George A. Alers
NIST, MS 853, 325 Broadway, Boulder, CO 80303
Lamb waves represent a very natural choice of interrogating energy for problems involving ultrasonic inspection of sheet and plate shaped materials. They have not enjoyed wide use in nondestructive evaluation because their excitation and detection by piezoelectric transducers require special mechanical supports and corrections for the acoustic loading of the sheet by the coupling medium must be made. By using properly designed electromagnetic acoustic transducers (EMATs), the transducer supports can be simplified, corrections for leaky waves can be eliminated, and very specific modes can be used to optimize a particular inspection process. Several examples of using special Lamb wave modes to inspect pipes and tubes in industrial environments will be presented, and their use for materials characterization in ferromagnetic metals will be emphasized.