Abstract:
Sonobuoy apparatus which fits into an A sized canister for use in the water environment. The apparatus includes an array of telescopic arms connected by hinges to a housing which contains receiver transducer electronics. An acoustic projector bears against projections on the last arm section of each arm such that it will cause the nested arm sections to extend while dropping through the water. When the canister falls free, an arm deployment arrangement causes the arms to assume a horizontal orientation. These deployed arms carry receive transducers for detecting acoustic echos from a potential target.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     A sonobuoy is a device utilized for the detection of submerged targets in the water environment. Typically, a sonobuoy is launched from a relatively slow flying aircraft, and after launch a parachute is deployed to slow the sonobuoy descent. Upon entering the water, the parachute is decoupled and a surface flotation unit is activated. This surface floatation unit generally contains transmitter/receiver equipment, along with an antenna. 
     Tethered to this surface flotation unit, and extending vertically in the water column below the surface flotation unit, is a transducer array utilized to detect acoustic signals from a potential target. In a passive system, these acoustic signals may emanate from a target to be detected and are received by a transducer array. Alternatively, the sonobuoy apparatus may include an active acoustic projector, in which case the transducer array detects the acoustic signals reflected from the target. These detected signals are provided to the transmitter at the floatation unit which, upon command, transmits them to a remote location, such as the deploying aircraft. 
     A common type of sonobuoy in use is an active “A” size sonobuoy which is packaged in a cylindrical container having a length of around 3 feet and a diameter of around 5 inches. Basically, in acoustic systems, the larger the receive array, the greater will be the sensitivity of the system. However, a large receive array is incompatible with a relatively small sonobuoy container. To achieve the sensitivity of a large receive array, many small sonobuoys, or larger sized containers must be utilized. The present invention provides a solution to this incompatibility problem. 
     SUMMARY OF THE INVENTION 
     Sonobuoy apparatus in accordance with the present invention includes a weighted canister for insertion into a water environment to detect potential targets. Packaged within the canister is a surface unit containing transmitter/receiver equipment for communication with a remote location, such as the launching aircraft or vessel. The canister also includes a support unit, which may be constituted by a housing for receive transducer electronics. A plurality of arms is provided, each arm including a plurality of nested telescopic arm sections, with a first of said arm sections being connected to the support unit in a manner such that the arm is capable of limited upward rotation after the canister pulls free and falls away. A weight member, which may be an acoustic projector if the sonobuoy is an active sonobuoy, bears against the lower portion of each arm section and causes extension of the nested arm sections, as the sonobuoy falls through the water column, and before the canister pulls away and falls free. After the canister pulls away and falls free, an arm deployment arrangement deploys the extended arms to a desired orientation, such as horizontal. The deployed arms carry receiver transducers for the detection of target signals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood, and further objects, features and advantages thereof will become more apparent from the following description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 illustrates the deployment of a sonobuoy. 
     FIG. 2 is a cut-away view of a sonobuoy in accordance with one embodiment of the present invention. 
     FIG. 3 illustrates the sonobuoy of FIG. 2 as it descends in the water column. 
     FIG. 4 illustrates the extension of telescopic arms of the sonobuoy. 
     FIG. 5 illustrates the unfolding of the telescopic arms. 
     FIG. 6 is a cross-sectional view of a wire-guiding component of the apparatus. 
     FIG. 7 illustrates the apparatus in a fully deployed condition. 
     FIG. 8 is a plan view of the deployed telescopic arms. 
     FIG. 9 illustrates the placement of transducers of the receiver array. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
     FIG. 1 depicts an aircraft  10  launching a sonobuoy  12  into the water environment  14 , in order to detect acoustic emissions or reflections from a potential target  16 . Sonobuoy  12  is ejected from the aircraft, and a parachute  18  is opened to slow the descent and entry into the water of the sonobuoy  12 . Upon entry into the water  14 , the parachute  18  is automatically separated from the remainder of the sonobuoy. Although a conventional aircraft  10  is illustrated, the sonobuoy may also be launched from a helicopter or surface vessel. 
     As illustrated in the simplified cut-away view of FIG. 2, the components of the sonobuoy  12  are packaged in an A-sized canister  20  having a plurality of apertures  21  to facilitate water entry into the interior of the sonobuoy. The sonobuoy  12  includes, at its upper end, a first section  24  which contains components such as the parachute  18 , as well as a surface flotation element, transmitter/receiver equipment and an antenna. 
     A second section  26  includes cables and other tether lines and baffles commonly used to counter effects of rapid underwater currents. A vertical motion damper  28  is disposed directly below section  26 . 
     In accordance with the present invention, there is included a support unit  30  which carries a plurality of vertically disposed telescoping arms  34 , connected to the support unit  30  by means of respective hinge members  36 . In a preferred embodiment, to conserve space, the support unit  30  is constituted by a housing for the receiver electronics associated with transducers of a receiver array, to be described. These receiver transducers, along with certain wires are located within the volume below the support unit  30 , but are not shown in FIG. 2, for clarity. 
