Abstract:
An adjustable EMI suppression core has an outer core having a first reluctance. The outer core has three apertures aligned horizontally. A first aperture and a third aperture are each suitable for a wire to be placed therein. A second aperture is located between the first and third apertures. An inner core is rotatable engaged in the second aperture, for example, using matching threads on an inner surface of the second aperture and an outer surface on the inner core. The inner core has first and third portions having a second reluctance similar to the first reluctance and a third portion having a reluctance considerably higher than the first and second reluctances. Rotating the inner core varies a normal mode and a common mode suppression of currents in the wires placed in the first and second apertures.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to electromagnetic compatibility (EMC), and more specifically to electromagnetic interference (EMI) suppression cores. 
     SUMMARY OF EMBODIMENTS OF THE INVENTION 
     An adjustable EMI suppression core comprises an outer core and an inner core. The outer core further comprises three horizontally aligned apertures. The inner core is rotatably engagable within the second aperture. The outer core has a first reluctance. The inner core comprises three sections. The first and third sections of the inner core have a second reluctance similar to that of the outer core. The second section of the inner core has a third reluctance much greater than the first and second reluctances. 
     The inner core may comprise a means of rotation with a tool adapter such as a key slot. A further embodiment of the adjustable EMI suppression core comprises threads on the exterior of the inner core and threads on the interior of the second aperture. Another embodiment of the adjustable EMI suppression core comprises a plastic case to enclose the outer core for protection. 
     Additional embodiments of the outer core comprise dividing the outer core into two portions. The two portions may be separated and later mechanically joined; for example, the two portions of the outer core may further comprise a hinge and a latch mechanism on opposite ends as a means of opening, closing, and locking the two outer core portions together. A separate embodiment comprises a latch mechanism at each end. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a three-dimensional view of an adjustable EMI suppression core.  FIG. 1A  shows the adjustable EMI suppression core comprised of an outer core, an inner core, a first aperture, a second aperture, and a third aperture. A first wire is shown inserted into the first aperture. A second wire is shown inserted into the third aperture. 
         FIG. 1B  is a three-dimensional view of the inner core comprised of three sections and a means for rotating. 
         FIG. 2  is a three-dimensional view of the adjustable EMI suppression core divided into two portions attached at one end with a hinge and the other end fitted with a hook and latch mechanism. 
         FIG. 3  is a three-dimensional view of the inner core further comprising threads. 
         FIG. 4A  is an end view of the adjustable EMI suppression core further comprising a plastic shell.  FIG. 4A  shows the inner core in Common Mode Position. 
         FIG. 4B  is an end view of the adjustable EMI suppression core with the inner core in Normal Mode Position. 
         FIG. 5A  is an end view of the adjustable EMI suppression core with the inner core in Common Mode Position and an exemplary common mode flux path. 
         FIG. 5B  is an end view of the adjustable EMI suppression core with the inner core in Normal Mode Position and two exemplary normal mode flux paths. 
         FIG. 6  is a top cross-sectional view of the adjustable EMI suppression core.  FIG. 6  shows an exemplary distance the inner core is rotatably engaged in the outer core. 
         FIG. 7A  is an end view of the adjustable EMI suppression core with the height of the outer core reduced to less than the diameter of the inner core. The inner core is shown in the Common Mode Position and an exemplary common mode flux path is also displayed. 
         FIG. 7B  is an end view of the adjustable EMI suppression core with the height of the outer core reduced to less than the diameter of the inner core. The inner core is shown in the Normal Mode Position and a set of exemplary normal mode flux paths is also displayed. 
         FIG. 8  shows a graph of increasing permeance in common mode and normal mode paths as the inner core becomes more deeply rotatably engaged within the outer core. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In the following detailed description of embodiments of the invention, reference is made to the accompanying drawings, which form a part hereof, and within which are shown by way of illustration specific embodiments by which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention. 
     Embodiments of the present invention provide for an apparatus for adjustable common mode/normal mode balance in emission suppression, shown completed in the figures. 
     When a signal travels through a conductor, a magnetic field is generated around that conductor. A ferrite core, having a relatively low reluctance, if placed around the conductor, can interact with this magnetic field. The magnetic field activates (permeates) the ferrite, which, in response to the magnetic field, imposes impedance that reduces a magnitude of EMI associated with the currents in wires passing through the ferrite core. 
     Referring to  FIG. 1A  and  FIG. 1B ,  FIG. 1A  shows a three dimensional view of an adjustable EMI suppression core  100 . Adjustable EMI suppression core  100  comprises an outer core  101  and an inner core  105  (shown in more detail in  FIG. 1B ). 
     The outer core  101  has a first reluctance. The outer core  101  also has a first aperture  102 ; a second aperture  103 ; and a third aperture  104 . First aperture  102 , second aperture  103 , and third aperture  104  are arranged horizontally in sequence as shown in  FIG. 1A . The first and third apertures are each suitable for a wire, shown as wire  106  and wire  107 , to pass through. 
