The peculiarities of measuring the ultrasound attenuation using an acoustic interferometer in continuous and pulsed modes.

The paper is devoted to the features of measuring the attenuation of acoustic waves in a liquid using an acoustic interferometer consisting of radiating and receiving transducers of longitudinal acoustic wave located opposite each other. It is known, that the dependence of the wave transmission coefficient on the distance between the transducers is in this case a quasi-periodic function with a decreasing amplitude. The period of this dependence is equal to half the wavelength, which allows determining the wave velocity. The decrease in amplitude with increasing pointed distance is associated not only with the true attenuation of the acoustic wave in the liquid, but also with false attenuation. The false attenuation is due to the diffraction effects, the loss of part of the wave power through the transducers, and the non-parallelism of the transducer sides. The method of determining the true attenuation taking into account the listed factors for operation of interferometer in continuous and pulse modes is developed using glycerol and a mixture of "90 % glycerol + 10 % water" as an example. The importance of the problem under consideration is determined by the fact that the attenuation of a longitudinal acoustic wave is uniquely related to the longitudinal viscosity, which for the most Newtonian liquids is unknown, unlike the shear viscosity measured by standard viscometers.