Atalar A
Dept. of Electr. and Electron. Eng., Bilkent Univ., Ankara.
IEEE Trans Ultrason Ferroelectr Freq Control. 1989;36(2):264-73. doi: 10.1109/58.19160.
The response of the conventional scanning acoustic microscope (SAM) to anisotropic materials is theoretically investigated. For this purpose, the reflection coefficient of plane acoustic waves incident on a liquid-solid interface is numerically calculated for a general anisotropic solid oriented in any arbitrary direction. In general, the reflection coefficient depends on polar and azimuthal angles of incidence. For the case of a circularly symmetric acoustic microscope lens, a mean reflectance function can be defined that depends only on the polar angle. With this mean reflectance function, it is very easy to predict the anisotropic material response of the acoustic microscope. It is found that, under certain conditions, the amplitude response of the acoustic microscope can depend heavily on the orientation of the solid material under investigation. The amplitude of the acoustic microscope signal is influenced by the orientation of the material because there is a cancellation of acoustic rays reflected from the object surface at different azimuthal angles. This cancellation is revealed as a minimum in the mean reflectance function. It is shown by numerical simulation that the sensitivity to orientation can be increased by the use of a ring-shaped insonification at the back of the acoustic lens.
对传统扫描声学显微镜（SAM）对各向异性材料的响应进行了理论研究。为此，针对任意取向的一般各向异性固体，数值计算了平面声波入射到液-固界面的反射系数。一般来说，反射系数取决于入射角的极角和方位角。对于圆形对称声学显微镜透镜的情况，可以定义一个仅取决于极角的平均反射率函数。利用这个平均反射率函数，很容易预测声学显微镜的各向异性材料响应。结果发现，在某些条件下，声学显微镜的幅度响应可能严重依赖于被研究固体材料的取向。声学显微镜信号的幅度受材料取向的影响，因为从物体表面以不同方位角反射的声线会相互抵消。这种抵消表现为平均反射率函数中的一个最小值。数值模拟表明，通过在声学透镜背面使用环形声照射，可以提高对取向的灵敏度。
