Influence of the object edge on the efficiency of Lamb wave excitation

Abstract

One of the main problems in a long-range ultrasonics is effective generation of a desired wave mode. The efficiency of excitation can be affected by object boundaries existing at close distance from the transmitter, especially taking into account the relatively big wavelength of the guided waves. The objective of this paper was to determine the regularities of the influence of the edge on the efficiency of Lamb wave generation. The investigations were carried out on the steel plate having thickness 40 mm using the modelling by the finite difference method. Obtained dependencies of the amplitudes of the excited waves on the distance of the transmitter with respect to the plate edge demonstrated that most optimal distances are λ/8 and λ/2, where λ is the wavelength of the excited Lamb wave mode. It was demonstrated, that positioning of the transducer at the distance less then λ/8 is not recommended due to essential reduction of the amplitude of the generated waves.