Abstract:
A novel conductive gasket including an internal contact-enhancing strip provides improved contact performance in electromagnetic interference prevention and other applications. A metal mesh or conductive plastic covers a substantially rigid internal strip that includes protrusions that either bend or penetrate the gasket cover in order to enhance contact with another conductive surface. The cover may include holes aligned with the protrusions so that the protrusions pass through the holes when the gasket is compressed, or the protrusions may penetrate a mesh or plastic cover. An internal foam piece may be provided behind the internal strip to restore the shape of the when compressive force is removed and a second internal foam piece may be provided between the strip and the cover for maintaining the shape of the gasket. The protrusions on the internal strip may range from needle-shaped protrusions for puncturing a coating to relatively smooth bumps for bending the surface of the cover when the gasket is compressed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to conductive gaskets for shielding against electromagnetic interference (EMI gaskets), and more particularly, to a conductive gasket having improved performance when providing contact through non-conductive coatings. 
     2. Background Information 
     Conductive gaskets are widely used to prevent electromagnetic interference (EMI) leakage and entrance into and from electronic equipment. In particular, EMI gaskets are provided at the interfaces of computer cabinets and cabinets containing other electronic equipment so that radiated emissions fall below maximum radiated emissions requirements of various authorities such as the U.S. Federal Communications Commission (FCC) standards and Canadian Standards Association (CSA). 
     Typically, a wire mesh gasket including an internal foam material is provided on flanges and other interfaces of cabinets having exposed conductive surfaces. When the cabinet is closed, the gaskets are compressed providing a low-impedance contact between cabinet portions via the conductive wire mesh. 
     However, non-conductive coatings such as organic anti-fingerprint coatings are often used on equipment surfaces in order to provide improved appearance and to avoid oxidation initiated by contact with acids transferred from human skin. In addition, such coatings prevent oxidation occurring naturally on exposed metal surfaces that do not have anti-corrosion platings. When a gasket, or the surface that a gasket is to contact is coated with such a material, the surface conductivity may be dramatically reduced, requiring removal of the coating before a sufficiently low-impedance contact may be made with the gasket. 
     Also, in general, as frequencies of electronic equipment (in particular digital computing systems) continue to increase, improved shielding is necessary, and therefore the performance of conductive gaskets becomes more critical. 
     Therefore, it would be desirable to provide a conductive gasket and method of manufacture for a conductive gasket having improved performance, and in particular a conductive gasket that will operate reliably when either the gasket or a mating surface is coated with a non-conductive coating. 
     SUMMARY OF THE INVENTION 
     The objective of providing improved conductive gasket performance, particularly in the presence of non-conductive coatings, is accomplished in a new conductive gasket and method of manufacture. 
     The gasket includes a contact strip provided beneath a flexible conductive cover. The cover may be a conductive wire mesh, or alternatively, a flexible plastic with a conductive coating on an exterior surface. The contact strip includes multiple protrusions that may pass through the cover when the gasket is compressed, providing improved contact with the surface that the protrusions contact and penetration of any non-conductive coating that is present. Holes may also be provided in a flexible plastic cover so that protrusions may pass through without damaging the cover. 
     Alternatively, the protrusions may be relatively smooth projections or bends in the contact strip that cause the flexible cover to bend sharply, providing corners in the cover that will break through any non-conductive coating that is present. The gasket may include a foam insert to restore the shape of the gasket when a compressive force is removed. A foam section may be included above the protrusions in order to preserve the shape of the gasket. Or, the gasket may be made entirely from a wire mesh with a contact strip woven inside. The contact strip may include protrusions on both faces so that contact is enhanced with two surfaces when the gasket is compressed. 
     The foregoing and other objectives, features, and advantages of the invention will be apparent from the following, more particular, description of the preferred embodiment of the invention, as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein like reference numerals indicate like components, and: 
     FIG. 1A is a pictorial diagram depicting an open electronics cabinet including a gasket in accordance with an embodiment of the present invention. 
     FIG. 1B is a pictorial diagram depicting further details of the cabinet and gasket of FIG.  1 A. 
     FIGS. 2A-2D are pictorial diagrams depicting cross-sectional views of gaskets in accordance with various embodiments of the present invention. 
     FIG. 3A is a pictorial diagram depicting a side cross-sectional view of a gasket in accordance with another embodiment of the present invention. 
     FIG. 3B is a pictorial diagram depicting a side cross-sectional view of a gasket in accordance with an alternative embodiment of the present invention. 
     FIGS. 4-6 are pictorial diagrams depicting cross-sectional views of gaskets in accordance with other embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention will now be described in more detail by way of example with reference to the embodiments shown in the accompanying figures. It should be kept in mind that the following described embodiments are only presented by way of example and should not be construed as limiting the inventive concept to any particular physical configuration. 
