Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
2002-12-06
2004-03-30
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C174S068300, C439S607560, C439S927000
Reexamination Certificate
active
06713672
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to electromagnetic interference (“EMI”) shielding and, more specifically, to shielding cable connection ports from the transference of EMI therethrough.
BACKGROUND OF THE INVENTION
As used herein, the term EMI should be considered to refer generally to both EMI and radio frequency interference (“RFI”) emissions, and the term electromagnetic should be considered to refer generally to electromagnetic and radio frequency.
During normal operation, electronic equipment generates undesirable electromagnetic energy that can interfere with the operation of proximately located electronic equipment due to EMI transmission by radiation and/or conduction. The electromagnetic energy can be of a wide range of wavelengths and frequencies. To minimize the problems associated with EMI, sources of undesirable electromagnetic energy may be shielded and/or electrically grounded. Shielding is designed to prevent both the ingress and egress of electromagnetic energy relative to a housing or other enclosure in which the electronic equipment is disposed. Since such enclosures often include vent panels and gaps or seams between adjacent access panels, around doors, and at cable connection ports, effective shielding is difficult to attain, because the gaps in the enclosure permit the transference of EMI therethrough. Further, in the case of electrically conductive metal enclosures, these gaps can inhibit the beneficial Faraday Cage Effect by forming discontinuities in the conductivity of the enclosure which compromise the efficiency of the ground conduction path through the enclosure. Moreover, by presenting an electrical conductivity level at the gaps that is significantly different from that of the enclosure generally, the gaps can act as slot antennae, resulting in the enclosure itself becoming a secondary source of EMI.
Specialized EMI gaskets have been developed for use in shielding small gaps in electronic enclosures. These include, but are not limited to, metal spring fingers, wire mesh, fabric-over-foam, and conductive elastomers. To shield EMI effectively, the gasket should be capable of absorbing or reflecting EMI as well as establishing a continuous electrically conductive path across the gap in which the gasket is disposed.
One particularly challenging shielding issue on electronic enclosures is cable connection ports. In most instances, an electronic circuit disposed within an EMI shield requires interconnections with one or more external sources and/or destinations. Consequently, the shield provides interface ports, such as cable connection ports, to allow communication therethrough. Exemplary interfaces include power leads and signal cables. To maintain the integrity of a shield, prior art solutions use shielded cable. A shielded cable generally includes one or more signal and/or power leads substantially surrounded by a conductive jacket. Ideally, the conductive jacket is in electrical communication with the shield, thereby becoming an extension of the shield to the remote source/destination. Depending on a desired level of shielding effectiveness, and the wavelengths of the EMI, the conductive jacket may be one or more electrically conductive braids, an electrically conductive foil, and even an electrically conductive conduit (i.e., a pipe).
Some applications, however, require that a shielded electronic circuit be electrically isolated from its interfacing source/destination. Conductive shields generally preclude such electrical isolation, as they are often used to extend one electrically conductive boundary to another. One solution allowing such electrical isolation is an optical interface, such as a fiber optic interface. It is common for networked computers and other electronic devices to have multiple optic-to-electric transceivers and other electronic devices attached to circuit boards. Typically, non-conductive, plastic bulkhead connectors attach fiber optic cables to a circuit module containing a circuit board having at least one optic-to-electric interface.
Referring to
FIG. 1
, shown is a representative portion of a circuit module
45
connected to a fiber optic cable
50
within a networked computer system. The portion of the circuit module shown in
FIG. 1
includes a circuit board
55
attached to a fiber optic device, such as a high-speed fiber optic transceiver
60
, and a fiber optic pigtail
65
. A fiber optic cable
50
external to the circuit module
45
connects to the fiber optic pigtail
65
through an aperture
70
in a faceplate or bezel
75
. Typically, a non-conductive, plastic bulkhead connector
80
extends through the faceplate
75
to connect one end of the fiber optic cable
50
to the fiber optic pigtail
65
. One or more EMI gaskets
85
are provided between the faceplate and adjacent modules.
Generally, circuit modules have multiple bulkhead connectors to service multiple fiber-optic cables representing multiple channels. Each bulkhead connector requires a mounting aperture, or hole, typically on the order of 0.5 inches square in the faceplate
75
covering the circuit module
45
. Unfortunately, these holes are large enough to pass considerable EMI through the shielding barrier formed by a row of faceplates.
One prior art solution to limit the amount of interference passed to the transceivers is to have the fiber optic cables pass through a set of compliant compression flanges that sandwich the cables. See, for example, shielding devices described in U.S. Pat. No. 6,162,989, entitled “Cable Entry Shield (EMI-RFI) for Electronic Units” issued to Garner, the disclosure of which is herein incorporated by reference in its entirety. Another proposed solution is to have cables pass through slits in an electrically conductive cloth. See for example, a shielding device described in U.S. Pat. No. 6,101,711 “Method for Reducing Electromagnetic Waves Radiated from Electronic Device” issued to Kobayashi, the disclosure of which is herein incorporated by reference in its entirety.
One problem with the shielding devices described in these patents is that these devices do not sufficiently shield the openings around bulkhead connectors, especially bulkhead connectors with varying dimensions. Additionally, gaps around the cables may still transmit emissions, which are then passed to sensitive circuitry. These gaps that may have proved effective in the past are becoming unacceptable in view of the trends in electronic circuits to operate at higher speeds and greater sensitivities.
Another prior art solution to limiting the amount of interference passed to the transceivers is to externally cover the bulkhead connectors within an externally mounted shielding device (i.e., a “boot”). See, for example, externally mounted shielding devices described in U.S. Pat. No. 6,158,899, entitled “Method and Apparatus for Alleviating ESD Induced EMI Radiating from I/O Connector Apertures” issued to Arp et al., the disclosure of which is herein incorporated by reference in its entirety.
One of the problems with the externally mounted shielding devices described in Arp et al., is that these devices are too cumbersome and take up too much space to enclose and shield all of the cables in a networked computer system.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a compact, EMI shielded interface, such as a cable connection port or access hole, for attenuating the transference of EMI therethrough over a wide range of frequencies (e.g., above 10
9
Hz).
In one aspect, the invention relates generally to a device for reducing transference of EMI across a conductive boundary defining an aperture in a structure, such as an equipment enclosure or faceplate. The device includes a conformable member having a conductive external surface extending along at least a portion thereof. The conductive external surface is in electrical communication with the conductive boundary. The conformable member also defines a first conductive channel of a predetermined minimum length extending therethrough. The first conducti
Laird Technologies Inc.
Oliva Carmelo
Reichard Dean A.
Testa Hurwitz & Thibeault LLP
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