GB2369178A

GB2369178A - Acoustic jamming

Info

Publication number: GB2369178A
Application number: GB9010655A
Authority: GB
Inventors: Timothy Jone
Original assignee: Marconi Co Ltd; BAE Systems Electronics Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1990-05-11
Filing date: 1990-05-11
Publication date: 2002-05-22
Anticipated expiration: 2010-05-11
Also published as: GB2369178B; GB9010655D0

Abstract

A method of sonar jamming comprises causing a series of pyrotechnic explosions under water in the region of sonar apparatus to be jammed such that not less than one explosion occurs in every integration period of the apparatus. A jamming device comprises a plurality of pyrotechnic charges and a trigger mechanism for sequentially firing the charges over a period of time transported away from a target ship in a torpedo like device. Cartridges (figure 2, not shown) each comprising a pyrotechnic charge (42) and an ejection charge (40) therefore are mounted in cells 26 and triggered in turn by trigger device 30.

Description

Acoustic Jamming The present invention relates to a method of acoustically jamming sonic detection systems and to a device which can be used in such a method. The particular relevance of the invention is in underwater situations.

Underwater sonic detection systems such as sonar operate by monitoring the acoustic noise given off by a body in water and often rely on reflected sound signals to identify range, direction and type of target. Such systems are susceptible to jamming but continuous jamming systems mounted on ships or submarines are always with the vessel which it is desired to protect. Consequently, it is not possible for the vessel to leave the jamming area whilst jamming is in progress.

Electronic systems also require a constant power supply making it difficult to deploy the jamming devices away from the target vessel.

The present invention has arisen in an attempt to provide an easily deployable underwater acoustic jamming system which is entirely self contained.

In accordance with the broadest aspect of the present invention, there is provided a method of sonar jamming comprising causing a series of pyrotechnic explosions under water in the region of sonar apparatus to be jammed and characterised in that not less than one explosion occurs in every integration period of the apparatus.

It is particularly preferred that the series is an irregular series of explosions.

In another aspect of the invention, there is provided a jamming device comprising a plurality of pyrotechnic charges and a trigger mechanism for sequentially firing the charges over a period of time.

Preferably, the device comprises a main body having the charges housed therein and from which each charge is ejected before firing. The body is typically submersible.

Ejection of the charge can be provided by the explosion of a propellant charge or by any other suitable mechanism.

The body can typically comprise a stack of disc members having bores defined therein for locating the charges. In one arrangement, the bores are formed by two adjacent discs and in another arrangement, complete bores are provided in each disc.

The device can typically include propulsion means and steerage means, the propulsion means preferably comprising an electric motor.

A triggering mechanism for the charges can comprise a rotary shaft having a trigger member mounted thereon which can be caused to move along the shaft during rotation so as to sequentially trigger the charges. The charges typically comprise cartridges including a detonator, a propulsion charge and a pyrotechnic charge. The propulsion and pyrotechnic charges are suitably arranged to communicate such that the propulsion charge ignites the pyrotechnic charge after a period of time. The propulsion charge is arranged to expel a cartridge from a bore to a distance from the body such that explosion of the pyrotechnic charge will not cause sympathetic explosions of other charges.

The present invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 shows a cut away view of one embodiment of the invention with parts omitted for clarity; Figure 2 shows a cartridge for use in the embodiment of Figure 1; Figure 3 shows the noise spectrum from detonation of a cartridge as shown in Figure 2; Figure 4 shows the mean noise for the spectrum in Figure 3; and Figure 5 shows the variation in acoustic performance with differing quantities of pyrotechnic charge.

Referring now to Figure 1, the jamming device showing therein comprises a submersible vehicle similar to a torpedo and comprising a tail section A, a payload section B and a nose section C.

The tail section A comprises a housing 10 containing an electric motor 12 driving a propeller 14. Also enclosed in the housing are the guidance systems, processors and gyros and a deployment mechanism (all not shown) for control surfaces 16. The shaft 18 is also lead forward from the tail section A into the payload section B.

The payload section B comprises a elongate cylindrical body 20 (shown dashed) having a splined shaft 22 running along the axis thereof and attached to the shaft 18. A plurality of annular discs 24 are arranged around the shaft 22 in a side by side arrangement. The discs are moulded from a plastic material and when stacked together create an open cell-structure 26. A trigger disc 28 is mounted on the shaft 22 and is provided with a part screw thread formation 30 on an outer surface thereof which engages with a corresponding thread on the inside of each disc 24. The trigger disc 28 is free to slide on the shaft 22 such that the disc will progress along the structure 26 when the shaft 22 is rotated.

The trigger disc 28 serves to complete electrical contact with detonators in each cell (not shown) and thus fire any cartridges located therein.

A cartridge for use in this device is shown in Figure 2 and comprises a hollow cartridge body 32 divided into bottom and top sections 34,36 with a communicating passage 38 therebetween. The bottom section contains a small propellant charge of black powder 40 and the top section a pyrotechnic charge of potassium perchlorate (cl04) 42, typically about 2.5 g. The cartridge is retained in a cell 44 by a sealing ring 46 and a detonator 48 is positioned adjacent to the bottom section.

The interior of the payload section B might be filled with an inert fluid which allows electrical contacts to be made if required.

The nose section C contains a buoyancy device 50 incorporating bellows 52 for changing the buoyancy thereof.

