Abstract:
The present invention is directed to a common integrated shielded cable interface which constitutes a cost-effective alternative to using expensive size/type dependent connector backshells and metal shell connectors to provide EMI shielding for single and multiconductor electrical cables that is fundamentally mechanical in nature.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a shielded cable interface plate and associated cable bushings and, more specifically, to a mechanical labyrinth that provides efficient shielding from electromagnetic interference (EMI). 
     2. Description of Related Art 
     Electromagnetic interference (EMI) can result when, for example, multiple electrical circuits are located in close proximity to each other. Generally, metal connector backshells are used in conjunction with metal shell connectors and cable shield braid to shield circuits, electrical wires and cables that are sensitive to EMI. However, metal connector backshells are expensive and time consuming to implement because they must be designed or procured specifically for a particular size and type of metal shell connector. Additionally, metal shell connectors themselves are inherently expensive and time consuming to implement when compared to their commercially available plastic equivalents. 
     Other types of EMI shielding rely on the establishment of a continuous electrical shield to prevent EMI from degrading the effectiveness of circuitry. For example, U.S. Pat. No. 5,170,008 describes an enclosure structure having an electrically conductive grommet and a two-piece interface plate. The grommet provides a conductive elastomer connection that surrounds a stripped portion of an external cable shield. The cable is inserted through the central passage of the grommet, and the grommet is fit into a U-shaped opening in one-piece of the two-piece interface plate. The open side of the U-shaped opening is closed by the other half of the interface plate. A one-piece metal band within the grommet provides a direct low resistance path from the cable shield to the interface plate. The band forms to an outer groove of the grommet and the elasticity of the grommet holds the band in place. Thus, a continuous, contiguous and electrically conductive contact between the cable shield, the conductive grommet, the band, and the enclosure structure is used to provide EMI shielding. 
     U.S. Pat. No. 5,012,042 describes providing EMI shielding by mechanically fastening a cable shield to an enclosure. As with other known connector elements, uniform and consistent electrical contact between the cable shield and the enclosure is used to shield EMI. 
     It would be desirable to provide a shielded interface which is less expensive, less complex and therefore more cost effective to implement than conventional EMI shielding techniques used on electrical cables. Furthermore, it would be desirable to provide a shielded interface which is not dependent upon the connector type or size, such that it is more versatile. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a common integrated shielded cable interface which constitutes a cost-effective alternative to using expensive size/type dependent connector backshells and metal shell connectors to provide EMI shielding for single and multiconductor electrical cables that is fundamentally mechanical in nature. 
     In an exemplary embodiment of the present invention, a shielded connector assembly comprises a cable interface assembly for establishing an electromagnetic interference (EMI) shield for shielding an area, the shield being formed of multiple components assembled together with a joint between the components of the shield, the joint being susceptible to EMI; and a connector, electrically shielded by the cable interface assembly, for connecting a conductive wire to an electronic assembly, the components of the cable interface assembly further including: at least two interface plates mated at an interface for establishing the joint and at least one opening the joint being configured to reflect EMI away from the shielded area; and at least one cable bushing for receiving the conductive wire, mounted between the interface plates in the at least one opening. 
     In another exemplary embodiment of the present invention, a cable interface assembly for establishing an electromagnetic interference (EMI) shield for shielding an area, the shield being formed of multiple components assembled together with a joint between the components of the shield, the joint being susceptible to EMI, comprises: at least two interface plates mated at an interface for establishing the joint and at least one opening the joint being configured to reflect EMI away from the shielded area; and at least one cable bushing for receiving a conductive wire, mounted between the interface plates in the at least one opening. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments, when read in conjunction with the accompanying drawings wherein like elements have been represented by like reference numerals and wherein: 
     FIGS. 1A and 1B illustrate exploded top and bottom views of an interface assembly in accordance with an exemplary embodiment of the present invention; 
     FIGS. 2A and 2B illustrate exemplary side views of the FIG. 1 interface assembly; 
     FIG. 3 illustrates a side view of the FIG. 1 interface assembly of the present invention used with a circuit cover, in accordance with an exemplary embodiment of the present invention; and 
     FIG. 4 illustrates bushings used in accordance with an exemplary embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1A illustrates an exploded top view of an interface plate  120  configured in accordance with an exemplary embodiment of the present invention. The interface plate  120  establishes an electromagnetic interference shield for shielding an area. The interface plate  120  comprises a left half plate  125  and a right half plate  130  each having arcuate cutouts  150 . When both the left half plate  125  and right half plate  130  are joined, a plurality of holes are formed by the cutouts  150  and provide space for a plurality of cable bushings  110 . The left half plate  125  and the right half plate  130  are identical except that the left half plate  125  has an upper lip  135  and the right half plate  130  has a lower lip  140 . Accordingly, when the left half plate  125  and right half plate  130  are joined, a lap joint is created between the holes for receiving and holding cable bushings  110 . One skilled in the art will recognize that either the left half plate  125  or the right half plate  130  can have the upper lip as long as the other plate is equipped with the lower lip. Alternately, the upper/lower lips can be mixed among the two plates, provided that each upper lip mates with an opposing lower lip. 
