Prediction on laser-generated higher-order anti-symmetric Lamb wave mode in copy paper

摘要

An unexpected anti-symmetric nature of the fast-propagating modes has been reported recently in laser ultrasonic detection of copy paper. It is necessary to understand the feature of this mode for development of non-contact laser ultrasonic measurement. The theoretical analyses in this paper show that an higher order anti-symmetric Lamb wave mode can excited by a laser pulse for some elastic constants, although copy paper with thickness 90μm is very thin. In fact, our calculation indicates that this unexpected fast-propagating mode is first-order anti-symmetric mode a_1. The existence of a_1. depends strongly on the elastic constant c_(33) and c_(55).