Patent Publication Number: US-7896697-B2

Title: Screening device for reducing electromagnetic coupling

Description:
This application is a National Stage Application of PCT/EP2007/006368, filed 18 Jul. 2007, which claims benefit of Ser. No. 2006905178, filed 19 Sept. 2006 in Australia and which application(s) are incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above disclosed applications. 
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a screen for reducing electromagnetic coupling between adjacent groups of electric connectors in a connector block. 
     BACKGROUND OF THE INVENTION 
     In the telecommunications industry, voice and data signals are often transmitted over long distances along groups of closely spaced transmission lines. In order to maintain flexibility as equipment is added or replaced in a telecommunications system, it is important to have connection stations at one or more locations where connections to a large number of pieces of equipment can be made. 
     Electromagnetic radiation and interference are generated between adjacent transmission lines, particularly where the lines are spaced closely together. The radiation can cause electromagnetic coupling between adjacent transmission lines which can adversely affect the information being transmitted. For example, the radiation can generate “crosstalk” in the transmission lines. The effects of crosstalk can be reduced by transmitting the information over twisted pairs, or over wires that are encased in a conductive sheath, for example. Such techniques may be useful for reducing crosstalk over the extent of the transmission lines. However, the transmission lines are ultimately terminated at connector blocks located at connection stations. The conductors in the connector blocks are closely spaced apart and, as such, there is a tendency for crosstalk. However, it may not be practical to use the described techniques for reducing crosstalk in connector blocks. 
     The problem of crosstalk may not be particularly severe at low frequencies of less than 16 megahertz (MHz), for example. However, there is a demand for transmission at much higher frequencies, such as 100 MHz and more, and, at those frequencies, radiation is higher and there is a greater tendency for crosstalk. 
     A screening device for the insulation displacement contacts (IDCs) of a connector block is described in U.S. Pat. No. 5,160,273. Here the problem of crosstalk between adjacent groups of electric connectors, such as IDCs, is solved by inserting electrically conductive screening plates between adjacent pairs of IDCs. The plates are inserted into slots which extend transversely to the longitudinal direction of the plastic body of the connector block and contact a base rail situated in the longitudinal direction of the inside of the plastic body of the connector block. A disadvantage of this arrangement is that, when fitting the component into the plastic body, it is first necessary to fit the base rail, which has contact tongues for contacting the individual screening plates, and that it is subsequently necessary to push the individual screening plates into the connector block. Consequently, the complexity of assembly is relatively high. 
     Notwithstanding the fact that the screening taught by U.S. Pat. No. 5,160,273 may reduce crosstalk in connector blocks, it may still allow unacceptably high levels of crosstalk at high frequency data transmission rates. 
     It is generally desirable to overcome or ameliorate one or more of the above mentioned difficulties, or at least provide a useful alternative. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, there is provided a screen for reducing electromagnetic coupling between first and second adjacent pairs of electric connectors arranged in at least one series of pairs of electric connectors in a connector block, including:
     (a) a first electrically conductive surface shaped for arrangement between the first and second adjacent pairs of electric connectors;   (b) two spaced apart electrically conductive surfaces electrically coupled to, and extending transversely away from, respective sections of said first electrically conductive surface in a substantially common direction,
 
wherein said first electrically conductive surface and said spaced apart electrically conductive surfaces are adapted to provide electrically conductive screening on three sides for a pair of connectors in the series. Transversely is to be understood in this sense in such a way that the two other surfaces lead off from the first surface and form a three-sided open structure, the pair of connectors being surrounded on three sides within the structure. In this case, individual ones of or all of the surfaces can also be curved.
   

     Preferably, this screen is integrally formed. 
     Further preferably, the screen has at least one means, by means of which the screen can be electrically and/or mechanically connected to a further screen. Four-sided screening is thus realized. An electrical connection without a mechanical connection can be achieved, for example, by pressing the screens against one another in a sprung manner. A mechanical connection without an electrical connection can be achieved, for example, by virtue of the fact that at least one screen is not electrically conductive at the mechanical fixing point but has electrically conductive regions which bring about screening. Preferably, however, the screens are at least electrically connected. Mention will be made of the fact that the formulation should also include at least one means or else precisely one means. 
