Patent Publication Number: US-2006011054-A1

Title: Electromagnetically shielded, flexible bomb suppression device

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an electromagnetically shielded, portable device for protection against remote detonation of an explosive device, and also having ballistic shielding capabilities.  
      2. Related Art  
      As used herein, “ballistic materials” means materials that provide blast-fragment mitigation. The construction of ballistic materials is well known in technology. Typical ballistic materials would consist of multiple layers of a woven or non-woven Aramid, such as Kevlar® or Twaron®, or high molecular weight polyethylene, such as Dyneema® or Spectra®, fibers or fabrics or a combination thereof. As used herein, “Aramid” means a manufactured fiber in which the fiberforming substance is a long-chain synthetic polyamide in which at least 85% of the amide (—CO—NH—) linkages are attached directly between two aromatic rings.  
      Most ballistic materials have been incorporated in clothing such as flak jackets for protection against ballistic rounds and fragments. Ballistic materials have also been used for the containment of explosive devices. The specific fiber and/or fabric have the ability to absorb the energy of impact of a ballistic projectile as described by Van der Loo (U.S. Pat. No. 5,569,528). Other containment systems often include a metal structure, which are of a set size and, due to the weight, not very portable.  
      All of the prior art to date addresses the containment of the fragments after the detonation of the blast.  
      In recent years, the ability to detonate an explosive device from a remote location has become easier. An electronic device as simple as the common cellular phone can be used as a detonation device, which can be activated from a remote location.  
      Current portable blast suppression devices do not address the protection against remote detonation by a radio frequency (RF) signal.  
      It is to the solution of these and other problems that the present invention is directed.  
     SUMMARY OF THE INVENTION  
      It is accordingly a primary object of the present invention to provide a portable ballistic shield that is lightweight, flexible, and can be easily placed over an explosive device.  
      It is another object of the present invention to provide a ballistic shield that will give radio frequency (RF) shielding for the prevention of remote detonation.  
      It is still another object of the present invention to mitigate the use of RF signals to detonate an explosive device.  
      It is still another object of the present invention to provide a ballistic shield that will have some fragment control capabilities in the instance that an explosive device is not detonated by a RF signal.  
      These and other objects of the invention are achieved by a multi-layered flexible shield comprising two main components, a RF shielding layer and a ballistic control layer.  
      The RF shielding layer is constructed using a conductive fabric, preferably a copper/nickel coated polyester woven fabric. A flexible conductive coating is applied to the conductive fabric. The flexible conductive coating is preferably an emulsion coating with high attenuating capabilities, and more preferably, is an electrically conductive and electromagnetic radiation absorptive coating composition.  
      The ballistic control layer comprises upper and lower sub-layers and a middle sub-layer between the upper and lower sub-layers. The upper and lower sub-layers are made of a woven ballistic material such as a woven Aramid or ultra high molecular weight polyethylene fibers. The middle sub-layer comprises sheets of a non-woven ballistic material such as Aramid or ultra high molecular weight polyethylene fibers in a random orientation.  
      A thin, protective cover formed of a woven ballistic material is provided as a third component to cover the lower surface of the conductive fabric and protect the RF shielding layer from abrasion and environmental conditions.  
      The outer edge of the bomb suppression device has a weighted, flexible rim that aids in securing the unit to the surrounding surface, thereby electronically isolating the explosive device.  
      Other objects, features and advantages of the present invention will be apparent to those skilled in the art upon a reading of this specification including the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention is better understood by reading the following Detailed Description of the Preferred Embodiments with reference to the accompanying drawing figures, in which like reference numerals refer to like elements throughout, and in which:  
       FIG. 1  is a diagrammatic, cross-sectional view of a bomb suppression device in accordance with the present invention.  
       FIG. 2  is a graph of the data in Table 1, illustrating RF attenuation of a conductive coating, and a copper/nickel polyester fabric coated with the flexible conductive emulsion coating, in accordance with the present invention.  
       FIG. 3A  is a top view of a bomb suppression device in accordance with the present invention, with a mock explosive device positioned thereon.  
       FIG. 3B  is a top view of the bomb suppression device of  FIG. 3A  covering the mock explosive device.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose.  
      The present invention relates to an electromagnetically-shielded bomb suppression device  10  that serves as a portable ballistic shield that is lightweight, flexible, and can be easily placed over an explosive device. The invention also provides a ballistic shield that will give radio frequency (RF) shielding for the prevention of remote detonation of an explosive device. In the instance that the explosive device is not detonated by a RF signal, the ballistic shield will have some fragment control capabilities.  
