From Current Literature

Optical method for studying ultrasound in liquids. To determine the absorption coefficient of ultrasonic waves in liquids, Biquard used the phenomenon of diffraction of a light ray passing through a layer of liquid penetrated by ultrasound (“Uspekhi fizicheskikh nauk,” XIII, 460, 1933). A ray of light, after undergoing diffraction, falls on a photoelement, which gives a photocurrent of a certain intensity. By varying the intensity of the ultrasonic oscillations and each time measuring the magnitude of the photocurrent, the author establishes the dependence between the magnitude of the photocurrent and the intensity of the ultrasonic beam. At low ultrasound intensities this dependence is linear. By varying the distance from the piezoquartz to the plane through which the light ray passes, it is possible to establish the law of absorption of ultrasonic oscillations in a liquid, expressed by the equation:

\[ I_x = I_0 e^{-2\alpha x}, \]

where \(x\) is the distance from the surface of the quartz, \(I_x\) and \(I_0\) are the intensities of the ultrasonic beam in the plane under study and at the surface of the quartz, and \(\alpha\) is the absorption coefficient, equal to 0.05 for petroleum ether (at a frequency \(f = 7.6\) megahertz) (P. Biquard, C. R., 196, 257, 1933).

Study of the propagation of ultrasonic waves in air. To study the propagation of ultrasonic waves in air, Yagi and Matmo used the following method: upon an ultrasonic tone with a frequency of several tens of thousands of hertz, produced by a magnetostriction generator, another ultrasonic tone of nearby frequency is superimposed.

To receive the resulting difference tone, having a frequency on the order of several hundred hertz, the authors used a peculiar detector consisting of a glass tube, one end of which was drawn out and blown upon from the side by a jet of air, while near the broad end of the tube there was a microphone connected to an amplifying installation and a loudspeaker, whose sound made it possible to judge the presence and intensity of the ultrasonic tones responsible for the appearance of the difference tone of audible frequency. The sensitivity of this method proved so high that it was possible to trace the propagation of ultrasonic oscillations at a distance of 200 m from the generator (H. Yagi and S. Matmo, Rep. Radio Res. and Works, Japan, 2, 287, 1932).

N. Malov