Flaw-to-grain echo enhancement by cross-correlation weighting and split-spectrum processing

Ultrasonic nondestructive testing of coarse grained materials is limited by the signal-to-noise ratio (SNR) because of backscattering noise.This type of noise is coherent and its effects cannot be reduced by time averaging techniques.Split spectrum signal processing (SSP) has proven to be effective in improving the SNR of backscattered signals.Many authors have developed frequency splitting theory as the postprocessor.This paper introduces a cross-correlation weighted method as the preprocessor for ultrasonic echo signal enhancement.A short ultrasonic echo from a typical defect in large grained materials is defined as standard ultrasonic wavelet.Then the cross-correlation function between the wavelet and an ultrasonic testing signal is used as weight function for the testing signal.This technique and split-spectrum processing can be combined to achieve better Performance.Experimental results are presented to demonstrate the effectiveness of ultrasonic testing in coarse grained materials such as austenitic stainless steel.