Abstract:
The present invention discloses a system for wireless communications and/or data transfer through a sea-vessel hull by means of electric and/or magnetic coupling between first and second transducers located on opposing sides of the hull. Transmit and receive transducers located on opposing sides of the hull are clamped around cables which penetrate the hull and which are fed through pressure hull glands in the hull. The inductive transducers couple electric and/or magnetic signals through the sea vessel hull via paths through the pressure hull glands or via paths through the cables. The system for wireless communication and/or data transfer of the present invention is capable of operation through an electrically conductive sea vessel hull which would ordinarily present a physical barrier against the transmission of such signals. The system can be deployed on an ad ad-hoc basis and is capable of providing high data rate and high bandwidth communications and/or data transfer through the sea vessel hull. The system does not interfere with existing cabled systems penetrating the hull via the pressure hull glands. In particular, the system of the present invention requires no modification of existing hardware nor does it require any modification of the hull for operation.

Description:
FIELD USE 
       [0001]    The present invention relates to the field of communications through the hull of a sea vessel. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    Wireless communications, data transfer and/or the transmission of control signals through the hull of a sea vessel are desirable for a range of applications. For example, on submarines, various external equipment, such as sonar, mast raising gear etc is located under the upper casing. This equipment, requires a communication means with associated internally located equipment which sends and receives data or control signals to the external equipment. Typically, the communications means between the internal and external equipment is via wired connections. Applications of wireless communications through a sea vessel hull also include systems for voice telephony or video streaming between a diver located on the outside of the vessel, and the crew located on the inside of the sea vessel. Wireless communications between the inside and the outside of the vessel hull is also desirable when the sea vessel is located in a dry dock. 
         [0003]    Communications through a sea vessel hull, by means of acoustic signaling, is known. However, acoustic signaling has the drawback that the signal path cannot be controlled. Acoustic signaling thus suffers from the effects of multi-path interference which limits the available bandwidth for signals 
         [0004]    Electromagnetic signaling can provide a higher bandwidth than acoustic signaling. Signaling via electromagnetic means has the benefit over acoustic signaling that the signal path is well defined. Moreover, signaling by electromagnetic means provides the opportunity to use mature protocols and systems for establishing the radio channel can operate over multiple co-existing channels without interference. 
         [0005]    Commonly assigned United States Patent Application Publication: 2009/0156119 “Communications through a Barrier” Rhodes et al. describes a system and apparatus for communication through an electrically conductive barrier, and is incorporated herein by reference. 
         [0006]    Nonetheless, the ferrous nature of a typical sea vessel hull creates a barrier against the transmission of electromagnetic signals through the hull. Thus, typical communications through a sea vessel hull is by means of wired links via conventional cables. Cables which feed the wired links are fed through what is commonly referred to as pressure hull glands. Pressure hull glands can have various cable entry configurations including multi-core, paired, screened paired, tripled, coaxial etc. 
         [0007]    The ever increasing demand for electronic systems, communications, data transfer and automation etc in modern submarines produce a demand for ever increasing communications data transfer and/or control systems to be installed in existing submarines. This constant need for upgrading of systems also arises from the fact that submarines have a typical lifetime extending into decades. Pressure hull glands are the recognized method used for passing electrical wires and other cables through submarine hulls. However, retro-fitting of pressure hull glands is a costly and time consuming exercise. 
         [0008]    A system which could add additional data transfer and/or communications channels to existing hardware installed via pressure hull glands would be highly beneficial. 
       SUMMARY OF THE INVENTION 
       [0009]    Accordingly, an object of the present invention is to provide a system for wireless communications, data transfer and/or the transmission of control signals through a sea vessel hull by wireless coupling of electric and/or magnetic signals through the hull via existing pressure hull glands penetrating the hull. 
         [0010]    A further object of the present invention is to provide a system for wireless communications, data transfer and/or the transmission of control signals through a sea vessel hull which can deployed on the sea vessel hull without any modification thereof. 
         [0011]    Advantageously, the system of the present invention is capable of providing high data rate and high bandwidth communications and/or data transfer through the sea vessel hull. 
