Abstract:
An electro-optical cable ( 38 ) which includes an optical element ( 48 ) having an elongated glass fiber core ( 50 ), a medial cushioning layer ( 54 ) concentrically surrounding the glass fiber core, and an outer hard shell ( 56 ) material surrounding the medial cushioning layer. The cable also includes at least one electrically conductive element ( 40 ) comprising an elongated conductive core ( 42 ) and a dielectric layer ( 44 ) concentrically surrounding the electrically conductive element.

Description:
STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein was made under Contract No. N0019-96-C005 with the Government of the United States of America and may be manufactured and used by and for the Government of the United States of America for Governmental purposes without the payment of any royalties thereon or therefor. 

   CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims rights under 35USC119(e) from U.S. Application Ser. No. 60/428,156, filed Nov. 21, 2002. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to towed decoys for use in aviation, and more particularly to electro-optical cables for use in such towed decoys. 
   2. Brief Description of Prior Developments 
   It is known in the art to provide a decoy which is towed on an electro-optical cable from a combat aircraft. U.S. Pat. No. 5,042,903 for example, discloses a relatively small diameter tow cable including a plurality of high and low voltage electrical conductors and a high bandwidth optical fiber for both electrical and data transmission between an aircraft and a towed body. The tow cable is implemented by a coaxial arrangement of a central optical fiber encased by a stainless steel jacket surrounded by a first set of high voltage conductors. A second set of high voltage conductors concentrically surrounds the first set of conductors but is separated therefrom by a layer of high voltage insulation. A layer of high voltage insulation surrounds the second set of high voltage conductors and a set of relatively low voltage conductors and their respective return conductors are circumferentially spaced around this layer of insulation along with opposing sets of insulating spacers. A third layer of insulating material surrounds the low voltage conductors and the spacers. Outwardly of the third layer of insulating material are a pair of coaxial strength members comprised of synthetic aramid fibers and which are then covered with a polyester and metallic braid. An outermost jacket of semiconductive material is also provided which serves as an electrostatic drain to ground for the cable. 
   The prior are also discloses other electro-optical cables used for other purposes. 
   U.S. Pat. No. 5,468,913, for example, discloses a marine tow cable having both coaxial electronic and fiber optic data transmission capabilities wherein the coaxial core conductors are positioned at the neutral axis or center line of the cable with the coaxial shield conductor circumscribing a dielectric material therebetween. Embedded within the dielectric material matrix, separating the core conductors and the shield conductor, are fiber optic transmitters helically circumscribing the core conductors. Surrounding the electro-optical assembly is a watertight jacket and a protective armor cover to carry the tensile forces imparted to the cable during towing operations. 
   U.S. Pat. No. 6,343,172 discloses composite cables which are operative to transmit information in electrical and/or optical transmission modes. The cables can include an electrical coaxial conductor comprising a generally central electrical conductor in a dielectric matrix. At least one optical transmission component is integrated with the matrix. The matrix can include at least two optical transmission components disposed on generally opposed sides of the central electrical conductor. 
   While such arrangements have generally performed well, there is a need to still further improve the temperature, mechanical, electrical and environmental durability of such electro-optical cables. 
