Innovation: French lesson in catching a wave

FRENCH knitting is providing an answer to the problem of electromagnatic radiation - produced when an electric current flows, writes Anna Kochan.

Electronic equipment is particularly vulnerable to the effects of electromagnetic radiation. Problems range from the automatic barriers at car parks breaking down because of radiation from the electronic braking system of the car trying to enter, to suspicions that radiation has caused plane crashes. On 1 January 1995, new European rules come into force limiting the levels of radiation emitted from electrical equipment. This is forcing manufacturers to introduce electromagnetic insulation in casings and enclosures.

One solution is to apply electrically conducting paint; another is to mix tiny conducting fibres into the plastic. Neither of these methods is very reliable, according to Bruno Thevenet of the French company Protecma, because paint scratches, and it is difficult to distribute the fibres evenly in the plastic.

Mr Thevenet's answer is a continuous copper thread, with a diameter of 30 to 40 microns. This is knitted into a form of chain mail using a loopy stitch so that the copper fabric can be stretched to three times its length without breaking. The knitting can be done on existing industrial knitting machines.

For an electrical cabinet made from moulded plastic, the knitted fabric is positioned in the mould prior to injection of the plastic. Alternatively, the knitting could be integrated into sheets of plastic by hot fusion. These sheets can be made into any shape without affecting their insulation properties because of the stretchiness of the knitting.

Mr Thevenet says the material could be used to insulate a room, or even an entire house, by trapping it between two layers of a fine non-woven fabric like polyester or viscose to make a wall covering.

This could be an important development for those living close to airports, power stations or power lines, where radiation levels are at their highest, Mr Thevenet says.