     An acoustic projector  40  is located near the distal ends of the telescoping arms  34  and is supplied with drive signals from unit  42 , which also includes a heavy battery for supplying power to projector/transducer components of the sonobuoy  12 . A standard sonobuoy weight  46  attached to the end of canister  20  will carry the canister  20  away from the apparatus when fully deployed in the water column. 
     FIG. 3 illustrates the apparatus in the water with the first and second sections  24  and  26  deployed out of the canister  20 . Shown in FIG. 3 is a surface flotation element  50  which carries the transmitter/receiver equipment and an antenna  51 , for communication with a remote location, such as the launching aircraft. Tethered below the flotation element  50  are baffles  53  and  54 , as well as the vertical movement damper  28 . Tether line  56  passing vertically through the depicted elements represents various electrical/mechanical lines, in the form of cables and high strength synthetic polymer wires of a material such as Kevlar, a registered trademark and product of E. I. DuPont de Nemours and company. 
     Some of these high strength synthetic polymer wires, designated by the numeral  60 , are attached to the projector  40  and are utilized as part of an arrangement to deploy the arms  34 , when fully extended, into a horizontal configuration. The arrangement includes a wire guide  62  for directing the wires  60  which are attached to the projector  40 , to the respective ends of the arms  34 . The arms  34  include, at their lower end, an angular projection  66  which bears against the bottom of the projector. When that portion of line  56  which is connected from the surface float to the receiver electronics unit  30  is taut, downward movement of the receiver electronics unit  30  is stopped. The forward momentum of the projector  40  however, acting on the projections  66  at the end of the arms, causes the telescopic arms  34  to extend, as illustrated in FIG.  4 . 
     FIG. 4 shows each arm  34  fully extended and consisting of  5  sections labeled  34 - 1  to  34 - 5 . Five sections are shown by way of example, it being understood that more (or fewer) sections, as well as more or fewer arms, could be utilized, depending upon the size of the receiver array desired and the physical space available in the canister  20 . In FIG. 4 the projector  40  still has downward momentum, as does the battery/driver unit  42  and weighted canister  20 . The arms  34  however are constrained from upward rotation about their respective hinge members  36  since the lower ends of the arms  34  are still in the upper portion of the downwardly falling canister  20 . 
     When the descending canister  20  drops beyond the lower ends of the arms  34 , and as illustrated in FIG. 5, the arms  34  are allowed to rotate about their respective hinge members  36 . This is the result of projections  66 , at the end of arms  34  becoming decoupled from the bottom of projector  40 . This decoupling may be activated by the normal lateral water currents encountered, or may be accomplished by spring loading the projections  66 , by way of example. Continued downward momentum of projector  40  causes lateral deployment of arms  34  by virtue of wires  60  connected from projector  40  to the end of each arm  34 , via wire guide  62 . This operation may also be accomplished by means of a weight to which the wires  60  would be attached, such as in a passive system which would not carry a projector. 
     With additional reference to FIG. 6, the wire guide  62 , securely attached to line  56 , may take the form of a toroid through the center of which passes line  56 , as well as wires  60 . The cross-sectional view of FIG. 6 shows a smooth, gently curving surface of the toroid, over which the wires  60  pass, to ensure for a smooth deployment of the arms  34 . In one embodiment, this deployment of the arms  34  results in a horizontal orientation, as illustrated in FIG. 7, although a conical shape is also possible by providing hinge members  36  with limited angular movement, that is, less than 90°. 
     The weight of projector  40  and battery  42  is such as to apply enough tension on wires  60  to maintain the desired arm orientation. A plan view of the deployed arms  34  is shown in FIG. 8 which also shows a plurality of receive transducers  70  arranged on the surface of the arms. In addition, receive transducers  70  may also be attached to chordal tension lines  72  stretched between the arms  34  near their lower ends. The arrangement provides for a relatively large and structurally rigid array with excellent sensitivity in a dynamic sea state. 
     The operative relationship of the receive transducers  70  with the arm sections  34 - 1  to  34 - 5  (or broadly,  34 -n) may be accomplished in a number of ways. For example, FIG. 9 illustrates a first receive transducer  70  firmly attached to the outside surface of the first arm section  34 - 1 . Subsequent receive transducers  70  are interconnected by an electromechanical line  84 , the end of which is attached to the end of arm section  34 -n. As the arm  34  is deployed, and line  84  extended, each receive transducer  70  will come into contact with a respective arm section and will be carried by it, as illustrated in the plan view of FIG.  8 . If desired, additional attachments may be made to the last arm section to accommodate more such transducers. 
     It will be readily seen by one of ordinary skill in the art that the present invention fulfills the object set forth herein. After reading the foregoing specification, one of ordinary skill in the art will be able to effect various changes, substitutions of equivalents and various other aspects of the present invention as broadly disclosed herein. It is therefore intended that the protection granted hereon be limited only by the definition contained in the appended claims and equivalents. Having thus shown and described what is at present considered to be the preferred embodiment of the present invention, it should be noted that the same has been made by way of illustration and not limitation. Accordingly, all modifications, alterations and changes coming within the spirit and scope of the present invention are herein meant to be included.