Claims
- 1. Sound detecting apparatus for detecting sound moving in an environment containing a first fluid, comprising:
- a concave acoustic mirror;
- a microphone positioned in front of said mirror, so that sound impinging on said mirror can be concentrated by it onto said microphone;
- an enclosure positioned to enclose at least some of the space lying between said mirror and microphone, including the space immediately in front of the mirror; and
- a quantity of second fluid disposed in said enclosure, said second fluid being of a type which carries sound at a lower speed than does said first fluid, whereby to decrease the wavelength of sound to increase the resolution of said mirror.
- 2. The apparatus described in claim 1 wherein:
- said first fluid in the environment is air; and
- said second fluid is a gas of greater density than air when at the same pressure as air.
- 3. The apparatus described in claim 2 wherein:
- said second fluid is Freon.
- 4. The apparatus described in claim 1 wherein:
- said second fluid has a different density than said first fluid;
- said enclosure comprises a thin sheet of material lying in front of said mirror; and
- said mirror faces vertically and said thin sheet lies over said mirror.
- 5. The apparatus described in claim 1 wherein:
- said enclosure comprises a plurality of walls, including a front wall formed by a pair of thin sheets of material lying substantially in front of said mirror, and a quantity of fluid of a type which carries sound at a higher speed than said second fluid and which is at a higher pressure than the pressure in the environment, disposed between said sheets to press them apart.
- 6. The apparatus described in claim 1 wherein:
- said enclosure comprises a thin sheet of material lying in front of said mirror, said sheet of material formed in a bulge wherein the middle of the sheet is closer to the mirror than it would be if the sheet were flat, whereby to minimize distortions, by reason of passage through the sheet, of sound emanating from a nearby source.
- 7. Acoustic apparatus for controlling the movement of sound between a transducer and an object located in air, comprising:
- an acoustic mirror;
- a sound transducer positioned in front of said mirror;
- an enclosure disposed about at least some of the volume lying between said mirror and said transducer; and
- a gas that transmits sound at a lower speed than does air, disposed in said enclosure.
- 8. The apparatus described in claim 7 wherein:
- said enclosure includes a plurality of walls, one of said walls formed by a pair of thin sheets in front of the mirror, and a gas under a higher pressure than ambient pressure, disposed between said sheets.
- 9. A method for increasing the directionality of a mirror-microphone system wherein the mirror can be aimed to try to determine the precise location of a sound source in the environment, by sensing the output of the microphone which is mounted along the axis of the mirror, comprising:
- enclosing said mirror-microphone system; and
- establishing a sound-transmission medium which carries sound at a lower speed than the fluid in the environment, in said enclosure.
- 10. A method for increasing the directionality of a mirror-microphone system wherein the mirror can be aimed to try to determine the precise location of a sound source in the environment, by sensing the output of the microphone which is mounted along the axis of the mirror, comprising:
- enclosing said mirror-microphone system in an enclosure and positioning said system, wherein said mirror is a portion of an ellipsoid, said microphone is positioned at one focal point of the ellipsoid, and the sound source lies on the other focal point of the ellipsoid; and
- establishing a sound-transmission medium which carries sound at a lower speed than the fluid in the environment, in most of the space between the mirror and microphone;
- said step of enclosing including establishing a thin sound-transmitting wall in front of said mirror at a surface of the enclosure furthest from the mirror, wherein the wall is at a curvature and position so that sound waves originating from said other focal point and moving toward said mirror, pass perpendicular to said thin wall.
ORIGIN OF THE INVENTION
The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42 USC 2457).
US Referenced Citations (6)
Non-Patent Literature Citations (3)
Entry |
R. Schlinker et al., "Enhancement of Directional Microphone," AIAA Paper No. 73-1040, Oct. 15, 1973. |
F. Grosche et al., "On Aero Acoustic Measurements", AIAA, 1976. |
L. Knox, "Underwater Detection", IBM Tech. Discl. Bull., Nov. 1961. |