Quantitative materials characterization using air-coupled leaky Lamb waves

Air-coupled ultrasonic materials characterization has been accomplished in composite plates through accurate reconstruction of the transmission coefficient using leaky guided waves. The spatial and frequency dependencies of the transmitted leaky waves have been measured for a variety of composite plates including aluminum-aramid and graphite-epoxy. Furthermore, a general method has been introduced to reconstruct the transmission coefficient experimentally from a one-dimensional transducer position scan, obtaining a synthetic focused aperture by summing measured signals for many transmitter-receiver separations and transducer incident angles. These results have been employed to deduce, with high precision, the transmission coalescents of the plate over the frequency and angular bandwidths covered by the measurements. The high degree of accuracy in the measured transmission coefficient has been exploited to construct an efficient inversion algorithm to estimate the viscoelastic material properties and/or sample thickness.