介绍了两种常用的材料薄层超声表征方法——纵波脉冲回波法和兰姆波法。阐述了其基本原理，并结合实例比较了它们的应用情况、优缺点和适用条件等。纵波脉冲回波法简单易行，能够获得薄层厚度、声速和衰减等信息。但实验结果受薄层介质的声衰减和表面粗糙度影响较大，对探头的性能要求较高。兰姆波法主要用于表征薄板类材料，无需较高检测频率，可以测得板中纵波和横波的声速、板厚和板与板之间的结合特性等，检测精度较高。缺点是发射和接收探头之间的距离和倾斜角度需要严格控制，影响因素较多。

This paper introduces two methods of ultrasonic characterization of thin layers: longitudinal pulse-echo and Lamb waves. The principles have been explained, their advantages and applied conditions have been compared. The application of longitudinal pulse-echo is relatively simple, which can provide information of the thin layers such as the depth, ultrasonic velocity, attenuation etc. The disadvantage of this method is that the attenuation in the layered media and the surface roughness affect the experimental results greatly, the ultrasonic probe should have good performance. Lamb waves method is mainly used to characterize thin plate materials, without using very high frequency, it can measure the velocity of transverse wave and longitudinal wave, depth of the plate, and the bonding quality between plates. Lamb waves method is relatively accurate, however, the experimental results may be influenced by many factors, for example, the distance and oblique angle of the transmitting and receiving probe should be carefully controlled.