         [0012]    The present invention provides a system for wireless communications and/or data transfer through a sea-vessel hull by means of electric and/or magnetic coupling between first and second transducers located on opposing sides of the hull. Transmit and receive transducers are clamped around cables and/or other protrusions which penetrate the hull and which are fed through pressure hull glands in the hull. The inductive transducers couple electric and/or magnetic signals through the sea vessel hull via paths through the pressure hull glands. The system for wireless communication and/or data transfer of the present invention is capable of operation through an electrically conductive sea vessel hull which would ordinarily present a physical barrier against the transmission of such signals. The system can be deployed on an ad ad-hoc basis and is capable of providing high data rate and high bandwidth communications and/or data transfer through the sea vessel hull. The system does not interfere with existing cabled systems penetrating the hull via the pressure hull glands. In particular, the system of the present invention requires no modification of existing hardware nor does it require any modification of the hull for operation. 
         [0013]    Embodiments of the present invention will now be described in detail with reference to the accompanying figures in which: 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1A  shows a side view drawing of a system for wireless communications through a sea vessel hull according to a first embodiment the present invention. 
           [0015]      FIG. 1B  shows a front view drawing of a first transducer according to the system for wireless communications through a sea vessel hull depicted in  FIG. 1A . 
           [0016]      FIG. 1C  shows a front view drawing of a first transducer according to the system for wireless communications through a sea vessel hull depicted in  FIG. 1A  comprising a pair of associated transducer coils. 
           [0017]      FIG. 2A  shows a side view drawing of a system for wireless communications through a sea vessel hull according to a second embodiment the present invention. 
           [0018]      FIG. 2B  shows a front view drawing of a first transducer according to the system for wireless communications through a sea vessel hull depicted in  FIG. 2A . 
           [0019]      FIG. 3  shows a front view drawing of a first transducer for use in a system for wireless communications through a sea vessel hull according to a third embodiment of the present invention. 
           [0020]      FIG. 4  shows a front view drawing of a first transducer for use in a system for wireless communications through a sea vessel hull according to a fourth embodiment of the present invention. 
           [0021]      FIG. 5  shows a drawing of a system for wireless communications through a sea vessel hull according to a fifth embodiment of the present invention comprising a transmitter a receiver and first and second inductive transducers. 
           [0022]      FIG. 6  shows a drawing of a system for wireless communications through a sea vessel hull according to a sixth embodiment of the present invention comprising a transmitter a receiver and an inductive transducer. 
           [0023]      FIG. 7  shows a prior art drawing of a pressure hull gland for use in the systems for communications through sea vessel hulls according to the present invention. 
           [0024]      FIG. 8  shows a prior art arrangement for inductive coupling between first and second coils wound on opposing sides of a annular or toroidal core. 
           [0025]      FIG. 9  shows a current coupling mechanism comprising first and second toroidal cores each having coils wound thereon and further comprising an electrically conducting rod threading both cores. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    According to a first aspect, the present invention provides a system for wireless communications through an electrically conductive hull of a sea vessel comprising: a first transmitter, located on a first side of said hull and comprising a first inductive transducer, a first receiver located on a second side of said hull and comprising a second inductive transducer, an access point penetrating said hull from said first side to said second side; wherein, during operation, said access point of said hull provides a path for coupling electric and/or magnetic signals from said first transmitter to said first receiver through said sea vessel hull via said first and second inductive transducers. 
         [0027]    In some embodiments, the system of the present invention further comprises a second transmitter located on said second side of said hull, and a second receiver located on said first side of said hull, said first transmitter and receiver and said second transmitter and receiver providing two way communications and/or data transfer through said sea vessel hull via said first and said second inductive transducers. Said first transmitter and said second receiver are may be connected to said first inductive transducer via a switch, similarly, said second transmitter and said first receiver are may be connected to said second inductive transducer via a switch. 
         [0028]    In some embodiments, at least one of said first and second inductive transducers is divided into two sub-sections so that said at least one inductive transducer can be mounted around an elongate protrusion from said access point. 
