Non-contact air-coupled velocity measurements in planar samples

Non-contact air-coupled technique has been applied to measure ultrasonic velocities in two planar samples, Plexiglas and mortar. Longitudinal waves and mode-converted shear velocities were obtained by three approaches. The obtained velocities were compared with that measured by contact method. The results demonstrate that non-contact air-coupled technique has great potential for the comparatively accurate measurement of velocity in 'difficult' materials, such as mortar.