Lamb wave thickness measurement potential with angle beam and normal beam excitation

It is shown that guided waves can be effectively used for thickness measurement. The measurement gives an estimate of thickness value over some distance, therefore it is valuable for large area thickness measurement or monitoring. In this paper, lamb wave thickness measurement was studied utilizing guided waves generated from normal beam and angle beam transducers. A stainless steel plate with four sections of different thickness was used for the experiments. Experiments were carried out for studying the thickness measurement potential by using peak frequency shifts and group velocity changes. A broadband shock excitation system and a narrowband tone burst excitation system were used for guided wave generation. It was found that normal beam transducers and angle beam transducers with small incident angles were good for the peak frequency shift method while the group velocity method was suitable for angle beam transducers with large incident angles. A difference study of angle beam and normal beam transducer utilization was carried out by using source influence theory.