GB2093996A - Improvements in or relating to sonar arrays - Google Patents

Abstract

A sonar receiver array has a body (10) provided with hydrophone support arm (11). The support arm (11) is pivotable on the body (10) between a stowed position alongside or within the body (10) and a deployed position where it extends laterally of the body (10). <IMAGE>

Description

SPECIFICATION Improvements in or relating to sonar arrays This invention relates to sonar arrays such as are employed in transmission or reception of signals under water.

Certain sonar acoustic arrays, particularly those used in sonobuoys and in helicopter dunking sonar, require to be small in physical dimensions when in a quiescent condition and large when in operation so as to achieve the required acoustic characteristics. This invention seeks to provide an array which achieves this requirement.

One way that this requirement can be met is by constructing the array of folding members which collapse to small dimensions for stowage in a sonobuoy or recovery into a helicopter, and which expand to the full array dimensions when at working depth and required to operate. This invention in a preferred form seeks to achieve near optimum configurations for the array in both the folded and deployed, or unfolded, conditions.

This invention may include various additional features which lead to advantageous operation for specific application. For example, in some sonar systems the acoustic array in use is suspended from or above the surface by an electrical cable, the depth of the array being set to obtain the most favourable conditions for acoustic transmission and reception. It is, therefore, desirable in most cases that in array sinks to operating depth in the minimum of time and that in turn makes desirable a long slim shape for the folding array. At operating which make up the array to be properly spaced with respect to one another to give the correct acoustic beam pattern.

Lastly, the array requires the means to deploy when at operating depth, and to fold up on command when it is to be recovered. In the case of sonobuoys, where recovery is rarely attempted, natural forces can be used to deploy the array.

In order that the invention and its various other preferred features may be understood an embodiment thereof will now be described by way of example only, with reference to the drawings, in which: Figure 1 is an elevational view, taken from slightly above, of an array constructed in accordance with the invention, and Figure 2 is a schematic front elevation of parts of the array of Figura 1 to an enlarged scale and showing one part folded in a non-deployed configuration and another part in a deployed configuration.

In the drawing of Figure 1, 10 is a central structural member of the array which can also be used to house transmitting transducers when required for an active system. This member 10 is hollow and free flooding to avoid unwanted buoyancy. Connected to 10 by pivots are receiving array suspension arms 1 and 12, arranged in this example as 5 pairs with equal angular spacing around the member 10.

Suspended on pivots between the pairs of arms, 11, 12, are vertical staves, 13, which contain receiving hydrophones. These staves are positioned at equal increments of distance from each other and the central core, the spacing usually being t2, where A is the wavelength of the acoustic signal to be received. It will be observed that the staves are of increasing length as positioned out from the central core. At the extremities of the member 10 there are end caps, 14 and 15. The purpose of the end caps is to give a streamline shape to the folded array and to house associated electronics and any other sensors required by the system such as a compass, sound velocity sensor, array tilt indicators, depth sensor, and telemetry electronics.The end caps can also be used to house the mechanism for folding the array operating inside the member 10 on the ends of the arms, 11, 12, taken through 10 at their pivot points. Figure 1 shows the array in its deployed condition, in this example having a vertical aperture of 4R and a horizontal aperture of 5R plus the diameter of the central core, 10.

Figure 2 illustrates part of the same construction as Figure 1 showing only one pair of suspension arms 11, 12, on the left in the deployed condition and on the right in the retracted or folded condition. For the sake of clarity this diagram exaggerates the thickness of the staves which, as they only have to house hydrophones and possibly their associated preamplifiers can be thin, thus giving a slim assembly in the folded condition. The retracting mechanism, not shown in the diagram, can take a number of forms. In the dunking sonar case, where it is necessary to both expand and retract the array, an electric motor driving a lead screw in turn coupled to the ir.board ends of either or both of the arms 11 and 1 2 or an electrical solenoid, could be used to generate the appropriate motion.

In the sonobuoy case the folded array could be housed inside a cylindrical extension of the surface flotation unit, as is customary with current designs, and would slide out of the surface unit after the buoy enters the water. The arms may be held in the folded position by water pressure as the array sinks to operating depth as set by the suspension cable length. Small fins could be fitted to the suspension arms to assist the hydrodynamic closure of the array if necessary. At operating depth when the array is no longer sinking the suspension arms being negatively buoyant will open out under gravity so obviating the need for a power driven deployment mechanism. In both the sonobuoy and dunking sonar application mechanical stops could be used to accurately define the position of the suspension arms in the deployed condition.

Active sonar systems usually require an acoustic projector which radiates uniformly in the azimuth plane and with a defined beamwidth in the vertical plane, vertical apertures of around 4R being common. The slim tubular vertical core 10 of this array is well suited to housing the transmitting transducers required to form such a projector.

Receiving arrays are usually of cylindrical form and ideally should accommodate as many hydrophones at t2 spacing as is possible in order to avoid the folded array being longer than the central core the inner staves of this array are reduced in length. In the example illustrated the loss in isotropic noise gain which resuits from this reduction in the possible number of receiving hydrophones is only 1.2db which has only a very small effect on noise limited range performance.

