A finite-difference simulation of ultrasonic Lamb waves in metal sheets with experimental verification

This paper describes a simple finite-difference method to simulate s(0) and a(1) Lamb wave modes in plane metal sheets. The simulation is used to predict time-domain histories of field displacements vertical to the sheet at groups of points on the sheet. The time-space data so obtained are transformed by two-dimensional FFT to yield frequency-wavenumber representations for comparison with the Lamb mode dispersion waves. An experimental rig is developed for transmission and reception of Lamb waves in sheet metal, with adjustable transducer positions on the Lamb wave axis. The rig enables two-dimensional time-space, and by transformation, frequency-wavenumber, data to be obtained experimentally. An electronic system to provide appropriate band-limited signals for single-mode Lamb wave excitation is outlined and used in conjunction with the physical rig. Experimental results show good agreement with simulation.