     FIG. 1B shows a bottom view of the left and right half plates  125  and  130  of the interface plate  130 , including a metal lip  170 . The metal lip  170  is formed along the entire outer periphery of the interface plate  120  so that the interface plate  120  can mate with other devices (e.g., another housing cover or rack panel). 
     Both the cable bushing  110  and interface plate  120  can be made from any metal (e.g., aluminum), metallized plastic, or any other structural material that has desired EMI shielding characteristics. The cable bushing  110  can also be part of an electrical cable assembly, and be terminated to a cable braid shield in the same manner as conventional connector backshells. 
     FIG. 2A illustrates a side view of the joined left and right half plates  125  and  130 . The joining of the left half plate  125  and right half plate  130  results in a lap joint  210  which comprises at least two perpendicular surfaces to reflect EMI. The lap joint is series of mated surfaces formed by interfacing the left half plate  125  with the right half plate  130 . The joint created at the interface of the left and right half plates is susceptible to EMI. However, in accordance with an exemplary embodiment of the present invention, the result of the lap joint  210  is essentially a series of roadblocks, e.g., a mechanical labyrinth, which reflects EMI so as to prevent EMI from penetrating entirely through the interface plate  120 . The dashed lines  220  represent boundaries of holes in the interface plate  120  for the cable bushings  110 . 
     Any EMI that exists on the outside of the interface plate  120  will penetrate the interface plate  120  at the joint between the left half plate  125  and the right half plate  130  and will also penetrate the plate at the joint between the plate  120  and the cable bushing  110 . As illustrated in FIG. 2A, if the EMI existed at the joint between the plates of the two piece interface plate  120 , it would enter the joint vertically. The interference would first encounter the upper portion of the lower lip  140  of the right half plate  130 . At this point, much of the EMI will be reflected away from the plates. Any residual EMI will continue to follow horizontally along the lap joint  210  between the left and right half plates. However, as shown in FIG. 2A, this EMI will encounter a portion of the left half plate  125 . Any remaining EMI will be reflected and will not pass through the remaining joint area. As a result, EMI is unable to penetrate through the entire interface plate  120  and the interface creates a path to reflect EMI in at least two orthogonal directions away from the interface. 
     Alternately, as illustrated in FIG. 2B, the joint between the left half plate  125  and right half plate  130  can also be configured as a tongue-and-groove joint  230 . Any EMI that exists on the outside of the interface plate  120  will penetrate the interface plate  120  at the joint between the left half plate  125  and the right half plate  130  and will also penetrate the plate at the joint between the plate  120  and the cable bushing  110  (illustrated in FIGS. 1 A and  1 B). As illustrated in FIG. 2B, if the EMI existed at the joint between the plates of the two piece interface plate  120 , it would enter the joint vertically. The interference would first encounter the upper portion of the tongue  240  of the right half plate  130 . At this point, much of the EMI will be reflected away from the plates. Any residual EMI will continue to follow horizontally along the tongue and groove joint  230  between the left and right half plates. However, as shown in FIG. 2B, this EMI will encounter a portion of the left half plate  125 . Any remaining EMI will be reflected and will not pass through the remaining joint area. As a result, EMI is unable to penetrate through the entire interface plate  120  and the interface creates a path to reflect EMI in at least two orthogonal directions away from the interface. 