     The diameters of aperture  102  and aperture  104  should be advantageously equal to the diameters of corresponding wire  106  and wire  107 . As the diameters of aperture  102  and aperture  104  get larger than the corresponding diameters of wire  106  and wire  107 , sensitivity to normal mode/common mode control decreases. One embodiment of this invention has the diameters of aperture  102  and aperture  104  equal to 105% of the diameters of corresponding wire  106  and wire  107 . A second embodiment has the diameters of aperture  102  and aperture  104  equal to 110% of the diameters of corresponding wire  106  and wire  107 . Additionally, aperture  102  and aperture  104  should be advantageously placed close to aperture  103 . As aperture  102  and aperture  104  are placed farther away from aperture  103 , control sensitivity of normal mode/common mode decreases. One embodiment of this invention has aperture  102  and aperture  104  at a distance from the nearest point of aperture  103  less than the diameters of apertures  102  and  104 . 
       FIG. 1B  shows a three dimensional view of inner core  105 . Inner core  105  comprises a first section  105 A having a second reluctance; a second section  105 B having a third reluctance; and a third section  105 C having the second reluctance. Sections  105 A,  105 B, and  105 C are also shown in  FIG. 1A . The shape of inner core  105  is generally cylindrical. Exemplary shapes of sections  105 A,  105 B, and  105 C are shown in  FIG. 1A . Deviations from the depicted shapes of sections  105 A,  105 B, and  105 C are contemplated. For example, whereas the shapes of sections  105 A and  105 C are shown to be curved on boundaries  109  and  110  ( FIG. 1B ) with section  105 B, the boundaries  109  and  110  could be straight or less convex than shown and still be within the scope and spirit of the invention. 
     The inner core  105  is rotatably engagable in the second aperture  103  of the outer core  101 . Tool adapter  108 , shown in  FIGS. 1A and 1B , allows for insertion of a tool, such as a screwdriver blade, for rotation of inner core  105 . 
     Inner core sections  105 A and  105 C have a second reluctance similar to the reluctance of the outer core  101 . Inner core section  105 B has a third reluctance. The second reluctance of inner core sections  105 A and  105 C may for example be less than or equal to twice the first reluctance of outer core  101 . The greater the second reluctance is relative to the first reluctance, the common mode/normal mode control sensitivity decreases. In an embodiment the second reluctance is equal to or less than the first reluctance. Additionally, the third reluctance of inner core section  105 B may for example be at least five times greater than the first and the second reluctance. The closer the third reluctance is relative to the first and second reluctance, the common mode/normal mode control sensitivity decreases. 
       FIG. 2  shows a three-dimensional view of an embodiment of adjustable EMI suppression core  100  wherein outer core  101  is separable into two parts to facilitate insertion of wires  106  and  107 . In this embodiment, outer core  101  is comprised of two parts,  101 A and  101 B. Aperture  102  of  FIG. 1  is shown as aperture portions  102 A and  102 B in  FIG. 2 . Aperture  103  of  FIG. 1  is shown as aperture portions  103 A and  103 B in  FIG. 2 . Aperture  104  of  FIG. 1  is shown as aperture portions  104 A and  104 B in  FIG. 2 . 
     The embodiment of the adjustable EMI suppression core in  FIG. 2  comprises the hinging of outer core part  101 A to outer core part  101 B with hinge  204  as shown in  FIG. 2 . This allows the outer core  101  to open and outer core parts  101 A and  101 B to separate. The separation of outer core parts  101 A and  101 B allows for wires  106  and  107  to be placed in aperture portions  102 A and  104 A followed by the closing of outer core parts  101 A and  101 B. Also, the separation of outer core parts  101 A and  101 B allows for the inner core  105  to be placed in either aperture portion  103 A or  103 B followed by the closing of outer core parts  101 A and  101 B. 
     The embodiment in  FIG. 2  further comprises the ability to lock outer core part  101 A to outer core part  101 B with lock  203  at the opposite end of outer core  101  from hinge  204 . An example embodiment of lock  203  comprises a hook  203 B and a pin  203 A. Hook  203 B goes around pin  203 A and locks outer core part  101 A to outer core part  101 B to prevent them from separating. Unhooking hook  203 B from around pin  203 A unlocks outer core part  101 A from outer core part  101 B and allows them to separate. Whereas a hook and a pin are shown as an exemplary means to maintain the assembly, any suitable securing means may be used to maintain the assembly. 
     In an alternative embodiment not shown, a lock such as lock  203  above is used on each end of outer core  101  removing the requirement for hinge  204 . 
       FIG. 3  shows a further embodiment of inner core  105  comprising the addition of threads  301 . Matching threads are formed along the inside of aperture  103 . Threads  301  enable inner core  105  to be rotatably engaged in aperture  103  of outer core  101 . This embodiment allows control of how deeply inner core  105  is engaged within aperture  103  of outer core  101 . 
