Determining Mechanical Properties of Cardboard from Photoacoustic Lamb Wave Transmission Data

Abstract

Laser-generated transient Lamb waves have been proven to be a useful tool for determining thin plate thickness and elastic constants. The measurement relies on the wide range of frequencies generated by the thermoelastic or ablation laser source [1]. The dispersion relation of the lowest Lamb-wave modes can be determined using established signal processing techniques. Usually the Lamb-wave packet propagating on a plate is observed using for example a) a contact “wedge” transducer, b) by observing the leakage of energy in directions where the k-matching condition is fulfilled or c) an interferometer, d) with near-field microphones with spatial periodicity on the sensitive surface to pick a particular wavelength [2,3,4,5]. The last three of these methods are non-contacting and therefore attractive for practical applications.