Caterpillar Inc., Advanced Materials Technology, Technology & Solutions Division, Mossville, IL, USA.
IEEE Trans Ultrason Ferroelectr Freq Control. 2010;57(2):363-78. doi: 10.1109/TUFFC.2010.1416.
In ultrasonic pulse/echo inspections of metals, backscattered grain noise signals observed at different nearby transducer positions will be correlated. Such correlations have important practical implications. For example, the spatial correlation length (SCL) of the backscattered noise is a crucial quantity in designing denoising algorithms for image processing, and in inspection simulations of the probability of detection (POD) of a defect. In this paper an existing theory for the average backscattered grain noise level, based on the single scattering assumption and the Born approximation, is extended to obtain a formal theory for the spatial correlation of the backscattered grain noise. A special form of the theory for an incident Gaussian sound beam is also presented to demonstrate that the specimen microstructure and an overlap integral for the incident sound field are the important physical parameters controlling the grain noise level and spatial correlation, respectively. To validate the theory, a series of experiments are performed to collect backscattered grain noise signals from nickel alloy specimens having equiaxed microstructures. Good agreement between measured and predicted correlations is generally found. Further model computations are performed to better illustrate how amplitude and phase variations within the incident sound field control the dependence of the grain noise spatial correlation upon transducer separation.
在金属的超声波脉冲/回波检测中，不同附近换能器位置观察到的背散射晶粒噪声信号将相关联。这种相关性具有重要的实际意义。例如，背散射噪声的空间相关长度（SCL）是图像处理去噪算法设计和缺陷检测概率（POD）检测模拟中的关键数量。本文基于单散射假设和玻恩近似，对基于单散射假设和玻恩近似的平均背散射晶粒噪声水平的现有理论进行了扩展，以获得背散射晶粒噪声的空间相关性的正式理论。还提出了一种用于入射高斯声波的理论的特殊形式，以证明试件微观结构和入射声场的重叠积分分别是控制晶粒噪声水平和空间相关性的重要物理参数。为了验证理论，进行了一系列实验以从具有等轴微观结构的镍合金试件收集背散射晶粒噪声信号。通常可以发现测量值和预测值之间具有良好的相关性。进一步的模型计算更好地说明了入射声场中的幅度和相位变化如何控制晶粒噪声空间相关性随换能器分离的变化。
