WO1994013123A1

WO1994013123A1 - Emi-shielding gasket

Info

Publication number: WO1994013123A1
Application number: PCT/US1993/011392
Authority: WO
Inventors: Peter E. Mertinooke; Joseph J. Kaplo; Alan De Mello
Original assignee: Amesbury Group, Inc.
Priority date: 1992-11-25
Filing date: 1993-11-23
Publication date: 1994-06-09
Also published as: CA2150143A1; AU5617594A; EP0671117A1; JPH08504059A

Abstract

A gasket (10) for shielding electromagnetic interference passing through a seam between two electrically conductive bodies includes an EMI shield (14) embedded in a resilient foam profile (12) for shielding electromagnetic interference passing through the seam. The gasket further includes a seamless, electrically conductive skin (16) covering at least part of the outer surface of the foam profile (12). The skin (16) is arranged so that electric charge which accumulates on the EMI shield (14) can be dissipated to ground. Another gasket includes a base for securing the gasket to the first, electrically conductive body and a multiplicity of discrete, elongate, metallized filaments projecting from the base so that a substantial amount of the filaments contacts the second, electrically conductive body when electromagnetic interference passing through a seam between the bodies is to be shielded. The gasket further includes structure, arranged with the base, so that energy absorbed by the shielding member as a result of the shielding of passing electromagnetic interference can be dissipated to ground through the first, electrically conductive body.

Description

EMI-SHIELDING GASKET

Background of the Invention The invention relates generally to the field of gaskets for shielding electromagnetic interference (EMI). In particular, the invention concerns EMI shielding gaskets which include EMI shields embedded in resilient foam profiles. Most electronic equipment generates unwanted electromagnetic energy during operation which, if not properly shielded, can interfere with other electronic equipment by way of radiation and/or conduction. This can include electromagnetic energy of wavelengths along various points of the spectrum such as radio frequency interference. As used herein, therefore, the term electromagnetic interference pertains to interfering electromagnetic energy of any wavelength. To avoid the problems associated with electromagnetic interference, all sources of electromagnetic energy should be properly shielded and grounded. Shielding should be designed to prevent both incoming and outgoing interference. In the case of equipment permanently contained in a housing, effective shielding can be accomplished through proper construction of the housing. It is difficult to shield effectively, however, equipment having access panels or This is because the seams between the access panels or doors and the housing body provide natural escape and entry routes for electromagnetic interference. In the case of metal housings, gaps can also inhibit the beneficial Faraday Cage effect by presenting conductivity discontinuities in the electrically conductive surfaces of the housings. The gaps also reduce the efficiency of the ground conduction path. Moreover, by presenting an electrical conductivity level which is significantly different from that of the housing, the gaps can act as slot antennae and result in the housing becoming a secondary source of EMI radiation.

In the case of electrical apparatus housings which include seams, therefore, an effective shielding mechanism must be configured both to provide sufficient EMI shielding characteristics and to allow proper closure of the door or access panel. Various configurations of gaskets have been developed for serving these purposes. They are intended to provide maximum EMI shielding, while minimizing the force required to close the door or access panel.

To present an effective shield to electromagnetic interference, a gasket should be capable of absorbing and/or reflecting electromagnetic interference and of establishing as continuous an electrically conductive path as possible across the seam in which the gasket is positioned. Typically, metallic structures are used for EMI shielding because of their high degree of electrical conductivity. Because that conductivity is not infinite, however, part of the electromagnetic field being shielded is transmitted across the shield and supports a current in the shield. Accordingly, an effective EMI shielding gasket should provide an electrically conductive path for dissipating this current to ground, otherwise the current could serve to radiate an electromagnetic field on the other side of the shield.

Known EMI shielding gaskets have been unable to combine effectively these qualities with the other requirements of suitable gaskets, such as presenting a consistent, minimal closure resistance. Another important characteristic of an EMI shielding gasket is that it not break down due to galvanic corrosion, such as can occur when dissimilar metals are in contact with one another.

It is an object of the invention, therefore, to provide a gasket which affords improved shielding of electromagnetic interference passing through seams in electronic apparatus housings. Another object of the invention is to provide such a gasket which is of a cost effective construction. Still another object of the invention is to provide such a gasket which can utilize a broad range of materials for shielding. Still another object of the invention is to provide such a gasket which presents a narrow profile and thereby presents a minimum of closure resistance to housing doors and access panels.

Summary of the Invention These and other objects are achieved by the present invention which features a gasket for shielding electromagnetic interference passing through a seam between two electrically conductive bodies. In one embodiment, the gasket includes an electromagnetic shield embedded in a resilient foam profile. When the gasket is positioned in a seam between the two bodies, the shield inhibits the passage of electromagnetic interference through the seam by reflecting and/or absorbing the electromagnetic energy. In some embodiments, the gasket further includes a seamless, electrically conductive skin which covers at least part of the outer surface of the foam profile. The skin is arranged on the foam profile so as to be in electrical contact with the EMI shield as well as with at least one of the electrically conductive bodies defining the seam. In this manner, energy absorbed by the EMI shield as a result of the passing electromagnetic interference can be dissipated to ground, thereby facilitating the proper operation of the gasket.

