粗晶材料晶粒散射波的实验鉴别

在利用超声波束对粗晶材料样品或工件进行检测时，接收回波中，除伤波、底波外，还存在晶粒散射波及其它干扰杂波。本文对晶粒散射波主要特征：晶粒散射波随传播时间出现的最大值位置；晶粒散射波最早到达时间；以及传播过程中晶粒散射波的频谱特性进行了实验验证。其中，用脉冲频谱合成方法，计算了双探买发．收复合声场声轴上声压分布，据此对最大值的出现位置给予了物理解释。并用短时傅立叶变换分析了声波传播过程中晶粒散射波的频谱特性。获得了一些有用结果。

Experimental identification of the scattered wave in coarse-grained material

In ultrasonic detecting of coarse -grained material specimen or workpiece with limited size, there will always be grain-scattered waves and many kind of noise in received signal besides the flow echo and the bottom echo. In this paper, primary characteristics of the scattered wave, such as the position of its maximum value, the time of earliest it arrival to receiving transducer and its frequency spectrum characteristic in the propagation process have been verified experimentally. In theoretical analysis, we calculate the sound pressure distribution on the axis for transmitting and receiving complex field, using the pulse frequency spectrum composition method. According to the above calculation we give a physical explanation to the position of the maximum pressure value. We also use short time Fourier transforms to analyze the spectrum of the scattered wave during the propagation process, and obtain some useful results.