Patent Publication Number: US-7218571-B2

Title: Magnetically driven underwater pulse generator

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention was made with United States Government support under Contract No. N00174-03-C-0046 awarded by DARPA. The United States Government has certain rights in this invention. 
    
    
     BACKGROUND 
     The present invention is directed to an apparatus and method for counteracting and defeating underwater threats posed to surface ships, submarines, marine facilities and underwater installations, specifically, those threats posed by objects such as torpedoes, underwater mines, explosives and hostile demolition personnel. In particular, the invention relates to an apparatus and method for generating high pressure shock waves that are capable of disabling or destroying underwater threats. 
     Marine assets are critical in maintaining both a viable military defense and a viable national economy. The ability to safely station and maneuver surface ships and submarines within a threat environment is critical to the success of a naval component of a national defense program. Similarly, marine facilities such as ports, underwater communication lines, drilling rigs and underwater pipelines are crucial to maintaining a viable national economy. Surface ships, submarines, ports and underwater installations, however, are susceptible to a variety of marine weapon systems including torpedoes, underwater mines, and explosives as well as hostile underwater demolition personnel. Thus, the protection of these assets is critical with respect to both military and economic defense programs. 
     A conventional method of countering a marine attack is to detect the presence of an incoming threat in sufficient time to launch a counter attack, and then to respond in kind with conventional weapons in an attempt to destroy the incoming threat. Although various conventional counter measure weapons may be employed, such counter measure weapons generally rely on conventional explosive ordinance that must be carried by the very ships that must be defended. The amount of ordinance that can be carried for the purpose of self-defense on a ship is limited, however, thereby necessitating a trade off between the offensive ability of a ship versus the ship&#39;s own self-defense capability. Further, conventional counter measure weapons require sophisticated firing control mechanisms to enable rapid target acquisition, and—given the limited amount of reaction time available after threat detection—such systems are necessarily susceptible to targeting errors that could prove detrimental or even fatal. Finally, the use of conventional explosives limits the possibility of a defense system that periodically fires to prevent infiltration, which would eliminate the need for sophisticated detection technology. For example, it is not practical to have large periodic conventional explosions occurring in a commercial port. Accordingly, conventional explosive ordinance defense systems are fired only when an actual threat has been detected, which in some cases may be too late for an effective response. 
     In view of the above, it would be desirable to provide an apparatus and method for counteracting and defeating underwater threats posed to surface ships and submarines without require the use of conventional explosives. It would further be desirable to provide an apparatus and method for defeating underwater threats that would allow for systematic and periodic firing to prevent infiltration of a marine threat. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus and method for counteracting and defeating underwater threats posed to surface ships, submarines, ports and underwater installations. Specifically, an apparatus and method for magnetically generating an underwater high pressure pulse of sufficient strength to destroy underwater threats utilizes a pair of electrically conductive elements. The electrically conductive elements are arranged substantially parallel with each other and are separated by a gap. A pulse generator supplies an electrical pulse to at least one of the electrically conductive elements, which causes the generation of a magnetic repulsion force between the elements. The magnetic repulsion force causes at least one the electrically conductive elements to be displaced; thereby inducing a high pressure pulse in the liquid in which the pair of electrically conductive elements are submerged. The conductive elements are returned to their initial positions after the electrical pulse dissipates. 
     The electrically conductive elements may comprise a variety of different elements. For example, in one preferred embodiment, at least one of the electrically conductive elements comprises a plate. In other preferred embodiments, at least one of the electrically conductive elements comprises a coil. Still other configurations and alternatives are possible, and will become apparent to those skilled in the art from the following detailed description of the preferred embodiments of the invention and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in greater detail with reference to certain preferred embodiments thereof and the accompanying drawings, wherein: 
         FIG. 1  is a schematic illustration of an apparatus in accordance with a first embodiment of the invention; 
         FIG. 2  is a circuit diagram of a pulse generator utilized in the apparatus illustrated in  FIG. 1 ; 
         FIG. 3  is a schematic illustration of an embodiment of the invention that utilizes an array of conductive plate pairs; 
         FIG. 4  is a schematic illustration of an embodiment of the invention that utilizes plates configured in a solenoid arrangement; 
         FIG. 5  is a schematic illustration of a further embodiment of the invention that utilizes inductively coupled coils; 
         FIG. 6  is a schematic illustration of a still further embodiment of the invention that utilizes a DC coil; 
         FIG. 7  is an electrical schematic diagram of a further embodiment of a pulse generator to be employed in the present invention; 
