Coded Waveform Excitation for High-Resolution Ultrasonic Guided Wave Response

Ultrasonic guided wave-based nondestructive testing systems are widely used in various fields of industry where the structural integrity of components is of vital importance. Signal interpretation in these systems might become challenging due to multimodal and dispersive response of the interrogated structure. These phenomena degrade the signal-to-noise ratio and also lower the spatial/temporal resolution. This paper compares the use of Maximal Length Sequences and linear chirp excitation signals to develop a novel signal processing technique using dispersion compensation and cross-correlation. The technique is applied to both simulated and experimental multimodal signals from an aluminium rod for performance assessment. It is quantitatively validated that the technique noticeably improves the signal-to-noise ratio of the guided wave response and is able to acquire an accurate time of flight of the individual wave modes, and hence, the propagation distance. The technique is compared for both linear chirp and maximal length sequences excitation signals. Noise analysis for these excitation signals is also presented.