Abstract:
An improvement in an electric armor system designed to prevent, among other things, a rocket-propelled grenade (RPG) from penetrating the hull of a fighting vehicle. The system includes a self-clearing electrode that will make the system less vulnerable to non-plasma objects that might otherwise short out the active armor electrodes. It optionally further allows for the early initiation of current flow at the point of penetration making it even easier to defeat incoming threats by allowing more time to break-up an incoming plasma jet.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. application Ser. No. 12/891,599, filed Sep. 27, 2010, which is a division of U.S. application Ser. No. 11/507,205, filed Aug. 11, 2006, now U.S. Pat. No. 7,819,050, issued Oct. 26, 2010, which claims priority from U.S. Provisional Application No. 60/479,976 filed Aug. 18, 2005, the disclosures of all of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to armaments and more particularly to reactive and active electric armor systems. 
     BRIEF DESCRIPTION OF PRIOR DEVELOPMENTS 
     The prior art discloses a number of various arrangements of active armor in which a medial layer is positioned between an outer and an inner armor layer with a medial explosive or non-explosive layer that is designed to disrupt a shaped charge to prevent penetration of the overall armor system. 
     It has previously been suggested that performance of active armor may be improved by providing a medial space between an outer and an inner armor layer and providing an electrical generator to create an electric or magnetic field in this medial space between the outer and inner armor layers that would disrupt a shaped charge gas jet to prevent armor penetration. U.S. Pat. No. 6,758,125 discloses an active armor system, which includes first and second armor layers with an interior space interposed therebetween and a third layer, preferably positioned adjacent to and on the inner side of the first layer, that is comprised of a piezoelectric material, an electrostrictive material, or a magnetostrictive material. The third layer is selected so as to be capable of producing an electrical or magnetic field within the space in response to the application of mechanical force on this third layer. The application of force on the third layer as a result of impact of a shaped charge projectile on the first armor layer is alleged to produce an electric or magnetic charge in the interior space that will disrupt the formation of the shaped charge gas jet so as to prevent the penetration of the second armor layer. 
     The results of such prior art constructions have not been satisfactory, so a need exists for an efficient active armor system in which an electrical field may be provided in a space exterior of a vehicle armored hull which is capable of protecting the hull against multiple incoming projectiles. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention provides an active armor system comprising at least two electrode plates wherein at least one of the electrode planes is constructed to be self-clearing. In another aspect, the invention provides an active armor system comprising inner and outer generally equidistantly spaced apart electrode plates and electrically joined to one of said plates a plurality of electrical conductors located between said two plates and that can provide an electrical connection between said plates for the purpose of effecting early initiation of current flow in the system. In a further aspect, the invention provides an active armor system which comprises an outer electrode, a group of individual panels arranged to constitute an inner electrode spaced from said outer electrode, a plurality of individual energy storage capacitors distributed throughout the system and connected to said individual panels, and self-clearing tabs which connect said individual capacitors to said outer electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a prior art electric armor system shown in association with an incoming rocket-propelled grenade (RPG). 
         FIG. 2   a  is a schematic representation of the prior art system of  FIG. 1  showing its penetration by two different elongated objects that are electrically conductive. 
         FIG. 2   b  is a schematic representation of an electric armor system embodying various features of the present invention which has also been penetrated by two elongated objects that are electrically conductive. 
         FIGS. 3   a  and  3   b  are fragmentary front views of a self-clearing electrode embodying various features of the invention shown prior to and subsequent to attack by a RPG. 
         FIGS. 4   a ,  4   b  and  4   c  are views similar to  FIG. 3   a  illustrating alternative embodiments of such electrodes incorporating various features of the invention. 
         FIG. 5   a  is a schematic view of an electric armor system generally similar to that shown in  FIG. 2   b  which incorporates an optional feature that promotes early initiation of current flow. 
         FIGS. 5   b  and  5   c  are similar views to  FIG. 5   a  which show the system of  FIG. 5   a  at the time of attack by a RPG and subsequent thereto. 
         FIGS. 6   a ,  6   b  and  6   c  are fragmentary front views taken respectively along the lines A-A of the respective  FIGS. 5   a ,  5   b  and  5   c.    
         FIGS. 7   a ,  7   b  and  7   c  are schematic illustrations of an alternative embodiment of an early initiation system generally similar to that shown in  FIGS. 5   a ,  5   b  and  5   c , with  FIG. 7   a  being a fragmentary side view,  FIG. 7   b  being a fragmentary perspective view, and  FIG. 7   c  being an isometric front view of an electrode embodying various features of the present invention. 
