Patent Publication Number: US-11665461-B2

Title: Electronic device accessories formed from intertwined fibers

Description:
This application is a continuation of patent application Ser. No. 15/476,793, filed Mar. 31, 2017, now U.S. Pat. No. 10,681,447, which is a continuation of patent application Ser. No. 12/637,355, filed Dec. 14, 2009, now U.S. Pat. No. 9,628,890, which claims the benefit of provisional patent application No. 61/185,934, filed Jun. 10, 2009, all of which are hereby incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     This invention relates to structures formed from intertwined fibers, and more particularly, to ways in which to form structures for electronic devices from intertwined fibers. 
     Modern weaving, braiding, and knitting equipment can be used to create structures that would be difficult or impossible to implement using other fabrication technologies. For example, woven carbon fiber sheets may be used to form housing structures for electronic devices that are lighter and stronger than housing structures formed from other materials. Flexible cable sheaths may be formed using fiber braiding tools. Many medical devices are formed from fibers. For example, bifurcated vascular grafts and other cardiovascular devices may be formed from fibers. 
     SUMMARY 
     Intertwined fibers may be used in forming sheaths for cables, parts of accessories such as headsets, and other structures. 
     Fiber intertwining equipment such as tools for weaving, braiding, and knitting may be used to intertwine fibers. The fibers that are intertwined with this equipment may include polymer fibers, metal fibers, insulator-coated metal fibers, glass fibers, or other suitable fibers. Once intertwined, a binder such as epoxy or other suitable matrix may foe incorporated into the intertwined structure and cured. 
     Parameters that may be varied during the fabrication process include the number of fibers that are incorporated into a particular region of the structure, the spacing between fibers, fiber type, binder type, binder location, etc. By selectively varying these factors, structures can be formed in which different regions of the structures have different flexibilities, different densities (e.g., to adjust audio transparency, moisture penetration, etc.), different conductivities, etc. Shapes that may be formed using the intertwining equipment include forking structures (e.g., bifurcated structures), tubular structures of variable diameter, structures that have potentially complex compound curves, etc. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of illustrative fabrication equipment that may be used to fabricate structures with intertwined fibers in accordance with an embodiment of the present invention. 
         FIG.  2    is a graph showing how parameters such as intertwining parameters and binder incorporation parameters may be varied as a function of position within a structure when fabricating the structure in accordance with an embodiment of the present invention. 
         FIG.  3    is a side view of an illustrative structure showing how the number of fibers per unit area may be varied as a function of position in accordance with an embodiment of the present invention. 
         FIG.  4    is a side view of an illustrative structure showing how the type of fiber that is used may be varied as a function of position in accordance with an embodiment of the present invention. 
         FIGS.  5 ,  6 , and  7    are side views of illustrative binder incorporation patterns that may be used when forming structures in accordance with an embodiment of the present invention. 
         FIG.  8    is a view of an illustrative tubular structure with a diameter that has been varied during a fiber intertwining process in accordance with an embodiment of the present invention. 
         FIG.  9    is a perspective view of an illustrative electronic device having housing with compound curves that have been formed by intertwining fibers in accordance with an embodiment of the present invention. 
         FIG.  10    is a cross-sectional side view of an illustrative electronic device having compound housing curves that have been formed by intertwining fibers and that contains electronic components and a display screen in accordance with an embodiment of the present invention. 
         FIG.  11    is a rear view of an electronic device of the type shown in  FIG.  10    in accordance with an embodiment of the present invention. 
         FIG.  12    is a cross-sectional side view of an illustrative structure having a layer of intertwined fibers that have been used to form a cosmetic cover layer and a fiber sheet that has been used to implement a structural support member in accordance with an embodiment of the present invention. 
         FIG.  13    is a top view of an illustrative fiber sheet of the type shown in  FIG.  12    showing portions where material may be removed to help the fiber sheet accommodate a compound curve shape in accordance with an embodiment of the present invention. 
         FIG.  14    is a cross-sectional side view of an illustrative structure in which an inner support structure such as a solid support or a skeletal frame has been covered with a layer of fiber that has been intertwined to accommodate a compound curve shape in accordance with an embodiment of the present invention. 
         FIG.  15    is a perspective view of an illustrative electronic device that may be formed using intertwined fiber in accordance with an embodiment of the present invention. 
         FIG.  16    is a perspective view of a forked (bifurcated) tubular structure formed with intertwining equipment in accordance with an embodiment of the present invention. 
         FIG.  17    is a cross-sectional view of a tubular structure such as a cable for an electronic device in accordance with an embodiment of the present invention. 
         FIG.  18    is a cross-sectional side view of illustrative resin transfer mold equipment that may be used to selectively incorporate binder into intertwined fibers in accordance with an embodiment of the present invention. 
         FIG.  19    is a top view of illustrative manufacturing equipment that may be used to incorporate binder into a tubular structure in accordance with an embodiment of the present invention. 
         FIG.  20    is a view showing how a headset cables may be formed by cutting lengths of tube from a continuous tube of intertwined fiber having bifurcated sections in accordance with an embodiment of the present invention. 
         FIG.  21    is a cross-sectional view of an illustrative switch formed from intertwined conductive fibers in accordance with an embodiment of the present invention. 
         FIG.  22    is a perspective view of a tube of intertwined fibers having a conductive electrode portion for use in a switch or other structure in accordance with the present invention. 
         FIG.  23    is a cross-sectional view of an illustrative switch formed from a fiber tube with multiple branches with conductive fibers and insulating branch separator members in accordance with the present invention. 
         FIG.  24    is a side view of an illustrative fiber earbud structure having portions that are more dense and that pass relatively small amounts of sound and having portions that are less dense and that pass relatively large amounts of sound in accordance with an embodiment of the present invention. 
         FIG.  25    is a side view of an illustrative audio connector such as a 3.5 mm audio plug showing how different parts of an associated sheath tube may be provided with different amounts of rigidity in accordance with an embodiment of the present invention. 
         FIG.  26    is a cross-sectional side view of an illustrative audio plug and associated cable sheath that may be formed of intertwined fibers in accordance with an embodiment of the present invention. 
         FIG.  27    is a side view of an illustrative audio plug having a fiber cable into which binder has been selectively incorporated to adjust cable flexibility along the length of the cable in accordance with an embodiment of the present invention. 
         FIG.  28    is a perspective view of an audio plug and fiber cable showing how binder may be incorporated into the cable in a pattern that is radially asymmetric to gradually adjust cable flexibility in accordance with an embodiment of the present invention. 
         FIG.  29    is a perspective view of an illustrative complex structure of the type that may be formed in an electronic device structure using fiber intertwining and binder incorporation equipment in accordance with an embodiment of the present invention. 
         FIG.  30    is a perspective view of a fiber-based structure such as a computer housing or a protective detachable case for an electronic device that may foe provided with a flexible hinge portion and rigid upper and lower planar portions in accordance with an embodiment of the present invention. 
         FIG.  31    shows how a fiber-based structure may be provided with a flexible pocket portion and a rigid planar portion in accordance with an embodiment of the present invention. 
         FIG.  32    is a perspective view of an illustrative electronic device having a housing formed of fibers with different properties in different regions to form, a radio-frequency (RF) antenna window in accordance with an embodiment of the present invention. 