     FIG. 3 illustrates a cross sectional view of an interface plate  120  at the location of the bushing  110  and also shows the use of metal lip  170  to form a lap joint with a cover  310  used to protect an electronic assembly (i.e., a circuit board or circuit component)  330 . A cable  320  is attached to a cable bushing  110  located in one of the available holes in the interface plate  120 . Each cable  320  can contain a plurality of wires  335  that are connected to the electronic assembly  330  enclosed by the cover  310  using an inexpensive commercially available plastic connector  360 . While connector  360  is shown connecting the wires to the electronic assembly, many other types of connections (e.g., solder joints, etc.) could also be employed. The cable  320  is protected from EMI along its length by a braid  325  which surrounds an outer diameter of the cable  320 . The end of braid  325  can be secured to the cable bushing  110  using, for example, a band clamp  350  or any other attachment means. 
     In accordance with an exemplary embodiment of the present invention, the cover  310  contains a lower lip  340  which forms a lap joint  345  with the peripheral upper lip  170  of the interface plate  120 . As discussed with respect to the left and right half plates  125  and  130  in FIG. 2, EMI is unable to penetrate the interface between the periphery of the interface plate  120  and the cover  310 . If the EMI were to penetrate the lap joint  345  formed between the cover  310  and the interface plate  120 , it would enter the joint horizontally. The EMI would first encounter a portion of the left half plate  125 . At this point, much of the EMI will be reflected away from the left half plate  125 . Any residual EMI would continue to follow along the joint between the cover  310  and the left half plate  125 . However, this residual EMI would encounter the upper portion of the lower lip  340  of cover  310 . The remaining EMI would thus be reflected and would not pass through the remaining joint area. As a result, EMI is unable to penetrate through the lap joint  345  connecting the interface plate  120  and the top cover  310 . Similarly, EMI is unable to penetrate the joint created on the right of FIG. 3, between the right half plate  130  and the cover  310 . 
     The interlocked left and right half plates  125  and  130  and the periphery of the interface plate  120  and the cover  310  provide adequate EMI shielding. 
     The interface plate  120  can, for example, be rigidly attached to a panel, box, or bulkhead using threaded fasteners, rivets, or conductive adhesives. When the interface plate  120  is employed with a circuit cover, as shown in FIG. 3, an efficient conduit is created for wires  320  which eliminates the requirement for specially made metal shell connectors and backshells. Instead, commonly used cable bushings  110  can be placed at the interface plate as illustrated in FIG.  3 . The cable bushing  110  provides an efficient conduit for the wire within the cable to be run to the circuit board. At the electronic assembly  330 , a commonly available connector  360  can be employed to connect the wires  320  to the electronic assembly. This significantly reduces the cost of building electronic assemblies, since special (i.e., application specific) metal connectors and backshells do not have to be procured or fabricated. The cable bushing  110  can be locked in place at the next-level assembly by the interface plate. 
     Like the joint between the left and right half plates, EMI would enter the joint between the cable bushing  110  and interface plate  120 . As illustrated in FIG. 3, if the EMI existed at the joint between the plates of the two piece interface plate  120  and cable bushing  110 , it would enter the joint horizontally. The interference would first encounter a portion of the cable bushing  110 . At this point, much of the EMI will be reflected away from the interface plate. Any residual EMI will continue to follow vertically along joint between the cable bushing  110  and interface plate  120 . However, as shown in FIG. 3, this EMI will encounter the another portion of the cable bushing  110 . Any remaining EMI will be reflected and will not pass through the remaining joint area. As a result, EMI is unable to penetrate through the entire joint between the cable bushing and interface plate  120  because there exists at least two perpendicular surfaces interface to reflect the EMI in directions away from the interface. 
     As illustrated in FIG. 4, the cable bushings  110  can be of a standardized size, to fit in the holes of the interface plate. If desired, however, a single cable bushing  110  can be designed to accommodate a wide range of cable bundle diameters. Each cable bushing can contain a cap  410  that can be drilled or punched out to the user&#39;s need specification. The parts required by the present invention are common for most electrical cables and can be kept on-hand to reduce lead times. Additionally, the interface plate provides strain relief for wires and contacts by transferring loads to the cable bushing, interface plate, and cable braid. 
     It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced within.