GB2427746A

GB2427746A - Electrical-cable Shielding

Info

Publication number: GB2427746A
Application number: GB0612922A
Authority: GB
Inventors: Gregory Neil Burland
Original assignee: Icore International Ltd
Current assignee: Safran Electrical Components UK Ltd
Priority date: 2005-06-29
Filing date: 2006-06-29
Publication date: 2007-01-03
Also published as: GB0612922D0

Abstract

A bundle of electrical cables 20 are shielded from electromagnetic interference by an elongate tape 1 wrapped widthwise round the bundle with its longitudinal edges 8,11 overlapping one another. The tape includes a woven mesh 2 Preferably of bare-metal strands 5 sandwiched between outer and inner layers 4,3 of sheet-plastics, the weave being a narrow-fabric weave having warp strands 5 running longitudinally of the tape 1 and a single unbroken weft-strand 6. The mesh is bare on the outside along one longitudinal margin 11 and also on the inside along the other longitudinal margin 8 for direct electrical contact between them within the overlap in establishing closed electrical circuits encircling the cable-bundle throughout the length of the tape 1. The margin 11 of the mesh 2 innermost in the wrap may instead be insulated. Preferably a securing means such as Velcro¹ can be used to the wrapped tape in position.

Description

Electrical-Cable Shielding This invention relates to the shielding of

electrical cables, and is concerned particularly with methods of electromagnetically shielding a bundle of electrical cables, and a flexible tape for use in such shielding.

According to one aspect of the present invention there is provided a method of electromagnetically shielding a bundle of electrical cables wherein an elongate, flexible tape that extends lengthwise of the bundle is wrapped widthwise round the bundle with the longitudinal margins of the tape overlapping one another, the tape comprising a mesh of electrically-conductive strands with some of those strands running longitudinally of the tape, and the tape is retained wrapped round the bundle as aforesaid with the mesh providing closed electrical-circuit encirclement of the bundle via the overlap.

According to another aspect of the invention there is provided a flexible tape for extending lengthwise of a bundle of electrical cables and wrapping widthwise round the bundle for electromagnetic shielding of the bundle with the longitudinal margins of the tape overlapping one another, the tape comprising a mesh of electrically- conductive strands with some of those strands running longitudinally of the tape, and means for retaining the tape wrapped round the bundle as aforesaid with the mesh providing closed electrical-circuit encirclement of the bundle via the overlap.

The mesh of the method and tape of the invention may be of woven electrically-conductive strands with the warp of the weave running longitudinally of the tape. In this case, the weave may be a narrowfabric weave, and may have a single unbroken weft strand.

The electrically-conductive strands may be individual wire-filaments or a plurality of wire-filaments twisted together, and the wire-filaments, which may be of nickel- coated copper, are preferably bare so that good electrical contact is established between all of them in common in the mesh.

The woven mesh of the method and tape of the invention may be covered by electrically-insulating material apart from along the longitudinal margins where there is to be overlap. In particular, the electrically- insulating material may be in the form of a plastics sheet that is secured to one of the two faces of the mesh for insulating the mesh electrically from the bundle of cables. Furthermore, the mesh may be backed on its other face by another plastics sheet for affording the tape resistance to physical damage resulting, for example, from abrasion. The sheet or sheets may be secured to the mesh by stitching.

Fabric fastening elements of the form sold under the Registered Trade Mark VELCRO, may be used for retention of the tape wrapped round the bundle.

A method of electromagnetically-shielding a bundle of electrical cables, and a flexible tape for such use, all in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a representative crosssection of the electromagnetically-shielding tape according to the invention; Figure 2 is illustrative of a plan view of the tape of Figure 1; Figure 3 is illustrative schematically of the weave of a wire-mesh that forms part of the tape of Figures 1 and 2; Figure 4 is a cross- sectional view of a bundle of electrical cables wrapped in the tape of Figures 1 and 2 for electromagnetic shielding according to the method of the invention; and Figure 5 is illustrative to an enlarged scale of a portion of the overlap between longitudinal margins of the tape of Figures 1 and 2 shown in Figure 4; and Figure 5 is illustrative of a modification of the tape of Figures 1 and 2.