     Further, if used and unless otherwise stated, the terms “upper,” “lower,” “front,” “back,” “over,” “under,” and similar such terms are not to be construed as limiting the invention to a particular orientation. Instead, these terms are used only on a relative basis. 
     With reference now to the figures, and in particular with reference to FIG. 1A, there is depicted an electronics cabinet  12  including an EMI gasket  10  in accordance with an embodiment of the present invention. Gasket  10  is installed on a flange  14  of cabinet  12  on which a cover (not shown) will be mounted. Gasket  10  provides a low-impedance connection between a cover and flange  14  so that electronics  16  is shielded from outside EMI and also reduces emissions from electronics  16  into the environment outside of cabinet  12 . While the installation of FIG. 1A shows a typical use of an EMI gasket, gasket  10  is atypical, as gasket  10  includes improvements as will be detailed in the description below. 
     FIG. 1B illustrates installation details of gasket  10 , including the contact of gasket  10  with a first surface  16 A of cover  16  as well as a second surface  14 A of flange  14  to which gasket  10  is attached via an adhesive or other mounting mechanism. Contact of first surface  16 A with gasket  10  is a pressure contact that provides the electrical path from gasket  10  to cover  16  so that a highly conductive path is established through gasket  10  from cover  16  to flange  14 . Gasket  10  includes improvements detailed herein below, that aid in providing a highly conductive (low-impedance) path between two or more surfaces. In particular, if any of surfaces  14 A or  16 A, as well as the surfaces of gasket  10  are coated with a non-conductive coating, such as anti-fingerprint organic coatings or anti-oxidation coatings, gasket  10  includes features such that when gasket  10  is compressed, the coatings will be penetrated and a highly-conductive path established between the mating surfaces contacting the gasket. 
     In general, the surface to which gasket  10  is mounted will be conductive, and the surface of gasket  10  and the opposing surface to be contacted by gasket  10  will be coated and the surface of gasket may be coated as well. However, certain embodiments of gasket  10  that will be illustrated in detail below, are designed to penetrate non-conductive coatings at two or more surfaces of gasket  10  when gasket  10  is compressed. 
     Referring now to FIG. 2A, details of gasket  10  are illustrated. Gasket  10  includes an outer conductive cover  26  in the form of a wire mesh, as is well known in the art of electromagnetic shielding gaskets. Within gasket  10 , a foam core  24  is introduced in order to shape wire mesh cover  26  into a D-shaped cross-section. Also within gasket  10  a conductive metal strip  20  including a plurality of protrusions  22  is located so that when gasket  10  is compressed, protrusions  22  protrude through cover  26 , penetrating any coating present on a surface that contacts the top surface of gasket  10 . 
     The bottom surface of gasket  10  is electrically coupled to the mounting surface  14 A by a conductive adhesive  28 , so that a conductive path is established between mounting surface  14 A, cover  26 , metal strip  20  and protrusions  22 . The combination of the electrically interconnected components listed above yield a very low-impedance path between surface  14 A and a surface placed in pressure contact with protrusions  22  and cover  26 . Alternative conduction mechanisms are possible and particular conduction mechanisms are illustrated herein below. Also, foam  24  may be a conductive foam, further reducing the impedance of the connection between metal strip  20  and surface  14 A. Protrusions  22  are generally of sufficient sharpness to provide for penetrations of surface coatings, but not so sharp as to pose an installation or handling hazard to persons handling or installing gasket  10 . 
     While most of the embodiments depicted herein are illustrated as having a D-shaped gasket cross-section, it will be understood that gaskets are supplied in a variety of shapes and sizes, and that the techniques of the present invention can be applied to other gasket shapes such as cylindrical, rectangular and hemispherical cross-sections. 
     Referring now to FIG. 2B, details of a gasket  10 A in accordance with another embodiment of the present invention are illustrated. Gasket  10 A has a body formed from a wire mesh  26 A, as is well known in the art of electromagnetic shielding gaskets. Within gasket  10 , a conductive metal strip  20 A including a plurality of protrusions  22 A is located so that when gasket  10 A is compressed, protrusions  22  protrude through the top surface of wire mesh  26 A, penetrating any coating present on a surface that contacts the top surface of gasket  10 A. 
     The bottom surface of gasket  10 A is mechanically attached to mounting surface  14 A by an adhesive strip  28 A, but the conductive path that is established between mounting surface  14 A, wire mesh  26 A, metal strip  20 A and protrusions  22 A is provided by contact of wire mesh  26 A. The mounting arrangement shown, which is particularly suited to mounting via a double-sided adhesive strip that is non-conductive may also replace the illustrated mounting configurations depicted in the other illustrated embodiments and is shown here as an alternative mounting arrangement. The embodiment depicted in FIG. 2B illustrates a conductive gasket in accordance with the present invention that does not require an internal foam insert, as the shape of gasket  10 A is maintained by solid wire mesh body  26 A. 
