Patent Publication Number: US-2006011376-A1

Title: Multi-axial electrically conductive cable with multi-layered core and method of manufacture and use

Description:
BACKGROUND OF THE INVENTION  
      This invention relates to a multi-axial electrically conductive cable with a multi-layered core that enables the cable to be utilized over a range of electrical impedance connections and diverse applications of the connections. In particular, this invention relates to a multi-axial cable with a multi-layered core and use of the cable to manufacture multi-impedance transducers for use in high temperature environments. This invention also relates to a method for manufacturing the multi-axial cable such that the cable fits in several sized electrical connections.  
      A coaxial electrically conductive cable method of manufacture is disclosed in U.S. Pat. No. 4,508,585 to Frakes. The use of coaxial cable for the transmission of high frequency electrical signals and like applications is well known in the art. Typically, a multi-axial electrically conductive cable, specifically coaxial cable, comprises an inner conductor encased in an annular layer of electrically insulating dielectric material. An outer electrical conductor is typically disposed about the electrically insulating material layer. This outer electrical conductor has several uses, including as an electrical ground or for the transmission of low frequency electrical signals.  
      Standard multi-axial electrically conductive cable, as typically used in the industry, is sold in fixed diameters for varying electrical connections and applications. These electrical connections vary by, for example, impedance with the diameter of the cable dependent upon the impedance of the connection in an electrical application. For example, a typical 75 ohm multi-axial electrically conductive cable has a smaller diameter than a typical 95 ohm multi-axial electrically conductive cable. These fixed diameter sizes create difficulties with manufacturing costs and flexibility and with inventory control, because a separate electrically conductive cable is needed for each different electrical connection which size varies with impedance.  
      Therefore, a need exists for an electrical cable with a construction that allows one cable to be utilized in several electrical connection applications to lower manufacturing costs and increase manufacturing flexibility of electrical devices and to enable inventory control of spare parts in electrical device manufacturing and/or services. A further need exists to develop a method of manufacture of the multi-axial electrically conductive cable with a multi-layered core to enable the multiple layers of the core to be separated. Finally, a need exists for stripping and crimping a multi-axial cable to ensure accurate installation in and attachment to an electrical device.  
     BRIEF DESCRIPTION OF THE INVENTION  
      Accordingly, a multi-axial electrically conductive cable, as embodied by the invention, comprises a center conductor; a multi-layered, non-conducting dielectric core, the multi-layered, non-conducting dielectric core surrounding the center conductor; at least one conductive shield surrounding the multi-layered, non-conducting core; and at least one non-conducting insulator surrounding the at least one conductive shield.  
      A further aspect of the invention, provides a method of manufacture of a multi-axial electrically conductive cable. The multi-axial electrically conductive cable, as embodied by the invention, comprises a center conductor, a multi-layered, non-conducting dielectric core, at least one conductive shield, and at least one non-conducting insulator. The method, as embodied by the invention, comprises steps of providing center conductor; providing a multi-layered, non-conducting dielectric core; providing at least one conductive shield; and providing at least one non-conducting insulator. The step of providing a multi-layered, non-conducting dielectric core comprises providing a first layer of dielectric material and at least one additional layer of dielectric material, and the at least one additional layer is separable from the first layer of dielectric material.  
      A yet further aspect of the invention includes a method of use of a multi-axial electrically conductive cable. The cable, as embodied by the invention, is provided with a multi-layered core, a center conductor, a multi-layered non-conducting dielectric core surrounding the center conductor. The multi-layered non-conducting dielectric core comprises a first layer of dielectric material and at least one additional layer of dielectric material. The cable, as embodied by the invention, is provided with at least one conductive shield surrounding the multi-layered non-conducting dielectric core, and at least one non-conducting insulator. The method, as embodied by the invention, comprises the steps of determining a length for the outer conductor; removing the outer insulation to the length thus exposing the outer conductor; determining a length of inner insulation; removing outer conductor to expose the multi-layered non-conducting dielectric core; determining a length for inner conductor; removing the multi-layered non-conducting dielectric core to expose the inner conductor; and crimping braided outer conductor.  
      Another aspect of the invention sets forth a multi-axial electrically conductive cable comprising a center conductor; a multi-layered, non-conducting dielectric core, the multi-layered, non-conducting dielectric core surrounding the center conductor; at least one conductive shield surrounding the multi-layered, non-conducting core; and at least one non-conducting insulator surrounding the at least one conductive shield. The multi-layered non-conducting dielectric core comprises a first layer of dielectric material and at least one additional layer of dielectric material. The multi-layered non-conducting core comprises a first layer of non-conducting dielectric material selected from a group comprising at least one of polytetrafluoroethylene, fluorinated ethylene propylene, ethylene tetrafluoroethylene copolymer, perfluoroalkoxy copolymer, polyvinylidene fluoride, fluoropolymer, polyvinyl chloride, and polyurethane. Also, the at least one additional layer of the multi-layered non-conducting core is selected from a group comprising at least one of fluorinated ethylene propylene, ethylene tetrafluoroethylene copolymer, perfluoroalkoxy copolymer, polyvinylidene fluoride, fluoropolymer, polyvinyl chloride, and polyurethane. The at least one additional layer of the multi-layered non-conducting core is separable from the first layer of dielectric material.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic diagram of a multi-axial electrically conductive cable with multi-layered core.  
