Variable Frequency Acoustic Filter.
DEPARTMENT OF THE NAVY WASHINGTON DC
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This invention relates to an hydroacoustic filter device for use with underwater acoustic detecting mechanisms of a character adapted for inclusion in naval mine mechanisms. More particularly the instant hydro-acoustic filter is of a character adapted to provide selection of a plurality of different band pass frequencies to render the mechanism effective in response to signals from targets of predetermined selectable acoustic frequency bands indicative of certain types of target vessels. The instant filter system is of a character well adapted for usage with an electrolytic detector and this type of detector may be incorporated in a common housing with the filter mechanism herein to be described. A detector cell is a device which utilizes the phenomenon known as concentration polarization to detect andor indicate flow in a solution containing oxidizable and reducible ions. Examples of suitable redox systems are ferricyanide-ferrocyanide, ceric-cerous, ferric-ferrous, or iodine-iodide. If an iodine-iodide solution is employed the cathodic reduction of iodine is made the controlling reaction by using a low concentration of iodine about 0.1 N and a relatively high iodide concentration about 0.5 N. When the solution is quiescent, the current is controlled by diffusion. If however, fluid flow of the electrolyte increase, the number of iodine ions available at the cathode increases thereby increasing the current in the system. This fluid flow is usually induced by flexure of a diaphragm in contact with the solution which flexure may be initiated by heat, mechanical pressure or acoustical pressure. The increase of current in the system can therefore be equated to the heat or pressure which caused flexure of the diaphragm.
- Acoustic Detection and Detectors