Simultaneous laser ultrasonic measurement of sound velocities and thickness of plates using combined mode local acoustic spectroscopy.

Standard ultrasonic thickness measurements require the sound velocity of the sample to be known and vice versa. We present a method, which we have termed combined mode local acoustic spectroscopy (CoMLAS) for simultaneously determining a plate's thickness and sound velocities without requiring such a priori knowledge. It is based on a combination of three guided wave modes sustained by a plate at discrete frequencies, which we generate and detect using laser ultrasound.

Determining longitudinal and transverse elastic wave attenuation from zero-group-velocity Lamb waves in a pair of plates.

A method for the determination of longitudinal and transverse bulk acoustic wave attenuation from measurements of the decay-rate of two independent zero-group-velocity resonances in a couple of matched plates is presented. A linear relation is derived, which links the bulk-wave attenuation coefficients to the decay-rate of plate-resonances. The relation is used to determine the acoustic loss of tungsten at GHz frequencies from noncontact laser-ultrasonic measurements in plates with thicknesses of about 1 µm.