         [0029]    In one embodiment, each said first and said second inductive transducers comprises a respective first and second annular core where said first inductive transducer comprises an associated transducer coil wound around a portion of said first annular core and said second inductive transducer comprises an associated transducer coil wound around a portion of said second annular core. At least one of said first and second annular cores may be a toroidal core. Preferably, at least one of said first and second annular cores further comprises two sub-sections which, in use, are assembled around said access point so that a protruding cable of said access point passes through the centre of said at least one annular core. Separate associated transducer coils may be wound around each sub-section of said at least one annular core. Preferably, said access point comprises a cable gland feeding at least one cable from said first side to said second side of said hull. Said access point may also comprise a flange of an electrically non-conductive material. 
         [0030]    During operation, input signals of said first transducer are electrically coupled to said second transducer via said at least one cable. In some embodiments, signals of said first transducer are electrically coupled to said second transducer via a metal screen of said at least one cable. At least one of said first and second annular cores may be formed of a material having a high magnetic permeability. 
         [0031]    In another embodiment at least one of said first and said second inductive transducers comprises a core having first and second sides and further comprises an inner annular portion, an outer annular portion concentric with said inner annular portion, and a flange portion bridging said inner and said outer annular portions at said first sides of said core. Preferably, said core is formed of a material having a high magnetic permeability. Said core may comprise two sub-sections which, in use are assembled around said access point. 
         [0032]    Preferably, a transducer coil is formed around said inner annular portion of said core. Said transducer coil may further comprise pairs of mateable connectors at opposite sides thereof so that said coil can be mounted over an elongate protrusion from said access point. 
         [0033]    During operation input signals of said first transducer are magnetically coupled to said second transducer via a flange of said access point formed of an electrically non-conductive material. Said second side of said core may be arranged so that it is flush against said sea vessel hull. 
         [0034]    In some embodiments, the system for wireless communications of the present invention, further comprises an input device for inputting control, communications and/or data signals to said first transmitter. 
         [0035]    In some embodiments, the system for wireless communications of the present invention, further comprises an output device for outputting control, communications and/or data signals received by said first receiver from said first transmitter. 
         [0036]    Electrical signals can be inductively coupled from a first transducer coil to a second transducer coil via induced magnetic fields even when there is no direct contact between the coils of the transducers. For example, the induced magnetic fields may be coupled between the transducers via a common core of both transducers. Such an arrangement is the basis upon which an electrical transformer operates. The core of a transformer has a wide range of alternative designs options; an annular core, having one or more elongated sections, connecting together and forming a closed loop is one such option. A toroidal core which is formed by rotation of a 2D cross section through 360 degrees about an axis which does not intersect the 2D cross section is another option. 
         [0037]    A common material for use in magnetic cores is ferrite. For example, transformers comprising ferrite cores are used in applications having frequencies over a very wide range. Limiting values for operation of ferrite cores range from a lower extreme of approximately 1 Hz, to an upper extreme of approximately 100 MHz. 
         [0038]    In the simplest embodiment, an inductive coupling mechanism comprises first and second coils would on opposing sides of an annular or toroidal core.  FIG. 8  shows such an arrangement. The toroidal core  810  provides a path for a magnetic field induced by the first coil  822  so the field also threads through the second coil  872 . In operation, an alternating current in the first coil  822  induces an alternating magnetic field in the core  810 . The same alternating magnetic field passes through the second coil  872  via the core  810 . From Faraday&#39;s law of electromagnetic induction, an alternating magnetic field threading a coil produces an alternating current in the coil; thus, an alternating current is produced in the second coil  872 . The ratio of the current in the first and second coils is determined by the number of windings in each coil and the efficiency of coupling the magnetic field induced by the first coil to the second coil. 
         [0039]    Magnetic fields can also be coupled between first and second inductive elements which are physically separated and which do not share a common core. The degree of coupling depends mostly on the geometry and nature of the material between the coils. Magnetic fields always form a closed path, and substantially follow the path offering the lowest magnetic reluctance. 
         [0040]    According to a similar analysis, magnetic signals can be coupled from a first transducer to a second transducer via induced currents even when there is no direct contact between the pair of transducers. 