         FIG.  33    is a cross-sectional side view of an illustrative electronic device of the type shown in  FIG.  32    showing how an antenna and transceiver circuitry may be mounted within the device in accordance with an embodiment of the present invention. 
         FIG.  34    is a flow chart of illustrative steps involved in forming fiber-based structures with selectively incorporated binder in accordance with embodiments of the present invention. 
         FIG.  35 A  is a cross-sectional view of an illustrative monofilament fiber that may be used in forming fiber-based structures in accordance with an embodiment of the present invention. 
         FIG.  35 B  is a cross-sectional view of an illustrative multifilament fiber that may be used in forming fiber-based structures in accordance with an embodiment of the present invention. 
         FIG.  35 C  is a cross-sectional view of an illustrative monofilament fiber formed from a composite structure containing multiple materials that may be used in forming fiber-based structures in accordance with an embodiment of the present invention. 
         FIG.  35 D  is a cross-sectional view of an illustrative multifilament fiber having filaments formed from different types of materials that may be used in forming fiber-based structures in accordance with an embodiment of the present invention. 
         FIG.  35 E  is a cross-sectional view of an illustrative multifilament fiber formed of composite fibers in accordance with embodiments of the present invention. 
         FIG.  36 A  is a cross-sectional view of a fiber-based cable containing insulated wires and monofilament fibers in accordance with an embodiment of the present invention. 
         FIG.  36 B  is a cross-sectional view of a fiber-based cable containing insulated wires and multifilament fibers in accordance with an embodiment of the present invention. 
         FIG.  37    is a cross-sectional view of a fiber-based cable containing insulated wires and more than one type of fiber in accordance with an embodiment of the present invention. 
         FIG.  38    is a perspective view of a tube-shaped bifurcated fiber-based cable in accordance with an embodiment of the present invention. 
         FIG.  39 A  is a perspective view of a ribbon-shaped fiber-based cable having a converging bifurcation in accordance with an embodiment of the present invention. 
         FIG.  39 B  shows cross-sectional side views of a cable in accordance with an embodiment of the present invention. 
         FIG.  40    is a perspective view of a ribbon-shaped fiber-based cable having an overlapping bifurcation in accordance with an embodiment of the present invention. 
         FIG.  41 A  is a cross-sectional view of an illustrative ribbon-shaped fiber-based cable having a rectangular profile in accordance with an embodiment of the present invention. 
         FIG.  41 B  is a cross-sectional view of an illustrative ribbon-shaped fiber-based cable having a rectangular profile with rounded corners in accordance with an embodiment of the present invention. 
         FIG.  41 C  is a cross-sectional view of an illustrative ribbon-shaped fiber-based cable having a flattened oval profile in accordance with an embodiment of the present invention. 
         FIG.  41 D  is a cross-sectional view of an illustrative ribbon-shaped fiber-based cable having an oval profile in accordance with an embodiment of the present invention. 
         FIG.  42    is a perspective view of an illustrative headset formed from fiber-based cables that has a switch located on one arm in accordance with an embodiment of the present invention. 
         FIG.  43 A  is a perspective view of a segment of an illustrative fiber-based cable that may be used in an accessory in accordance with an embodiment of the present invention. 
         FIG.  43 B  is a cross-sectional view of an illustrative fiber-based cable showing how conductive wires may be located in the central core of the cable in portions of the cable such as at cross-sectional line X-X of  FIG.  43 A  in accordance with an embodiment of the present invention. 
         FIG.  43 C  is a cross-sectional view of an illustrative fiber-based cable showing how conductive wires may be selectively brought to the surface of the cable to form part of a switch structure in accordance with an embodiment of the present invention. 
         FIG.  43 D  is a cross-sectional view of an illustrative fiber-based cable showing how conductive wires may be located in the central core of the cable in portions of the cable such as at cross-sectional line Z-Z of  FIG.  43 A  in accordance with an embodiment of the present invention. 
         FIG.  44 A  is a perspective view of a portion of a fiber-based cable having a button assembly in accordance with an embodiment of the present invention. 
         FIG.  44 B  is a cross-sectional view of a cable of the type shown in  FIG.  44 A  taken along cross-sectional line X-X of  FIG.  44 A  in accordance with an embodiment of the present invention. 
         FIG.  44 C  is a cross-sectional view of a cable of the type shown in  FIG.  44 A  taken along cross-sectional line Y-Y of  FIG.  44 A  through the button assembly portion of the cable of  FIG.  44 A  in accordance with an embodiment of the present invention. 
         FIG.  44 D  is a cross-sectional view of a cable of the type shown in  FIG.  44 A  taken along cross-sectional line Z-Z of  FIG.  44 A  in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     A schematic diagram of illustrative fabrication equipment that may be used to fabricate structures with intertwined fibers in accordance with an embodiment of the present invention is shown in  FIG.  1   . Fabrication equipment may be used to form fiber-based structures for any suitable device. Examples in which fabrication equipment  10  is used to form parts of electronic devices such as electronic device housings, cable sheaths for headsets, electrical connectors, and other electrical equipment are sometimes described herein as an example. In general, however, fabrication equipment  10  may be used to form any suitable parts (e.g., parts for medical application, for industrial equipment, for mechanical structures with no electrical components, etc.). 
     As shown in  FIG.  1   , fabrication equipment  10  may be provided with fibers from fiber sources  12 . Fiber sources  12  may provide fibers of any suitable type. Examples of fibers include metal fibers (e.g., strands of steel or copper), glass fibers (e.g., fiber-optic fibers that can internally convey light through total internal reflection), plastic fibers, etc. Some fibers may exhibit high strength (e.g., polymers such as aramid fibers). Other fibers such as nylon may offer good abrasion resistance (e.g., by exhibiting high performance on a Tabor test). Yet other fibers may be highly flexible (e.g., to stretch without exhibiting plastic deformation). The fibers provided by sources  12  may be magnetic fibers, conducting fibers, insulating fibers, or fibers with other material properties. 
     Fibers may be relatively thin (e.g., less than 20 microns or less than 5 microns in diameter—i.e., carbon nanotubes or carbon fiber) or may be thicker (e.g., metal wire). The fibers provided by sources  12  may be formed from twisted bundles of smaller fibers (sometimes referred to as filaments) or may be provided from sources  12  as unitary fibers of a single untwisted material. Regardless of their individual makeup (i.e. whether thick, thin, or twisted or otherwise formed from smaller fibers), the strands of material from fiber sources  12  are referred to herein as fibers. The fiber from sources  12  may also sometimes be referred to as cords, threads, ropes, yarns, filaments, strings, twines, etc. 
     Intertwining tool(s)  14  may be based on any suitable fiber intertwining technology. For example, intertwining equipment  14  may include computer-controlled weaving tools, computer-controlled braiding tools (e.g., for forming tubular structures), and/or computer-controlled knitting equipment (e.g., three-dimensional knitting tools capable of producing intertwining fiber structures with bifurcations/compound curves, and other such complex shapes). These tools are sometimes referred to collectively herein as intertwining tool(s)  14 . 
