Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
2003-02-18
2004-04-20
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C277S920000
Reexamination Certificate
active
06723916
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates broadly to gaskets for providing electromagnetic interference (EMI) shielding and weather, dust, or other environmental sealing, and particularly to a combination or composite gasket construction and method of its manufacture combining a metal mesh strip gasket with an integral solid or foam elastomeric weather-sealing strip which is especially adapted for use within cabinets and other enclosures for electrical or electronic systems or devices.
The operation of electronic devices such as televisions, radios, computers, medical instruments, business machines, communications equipment, and the like is attended by the generation of electromagnetic radiation within the electronic circuitry of the equipment. As is detailed in U.S. Pat. Nos. 5,202,536; 5,142,101; 5,105,056; 5,028,739; 4,952,448; and 4,857,668, such radiation often develops as a field or as transients within the radio frequency band of the electromagnetic spectrum, i.e., between about 10 KHz and 10 GHz, and is termed “electromagnetic interference” or “EMI” as being known to interfere with the operation of other proximate electronic devices.
To attenuate EMI effects, shielding having the capability of absorbing and/or reflecting EMI energy may be employed both to confine the EMI energy within a source device, and to insulate that device or other “target” devices from other source devices. Such shielding is provided as a barrier which is inserted between the source and the other devices, and typically is configured as an electrically conductive and grounded housing which encloses the device. As the circuitry of the device generally must remain accessible for servicing or the like, most housings are provided with openable or removable accesses such as doors, hatches, panels, or covers. Between even the flattest of these accesses and its corresponding mating or faying surface, however, there may be present gaps which reduce the efficiency of the shielding by presenting openings through which radiant energy may leak or otherwise pass into or out of the device. Moreover, such gaps represent discontinuities in the surface and ground conductivity of the housing or other shielding, and may even generate a secondary source of EMI radiation by functioning as a form of slot antenna. In this regard, bulk or surface currents induced within the housing develop voltage gradients across any interface gaps in the shielding, which gaps thereby function as antennas which radiate EMI noise. In general, the amplitude of the noise is proportional to the gap length, with the width of the gap having less appreciable effect.
For filling gaps within mating surfaces of housings and other EMI shielding structures, gaskets and other seals have been proposed both for maintaining electrical continuity across the structure, and for excluding from the interior of the device such contaminates as moisture and dust. Such seals are bonded or mechanically attached to, or press-fit into, one of the mating surfaces, and function to close any interface gaps to establish a continuous conductive path thereacross by conforming under an applied pressure to irregularities between the surfaces. Accordingly, seals intended for EMI shielding applications are specified to be of a construction which not only provides electrical surface conductivity even while under compression, but which also has a resiliency allowing the seals to conform to the size of the gap. The seals additionally must be wear resistant, economical to manufacture, and capability of withstanding repeated compression and relaxation cycles. EMI shielding gaskets and other electrically-conductive materials, their methods of manufacture, and their use are further described in U.S. Pat. Nos. 6,121,545; 6,096,413; 6,075,205; 5,996,220; 5,910,524; 5,902,956; 5,902,438; 5,882,729; 5,804,762; 5,731,541; 5,641,438; 5,603,514; 5,584,983; 5,578,790; 5,566,055; 5,524,908; 5,522,602; 5,512,709; 5,438,423; 5,294,270; 5,202,536; 5,142,101; 5,141,770; 5,136,359; 5,115,104; 5,107,070; 5,105,056; 5,068,493; 5,054,635; 5,049,085; 5,028,739; 5,008,485; 4,988,550; 4,979,280; 4,968,854; 4,952,448; 4,931,479; 4,931,326; 4,871,477; 4,864,076; 4,857,668; 4,800,126; 4,529,257; 4,441,726; 4,301,040; 4,231,901; 4,065,138; 3,758,123; 3,026,367; 2,974,183; and 2,755,079, in U.S. patent appln. Publ. No. 20020010223, International (PCT) Patent Appln. Nos. WO 01/71223; 01/54467; 00/23,513; 99/44,406; 98/54942; 96/22672; and 93/23226, Japanese Patent Publication (Kokai) No. 7177/1993, European Pat. Appln. No. 1,094,257, German Patent No. 19728839, and Canadian Patent No. 903,020, in Severinsen, J., “Gaskets That Block EMI,” Machine Design, Vol. 47, No. 19, pp. 74-77 (Aug. 7, 1975), and in the following publications of the Chomerics Division of Parker Hannifin Corporation, Woburn, Mass.: “SOFT-SHIELD® 1000 Series;” “SOFT-SHIELD® 2000 Series;” “SOFT-SHIELD® 4000 Series;” “SOFT-SHIELD® 5000 Series;” and “SOFT-SHIELD® 5500, Preliminary Product Data Sheet (1998) Series; “COMBO® STRIP Gaskets;” “SPRINGMESH™ Highly Resilient EMI Mesh Gasket,” Technical Bulletin 114; “METAL STRIP® All Metal Gaskets;” “SHIELDMESH™ Compressed Mesh Gaskets;” and “METALKLIP® Clip-On EMI Gasket.”