       FIG. 2  is a cross-sectional view of the multi-axial electrically conductive cable in this invention.  
       FIG. 3  illustrates the steps of the stripping and crimping process for the multi-axial electrically conductive cable with multi-layered core.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIGS. 1 and 2  schematically illustrate a multi-axial electrically conductive cable  28  comprising an inner conductor  30 , a first layer of dielectric insulating material  32 , at least one second layer of dielectric insulating material  35 , at least one outer conductor  38 , and at least one outer insulator or “jacket”  40 . In one embodiment, the layers of dielectric insulating material  32 ,  34 ,  36  include at least two separable layers comprising any suitable dielectric material. In this embodiment, the multi-axial electrically conductive cable  28  comprises of a first layer  32  of insulating dielectric material and a second layer of insulating dielectric material  34 .  
      The exemplary multi-axial cable in this embodiment comprises a coaxial cable  28  that is utilized in 75 ohm and 95 ohm electrical assembly connections in high temperature environments. The cable  28  comprises an inner conductor  28  made of seven strands of silver-covered, annealed copper steel wire. The overall diameter of the core conductor is about 0.012 inch. This diameter and the dimensions and values provided herein are merely exemplary of the cable as embodied by the invention and are not meant to limit the invention mentioned herein. Other dimensions and values are within the scope of the invention.  
      Next, the cable in the exemplary embodiment comprises an insulative core  6  surrounding the inner conductor  30 . This core  6  comprises two separable layers. The first layer  32  of the core  6  comprises solid extruded polytetrafluoroethylene with an overall diameter of about 0.068 inches. The second layer  34  of the core comprises heavy-metal free, extruded fluorinated ethylene propylene with an overall diameter of about 0.12 inches. These materials and others provided herein are merely exemplary of the cable as embodied by the invention and are not meant to limit the invention mentioned herein. Other materials for the insulative core for use in different environments are within the scope of the invention.  
      Finally, the exemplary cable  28  comprises an outer conductor  38  comprising single braid, hard drawn silver-covered, copper clad steel wire with an overall diameter of about 0.125 inches. The exemplary cable  28  is enclosed in extruded fluorinated ethylene propylene with a will thickness of about 0.010 inches. The overall diameter of the cable is about 0.138 inches.  
      The inner conductor  30  is used to transmit high frequency or low frequency electrical signals or direct current. This conductor  30  may be a solid metal or twisted wire. The inner conductor  30  is formed from an electrically conductive material. In this embodiment, the inner conductor  30  comprises 7-stranded steel wire clad with copper and covered with silver.  
      The insulative layers  32 ,  34 ,  36  comprise the “core”  6  of the multi-axial electrically conductive cable  28  in this embodiment. These insulative layers  32 ,  35  are formed from suitable non-conducting dielectric material, and are separable because of a manufacturing method embodied by the invention and discussed hereinafter. In this embodiment, the core  6  of the multi-axial electrically conductive cable comprises two layers.  
      The first non-conducting dielectric insulative layer  32  is selected from a group comprising at least one of polytetrafluoroethylene, fluorinated ethylene propylene, ethylene tetrafluoroethylene copolymer, perfluoroalkoxy copolymer, polyvinylidene fluoride, fluoropolymer, polyvinyl chloride, and polyurethane. The materials listed here and throughout the rest of this specification are applicable for multi-axial cables used in high temperature environments. However, the first layer  32  and the other layers of the core can comprise any other suitable non-conducting dielectric material, depending on the use of the cable in, for example, a low temperature environment. In this embodiment, the first layer  32  of dielectric insulative material comprises polytetrafluoroethylene.  
      The core also contains at least one additional layer of non-conducting dielectric insulative material  35  formed from a group comprising at least one of fluorinated ethylene propylene, ethylene tetrafluoroethylene copolymer, perfluoroalkoxy copolymer, polyvinylidene fluoride, fluoropolymer, polyvinyl chloride, and polyurethane. In this embodiment, this additional layer  34  comprises fluorinated ethylene propylene.  
      The at least one additional layer of non-conducting dielectric material  35  is separable from the first layer of non-conducting dielectric material  32 . This at least one additional layer  35  should be separable from the layer  32  below it to allow the cable to be stripped and crimped to fit into the desired electrical connection. This separability can be achieved by utilizing a releasing agent between the first non-conducting dielectric layer  32  and the at least one additional dielectric layer  35 , manufacturing process, or a combination of releasing agent or manufacturing process.  