     Tools  14  form intertwined fiber structures. Matrix incorporation tools(s)  16  may be used to incorporate binder material into the intertwined fiber (e.g., to provide these structures with rigidity or other suitable properties). The binder, which is sometimes referred to as a matrix, may be formed from epoxy or other suitable materials. These materials may sometimes be categorized as thermoset materials (e.g., materials such as epoxy that are formed from a resin that cannot be reflowed upon reheating) and thermoplastics (e.g., materials such as acrylonitrile butadiene styrene, polycarbonate, and ABS/PC blends that are reheatable). Both thermoset materials and thermoplastics and combinations of thermoset materials and thermoplastic materials may be used as binders if desired. 
     Tools  16  may include molds, spraying equipment, and other suitable equipment for incorporating binder into portions of the intertwined fibers produced by intertwining equipment  14 . Tools  16  may, if desired, include computer-controlled equipment and/or manually operated equipment that can selectively incorporate binder into different portions of a workpiece in different amounts. For example, when it is desired to stiffen a fiber structure, more resin can be incorporated into the intertwined fiber, whereas less resin can be incorporated into the intertwined fiber when a flexible structure is being formed. Different portions of the same structure can be formed with different flexibilities in this way. Following curing (e.g., using heat or ultraviolet light, the binder will stiffen and harden). The resulting structure (called finished part  20  in  FIG.  1   ) can be used in a computer structure, a structure for other electrical equipment, etc. 
     A graph showing how parameters such as intertwining parameters and binder incorporation parameters may be varied as a function of position within a structure when fabricating the structure is shown in  FIG.  2   . The horizontal axis in the graph of  FIG.  2    represents position within a fiber-based structure (e.g., length along a cable or lateral distance across a planar surface). The vertical axis represents the magnitude of the parameter that is being varied. As the lines of the graph of  FIG.  2    indicate, parameters can be varied smoothly and continuously, discretely, in an increasing fashion, decreasing, periodically, etc. Examples of parameters that can be varied according to the lines of the graph of  FIG.  2    include the number of fibers in a given area, the size of the individual fibers, the spacing between adjacent fibers (porosity or fiber density), the type of filaments being used (e.g., the amount which a fiber or collection of fibers is insulating, abrasion-resistant, conducting, strong, magnetic, etc.), and the amount and/or type of binder being incorporated. 
       FIG.  3    is a side view of an illustrative structure such as a tube or planar patch of intertwined fiber showing how the number of fibers per unit area may be varied as a function of position. In region  22  there are more fibers per unit area than in region  24 . The portion of the structure in region  24  will tend to be weaker, more porous, and therefore transparent to moisture and sound, lighter, and more flexible than the portion of the structure in region  22 . 
     As shown in  FIG.  4   , structure  26  may have two or more different types of fibers such as fibers  28  and fibers  30 . These fibers may have different properties. In the  FIG.  4    example, there are more of fibers  28  in region  32  than fibers  30 . In region  34 , however, fibers  30  are more prevalent than fibers  28 . This type of spatial variation of fiber type allows the properties of structure  26  to be spatially adjusted during fabrication with equipment  10 . 
       FIGS.  5 ,  6 , and  7    are examples of structures in which binder has been incorporated in different patterns. In structure  36  of  FIG.  5   , intertwined fiber portions  38  may be formed without binder, whereas portions  40  may include binder. Structure  36  may be a fiber tube or a planar fiber-based structures (examples). In structure  42  of  FIG.  6   , there is only a single relatively large portion of binder (region  44 ), while regions  46  are free of binder. In structure  48  of  FIG.  7   , regions  50  are binder-free, whereas regions  52  incorporate binder in different patterns. 
     Equipment  10  can be used to form fiber-based structures of various shapes (e.g., tubes, planar members such as housing surfaces, spheres or parts of spheres, shapes with compound curves, cylinders or partial cylinders, cubes, tubes with bifurcations or regions of three or more forked branches, combinations of these shapes, etc.).  FIG.  8    shows how equipment  10  can form a tube or other structure  58  with a diameter D that is narrower in some regions (e.g., regions  54 ) than in other regions (e.g., region  56 ). 
     A perspective view of an illustrative electronic device having a housing with compound curves is shown in  FIG.  9   . As shown in  FIG.  9   , device  60  may have a housing or other structure that has a planar rear surface portion such as portion  64 . Device  60  may also have four corner portions  62 . Each corner portion  62  has compound curves. These curves may be difficult or impossible to form from conventional woven-fiber sheets. 
     With equipment  10  of  FIG.  1   , three-dimensional (3D) knitting equipment or other intertwining tools  14  can be used to form a fiber-based structure (e.g., a housing or covering) that conforms to both the planar rear surface  64  and compound curve corners  62  of structure  60 . 
     A cross-sectional side view of device  60  of  FIG.  9    taken along line  66  of  FIG.  9    and viewed in direction  68  is shown in  FIG.  10   . As shown in  FIG.  10   , device  10  may have curved sidewalls  70 , a display or other front-mounted component  74 , and internal electronic devices  72  (e.g., processor and memory circuitry). A rear view of device  60  is shown in  FIG.  11   , illustrating part of the curved shapes of corners  62  that can be covered smoothly without wrinkles or seams using the knit fiber produced by equipment  10 . 
     The ability of equipment  10  to produce thin layers of intertwined fiber that conform to complex non-planar shapes can be used to create a cosmetic cover layer with compound curves. As shown in  FIG.  12   , device housing  80  may have an inner layer  78  that is formed from a planar sheet of fiber with cut-away portions to accommodate compound curve housing shapes (e.g., corners  62  of  FIG.  9   ). Layer  76  may be a conformal cosmetic cover layer formed using equipment  10 . Layers  76  and/or layer  78  may be impregnated with binder using a matrix incorporation tool. 
       FIG.  13    is a top view of a planar layer such as layer  78  that has removed portions  82  to accommodate compound curve shapes (e.g., housing corners). This process leaves unsightly seams that are hidden by cosmetic layer  76  ( FIG.  12   ). 
       FIG.  14    is a cross-sectional side view of device  80  showing how layer  76  may conformally cover an inner support structure (i.e., structure  84 ) and how device  80  may have a display module or other component  86  mounted to its front surface. Structure  84  may be solid, may be hollow (e.g., as in a frame or skeletal support), may include components, etc. 
     An example of an electronic device accessory that may be formed from intertwined fiber structures is a pair of audio headphones. An illustrative headset is shown in  FIG.  15   . As shown in  FIG.  15   , headset  88  may include a main cable portion  92 . Cable  92  may be formed from intertwined fibers and may have portions formed from different types and amounts of fibers and different patterns and amounts of binder (as examples). Earbuds  90  (i.e., earbuds that each contains one or more speakers) may be mounted at the ends of the right and left branches of cable  92 . In region  94 , cable  92  may have a bifurcation (forked region). Feature  96  may be an enclosure for a switch, microphone, etc. The end of cable  92  may be terminated by audio connector (plug)  98 . Connector  93  may be, for example, a 3.5 mm audio plug that mates with a corresponding 3.5 mm audio jack in a media player, cellular telephone, portable computer, or other electronic device. 
