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Lamb Wave Diagnostics with the Acoustic Microscope

The excitation of Lamb Waves is easily and simply accomplished in the acoustic microscope. Velocity measurements of Lamb waves in a variety of thin plates will be described and compared with the computed dispersion in an isotropic plate. Velocity measurement is obtained through the Acoustic Material Signature technique (AMS). Symmetric Lamb wave velocities in a Cu sheet and of the antisymmetric Lamb wave in a thin Si membrane are reported. A particular use of nondestructive diagnostics with Lamb Waves is in materials elastic property investigation. The excitation of Lamb waves of both symmetry groups in sheets of metallic glass has been achieved. From the measurement of velocity dispersion in both modes, the sheet thickness and computed dispersion curves, it is shown how elastic material properties may be obtained.