Absolute measurements of elastic-wave phase and group velocities in lossy materials

A measurement method for determining phase and group velocities in many thick-section materials that exhibit greater than 30 dB, frequency-dependent propagation losses across the passband of a transducer is presented. The method is mechanized as a pulsed swept-frequency interferometer. The accuracy and reliability of the method are enhanced by a combination of circuit-design improvements, which increase the signal-to-noise ratio and linearity, and signal-processing methods, which effectively remove circuit-related measurement errors and compensate for diffraction. The foundations and details of the measurement method are described. The method is illustrated by determining the phase velocities in a very lossy, 50-mm-thick, glass/epoxy specimen in the 0.3-1.2-MHz region. The results are compared with data obtained using traditional methods