       FIG.  16    shows how intertwining tool  14  may, if desired, form Y-junction  94  of cable  92  without visible seams. A cross-sectional view of cable  92  is shown in  FIG.  17   . As shown in  FIG.  17   , cable  92  may have a tubular sheath such as sheath  100  that surrounds one, two, or more than two wires. In the  FIG.  17    example, there are two conductive wire bundles within sheath  100 . Wire bundle  102  may be formed from a first set of metal fibers and wire bundle  104  may be formed from a second set of wire bundles. The individual wires in bundles  102  and  104  may be coated with a thin layer of insulator (if desired). Sheath  100  may be formed from a fiber with sufficient strength to resist damage during use by a user and sufficient flexibility to allow cable  92  to flex. If desired, regions such as Y-junction region  94  and portions of device  88  near earbuds  90  and plug  98  may be provided with stronger fibers and more binder to strengthen these regions. 
     Structure  96  may also be strengthened in this way. As an example, structure  96  may be impregnated with binder, whereas most of the rest of cable  92  may be left binder-free.  FIG.  18    shows how a resin transfer molding tool such as tool  106  may be used to selectively incorporate binder  110  into region  96  of cable  92  (e.g., by introducing binder  110  into the interior of tool  106  through opening  108 ). 
     As shown in  FIG.  19   , cable  92  may be rotated in direction  124  about longitudinal axis  126  while binder  110  is being sprayed onto cable  92  from spraying tool  114 . Binder  110  may be cured using ultraviolet light  122  from ultraviolet light source  120 . Shield  116  may prevent binder  110  from striking source  120  and may prevent light.  122  from curing binder  110  at the exit of nozzle  128 . 
     Equipment  10  may produce cable  92  using a continuous process. As shown in  FIG.  20   , equipment  10  may produce a cable shape that periodically forks to form two separate branches and then fuses so that the two branches form a single tubular structure. With this type of arrangement, post processing tools  18  of  FIG.  1    may be used to cut cable  92  along cut lines  130 . 
     As shown in  FIG.  21   , cable  92  may be provided with conductive fibers such as fibers  132  and  134 . This type of configuration may be produced when it is desired to form a switch in structure  96 . As shown in  FIG.  21   , conductive fibers  132  and conductive fibers  134  in structure  96  may be separated by gap region  136 . Region  136  may be filled with air (as an example). When a user squeezes outer edges inwardly in directions  140 , opposing inner portions  142  of conductors  132  and  134  can meet, thereby closing the switch. 
     Conductive fibers on cable  92  may be used to form a capacitor electrode (e.g., as part of a switch based on a capacitive sensor). This type of configuration is illustrated by conductive fiber band  144  on cable  92  in  FIG.  22   . 
     In the example of  FIG.  23   , switch  96  has been formed from opposing metal conductor portions  132  and  134  (each of which may be connected to a respective cable wire such as wires formed from wire bundles  102  and  104 ). Cable  92  may have two branches that rejoin each other on either end of switch structure  96 . In the center of structure  96 , outward biasing members  146  (e.g., air filled balloons or spring-filled members) may be used to bias switch contacts  132  and  134  away from each other in outward directions  143  so that switch  96  is off when not compressed inwardly by a user. 
     A side view of an illustrative fiber-based earbud and associated cable is shown in  FIG.  24   . As shown in  FIG.  24   , earbud  90  may have regions  150  and  152 . Region  150  may be more porous than region  152  and may be more (or less) flexible than region  152 . The increased porosity of region  150  may make region  150  transparent to audio, so that sound from internal speaker drivers may pass through regions  150  unimpeded. Regions  150  may have fewer and less densely intertwined fibers than region  152  and may incorporate less binder than region  152  or no binder. It may be desirable to make region  152  less porous (e.g., to block sound, to increase rigidity or durability, etc.). Accordingly, more binder may be incorporated into region  152  than in region  150  and/or fibers may be more densely intertwined. In addition to increasing the fiber density and/or binder quantity in region  152 , different (e.g., denser, thicker, etc.) fibers may be used in region  152 . Cable  92  in region  154  may be formed of flexible fibers (e.g., with little or no binder). If desired, some of cable  92  near region  152  may be provided with stronger fibers, more fibers, more binder for rigidity and strength, etc. 
     As shown in  FIG.  25   , audio plug  98  (or other electrical connectors) may be provided with a flexible cable portion  92  and a rigid inner strain relief structure  158 . Metal plug structure  160  may be connected to wires within cable  92 . In region  156 , binder may be incorporated into the fibers of cable  92  to increase strength and rigidity. If desired, cable  92  may also be provided with an increased number of strong fibers in region  156  and/or may be provided with a higher fiber density to further increase strength. These types of structural features may be used for any suitable electrical connector. The use of an audio connector in  FIG.  25    is merely an example. 
       FIG.  26    shows how cable  92  may form a conformal sheath over support (strain-relief) structure  158  and wires  102  and  104 . 
     The flexibility of cable  92  can be adjusted along its length by selectively incorporating binder in appropriate areas. This type of arrangement is shown in  FIG.  27   . In the example of  FIG.  27   , connector  98  may have a metal multi-contact portion such as portion  160  (e.g., a three-contact or four-contact audio plug). Region  162  of connector  98  may be completely filled with binder. Only some portions (e.g., rings  168 ) of region  164  are provided with binder (in this example), so cable  92  will be more flexible in region  164  than in region  162 . In region  170 , there is no binder in the fibers of cable  92 , so cable  92  has maximum flexibility in region  170 . 
     Another suitable arrangement for connector  98  is shown in  FIG.  23   . In the example of  FIG.  23   , cable  92  has no binder in region  178  and is therefore flexible in this region. In region  176 , a non-radially symmetric pattern of binder  172  is used to provide a decreased flexibility. Region  174  has more binder than region  172  and is therefore rigid and structurally strong. This type of configuration allows the binder pattern in region  176  to serve as a moderate-flex interface between rigid region  174  and flexible region  178 . 
       FIG.  29    shows how equipment  10  may be used to form complex shapes for part  20  such as hook  180  with hole  182 . The fiber in hook  180  may be formed of stronger material than the fiber elsewhere in the structure. Part  20  may be formed as an integral portion of an electronic device housing (as an example) 
     As shown in  FIG.  30   , equipment  10  may form structures such as structure  184  that have rigid planar portions such as rigid planar portions  186  and  188  and flexible hinge portions such as flexible hinge  190 . This type of arrangement may be provided by incorporating binder into portions  186  and  188 , but not into hinge  190 . Structure  184  may be used for a portable computer housing, a folio-style case for a detachable electronic device such as a media player or cellular telephone, etc. 
     As shown in  FIG.  31   , a fiber-based case or other fiber-based structure  192  may be formed from a rigid binder-filled planer portion  194  and a flexible binder-free portion  196 . Portion  196  may serve as a flexible pocket that holds a cellular telephone or music player. Portion  194  may be provided with a matching front face if desired. 
