An acoustooptic method for sound velocity measurements in strongly sound-absorbing materials

An acoustooptic method for determining the velocities of longitudinal ultrasonic waves in a 10(5) to 10(8)-Hz range in strongly absorbing (scattering) materials, when methods based on the sound transmission through a sample are unfit, is described. This method employs the acoustooptic determination of the acoustic impedance of the studied sample by measuring the reflection coefficient from the boundary between two contacting substances, namely, a liquid with the known (or measured) acoustic impedance and the studied solid sample. The method features the following advantages: (i) it is acceptable, when standard methods do not work due to the sound attenuation (scattering); (ii) there is no need for exact knowledge of sample sizes, the operating frequency, and the electromechanical coupling factor, and also for using reference samples; and (iii) the sound attenuation in a liquid and the distance from the sample surface to measurement points (required for calculations of the sound velocity) are easily measured. In this case, the velocity measurement error is usually 5-10%.