In another embodiment of the invention, the EMI shield is arranged against an outer surface of the foam profile. This embodiment of the invention also includes a seamless, electrically conductive skin which covers at least part of the outer surface of the foam profile. Again, the skin is arranged for electrical contact with both the EMI shield and at least one of the electrically conductive bodies defining the seam so that energy absorbed by the shield can be dissipated to ground.

In the various embodiments of the invention, the EMI shield can comprise strands of metallic material, metallized yarns, metallized cloths, metallized fibers, and combinations thereof. In the case wherein the shield comprises strands of metallic material, the strands may or may not be arranged to intersect with one another. Moreover, the strands can be arranged along a substantially straight path as well as along a jagged or serpentine path. These features of the invention will vary depending on the application for which the inventive gasket is intended.

In some embodiments of the invention, the EMI shield is formed for partial direct contact with one or both of the bodies defining the seam in which the gasket is arranged. In cases where the shield is formed of a material suitable for being placed in intimate contact with the bodies, allowing for direct contact in this manner can improve the dissipation to ground of energy absorbed by the shield. It also provides a more consistent degree of electrical conductivity across the seam. These features further enhance the gasket's EMI shielding capacity. In some embodiments, the invention includes a semi¬ rigid carrier coupled to the foam profile for securing the gasket to one of the electrically conductive bodies. The carrier is rigid in relation to the foam profile and may include various mechanisms for enabling attachment, such as arms and barbs. Depending upon the application, the carrier may or may not be electrically conductive.

In some embodiments of the invention, the gasket includes an EMI shield embedded in a resilient foam profile such that it is not in electrical contact with any of the electrically conductive bodies defining the seam in which the gasket is arranged. These embodiments of the invention are useful in applications where EMI energy is primarily reflected rather than absorbed.

The present invention also features another gasket which, for example, is suitable for shielding electromagnetic interference passing through a seam between a door or access panel and a housing wall of a piece of electronic equipment.

In one embodiment, the gasket includes a base for securing the gasket to the first, electrically conductive body and an EMI-shielding member projecting substantially perpendicularly from the base to contact the second body when EMI passing through the seam between the bodies is to be shielded. Resilient means is arranged to cooperate with the EMI shielding member to position properly the shielding member throughout repeated openings and closings of the door or access panel. The gasket further includes electrically conductive means arranged with the base for conducting electric current between the shielding member and the first, electrically conductive body. In this manner, energy which is absorbed by the shielding member can be dissipated to ground.

In various embodiments, the shielding member can be metallized cloth, strands of metallic wire, metallized yarn, or combinations thereof. The electrically conductive means can be conductive particles embedded in the base such as electrically conductive carbon, a conductive coating laid over the base, a conductive skin wrapped around the base, or combinations thereof. The base itself can also be formed of an electrically conductive material.

The resilient means for supporting the EMI shielding member can be a thermoplastic elastomeric foam substrate, an electrically conductive polymer backing, or a multiplicity of discrete, elongate filaments arranged against the shielding member. In some embodiments of the invention, the filaments are electrically conductive and help complete the electrically conductive path for dissipating absorbed energy to ground. In other embodiments, the filaments includes non-electrically conductive filaments, which are provided for their ability to shield environmental effects such as wind, dust, and noise.

In some embodiments, EMI shielding is provided by a multiplicity of discrete, elongate, metallized filaments which project substantially perpendicularly from the base. The filaments act has hundreds of individual "walls" inhibiting the passage of electromagnetic waves. In these embodiments, energy which is absorbed by the filaments is dissipated to ground via an electrically conductive path formed in any of a number of ways such as are described above. For example, electric current may flow from the metallized filaments to ground via an electrically conductive coating laid over the base, an electrically conductive covering enveloping the base, electrically conductive particles embedded in the base, or the base itself. Also, the metallized filaments can be attached to the base in such a way that a portion of the filaments extends through the base to contact on the back of the base a connection to an electric current path to ground.

These and other features of the invention will be more fully appreciated by reference to the following detailed description which is to be read in conjunction with the attached drawing.

