Hydrodynamic modulation, an experimental study of the modulation phenomenon for underwater application
Fluid modulation is that process in which pressure fluctuations are produced in a flowing fluid by a local time-dependent variation in the area constraining the flow. This process is involved in the production of human speech. A theoretical and experimental investigation has been made of this phenomenon to ascertain its applicability to the problem of underwater communication. The theoretical portion of the text contains an analog study of sirens and other modulators based on vacuum-tube analyses. Mechanical devices were constructed which produced acoustic signals of from 20 Hz to 2 kHz in water by modulating a liquid flow. The experimental results showed that hydrodynamic modulation can be developed further as a practical means for producing acoustical signals underwater.