     Some parts that are formed from fiber-based structures may be used for electronic device housings or other applications in which at least a portion of the structure is adjacent to an antenna. In situations such as these, it may be desirable to incorporate one or more antenna windows into the part. For example, in an electronic device housing that is formed from conductive fibers, an antenna window that is transparent to radio-frequency antenna signals can be formed over an antenna within the electronic device housing. The antenna window  30  can be formed by incorporating a solid dielectric window in the housing and by attaching the conductive fibers to the solid window (e.g., using epoxy or other adhesive). Antenna window structures can also be formed by using equipment  10  to form an integral fiber-based antenna window structure within part of the electronic device housing. The antenna window structure may be formed from a fiber that contains primarily polymer, glass, or other dielectric. Because this material is nonconducting, the antenna window structure will be able to pass radio-frequency signals without interference from the fibers in the window. 
     An illustrative fiber-based structure with an antenna window is shown in  FIG.  32   . Structure  200  of  FIG.  32    may be, for example, a housing for an electronic device such as a media player, cellular telephone, portable computer, or other electronic device. Structure  200  may be formed using equipment  10 . For example, structure  200  may include corner portions that have compound shapes that have been created using intertwining tool  14  (e.g., 3D knitting equipment). In regions  198 , housing walls can be formed from insulating or conductive materials or combinations of insulating and conductive materials (e.g., carbon fibers, polymers, steel filaments, etc.). The materials in regions  198  may include conductors (nondielectrics) and may therefore block radio-frequency wireless signals. Equipment  10  can use dielectric fiber when forming the intertwined fibers of antenna window  202 , thereby ensuring that the material in window  202  will be transparent to antenna signals. 
     A cross-sectional side view of structure  200  of  FIG.  32    taken along line  201  is shown in  FIG.  33   . As shown in  FIG.  33   , structure  200  may have housing walls  198  that are formed from intertwined fibers and associated binder. In region  202 , an antenna window is formed by using dielectric fibers and binder that are transparent to wireless radio-frequency signals. This allows radio-frequency signals  212  to pass through window  202  during wireless transmission and reception operations with antenna  206 . Antenna  206 , which may be a single band antenna or a multi-band antenna and which may include one or more individual antenna structures, may be coupled to radio-frequency transceiver circuitry  210  on printed circuit board  204  using transmission line path  208 . 
     Illustrative steps involved in forming fiber-based structures using equipment  10  of  FIG.  1    are shown in  FIG.  34   . At step  214 , equipment  10  may be provided with one or more different sources of fibers (e.g., fiber sources  12  of  FIG.  1   ). Fibers may be used that provide suitable amounts of strength, stretchability, flexibility, abrasion resistance, insulation, conductivity, color, weight, magnetism, etc. Some of the fibers may be formed from metals such as ferrous metals. Other fibers may be formed from polymers or glasses. There may be one, two, three, or more than three different types of fiber sources available to a given intertwining tool  14 . Each fiber may have a different property and may be incorporated into a workpiece in an accurately controlled percentage. This allows tools  14  to form structures that have portions with different properties. 
     At step  216 , tools  14  may be used to form fiber-based structures of appropriate shapes and sizes. Different types of tools may be used for different types of operations. For example, a computer-controlled braiding machine may be used to form a continuous or semi-continuous fiber-based tube for a headset cable sheath, a weaving tool may be used to form housing sidewalls for a portable computer with an integral antenna window or a flexible hinge portion, and a 3D knitting tool may be used to form housing shapes with compound curves for a cosmetic or structural housing surface. These tools may each be used to form separate parts that are assembled together by hand or by automated assembly tools or may be used to form unitary structures that are complete without the addition of further fiber-based parts. 
     During the operations of step  218 , matrix incorporation equipment  16  may be used to selectively incorporate binder into the intertwined fibers that were produced during the operations of step  214 . Binder may be incorporated in patterns that provide controlled amounts of flexibility. For example, binder patterns may include rings of the same shape or different shapes (e.g., rings of varying width of other patterns that provide a smooth transition in the amount flexibility at various points along the length of a tube or other elongated structure). Binder patterns may also include solid regions (e.g., for forming rigid planar structures such as housing walls for a portable computer, handheld electronic device, or other structure). Other regions of a structure may be provided with little or no binder (e.g., in a hinge structure, cable, or pocket where maximum flexibility is desired or in an earbud speaker port or computer housing speaker port where audio transparency is desired). 
     After incorporating desired patterns of binder into the intertwined fiber structures, additional processing steps may toe performed during the operations of step  220 . These operations may include, for example, assembling a headset by cutting headset parts from a continuous stream of parts, adding a cosmetic cover to a structural housing member, using adhesive or other fasteners to connect separate fiber-based structures to each other or to parts that do not include fibers, etc. 
     If desired, the steps of  FIG.  34    may be repeated and/or performed in different orders. For example, it may be desirable to assemble two or more intertwined fiber parts before matrix incorporation operations are performed at step  218 . It may also be desirable to build up complex structures by using a series of incremental operations. During each such incremental step, a layer of fiber-based material may be added to a workpiece and additional binder may be incorporated and cured. An incremental approach such as this may be used for part of a fiber-based structure while other parts of the structure are formed using a single intertwining operation and a single binder incorporation operation (as examples). 
     The fibers that are used for constructing fiber-based cables and other fiber-based structures may be formed from materials such as nylon, polyester, polypropylene, para-aramid (long-chain polyamide) synthetic fibers such as KEVLAR® fiber, other polymers, glass, metals such as steel, or ether suitable material. If desired, fibers may be formed from a super-elastic shape memory alloy such as nickel titanium (sometimes referred to as nitinol). Combinations of these materials may also be used. 
     Fiber materials may be chosen so as to provide device housings, cables, and other structures that are formed from intertwined fibers with desired properties. For example, materials may be selected that are strong, exhibit good abrasion resistance, and are not difficult to color (e.g., by incorporating pigments). It may be desirable to choose materials based on their conductive (or non-conductive) or magnetic properties. It may also be desirable to use cost-effective materials. Materials such as nylon (polyamides) and polyester may be receptive to coloring additives. A material such as a para-aramid synthetic polymer may be strong, but may exhibit relatively poor abrasion resistance. It may therefore be desirable to incorporate para-aramid synthetic fibers into cables that also incorporate other fibers (e.g., fibers with good abrasion resistance such as an appropriate nylon). A fiber-based cable formed from a material such as steel may exhibit magnetic properties. For example, a steel-based cable may be magnetized. Magnetized cables may be magnetically attracted to themselves, thereby facilitating cable management. Magnetic cables may also be held in place using magnets (e.g., when the cables are being stored between uses). Fiber-based cables and other structure may be provided with these magnetic properties by incorporating steel fibers into at least part of the structures. It may be desirable to form individual fibers from a composite of materials to take advantage of the properties of different materials. Fibers may also be formed from multiple filaments. 
     An illustrative fiber that is formed from single filament (i.e., a monofilament fiber structure) is shown in  FIG.  35 A . In particular,  FIG.  35 A  shows a cross-sectional view of monofilament fiber  222 . Fiber  222  may be, for example, a monofilament of nylon or other suitable material. Fiber  222  may have any suitable diameter (e.g., 0.5 mm or less, 0.2 mm or less, 0.1 mm or less, 0.05 mm or less, 0.02 mm or less, 0.01 mm or less, etc.). 