      Referring to  FIG. 1 , the bomb suppression device  10  is a multi-layered flexible shield comprising two main components, a RF shielding layer  20  and a ballistic control layer  30 .  
      The RF shielding layer  20  comprises upper and lower sub-layers  22  and  24  (“upper” and “lower” being used herein relative to the orientation of the bomb suppression device  10  when in use). The lower sub-layer  24  is constructed of a conductive fabric, preferably a copper/nickel polyester woven fabric. The upper sub-layer  22  is a flexible conductive coating, preferably an emulsion coating with high attenuating capabilities, applied to the conductive fabric. This conductive coating enhances the RF attenuating properties of the lower sub-layer  24 .  
      The flexible conductive coating for the present invention can be formed of an electrically conductive and electromagnetic radiation absorptive coating composition as disclosed in U.S. Pat. No. 6,576,336, which is incorporated herein by reference as if set forth in its entirety. The conductive coating composition disclosed in U.S. Pat. No. 6,576,336 comprises an emulsion polymer binder, which is a blend of a first emulsion containing a conjugated diene monomer or comonomer, and a second emulsion containing an acrylic polymer. It also contains an effective amount of electrically conductive particles dispersed in the binder, and water as a carrier. The electrically conductive particles include a combination of graphite particles and metal-containing particles, the graphite particles preferably being natural flake graphite and the metal-containing particles preferably being silver or nickel containing particles.  
      The flexible conductive coating can also be formed of a composition as disclosed in International application Serial No. PCT/US02/07039, filed Mar. 8, 2002 (International Publication No. WO 03/078531), which corresponds to U.S. application Ser. No. 10/358,375, filed Feb. 5, 2003 (U.S. Published Appl. No. 20040028859), both of which are incorporated herein by reference as if set forth in their entirety. As disclosed in International Publication No. WO 03/078531 and U.S. Published Appl. No. 20040028859, the second emulsion of the polymer binder for the conductive coating can be selected from any of an acrylic, aliphatic or aromatic polyurethane, polyester urethane, polyester, epoxy, polyamide, polyimide, vinyl, modified acrylic, fluoropolymer, and silicone polymer, or a combination thereof. Also, the electrically conductive particles for the conductive coating composition can be selected from any of graphite particles, carbon nanotubes, and metal containing particles, or a combination thereof. The graphite particles are preferably natural flake graphite. The carbon nanotubes are preferably 10 to 60 nanometers in diameter and from less than 1 micron to 40 microns in length. The metal containing particles are preferably silver or nickel containing particles; however, other metals may also be employed such as gold, platinum, copper, aluminum, iron or iron compounds and palladium. The metal containing particles are more preferably metal coated ceramic microspheres or metal coated ceramic fibers; however, other metal coated particles may also be employed such as metal coated glass flake, glass spheres, glass fibers, boron nitride powder or flake, mica flakes, and copper flakes.  
      Preferably, the flexible conductive coating for the present invention includes as the first emulsion a butadiene-acrylonitrile latex. A preferred polymer is a highly saturated butadiene/acrylonitrile copolymer latex available from the Goodyear Tire and Rubber Company, Akron, Ohio (“Goodyear”) as Chemisat LCH-7302X latex. Another preferred polymer is a highly saturated carboxylated butadiene/acrylonitrile latex available from Goodyear as Chemisat LCH-7505X latex. For the second emulsion, a urethane in water emulsion is selected. A preferred urethane in water emulsion is a dispersion of aliphatic polyester urethane polymer in water available from Bayer Corporation. The electrically conductive particles are in the form of silver coated microspheres. Miscellaneous additives comprise water, ethylene glycol monobutyl ether, and dimethylpolysiloxane (defoamer).  
      The components of the conductive coating composition for the present invention is composed of 30%-50% by weight, and preferably 35%-40% by weight of the urethane emulsion, 5%-20% by weight, and preferably 10%-15% by weight, of the carboxylated butadiene-acrylonitrile, and 15%-25% by weight, and preferably 18%-22% by weight of the silver coated microspheres. The resistivity of the conductive coating composition is 0.1 to 0.5 Ohm/square, and its viscosity is 35-45 seconds #2 Zahn Cup ASTM D 4212.  
