Abstract:
Ferrite cores are provided with rounded, convex head ends and complimentary rounded, concave tail ends. The configuration of the head and tail ends permits a reduction in gap width between adjacent cores when they are joined together into a core assembly that suppresses electromagnetic interference emitted from a cable.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This is a division of application Ser. No. 10/879,811, filed Jun. 29, 2004, now U.S. Pat. No. 7,138,896 the entire disclosure of which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   The present application is directed to a ferrite core and to a ferrite core assembly for suppressing electromagnetic interference (EMI), and more particularly to an assembly of ferrite cores that are configured to fit together flexibly, with enhanced magnetic coupling between the cores. 
   A cable that carries analog signals or digital signals has a tendency to act as an antenna, radiating energy in the form of electromagnetic radiation. This tendency depends on several factors, including the frequency of the signals and the length and geometric layout of the cable. The electromagnetic radiation emitted by a cable increases the noise level of the electromagnetic environment. That is, it may create electromagnetic interference (EMI). It is known that one or more ferrite cores may be placed on a cable to suppress the effects of EMI. To be effective, the core or cores should allow the magnetic flux produced by current in the cable to flow through the ferrite material. The EMI suppression effect of ferrite cores is reduced if air gaps exists between the cores. 
   Ferrite cores are generally produced by sintering suitable materials into rigid bodies, which materials are known in the art. Such materials include, for example, MnZn for lower frequencies and NiZn for middle and higher frequencies. The sintered ferrite material is dense and brittle, and can be somewhat bulky. The use of ferrite cores to suppress EMI can therefore be challenging from an electronics packaging perspective. 
   In preassembled cable assemblies, ferrite cores are typically retained on a cable at a particular location with a plastic shrink-wrap. Cables may also be retrofit with ferrite cores by mounting the cores in plastic housings that are then clipped or clamped to the cable. Both of these ferrite core solutions for reducing EMI are detrimental to compact and inexpensive system packaging, since there are usually tight space limitations and since the ferrite cores not only take up space and block air flow, but they also limit the flexibility of the cable. 
   SUMMARY OF THE INVENTION 
   One object of the invention is to provide ferrite cores having a configuration which permits them to be linked together in a flexible assembly. 
   Another object is to provide ferrite cores which are configured to minimize gaps between the cores. 
   A further object is to provide ferrite cores that can be used to provide a single toroidal EMI suppressor around a cable, an elongated EMI suppressor that is wrapped helically around a cable, or an elongated EMI suppressor that is attached to a side or face of a flat cable. 
   In accordance with one aspect of the present invention, these and other objects that will become apparent from the ensuing detailed description can be attained by providing a ferrite core assembly, for use with a signal-carrying cable to suppress electromagnetic interference radiated by the cable, that includes a plurality of ferrite cores. Each ferrite core has a head end with a rounded, convex shape and a tail end with a rounded, concave shape that provides a recess at the tail end. The ferrite cores are assembled in an articulated, flexible sequence such that the head ends of at least some of the ferrite cores extend into the recesses of adjacent ferrite cores. 
   The head end of each ferrite core may have approximately the shape of a portion of a cylinder having a predetermined radius, and the tail end may also have approximately the shape of a portion of a cylinder with a radius that is approximately the same as the predetermined radius. As a result, adjacent ferrite cores fit together in what might be called a “cylinder-and-socket” arrangement (a phrase inspired by the more-familiar term, “ball-and-socket”). Due to the cylinder-and-socket engagement, adjacent ferrite cores are movable with respect to one another, and moreover the gap between them is minimized. 
   The head end of each ferrite core may have approximately the shape of a portion of a sphere having a predetermined radius, and the tail end may also have approximately the shape of a portion of a sphere with a radius that is approximately the same as the predetermined radius. This provides a true ball-and-socket joint, with advantages similar to those discussed above that flow from a cylinder-and-socket joint. 
   In accordance with another aspect of the invention, a plurality of ferrite cores are joined together into a group. Each ferrite core is made of sintered material, and has a curved head end with a rounded, convex shape and a curved tail end with a rounded, concave shape that provides a recess at the tail end. The ferrite cores are joined together in a flexible sequence, with the head ends all facing in one direction and the tail ends facing in the opposite direction. Ferrite cores joined together in this way may then be conveniently used later to fabricate core assemblies for suppressing electromagnetic interference from signal-carrying cables. 
   Among other options, the ferrite core assemblies may be joined together using one or more filaments that extend through bores in the ferrite cores. Alternatively, link members may be used to pivotably join pairs of adjacent ferrite cores. Another option is to tack the ferrite cores to a flexible tape. 