Brief Description of the Drawings

FIGURE 1 is a perspective view of an inventive EMI shielding gasket including an EMI shield embedded in a foam profile which is surrounded by a seamless, electrically conductive skin,

FIGURE 2 is a perspective view of another embodiment of the inventive EMI shielding gasket shown in FIGURE 1 wherein the EMI shield is exposed for direct contact with an external electrical conductor, FIGURE 3 is a cross-section view of an inventive EMI shielding gasket including an EMI shield arranged against the outer surface of a foam profile, FIGURE 4 is a cross-section view of an inventive EMI shielding gasket including an EMI shield embedded in a foam profile which is only partially covered with a seamless, electrically conductive skin. FIGURE 5 is a cross-section view of an inventive EMI shielding gasket including an EMI shield embedded in a foam profile which is covered by a skin, only portions of which are electrically conductive, FIGURES 6A and 6B are partial cross-section views of variations of the embodiment of the invention shown in FIGURE 5,

FIGURE 7 is a cross-section view of an inventive EMI shielding gasket including a semi-rigid carrier, FIGURES 8A through 8E depict the sequential assembly of an EMI shielding gasket constructed in accordance with the teachings of the invention.

FIGURE 9 is a perspective view of an inventive EMI shielding gasket including metallized filaments, FIGURE 10 is a cross-section view of the gasket shown in FIGURE 9, the gasket being arranged in a seam between two bodies,

FIGURE 11 is a cross-section view of an inventive EMI shielding gasket including conductive filaments and a metallic shielding member,

FIGURE 12 is a cross-section view of an inventive EMI shielding gasket including non-conductive and metallized filaments,

FIGURE 13 is a cross-section view of another inventive EMI shielding gasket including non-conductive and metallized filaments,

FIGURE 14 is a cross-section view of an inventive EMI shielding gasket including a metallic shielding member having a polymeric backing, FIGURE 15 is a cross-section view of an inventive EMI shielding gasket including a metallic shielding member having foam backing, and FIGURE 16 is a cross-section view of an inventive EMI shielding gasket having metallized filaments embedded in an extruded base.

Detailed Description

As stated, the invention features a gasket for shielding electromagnetic interference passing through a seam between two electrically conductive bodies. The gasket includes a seamless, electrically conductive skin which provides several advantages as set forth in greater detail below.

One embodiment of the invention is shown in FIGURE 1 which is a perspective view of an EMI shielding gasket 10 including a resilient foam profile 12. The foam profile 12, and thereby the gasket 10, has a rectangular cross-section and is elongated along an axis L. Typical gaskets range in size from approximately 0.1 inches to 0.5 inches on each edge. Depending upon the application for which the EMI shielding is required, however, gaskets encompassing the features of the invention can be formed in a variety of profiles and sizes, some of which are detailed below. Such variations will be readily apparent to those skilled in the art. Typically, two components are desired for proper EMI shielding, a shielding mechanism for reflecting and/or absorbing electromagnetic interference, and a conductive path to ground for dissipating absorbed energy from the shield. While grounding of the gasket enhances its shielding capacity, it may not be absolutely essential in applications involving the shielding of a high impedance wave (high electric field) with a low impedance shield (metal) because in such a case most of the energy is reflected rather than absorbed. Conversely, for shielding of low impedance waves (high magnetic fields) low impedance shields such as metal absorb a lot of energy, which energy should be dissipated to ground. Otherwise, the energy absorbed by the shield can become so great that it arcs in the form of electrotastic discharge from the shield to the nearest electrical conductor such as a circuitry component of the electrical apparatus the gasket is supposed to be protecting from electromagnetic interference. Obviously, this phenomenon can seriously damage the apparatus.

The gasket 10 includes^' an EMI shield 14 embedded in the foam profile 12. In the illustrated embodiment, an electrically conductive skin 16 completely surrounds the foam profile 12. The EMI shield 14 is arranged in electrical contact with the electrically conductive skin 16 so that energy absorbed by the EMI shield 14 can be dissipated to ground through the electrically conductive skin 16. This is achieved by ensuring that when the gasket 10 is in use, the skin 12 is in electrical contact with an electrical conductor which is connected to ground. Typically, this conductor will be a wall of the housing of the electrical apparatus with which the gasket 10 is being used. Additionally, the electrically conductive skin preserves the continuity of electrical conductivity across the seam in which it is positioned.

The EMI shield 14 may comprise a variety of materials and configurations. For example, in one embodiment the shield 14 consists of a membrane formed of polyester non-woven fabric which has been metallized on both sides with copper over a 1.5 thousandths of an inch thick polypropylene film laminate. Other commonly known materials such as metallized yarns and metal foils may be used as well. Similarly, a variety of materials is available for use as the electrically conductive skin 16. For example, it has been found that blending approximately 85% be weight of Santoprene brand thermoplastic elastomer resin which is available from the Advance Elastomer Systems company, with approximately 15% by weight of conductive carbon particles renders a compound which is well suited for being extruded over the foam profile 12. An advantage of the embodiment of the invention shown in FIGURE 1 is that the EMI shield 14 does not come into direct contact with the housing of the electronic apparatus with which the gasket is being used. As a result, there are no concerns of galvanic corrosion stemming from the intimate contact of dissimilar metals and, therefore, few restrictions with respect to the materials which can be used to form the shield 14. Additionally, the shield 14 is not ,exposed to natural elements which can break it down. The embodiment of the invention shown in FIGURE 2 is suitable for applications in which the above-noted concerns such as galvanic corrosion and exposure of the shield to natural elements are not present. The figure depicts an EMI shielding gasket 20 including a resilient foam profile 22 surrounded by an electrically conductive skin 26. The gasket 20 differs from the gasket 10 in that the gasket 20 includes an EMI shield 24 having serrations 28 along its longitudinally extending edges. The EMI shield 24 is sized so that the serrations 28 protrude above the electrically conductive skin 26 to provide direct electrical contact between the shield 24 and other electrically conductive bodies, such as the housing of an electrical apparatus. This embodiment of the invention provides an EMI shielding gasket in which absorbed energy can be dissipated more effectively from the shield 24 to ground. As noted, however, since the shield is exposed for direct contact with the apparatus housing, the material of which it is formed should be selected with the above-noted considerations in mind.