         FIG. 8  is a cut away perspective view of a device in accordance with the invention in which a moveable plate is shown in an initial position; 
         FIG. 9  is a cut away perspective view of a device in accordance with the invention in which a moveable plate is shown displaced from a corresponding fixed coil; 
         FIG. 10  is a graph illustrating voltage vs. time of a pulse applied to the device of  FIG. 8 ; 
         FIG. 11  is a graph illustrating current vs. time of a pulse applied to the device of  FIG. 8 ; 
         FIG. 12  is a graph illustrating pressure vs. time of a pulse generated by the device of  FIG. 8 ; 
         FIG. 13  is a graph illustrating plate velocity vs. time of a pulse generated by the device of  FIG. 8 ; 
         FIG. 14  is a graph illustrating peak pressure and efficiency vs. bank voltage of the device illustrated in  FIG. 8 ; and 
         FIG. 15  is a graph illustrating peak pressure vs. time for a pulse generated by the device of  FIG. 8  having a voltage of 10 kV. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A magnetically driven underwater pressure pulse generator  10  in accordance with the present invention is schematically illustrated in  FIG. 1 . As shown in  FIG. 1 , a moveable electrically conductive plate  11  is positioned substantially parallel to a fixed electrically conductive plate  12  in a manner that provides a separation gap  13  between the movable electrically conductive plate  11  and the fixed electrically conductive plate  12 . The movable electrically conductive plate  11  and the fixed electrically conductive plate  12  form an electrically conductive plate pair. An electrical connection  14  is placed in contact with the movable electrically conductive plate  11  and with the fixed electrically conductive plate  12 , so as to allow current to flow between the movable electrically conductive plate  11  and the fixed electrically conductive plate  12 . An electrical insulator  15  is placed within the separation gap  13 . An electrically insulating mechanical edge connection  16  is placed at the edges of the movable electrically conductive plate  111  and the fixed conductive plate  12 , so as to allow the movable electrically conductive plate  11  to be displaced vertically with respect to the fixed electrically conductive plate  12 . The edge connection  16  essentially holds the combined structure together while allowing for the displacement of the conductive plate  11 . 
     An electric pulse generator  20  is electrically connected to both the movable electrically conductive plate  11  and the fixed electrically conductive plate  12  by electrical connection  17  and electrical connection  18  respectively. An electrical circuit design of one preferred embodiment of the electric pulse generator  20  is depicted in  FIG. 2 . A capacitor bank  22  is preferably connected in parallel with a diode array  24 . A switch  26  is connected in series with the capacitor bank  22 , and is used to connect the capacitor bank  22  with the electrical connection  17  associated with the movably electrically conductive plate  11  shown in  FIG. 1 . 
     The magnetically driven underwater pressure pulse generator  10  functions by propagating a high pressure shock wave through the water in which it is submerged. The manner by which the shock wave is generated can be best understood with reference to  FIG. 1  and  FIG. 2 . Referring first to the electric pulse generator  20  of  FIG. 2 , pulse initiation occurs by closing the switch  26  to complete the electrical circuit, which results in the discharge of the capacitor bank  22 . In the illustrated preferred embodiment, the switch  26  is an ignitron tube (but other devices such as solid state or vacuum switches may be employed), and the capacitor bank  22  may consist of a single capacitor or multiple capacitors connected in parallel. The discharge produces a current pulse through the electrical connection  17  to the movable electrically conductive plate  11 . The diode array  24 , which may be composed of a single diode or of multiple diodes connected in parallel, is used to shape the electrical current pulse generated by the discharge of the capacitor bank  22 . Accordingly, the high pressure pulse produced by the magnetically driven underwater pressure pulse generator  10  is shaped based on the shaping of the electrical current pulse. 
     Referring to  FIG. 1 , the current pulse is transmitted via connection  17  to the movable electrically conductive plate  11 . The current pulse flows through the movable electrically conductive plate  11  and is transmitted to the fixed electrically conductive plate  12  via the electrical connection  14 . The current flow in the fixed electrically conductive plate  12  is oriented in a direction opposite to the current flow in the moveable electrically conductive plate  11 , which results in a magnetic repulsion force being generated between the electrically conductive plate  11  and the fixed electrically conductive plate  12 . The magnetic repulsion force causes the electrically conductive plate  11  to be displaced away from the electrically conductively plate  12  and against the water in which the device is placed. Accordingly, in this embodiment, the electrically conductive plate  11  is the “active” side of the device that induces a pressure pulse in the water. Namely, the displacement of the electrically conductive plate  11  due to the magnetic repulsion force in turn induces a high pressure shock wave in the water. 
     As noted above, the electrically insulating edge connections  16  are designed to allow for the displacement of the movable electrically conductive plate  11 . In the preferred illustrated embodiment, the electrically insulating edge connections  16  are arranged to create a vacuum between the movable electrically conductive plate  11  and the fixed electrically conductive plate  12  when the movable electrically conductive plate  11  is displaced. The vacuum causes the movable electrically conductive plate  11  to return to its original position after displacement, thereby restoring the separation gap  13  to its initial distance. 
