The present invention relates to an underwater acoustic projector having very low frequency and a wide bandwidth.
Very low frequency, low cost, wide bandwidth and portability are all desirable assets for underwater acoustic projectors. Present flextensional designs such as the folded shell projector (FSP) taught in U.S. Pat. No. 5,805,529 by Purcell and the barrel stave projector (BSP) as described in U.S. Pat. No. 4,922,470 by McMahon et al are portable but operate at frequencies far above what is required. The DRDC-Atlantic moving coil projector (MCP) operates over the frequency band required but weighs many tons and is not easily deployable. That projector can produce sound levels in excess of 180 dB at 10 Hz.
Presently very low frequency sound sources are created either by using radiating pistons driven by large displacement-high force mechanisms, by airgun driven cavity collapse, by spark induced cavity collapse, by edge driven flexural disk projectors or multi-motor driven flexural disk projectors.
Present low frequency projectors such as the moving coil projector, airgun and sparker are typically heavy and expensive devices.
It is an object of the present invention to provide an underwater low frequency light weight projector.
Very low frequency, low cost, wide bandwidth and portability are all desirable assets for underwater acoustic projectors. Present flextensional designs such as the folded shell projector (FSP) taught in U.S. Pat. No. 5,805,529 by Purcell and the barrel stave projector (BSP) as described in U.S. Pat. No. 4,922,470 by McMahon et al are portable but operate at frequencies far above what is required. The DRDC-Atlantic moving coil projector (MCP) operates over the frequency band required but weighs many tons and is not easily deployable. That projector can produce sound levels in excess of 180 dB at 10 Hz.
Presently very low frequency sound sources are created either by using radiating pistons driven by large displacement-high force mechanisms, by airgun driven cavity collapse, by spark induced cavity collapse, by edge driven flexural disk projectors or multi-motor driven flexural disk projectors.
Present low frequency projectors such as the moving coil projector, airgun and sparker are typically heavy and expensive devices.
The low frequency acoustic projector according to the present invention has a pair of electrodynamic drive motors (coils 12 and oscillating masses 14 that move in opposition to each other) that are each inertially coupled to its optimized flexurally radiating surfaces 2 and installed in a pressure compensated cylindrical enclosure formed by surfaces 16 as illustrated in
Using a pair of low cost electrodynamic inertial drive motors 12 to drive the flexural surfaces 2 along their central axis is a novel implementation of the flexural disk transducer concept according to the present invention.
Two prototype versions of this low frequency acoustic projector have been built and tested.
A first prototype was constructed from mild steel with radiating surfaces being 3.2 mm thick. The radiating surface spacer ring 10 was aluminum. One prototype consisted of two central diaphragms (disc) 20 having a radius of 9.6 inches separated by a cylindrical spacer ring 10 with the two coils 12 and two oscillating mass 14 being located in the space inside of two pipes 16. The spacer ring 10 is attached to diaphragms 20 by bolts 8. A central pipe (tube) 16 having a 4.57 inch outside diameter extends outward 5.50 inches from the center opening of each diaphragm 20, the tubes being open to the space between the diaphragms 20. The outer ends of the tubes are welded closed by a disc with the interior portion of the transducer being pressure compensated with a gas. An O-ring 6 is located at closed ends of the tubes. Power is applied to the coils by a connector 22 extending through and sealed to cylindrical ring 10 as illustrated in
Possible uses for this projector include underwater loudspeakers, in-air tactile alarm systems, shakers of vibrators. This projector can be used as low frequency small, high source level acoustic projector; in naval sonar, as a naval underwater towed acoustic target, in a naval acoustic minesweeping system and in air deployed underwater sensor systems. A prototype revealed a sound level of approximately 186 dB re 1 μPa@1 m at 62.5 Hz at a depth of 0.2 m when driven at 1000 watts (10 amps at 100 volts rms).
Various modifications may be made to the preferred embodiment without departing from the spirit and scope of the invention as defined in the appended claims.
This Claims the benefit of PROVISIONAL APPLICATION Ser. No. 60/637,643 filed 21 Dec. 2004.
Number | Name | Date | Kind |
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4353120 | Pickens | Oct 1982 | A |
4922470 | McMahon et al. | May 1990 | A |
5268879 | Flanagan | Dec 1993 | A |
5805529 | Purcell | Sep 1998 | A |
5959939 | Tengham et al. | Sep 1999 | A |
Number | Date | Country | |
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20060133212 A1 | Jun 2006 | US |
Number | Date | Country | |
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60637643 | Dec 2004 | US |