   SUMMARY OF INVENTION 
   The present invention is an electro-optical signal cable which has improved the temperature, mechanical, electrical, and environmental durability. Volumetric and weight impacts are minimized, thus significantly extending applicability beyond current existing design limitations. This electro-optical cable is comprised of an optical element which includes an elongated glass fiber core, a medial cushioning layer concentrically surrounding the glass fiber core, and an outer hard shell material surrounding the medial cushioning layer. This electron-optical cable also includes at least one electrically conductive element comprising an elongated conductive core and a dielectric layer concentrically surrounding the electrically conductive core. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is further described with reference to the accompanying drawings, wherein: 
       FIG. 1  is a vertical cross sectional view of a preferred embodiment of the electro-optical cable of the present invention; and 
       FIG. 2  is a vertical cross sectional view of an alternate preferred embodiment of the electro-optical cable of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Improved durability has been achieved by acknowledging the three distinct elements of the cable and addressing each separately then merging the elements into a single design. The constituent layers are combined in a synergistic manner. The electrical conductors make use of adhesive materials in order to fuse the dielectric materials to the wire. The resulting wire construction method demonstrates excellent dielectric withholding potential, over 5 kV, at temperatures of up to 700° F. The fiber optic element has been improved through consideration of the optical fiber as a portion of a composite beam, in which the fiber was encased in a cushion of polytetrafluorethylene (PTFE, Teflon), then a thermoplastic resin, polyetheretherketone (PEEK), was utilized to provide a tough, hard, outer shell which improved both thermal and mechanical durability to levels in excess of 700° F. The electrical conductors may have layers of dielectric PTFE and aromatic co-polyimides such as poly(p-phenylene bihenyltetracarboximide) (BPDA-PDA) and pyromellitimio-oxydianilinecarboximide (PMDA-ODA). The conductors are preferably copper with a plating of a diffusion barrier such as nickel. The braid selected consisted of a poly(p-phenylene-2,6-benzobisoxazole) (PBO, Zylon), with a friction reducing coating included to aid in deployment of the material. The resulting cable system has proven performance when subjected to the rigors of the after-burning plume of a jet engine installed in the U.S. Navy&#39;s F/A-18E/F aircraft. It is believed that enhanced thermal and mechanical performance may also be obtained through the use of advanced polymers such as poly(p-phenylene bihenyltetracarboximide (BPDA-PDA, Upilex-S) and other co-polymers based on aromatic polyimides such as PMDA-ODA and films made of poly(p-phenylene-2,6-benzobisoxazole (PBO, Zylon)). 
   Referring to  FIG. 1 , cable  10  includes an electrical conductive element  12  which is comprised of a metallic core  14  which is preferably 32 gage copper wire. The metallic core  14  is peripherally surrounded by a dielectric element  16  which is preferably 0.002″/0.003″ MIL-ENE. The cable  10  also includes an optical conductive element  18 . This optical conductive element  18  is comprised of a glass core  20  which is peripherally overlaid by an arcylate section  22  which is preferably 245 microns in thickness. A PTFE layer  24  which is preferably 0.003″ in thickness peripherally overlays the arcylate section  22 . A FEP section  26  peripherally overlays the PTFE section  24 . The FEP section  26  preferably has an outside diameter of 600 microns. The cable  10  also includes a plurality of additional electrical conductive elements as at electrical conductive elements  28 ,  30 ,  32 , and  34  which are essentially identical to electrical conductive element  12 . Cable  10  also includes an outer peripheral jacket  36  which is comprised of Zylon. 
   Referring to  FIG. 2 , in another embodiment of this invention cable  38  includes an electrical conductive element  40 . This electrical conductive element  40  is comprised of a metallic core  42  which is peripherally surrounded by a PTFE layer  44  which is preferably 0.005″ in thickness. A EKJ layer  46  peripherally overlays the PTFE layer  42  an is preferably from 0.003″ to 0.006″ in thickness. The cable  38  also includes an optical conductive element  48  which has glass core  50  which is peripherally overlaid by a polyimide section  52  which is preferably 152 microns in thickness which is itself peripherally overlaid by a PTFE layer  54  which is preferably 0.003″ in thickness. The PTFE layer  54  is peripherally overlaid by a PFA and PEEK composite layer  56  which has a 600 micron outer diameter. In the PFA and PEEK composite layer  56  there is an inner layer of the softer PFA which is overlaid by a shell of the harder PEEK. The stiff PEEK shell provides crushing protection during winding, storage and deployment of the cable. The softer PFA and the softer PTFE layer  54  allow the fragile glass core  50  to more or less float within the PEEK shell so as to absorb energy during deployment and reduce thermal shock during exhaust plume exposure. This combination of PEEK, PFA and PTFE also protects the glass core  50  from water. The cable  38  also includes additional electrical conductive elements  60 ,  62 ,  64  which are essentially identical to electrical conductive element  40 . Cable  10  also includes an outer peripherally jacket  66  which is comprised of Zylon. 
   It will be appreciated that an electro-optical cable has been described which is durable under adverse temperature, mechanical, electrical and other environmental conditions. 
   While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.