     In the embodiment described above, the capacitor bank  22  and the diode array  24 , in conjunction with the inductance of the movable electrically conductive plate  11  and the fixed electrically conductive plate  12 , combine to form a pressure pulse with an abrupt beginning and a long exponential tail. The pressure pulse is similar to a pressure pulse generated by an underwater explosion caused by conventional explosives, and is sufficient to severely damage or destroy underwater threats of the type discussed above. Namely, the shock wave causes the detonation or crushing of underwater mines and torpedoes while incapacitating personnel under the water. Pulse shapes of other forms may be obtained by varying the arrangement of the capacitor bank  22 . 
     It is preferable that the stray capacitance be kept to a minimum, as the stray inductance of the circuit impacts the shape of the pressure pulse generated. Likewise the efficiency of the device is impacted by the stray resistance of the circuit and the resistance of the movable electrically conductive plate  12  and fixed electrically conductive plate  11 . In a preferred embodiment, in order to minimize the resistance, the movable electrically conductive plate  111  and the fixed electrically conductive plate  12  are made of copper, with a thickness that is several electrical skin depths thick. In alternative embodiments, the movable electrically conductive plate  12  and fixed electrically conductive plate  11  may be made from other conductors such as aluminum. 
       FIG. 3  illustrates a further embodiment of the invention in which the single pair of the movable electrically conductive plate  11  and fixed electrically conductive plates  12  of the embodiment of  FIG. 1  is replaced with an array of electrically conductive plate pairs. Each of the electrically conductive plate pairs includes a movable electrically conductive plate  31  and a fixed electrically conductive plate  32 . The movable electrically conductive plate  31  is electrically connected with its paired fixed electrically conductive plate  32  via connection  34 . The fixed electrically conductive plate  32  of one pair is connected with the movable electrically conductive plate  31  of a separate pair by connection  35 , so as to allow current to flow through all pairs contained in the array. The array pairs are connected with an electric pulse generator (not shown) via electrical connection  37  and electrical connection  38  (corresponding to electrical connection  17  and electrical connector  18  of  FIG. 1 ). The electrically insulating end connections and electrical insulator within the separation gap shown in  FIG. 1  are not repeated in subsequent embodiments in order to simplify the drawings, but will be understood as being present by those skilled in the art. The array of electrically conductive plate pairs illustrated in  FIG. 3  can be designed to generate a pressure pulse of desired shape, amplitude and propagation distance. 
     A further embodiment of the present invention is illustrated in  FIG. 4 . In this embodiment, pairs of movable electrically conductive plates  41  and fixed electrically conductive plates  42  are arrayed to form a flattened solenoid winding arrangement. Each movable electrically conductive plate  41  is positioned parallel to a fixed electrically conductive plate  42  with a gap there between, and is interconnected by electrical connections  42 . The flattened solenoid arrangement of electrically conductive plates  41  and  42  is electrically connected to an electric pulse generator (not shown) via electrical connections  47  and  48 .  FIG. 4  depicts a 4-turn solenoid arrangement. Each movable electrically conductive plate  41  is positioned parallel to a corresponding fixed electrically conductive plate  42 , and is displaced away from the fixed electrically conductive plate  42  due to a magnetic repulsion force generated when an electrical pulse is applied to the electrical connections  47 ,  48 . 
       FIG. 5  illustrates yet a further embodiment of the present invention. In this embodiment, the movable electrically conductive plate  11  and the fixed electrically conductive plate  12  of  FIG. 1  are replaced with inductively coupled electrically conductive movable pancake coils  51  and  52 , respectively. Elements  51  and  52  are individual strips of conductor arranged in spiral or coiled pattern. The movable electrically conductive pancake coil  51  is positioned parallel to the fixed electrically conductive pancake coil  52  and separated there from by a gap  53 . Only the fixed electrically conductive pancake coil  52  is connected to the electric pulse generator (not shown). Current in the fixed electrically conductive pancake coil  52  causes an inductive current to flow in the movable conductive pancake coil  51 , thereby resulting in magnetic repulsion that causes the movable electrically conductive pancake coil  51  to be displaced, thus generating a pressure pulse through the surrounding water. 