         FIGS. 8   a - 8   c  are views of another alternative embodiment of a self-clearing electrode for use in an active armor system wherein a plurality of independent capacitors are respectively carried on adjacent panels on an electrode of the type generally shown in  FIG. 5   a , with  FIG. 8   a  being an assembled view of one such capacitor assembly,  FIG. 8   b  being an exploded perspective view thereof and  FIG. 8   c  being a fragmentary perspective view of a portion of the electrode. 
         FIG. 9  is a schematic view, similar to  FIG. 5   a , of an alternative embodiment of an active armor system designed to promote early initiation of current flow. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The basic concept of electric armor is shown in  FIG. 1 . The hull of an armored vehicle  100  is protected from an incoming rocket-propelled grenade (RPG)  107  by two composite armor electrode layers which include electrodes  104  and  105  that are connected to an energy storage device, such as a capacitor  116 . In practice and prior art, the energy storage capacitor  116  is part of a pulse forming network complete with a charging power supply that is designed to defeat the threat. The electric armor electrodes  104  and  105  are mounted via non-conducting members  103  and  106  that provide mechanical structural support for the electrodes and electrical insulation from the other parts of the vehicle when required. The combination of an electrode and its associated member, which may be of a non-conducting ceramic, like alumina, or may be armor sheet material, e.g. aluminum or steel, with an electrically insulating layer or the like, constitute the inner and outer composite electrodes  101  and  102  of the electric armored system. 
     An RPG is typically made up of several individual parts including a rocket motor  110  and stabilizing fins  111 . The business end of the RPG generally consists of a copper cone  109  and a shaped charge  108 . On impact with the outer wall of the vehicle  106 , the shaped charge detonates (see  112 ) transitioning the copper cone  109  into a gas-jet or plasma penetrator  113  that penetrates the armor. 
     Once the extended plasma penetrator  114  stretches out such that it electrically connects the two electrodes  104  and  105 , the energy stored in the capacitor  116  is discharged through the plasma. This electrical discharge effectively breaks up the plasma  115  that is directed toward the vehicle hull  100  and has come in contact with the inner electrode  103 . The military utility of electric armor stems from the observation that the damage done to the hull by such a broken-up plasma is significantly less than the damage that would be done by the original plasma penetrator, allowing the hull to withstand the RPG hit. 
     There are two open regions in a typical set of active armor panels. The first is the active space  117  area between electrodes  104  and  105  where the plasma jet or projectile is being broken-up. During the breaking-up process, a blast of high pressure is felt in this region. The second open region is the drift space  118  where the broken-up and disoriented plasma is allowed to expand. 
     As shown in the cross section of an active armor system in  FIG. 2 , it may be possible to penetrate the relatively thin active armor layers  101  and  102  with an object  200  that is not a plasma. If such an object  200  is an electrical conductor, it will short out the active armor electrodes  104  and  105  and thus prevent the active armor system from continuing to function as intended. If a capacitor is charged up and connected to such a shorted-out electric armor system, the capacitor will simply discharge through the non-plasma conductor  200 . This effectively disables the electric armor system in the sense that the plasma penetrator produced by a subsequent incoming RPG would not be broken-up by the active armor system that is in the state shown in  FIG. 2   a.    
     It has been found that this performance shortcoming is overcome by the use of structures embodying features of applicant&#39;s invention, which may be termed a self-clearing electrode system. Shown in  FIG. 2   b  is one embodiment of such a self-clearing electrode  203 . By a self-clearing electrode  203  is meant one which inherently clears away or removes a region of the electrode in the area where the penetrator  200  strikes it. The pulse forming network associated with capacitor  116  is designed to produce a pulse that will defeat the threat. The self-clearing electrode is designed to allow this pulse to pass before becoming an open circuit. Typically the self-clearing electrode will open circuit at a current zero. This thus effectively removes the short circuit that would otherwise occur between electrodes  203  and  105 , and as a result, the circuit is able to charge up normally and be ready to defeat the next RPG that might attack the vehicle. 
       FIGS. 3   a  and  b  are fragmentary sectional views of this one embodiment of an electric armor self-clearing electrode  203  in which small individual panels  301  are interconnected to one another via fusible links  300 . Individual ones of these panels  301  are hereinafter referred to as numbers  302  and  303  for explanation of operation. These panels  301  would be made of conducting material, e.g. aluminum or conductive polymeric material and might be, e.g., 3 to 6 inch squares. They could be mounted in an insulating frame that would mechanically support them and electrically insulate them from one another. Alternatively they could be suitably adhered to an overall sheet  103  of insulating material as depicted in  FIG. 1 . 