EMI shielding gaskets typically are constructed as a resilient element, or a combination of one or more resilient elements having gap-filling capabilities. One or more of the elements may be provided as a tubular or solid, foamed or unfoamed core or strip which is filled, sheathed, or coated to be electrically-conductive, or otherwise which is formed of an inherently conductive material such as a metal wire spring mesh. One or more of the other elements, and particularly in the case of a composite or “combination gasket” having a conductive EMI shielding element in combination with an integral weather sealing strip (such as is sold commercially by the Chomerics Division of Parker-Hannifin Corporation (Woburn, Mass.) under the name “COMBO® STRIP Gasket”), may be formed of a sheet, strip, “picture-frame,” or other open or closed geometry of a solid, i.e., unfoamed, or foamed elastomeric material providing enhanced environmental sealing capabilities to which the conductive element is adhesively-bonded or otherwise joined. Each of the core or strip of the conductive element and the elastomeric material of the environmental sealing element may be formed of an elastomeric thermoplastic material such as polyethylene, polypropylene, or polyvinyl chloride, a thermoplastic or thermosetting rubber such as a butadiene, styrene-butadiene, nitrile, chlorosulfonate, neoprene, urethane, or silicone, or a blend such as polypropylene-EPDM. Conductive materials for the filler, sheathing, or coating of the conductive element include metal or metal-plated particles, fabrics, meshes, and fibers. Preferred metals include copper, nickel, silver, aluminum, tin or an alloy such as Monel, with preferred fibers and fabrics including natural or synthetic fibers such as cotton, wool, silk, cellulose, polyester, polyamide, nylon, polyimide. Alternatively, other conductive particles and fibers such as carbon, graphite, or a conductive polymer material may be substituted.
Conventional manufacturing processes for EMI shielding gaskets include extrusion, molding, or die-cutting, with molding or die-cutting heretofore being preferred for particularly small or complex shielding configurations. In this regard, die-cutting involves the forming of the gasket from a cured sheet of an electrically-conductive elastomer which is cut or stamped using a die or the like into the desired configuration. Molding, in turn, involves the compression or injection molding of an uncured or thermoplastic elastomer into the desired configuration.
More recently, a form-in-place (FIP) process has been proposed for the manufacture of EMI shielding gaskets. As is described in commonly-assigned U.S. Pat. Nos. 6,096,413; 5,910,524; 5,641,438; 4,931,479, and International (PCT) Patent Appln. No. 96/22672; and in U.S. Pat. Nos. 5,882,729 and 5,731,541, International (PCT) Pate
Flaherty Brian F.
Mitchel Jonathan E.
Perkins John M.
Romano Ronald P.
Molnar, Jr. John A.
Oliva Carmelo
Parker-Hannifin Corporation
Reichard Dean A.
LandOfFree
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