      In this embodiment, separability of the core  6  is achieved by a fluoropolymer extrusion manufacturing process. The separability of the first layer  34  and the at least one additional layer  35  is achieved because the melting point of the first layer  32  is higher than the melting point of the second layer  34 .  
      The core  6  can comprise several layers  35  of insulating dielectric material to allow the multi-axial electrically conductive cable  20  to be utilized in various electrical connections. Each additional layer should be separable from the layer beneath it and able to withstand processing conditions if another dielectric material layer is deposited on it. The number of layers of non-conducting dielectric material  35  is only limited by an amount that enables the cable  28  to be practically usable.  
      The multi-axial electrically conductive cable  28  also comprises at least one conductive shield  38 . This outer conductor layer  38  is utilized to transmit high frequency or low frequency electrical signals, to direct current, or to ground an electrical device. This outer conductor layer can comprise more than one layer of outer conductor as disclosed in Van Den Berg &#39;884. Additionally, this outer conductor can be selected from at least one of a group comprising braided wire, solid metal, or foil. In this embodiment, the outer conductor  38  comprises silver-covered, copper-clad braided steel wire.  
      The last layer on the coaxial cable  28  is a non-conducting insulator or “jacket” 40 . This jacket protects the coaxial cable  28  and keeps the cable  28  electrically isolated so that the cable  28  or the electrical assembly is not shorted. This jacket can be selected from a group comprising at least one of polytetrafluoroethylene, fluorinated ethylene propylene, ethylene tetrafluoroethylene copolymer, perfluoroalkoxy copolymer, polyvinylidene fluoride, fluoropolymer, polyvinyl chloride, and polyurethane. In this embodiment, the outer insulator  40  comprises fluorinated ethylene propylene.  
      In another embodiment, a method of manufacture of a multi-axial electrically conductive cable  28  is provided. The method of manufacture provides a center conductor  30 , a multi-layered, non-conducting dielectric core  6 , at least one conductive shield  38  and at least one non-conducting insulator  40 . The method of manufacture provides for a core  6  comprising separable layers. The method of manufacture for the core  6  comprises at least one of extrusion, tape wrapping, weaving, or any other method of manufacture such that the layers of the core  6  are separable. In this embodiment, the method of manufacture for the core  6  is extrusion.  
      The method of manufacture also provides for a core  6  formed from at least one of a group comprising polytetrafluoroethylene, fluorinated ethylene propylene, ethylene tetrafluoroethylene copolymer, perfluoroalkoxy copolymer, polyvinylidene fluoride, fluoropolymer, polyvinyl chloride, and polyurethane. In this embodiment, the first layer  32  of the core  6  comprises polytetrafluoroethylene and the second layer of the core  34  comprises fluorinated ethylene propylene.  
      The method of manufacture determines whether the first layer of dielectric material  32  and the at least second layer of dielectric material  35  is separable. In one example, a releasing agent is used between the first dielectric layer  32  and the at least one additional layer  35 . In another example, the first layer  32  is tape wrapped separately than the at least one additional layer  35 . In a different example, the first layer  32  is woven separately from the second layer  36 . In this embodiment, because the extrusion process is utilized with a fluoropolymer, the first layer  32  comprises a material of a higher melting point than the second layer  34 .  
       FIG. 3  illustrates a method for stripping and crimping the multi-layered core of the multi-axial electrically conductive cable  28  discussed in this invention. In step  100 , the method involves first measuring the required length for the outer conductor  38  for both higher and lower impedance connections. Tooling is then used to cut the outer insulation  40  back to expose the desired length of the outer conductor  38 , in step  110 .  
      Next, the required length of inner insulation  32 ,  35  is measured to install an elastomer seal, in step  120 . An exemplary elastomer seal is disclosed in Van den Berg &#39;884. In step  130 , the outer conductor  38  is cut to expose the outer layer  36  of core insulation. The required length for the inner conductor  30  is then measured in step  140 , and the inner insulation  32 ,  35  is cut to expose the required length of inner conductor  30  in step  150 . The method ends by crimping the outer conductor  38  to the required diameter for larger impedance assemblies in step  160 . For lower impedance connections, the outer conductor  38  may have to be crimped at least one additional time to fit into a smaller assembly. Finally, a moisture resistant elastomer seal is added over the core  6  to protect the cable  28 . The coaxial cable  28  is now ready to be connected to an electrical device as disclosed in Frakes &#39;585.  
      The multi-axial electrically conductive cable with a multi-layered core, as embodied by the invention, has been developed to lower costs, to increase flexibility, and to enhance inventory control of spare parts in electrical device manufacturing operations. The multi-layered core has a first layer of insulating dielectric material and at least one additional layer of insulating dielectric material. By making a multi-layered core, it is feasible to use one cable in several electrical connections that vary by impedance or size.  
      While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made by those skilled in the art, and are within the scope of the invention.