     In a further preferred embodiment, the distal ends of the spaced apart surfaces have a curvature which is further preferably directed inwards towards one another. These then form the means for electrical and/or mechanical connections. In the case of a purely electrical connection, a deformation of the spaced apart electrical surfaces is controlled via the end sections if the end sections press elastically against the further screen. 
     Preferably, the distal ends only extend over some of the length of the end faces of the spaced apart surfaces. 
     In a further preferred embodiment, the screen has at least one further means, which, with a first means of a second screen, can produce an electrical and/or mechanical connection. 
     The second means is preferably at least one opening and further preferably a slot. 
     In a further preferred embodiment, the at least one slot is located between adjacent edges of the first surface and at least one of the two spaced apart surfaces, further preferably the slot being located at the bottom end of the surfaces, with the result that the distal ends can then pass through. 
     In a further preferred embodiment, the first electrically conductive surface and/or the two spaced apart surfaces are electrically conductive plates. 
     In a further preferred embodiment, the two spaced apart electrical surfaces extend at an angle of 90° (+/−10°) with respect to the first electrical surface, with the result that a U-shaped cross section is set. 
     In a further preferred embodiment, two spaced apart projections are arranged at a common end of the first electrically conductive surface, which projections extend into hollow pedestals in the front side of the housing and are therefore arranged directly in the region of the contact points of the connectors. Preferably, the projections in this case lie in the same plane as the first surface. 
     In a further preferred embodiment, the screen is substantially constructed from metal or a non-metallic electrical material. 
     In an alternative embodiment, the screen is constructed from an electrically non-conductive material with at least a partial conductive coating or metallic structures arranged in the interior. 
     A further solution consists in the provision of a screening device, at least two screens according to the invention being mechanically and/or electrically connected and forming four-sided screening for at least one pair of connectors. If the screens are mechanically connected to one another, the complete screening device or groups of screens can be inserted as one component part. 
     A further solution consists in providing a connector block for terminating a plurality of conductors of electric data cables, including a plurality of pairs of electric connectors for terminating said conductors and a plurality of screens according to the invention, wherein the screens are arranged around respective pairs of electric connectors. 
     In a preferred embodiment, the electric connectors are arranged in groups, the groups having a distance from an adjacent group which is greater than the distance between pairs of one group, which is in turn greater than the distance between the connectors of a pair. Preferably, the pairs of one group are split into two rows, in each case one connector in a row being connected to a connector of the other row. In this case, the pair in one row and the associated pair in the other row are screened by a common screen. 
     In a further preferred embodiment, the screens are arranged in such a way that each pair of electric connectors is provided with four-sided screening. Given the arrangement in groups, this is achieved by virtue of the fact that a screen is arranged between the groups in which no connectors are arranged and a redundant accommodating zone is provided for the screen in a group at the edge of the distribution block. Alternatively, in each case the last pair of connectors in a group can be terminated by a single plate with respect to the four-sided screening. In this case, it is also possible for the redundant accommodating zone to be dispensed with, which allows for a narrower design of the connector block. In this case, a screen is required for each pair and in each case one terminating plate per group. Alternatively, it is possible to dispense with the terminating plates, in particular if the distance between the groups is sufficiently large. In this case, apart from one pair in a group, all other pairs have four-sided screening. 
     In a further preferred embodiment, the connectors are insulation displacement contacts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the present invention are hereafter described, by way of non-limiting example only, with reference to the accompanying drawing, in which: 
         FIG. 1  is a top view of a connector block; 
         FIG. 2  is a front view of the connector block shown in  FIG. 1 ; 
         FIG. 3  is an exploded view of the connector block shown in  FIG. 1 ; 
         FIG. 4  is a perspective view of a screen; 
         FIG. 5  is a top view of the screen shown in  FIG. 4 ; 
         FIG. 6  is a bottom view of the screen shown in  FIG. 4 ; 
         FIG. 7  is a side view of the screen shown in  FIG. 5 ; 
         FIG. 8  is another side view of the screen shown in  FIG. 4 ; 
         FIG. 9  is a front view of the screen shown in  FIG. 4 ; 
         FIG. 10  is a back view of the screen shown in  FIG. 4 ; 
         FIG. 11  is a top view of the connector block shown in  FIG. 1  with part of the housing removed; and 
         FIG. 12  is an exploded view of the connector block shown in 
         FIG. 1  with an alternative arrangement of screens. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
     The connector block  10  shown in  FIGS. 1 and 2  is used to terminate the insulated conductors of electric data cables (not shown). The connector block  10  includes a generally rectangular housing  12  having a front side  14 ; a back side (not shown); a top side  16 ; and a bottom side  18 . The housing  12  extends in the longitudinal direction L from a first end  20  to a second end  22 . The housing  12  preferably includes a front piece  24  that connects to a base piece  26 . In one embodiment, the front piece  24  is connected to the base piece  26  by a snap-fit connection. It will be appreciated that the front piece  24  defines the front side  14  of the housing  12  and the base piece  26  defines the back side of the housing  12 . 