FIGURE 3 depicts an embodiment of the invention wherein an EMI shielding gasket 30 includes a resilient foam profile 32 surrounded by an electrically conductive outer skin 36. The gasket 30 further includes an EMI shield formed of metal strands 34. The strands 34 are arranged against the outer surface of the foam profile 32, inside of the electrically conductive skin 36. In this embodiment of the invention, it is desirable, for the above stated reasons, for at least a portion of the metal strands 34 to be positioned against the skin 36 so that energy absorbed by the strands 34 during EMI shielding can be dissipated through the electrically conductive skin 36 to ground. Accordingly, while the strands 34 may be arranged to weave back and forth through the foam profile 32, they typically will be in electrical contact with the skin 36 at at least one point along the length of the gasket 30. It is possible, however, such as in the case of metallic strands used for shielding high impedance waves (high electric fields), that because sufficient EMI shielding is provided by reflection, grounding of the strands 34 is not required. In such applications, the strands 34 may be embedded in the foam profile 32 without contacting the electrically conductive skin 36.

It will be appreciated that EMI shielding gaskets can be constructed combining various features of the embodiments of the invention shown in FIGURES 1, 2 and 3. That is, it is possible to construct a gasket which utilizes both an embedded EMI shield, such as EMI shield 14, and an EMI shield arranged against the outer surface of a foam profile, such as metal strands 34. Additionally, in such a gasket, either or both of the types of EMI shields may be arranged for direct electrical contact with an external conductor.

Another embodiment of the invention is shown in FIGURE 4 which is a cross-section view of an EMI shielding gasket 40 including a resilient foam profile 42 and an embedded EMI shield 44. Notably, the gasket 40 includes an electrically conductive skin, shown as sections 46A and 46B, which does not completely surround the foam profile 42. Rather, the skin sections 46A and 46B are arranged against the outer surface of the foam profile 42 only where the edges of the EMI shield 44 breach that outer surface, to effect electrical contact between the skin sections 46A and 46B and the EMI shield 44. Such a gasket may be desirable in applications where low closure force is required. Additionally, the gasket 40 may be desirable where, due to the arrangement of the gasket during use, abrasion and wear resistance are not factors.

Another embodiment of the invention, the gasket 50, is depicted in FIGURE 5. The gasket 50 includes a resilient foam profile 52 and embedded EMI shield 54. The EMI shield 54 includes a shielding membrane 53, such as a copper metallized non-woven fabric, as well as shielding wires 55, such as copper wires. As mentioned with respect to the above discussed embodiments of the invention, the shield 54 may be constructed in a variety of ways utilizing a variety of shielding components. The gasket 50 further includes electrically conductive skin sections 56A and 56B as well as non-electrically conductive, abrasion resistant skin sections 57A and 57B. Various non-electrically conductive thermoplastic elastomer materials are suitable for use as the skin sections 57A and 57B. Moreover, the same materials can be blended with electrically conductive carbon particles, for example, for use as skin sections 56A and 56B.

The gasket 50 includes adhesive strips 59 for attaching the gasket 50 to the body Bl, such as an edge of an opening in an electrical apparatus housing. While the adhesive strips 59 may be electrically conductive, the EMI shield 54 includes a tab 51 for making electrical contact between the shield 54 and the body Bl. As shown, the tab 51 protrudes through the skin section 56B from the foam profile 52 to lay against the body Bl when the gasket 50 is attached to the body Bl. Other structures for making electrical contact between the EMI shield 54 and the electrically conductive body Bl are shown in FIGURES 6A and 6B. In these figures it is shown that the electrically conductive skin section 56B can be formed with fingers F for contacting the body Bl. In this manner, when the gasket 50 is attached to the body Bl via adhesive strips 59, or by other means which will be apparent to those skilled in the art, a conductive path is formed between the EMI shield 54 and the body Bl. Additionally, in cooperation with the electrically conductive skin section 56A, continuity of electrical conduction from body Bl to body B2 is provided. As discussed above, this helps to preserve the beneficial Faraday Cage effect across housing seams.