         [0041]    Circular magnetic fields in an annular or toroidal core may be coupled between a pair of transducers via a conducting rod which threads both transducers. For example, a current coupling mechanism might comprise first and second coils would on first and second toroidal cores and having an electrically conducting rod which threads both cores.  FIG. 9  shows such an arrangement; the electrically conducting rod  942  which threads both toroidal cores  910 ,  960  provides a path for a coupled electrical current I. In operation, an alternating current in the first coil  922  induces a circular magnetic field in the first core B, this induces an alternating current in the electrically conducting rod  942 . The alternating current in the electrically conducting rod  942  produces a corresponding circular alternating magnetic field in the second toroidal core  960 , and this alternating field threading the second toroidal core  960  produces an alternating current in the second coil  972 . The ratio of the current in the first and second coils  922 ,  972  is determined by the number of windings in each coil and the efficiency of coupling between the magnetic field in the first core to the electrically conductive wire. 
         [0042]    Coupling of a magnetic field through a sea vessel hull is difficult to achieve due to the typically conductive material used for the hull. A magnetic field induced by a first coil located on one side of the hull, will find a low reluctance closed path via the core of the first coil and back via the ferrous hull. However, magnetic fields can be coupled from a first side of a sea vessel hull to the second side through the sea vessel hull if the low reluctance path for magnetic fields via the ferrous hull is eliminated. A penetration in the sea vessel hull provides just such a path if the cores of the transducers located on opposing sides of the hull are carefully designed. 
         [0043]      FIG. 1A  shows a side view drawing of a system for wireless communications through a sea vessel hull  190  according to a first embodiment of the present invention. The generic term communications here and elsewhere implicitly refers to any or all of: transmission and/or reception of communications signals, transmission and/or reception of control signals and transmission and/or reception of data. 
         [0044]    The system of  FIG. 1A  comprises a first transducer  101  comprising a first transducer coil  122  formed over a magnetic permeable toroidal core  110 . First transducer coil  122  is wound of electrically conductive wire having an electrically insulating outer coating. First transducer coil  122  comprises input terminals  121 A,  121 B across which a voltage differential V may be applied. First transducer  101  is located so that the plane of toroidal core  110  is parallel to the plane of sea vessel hull  190 . During use, one side of toroidal core  101  is positioned so that it is close to or flush against sea vessel hull  190  and so that the centre axis of toroidal core  110  intersects the centre point of pressure hull gland  140 . Pressure hull gland  140  comprises flange  141  and cable bundle  142  which penetrates flange  141 . 
         [0045]    A second transducer  151  is positioned on the opposite side of sea vessel hull  190 , and is in register with first transducer  101 . Second transducer  151  comprises a second transducer coil  172  formed over a toroidal core  160 . Second transducer coil  172  comprises output terminals  171 A,  171 B. 
         [0046]    First and second toroidal cores  110 ,  160  may be formed from a wide range of alternative materials. A material having a high relative magnetic permeability is preferable. One specific material which may be used for magnetic cores  110 ,  160  is ferrite. Ferrite is commonly used for transformer and inductor cores because of its high magnetic permeability. Ferrite is suitable for use in applications requiring the coupling of magnetic fields having frequencies ranging from a lower extreme of approximately 1 Hz, to an upper extreme of approximately 100 MHz. 
         [0047]      FIG. 1B  shows a front view drawing of first transducer  101  according to the system for wireless communications through a sea vessel hull embodying the present invention and depicted in  FIG. 1A . 
         [0048]    Toroidal core  110  is split into two identical sub-sections  112 ,  114 . To assemble toroidal core  110 , the two sections  112 ,  114  are affixed to each other by threaded screw  116 . The two sections  112 ,  114  of toroidal core  110  may alternatively be fixed to each other by an alternative means. 
         [0049]    When assembled, transducer  101  fits around a pressure hull gland  140  of sea vessel hull  190  ( FIG. 1A ). Pressure hull gland comprises flange  141  and cable bundle  142  which penetrates flange  141 . The split structure of toroidal core  110  comprising sections  112 ,  114  enables first transducer  101  to be assembled so that it fits around an existing cable which protrudes from cable gland  140  and which penetrates sea vessel hull  190 . Thus, first transducer  101  can be deployed around pressure hull gland  140  without any modification thereof, without any modification of the cable bundle  142  passing through pressure hull gland  140  or without any modification of the sea vessel hull  190 . 
         [0050]    First transducer coil  122  is wound around one of the two sections  112 ,  114  of toroidal core  110  and is formed of electrically conductive wire having an insulating coating. A current entering first transducer coil  122  at terminal  121 A, and exiting at terminal  121 B, induces a magnetic field in toroidal core  110  which follows the path and direction of magnetic field lines  130 . 