Referring to Figures 1 and 2, the shielding tape 1 is of a three-layered, light-weight Construction including a woven mesh 2 of bare metal-wire strands (for example, in a twill weave). The mesh 2 is sandwiched between Inner and outer electrically-insulating layers 3 and 4 respectively. The layers 3 and 4 are formed by strips of plastics sheet (the thicknesses of the layers 3 and 4 and the mesh 2 are exaggerated in the drawings). More particularly, the inner layer 3 is, for example, of polytetrafluoroethy]. ene (PTFE) or polyvinyl chloride (PVC), and the outer layer 4 is of a hard-wearing plastics material, for example, a ketone-based resin such as polyetheretherketorie (PEEK), for providing physical strength with resistance to abrasion.

As indicated schematically by Figure 3, the warp of the woven mesh 2 is formed by fine wire-strands 5 that run lengthwise of the tape 1, whereas the weft is formed by a fine wire-strand 6 running back and forth without break, in a narrow-fabric weave with the warp strands 5. The strands 5 and 6 are, for example, single wire-filaments or twisted pairs, of nickelcoated copper wire, and the strands 5 are fine enough that a group (in the case illustrated, of four) of them are drawn together through the dent-space of the loom in the weaving process; the gap G between the adjacent groups, resulting from the dents (and shown exaggerated in Figure 3), is small enough that it does not materially affect the shielding provided. The weft strand 6 passes successively over one group of warp strands 5 and under the next in the weave.

The inner layer 3 is of a width to cover the inside face 7 of the woven mesh 2 apart from throughout a longitudinal marginal strip 8 of the face 7 at one longitudinal edge 9 of the bare mesh 2. The outer layer 4 correspondingly covers the outside face 10 of the mesh 2 apart from throughout a longitudinal marginal strip 11 of the face 10 at the other longitudinal edge 12 of the mesh 2. An edge 13 of the layer 4 lies beyond the edge 9 of the mesh 2 to carry a strip 14 of upstanding fibres that abuts the edge 9.

The strip 14 forms in conjunction with a second strip 15 of upstanding fibres, a pair of interengaging elements of a selectively-disengageable fabric-fastening of the kind, such as that sold under the Registered Trade Mark VELCRO, in which hook-ended fibres of one element engage with upstanding loop-ended fibres of a second element; in this case, for example, the element 14 has the loop-ended fibres and the strip 15 has the hook-ended fibres. The strip 15, which is supported along the opposite edge 16 of the layer 4, has a central, red-coloured line 17 running throughout its length.

The mesh 2 together with the layers 3 and 4 and the strips 14 and 15 are retained in assembly with one another by stitching. By way of alternative, retention may be by bonding, and the strips 14 and 15 may be encapsulated into the plastic layer 4.

The tape 1 is used for electromagnetic shielding of a bundle of cables as will now be described principally with reference to Figure 4.

Referring to Figure 4, the tape 1 is deployed running lengthwise of the bundle of electrical cables 20 with the inner layer 3 abutting the cables 20 of the bundle. The tape 1 is now wrapped widthwise round the bundle by folding its longitudinal margins round the bundle as indicated generally by arrows A in Figure 1. Wrapping of the tape 1 round the bundle is carried through to bring the bare strip 8 of the mesh 2 over the bare strip 11 into an overlapping relationship with it as illustrated to a very enlarged scale in Figure 5, and to engage the element 14 with the element 15; this overlap and engagement are established throughout the full length of the tape 1. Sufficiency of the area of engagement between the element 14 and the element 15 at each position throughout the length of the tape 1, so as to ensure that the tape 1 is correctly wrapped and secured, is confirmed if the red line 17 cannot be observed anywhere along that length; the red line 17 can be omitted and in these circumstances correct wrapping is confirmed if there is edge-to-edge alignment between the elements 14 and 15.

When the tape 1 is correctly wrapped, the strips 8 and 11 of the woven mesh 2 are in hard abutment with one another so as to ensure that there is good electrical contact between them and that optimum shielding is provided.

With such contact, there is complete closed-circuit encirclement of the bundle, and low-resistance connection of that circuit with the weft strand 6 and each warp strand 5. The strands 5 and 6 are clamped into couplings (not shown) at either end of the bundle to ensure good ground connection. Moreover, the shortest possible path for discharge from and lengthwise of the bundle is provided by the warp strands 5 running longitudinally of the shielding tape 1; this is of especial importance for lightning protection, and is advantageous for maintaining a lightweight construction.

A modification of the tape 1 is illustrated in Figure 6.

More particularly in this regard, the layer 3 is extended round the edge 12 of the mesh 2 and covers the strip 11.