Still another embodiment of the invention is shown in FIGURE 7 which depicts in cross-section an EMI shielding gasket 70 including a carrier 78. Typically, the carrier 78 is semi-rigid relative to the resilient foam profile 72. For example, polypropylene is often used for forming such carrier structures. The carrier 78 can be formed in virtually limitless profiles for anchoring the gasket 50 to appropriately analogous substrates. Additionally, the carrier 78 may or may not be electrically conductive. As shown, the gasket 70 includes an EMI shielding member 74 which spans the diameter of the resilient foam profile 72. As a result, the shielding member 74 is in electrical contact with both the electrically conductive outer skin 76 and the carrier 78. In cases of the carrier 58 being electrically conductive, however, it may not be necessary for the shielding member 74 to contact the electrically conductive skin 76. This is because where the carrier 78 is electrically conductive, energy absorbed by the shield 74 can be dissipated through the carrier 78. Conversely, in cases where the carrier 78 is an insulator, there will typically be no need for the EMI shield 74 to be in contact with the carrier 78. FIGURES 8A through 8E schematically represent the construction stages of a typical EMI shielding gasket in accordance with the invention. First, a foam profile is formed, typically by extrusion, in the desired configuration. Various extrusion techniques are available and will be readily known to those skilled in the art. For example, the commonly assigned United States Patent No. 4,898,760 to Halberstadt et al., the teachings of which are hereby incorporated herein by reference, describes a suitable process.

Accordingly, the process is not described here in great detail. Generally, however, a thermoplastic elastomer resin is pumped with a blowing agent such as water or a chlorofluorocarbon, at high temperature through a suitable extrusion die. The resin and blowing agent. are thoroughly mixed together under pressure and travel through an adaptor prior to passing into the extrusion die. Upon exiting the die, the pressure of the mixture rapidly drops, thereby engendering a substantially closed cell structure having a cross-section matching that of the die, such as foam profile 82 of FIGURE 8A. As shown, the foam profile 82 is extruded with a cleft C for receiving an EMI shield 84 (FIGURE 8B). The profile 82 is then cooled using, for example, a standard conveyor system with a heat resistant belt. Typically, the conveyor belt moves at a line speed of between approximately forty and eighty feet per minute.

The EMI shield 84 is coated on both sides with a hot melt adhesive such as the Numel 5430 brand which is a polypropylene based adhesive and which can be purchased from the Baychem Company of Houston Texas. One edge of the EMI shield 84 should be left free of adhesive. A polytetrafluoroethylene guide can be utilized to spread the cleft C of the foam profile 82, after which the adhesive coated EMI shield 84 is inserted therein as shown in FIGURE 8C. The foam profile 82 is then closed around the EMI shield 84 (FIGURE 8D) and the assembly coated with a thermoplastic elastomer, electrically conductive skin 86 as discussed above (FIGURE 8E). For applying the skin 86, a standard crosshead coating die can be mounted on an extruder, such as described in the commonly assigned United States patent application serial number 07/650,974 to Mertinooke et al, the teachings of which are hereby incorporated herein by reference. After the skin has been applied, the gasket is passed through a spray tank to cool the skin. After cooling, the gasket can be coiled or cut to length. Gaskets in accordance with the invention can also be constructed by extruding separate foam profiles and joining them in a laminate with an EMI shield using hot melt adhesive as described above. This fabrication method is useful for embodiments of the invention in which the EMI shield spans the entire width of the foam profile, such as the gaskets 40 and 50 shown in FIGURES 4 and 5.

The invention also features a gasket for shielding electromagnetic interference passing through a seam between two electrically conductive bodies which includes structure for reflecting and/or absorbing passing EMI, and for dissipating absorbed energy to ground via one or both of the electrically conductive bodies. FIGURE 9 shows an EMI shielding gasket 110 constructed in accordance with an embodiment of the invention. The gasket 110 includes a base 112 which has a rectangular cross-section and is elongated along an axis L. The base 112 is typically approximately one quarter of an inch wide and can be cut to any length. For a specified application the width of the base can be set appropriately and will typically be between approximately 0.1 inches and approximately 0.5 inches. As illustrated, the gasket 110 has a strip-like appearance. It should be appreciated, however, that the base 112 can be configured in virtually unlimited ways depending upon the application for which the gasket 110 is constructed. For example, the base 112 may include various attachment mechanisms, such as arms and barbs, for securing the gasket 110 to various types of analogous substrates. These variations will be readily apparent to those skilled in the art and are therefore not described herein with great detail. A multiplicity of discrete, elongate filaments 114 project substantially perpendicularly from the base 112. The filaments 114 provide the gasket 110 with its EMI shielding capability. For this purpose, the filaments 114 include a metallic component. For example, silver metallized nylon multifilament yarn,

1800 denier scale, is suitable for use as the filaments 114. Typically, after the filaments 114 have been properly secured to the base 112 they are cut to a length of approximately one-eight of an inch. Of course, however, depending on the application for which the gasket 110 is intended, this length can be altered.