         [0051]    Cable bundle  142  may comprise several cables, but nonetheless occupies only a portion of the area occupied by flange  141  of pressure hull gland  140 . Ideally, cable bundle  142  comprises one or more screened cables. 
         [0052]    In use, an electrical signal is fed to port P 11  of first transducer  101 . The electrical signal induces a circular magnetic field in first transducer core  110 , which induces a corresponding electrical signal in the screen of at least one of cable bundle  142 . The current flowing in the screen of at least one of cable bundle  142  induces a circular magnetic field in second transducer core  160  ( FIG. 1A ). This, in turn, induces a current in second transducer coil  172 , which may be detected using conventional electronic communications equipment. Input electrical signals may have carrier frequencies ranging from 1 Hz, to 100 MHz. 
         [0053]    The one or more screened cables of cable bundle  142  are ideally grounded on the inside and on the outside of sea vessel hull  190 . For example, one or more of the cables of cable bundle  142  may be grounded either directly to earth or indirectly via the electrically conductive sea water on the outside of the hull, and may also be grounded to the vessel hull at some point on the inside thereof. Direct or indirect grounding of one or more of cable bundle  142  provides an improved coupling of electrical signals from first transducer  101  to second transducer  151 . 
         [0054]      FIG. 1C  shows a front view drawing of first transducer  101  according to the system for wireless communications through a sea vessel hull depicted in  FIG. 1A  comprising a pair of associated transducer coils. 
         [0055]    The transducer depicted in  FIG. 1C  is identical to that of  FIG. 18 , except that a pair of associated transducer coils  122 ,  127  are provided instead of the single transducer coil  122  for the transducer shown in  FIG. 1B . Transducer coil  127  comprises input terminals  126 A,  126 B, across which a voltage differential V may be applied. In use, electrical signals are fed to terminals  121 A,  1218  and  126 A,  126 B so that magnetic field lines  130  produced by each of associated transducer coils  122 ,  127  are aligned. 
         [0056]    Passing electrical currents through of a pair of transducer coils  122 ,  127  as shown in  FIG. 10  provides an increased magnetic field inside toroidal core  110 , when compared with a transducer comprising only a single coil  122  ( FIG. 1B ). 
         [0057]      FIG. 2A  shows a side view drawing of a system for wireless communications through a sea vessel hull according to a second embodiment the present invention. 
         [0058]    The system of  FIG. 2A  comprises a first transducer  201 . First transducer  201  comprises a first transducer coil  222  formed of electrically conductive wire and having an electrically insulating outer coating. Coil  222  is wound over a portion of magnetic permeable annular core  210 . 
         [0059]    Annular core  210  has a first side S 1  and a second side S 2 , both sides S 1 , S 2  being perpendicular to a central axis of annular core  210 . First side S 1  faces away from sea vessel hull  290 , and second side S 2  faces towards sea vessel hull  290 . Annular core  210  comprises three sections: an inner annular portion  215 , an outer annular portion  217  and a flange portion  216 . Flange portion  216  bridges between inner annular portion  215  and outer annular portion  217  at the first side S 1  of annular core  210 . 
         [0060]    Annular core  260 , similarly, has a first side and a second side (not shown), both sides being perpendicular to a central axis of annular core  260  where the first side faces away from sea vessel hull  290 , and the second side faces towards sea vessel hull  290 . Annular core  260  comprises three sections: an inner annular portion  265 , an outer annular portion  267  and a flange portion  266 . Flange portion  266  bridges between inner annular portion  265  and outer annular portion  267  at the first side of annular core  260 . 
         [0061]    In use, first transducer  201  is positioned so that the first side S 1  is parallel to the plane of sea vessel hull  290  and is close to or is flush against sea vessel hull  290 . First transducer  201  is optimally positioned when a central axis of annular core  210  intersects the centre point of pressure hull gland  240 . Pressure hull gland  240  comprises flange  241  and cable bundle  242  which penetrates flange  241  and which similarly penetrates sea vessel hull  290 . In general, the material of flange  241  is a poor conductor of electricity. Flange  241  may be formed of an electrically insulating material such as polyethylene. 