   According to a further aspect of the invention, a ferrite core for use in a ferrite core assembly to suppress electromagnetic interference includes a body of sintered ferrite material. The body has a curved head end with a rounded, convex shape and a curved tail end with a rounded, concave shape. The concave shape conforms substantially to the convex shape. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view illustrating a ferrite core in accordance with a first embodiment of the present invention; 
       FIG. 2  is a top plan view of the ferrite core shown in  FIG. 1 ; 
       FIG. 3  is a perspective view of a ferrite core assembly made of ferrite cores as shown in  FIG. 1 ; 
       FIG. 4  is a perspective view of a prior art ferrite core assembly that is made from brick-shaped ferrite cores; 
       FIG. 5  is a top view of a ferrite core assembly that is attached to a cable with the aid of heat-shrunk tubing; 
       FIG. 6  is a perspective view of ferrite cores that are joined by a link; 
       FIG. 7  is a top view of ferrite cores that are joined together in a group by filaments; 
       FIG. 8  is a top view of ferrite cores that are tacked to a tape; 
       FIG. 9  is a perspective view of a ferrite core formed by joining top and bottom portions together, with a filament or cable running through a passage in the core; 
       FIG. 10  is a perspective view of a ferrite core in accordance with the second embodiment of the invention; 
       FIG. 11  is a perspective view illustrating how the ferrite cores of the second embodiment fit together; 
       FIG. 12  is a view illustrating a ferrite core assembly that is made from cores of the second embodiment and that is attached to a flat cable; 
       FIG. 13  is a perspective view of a ferrite core in accordance with the third embodiment of the present invention; 
       FIG. 14  is a perspective view illustrating how the ferrite cores of the third embodiment fit together; 
       FIG. 15  is a perspective view illustrating a modification of the ferrite core of the third embodiment to provide a passage from the head end to the tail end; 
       FIG. 16  is a cross sectional view of the modification shown in  FIG. 15 ; and 
       FIG. 17  is a cross sectional view illustrating another modification in which ferrite cores in accordance with the third embodiment are provided with plastic jackets, the plastic being somewhat compliant or flexible to permit the ferrite cores to be snapped together. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Three preferred embodiments of the invention, and variations thereof will now be described with reference to the accompanying drawings. 
   The First Embodiment 
   With initial reference to  FIGS. 1 and 2 , a ferrite core  20  has a front or head end  22  and a back or tail end  24 . The head end  22  has a curved, convex shape and the tail end  24  has a curved, concave shape. Specifically, the head end  22  is shaped as a segment of the cylinder having a radius R and, similarly, the tail end  24  is shaped as a segment of the cylinder having the radius R or a radius slightly greater than R. It will be apparent, then, that the head end  22  of one ferrite core  20  can be accommodated in a recess provided at the tail end  24  of an adjacent ferrite core in a manner of a cylinder-and-socket joint. 
     FIG. 3  illustrates an example of a ferrite core assembly  26  formed by a number of ferrite cores  20  that had been arranged, head-end to tail-end, in a toroidal configuration. Since the head ends fit snuggly against the tail ends of the ferrite cores  20 , the gaps  27  between the ferrite cores have minimal gap widths. The core assemblies  26  conform to a cable that is round or oval in cross section. Cables with different cross sectional areas can be accommodated by varying the number of cores  20  in the assembly  26  or by varying the size or length of the cores. 
   A very significant advantage that is provided by ferrite cores  20  can be appreciated by comparing the prior art arrangement shown in  FIG. 4  with the core assembly  26  shown in  FIG. 3 . In  FIG. 4 , a toroidal coil assembly  28  is formed from brick-shaped ferrite cores  30 . Except at their inner edges, it will be seen that the sides of the cores  30  are separated by gaps. This increases the magnetic resistance provided by the core assembly  28 , which reduces the EMI suppression provided by the core assembly  28 . These gaps could be avoided by making the cores  30  trapezoidal in cross section, so that the cores  30  would be generally keystone-shaped, but the angle needed for the sides of the cores  30  in order to avoid gaps would vary with the cross sectional area of the core assembly. Furthermore, the assembly would be inflexible from cable application to cable application. 
     FIG. 5  illustrates an example of how the core assembly  26  that is shown in  FIG. 3  can be mounted on a cable  32 . The core assembly  26  is threaded onto the cable  32  and enclosed in a segment of tubular heat-shrink plastic. Hot air is then blown against the heat-shrink plastic, which contracts to form a cover  34  that not only secures the core assembly  26  to the cable  32 , but also urges the individual ferrite cores  20  toward one another. 
   The ferrite cores  20  may be made by sintering powdered ferrite material in molds. Although they could simply be dumped from the molds into a storage container until they are needed, it is convenient to package them in a head-end to tail-end state prior to using them in core assemblies. It will be apparent to those skilled in the art that a variety of techniques might be used to package the ferrite cores  20 . Several of these techniques are illustrated in  FIGS. 6-9  (which are presented as examples, and not an exhaustive compilation of the possibilities). 
   In  FIG. 6 , the ferrite cores shown in  FIG. 1  are modified to provide ferrite cores  36 . The modification is that each core is provided with two bores  38 . Links  40  can then be used above and below the cores  36  in order to join pins (not shown) that extend through the bores  38 . 
