Direct measurement of the sound velocity in water based on the acousto-optic signal

Abstract

Based on the acousto-optic effect, we propose a new method to directly measure water sound velocity that avoids the error-like phase ambiguity brought by the piezoelectric effect that is broadly adopted in current methods. In the experimental setup we designed, the laser signal modulated by the propagating acoustic wave changes its phase suddenly when the wave crosses the two or more intercepting laser lines simultaneously. This new design creatively realizes the possibility to capture time information at the phase level in sound velocity measurement, which is hardly realized in the piezoelectric-effect-based methods. Utilizing the above principle and the derived mathematical calculation, the accuracy of sound velocity with good traceability can be obtained. The experimental results show that the repeatability of the measurement results is less than 0.0159 m/s, and the accuracy compared with the commercial sound velocity profiler is better than 0.02 m/s.