      The data in Table 1, which are represented graphically in  FIG. 2 , show the RF attenuation of a conductive coating, and a copper/nickel fabric coated with the flexible conductive emulsion coating, in accordance with the present invention. The frequency shielding testing was conducted according to ASTM D4935-99. 
                       TABLE 1                           Coating   Coated Fabric       Frequency (Hz)   SE (dB)   SE (dB)                                            30000000   60.76275   58.06238       101412500   57.00528   63.62686       201143800   56.22693   60.01981       300875000   55.53969   68.93812       399375000   55.84046   66.08271       500337500   55.67454   69.89711       601300000   59.85375   68.17653       701031300   57.34368   74.29801       800762500   56.11692   64.57983       901725000   59.70403   71.75521       1001456000   55.39363   69.87521       1102419000   59.04003   69.15003       1202150000   59.11301   69.56802       1300650000   59.00401   82.29104       1400381000   58.01009   61.09758       1500113000   58.66769   68.98509       1601075000   65.09308   81.69582       1700806000   57.90765   69.10004       1803000000   63.14693   63.05803       1900269000   66.99431   65.81694       2000000000   61.84815   69.23119                  
 
      On average, the shielding effectiveness of the enhanced material is greater than 60 dB, which relates to a 1000:1 reduction in signal strength.  
      The RF shielding layer  20  can be provided with a thin protective cover  40  that covers the lower sub-layer  24 . The protective cover  40  preferably comprises a woven ballistic material such as an Aramid or high molecular weight polyethylene. The cover  40  is preferably designed to protect the RF shielding layer  20 , and more particularly, the lower surface of the conductive fabric lower sub-layer  24 , from abrasion and environmental conditions. It is removably attachable to the lower sub-layer  24  by means of fasteners (not shown), such as hook and loop fasteners, for easy repair or replacement.  
      The ballistic control layer  30  of the invention preferably comprises a multi-layer construction of upper and lower sub-layers  32  and  34  and a middle sub-layer  36  between the upper and lower sub-layers  32  and  34 . The upper, lower, and middle sub-layers  32 ,  34 , and  36  are attached to each other, for example by sewing.  
      The upper and lower sub-layers  32  and  34  each comprise a woven ballistic material such as Aramid or ultra high molecular weight polyethylene fibers. The middle sub-layer  36  comprises sheets of a non-woven ballistic material such as Aramid or ultra high molecular weight polyethylene fibers in a random orientation, similar to a felt fabric construction. The number of non-woven sheets can vary from one to  40 , depending upon the amount of ballistic control desired.  
      Referring now to  FIGS. 3A and 3B , the outer edge of the bomb suppression device  10  has a weighted, flexible rim  50  that aids in securing the bomb suppression device  10  to the surrounding surface, thereby electronically isolating an explosive device  60  placed under it. The rim  50  can be in the form of a sand-filled channel, which is attached to the perimeters of the ballistic control layer  30  and the RF shielding layer  20 . The upper surface of the upper sub-layer  32  of the ballistic control layer  30  is preferably reinforced by strong nylon ribbing  32   a  with a center sewn loop handle  32   b  for easy of use. Preferably, the upper sub-layer  32  of the ballistic control layer  30  is a highly visible color, for example, bright orange, to help identify the system from a distance.  
      As shown in  FIGS. 3A and 3B , because of its flexibility, the bomb suppression device  10  can be draped over an explosive device  60 , while the rim  50  secures the RF shielding layer  20  and the ballistic control layer  20  to the surrounding surface.  
      The bomb suppression device  10  in accordance with the present invention was tested for electromagnetic shielding effectiveness. Testing was conducted on a concrete surface, an asphalt surface, and earth. Testing was conducted with a Portable Attenuation Measurement Set. The Portable Attenuation Measurement Set includes a transmitter to produce a calibrated signal transmission at 900 MHz and a receiver to measure the signal strength or reduction in strength. In each substrate tested, the bomb suppression device  10  in accordance with the invention demonstrated a minimum −40 dB attenuation from a distance of 25 feet. Additional tests were conducted with a Motorola® brand cellular phone being placed under the bomb suppression device  10  and a call being placed to the cell phone. Tests conducted on each substrate showed the bomb suppression device  10  blocked the signal from reaching the cell phone under it and prevented a signal from connecting. When retrieving the cellular phone from underneath the bomb suppression device  10 , the display read “no service” in all instances.  
      Modifications and variations of the above-described embodiments of the present invention are possible, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described.