     As shown in particular in  FIG. 3 , the connector block  10  includes five groups  30 ,  32 ,  34 ,  36 ,  38  of insulation displacement contact slots  40  arranged in series along the front side  14  of the housing  12 . Each group  30 ,  32 ,  34 ,  36 ,  38  includes first and second rows  40   a ,  40   b  of insulation displacement contact slots  40  that extend side by side along the front side  14  of the housing  12 . The insulation displacement contact slots  40  of each group  30 ,  32 ,  34 ,  36 ,  38  of slots are arranged in pairs  41 ,  43  for terminating the insulated conductors of corresponding twisted pairs of the above-mentioned data cables. 
     The connector block  10  includes five groups  42 ,  44 ,  46 ,  48 ,  50  of electric connectors  52 , such as insulation displacement contacts (IDCs), arranged between the front piece  24  and the base piece  26 . Each IDC  52  is preferably formed from a contact element which is bifurcated so as to define two opposed contact portions  54 ,  56  separated by a slot into which an insulated wire (conductor lead) may be pressed so that edges of the contact portions engage and displace the insulation and such that the contact portions resiliently engage and make electrical connection with the conductor of the insulated wire. The described IDCs  52  are explained in greater detail in U.S. Pat. No. 4,452,502 and U.S. Pat. No. 4,405,187, for example. 
     The IDCs  52  are arranged in fixed positions with respect to the insulation displacement contact slots  40  such that the contact portions  54 ,  56  of each IDC  52  extend, at least partially, into a corresponding insulation displacement contact slot  40 . Each insulation displacement contact slot  40  is adapted to receive an end portion of a corresponding insulated conductor of a data cable. The end portion of each insulated conductor can be electrically connected to a corresponding IDC  52  by pressing the end portion of the conductor between the opposed contact portions  54 ,  56 . An example of the described arrangement of insulation displacement contact slots  40  and IDCs  52  of the connector block  10  is set out in U.S. Pat. No. 4,541,682. 
     The IDCs  52  of the row  40   a  of slots are electrically connected to respective IDCs  52  of the row  40   b  of slots by spring finger contacts  53  extending there between. Accordingly, the insulated conductors of a first data cable (not shown) that are electrically connected, for example, to the IDCs  52  of the first row  40   a  of the first group  42  of connectors are also electrically connected to respective insulated conductors of another data cable (not shown) electrically connected to the IDCs  52  of the second row  40   b  of the first group  42  connectors. An example of the described arrangement of insulation displacement contact slots  40  and IDCs  52  of the connector block  10  is set out in U.S. Pat. No. 4,541,682. 
     The group  30  of insulation displacement contact slots  40  includes in each case five pairs of slots in the first and second rows  40   a  and  40   b . The pair of insulation displacement contact slots  40  of the first row  40   a  and of the second row  40   b  closest to the first end  20  of the housing  14  is redundant. The connector block  10  preferably does not include corresponding insulation displacement contacts  52  for these two pairs of insulation displacement contact slots  40 , four-sided screening for the adjacent pair of insulation displacement contacts  52  being formed here by insertion of a screen  60 . 
     The connector block  10  includes a plurality of electrically conductive screens  60  arranged between the front piece  24  and the base piece  26  of the housing  12 . The screens  60  are arranged to reduce electromagnetic coupling between adjacent pairs  62 ,  64  of IDCs  52 , for example. In this case, each pair  62 ,  64  includes in each case two IDCs  52  for the first row  40   a  and two IDCs  52  for the second row  40   b , the contacts of the first row  40   a  being connected to the contacts of the second row  40   b  via the spring finger contacts. 