       FIG. 3   a  shows the self-clearing electrode  203  before an event, and  FIG. 3   b  shows the electrode after an event. If a plasma jet should penetrate the electrode  203  in the region of the panel  301  which is labeled  302  and also penetrate an electrode  105  at a different voltage, current would flow through the plasma jet, causing the capacitor bank  116  to discharge to break up the penetrator jet and at the same time blowing the fuse links  300  in the immediate area of the penetration which is labeled “P” in  FIG. 3   b . In the configuration shown, each of the four fuse links connected to panel  302  will carry approximately ¼ of the current that flows through the plasma jet. The panels  300  adjacent to panel  302  have been labeled  303 . The fuse links associated with panels  303  and other contiguous panels will carry less current than the fusible links associated with  302 , and all may not blow; however, in  FIG. 3   b , all of the links associated with panels  302  and the 8 surrounding panels  303  are shown as blown. 
     The self-clearing event is not important if the object bridging between electrodes  104  and  105  is a plasma jet since the plasma jet is naturally self-clearing, i.e. it dissipates. If however, the penetrating object is a solid conductor  200 , the self-clearing of the electrode will prevent the permanent shorting of active armor electrodes and allow the electric armor system to recharge and rearm in anticipation of another event. Either of the electrodes or both of the electrodes can be self-clearing in order to achieve the desired effect of preventing such a short circuit. It is anticipated that such a system to protect against RPGs or the like would include a capacitor bank of at least about 5 kilojoules, preferably at least 10 kilojoules and more preferably at least about 100 or more kilojoules. If all of the fusible links are not blown automatically at the time of the destruction of the plasma jet, the operator will simply discharge the charged capacitor bank  116  which will destroy fuses at any point of remaining short circuit. 
       FIGS. 4   a, b  and  c  show three different structural configurations using fusible links  300  and panels  401 ,  402  and  403  of various shapes in combination to provide other embodiments of self-clearing electrodes.  FIG. 4   a  shows hexagon-shaped panels  401  with one fuse link  300  between each panel and the next adjacent panel.  FIG. 4   b  shows triangular panels  402  arranged as composite hexagons with two fuse links  300  between each panel and the panel  402  in the next adjacent hexagon. Panels  403  are shown in  FIG. 4   c  which are interconnected with three fusible links  300  that are spread wide apart to the next adjacent panel. Placing the three fusible links  300  relatively wide apart reduces the inductance associated with the interconnection of the panels  403  through the fusible links  300 . 
     The fusible links in  FIG. 4  could be individual elements, such as those disclosed in U.S. Pat. Nos. 4,123,738 and 4,150,353 to Huber and Huber et al. Using this type of link has the advantage that it is relatively easy to build a melt point into the link. Should a conducting penetrator short out electrodes  104  and  105  while the system is not energized, the system can be energized at low power forcing current through the fusible links near the point of penetration and causing those links to preferentially melt open. The fusible links could be a thin wire mesh of fusible elements upon which the panels are placed. Another possibility is to have a continuous self-clearing electrode rather than specific fusible links. With a continuous self-clearing electrode, the electrode would burn back an adequate distance from the closest conductor so that, on subsequent operation, there would not be a short circuit between electrodes  104  and  105  even though a conductive projectile is stuck between the panels  101  and  102 . The general requirement would be for the fuse element or continuous self-clearing electrode, to melt or vaporize or become a non-conductor, e.g. turning from a conductor like aluminum to an insulator like aluminum oxide, during the event. 
     In an electric armor system like that of  FIG. 1 , it is advantageous to initiate the flow of current as quickly as possible so that the plasma jet  114  is broken-up as far from the hull or of the vehicle as possible, thus minimizing the damage inflicted by the round. Initiating the flow of current through the plasma jet well before the tip of the jet reaches the inner electrode  104  or  203  increases the effectiveness of the system. There is some inherent delay in the flow of current from the capacitor  116  to the plasma jet  114  due to the inductance of the system. In practice, this delay limits the types of rounds against which the electric armor is particularly effective. However, it has been found that this situation can be improved by initiating the flow of current before the plasma jet  113  reaches the second or inner electrode  104 . 
       FIG. 5   a  shows an inner composite electrode  101  that includes a self-clearing electrode  104  which may be any of the types shown. The  FIG. 3   a  panels are illustrated to which elongated electrical conductors which serve as current flow initiators  500  have been added to the electrode so as to extend into the space  117  toward the outer composite electrode  102 . The conductors have limited current carrying capability and are preferably conical, resembling thin metal spikes, and are essentially parallel to one another. In addition, a network  501  of thin initiator wire mesh  501  of metal or other conductive filaments has been added to the tip ends of the initiators  500 . When a penetrator penetrates the outer composite electrode  102  at region  502  and then bridges the gap between it and the initiators  500  or initiator wires  501 , as shown in  FIG. 5   b , the electrical circuit will be completed, and current will start to flow even though the penetrator jet  113  has not yet reached the second inner composite electrode  101 . This early initiation of current flow substantially improves the effectiveness of the active armor system. Once a large amount of current flows through the initiator  500  and initiator network  501 , they will be vaporized at region  502 , but they will leave behind a plasma that will maintain the electrical connection until a current zero is reached in the circuit. When current zero is reached, the self-clearing electrode may have the appearance shown in  FIG. 5   c , where the fusible links  300 , the initiators  500  and the initiator network  501  in the immediate area  502  of the hit have melted and become open-circuited. Even if the remnants of a solid electrically-conducting penetrator  200  should remain at the point of the hit in the region  502  of the self-clearing electrode and the opposite electrode, the electrical circuit will remain open-circuited, so that the system will still be able to rearm for the next event. 
