A novel technique to measure the group velocity of sound in dispersive media

A technique is proposed for measuring the group velocity of sound by a frequency-modulated (FM) continuous wave (CW) technique. Detailed calculations are presented, showing that V/sub g/=( delta omega /sub m// delta phi )d, where V/sub g/, delta omega /sub m/, delta phi , and d are, respectively, the group velocity, change of modulation frequency, phase change of the received signal detected by a biphase lock-in amplifier, and the distance traveled by the sound. The approach has the advantage of high resolution compared to the conventional time-of-flight measurement technique.<>