         [0062]    First transducer coil  222  comprises input terminals  221 A,  221 B across which a voltage differential V may be applied. 
         [0063]    In use, a time varying electrical signal is fed to port P 21  of first transducer  201 . The electrical signal induces an alternating magnetic field H in annular core  210  of first transducer  201 , which couples to annular core  260  of second transducer  251 . The alternating magnetic field in annular core  260 , induces an alternating current in second transducer coil  272 . This current in second transducer coil  272  may be received and/or detected using conventional electronic communications equipment. 
         [0064]      FIG. 2B  shows a front view drawing of first transducer  201  according to the system for wireless communications through a sea vessel hull embodying the present invention and depicted in  FIG. 2A . 
         [0065]    A current entering first transducer coil  222  at terminal  221 A, and exiting at terminal  221 B, produces a magnetic field (not shown) following a path which is perpendicular to and directed towards the plane of the drawing. 
         [0066]    The induced magnetic field follows a path through the electrically insulating material of flange  241  to annular core ( 260   FIG. 2A ) of second transducer ( 251   FIG. 2A ) located on the far side of sea vessel hull  290 . 
         [0067]      FIG. 3  shows a front view drawing of first transducer  301  for use in a system for wireless communications through a sea vessel hull according to a third embodiment of the present invention. 
         [0068]    Annular core  310  of  FIG. 3  comprises three portions: an inner annular portion  315 , an outer annular portion  317  and a flange portion (not shown) which bridges between inner annular portion  315  and outer annular portion  317 . 
         [0069]    Annular core  310  further can be divided into a pair of substantially equal sub-sections: first section  312  and second section  314 . First section  312  and second section  314  may be secured together by a fixing bolt (not shown). 
         [0070]    Transducer coil  322  is wound around inner annular portion  315  of annular core  310 . Transducer coil  322  is formed of electrically conductive wire having an electrically insulating outer coating. Transducer coil  322  comprises input terminals  321 A,  321 B across which a voltage differential V may be applied. 
         [0071]    Transducer coil  322  further comprises a first plug and socket pair  328 A,  3286  and a second plug and socket pair  329 A,  3298 . Each plug and socket pair  328 A,  328 B and  328 A,  328 B is disposed at opposing sides of transducer coil  322 . Plug and socket pairs  328 A,  328 B and  328 A,  328 B facilitate the separation of transducer coil  322  into two sections which can be clamped around a pressure hull gland of a sea vessel hull. Advantageously, each plug and socket pair  328 A,  328 B and  328 A,  328 B of transducer coil  322  are designed so that when fitted together they exclude water. 
         [0072]    Transducer  301  is fixed around pressure hull gland comprising flange  341  and cable bundle  342  which penetrates a sea vessel hull. Transducer  301  is optimally positioned when a central axis of annular core  310  intersects the centers of pressure hull gland flange  341  and cable bundle  342 . 
         [0073]    Transducer  301  might be used, for example, as one part of a communications system, comprising transducer  201  of  FIG. 2A  and  FIG. 2B . For example, transducer  301  could be clamped around pressure hull gland  240  of  FIG. 2A  of the present invention in place of transducer  201 . Alternatively, a system for wireless communications through a sea vessel hull might comprise a pair of transducers  301  positioned on opposite sides of the hull, each transducer being positioned around a pressure hull gland. 
         [0074]      FIG. 4  shows a front view drawing of first transducer  401  for use in a system for wireless communications through a sea vessel hull according to a fourth embodiment of the present invention. 
         [0075]    Transducer  401  comprises annular core  410  which can be divided into a pair of substantially equal sections: first section  412  and second section  414 . First section  412  and second section  414  of annular core  410  may be secured together by a fixing bolt or some other securing means (not shown). 
         [0076]    Transducer  401  further comprises first transducer coil  422  and second transducer coil  427 . First transducer coil  422  and second transducer coil  427  are respectively wound over inner annular portions of first core section  412  and second core section  414  of magnetic permeable annular core  410 . Advantageously, during use, transducer coil  422  and second transducer coil  427  are electrically connected together in parallel. 
