EP1148517A1

EP1148517A1 - Telecommunication cable

Info

Publication number: EP1148517A1
Application number: EP01400948A
Authority: EP
Inventors: Koenrad Vermout
Original assignee: Nexans SA
Current assignee: Nexans SA
Priority date: 2000-04-18
Filing date: 2001-04-12
Publication date: 2001-10-24

Abstract

The invention is directed to a telecommunication cable (20) comprising at least two telecommunication sub-assemblies (10, 11, 12, 13), each sub-assembly comprising at least one group of at least two signal conductors (11, 12), said at least one group being surrounded by a conductive shield (14), and the conductive shields of adjacent sub-assemblies being in electrical contact with each other, characterized in that said at least one group is surrounded by an insulating medium (13) and in that each of said conductive shields (14) is made of a layer of conductive material deposited on said insulating medium (13).

Description

The present invention relates to a telecommunication cable comprising at least two telecommunication sub-assemblies, each sub-assembly comprising at least one group of at least two signal conductors, said at least one group being surrounded by a conductive shield, and the conductive shields of adjacent sub-assemblies being in electrical contact with each other.
Such a telecommunication cable is already known in the art, e.g. from the International Patent Application PCT/US98/08027 (WO 98/48430). In such a cable, the individual telecommunication sub-assemblies need to be separated from each other by shielding means in order to avoid cross-talk and electro-magnetic interferences. Therefore, in the cable of this document, four unshielded twisted pairs or telecommunication sub-assemblies are nested in channels formed by fins of a cross-shaped core, the core material being conductive and forming a longitudinal shield, and the core itself is surrounded by a conductive shield. The construction of the cross-shaped shielding core is complex and the corresponding production cost is high.
An object of the present invention is to provide a telecommunication cable of the above known type but which is easier to manufacture, relatively cheaper in production and in material, and more resistant to cable bending.
According to the invention, this object is achieved due to the fact that said at least one group is surrounded by an insulating medium and that each of said conductive shields is made of a layer of conductive material deposited on said insulating medium.
In the present invention, because the transmission sub-assemblies are individually shielded by providing a deposited metal layer on an insulation medium surrounding the signal conductors, the cross-shaped shielding core of the cable is no longer necessary. This reduces dramatically the production cost and the complexity of the cable assembly.
In this way, the disadvantages of the above existing solution are solved. Additionally, the conductive material deposition technology allows applying an acceptable metal thickness at a speed of several hundred meters per minute. The deposition can be done either in a separate production step or on-line on the insulation line before the "take-up". The total insulation process time may so be reduced.
Moreover, owing to the individual shielding of each telecommunication sub-assembly, all these sub-assemblies are protected from mutual cross-talk or any other outside influence.
In a preferred embodiment of the present invention, the cross-section of the telecommunication sub-assemblies has the shape of a portion of a pie. A cable assembly with a circular section can so easily be obtained.
According to the invention, the signal conductors of each group may be twisted inside the insulating medium. They can also be longitudinally spaced and located in parallel with respect to one another.
In another advantageous embodiment, the conductors are embedded within the insulating medium.
When the conductors are located parallel in parallel with respect to one another and embedded within the insulating medium, they are thus regularly spaced, and the twisting of the conductors may no longer be necessary. This also simplifies the production process while maintaining efficient characteristics against cross-talk and electro-magnetic interferences owing to the signal conductors being embedded into the insulating medium. This will also give a better guarantee for overall uniformity of the transmission cable and therefore on the transmission properties.
Further characterizing embodiments of the present telecommunication cable are mentioned in the appended claims.
It is to be noticed that the term 'comprising', used in the claims, should not be interpreted as being limitative to the means listed thereafter. Thus, the scope of the expression 'a device comprising means A and B' should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.
The above and other objects and features of the invention will become more apparent and the invention itself will be best understood by referring to the following description of an embodiment taken in conjunction with the accompanying drawings wherein:
Fig. 1 shows two signal conductors embedded within an insulating medium surrounded by a conductive shield in order to form a telecommunication sub-assembly for use in a cable according to the invention;
Fig. 2 shows four telecommunication sub-assemblies as of Fig. 1 and arranged so as to form a cable assembly;
Fig. 3 shows an improved version of the cable assembly of Fig. 2.
All the figures show cross-sectional views of a telecommunication cable according to the present invention. Such a telecommunication cable and a cable sub-assembly for use therein will be described below.
The telecommunication sub-assembly 10 shown at Fig. 1 comprises two signal conductors 11 and 12 embedded in parallel in an insulating medium 13 in order to form a balanced transmission pair. The single body insulating material 13 embedding the conductors is preferably polyethylene and the distance between the conductors 11 and 12 is maintained constant along the whole transmission path. The external surface of the so obtained form is covered with a conductive material deposited layer 14 uniformly applied through e.g. plasma deposition. The conductive material is preferably copper [Cu] or aluminum [Al]. The applied thickness should be of several micrometers depending upon the required shielding performance and on the used material.
This layer 14 will act as an electro-magnetic shield around the pair of conductors 11 and 12. As a result, the so obtained shielded telecommunication sub-assembly 10 shows efficient characteristics against cross-talk and electro-magnetic interferences, even at relatively high frequencies, although there is no need to twist the signal conductors inside the embedding insulating medium 13. The choice of material used for the conductive layer 14, its thickness and uniformity influence the shielding efficiency. For example, the applied layer 14 should minimally be sufficient to meet the IS011801 Cat.7 cross-talk specification.
By use of a metal plasma-deposit conductive layer 14, a relatively costly production step is avoided. However, other known deposition techniques may be used without going out of the scope of the present invention, as e.g. a sputteringdeposition or ion-deposition techniques.
The current plasma deposition technology allows applying the requested thickness at a speed of several hundred meters per minute. The deposition can be done in a separate production step or on-line on the insulation line before the "take-up". By making the sub-assembly in one production step on the insulation line, the total insulation process time will be reduced, and the pairing of the individual wires is not necessary. This will also give a better guarantee for overall uniformity and therefore transmission properties.
The cross-section of the telecommunication sub-assembly 10 substantially has the shape of a portion of a pie.
Several, e.g. four, individually embedded shielded pairs 11, 12, 13, all similar to the transmission cable 10, are arranged in order to form a cable 20 as shown at Fig. 2. In this cable 20, the telecommunication sub-assemblies 10 to 13 fit together with their metal plasma-deposit conductive shields, as 14, into electrical contact with each other. The resulting cable assembly 20 has a circular cross-section.
In a preferred embodiment, the cable assembly 20 is provided with a central channel adapted to receive one or more drain wires 31 as shown at Fig. 3. The drain wire 31 is into electrical contact with the conductive shields of all the telecommunication sub-assemblies 10 to 13.
The cable 20 further has an external metallic shield 32 surrounding the telecommunication sub-assemblies 10, 11, 12 and 13, as shown at Fig. 3. The external metallic shield 32 is constituted by a metallic tape or braided wires applied around the cable core and into electrical contact with the conductive shields, as 14, of all the sub-assemblies.
It is to be noted that the flexibility of the cable 20 will be improved if the transmission cables 10, 11, 12 and 13 are helicoidally arranged.
This also facilitates the application of a wrapped metallic tape around the cable.
An extruded outer jacket 33 protecting and maintaining together the sub-assemblies 10 to 13, with or without the external metallic shield 32, finally covers the cable 20.
It is to be noted that in the above description reference is made to telecommunication sub-assemblies with a pair of signal conductors. This is however not a limitation of the invention which can easily be extended to cables with groups of more than two signal conductors in each sub-assembly.
The indicated amount and shape of individually shielded telecommunication sub-assemblies forming the cable is also not a limitation of the invention.
Depending on the shape of the cross-section of each sub-assembly, more or less than four sub-assemblies may be used to form the cable according to the invention.
Moreover, all the sub-assemblies forming the cable need not to have a same section, or a section having the shape of a portion of a pie.
Besides, even if the cable and sub-assemblies of the invention have been described as containing parallel conductors embedded in an insulating medium, the invention also applies to such cables and sub-assemblies in which the conductors are twisted in the form of pairs or quads, and the twisted or parallel conductors need not necessarily be embedded in the insulating medium, as such a medium may only surround them.
While the principles of the invention have been described above in connection with a specific embodiment, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention, as defined in the appended claims.