     A cross-sectional view of an illustrative fiber that is formed from multiple filaments is shown in  FIG.  35 B . As shown in  FIG.  35 B , multifilament fiber  224  may be formed from numerous individual filaments  226 . Filaments  226  may be, for example, formed from nylon, polyester, or other suitable materials. Filaments  226  may be intertwined using intertwining tool  14  ( FIG.  1   ) or other suitable equipment to form fiber  224 . 
       FIG.  35 C  shows a cross-sectional view of a monofilament fiber (fiber  228 ) that is formed from a composite of different materials. Composite fiber  228  is formed from materials that remain distinct within fiber  228  so that some parts of fiber  228  are predominantly formed from a certain material, whereas other parts of fiber  228  are predominantly formed from another material. In the example of  FIG.  35 C , fiber  228  is shown as having two distinct materials  230  and  232 . In general, fiber  228  may be formed of any number of distinct materials (e.g. three or more different materials, four or more materials, etc.). If desired, each of the materials  230  and  232  may be in itself be formed from a mixture of materials. Fiber  228  is shown segmented radially in the illustrative cross-section of  FIG.  35 C . In general, fiber  228  may be divided into multiple different materials in any suitable fashion. For example, different materials may be formed in radially symmetric coatings (i.e., different layers). 
       FIG.  35 D  shows a cross-sectional view of a multifilament fiber (fiber  234 ) that has filaments  236  and  238  that are formed from different materials. Fiber  234  may have any suitable proportion of filaments  236  and  238 . Fiber  234  is shown as having two types of filaments, although, in general, fiber  234  may have any number of types of filaments. Filaments  236  and  238  may be intertwined using intertwining tool  14  or other suitable equipment. 
     Another illustrative arrangement that may be used for forming a multifilament fiber is shown in the cross-sectional view of  FIG.  35 E . As shown in  FIG.  35 E , multifilament fiber  240  may have filaments  242  that are formed from a composite of materials. In the  FIG.  35 E  example, each filament  242  is shown having radial segments of materials  244  and  246 . In general, filament  242  may be formed of any number of distinct materials and filament  242  may be segmented in any suitable manner. Fiber  240  of  FIG.  35 E  is shown as having only one type of composite filament  242 . If desired, fiber  242  may be formed of any number of types of composite filaments or may be formed of a mixture of composite filaments and unitary-material filaments (i.e., filaments that are not formed from a composite of multiple materials). Filaments  242  may be wound together like yarn to form fiber  240  using intertwining tool  14  or other suitable equipment. 
     Fiber-based cables may contain insulated wires. An arrangement of this type is shown in the examples of  FIGS.  36 A and  36 B .  FIG.  36 A  shows a cross-sectional view of a fiber-based sheath formed from intertwined monofilament fibers  245 . Fibers  245  may be intertwined in any suitable fashion and may be formed in one or more layers. For example, fibers  245  may be woven such that some fibers  245  form a warp and other fibers  245  form a weft. Fibers  245  may be knitted such that fibers  245  form interlocking loops. Fibers  245  may also be braided. One or more insulated wires  247  may lie inside cable  242 . Each insulated wire  247  may have a conductive center  248  and a layer of insulation such as insulation  250 . Conductive center  248  may be formed from copper or other suitable conductive material. Insulation  250  may be formed from plastic (as an example). Cable  242  is shown has having two insulated wires  247  in the example of  FIG.  36 A . In general, cable  242  may have any suitable number of insulated wires  247 . In  FIG.  36 A , insulated wires  247  are shown as being surrounded by one layer of fibers  245 . In general, insulated wires  247  may be surrounded by any suitable number of fiber layers. 
       FIG.  36 B  shows a cross-sectional view of a fiber-based cable  252  that has a fiber-based sheath formed from multifilament fibers  254 . Each fiber  254  may have many filaments  256 . Fibers  254  may be woven, knitted, braided, or otherwise intertwined using intertwining tool  14  or other suitable equipment. Cable  252  may have insulated wires  247  that each have a conductive center  248  surrounded by insulation  250 . Cable  252  of  FIG.  36 B  is shown as having two insulated wires  247 . If desired, cable  252  may have a different number of insulated wires  247  (e.g., three or more wires  247 , etc.). Cable  252  has a fiber-based sheath that is formed from one layer of multifilament fibers  254  although in general cable  252  may have a fiber-based sheath that has any suitable thickness and any number of layers of  252 . Cable  252  may have a fiber-based sheath that is formed from a mixture of monofilament and multifilament fibers. Cable  252  may have a fiber-based sheath that has fibers of different materials or fibers formed from composite materials. 
       FIG.  37    is a cross-sectional view of a fiber-based cable  258  that is formed from two types of fibers. Cable  258  has fibers  260  that may be, for example, nylon or another polymer. Fibers  262  may be a different material such as para-aramid, glass, steel, or other suitable material. Fibers  262  that are formed from strong materials such as para-aramid materials may add strength to cable  258 . 
     Fibers  262  that formed from magnetic materials such as steel may add magnetic properties to cable  258 . 
     Fibers  262  may be monofilament or multifilament fibers. Fibers  262  may also be formed from composite materials. Fibers  260  and  262  may be woven, knitted, braided, or intertwined in any other suitable fashion. The fiber-based sheath of cable  258  is shown as having a thickness of two fibers. In general, fiber-based sheaths for cables may have any suitable thicknesses. Fibers  262  are shown in  FIG.  37    as being part of an inner layer of cable  258 , but if desired, fibers  262  may also be formed as part of the outermost surface of cable  258 . Cable  258  is shown as having two insulated wires  247  each having conductive center  248  and insulation  250 . This is merely illustrative. Fiber-based cables such as cable  258  may have any suitable number of insulated wires  247 . 
     A seamless Y-junction (sometimes referred to as a bifurcation) may be formed in an accessory cable by forming the cable with intertwining tool  14 . As shown in  FIG.  38   , for example, cable  264  may be formed with a seamless Y-junction such as junction  272 . Fiber-based cable  264  in the example of  FIG.  38    has a round profile, so cable  264  has a cylindrical tube shape. Below Y-junction  272  (i.e., at the proximal end of a headset, near its audio plug), cable  264  has only one branch  266 . Branch  266  may have a diameter D 1 . After the Y-junction (i.e., at the distal end of the headset near its speakers), cable  264  may have two branches  268  and  270 . Branch  268  may have a diameter D 2  and branch  270  may have a diameter D 3 . Each of the diameters D 2  and D 3  may be less than diameter D 1  of branch  266  or may be equal or greater than the diameter D 1  of branch  266 . Diameters D 2  and D 3  may, if desired, be equal. 
     In a typical arrangement, fiber-based cable  264  has fibers that are intertwined so that the number of fibers that are present at one end of the cable is substantially same as the number of fibers that are present at another end of the cable. For example, branch  266  may contain N1 fibers (i.e., N1 fibers would pass through a cross-section of branch  266 ). Similarly, branch  268  may contain N2 fibers and branch  270  may contain N3 fibers. The fibers of cable  264  may be intertwined in such a way that the number of fibers that are present before the Y-junction is the same as the number of fibers after the Y-junction, i.e., N1=N2+N3. Each of the fibers in branches  268  and  270  in this type of arrangement passes through Y-junction  272  to branch  266 . Each fiber that has one end in branch  266  has another end in either branch  268  or branch  270 . In arrangements in which electrically insulated wires are contained in the structure, these wires typically pass uninterrupted from branch  266  to branches  268  and  270 , even if ail of the wires are not needed at the distal ends of branches  268  and  270 . This is because intertwining tool  14  typically does not interrupt delivery of particular wires to the cable during the cable formation process (i.e., the cable formation process is substantially continuous as described in connection with the example of  FIG.  20   ). 