     A still further embodiment of the invention is depicted in  FIG. 6 . Here, the configuration is similar to  FIG. 5 , but instead of an inductively coupled pair of electrically conductive pancake coils  51 ,  52 , a direct current (DC) wired electrically conductive pancake coil  60  is configured to operate as a pair of parallel electrically conductive plates as shown in  FIG. 1 . The DC wired electrically conductive pancake coil  60  consists of a movable coiled portion  62  and a fixed coiled portion  64  separated by a gap  63 . The two ends of the DC wired electrically conductive pancake coil  60  are connected to an electric pulse generator (not shown). A current pulse through the DC wired electrically conductive pancake coil  60  generates the magnetic repulsion force necessary to cause the displacement of the movable coiled portion  62 , which in turn generates a pressure wave through the water. 
     In addition to various embodiments of the types of conductive elements that may be employed,  FIG. 7  illustrates an alternative circuit design for an electric pulse generator. In this embodiment, fuses  27  are include to protect the capacitor bank  22  from internal short circuits. An ignitron  26  (or functionally equivalent device) is used to switch the electric pulse generator ON. To affect a lower stray inductance and resistance in the circuit, twelve parallel coaxial cables  25  are used to transmit the pulse to the load. A diode array  26  is arranged on the load side rather than on the sourced side to further reduce the circuit losses. 
       FIG. 8  illustrates a working embodiment of the invention. As shown in  FIG. 8 , the device includes an outer tube or shroud  81  connected to a bottom support base  82 . An extending guide rode  83  is secured in the bottom support base  83 . A fixed electrical coil  84  is located within the bottom support base  82  and is covered by an insulator  85 . A moveable aluminum upper plate  86  is provided that slides over the extending guide rod  83  and fits within the shroud  81 . The aluminum upper plate  38  includes a coil that is inductively coupled to the fixed electrical coil  84  located within the bottom support base  82 . For example, a thin copper plate provided on the lower surface of the aluminum upper plate  38  is preferably utilized to effectively function as a one turn coil. 
     In operation, a voltage pulse is applied to the fixed electrical coil  84  via conductors  87  from a pulse generator (not shown). The application of the electrical pulse to the electrical coil  84  results in a magnetic repulsion force being generated between the electrical coil  84  and the moveable plate  86 . As a result, the moveable plate  86  is displaced with respect to the fixed electrical coil  84  (as illustrated in  FIG. 9 ), thereby inducing a shock wave into the water in which the device is submerged. It should be noted that the movement of the moveable plate  86  is greatly exaggerated in  FIG. 9  for purposes of illustration. In fact, the actual displacement of the plate is quite small while still inducing a large shock wave in the water. 
       FIGS. 10 and 11  respectively illustrate voltage and current waveforms for actual tests conducted using the device of  FIG. 8 . As shown in  FIG. 10 , a voltage pulse having an amplitude of approximately 3 kV and a duration of 0.5 msec was employed.  FIG. 11  illustrates the current waveform related to the voltage pulse illustrated in  FIG. 10 . The resulting pressure pulse is illustrated in  FIG. 12  along with a graph illustrating the plate velocity. In the illustrated example, a peak pressure of close to 400 psi was obtained. 
       FIG. 14  illustrates a graph showing how the peak pressure and efficiency will vary with the voltage utilized. As illustrated in  FIG. 14 , higher voltages can result in peak pressures in the ranges of thousands of psi.  FIG. 15  illustrates a test conducted using a voltage of 10 kv which resulted in a peak pressure of nearly 3000 psi within 0.5 msec, sufficient to cause a shock wave on the order of magnitude of an explosive charge. 
     It should be noted that an array of devices may be employed that function in a coherent manner to operate in a high pressure regime. For example, an array of devices may be controlled such that the individual activation of devices within the array causes a series of pressure pulses to be generated. The series of pulses may be timed and configured to have an accumulative effect upon reaching a certain range and/or location from the array. Accordingly, while each individual pulse may not in itself represent sufficient energy to incapacitate the threat, the accumulation of the energy of multiple pulses from multiple sources at a given point provides a sufficient destructive force. Accordingly, it is possible to focus or steer the location of the accumulated pulse to scan within a region. 
     As illustrated above, the invention provides an apparatus and method for generating an underwater pressure pulse sufficient to generate a shock wave equivalent to an explosive charge. Accordingly, the apparatus and method can be used to defeat underwater threats by inducing a shock wave capable of setting off underwater mines or incoming torpedoes, as well as disabling hostile demolition personnel. Since the invention does not use conventional explosives, it does not have the drawbacks of conventional anti-marine countermeasure systems. Further, the invention can be employed to protect stationary targets as well as ships in transit. Still further, the shock wave can be “fired” periodically with much less subsidiary damage than the use of conventional explosives. Accordingly, a system can be employed in which the shock wave is periodically generated regardless if a threat is actually detected, thereby providing enhanced security without the requirement for improved detection. 
     The invention has been described with reference to certain preferred embodiments thereof. It will be understood, however, that modifications and variations are possible within the scope of the appended claims.