Adaptive and robust filtering techniques for ultrasonic flaw detection

An overview is presented of a number of adaptive flaw enhancement techniques based on the statistical properties of the order-statistic operation (e.g., median or minimization) or the group delay of the received ultrasonic signal. Nonlinear statistical-filtering techniques using frequency-diverse observations that utilize these adaptive properties to improve flaw detection are examined. These concepts are also applied to develop an adaptive-correlation receiver. Furthermore, it is shown that the geometric mean of the decorrelated observations yields outputs that are relatively insensitive to critical-processing parameters. Experimental results using stainless steel samples are presented to demonstrate the robust and adaptive nature of the filters.