     The initiator network  501  of  FIG. 5  could be configured in a number of different ways and still perform the same function of providing better coverage for the electrical path for early ignition of the flow of current in the circuit.  FIGS. 7   a, b  and  c  show one variation of such a network where a series of thin electrically conductive plates  701  are connected to initiator conductors in the form of posts  500  which protrude from the solid conductor panels  301  which plates are interconnected by the fusible elements  300 . A similar effect can be obtained by having a thin solid sheet of conducting material as the initiator network, localized regions of which will vaporize in the localized area of the strike after establishing the plasma that will initiate the early flow of current. In a further embodiment, a thin sheet of conductive material not greater than about 0.25 inch thick can be used as the primary electrode (affixed to an insulating support sheet  103 ); the material at such thickness will locally vaporize under the plasma jet and/or capacitor discharge. A thin aluminum film of about 5 to 20 microns or an indium tin oxide film of about 2 to 5 microns are examples. 
       FIGS. 8   a, b  and  c  show a modular approach to capacitor energy storage as a part of an active armor system with a self-clearing electrode.  FIG. 8   b  shows an exploded view of the module  800  which is illustrated in  FIG. 8   a  for use in an embodiment of an electric armor system. The module incorporates many of the elements described above, including an electrode panel  301 , four fusible links  300 , and multiple initiators  810 .  FIG. 8   a  shows the assembled module. In this embodiment of the concept, one electrical terminal of capacitor  801  is physically and electrically connected to panel  301  that forms a part of a self-clearing electrode that is mounted as part of composite inner electrode  101 . The second terminal of the energy storage capacitor  801  is connected to the other composite electrode  102  (not shown in  FIG. 6   c ) via a thin metal tab  803 . The tab  803  is designed to adequately carry the discharge current of a single capacitor (which may be of about 5 joules to 10 kilojoules), but to vaporize if high current associated with the incoming penetrator event should attempt to flow through the tab. In this manner, the electric armor system will clear the tab from the event with the system suffering only a small loss of capacitance. Alternatively, the capacitor  801  could be disposed on the opposite surface of the conductor panels  301 , with insulated tabs connections being routed between adjacent panels. 
     The early initiation of current flow offers an advantage to electric armor systems.  FIG. 9  shows another configuration that accomplishes this by moving a thin initiator network  501 ′ very close to the outer electrode  105 , separated only by a thin insulator layer  900 . The insulated initiator network layer  501 ′ will operate at the same voltage as the energy storage capacitor  116 . The thin initiator network  501 ′ is a thin conductive layer that, in one preferred embodiment, is an aluminum film or ITO that has been vapor-deposited onto the surface of the insulator  900  to a thickness of e.g. about 200 angstroms to 1 or 2 microns so that it becomes a physical part of the composite outer electrode  102 . This thin network  501 ′ is connected to a self-clearing electrode  203  through initiator posts  500 ″. On initial impact of a projectile or a plasma jet, the initiator posts  500 ″ and the thin initiator network  501 ′ are designed to initiate flow of current in the region of the incoming projectile or jet and focus the electrical discharge in the area of the plasma jet by increasing in impedance as the jet or projectile passes. The result is the provision of an open circuit between the remaining parts of the self-clearing electrode  203  and the outer electrode  105 , which in this embodiment is electrically connected to the hull of the vehicle  100 . 
     In all these systems, the self-clearing electrode  203  is electrically insulated from the hull  100  and from the outer electrode  105  by an insulating structural member  103 . In a preferred embodiment, the construction of the overall support system would be flexible, in the sense that the various components of the electric armor system, i.e. the inner and outer electrodes, would be allowed to move or flex in relation to the hull and other components of the system. 
     Although the invention has been described with regard to certain preferred embodiments, which constitute the best mode presently known to the inventor, it should be understood that changes and modifications may be made to these illustrated embodiments as would be obvious to one having ordinary skill in this art, without departing from the scope of the invention which is defined in the claims appended hereto. For example, although aluminum, ITO, copper and conducting polymers have been mentioned as conductive materials that may be employed, it should be understood that other conductive materials, as well known in this art, could be alternatively used. 
     The disclosure of the U.S. patent mentioned herein is expressly incorporated herein by reference. 
     Particular features of the invention are emphasized in the claims that follow.