Saniie J, Nagle D T
Dept. of Electr. and Comput. Eng., Illinois Inst. of Technol., Chicago, IL.
IEEE Trans Ultrason Ferroelectr Freq Control. 1992;39(5):618-30. doi: 10.1109/58.156180.
In the pulse-echo method using broadband transducers, flaw detection can be improved by using optimal bandpass filtering to resolve flaw echoes surrounded by grain scatterers. Optimal bandpass filtering is achieved by examining spectral information of the flaw and grain echoes where frequency differences have been experimentally shown to be predictable in the Rayleigh scattering region. Using optimal frequency band information, flaw echoes can then be discriminated by applying adaptive thresholding techniques based on surrounding range cells. The authors present order-statistic (OS) processors, ranked and trimmed mean (TM), to robustly estimate the threshold while censoring outliers. The design of these OS processors is accomplished analytically based on constant false-alarm rate (CFAR) detection. It is shown that OS-CFAR and TM-CFAR processors can detect flaw echoes robustly with the CFAR of 10 (-4) where the range cell used for the threshold estimate contains outliers.
在使用宽带换能器的脉冲回波法中，通过使用最优带通滤波来分辨被晶粒散射体包围的缺陷回波，可以提高探伤效果。通过检查缺陷和晶粒回波的频谱信息来实现最优带通滤波，在瑞利散射区域，频率差异已通过实验证明是可预测的。利用最优频带信息，然后可以基于周围距离单元应用自适应阈值技术来区分缺陷回波。作者提出了顺序统计（OS）处理器、排序均值和截尾均值（TM），以便在剔除异常值的同时稳健地估计阈值。这些OS处理器的设计基于恒虚警率（CFAR）检测通过解析完成。结果表明，在用于阈值估计的距离单元包含异常值的情况下，OS-CFAR和TM-CFAR处理器能够以10（-4）的CFAR稳健地检测缺陷回波。