In some cases the reduction in the number of hydrophones at the centre of the array can improve the horizontal beam pattern of the array and so improve reverberation limited performance. If the maximum isotropic noise gain is required then the staves can be projected above the suspension arm 11, by the amount they have been shortened below the arm, 12, so being of constant length and still folding within the length of the central core.

The substantial vertical aperture of this array is of particular value in the case of dunking sonar as it permits a high rejection of noise arriving in the vertical direction, such as noise induced into the sea by the supporting helicopter which can be a limiting factor in dunking sonar performance.

The large number of hydrophones achieved with this design make the array suitable for use with passive sonars operating in the wave or isotropic noise dominated part of the frequency spectrum.

The embodiment described uses 5 pairs of suspension arms and 5 staves per arm but clearly both more or less arms and staves could be used if the acoustic requirements made it necessary. In general the configuration illustrated gives a good compromise between performance and complexity.

It will be appreciated that variations of the structure described can be made to suit particular applications. Structures can be formed which provide an array with any of the following features a) Capability of use with active or passive sonars.

b) A central core supporting pivoted arms which, in turn, carry vertical staves, the pivoted arms being arranged to swing either up or down so as to fold the staves against the central core without extending beyond the ends of the core.

The folding of the arms may be achieved by any suitable means e.g. by using hydrodynamic forces and gravity, or by means of a powered mechanism if recovery of the array is required.

c) Foldability into a form suited to achieving high sinking speeds, a feature of importance to dunking sonar and sonobuoys. End caps may be fitted to a central core to further improve sinking speed.

d) The provision of a pre-flooded central core which doubles as a convenient housing for transducers needed to form the acoustic projector of an active sonar system.

e) An arrangement such that unfolded or deployed arms and staves form a convenient receiving array for both active and passive sonars with acoustic dimensions compatible with that of a projector.

f) Space within a central core or end caps which can be used to house the array retraction mechanism and any associated electronics and other sensors required by the sonar system.

Claims (Filed 16/4/81) 1. A sonar receiver array, comprising a body provided with a hydrophone support arm which is pivotable on the body between a stored position alongside or within the body and a deployed position where it extends laterally of the body.

2. An array as claimed in claim 1 , wherein a plurality of hydrophone support arms or pivotable on the body between a stowed position alongside or within the body and a deployed position where they extend laterally of the body in different directions.

3. An array as claimed in claim 2, wherein the arms in the deployed position are equiangularly distributed around the body.

4. An array as claimed in claim 2 or 3, wherein each arm is provided with at least one stave housing one or more hydrophones, which stave(s) is/are pivotally mounted on the arm and arranged to move from a position alongside or within the body and a position spaced from the body and extending laterally of the support arm upon movement of the support arm from the stowed position to the deployed position.

5. An array as claimed in claim 4, wherein for each support arm there is provided a cooperating arm pivotable on the body at a position spaced from its associated support arm, said stave(s) being pivotably coupled with the cooperating arm.

6. An array as claimed in claim 4 or 5, wherein on each support arm there are a plurality of staves which are arranged to be substantially parallel in the deployed position of the support arm.

7. An array as claimed in claim 6, wherein the staves on all of the support arms are arranged to be mutually substantially parallel.

8. An array as claimed in any one of claims 4 to 7, wherein there are a plurality of staves on each support arm which staves are spaced apart thereon by a distance substantially equal to half a wavelength at the operating frequency of the array.

9. An array as claimed in any one of claims 4 to 8, wherein there are a plurality of staves on each support arm which staves have progressively increasing lengths with distance along the arm from its end nearest the body.

10. An array as claimed in any one of claims 4 to 7, wherein there are a plurality of staves on each support arm, the mounting point of the staves on each arm being offset at progressively increased distances along the staves with distance along the arm from its end nearest the body.

1 An array as claimed in claim 9 or 10, the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (1)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   transmitting transducers required to form such a projector.

   Receiving arrays are usually of cylindrical form and ideally should accommodate as many hydrophones at t2 spacing as is possible in order to avoid the folded array being longer than the central core the inner staves of this array are reduced in length. In the example illustrated the loss in isotropic noise gain which resuits from this reduction in the possible number of receiving hydrophones is only 1.2db which has only a very small effect on noise limited range performance.

   In some cases the reduction in the number of hydrophones at the centre of the array can improve the horizontal beam pattern of the array and so improve reverberation limited performance. If the maximum isotropic noise gain is required then the staves can be projected above the suspension arm 11, by the amount they have been shortened below the arm, 12, so being of constant length and still folding within the length of the central core.

   The substantial vertical aperture of this array is of particular value in the case of dunking sonar as it permits a high rejection of noise arriving in the vertical direction, such as noise induced into the sea by the supporting helicopter which can be a limiting factor in dunking sonar performance.

   The large number of hydrophones achieved with this design make the array suitable for use with passive sonars operating in the wave or isotropic noise dominated part of the frequency spectrum.

