GB2385605A - Electromagnetic shield textile fabric - Google Patents

Abstract

The electromagnetic shield textile fabric comprises a fine mesh of conductive threads 11 which make electrical contact where they cross and non-conductive threads 12. The non-conductive threads are preferably warp knitted and the conductive threads are preferably laid in to the warp knitted thread structure. The conductive threads may be laid in by two bars of a warp knitting machine.

Description

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Electromagnetic Shield Fabrics This invention relates to electromagnetic shield fabrics, that is to say, fabrics which shield people of sensitive components against electromagnetic radiation at radio frequencies.

Such fabrics are know, for example, from US 5617713, which discloses an electromagnetic shield fabric including at least one textile thread containing metallic fibres and other, eg. man made fibres. The predominant portion of the metallic fibres, or, indeed the entire content of metallic fibres, is arranged in the inner cross-sectional area of the thread. The textile"sheath"fibres are preferably fibres which are well tolerated by the skin.

US 6155084 discloses a fabric which is claimed to provide protection against the harmful effects of electromagnetic energy as well as against chemical exposure, vibration and blunt instrument trauma. The fabric comprises metallic additives for this purpose.

So-called EMC Fabrics are manufactured by Swiss Shield AG of CH-8853 Lachen, Switzerland which shield against electromagnetic radiation. These fabrics are woven or knitted from fine yams of cotton or polyester fibres spun with an extremely thin, highly conductive silver plated metal core. They are claimed to offer excellent shielding efficiency of 40-60dB/-80dV over a range of radio frequencies from 0. 01 to 10,000 MHZ.

The present invention provides improved electromagnetic shield fabrics, offering better shielding with reduced material and manufacturing costs.

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The invention comprises an electromagnetic shield fabric comprising a fine mesh of conductive threads making electrical contact where they cross.

The fabric may comprise non-conductive threads, which may be knitted, in particular warp knitted. The conductive threads may then be laid in to the warp knitted thread structure.

The conductive threads may be laid in by two bars of a warp knitting machine.

It is, of course, possible for a fine mesh of metallic threads to be comprised in other kinds of textile structure, for example, woven structures, in which warp and weft metal threads are arranged to cross and contact, weft knitted structures in which metalcoated threads are knitted, and non-woven, eg. stitch bonded structures in which threads are laid in either in criss-crossing form as weft threads, or as warp and weft laid in threads.

Pure wire structures for shielding are, of course, well known, in the braided sheathing of co-axial cabling and in woven wire covers. These, however, are not textile fabrics, as that term is to be understood herein."Textile fabrics"denotes, herein, fabric comprising non-conductive threads such as are ordinarily used in the manufacture of textile fabrics for apparel, furnishing and like uses, threads such as natural fibre threads, and man made and synthetic fibres such as polyester, polyamide, acetate and so forth.

One embodiment of an electromagnetic shield fabric according to the invention will now be described with regard to the accompanying drawings, in which: Figure 1 is a magnified view of the fabric; and

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Figure 2 is a graph of field strength against frequency, with three traces representing non shielding, shielding using the best available prior art or fabric, and shielding using a fabric according to the invention.

The drawings illustrate an electromagnetic shield fabric comprising a fine mesh of conductive threads 11 making electrical contact where they cross, and comprising non-conductive threads 12.

The non-conductive threads 12 are knitted, in particular, warp knitted.

The conductive threads 11 are laid in to the warp knitted thread structure.

The conductive threads 11 are laid in by two bars of a warp knitting machine.

In a four bar machine, the inner two bars can be used to lay in the conductive threads 11.

A typical knitting construction is: 18 gauge Raschel machine, four bars. Bars 1 and 4 full set threading with eg.

4470 polyester fibres, Bars 2 and 3,56% metal wire, by weight.

Notation: Bar 1: 4-6/2-0 Bar 2: 0-0/4-4 Bar 3: 8-8/0-0 Bar 4: 2-0/2-4.

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Typical run in per rack: Bar 1 : 123. 75" Bar 2 : 75" Bar 3: 75"

11 Bar 4 : 90".

It will be seen that with this construction, the textile-polyester-fibres form a knitted fabric matrix in which the laid in metal wires are trapped, and that the metal wires are held against each other where they cross by the textile outer layers.

The traces in Figure 2 compare this fabric with two prior art fabrics. It will be observed that the fabric of the present invention out-performs the prior art fabrics across the range of radio frequencies.

It is thought that the fact that the conductive fibres establish electrical contact where they touch creates small, order of millimetre size, electric circuits, and that it is this that establishes a good shielding against electromagnetic radiation.

Claims (5)

1. CLAIMS 1. An electromagnetic shield textile fabric, comprising a fine mesh of conductive threads making electrical contact where they cross, and non-conductive threads.
2. 2. A fabric according to claim 1, in which the non-conductive threads are knitted.
3. 3. A fabric according to claim 2, in which the non-conductive threads are warp knitted.
4. 4. A fabric according to claim 3, in which the conductive threads are laid in to the warp knitted thread structure.
5. 5. A fabric according to claim 4, in which the conductive threads are laid in by two bars of a warp knitting machine.