Measurement Model-Based Prediction of Correlated Flaw Signal

Abstract

The Center for NDE, Iowa State University, has developed an ultrasonic pulse compression system using Golay codes, and demonstrated the enhanced signal-to-noise ratios (SNR) in highly energy absorbent materials such as rubber, plastics, corks, and some composites. Recently, an attempt has been made to theoretically predict ultrasonic pulse compression (correlated) flaw signals (e.g., voids) using the ultrasonic measurement model developed earlier at the same university. Predictions were made by the use of long coded waveforms (Golay codes) as inputs to the measurement model instead of the spike pulse in conventional ultrasonics. The results were then compared with experimentally measured conventional ultrasonic flaw signals. The results indicated that the ultrasonic pulse compression flaw signals can be predicted as accurate as conventional ultrasonic signals. In addition, the equivalent pulse of the Golay codes (delta-like pulse) was also used as an input to the measurement model to predict the same flaw signal, and it was demonstrated that the Golay codes and the equivalent pulse produce effectively the same results although the signal processing methods are significantly different.