   The embodiment described uses 5 pairs of suspension arms and 5 staves per arm but clearly both more or less arms and staves could be used if the acoustic requirements made it necessary. In general the configuration illustrated gives a good compromise between performance and complexity.

   It will be appreciated that variations of the structure described can be made to suit particular applications. Structures can be formed which provide an array with any of the following features a) Capability of use with active or passive sonars.

   b) A central core supporting pivoted arms which, in turn, carry vertical staves, the pivoted arms being arranged to swing either up or down so as to fold the staves against the central core without extending beyond the ends of the core.

   The folding of the arms may be achieved by any suitable means e.g. by using hydrodynamic forces and gravity, or by means of a powered mechanism if recovery of the array is required.

   c) Foldability into a form suited to achieving high sinking speeds, a feature of importance to dunking sonar and sonobuoys. End caps may be fitted to a central core to further improve sinking speed.

   d) The provision of a pre-flooded central core which doubles as a convenient housing for transducers needed to form the acoustic projector of an active sonar system.

   e) An arrangement such that unfolded or deployed arms and staves form a convenient receiving array for both active and passive sonars with acoustic dimensions compatible with that of a projector.

   f) Space within a central core or end caps which can be used to house the array retraction mechanism and any associated electronics and other sensors required by the sonar system.

   Claims (Filed 16/4/81) 1. A sonar receiver array, comprising a body provided with a hydrophone support arm which is pivotable on the body between a stored position alongside or within the body and a deployed position where it extends laterally of the body.

   2. An array as claimed in claim 1 , wherein a plurality of hydrophone support arms or pivotable on the body between a stowed position alongside or within the body and a deployed position where they extend laterally of the body in different directions.

   3. An array as claimed in claim 2, wherein the arms in the deployed position are equiangularly distributed around the body.

   4. An array as claimed in claim 2 or 3, wherein each arm is provided with at least one stave housing one or more hydrophones, which stave(s) is/are pivotally mounted on the arm and arranged to move from a position alongside or within the body and a position spaced from the body and extending laterally of the support arm upon movement of the support arm from the stowed position to the deployed position.

   5. An array as claimed in claim 4, wherein for each support arm there is provided a cooperating arm pivotable on the body at a position spaced from its associated support arm, said stave(s) being pivotably coupled with the cooperating arm.

   6. An array as claimed in claim 4 or 5, wherein on each support arm there are a plurality of staves which are arranged to be substantially parallel in the deployed position of the support arm.

   7. An array as claimed in claim 6, wherein the staves on all of the support arms are arranged to be mutually substantially parallel.

   8. An array as claimed in any one of claims 4 to 7, wherein there are a plurality of staves on each support arm which staves are spaced apart thereon by a distance substantially equal to half a wavelength at the operating frequency of the array.

   9. An array as claimed in any one of claims 4 to 8, wherein there are a plurality of staves on each support arm which staves have progressively increasing lengths with distance along the arm from its end nearest the body.

   10. An array as claimed in any one of claims 4 to 7, wherein there are a plurality of staves on each support arm, the mounting point of the staves on each arm being offset at progressively increased distances along the staves with distance along the arm from its end nearest the body.

   1 An array as claimed in claim 9 or 10, the

   mounting of the support arms and staves being such that in the stowed position they are disposed within the side length of the body.

   12. An array as claimed in any one of the preceding claims, wherein the arms are arranged to be deployed under the action of gravity.

   1 3. An array as claimed in any one of the preceding claims, wherein the arms are arranged to be held in the stowed position by hydrodynamic pressure induced whilst the body is sinking in water.

   14. An array as claimed in claim 13, wherein the arms have fins to assist maintenance of the stowed position by hydrodynamic pressure whilst the body is sinking.

   1 5. An array as claimed in any one af claims 1 to 12, including a drive mechanism operable to move the support arms between deployed and stowed positions.

   1 6. An array as claimed in any one of the preceding claims, including mechanical stops to define the position of the arms in the deployed position.

   17. An array as claimed in any one of the preceding claims, wherein the body is elongate.

   18. An array as claimed in any one of the preceding claims wherein the body is hollow.

   19. An array as claimed in claim 18, wherein the body is tubular and provided with end caps shaped to provide a streamline shape to the body.

   20. An array as claimed in claim 19, wherein the end caps house electrical equipment.

   21. An array as claimed in any one of claims 18, 1 9 or 20, wherein the body is free flooding to reduce buoyancy.

   22. A sonar buoy including a receiver array as claimed in any one of the preceding claims.

   23. An active sonar system including a receiver array as claimed in anyone of claims 18 to 21.

   wherein the body contains transmitter transducer means.

   24. A sonar buoy or systems as claimed in 22 or 23, including a housing for containing the array in the stowed position, which housing permits the array to slide out for deployment in the water.

   25. A sonar receiver array substantially as described herein with reference to and as illustrated in the drawings.

   26. A sonar buoy substantially as described herein with reference to and as illustrated in the drawings.