     The screen  60  shown in  FIGS. 4 to 10  includes a generally rectangular plate  66  and generally rectangular side plates  68 ,  70  extending in a common direction from respective left and right sides of the plate  66 . The printed circuit boards  68 ,  70  in this case lead off at right angles from the plate  66 , disregarding curvatures. The screen  60  includes two spaced apart projections  65 ,  67  extending upwardly from the plate  66 . The projections  65 ,  67  lie in the same plane as the plate  66 . The three plates  66 ,  68 ,  70  of the screen  60  are formed in a “U” shape when viewed from the top, as shown in  FIG. 9 . 
     The screen  60  is formed of an electrically conductive material, such as an electrically conductive metal or an electrically conductive polymer, or a non-conductive material that has been coated with an electrically conductive material. The screen  60  may be constructed of any material that allows substantial electrical conductivity to the majority of points on the screen  60 , thus forming a barrier to electromagnetic fields from three aspects. The screen  60  may be constructed entirely of an electrically conductive metallic material such as copper, a copper alloy, steel or aluminium, or of non-electrically conductive materials (for example plastic) coated with an electrically conductive metallic layer. 
     The screen  60  is preferably made of a conductive metallic material and is integrally formed, in particular punched, from a metal sheet (not shown) with the plate  66 ; the side plates  68 ,  70 ; and the two projections  65 ,  67  initially lying in the same plane as the metal sheet. In a work step that follows the cutting out process, the side plates  68 ,  70  are bent so that they extend outwardly at an angle of 90° with respect to the above-mentioned plane. A hinge  73  is formed between the plate  66  and the plate  68  if they have been bent in the described manner. The hinge  73  extends only partially along the common, adjacent, edges of the plates  66 ,  68  thereby leaving an aperture, or slot,  75  between the plates  66 ,  68  (see also  FIG. 8 ). The slot  75  is preferably located at a bottom end of the plates  66 ,  68 . Similarly, a hinge  77  is formed between the plate  66  and the plate  70  when they are bent in the described manner. The hinge  77  extends only partially along common, adjacent, edges of the plates  66 ,  70  thereby leaving an aperture, or slot,  79  between the plates  66 ,  70 . The slot  79  is preferably located at a bottom end of the plates  66 ,  70 . 
     In a further processing step, the distal end sections  72 ,  74  of side plates  68  and  70  are bent so as to curve inwardly towards each other. The distal ends  72 ,  74  are preferably shaped for at least partial insertion into the corresponding slots  75 ,  79  of a next successive screen  60  in a series of screens  60 . For this purpose, the distal ends  72 ,  74  are arranged on the bottom end of the end faces of printed circuit boards  68 ,  70  and do not extend over the full length of the end face. 
     In use, the screens  60  are arranged in a row along the extent of the base piece  26  between adjacent pairs  62 ,  64  of IDCs  52  in the manner shown in  FIG. 11 . The plate  66  of each screen  60  is of suitable size to fit between adjacent pairs  62 ,  64  of IDCs  52 . The plate  66  of each screen is also of suitable size and shape to extend between the rows  40   a ,  40   b  of IDCs  52 . The side plates  68 ,  70  of each screen  60  are of suitable size and shape to come into contact preferably with the plates  66  of the next screen  60  in the series. When so arranged, the screens  60  are held in electrical communication with each other. An electrical connection between all screens  60  is effected when they are arranged in the manner shown in  FIG. 11 . The series of electrically connected screens  60  is advantageous in the earthing of electrical and magnetic fields incident on the conductive surfaces of the conductive screens  60 . 
     The side plates  68 ,  70  are preferably slightly longer than the distance between adjacent pairs  62 ,  64  of IDCs  52 . In this embodiment, the side plates  68 ,  70  of each screen  60  are adapted to at least partially deform so as to resiliently bear against the next screen  60  in the series. The bent end sections  72 ,  74  control the deformation of the side plates  68 ,  70  so that they move towards each other when the screens are fitted in the manner shown in  FIG. 11 . The controlled deformation of the side plates  68 ,  70  advantageously holds the screens  60  in electrical communication with each other. 
     Alternatively, the side plates  68 ,  70  of each screen  60  are of suitable size and shape so that the bent end sections  72 ,  74  of each side plate  68 ,  70  are adapted to be at least partially inserted into corresponding slots  75 ,  79  of the next screen  60  in the series. When so arranged, the screens  60  are mechanically connected together. Further, when so arranged, the screens  60  are held in electrical communication with each other. An electrical connection between all screens  60  is effected when they are arranged in the manner shown in  FIG. 11 . The series of electrically connected screens  60  is advantageous in the earthing of electrical and magnetic fields incident on the conductive surfaces of the conductive screens  60 . 
