Study on high accuracy ultrasonic testing method by separating a composite ultrasonic waves

存在于非常靠近表面的缺陷不能用常规的超声检测方法和超声显微镜检测。在这项研究中，已经开发了一种检测非常接近表面的缺陷的方法。来自非常靠近表面的缺陷的反射回波与来自被测样品表面的反射回波叠加。因此，在本研究中，为了测量来自缺陷的反射回波与来自表面的反射回波之间的时间差，将复合回波分离为缺陷回波和表面回波。作为结果，得到以下结论。(1)利用单纯形法可以分离出复合回波。(2)当涂层和基底材料的材料时，通过考虑从两种材料的声阻抗计算的反射率，可以容易地分离复合回波。(3)基底材料的表面粗糙度对反射回波的幅度有影响。然而，可以通过测量散射回波的幅度来测量表面粗糙度。(4)当缺陷倾向于表面时，缺陷可以在与表面成10度的范围内被检测到。(5)可以看出，超声换能器的合适频率为20MHz。(6)聚焦型超声换能器聚焦的超声波直径为0.2mm。

A flaw existed very near the surface can not be detected by using normal ultrasonic testing method and a ultrasonic microscope. In this study, a method to detecting the flaw existed very near the surface has been developed. The reflected echo from the flaw existed very near the surface is superimposed to that from surface of the measured sample. Therefore, in this study, in order to measure the time difference between the reflected echo from the flaw and that from surface, the composite echo is separated to the flaw echo and the surface echo. As the result, the following conclusions are obtained. (1) The composite echo can be separated by using a simplex method. (2) When the materials of the coated layer and the base material, the composite echo can be easily separated by considering the reflected ratio that is calculated from the acoustic impedance of the both materials. (3) The surface roughness of the base material has an influences on the amplitude of the reflected echo. However, the surface roughness can be measured by measuring the amplitude of the scattering echo. (4) When the flaw inclines to the surface, the flaw can be detected within 10 degree to the surface. (5) It can be seen that the suitable frequency of the ultrasonic transducer is 20MHz. (6) The diameter of the focused ultrasonic waves by the focusing type ultrasonic transducer is 0.2mm.