Abstract: A low-frequency ultrasonic Lamb-like wave method suitable for characterizing the thickness, density, shear and longitudinal wave velocities of the ultra-thin bonding composite is presented. The dispersion property of the low-frequency Lamb-like wave propagating along the ultra-thin bonding composite is derived, which is the basis of the characterization method. In conjunction with the method of the least square, the secant algorithm is used to estimate each layer's parameters of the ultra-thin bonding composite. The reasons for evaluation error of the parameters and the sensitivity of the method for different parameters are analyzed. Using the ultrasound coupler and a pair of broadband longitudinal wave transducers with 1MHz center frequency, we can successfully estimate the parameters of the ultra-thin bonding layer (with h of each layer smaller than 0.05λ) of the steel/brass composite by employing the leaky guided wave frequency-domain analysis method.

Key words: ultrasonic QNDE, ultrasonic Lamb-like wave, dispersion property, bonding composites