Alternatively, a set of planes can be provided to create lift when the device is propelled under water. It proposed that the device should normally have negative buoyancy.

In use, cartridges are loaded in to the cells 44 and the device is fired or dropped in to the water and the motor started. Because of the negative buoyancy, the device will run submerged and as the trigger disc contacts each detonator, the cartridge is fired. The black powder charge propels the cartridge from the cell and away from the device. Once the black powder charge has burned through, the pyrotechnic charge is ignited causing a pyrotechnic explosion. This produces an acoustic signal typically as shown in Figure 3, the mean value of this signal being shown in Figure 4. Such a signal is typically sufficient to mask or jam any normal sonar signals for a distance of about 10 Km under favorable conditions. The device fires cartridges at a rate of about 5 per second which ensures at least one signal in each sonar integration period. The full payload typically comprises 6,000 cartridges giving 20 minutes total operational time. It will be appreciated that the firing mechanism could be controllable such that the firing could be stopped and restarted at will and the fact the device is self contained means that any deploying vessel can vacate the operating area.

Figure 5 shows the variation in signals strength with quantity of pyrotechnic charge at various depths. The signals are measured by a hydrophone at 75 meters and analysed using Hanning weighting. A signal strength of 204 dB or more is considered acceptable.

Further changes can be made while remaining within the scope of the invention.

Claims

CLAIMS 1. A jamming device comprising a plurality of pyrotechnic charges and a trigger mechanism for sequentially firing the charges over a period of time.
2. A device as claimed in claim 1, wherein the device comprises a main body having the charges housed therein and from which each charge is ejected before firing.
3. A device as claimed in claim 2, wherein the body is submersible.
4. A device as claimed in claim 2 or 3, wherein ejection of the charge is provided by the explosion of a propellant charge.
5. A device as claimed in any of claims 2 to 4, wherein the body comprises a stack of disc members having bores defined therein for locating the charges.
6. A device as claimed in claim 5, wherein the bores are formed by two adjacent discs.
7. A device as claimed in claim 6, wherein complete bores are provided in each disc.
8. A device as claimed in any preceding claim and including propulsion means and steerage means.
9. A device as claimed in claim 8, wherein the propulsion means comprises an electric motor.
10. A device as claimed in any preceding claim, wherein the triggering mechanism comprises a rotary shaft having a trigger member mounted thereon which can be caused to move along the shaft during rotation so as to sequentially trigger the charges.
11. A device as claimed in any preceding claim, wherein the charges comprise cartridges including a detonator, a propulsion charge and a pyrotechnic charge.
12. A device as claimed in claim 11, wherein the propulsion and pyrotechnic charges are arranged to communicate such that the propulsion charge can ignite the pyrotechnic charge.
13. A device as claimed in claim 11 or 12, wherein the propulsion charge is arranged to expel a cartridge from a bore to a distance from the body such that explosion of the pyrotechnic charge will not cause sympathetic explosion of other charges remaining within the body.
14. A method of sonar jamming comprising causing a series of pyrotechnic explosions under water in the region of sonar apparatus to be jammed and characterised in the not less than one explosion occurs in every integration period of the apparatus.
15. A method as claimed in claim 14, wherein the series is an irregular series of explosions.
16. A method of a sonar jamming which is substantially as herein described.

16. A jamming device which is substantially as herein described in relation to the accompanying drawings.

17. A method of sonar jamming which is substantially as herein described.

Amendments to the claims have been filed as follows 1. An acoustic jamming device comprising a plurality of pyrotechnic charges and a trigger mechanism for sequentially firing the charges over a period of time, the trigger mechanism comprising a rotary shaft having a trigger member mounted thereon which can be caused to move along the shaft during rotation so as to sequentially trigger the charges.

2. A device as claimed in claim 1 wherein the device comprises a main body having the charges housed therein and from which each charge is ejected before firing.

3. A device as claimed in claim 2 wherein the body is submersible.

4. A device as claimed in claim 2 or 3 wherein ejection of the charge is provided by the explosion of a propellant charge.

5. A device as claimed in any of claims 2 to 4, wherein the body comprises a stack of disc members having bores defined therein for locating the charges.

6. A device as claimed in claim 5, wherein the bores are formed by two adjacent discs.

7. A device as claimed in claim 6, wherein complete bores are provided in each disc.

8. A device as claimed in any preceding claim and including propulsion means and steerage means.

9. A devices as claimed in claim 8, wherein the propulsion means comprises an electric motor.

10. A device as claimed in any preceding claim, wherein the charges comprise cartridges including a detonator, a propulsion charge and a pyrotechnic charge.

11. A device as claimed in claim 10, wherein the propulsion and pyrotechnic charges are arranged to communicate such that the propulsion charge can ignite the pyrotechnic charge.

12. A device as claimed in claim 10 or 11, wherein the propulsion charge is arranged to expel a cartridge from a bore to a distance from the body such that explosion of the pyrotechnic charge will not cause sympathetic explosion of otter charges remaining within the body.

13. A method of sonar jamming comprising causing a series of pyrotechnic explosions under water in the region of sonar apparatus to be jammed and characterised in the not less than one explosion occurs in every integration period of the apparatus.

14. A method as claimed in claim 13, wherein the series is an irregular series of explosions. 15. A jamming device which is substantially as herein described in relation to the accompanying drawings.