         [0077]    First and second transducer coils  422 ,  472  are wound of electrically conductive wire having an electrically insulating outer coating. First transducer coil  422  comprises input terminals  421 A,  421 B across which a voltage differential V may be applied. Second transducer coil  427  comprises input terminals  426 A,  426 B across which a voltage differential V may be applied. Voltages are applied to input terminals  421 A,  421 B of first coil  422  and to input terminals  426 A,  426 B of second coil  427  so that magnetic fields induced in the enclosed areas of each of first and second coils  422 ,  427  constructively interfere. The direction of current flow in transducer coils  422  and  427  is represented by arrows in  FIG. 4 . This arrangement ensures that induced magnetic field pass through the inner annular portions of first core section  412  and second core section  414 . The induced magnetic fields point in a direction which is perpendicular to the plane of  FIG. 4  and are represented by arrays of the letter X drawn inside the inner annular portions of first and second core sections  412  and  414 . 
         [0078]    In use, electrical signals are fed to input terminals  421 A and  421 B of first transducer coil and input terminals  461 A and  462 B of second transducer coil  427 . The magnetic fields induced in the inner annular portions of first core section  412  and second core section  414  are coupled to a core of second transducer located on the opposite side of a sea vessel hull (not shown). The induced magnetic field follows a path through a pressure hull gland (not shown). 
         [0079]    Transducer  401  might be used, for example, as one part of a communications system, comprising transducer  201  of  FIG. 2A  and  FIG. 2B . Alternatively, a system for wireless communications through a sea vessel hull might comprise a pair of transducers  401  positioned on opposite sides of the hull, each transducer being positioned around a pressure hull gland. 
         [0080]      FIG. 5  shows a drawing of a system for wireless communications through a sea vessel hull according to a fifth embodiment of the present invention comprising a transmitter  53  a receiver  58  and respective first and second inductive transducers  501 ,  551 . The system further comprises a pressure hull gland  540 , having a flange  541  of an electrically non-conductive material, and a cable bundle  542  passing through pressure hull gland  540 . Inductive transducer  501  is electrically connected to transmitter  53  and inductive transducer  551  is electrically connected receiver  58 . 
         [0081]    Transmitter  53  comprises an input port  530 . Input signals fed to input port  530  may comprise any of voice or video signals, images, control signals or data. A suitable input device (not shown), which provides voice signals, video signals, images, control signals or data signals, as appropriate is connected to input port  530 . Such input devices are well known to those skilled in the art. 
         [0082]    During operation, an input signal is passed to processor  531  where it is encoded and modulated for transmission in accordance with the transmission system to be used. The encoded signal is output from processor  531 , where it is fed to mixer  532 , to be mixed with a signal generated by local oscillator  533  for frequency up-conversion. The frequency up-converted signal is then amplified by amplifier  534  and fed to first transducer  501 . 
         [0083]    First transducer  501  comprises annular core  510 , and associated coil  522 . Second transducer  551  comprises annular core  560 , and associated coil  572 . First transducer  501  is placed near or adjacent to sea-vessel hull  590 , and is assembled around a pressure hull gland  540 , so that a cable  542  protruding from pressure hull gland threads the centre of annular core  510 . The input signal fed to transducer  501  induces an alternating magnetic field in core  510 , which, in turn, induces an alternating current in one or more of the cables in cable bundle  542 . 
         [0084]    The alternating current induced in cable bundle  542  induces a corresponding signal in second transducer  551  which is received by receiver  58 . Thus, transmission and reception of the input signal is by means of electrical coupling of the signal in one or more of the cables in cable bundle  542  and is via a path through pressure hull gland  540 . 
         [0085]    The signal which is received by transducer  551 , is passed to amplifier  586 . The amplified signal is fed to mixer  587 , to be mixed with another signal generated by local oscillator  588  for frequency down conversion. The down converted data signal is then passed to processor  589  where it is demodulated and decoded and output at output port  685 . 
         [0086]    Receiver  58  also comprises an output port  585 . A suitable output device (not shown), which outputs voice signals, video signals, images, control signals or data signals, as appropriate and as would be known to a person skilled in the art, is connected to output port  655 . Output signals might comprise any of voice or video signals, images, control signals or data. 
         [0087]    Input and output devices for use with the embodiment of the present invention depicted in  FIG. 5  might include, microphones, cameras, video cameras, personal computers, communications handsets, or any device which provides an input and/or output electrical signal. 