An electrically conductive skin 116 surrounds a portion of the base 112 and is arranged in contact with some of the filaments 114. As more clearly evident in FIGURE 10, the skin 114 provides a path for the flow of current from the filaments 114 to ground G. In the figure, it is shown that the gasket 110 is constructed for placement in a seam S between two electrically conductive bodies Bl and B2. As schematically represented in the figure, electromagnetic energy wave E is shielded by the gasket 110 as the field E passes through the seam S. The filaments 114 reflect part of the energy of the electromagnetic field E and absorb part of the field E, dependent upon the impedance of the field and the conductivity of the filaments 114. Since the filaments 114 are not perfect conductors, energy absorbed by the filaments induces a current which, to ensure the effective operation of the gasket as an EMI shield and avoid electrostatic discharge, should be dissipated to ground G. This is achieved via the electrically conductive skin 116. Additionally, the electrically conductive skin 116 helps provide electrical conductivity across the seam S, thereby helping to preserve the benefits of the Faraday Cage effect discussed above.

Various electrically conductive materials are suitable for use as the conductive skin 116. For example, mixing approximately 85% by weight of thermoplastic rubber and approximately 15% by weight of electrically conductive carbon black forms a compound which can be extruded like a skin over the base 112 and which provides an efficient electrically conductive path for dissipating accumulated electric charge as discussed above.

Many other techniques are available for completing the electrically conductive path from the filaments 114 to the body Bl. For example, the base 112 can be covered with a coating including a dispersion of conductive particles such as silver, nickel, carbon, or graphite particles. Alternatively, a conductive covering such as a metal foil can be used. It is also possible to form the base out of a conductive material such as any suitable metal or to embed conductive particles such as carbon or graphite in the base.

An advantage provided by the EMI shielding gasket 110 over known EMI shielding gaskets stems from each of the shielding filaments 114 acting as an individual EMI shielding wall. Most known EMI shielding gaskets, on the other hand, provide only one or two EMI shielding walls. Enhanced EMI shielding is provided by the gasket 110, therefore, because, among other reasons, hundreds of individual filaments 114 each acts as an EMI shield. Another embodiment of the invention is shown in FIGURE 11 which is a cross-section view of an EMI shielding gasket 120 including an EMI shielding member 128. Various configurations of EMI shielding materials are available for use as the shielding member 128. For example, the member 128 can be formed of polyester non-woven fabric which has been metallized on both sides with copper over a 1.5 thousandths of an inch thick polypropylene film laminate. The member can also be formed of woven metal strands or metallized yarns. Combinations of these materials can be used as well. The gasket 120 also includes electrically conductive filaments 124 and a conductive covering 126 laid over a base 122.

Notably, the shielding member 128 is in electrical contact with the electrically conductive filaments 124. This enables electric current to flow from the shielding member 128 through the filaments 114, to the conductive covering 26 and then on to ground as discussed above. Significantly, in this embodiment of the invention, since effective EMI shielding is provided by the shielding member 128, the filaments 124 need only to be electrically conductive, they do not necessarily have to include a highly conductive, metallic component for EMI shielding. While utilizing filaments including a metallic component will provide even better EMI shielding, in applications where sufficient shielding is obtained by the shielding member 128 alone, only electrical conductivity sufficient for charge dissipation is required of the filaments 124. In such applications, the filaments may be formed, for example, of electrically conductive polymer fibers.

FIGURES 12 and 13 depict two additional embodiments of the invention wherein an EMI shielding gasket 130 includes both non-conductive filaments 134 and metallic or metallized filaments 138. In this embodiment of the invention, EMI shielding is provided by the metallic or metallized filaments 138 which extend through the base 132. Accordingly, energy absorbed by those filaments in the course of EMI shielding is dissipated to ground through the base 132, to the electrically conductive skin 136.

Two further embodiments of the invention are shown in FIGURES 14 and 15 which depict EMI shielding gaskets 140A and 14OB each of which includes an EMI shielding member 148 connected by, for example, ultrasonic welding to a base 142. In FIGURE 14 the shielding member 148 is supported by a resilient foam backing 147 while in FIGURE 15 the shielding member 148 is supported by a resilient, electrically conductive polymeric backing 149. Both the foam backing 147 and the conductive polymeric backing 149 provide the shielding member 148 with the resilience it needs to remain upright throughout repeated openings and closings of the door or access panel with which the gasket 140 interacts.