     The fibers of cable  264  may form a sheath. Insulated wires may be contained in the sheath. The number of insulated wires in branch  266  may be equal to the number of wires in branch  268  plus the number of wires in branch  270 . Each wire that has one end in branch  266  may have another end in either branch  268  or branch  270 . If cable  264  is a headphone cable, four wires may be present in branch  266 , with two of the wires continuing into branch  268  and the other two wires continuing into branch  270 . Cables for accessories with additional electronic components such as button assemblies and microphones may have more insulated wires (e.g., another two or four wires that extend from branch  266  to branch  268 ). 
     A fiber-based cable may also have a flat, ribbon-like profile. This type of fiber-based cable is shown as cable  274  in  FIG.  33 A . Cable  274  may have a rectangular or oblong cross-section. A Y-junction such as junction  276  may be formed in cable  274 . At one side of Y-junction  276  (i.e., at the proximal end of a headset or other accessory), cable  274  may have one branch  278 . At another side of Y-junction  276  (i.e., at the distal end of a headset or other accessory), cable  274  may have two branches  280  and  282 . The same number of fibers may be present before and after the Y-junction, e.g., the number of fibers in branch  278  may be equal to the number of fibers in branches  280  and  282 . Each of branches  280  and  282  may be thinner or have a smaller cross-section than single branch  278 . 
     Y-junctions such as Y-junction  276  of  FIG.  39 A  may sometimes be referred to as converging Y-junctions. Single branch  278  may have a width W 1  and a thickness T 1 . At the other side of Y-junction  276 , branches  280  and  282  may each have a width W 2  and a thickness  72 . The thickness of cable  274  may be substantially the same before and after the Y-junction, so that T 1 =T 2 , as shown in  FIG.  39 B . Single branch  278  may have a width W 1  that is approximately twice the widths W 2  of branches  280  and  282  (as an example). For example, branch  278  may have a width W 1  of 2 millimeters and a thickness T 1  of 0.5 mm. Branches  280  and  282  may each have a width W 2  of 1 millimeter and a thickness T 2  of 0.5 millimeters. These dimensions are merely illustrative. In general, cable  274  may have any suitable dimensions. In the example of  FIG.  39 A , branches  280  and  282  are shown as having the same cross-sectional dimensions, but, if desired, branches  280  and  282  may have different cross-sectional dimensions. 
     A fiber-based cable with a ribbon-like profile may also have an overlapping Y-junction, as shown in  FIG.  40   . Fiber-based cable  286  in  FIG.  40    has one branch  290  on one side of Y-junction  288  (i.e., at the proximal end of a pair of headphones) and two branches  292  and  294  on another side of Y-junction  288  (i.e., at the distal end of the headphones). Branches  292  and  294  may overlap slightly before uniting at Y-junction  288 . Ribbon-like cable  286  may have a rectangular or oblong cross-section. Single branch  290  may have a width W 1  that is greater than a thickness T 1 . Branches  292  and  294  may have widths K 2  that are greater than thicknesses T 2 . Single branch  290  may have a width W 1  that is the approximately the same as widths W 2  of branches  292  and  294 . Single branch  290  may have a thickness T 1  that is approximately twice the thickness T 2  of branches  292  and  294 . For example, single branch  290  may have a width of 1.5 millimeters and a thickness of 1.0 millimeters. Branches  292  and  294  may each have widths W 2  of 1.5 millimeters and thicknesses T 2  of 1.0 millimeters. These dimensions are merely illustrative. In general, branches  292  and  294  need not have the same dimensions, and the thickness of single branch  290  need not be twice the thicknesses of branches  292  and  294 . Overlapping Y-junction  288  may be a seamless Y-junction. Fibers may run seamlessly along the length of cable  236 . Fibers that are in single branch  290  may pass through Y-junction  299  and into one of either branches  292  and  294 . The number of fibers that are present in single branch  290  may be the sum of the number of fibers in branches  292  and  294 . 
     The ribbon-shaped cables of  FIGS.  39  and  40    may have rectangular, oblong, or oval profiles. Examples of ribbon-shaped cables are shown in the cross-sectional view of  FIGS.  41 A- 41 D . Each of the fiber-based cables of  FIG.  41 A- 41 D  has a width W that is greater than a thickness T. Cable  296  in  FIG.  41 A  has a cross-section that that is substantially rectangular with sharp corners. Cable  298  in  FIG.  41 B  has a cross-section that is substantially rectangular with rounded corners. Cable  298  may be said to have an oblong-shaped cross-section. Cable  300  in  FIG.  41 C  has a flattened oval-shaped cross-section. The cross-section of cable  302  in  FIG.  41 D  is an oval that is rounder than that of cable  300  in  FIG.  41 C . 
     Headphones  304  in  FIG.  42    may have a fiber-based cable such as cable  320  with a seamless Y-junction such as Y-junction  306 . One side of Y-junction  306  may have a single branch  308  leading to an audio connector  310  at the proximal end of cable  320 . Another side of Y-junction  306  may have two branches  312  and  314 , each leading to an earbud  316  at the distal portion of cable  320 . Branch  312  may have a user interface such as a button assembly or other suitable input-output component. The input-output component may include one or more microphones, status indicators, buttons, switches, etc. With one suitable arrangement, which is sometimes described herein as an example, branch  312  may be provided with a button controller assembly such as switch-based controller  318 . A user may use controller  318  to transmit information to an electronic device that is connected to audio connector  310 . For example, a user may actuate one of several different button-based switches (e.g., a rewind or back button, a stoop or pause button, a forward or play button, etc.). A microphone in controller  318  may be used to gather a user&#39;s voice (e.g., to serve as a voice microphone during a telephone call). Headphones  304  may also incorporate a microphone that is located at a location that is remote from controller  316 . 
     Fiber-base cable  320  of  FIG.  42    may have a fiber-based sheath that surrounds insulated conductive wires. Headphones  304  may have wires that connect contacts (terminals) in audio connector  310  to each earbud  316  to provide audio for a user. Headphones  304  may have, for example, two wires that run from audio connector  310  to each earbud  318 . One of the wires of each pair of wires may serve as a common ground. The other wire in each pair may serve as either a left audio wire or a right audio wire, respectively. Additional wires may run from audio connector  310  to controller  318  to provide button and optional microphone functionality. For example, two insulated wires, or a two-conductor coaxial cable, may be used to convey signals to and from controller  318 . If a microphone is incorporated into headphones  304  (e.g., in connection with additional circuitry in controller  318 ), there may be additional conductive wires that transmit signals from the microphone to connector  310 . If desired, the conductive wires may be intertwined with the fibers of fiber-based headphones  304 . 
