Patent Publication Number: US-6984789-B2

Title: Electrical cable and method of making

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of Ser. No. 10/336,869, now U.S. Pat. No. 6,735,862, entitled “METHOD OF MAKING ELECTRICAL CABLE”, filed on Jan. 7, 2003. 

   BACKGROUND 
   The present invention relates generally to the field of electrical cables and more specifically to the field of making litz wire. 
   In a wide variety of applications, litz wire (also called “litzendraht wire”) is used to reduce the high frequency impedance of electrical cables. A typical litz wire consists of a number of individually insulated conductors woven together so that each conductor assumes all possible positions in the cross section of the assembly. This arrangement of the conductors tends to reduce high frequency eddy current effects, thereby resulting in lower high frequency impedance. 
   The woven litz wire, while providing high performance, is sometimes prohibitively expensive for some applications owing to difficulty in its manufacture. Opportunities exist, therefore, to reduce the cost of litz wire and expand the number of applications by finding an alternative, less costly method of manufacture. 
   SUMMARY 
   The opportunities described above are addressed, in one embodiment of the present invention, by a method of making an electrical cable, the method comprising: bonding a plurality of electrical conductors to respective neighboring ones of the electrical conductors to form a ribbon, the electrical conductors being electrically insulated from the respective neighboring ones; folding the ribbon to form a cable assembly, each of the electrical conductors traversing the width of the cable assembly at least twice; optionally bonding the cable assembly; and optionally coiling the cable assembly. 

   
     DRAWINGS 
     These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
       FIG. 1  illustrates an orthographic view of a ribbon in accordance with one embodiment of the present invention. 
       FIG. 2  illustrates an orthographic view of an electrical cable in accordance with the embodiment of  FIG. 1 . 
       FIG. 3  illustrates an orthographic view of a ribbon in accordance with another embodiment of the present invention. 
       FIG. 4  illustrates an orthographic view of a ribbon in accordance with another embodiment of the present invention. 
       FIG. 5  illustrates an orthographic view of an electrical cable in accordance with another embodiment of the present invention. 
       FIG. 6  illustrates an orthographic view of a ribbon in accordance with another embodiment of the present invention. 
       FIG. 7  illustrates an orthographic view of a cable assembly bended to form a corner in accordance with one embodiment of the present invention. 
       FIG. 8  illustrates an orthographic view of a cable assembly folded lengthwise in accordance with another embodiment of the present invention. 
       FIG. 9  illustrates an orthographic view of an electrical conductor having various cross section lengthwise in accordance with one embodiment of the present invention. 
       FIG. 10  illustrates an orthographic view of a ribbon in accordance with another embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   In accordance with one embodiment of the present invention,  FIG. 1  illustrates an orthographic view of a ribbon  120 . A method of making an electrical cable starts by bonding a plurality of electrical conductors  110  to respective neighboring ones of electrical conductors  110  to form ribbon  120 , where electrical conductors  110  are electrically insulated from their respective neighbors. Ribbon  120  is then folded as shown in  FIG. 2  to form cable assembly  130 . The folding is performed so that each of electrical conductors  110  traverses the width of cable assembly  130  at least twice. In some embodiments, electrical cable  100  is then completed by bonding cable assembly  130  to hold the folded shape. In some embodiments, such as, for example, in magnetic component applications, electrical cable  100  is completed by coiling cable assembly  130 . In some embodiments, coiling cable assembly  130  is facilitated by bending cable assembly  130  to form corners during the act of folding as illustrated in  FIG. 7 . 
   In another embodiment of the present invention, cable assembly  130  is folded such that electrical conductors  110  do not describe spirals around cable assembly  130 . 
   In another embodiment of the present invention, cable assembly  130  is folded lengthwise before bonding to produce a thicker cable as illustrated in  FIG. 8 . 
   In another embodiment of the present invention,  FIG. 3  illustrates a bonding layer  170  applied to ribbon  120  prior to folding. In some embodiments, bonding layer  170  is electrically insulating. Examples of bonding layer  170  include, without limitation, adhesives and curable polymers. 
   In another embodiment of the present invention, bonding layer  170  is cured by exposure to a bonding stimulus. Examples of bonding stimuli include, without limitation, electromagnetic radiation, mechanical stimuli, and chemical stimuli. 
     FIG. 4  illustrates ribbon  120  in accordance with another embodiment of the present invention. In the embodiment of  FIG. 4 , bonding each of electrical conductors  110  to a respective neighbor is accomplished by bonding the plurality of electrical conductors  110  to a common cable substrate  140 . In some embodiments, cable substrate  140  is electrically insulating. In some embodiments, electrical conductors  110  are spaced apart from their respective neighbors. 
   In another embodiment, each of electrical conductors  110  has a non-rectangular cross section as illustrated in  FIG. 9 . By way of example, but not limitation, circular cross sections may be used. In some embodiments, ribbon  120  is further processed by being rolled flat prior to being folded. 
   In another embodiment, illustrated in  FIG. 4 , the capacitance of electrical cable  100  is influenced by selectively coupling electrical conductors  110 . At a first end of cable assembly  130 , a subset of electrical conductors  110  is electrically coupled to produce a first coupled subset  150 , leaving an uncoupled remainder of electrical conductors  110 . The uncoupled remainder of electrical conductors  110  are then electrically coupled at a second end of cable assembly  130  to produce a second coupled subset  160 . In some embodiments, the first end and second end are at the same end of cable assembly  130 . In other embodiments, the first end and second end are at opposite ends of cable assembly  130  as illustrated in  FIG. 10 . 
   In another embodiment in accordance with the embodiment of  FIG. 4 , members of first coupled subset  150  have different respective lengths. Members of second coupled subset  160  have lengths in one-to-one correspondence with the different respective lengths of the members of first coupled subset  150 . By varying the lengths of electrical conductors  110  in this embodiment, the capacitance is influenced as a function of length along electrical cable  100 , thus influencing the lengthwise current distribution. 
   In another embodiment in accordance with the embodiment of  FIG. 4 , a first insulating gap is produced at a first gap location along the length of first coupled subset  150 . In some embodiments, a second insulating gap is produced at a second gap location along the length of second coupled subset  160 . The first and second insulating gaps also serve to alter overall cable capacitance. 
   In another embodiment in accordance with  FIG. 4 , electrical conductors  110  are bonded to opposite faces of cable substrate  140 . In another embodiment, after folding, electrical conductors  110  are disposed on an outer surface of cable assembly  130 . 
     FIG. 5  illustrates another embodiment wherein ribbon  120  is folded around an insulating strip  180 . 
     FIG. 6  illustrates another embodiment wherein electrical conductors  110  are formed into diagonal patterns  190 . In another embodiment, diagonal patterns  190  are formed on opposite faces of cable substrate  140  with opposite face pairs of electrical conductors  110  being coupled through coupling holes in cable substrate  140 . In another embodiment, opposite face pairs of electrical conductors  110  are coupled at the edges of substrate  140 . 
   While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.