Lamb wave Structural Health Monitoring Using a Hybrid PZT-Laser Vibrometer Approach

Abstract

Lamb waves are dispersive and multi-modal, which makes the interpretation of Lamb wave signals very difficult in either the time or frequency domain. In the this article, we present our studies on Lamb wave propagation characterization and crack detection using a hybrid lead zirconate titanate (PZT)-laser vibrometer system and frequency–wave number analysis. A scanning laser Doppler vibrometer is used to acquiring high-resolution time–space Lamb wavefield excited by a PZT actuator. The recorded wavefield is then transformed to frequency–wave number domain by two-dimensional Fourier transform. Wave spectrum in the frequency–wave number domain shows clear distinction among Lamb wave modes being present. These concepts are illustrated through several experimental tests. However, the space information is lost during this transformation. A short-space two-dimensional Fourier transform is then adopted to obtain the frequency–wave number spectra at various spatial locations, resulting in the space–frequency–wave number representation, which can show how the frequency–wave number component varies with respect to space dimension. It provides a means to study the wave propagation from the perspective of wave number domain. The space–frequency–wave number analysis has successfully been used for the study of wave interaction with structural discontinuity and crack detection on an aluminum plate.