Kushibiki J I, Ohashi Y, Arakawa M
Department of Electrical Engineering, Tohoku University, Sendai 980-8579, Japan.
IEEE Trans Ultrason Ferroelectr Freq Control. 2000;47(1):274-84. doi: 10.1109/58.818771.
We investigated the velocity measurements of leaky surface acoustic waves (LSAW) by line-focus-beam (LFB) acoustic microscopy of thin specimens for which the waves reflected from the back surface of the specimen (back reflection) must be included in the measurement model. The influence of back reflection resulted in a serious problem in measurement accuracy of the apparent changes of measured velocities. Using several samples of thin synthetic silica glasses, the determination of LSAW velocity affected by the reflected waves and the relationship between the specimen thickness and the apparent velocity change with a periodic frequency interval in the frequency dependence of measured LSAW velocities are discussed in detail. Three useful methods for eliminating that influence are proposed and demonstrated: first, separating the radio frequency (RF) pulsed wave signal from the specimen surface and the pulses reflected from the back surface by reducing the RF pulse width; second, scattering acoustic waves from the roughened back surface; and third, taking the moving average of measured frequency characteristics of LSAW velocities. It is shown that, among these methods, the moving average method is the most useful and effective as a general means to eliminate the influence and to determine intrinsic velocity values because this method needs no specimen process and no system change, and the same conventional V(z) curve measurement and analysis can be employed.
我们通过线聚焦束（LFB）声学显微镜对薄样品进行了泄漏表面声波（LSAW）速度测量研究，对于此类薄样品，测量模型中必须包含从样品背面反射的波（背反射）。背反射的影响给测量速度的表观变化的测量精度带来了严重问题。使用几种薄合成石英玻璃样品，详细讨论了受反射波影响的LSAW速度的测定以及在测量的LSAW速度的频率依赖性中，样品厚度与具有周期性频率间隔的表观速度变化之间的关系。提出并证明了三种消除该影响的有效方法：第一，通过减小射频脉冲宽度，将来自样品表面的射频（RF）脉冲波信号与从背面反射的脉冲分离；第二，使来自粗糙背面的声波散射；第三，对测量的LSAW速度的频率特性进行移动平均。结果表明，在这些方法中，移动平均法作为消除影响并确定固有速度值的通用方法是最有用且有效的，因为该方法无需对样品进行处理，也无需对系统进行更改，并且可以采用相同的传统V(z)曲线测量和分析方法。