     Referring now to FIG. 2C, details of a gasket  10 B in accordance with yet another embodiment of the present invention are illustrated. Gasket  10 B is similar to gasket  10  of FIG. 2A, but is designed so that protrusions  22 B extend through cover  26 B, even when gasket  10 B is uncompressed. When gasket  10 B is compressed, protrusions  22  protrude further through the top surface of wire mesh  26 B, penetrating any coating present on a surface that contacts the top surface of gasket  10 B. 
     Referring now to FIG. 2D, details of a gasket  10 C in accordance with still another embodiment of the present invention are illustrated. Gasket  10 B is similar to gasket  10  of FIG. 2A, but cover  30  is a flexible plastic cover, which is generally a sputtered metal film. Perforations  32  may be pre-made in cover  30  and aligned with protrusions  22 C (or protrusions  22 C may self-align) so that cover  30  is not altered when gasket  10 C is compressed. Alternatively, in some applications such as for one-time installation, cover  30  may be made without perforations and may be perforated by protrusions  22 C when gasket  10 C is compressed. 
     Referring now to FIG. 3A, another gasket  10 D is illustrated. Gasket  10 D is similar to gasket  10 B of FIG. 2C, but includes a foam section  24 A that preserves the shape of outer conductive cover  26  above contact strip  20 B, which is formed form a wire mesh. Within gasket  10 D, foam core  24  also holds the shape of outer conductive cover  26  to produce a D-shaped cross-section. All other features are as described above for gasket  10 B. Foam section  24 A may be conductive or non-conductive and may be of the same as or may be of a material differing from that of foam core  24 . 
     Referring now to FIG. 3B, a cross-sectional view of a conductive gasket  10 E in accordance with an alternative embodiment of the invention is depicted. Gasket  10 E includes a strip  20 C that includes blunt protrusions  32  that do not penetrate gasket cover  26  when gasket  10 E is compressed. However, protrusions  32  cause the surface of cover  26  to bend sharply, when gasket  10 E is compressed, causing a break in any coating deposited on conductive cover  26 . Alternatively, bends or other shapes may be provided on contact strip  20 C as long as the bending requirement is satisfied. Strip  20 C is backed with a conductive or non-conductive foam  24  and is coupled electrically to surface  14 A by electrical contact with cover  26 , or via a conductive adhesive strip as described above. In the embodiment of FIG. 3B strip  20 C does not have to be a metal conductive strip, but only have sufficient stiffness to cause sharp bending of gasket cover  26  surface when gasket  10 E is compressed. 
     Referring now to FIG. 4, another gasket  10 F in accordance with an embodiment of the invention is shown. Gasket  10 F includes a metal contact strip  20 D having protrusions  22 D located on both a top and a bottom side. Providing protrusions  22 D on both sides of a gasket permits penetration of coatings on two gasket faces, or even penetration of an adhesive layer  28  when gasket  10 F is compressed. A wire mesh body  26 C is shown surrounding metal contact strip  20 D, but other forms of gaskets such as the foam and plastic cover embodiments described above may be adapted to include a double-sided contact strip such as metal contact strip  20 D. 
     Referring now to FIG. 5, another gasket  10 G in accordance with an embodiment of the invention is shown. Gasket  10 G includes a metal contact strip  20 E having protrusions  22 E located on two faces beneath wire mesh body  26 D and a protrusion-less third bottom face (optional) for support. Without the bottom face, contact strip  20 E may be formed as a single strip and then bent at the apex. Gasket  10 G provides a conductive path between two or three surfaces for corners of cabinets. 
     Referring now to FIG. 6, another gasket  10 H in accordance with another embodiment of the invention is shown. Gasket  10 H is a cylindrical gasket, as is often required for channel mounting. Gasket  10 H includes a metal contact strip  20 F in the form of a wire or rod  20 F having protrusions  22 F extending radially from the wire or rod  20 F and surrounded by a metal mesh  26 E. When gasket  10 H is compressed along a given radius, protrusions  22 F extending along that radius will penetrate mesh  26 E and provide improved conduction, penetrating any non-conductive coatings contacted by protrusions  22 F. 
     It should be understood, however, that the invention is not necessarily limited to the specific process, arrangement, materials and components shown and described above, but may be susceptible to numerous variations within the scope of the invention. 
     It will be apparent to one skilled in the art that the manner of making and using the claimed invention has been adequately disclosed in the above-written description of the preferred embodiments taken together with the drawings. 
     It will be understood that the above description of the preferred embodiments of the present invention are susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.