘要: 在陈-Haus1理论的基础上,本文首先从实验上研究了YZ-LiNbO3上的短路金反射栅及ST-X石英上的沟槽填铝短路反射栅的反射特性,证明了这两种结构存在异常反射现象。同时,在实验中发现YZ-LiNbO3上的短路金反射栅存在用改变栅条厚度无法消除的残余反射现象。我们将陈-Haus理论开拓到各向异性晶体的实际情况,从理论上解释了这一现象。
进而从耦合模理论出发讨论了叉指换能器的反射理论。在此基础上,本文着重从理论和实验上提出了利用异常反射现象实现单指无内反射换能器结构,具体分析和实现了两种无内反射叉指换能器结构:YZ-LiNbO3上的金单指结构和ST-X石英上的沟槽填铝单指结构。在YZ-LiNbO3上做出相对带宽14%,带内畸变小于±1dB的带通滤波器。与通常铝单指结构滤波器相比,带内畸变减小近10dB。在ST-X石英上做出了相对带宽0.9%,带内响应与理论设计要求完全相同的带通滤波器,而用通常铝单指结构,则滤波器的带内畸变将达到8dB。Abstract: Based on Chen-Haus' theory 1, a detailed experimental research on the reflection characteristic of SAW from a short-circuited Au-strip grating on YZ-LiNbO3 and a short-circuited Al-recessed groove on ST-X quartz is first presented in this paper where an anomalous reflection phenomena existing in the two grating are confirmed. In addition, a residual reflection which couldn't be completely cancelled by means of changing strip-thickness is pointed out for a short-circuited Au-strip grating both experimentally and theoretically through extending Chen-Haus' theory to anisotropic crystals.
Finally, two kinds of IDT composed of single electrodes (Au-single-electrode on YZ LiNbO3 and Al-recessed-groove-single-electrode on ST-X quartz) are proposed for high internal reflection suppression. The experimental results of bandpass filters constructed with the IDTs mentioned above show a great improvement in passband distortion and a potential usefulness of new structure in high frequency range.