表面聲波在彈性體上傳遞時大部分的能量皆集中在表面附近，因此其波傳特性不僅和聲波所在介質有關，也受彈性體表面邊界條件影響。表面聲波液體感測器即是利用此原理，藉由分析液體負載對波速、波傳衰減常數等波傳特性造成的變化來求得未知液體的各項特性參數。
本論文針對石英(Quartz)、鈮酸鋰(LiNbO3)及鉭酸鋰(LiTaO3)等常用單晶壓電材料的表面聲波波傳特性進行探討，將理論推導以數值分析方法配合電腦程式的撰寫求得各材料在不同切面、不同傳播方向時聲波之波速、機電耦合常數、機械位移量及電位分布；進一步並探討液體負載的相對介電常數、導電度、密度及黏滯度等各項參數對表面聲波波傳特性的影響。
本論文同時採用具有Rayleigh SAW型態的128∘YX LiNbO3、ST-X Quartz及具有SH Leaky SAW型態的36∘YX LiTaO3和SSBW型態的ST-Y Quartz為基板製作SAW感測器元件，利用這些元件進行液體導電度及黏滯度之感測以比較不同波傳型態作為液體感測器之優缺點。實驗發現Rayleigh SAW在壓電基板與液體介面之能量衰減太大並不適合用作液體感測；具有SH Leaky SAW型態的36∘YX LiTaO3對導電度及黏滯度均有不錯的辨識度；SSBW型態的ST-Y Quartz對液體導電度並無鑑別能力，但若在此元件上再成長一層氧化鋅(ZnO)薄膜使波傳型態變為Love wave時，則對於液體導電度亦有相當好的辨識度，且能量衰減趨近於零。

The surface acoustic wave (SAW) is a wave that propagates with its energy concentrated on the surface of an elastic substrate. Therefore, the propagation characteristics of the wave depend not only on the transmission media but the boundary condition of elastic surface. By detecting the variations of phase velocity and propagation attenuation constant, a SAW sensor can be realized. And further, we can obtain the acousto-electric parameters of the unknown liquid by analyzing the relationship between these parameters and SAW propagation characteristics.
In this dissertation, the propagation characteristics of Rayleigh SAW for common single crystal piezoelectric materials of different cutting axis and various propagation directions such as Quartz, LiNbO3 and LiTaO3 are completely discussed. First of all, wave propagation theory and numerical analysis techniques are applied to obtain the phase velocity, mechanical displacements, potential, electromechanical coupling factor and attenuation constant. Then, the change of wave propagation characteristics due to relative dielectric constant, conductivity, density and viscosity of the liquid loaded on the SAW sensor is also discussed.
In this study, we choose several different materials for SAW sensor application, they are (1) 128º YX LiNbO3、ST-X Quartz, which support Rayleigh SAW, (2) 36º YX LiTaO3, which support SH Leaky SAW, and (3)ST-Y Quartz, which support SSBW. Experimental results show that Rayleigh SAW is not suitable for liquid sensor application for its large attenuation between liquid/substrate interfaces. SH Leaky SAW is good for conductivity and viscosity identification. SSBW can not tell any difference of the conductivity in different liquid. Finally, Love mode sensor with ZnO film on the ST-Y Quartz substrate was introduced and show good ability for liquid conductivity sensing, and the attenuation due to liquid loading is very tiny.

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