     When cable  320  is formed using a continuous process of the type described in connection with  FIG.  20   , the same number of fibers may be present at each end of cable  320 . The number of fibers in branch  308  may be the sum of the number of fibers in branches  312  and  314 . The same number of insulated wires may also be present at each end of cable  320 . For example, if six insulated wires are present in branch  308 , then two insulated wires may be present in branch  314  and four insulated wires may be present along the entire length of branch  312 . Wires that connect connector  310  with controller  318  may continue upward on branch  312  to earbud  316 , even though these wires are not needed to convey signals between controller  318  and additional components in the vicinity of earbud  316 . 
     Conductive wires in a fiber-based cable need not be contained within a fiber-based sheath. Conductive wires may, for example, be intertwined directly with other fibers. If desired, the relative position of the conductive wires among the other fibers in the cable may be varied by intertwining tool  14  as a function of position along the length of the cable. For example, the conductive wires may be located in the central core of the cable at some locations along the cable and may be located on the surface of the cable at other locations along the cable. An arrangement of this type may be to connect contacts in audio connector  310  to circuitry in controller  318 . 
     An illustrative arrangement in which intertwining tool  14  adjusts the relative position of insulated wires within a fiber-based cable to allow the wires to be interconnected to circuitry in controller  318  is illustrated in the examples of  FIGS.  43 A- 43 D . 
     A perspective view of a segment of fiber-based cable  322  is shown in  FIG.  43 A . Section  324  may be a region of cable  322  that forms terminals for an integral switch. In this type of arrangement, a switch may be formed from a pair of exposed wires, so it is not necessary to include circuitry for implementing a more complex multi-function button controller for the headset.  FIG.  43 B- 43 D  are cross-sectional views of cable  322  taken along lines X-X, Y-Y, and Z-Z of cable  322 . 
       FIG.  43 B  is a cross-sectional view of cable  322  at location X, which is on one side of switch region  324 . Cable  322  of  FIG.  43 B  has intertwined fibers  332 . Fibers  332  may be monofilament or multifilament fibers. Fibers  332  may be arranged in a sheath around insulated conductive wires  247 . Fibers  332  are shown in  FIG.  43 B  as being arranged in a sheath with a thickness of two fiber layers. In general, fiber sheaths may have any suitable thickness. Each insulated wire  247  has insulation  250  surrounding a conductive center such as center  248 . Four insulated wires  247  are shown in  FIG.  43 B . In general, cable  322  may have any suitable number of insulated wires. Insulated wires  247  may be provided as individual wires, as twisted pairs, as parts of coaxial cables, etc. 
       FIG.  43 C  is a cross-sectional view through line Y-Y of cable  322 . In  FIG.  43 C , two of the wires  247  have been placed at the surface of cable  322  by intertwining tool  14  and have been stripped of their insulation to form terminals  342  and  344 . Two other wires  247  remain embedded in intertwined fibers  332 . 
     During the fabrication of cable  322 , intertwining machinery may be used to ensure that the insulated wires are contained within the core region of the cable (as in locations X and Z of cable segment  322  of  FIG.  43 A ) in regions outside of switch region  324 . This helps protect the wires from damages (e.g., from scratches). The intertwining tool may selectively bring the insulated wires to the surface of cable  322  at desired locations such as location Y in  FIG.  43 C . After (or before) fiber-based cable  322  has been formed, insulated wires  247  may be selectively stripped of their insulations  250  at locations such as location Y, leaving their conductive centers  248  exposed on the surface of the cable. Terminals  342  and  344  may form a switch  324 . Such a switch  324  may be shorted together when touched by a user. For example, terminals  342  and  344  may be electrically connected to each other by the skin on a user&#39;s finger (finger  346 ) when the user&#39;s finger bridges terminals  342  and  344 . Terminals  342  and  344  may also be bridged by a mechanical lever or other switching mechanism. 
       FIG.  43 D  is a cross-sectional view through fiber-based cable  322  at location Z. At location Z, insulated wires conductive wires  247  lie within fibers  332  and insulation  250  is unstripped. Fibers  332  may form a fiber-based sheath surrounding insulated wires  247  or fibers  332  may be intertwined with insulated wires  247 . 
       FIG.  44 A  shows a fiber-based cable  354  that has a controller (e.g., a controller such as controller  318  of  FIG.  42   ). As shown in  FIG.  44 A , controller  345  may have a housing that surrounds portions of the cable. Controller  345  may be a switch, circuitry such as circuitry in a switch-based button assembly with multiple buttons and an optional microphone, or other suitable user interface circuitry (as examples). Controllers such as controller  334  may include circuitry for supporting communications with electronic devices over the wires of cable  354 . Controller  345  may have one or more switched-based buttons, such as button  346 . Cross-sectional views of cable  354  taken at locations X, Y, and Z are shown in  FIGS.  44 B,  44 C, and  44 D . 
       FIG.  44 B  is a cross-sectional view of cable  354  taken through line X-X of  FIG.  44 A . Intertwined fibers  332  of  FIG.  44 B  may be monofilament or multifilament wires and may be formed from any suitable material. Insulated conductive wires  247  have insulation  250  surrounding conductive center  248 . Four wires  247  are shown in  FIG.  44 B . In general, cable  354  may have any suitable number of wires. If desired, wires  247  may also be provided in the form of coaxial cables. In  FIG.  44 B , intertwined fibers  332  are shown as surrounding insulated wires  247 . 
       FIG.  44 C  is a cross-sectional view through controller  345  and associated button  346  taken along line Y-Y of  FIG.  44 A . Two of the insulated wires  247  have been positioned on the surface of cable  354  by intertwining tool  14  and have been stripped of their insulations  250 . This exposes conductive centers  248  of wires  247  and forms terminals  342  and  344 . Terminal  342  may be connected by solder  348  to pad  352  of switch  346  or other circuitry in controller  345 . Terminal  344  may be connected by solder  350  to pad  654  of switch  346  or other circuitry in controller  345 . When button  346  is pressed by a user, terminals  342  and  344  may be electrically connected (i.e., shorted together) closing the switch. In other arrangements (e.g., arrangements in which controller  345  is formed from more complex circuitry), actuation of button  346  may result in the transmission of communications signals over the wires connected to terminals  342  and  344 . The use of a switch to form controller  345  is merely illustrative. 
       FIG.  44 D  is a cross-sectional view of cable  354  taken through line Z-Z of  FIG.  44 A . As in  FIG.  44 B , insulated conductive wires  247  may be embedded within intertwined fibers  332  by intertwining tool  14 . In this region of the cable, wires  247  typically have intact insulation  250  (i.e., insulation that has not been stripped and therefore surrounds conductive centers  248 ). 
     During the formation of fiber-based cables such as the cable of  FIG.  20   , intertwining tool  14  of  FIG.  1    may be used to bring insulated wires  247  from within cable  354  (at location X), to the surface of cable  354  (at location Y), and back inside cable  354  (at location Z). After cable  354  is formed, insulation  250  may be stripped from wires  247  at location Y to form terminals  342  and  344 . A switch or more complex input-output circuitry may then be connected to terminals  342  and  344 . If desired, more than two wires may be stripped and connected to the input-output circuitry. For example, three or more wires may be stripped and connected to switches or more complex circuitry within controller assembly  345 , four or more wires may be stripped and connected to switches or more complex circuitry within controller  345 , etc. 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.