Communications – electrical: acoustic wave systems and devices – Signal transducers – Underwater type
Reexamination Certificate
1999-06-10
2001-02-06
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Signal transducers
Underwater type
C367S001000
Reexamination Certificate
active
06185156
ABSTRACT:
The present invention relates to acoustic sources for generating acoustic signals or transmissions in an underwater environment, and more particularly to a system which provides a transmission having a spectrum (amplitude/frequency signature) of interest.
The invention is especially suitable for providing an acoustic system and source for emulating the noise spectrum of a ship which is useful for acoustic mine sweeping applications. The U.S. Navy has implemented a program for such applications, called the Advanced Lightweight Influence Sweep System (ALISS). Work under this program is described in an article by L. H. Fry, Jr., U.S. Navy Journal of Underwater Acoustics, vol. 47, no. 2, p. 579 (April 1997).
The invention provides an acoustic source array for use underwater which repetitively releases energy in the form of cavities of compressed air. The repetitive release of such pressurized cavities causes a series of broad frequency band impulses to be produced having a fundamental frequency component at the repetitive release rate. The release rate itself can be modulated in frequency so as to cause the transmission to smoothly cover the desired spectrum. The spectrum generated by such a source array is shown in the solid line in
FIG. 1
, and is to be compared with the ship-like target spectrum shown in the dashed line curve in
FIG. 1. A
source, which is adapted to be contained in a tow body, utilizes a generally cylindrical stator having a multiplicity of ports each of which produces an impulse and which are simultaneously opened momentarily by a rotor sleeve at the desired repetition rate. By virtue of the sizing of the ports and the timing of the release of the air the spectrum of interest may be generated. The number of ports may be varied by a ram which is movable through the rotor to control the amplitude of the spectral signature.
While air gun arrays have been used to generate acoustic signals underwater, most air guns are designed to be operated by a sliding valve which moves axially to open or close an exhaust port to release high pressure air into the underwater environment. See, for example, U.S. Pat. No. 5,646,910 issued Jul. 8, 1997 to John V. Bouyoucos and other patents which show typical air gun designs, for example, U.S. Pat. No. 5,572,486, issued Nov. 5, 1996 to M. Candro, et al., U.S. Pat. No. 5,825,719 issued Oct. 20, 1988 to E. R. Harrison, U.S. Pat. No. 4,852,071 issued Jul. 25, 1989 to B. Otto, U.S. Pat. No. 4,858,205 issued Aug. 15, 1989 to E. R. Harrison and U.S. Pat. No. 5,592,440 issued Jan. 7, 1997 and U.S. Pat. No. 5,001,679 issued Mar. 19, 1991, also to E. R. Harrison. Such air guns have been used in arrays of guns of different size to generate an acoustic spectrum preferably flat in shape over a broad frequency range. See, U.S. Pat. No. 5,841,733 issued Nov. 24, 1988 to J. V. Bouyoucos, D. C. Charvoz and D. R. Courtright.
Accordingly, it is the principal object of the present invention to provide an underwater acoustic source and source system for generating transmissions having a spectrum of desired shape and particularly a spectrum emulating that which is produced by a moving surface ship.
It is the further object of the present invention to provide an improved acoustic source and source system for use underwater having a desired dynamic range by controlling the number of synchronous (coherent) releases of energy which produce impulses and which combine to provide the level of the impulsive transmission. This is to simulate the passing of a surface vessel.
It is a still further object of the present invention to provide an improved acoustic source and source system which utilizes a multiplicity of synchronized small air guns, which may be emulated by series of ports through which air is released at desired repetition rates, so as to extend and shape the spectrum produced by the impulses from the ports, the number of ports being controlled from firing to firing (shot to shot) so as to vary the dynamic range of the spectrum.
It is a still further object of the present invention to provide an improved air gun source having a multi-port stator cooperative with a rotor valve for providing controlled and cyclical timed release of pressurized air energy which generates an acoustic spectrum of specified shape.
Briefly described, a source for transmitting acoustic impulses underwater has a body (by which term is meant also a plurality of elements in an array) which is locatable in an underwater environment and charged with energy and which produces a sequence of acoustic impulses released into the underwater environment. An energy controller may be actuated to govern the cyclical timed release of the energy thereby providing an acoustic transmission having a specified spectrum and whose amplitude may be varied with time.
REFERENCES:
patent: 4007805 (1977-02-01), Reber
patent: 4300653 (1981-11-01), Cao et al.
patent: 4852071 (1989-07-01), Otto
patent: 4858205 (1989-08-01), Harrison
patent: 5001679 (1991-03-01), Harrison
patent: 5572486 (1996-11-01), Landro et al.
patent: 5592440 (1997-01-01), Harrison
patent: 5646910 (1997-07-01), Bouyoucos
patent: 5825719 (1998-10-01), Harrison, Jr.
patent: 5841733 (1998-11-01), Bouyoucos et al.
James E. Barger and William R. Hambien, The air gun impulsive underwater transducer, Acoustical Society of America, vol. 68, No. 4, pp. 1038-1045, 1980.
Leolan H. Fry, Jr., A new acoustic transducer for minesweeping based on underwater plasma discharge technology, U.S. Journal of Underwater Acoustics, vol. 47, No. 2, 1997.
Hydroacoustics-Inc.
Lukacher M.
Pihulic Daniel T.
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