In these embodiments of the invention, the gasket base 142 is typically formed by extrusion of a conductive polymer as discussed above. For example, a blend of approximately 85% by weight of thermoplastic rubber and approximately 15% by weight of electrically conductive carbon black particles performs well. Again, the electrical conductivity of the base allows energy absorbed by the shielding member 128 to be dissipated to ground. For this purpose, the shielding member 148 must be in electrical contact with the base 142. As shown in FIGURE 14, therefore, the resilient foam member 147 is arranged inside of the shielding member 148, the shielding member 148 thereby being in electrical contact with the base 142 at its connection point to the base. In the case of the gasket 14OB, due to the electrical conductivity of the polymeric backing 149, its placement in relation to the shielding member 148 and the base 142 is less critical as far as electrical conductivity is concerned. That is, since the polymeric backing 149 is electrically conductive, it may be placed between the shielding member 148 and the base 142 without interrupting the flow of electric current desirable for dissipating energy absorbed by the shielding member.

FIGURE 16 shows still another embodiment of the invention wherein an EMI shielding gasket 150 includes EMI shielding filaments 154. The filaments 154 are embedded in and pass through the base 152. Accordingly, an electrically conductive skin, covering, or coating is not necessary to complete the electrically conductive path from the filaments 154 to the back of the base 152.

In the illustrated embodiment, the filaments 154 extend through the base 152 to contact an electrical contact member 156 provided on the back of the base 152. The electrical contact member 156 facilitates electrical contact between the filaments 154 and an electrically conductive path to ground. The electrical contact member 156 may be formed of the same material which forms the electrically conductive skins discussed above. Any number of other types of material are suitable as well, such as electrically conductive adhesives (which could also serve to anchor the gasket 150 in place) or various metals suitable for being arranged in intimate contact with the body with which the gasket 150 is to be arranged, such as body Bl of FIGURE 10.

While various embodiments of the invention have been set forth in detail, it should be understood that the above description is intended as illustrative rather than limiting and that many variations to the described embodiments will be apparent to those skilled in the art. The invention is to be described, therefore, not by the preceding description, but by the claims that follow. What is claimed is:

Claims

1. A gasket for shielding electromagnetic interference passing through a seam between first and second electrically conductive bodies, the gasket comprising a resilient foam profile, a shield embedded in the foam profile for shielding electromagnetic interference passing through a seam between first and second electrically conductive bodies, and a seamless, electrically conductive skin covering at least part of the outer' surface of the foam profile and in electrical contact with the shield, the skin being arranged on the profile for conducting electrical current from the shield to the first, electrically conductive body.

2. A gasket for shielding electromagnetic interference passing through a seam between first and second electrically conductive bodies, the gasket comprising a resilient foam profile, a shield arranged against an outer surface of the foam profile for shielding electromagnetic interference passing through a seam between first and second electrically conductive bodies, and a seamless, electrically conductive skin covering at least part of the outer surface of the foam profile and in electrical contact with the shield, the skin being arranged on the profile for conducting electrical current between the shield and the first, electrically conductive body.

3. A gasket as set forth in either of claim 1 or 2 wherein the shield comprises a metallic strand.

4. A gasket as set forth in either of claim 1 or 2 wherein the shield comprises a plurality of metallic strands.

5. A gasket as set forth in claim 3 wherein the strand is at least partially exposed for direct contact with at least one electrically conductive body.

6. A gasket as set forth in claim 4 wherein at least some of the strands are at least partially exposed for direct contact with at least one electrically conductive body.

7. A gasket as set forth in either of claim 1 or 2 wherein the shield comprises a metallic membrane.

8. A gasket as set forth in claim 7 wherein the metallic membrane has two elongate edges, both of which are arranged in contact with the electrically conductive skin.

9. A gasket as set forth in claim 7 wherein the metallic membrane is at least partially exposed for direct contact with at least one electrically conductive body.

10. A gasket as set forth in either of claim 1 or 2 wherein the shield comprises a metallic strand and a metallic membrane.

11. A gasket as set forth in either of claims 1 or 2 further comprising a semi-rigid carrier coupled to the foam profile for securing the gasket to the first, electrically conductive body.

12. A gasket for shielding electromagnetic interference passing through a seam between first and second electrically conductive bodies, the gasket comprising a resilient foam profile elongated along a longitudinal axis, a shield embedded in the foam profile for shielding electromagnetic interference passing through a seam between first and second electrically conductive bodies, a skin surrounding the outer surface of the foam profile and including a first electrically conductive portion extending in a direction substantially parallel to the longitudinal axis and being in electrical contact with the shield for conducting electricity between the shield and the first electrically conductive body, and means for making electrical contact between the shield and the second electrically conductive body.

13. A gasket as set forth in claim 12 wherein the skin further includes a non-electrically conductive portion which is abrasion resistant.

14. A gasket as set forth in claim 12 wherein the skin further includes a second electrically conductive portion substantially diametrically opposed to the first electrically conductive portion.

15. A gasket as set forth in claim 14 wherein the means for making electrical contact between the shield and at least one of the electrically conductive bodies comprises electrically conductive fingers formed integrally with the electrically conductive portion of the skin.

16. A gasket as set forth in claim 12 wherein the means for making electrical contact between the shield and the second electrically conductive body comprises a portion of the shield which protrudes through the skin for direct electrical contact with the second electrically conductive body.