   In  FIG. 7 , the cores shown in  FIG. 1  are modified to provide ferrite cores  42 , which have bores  44  that extend from side to side. A first filament  46  is looped through the bores  44 , as is a second filament  48 . The filaments  46  and  48  cross in a repeating figure- 8  configuration. The filaments  46  and  48  are shown looping outward in  FIG. 7  from the cores  42 , but this is merely for purposes of illustration, and in reality they would be tightened. Strung together in this way, the cores  42  can then be wound on a reel for convenient storage. 
   In  FIG. 8 , ferrite cores  20  as shown in  FIG. 1  are aligned, head to tail, beneath a tape  50  of elastic material. The tape  50  is attached to the cores  20  by small dabs of adhesive at tacking points  54 . 
     FIG. 9  shows another modification of the ferrite core shown in  FIG. 1 . In  FIG. 9 , a ferrite core  56  is assembled from a top portion  58  and a bottom portion  60 . The top portion  58  has a groove  62  that extends from the front end to the rear end. The bottom portion  60  has a similar groove, and an elastic filament  64  is disposed in these grooves and sandwiched between the top and bottom portions  58  and  60 . The top and bottom portions  58  and  60  are connected with adhesive (or other joining means), either before or after the filament  64  is installed. Although not shown, cores  56  can be strung, one after the other, on the filament  64  for convenient storage. Furthermore, it is possible to enlarge the grooves and string the ferrite cores on a cable. 
   Second Embodiment 
     FIG. 10  illustrates a second embodiment of a ferrite core in accordance with the present invention. The core  66  is similar to the core  20  shown in  FIG. 1 , but it has a width that is substantially greater. 
   The ferrite core  66  has a front or head end  68  with a curved, convex shape and a back or tail end  70  with a curved, concave shape. The head and tail end  70  are each configured as segments of a cylinder having approximately the same radius. 
     FIG. 11  illustrates several of the ferrite cores  66  arranged, head-end to tail-end, to provide a ferrite core assembly  72 . The core assembly  72  may be packaged using a variety of techniques, including those shown in  FIGS. 6-9 . 
   In use, the core assembly  72  can be attached to the face of a flat cable  74  (such as a ribbon cable or flex cable) by adhesive (or other attachment means). This is shown in  FIG. 12 . Alternatively, it can be attached using a segment of a plastic, heat-shrink tube. 
   Third Embodiment 
     FIG. 13  illustrates a ferrite core  76  having a front or head end  78  and a rear or tail end  80 . The head end  78  has a curved, convex shape, while the tail end  80  has a curved, concave shape. More particularly, the head end  78  is shaped as a segment of a sphere (or spherical cap) having a predetermined radius, and the tail end  80  is shaped as a segment of a sphere (or spherical cap) having the same predetermined radius (or a slightly larger radius). 
   It will be apparent that the head end  78  of one core  76  fits into the tail end  80  of an adjacent core  76  in the manner of a ball-and-socket joint. Such an arrangement is shown in  FIG. 14 . Strings of ferrite cores  76  arranged in this way can be used to form a toroidal core assembly, in the manner of  FIG. 3  for the first embodiment, or a train of core assemblies  76  may be wrapped around a cable to form a helical core assembly. The core assemblies may be attached, for example, using adhesive or heat-shrink tubing. 
   The ferrite core  76  may be packaged by being linked together with filaments in the manner shown in  FIG. 7  or by being tacked to an elastic tape in the manner illustrated in  FIG. 8  (although it would be desirable for the tape to have circular apertures that would permit the sides of the head ends  78  to protrude). They can also be strung together on an elastic filament, and  FIGS. 15 and 16  illustrate a modified ferrite core  82  having a bore  84  for this purpose. 
   As is shown in  FIG. 16 , the bore is preferably flared at the head end  78  and the tail end  80 . The flare is useful when an array of cores  82  is attached to a cable using a wire that runs through the bores  84 , since the wire can then follow a path around the cable. Notches (not illustrated) may be provided in the head and tail ends so that the ends of the wires can be bent outward from the ring of cores  82  and twisted together to secure the core assembly about the cable. 
   Furthermore, it is possible to string the ferrite cores on a cable to suppress EMI radiation from the cable. 
   In  FIG. 17 , ferrite cores  76  as in  FIG. 13  are provided with plastic jackets  86  in the region of the tail ends  80 . The plastic that is selected for use in the jackets  86  should be somewhat compliant or flexible rather than rigid. The jackets  86  are open-ended, and provide cavities  88  in association with the tail ends  80 . That is, the tail ends  88  together with the walls of the jacket  86  form recesses that are shaped as more than half of the surface of the sphere. These recesses provide sockets that permit the head end  78  of one core  76  to snap into the recess of an adjacent jacket to thereby hold the head end  78  against the adjacent tail end  80 . The cores  76  can thus be strung together and, in use, formed into a toroidal core assembly around a cable or a helical core assembly around a cable. 
   It will be apparent to those ordinarily skilled in the art that the techniques disclosed herein with reference to one embodiment for packaging ferrite cores or assembling them into core assemblies attached to cables may also be used in other embodiments. 
   It will be understood that the above description of the present invention is susceptible to various other modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalence of the appended claims.