       FIG. 4A  and  FIG. 4B  portray end views of adjustable EMI suppression core  100 . Outer core  101  is shown with the two halves,  101 A and  101 B, closed. The entire adjustable EMI suppression core  100  further comprises a plastic case  406  to enclose outer core  101 . Typically, the material of which outer core  101  is composed is brittle. Common examples of core materials include Material  43  or Material  61  from Fair-Rite Products Corporation, P.O. Box J, One Commercial Row, Wallkill, N.Y. 12589-0288. Thus, plastic case  406  contains and protects outer core  101  in adjustable EMI suppression core  100 . An embodiment comprising plastic case  406  removes the need for hinge  204  ( FIG. 2 ) and lock  203  ( FIG. 2 ). 
     In  FIGS. 4A and 4B , rotation vector  401  is not a physical embodiment. Rotation vector  401  represents the degrees of turn of inner core  105  with respect to axis  402 , also a non-physical embodiment.  FIG. 4A  shows inner core  105  rotated zero degrees with respect to axis  402 . This position of inner core  105  is known as “Common Mode Position”.  FIG. 4B  shows inner core  105  rotated ninety degrees with respect to axis  402 . This position of inner core  105  is known as “Normal Mode Position”. 
     Outer core  101  comprises a top surface  403  and a bottom surface  404 . Outer core  101  has a height H  405  between top surface  403  and bottom surface  404 . 
       FIG. 5A  and  FIG. 5B  show the respective end views from  FIG. 4A  and  FIG. 4B  of adjustable EMI suppression core  100 . The Common Mode Position shown in  FIG. 5A  shows an exemplary common mode flux line  501  which passes through the relatively low reluctance paths provided by inner core sections  105 A and  105 C. The Normal Mode Position shown in  FIG. 5B  shows exemplary normal mode flux lines  502 A and  502 B which pass through the relatively low reluctance paths provided by inner core sections  105 A and  105 C. As explained earlier, control sensitivity of common mode and normal mode increases as apertures  102  and  104  are made closer to aperture  103 . Additionally, control sensitivity increases as height H  405  becomes closer to, or even less than, a diameter of aperture  103 . 
     As shown in  FIG. 5A , if a common mode current flows through wires  106  and  107 , a relatively low reluctance path around both wires as shown as flux path  501  provides EMI suppression of the common mode currents. 
     As shown in  FIG. 5B , if a normal mode current flows through wires  106  and/or  107 , a relatively low reluctance path around each wire as shown as flux paths  502 A and  502 B provides EMI suppression of the normal mode currents. 
     A top-view cross-section of adjustable EMI suppression core  100  is shown in  FIG. 6 . A length L  604  of the outer core  101  is shown. An empty distance M  606  remaining in aperture  103  from inner core  105  is also shown. A distance D  605  within aperture  103  that contains inner core  105  is represented by distance L  604  minus distance M  606 . 
       FIGS. 7A and 7B  show an end view of adjustable EMI suppression core  100  wherein outer core  101  has a shorter height than depicted in  FIGS. 4A and 4B . The height of inner core sections  105 A and  105 C shown as I  704 . The Common Mode Position is shown in  FIG. 7A . The Normal Mode Position is shown in  FIG. 7B . In these two figures outer core  101  comprises two pieces,  701 A and  701 B. The height H  705  of outer core  101  in this embodiment equals I  704 . When H  705  equals I  704 , there is no low reluctance material in outer core  101  for flux paths to go around both wires  106  and  107  in the Normal Mode Position thereby providing very small common mode EMI suppression. The relative position of the normal mode flux paths  703 A and  703 B are shown in  FIG. 7B . There will be common mode flux paths through the air outside of the adjustable EMI suppression core  100  but they are small because air has high reluctance compared to the first and second reluctances. 
     In  FIG. 7A , the distance J  706  between the ends of inner core section  105 A and inner core section  105 C is shown. In the Common Mode Position of  FIG. 7A , for common mode flux paths  702  to pass through the lower reluctance material in the inner core section  105 A and  105 C, J  706  needs to be less than H  705 . 
       FIG. 8  shows a graph  800  of permeance versus distance D  605  ( FIG. 6 ) into outer core  101  versus degree of turn in radians of inner core  105 . Permeance is the inverse of reluctance. Line  801  represents the permeance in normal mode. Line  802  represents the permeance in common mode. Line  801  representing normal mode permeance and line  802  representing common mode permeance are ninety degrees out of phase and increase in amplitude as inner core  105  is further inserted into aperture  103 . Trend line  803  shows the increase in permeance with increasing degrees of turn. The slope of trend line  803  is dependant on the pitch of threads  301  ( FIG. 3 ). It should be understood that at zero turns there is non-zero common mode permeance and non-zero normal mode permeance. There will always be a non-zero amount of normal mode permeance within the outer core material around wire  106  and wire  107 . There will always be a non-zero amount of common mode permeance around both wires  106  and  107 . As normal mode permeance and common mode permeance increase, it is relative to when inner core  105  is not inserted into aperture  103 , i.e. zero turns. Axis  804  represents the ratio of distance D  605  divided by length L  604 . Axis  805  represents the ratio of permeance versus the maximum permeance achievable when inner core  105  is fully engaged in aperture  103 , i.e. when distance D  605  divided by length L  604  equals 1. Axis  806  represents the amount of rotation of inner core  105  in radians. The number of turns for D to equal L is dependant on the pitch of threads  301  ( FIG. 3 ).