Axisymmetric and non-axisymmetric Lamb wave excitation using rectangular actuators

Abstract

Lamb wave based structural health monitoring system has attracted increasing attention for the advantages of reducing maintenance cost and improving confidence level. Most published work concerning Lamb wave excitation is based on the solutions of plane Lamb wave with plane strain assumption. This assumption is not exact because it requires the plate and actuator to be infinite at least in one direction, which is impossible in practice. In fact, all Lamb wave excited by finite-dimensional actuators is circular crested Lamb wave. However, the excitation problem of this type of Lamb wave has not been solved with theoretical method. In this paper, excitation of axisymmetric and non-axisymmetric circular crested Lamb wave with rectangular actuators is solved analytically. Based on the amplitude expressions, circumferential distribution of Lamb wave field can be calculated. This contributes to the selection of rectangular actuators in damage detection to increase sensitivity. The effect of actuator dimension and configuration on the amplitude of each mode is discussed individually. The results suggest that dominant axisymmetric or non-axisymmetric mode can be excited by selecting appropriate actuators with corresponding frequencies. Finally, simulations and experiments are conducted on aluminum plates, the results of which provide good verifications for theoretical predictions.