When the modified tape 1 is wrapped round the cable- bundle, the extended portion 21 of the layer 3 enhances the integrity of the electrical insulation of the mesh 2 from the cable-bundle, but separates the strip 11 of the mesh 2 from its direct electrical contact with the strip 8. It has been found that this separation does not materially detract from the operation of the shielding tape, especially in relation to high- frequency interference. The closed-circuit encirclement of the bundle by the mesh 2 is now of low impedance with a small capacitative component instead of being solely resistive.

In some circumstances it may not be necessary or desired to provide insulation between the bare mesh 2 and the cables 20, so then a saving in cost and weight can be achieved simply by omitting the inner insulating layer 3 from the tape 1.

Claims

Claims: 1. A method of electromagnetically shielding a bundle of

electrical cables wherein an elongate, flexible tape that extends lengthwise of the bundle is wrapped widthwise round the bundle with the longitudinal margins of the tape overlapping one another, the tape comprising a mesh of electrically-conductive strands with some of those strands running longitudinally of the tape, and the tape is retained wrapped round the bundle as aforesaid with the mesh providing closed electrical-circuit encirclement of the bundle via the overlap.
2. A method according to Claim 1 wherein the tape comprises a mesh of woven electrically-conductive strands with the warp of the weave running longitudinally of the tape.
3. A method according to Claim 2 wherein the weave is a narrow-fabric weave.
4. A method according to Claim 2 or Claim 3 wherein the weave has a single unbroken weft strand.
5. A method according to any one of Claims 1 to 4 wherein the tape is retained wrapped round the bundle with strands of the mesh within each of the overlapping margins in electrical contact by abutment with strands within the other margin.
6. A method according to any one of Claims 1. to 5 wherein each electrically-conductive strand is an individual wire-filament.
7. A method according to any one of Claims 1 to 6 wherein each electrically-conductive strand comprises a plurality of wire-filaments twisted together.
8. A method according to any one of Claims 1 to 7 wherein the strands comprise nickel-coated copper wire- filaments.
9. A method according to any one of Claims 1 to 8 wherein the strands of the mesh are of bare metal so as to establish good electrical contact between them all in common in the mesh.
10. A method according to any one of Claims 1 to 9 wherein the mesh is sandwiched between electrically- insulating layers.
11. A flexible tape for extending lengthwise of a bundle of electrical cables and wrapping widthwise round the bundle for electromagnetic shielding of the bundle with the longitudinal margins of the tape overlapping one another, the tape comprising a mesh of electricallyconductive strands with some of those strands running longitudinally of the tape, and means for retaining the tape wrapped round the bundle as aforesaid with the mesh providing closed electrical-circuit encirclement of the bundle via the overlap.
12. A flexible tape according to Claim 11 comprising a mesh of woven electrically-conductive strands with the warp of the weave running longitudinally of the tape.
13. A flexible tape according to Claim 12 wherein the weave is a narrowfabric weave.
14. A flexible tape according to Claim 12 or Claim 13 wherein the weave has a single unbroken weft strand.
15. A flexible tape according to any one of Claims 11 to 14 wherein the tape is retained wrapped round the bundle with strands of the mesh within each of the overlapping margins in electrical contact by abutment with strands within the other margin.
16. A flexible tape according to any one of Claims 11 to wherein each electrically-conductive strand is an individual wire-filament.
17. A flexible tape according to any one of Claims 11 to wherein each electrically-conductive strand comprises a plurality of wire-filaments twisted together.
18. A flexible tape according to any one of Claims 11 to 17 wherein the strands comprise nickel-coated copper wire- filaments.
19. A flexible tape according to any one of Claims 11 to 18 wherein the strands of the mesh are of bare metal so as to establish good electrical contact between them all in common in the mesh.
20. A flexible tape according to any one of Claims 11 to 19 wherein the mesh is sandwiched between electrically- insulating layers.
21. A flexible tape according to any one of Claims 1 to wherein the means for retaining the tape wrapped round the bundle as aforesaid involves iriterengaging elements of a selectively-disengageable fabric-fastening.
22. A flexible tape according to any one of Claims 11 to 21 extending lengthwise of a bundle of electrical cables and wrapped widthwise round the bundle for electromagnetic shielding of the bundle with the longitudinal margins of the tape overlapping one another.
23. A method of electromagnetically shielding a bundle of electrical cables, substantially as hereinbefore described with reference to the accompanying drawings.
24. A flexible tape for electromagnetic shielding of a bundle of cables, substantially as hereinbefore described with reference to the accompanying drawings.