Performance Enhancement of On-line Lamb Wave Inspection System Using SSP Technique

Abstract

In order to improve the defect detectability of Lamb wave inspection system conventionally used for on-line detection of internal defects of steel strip, application of non-linear signal processing, SSP (split spectrum processing), to Lamb waves and the optimization of the SSP parameters were investigated. Sample strips with natural defects were used to evaluate the performance of SSP in this research. As a result, the improvement of the sensitivity of Lamb wave inspection was confirmed by optimum selection of SSP parameters (filter number 10, filter tap number 500, frequency range 2.1-2.4 MHz, algorithm : combination of minimization algorithm and polarity thresholding algorithm, S/N : about from 2 to 5 times improvement). Furthermore, real-time processing of SSP was realized. Consequently, the newly developed Lamb wave can perform SSP at a 500 Hz repetition rate that is sufficiently high repetition rate for the on-line Lamb wave inspection system.