Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
1998-03-27
2001-07-10
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C174S1020SP, C174S10500R
Reexamination Certificate
active
06259019
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a cable for transmitting data comprising a conductive shield for protecting one or more conductors against external electromagnetic interference.
2. Description of the Prior Art
Data is usually transmitted by means of insulated electrical conductors surrounded by one or more metallic shields, the shield or shields being enclosed within a jacket.
The shield isolates the conductors from external electromagnetic interference. The best protection is obtained when the conductive shield is continuous, without openings in it. However, the usual manufacturing techniques impose the use of one or more tapes to form the shield which necessarily leads to openings in the latter which limit the efficacy of the shield at the highest frequencies.
The best shields provide effective protection up to frequencies in the order of 30 MHz to 40 MHz. Until now the best results have been obtained with a metal tape disposed lengthwise with the longitudinal edges overlapping. A lengthwise tape gives better results than a helically wound tape because the opening extends a shorter distance.
Increasing data bit rates in cables are leading to an increase in the limiting frequency below which cables are protected from the external environment.
U.S. Pat. No. 4,510,346 proposes a cable including at least one electrical conductor surrounded by a shield to protect against high-frequency electromagnetic interference. The shield includes an inner tape disposed lengthwise and an outer tape disposed lengthwise, each tape having a conductive layer covered by an insulative layer. The conductive layer of the inner tape faces outwards and the conductive layer of the outer tape faces inwards so that the conductive layers are pressed together. At least one of the two tapes has overlapping longitudinal edges.
Although the shield of a cable of the above kind provides effective protection against electromagnetic interference up to very high frequencies (at least 100 MHz), it nevertheless gives rise to a major problem, namely that of ease of stripping. The outer tape, disposed lengthwise, with its conductive layer on the inside against the conductive layer of the inner tape prevents easy access to the conductive part of the shield and therefore makes it difficult to connect the cable.
An aim of the present invention is to solve this problem by proposing a cable that is effective at very high frequencies, typically above 100 MHz, and easier to strip than prior art cables effective at such frequencies.
SUMMARY OF THE INVENTION
To this end the present invention proposes a cable including at least one electrical conductor surrounded by a shield protecting against high-frequency electromagnetic interference, said shield including an inner tape disposed lengthwise having a conductive layer and an outer tape disposed lengthwise having a conductive layer covered by an insulative layer, said conductive layer of said outer tape facing inwards so that the respective conductive layers of said inner and outer tapes are in contact, and at least one of the two tapes having overlapping longitudinal edge regions, wherein said insulative material of said insulative layer of said outer tape is adhesively bonded to the inside wall of a jacket.
The cable of the invention is protected against interference at frequencies up to 1 GHz. The cable of the invention is particularly simple to connect because, on opening the jacket, the outer tape remains stuck to the latter and only the conductive layer of the inner tape remains visible. Connecting the cable of the invention to a connector is therefore facilitated.
The area of the longitudinal edges of the inner tape is advantageously covered by a continuous area of the outer tape. This assures good electrical continuity of the shield. In this case, the areas of the longitudinal edges of the tapes are preferably opposite each other.
The inner tape preferably further comprises a conductive layer covered with an insulative layer, for example a polyester layer. In this way the inner and outer tapes can slide correctly on guides during manufacture. This minimizes the risk of damage by rubbing.
The outer tape can be adhesively bonded to the jacket. To this end, in one embodiment, the material of the jacket is extruded at a sufficiently high temperature for the plastics material of the outer tape to soften and bond to the inside surface of the jacket.
An electrical continuity wire can be disposed between the two shields. This improves the contact between the electrical continuity wire and the metal of one of the two tapes, preferably the metal of the inner tape. Improved protection against interference at low frequencies has also been observed.
To manufacture the cable in accordance with the invention the jacket can be extruded at a temperature such that it bonds to the insulative layer of the outer tape.
The inner and outer tapes can be preformed in the same guide. In this way the two tapes do not move relative to each other which prevents potentially harmful rubbing between the conductive layer of the inner tape and the conductive layer of the outer tape.
REFERENCES:
patent: 3321572 (1967-05-01), Garner et al.
patent: 4510346 (1985-04-01), Bursh et al.
patent: 5132491 (1992-07-01), Mulrooney et al.
patent: 5144098 (1992-09-01), Van Deusen
patent: 5208426 (1993-05-01), Kennedy et al.
patent: 5216202 (1993-06-01), Yoshida et al.
patent: 5541361 (1996-07-01), Friesen et al.
patent: 0759624A1 (1997-02-01), None
Damilo Serge
Prudhon Daniel
Alcatel
Mayo, III William H
Reichard Dean A.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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