17. A gasket as set forth in claim 22 further comprising attachment means for securing the gasket to one of the electrically conductive bodies.

18. A gasket for shielding electromagnetic interference passing through a seam between first and second electrically conductive bodies, the gasket comprising a resilient foam profile elongated along a longitudinal axis, and a shield embedded in the foam profile for shielding electromagnetic interference passing through a seam between first and second electrically conductive bodies, the shield extending in a direction parallel to the longitudinal axis.

19. A gasket as set forth in claim 18 wherein the shield comprises on a metallic strand.

20. A gasket as set forth in claim 18 wherein the shield comprises a plurality of metallic strands.

21. A gasket as set forth in claim 19 wherein the strand is at least partially exposed for direct contact with at least one electrically conductive body.

22. A gasket as set forth in claim 20 wherein at least some of the strands are at least partially exposed for direct contact with at least one electrically conductive body.

23. A gasket as set forth in claim 18 wherein the shield comprises a metallic membrane.

24. A gasket as set forth in claim 23 wherein the metallic membrane is at least partially exposed for direct contact with at least one electrically conductive body.

25. A gasket as set forth in claim 18 wherein the shield comprises a metallic strand and a metallic membrane.

26. A gasket as set forth in claim 25 wherein the strand is at least partially exposed for direct contact with at least one electrically conductive body.

27. A gasket as set forth in claim 18 further comprising a semi-rigid carrier coupled to the foam profile for securing the gasket to the first, electrically conductive body.

28. A gasket as set forth in claim 18 further comprising an abrasion resistant skin surrounding at least part of the outer surface of the foam profile.

29. A gasket for shielding electromagnetic interference passing through a seam between first and second electrically conductive bodies, the gasket comprising a base for securing the gasket to a first, electrically conductive body, an electromagnetic shielding member projecting substantially perpendicularly from the base to contact a second, electrically conductive body when electromagnetic interference passing through a seam between the bodies is to be shielded, resilient means cooperating with the shielding member for maintaining the shielding member in contact with the second electrically conductive body, and electrically conductive means arranged with, the base, for conducting electric current between the shielding member and the first, electrically conductive body.

30. A gasket as set forth in claim 29 wherein the shielding member includes a metallic component.

31. A gasket as set forth in claim 29 wherein the shielding number includes a metallized fin.

32. A gasket as set forth in claim 29 wherein the resilient means comprises a multiplicity of discrete, elongate filaments projecting from the base and substantially parallel to the shielding member, some of the filaments being in contact with the shielding member so as to support the shielding member.

33. A gasket as set forth in claim 29 wherein the filaments are electrically conductive.

34. A gasket as set forth in claim 29 wherein the electrically conductive means is an electrically conductive coating laid over the base and in contact with the shielding member.

35. A gasket as set.forth in claim 29 wherein the electrically conductive means is an electrically conductive coating laid over the base and in contact with some of the filaments.

36. A gasket as set forth in claim 29 wherein the electrically conductive means comprises an electrically conductive material embedded in the base.

37. A gasket as set forth in claim 29 wherein the base is formed of an electrically conductive material and thereby forms the electrically conductive means.

38. A gasket as set forth in claim 29 wherein the electrically conductive means comprises an electrically conductive skin wrapped at least partially around the base.

39. A gasket for shielding electromagnetic interference passing through a seam between first and second electrically conductive bodies, the gasket comprising a base for securing the gasket to a first electrically conductive body, a multiplicity of discrete, elongate, metallized filaments projecting substantially perpendicularly from the base so that a substantial amount of the filaments contacts a second electrically conductive when electromagnetic interference passing through a seam between the bodies is to be shielded, and electrically conductive means arranged with the base, for conducting electric current between the filaments and the first, electrically conductive body.

40. A gasket as set forth in claim 39 wherein the electrically conductive means comprises an electrically conductive coating laid over the base and in contact with some of the filaments.

41. A gasket as set forth in claim 39 wherein the electrically conductive means comprises an electrically conductive material embedded in the base.

42. A gasket as set forth in claim 39 wherein the electrically conductive means comprises an electrically conductive skin wrapped at least partially around the base.

43. A gasket for shielding electromagnetic interference and environmental effects from passing through a seam between first and second electrically conductive bodies, the gasket comprising a base for securing the gasket to a first electrically conductive body, a multiplicity of discrete, elongate, fiber filaments projecting substantially perpendicularly from the base so that a substantial amount of the filaments contacts a second electrically conductive body when environmental effects and electromagnetic interference passing through a seam between the bodies is to be shielded, an electromagnetic interference shielding member arranged with the filaments for shielding electromagnetic interference passing through the seam, and electrically conductive means arranged with the base for conducting electric current between the shielding member and the first electrically conductive body.

44. A gasket as set forth in claim 43 wherein the shielding means comprises multiplicity of discrete, elongate, metallized filaments.