Acoustic Transmission through a Fluid Lamina Available to Purchase

The acoustic wave equation is derived for a moving fluid medium in which all changes follow an adiabatic law, and it is shown that it may be written in a form which is very similar to the usual wave equation. Following this, the transmission and reflection coefficients for a fluid lamina in uniform motion are derived, and it is shown that it is only the component of motion in the direction of incidence which affects these coefficients. Finally, measurements are reported on the transmission coefficients of a non‐turbulent thermal lamina whose motion has no component in the plane of incidence. The acoustic frequencies range from 2 kc to 14 kc and the angle of incidence from 0° to 89°. These measurements are compared with those calculated for a theoretically approximated lamina. The results are in reasonable agreement. It is shown that there is considerable transmission for angles greater than the critical angles and that for very thin lamina the transmission coefficient is a uniformly decreasing function of frequency.