The effect of dispersion on long-range inspection using ultrasonic guided waves

The dispersion of ultrasonic guided waves causes wave-packets to spread out in space and time as they propagate through a structure. This limits the r esolution that can be obtained in a long-range guided wave inspection syste m. A technique is presented for quickly predicting the rate of spreading of a dispersive wave-packet as it propagates. It is shown that the duration o f a wave-packet increases linearly with propagation distance. It is also sh own that the duration of a wave-packet after a given propagation distance c an be minimised by optimising the input signal. A dimensionless parameter c alled minimum resolvable distance (MRD) is defined that enables a direct co mparison to be made between the resolution attainable at different operatin g points. Some conclusions are made concerning the resolution of various op erating points for the case of Lamb waves in an aluminium plate. (C) 2001 E lsevier Science Ltd. All rights reserved.