     The spaced apart projections  65 ,  67  are shaped to screen the contact portions of the IDCs  52 . The projections  65 ,  67  extend into hollow pedestals  76  formed in the front side  14  of the housing  12  of the connector block  10 . 
     In the described arrangement, the series of screens  60  reduces the effects of electromagnetic radiation on pairs of IDCs  52  from four aspects. The series of screens  60  surrounds each pair  62  of IDCs  52  with four electrically conductive surfaces. The screens  60  thereby reduce the effects of electromagnetic radiation on each pair  62  of IDCs  52  from neighbouring pairs  64  of IDCs  52 . Advantageously, the series of screens  60  reduces the effects of crosstalk in high frequency data communications. It should be pointed out here that in each case two pairs of IDCs are then located within a screen, namely one pair for the row  40   a  and one pair for the row  40   b.    
     In an alternative arrangement, the series of screens  60  are mechanically coupled together so that they form a single structure. The side plates  68 ,  70  of each screen  60  are mechanically connected to the plate  66  of the next successive screen  60  in the series. The screens  60  are electrically coupled together by the mentioned mechanical connections. The series of screens  60  is adapted to be inserted into the base piece  26  of the housing as a single unit to reduce crosstalk. 
     The connector block  10  shown in  FIG. 12  includes five groups of electrically conductive screens  60   a ,  60   b ,  60   c ,  60   d ,  60   e  arranged in series along the extent of the housing  12  between the first and second ends  20 ,  22 . Each group  60   a ,  60   b ,  60   c ,  60   d ,  60   e  of screens  60  is held in electrical isolation from its neighbouring groups of screens. 
     The groups  60   a ,  60   b ,  60   c ,  60   d ,  60   e  of screens  60  provide electromagnetic screening for pairs  62 ,  64  of IDCs  52  of corresponding groups  42 ,  44 ,  46 ,  48 ,  50  of connectors. In this arrangement, the screens  60  of each group  60   a ,  60   b ,  60   c ,  60   d ,  60   e  provide electromagnetic screening for three out of four of the pairs  62 ,  64  of IDCs  52  from four aspects. The remaining pair of IDCs  52  is screened from three aspects only. The distance d between adjacent groups  30 ,  32 ,  34 ,  36 ,  38  of insulation displacement contact slots  40  is preferably sufficient to reduce the effects of electromagnetic radiation on the pair of IDCs  52  that is screened from three aspects only. 
     Alternatively, the distance d between adjacent groups  60   a ,  60   b ,  60   c ,  60   d ,  60   e  of screens  60  is sufficient to include an additional screen in the series so that each group  62 ,  64  is screened from four aspects. In this embodiment, each group  60   a ,  60   b ,  60   c ,  60   d ,  60   e  includes five screens  60 . Instead of a fifth screen  60 , a single additional plate can also screen the second side. 
     Electrically conductive materials for constructing each screen  60  preferably include aluminium, steel, iron, copper, silver, gold, doped silicon, and conductive polymer. Preferable electrically insulating materials for construction of parts of said screen include plastic, resin, glass and rubber. For screens constructed at least in part of insulating materials, at least one surface of each of the plates  66 ,  68 ,  70  is coated with an electrically-conductive coating. Preferable coatings for non-insulating surfaces include immersion coating and deposition of one or more of the following materials: aluminium, steel, iron, copper, silver, gold, doped silicon and conductive polymer. A sufficient coating may include a thin coating on one or both surfaces of each plate, or a grid pattern with sufficiently small gaps to attenuate electromagnetic transmission. The thickness of any conductive plate or conductive screening is sufficient to substantially attenuate the propagation of electromagnetic radiation at the frequencies radiated by the IDCs and any conductors which may be terminated therein. 
     While we have shown and described specific embodiments of the present invention, further modifications and improvements will occur to those skilled in the art. We desire it to be understood, therefore, that this invention is not limited to the particular forms shown and we intend in the appended claims to cover all modifications that do not depart from the spirit and scope of this invention. 
     Throughout this specification, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated feature or step or group of features or steps but not the exclusion of any other feature or step or group of features or steps. 
     The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that the prior art forms part of the common knowledge of those skilled in the art.