Claims

Telecommunication cable (20) comprising at least two telecommunication sub-assemblies (10, 11, 12, 13), each sub-assembly comprising at least one group of at least two signal conductors (11, 12), said at least one group being surrounded by a conductive shield (14), and the conductive shields of adjacent sub-assemblies being in electrical contact with each other,
characterized in that said at least one group is surrounded by an insulating medium (13) and in that each of said conductive shields (14) is made of a layer of conductive material deposited on said insulating medium (13).
Telecommunication cable according to claim 1, characterized in that the cross-section of the telecommunication sub-assemblies (10, 11, 12, 13) has a shape of a portion of a pie.
Telecommunication cable according to claims 1 or 2, characterized in that it is provided with a central channel adapted to receive at least one drain wire (31) that is into electrical contact with the conductive shields (14) of the telecommunication sub-assemblies (10, 11, 12, 13).
Telecommunication cable according to anyone of claims 1 to 3, characterized in that it has an external metallic shield (32) surrounding the plurality of telecommunication sub-assemblies (10, 11, 12, 13) and being into electrical contact with the conductive shields (14) of said sub-assemblies.
Telecommunication cable according to anyone of claims 1 to 4, characterized in that it has an outer jacket (33) covering the plurality of telecommunication sub-assemblies (10, 11, 12, 13).
Telecommunication cable according to anyone of claims 1 to 5, characterized in that said signal conductors (11, 12) of each group are twisted.
Telecommunication cable according to anyone of claims 1 to 5 characterized in that said signal conductors (11, 12) of each sub-assembly are longitudinally spaced and located in parallel with respect to one another.
Telecommunication cable according to anyone of claims 1 to 7 characterized in that said conductors are embedded in said insulating medium.
Telecommunication cable according to anyone of claims 1 to 7 characterized in that said layer of conductive material is chosen among a plasma-deposited layer, a sputtering-deposited layer and an ion-deposited layer.
Telecommunication cable according to anyone of claims 1 to 8, characterized in that the conductive material of said layer (14) is chosen among copper and aluminum.
Telecommunication cable according to anyone of claims 1 to 9, characterized in that said insulating medium (13) is polyethylene.