         [0088]      FIG. 6  shows a drawing of a system for wireless communications through a sea vessel hull according to a sixth embodiment of the present invention comprising a transmitter  63  a receiver  68  and an inductive transducer  601 . Inductive transducer  601  is connected to transmitter  63  and receiver  68  via switch  655 . In use, switch  655  is set to connect transmitter  63  with transducer  601  when signals are to be transmitter, and is set to connect receiver  64  to transducer  601  when signals are to be received. 
         [0089]    Transmitter  63  comprises an input port  630 . Input signals fed to input port  630  may comprise any of voice or video signals, images, control signals or data. A suitable input device (not shown), which provides voice signals, video signals, images, control signals or data signals, as appropriate is connected to input port  630 . Such input devices are well known to those skilled in the art. 
         [0090]    During operation, the input signal is passed to processor  631  where it is encoded and modulated for transmission in accordance with the transmission system to be used. The encoded signal is output from processor  631 , where it is fed to mixer  632 , to be mixed with a signal generated by local oscillator  633  for frequency up-conversion. The frequency up-converted signal is then amplified by amplifier  634  and fed to first transducer  601  via switch  655 . 
         [0091]    Receiver  68  comprises an output port  685 . Output signals might comprise any of voice or video signals, images, control signals or data according to the signal received by transducer  601 . A suitable output device (not shown), which outputs voice signals, video signals, images, control signals or data signals, as appropriate and as would be known to a person skilled in the art, is connected to output port  685 . 
         [0092]    During operation, a signal is received by transducer  601 , is passed to amplifier  686  via switch  655  where it is amplified. The amplified signal is fed to mixer  687 , to be mixed with a signal generated by local oscillator  688  for frequency down conversion. The down converted data signal is then passed to processor  689  where it is demodulated and decoded and output at output port  685 . 
         [0093]    First transducer  601  comprises annular core  610 , and associated coil  622 . During operation, first transducer  601  is placed near or adjacent to sea-vessel hull  690 , and is assembled around a pressure hull gland  640 , so that a cable  642  protruding from pressure hull gland threads the centre of annular core  610 . The alternating signals fed to transducer  610  induce alternating magnetic fields in core  610 , which, in turn, induce alternating currents in cable  642 . 
         [0094]      FIG. 7  shows a prior art drawing of a pressure hull gland  710  for use in the systems for wireless communications through sea vessel hulls according to the present invention. Pressure hull gland has a high pressure side and a low pressure side. The high pressure side can withstand the high pressures that exist on the outside of a sea vessel hull which is submerged well below the surface of the sea. 
         [0095]    Passing through the centre of pressure hull gland  710  is a cable gland  742 , which accommodates one or more cables. Cables which pass through cable gland  742  may include: cables carrying electrical data signals, cables carrying electrical control signals or cables carrying communications signals. 
         [0096]    A main body of pressure hull gland  741  is formed of an electrically non-conducting material. A suitable material for the main body of pressure hull gland  741  is polyethylene. Pressure hull gland  710  additionally comprises a threaded flange  724  and an O-ring  725 . Threaded flange  724  and O-ring  725  provide a water tight seal in the hull of the sea vessel where pressure hull gland  710  is installed. 
         [0097]    The systems for communications through sea vessel hulls of the present invention are particularly suited to underwater communications and/or data transfer by electric and/or magnetic signals having frequencies in the range from 1 Hz to 100 MHz. 
         [0098]    Thus, the present invention, embodied in the various figures and descriptions described herein, provides a system for wireless communications, data and/or control signal transmission through a sea vessel hull by coupling of electric and or magnetic signals through the hull via existing pressure hull glands penetrating the hull. The system of the present invention can be deployed on the sea vessel hull without any modification thereof. Moreover, the system of the present invention is capable of providing high data rate and high bandwidth communications and/or data transfer through the sea vessel hull. 
         [0099]    The descriptions of the specific embodiments herein are made by way of example only and not for the purposes of limitation. It will be obvious to a person skilled in the art that in order to achieve some or most of the advantages of the present invention, practical implementations may not necessarily be exactly as exemplified and can include variations within the scope of the present invention.