Fibres electromagnetic shielding

Catalyst-assisted CVD processes can also be used to fabricate delicate microcomponents. Coiled fibres of carbon and refractory carbides are examples of such components which may be used in functional applications such as microsprings, microsensors and fillers of electromagnetic shielding materials. The microstructure of some coiled fibres is shown in Figure 3.39a. The device for the production of coiled fibre fabrication is shown in Figure 3.39b. A graphite plate substrate is placed at the central part of a horizontal CVD reaction chamber, and a metal... 

In addition, there is also the possibility of tailoring the properties of plain composites further by adding particles (such as metallic fillers [29,30], carbon nanotubes [31] or urea formaldehyde [32]) to the composite layers to create multifunctional and self-healing materials, von Klemperer and Maharaj [29] added copper and aluminium powder fillers to carbon fibre epoxy laminates to improve the electromagnetic shielding capacity of the composite panels. Blast tests on the laminates [30] showed that the laminates with filler particles outperformed their plain composite counterparts, although the margin was small. 

Stainless steel fibres can also impart electromagnetic shielding performance. Between 4 and 7% w/w is usually required. Other eondueting materials sueh as metal dusts and metal-coated microspheres, barium or potassium titanate, titanium dioxide and metal-doped silica can reduce... 

Wldkiennictwa, I., 2004. Application of electrically conductive textiles as electromagnetic shields in physiotherapy. Fibres Text. East. Eur. 12 (4), 48. 

More recently, as pointed out earlier, doped PAn and blends of doped PAn have become commercially available in large quantities. They show superior electromagnetic shielding properties compared with previous materials [100,101]. The blends are easier to process than metal flake or fibre-filled polymers, and are non-abrasive. They also exhibit uniform and higher conductivities than is possible with carbon black fillers. It seems very likely that polythiophene blends that are currently being developed [102,103] may be used for similar purposes. 

Polymers are sometimes used to shield electromagnetic fields for this purpose they can be filled with metal fibres. 

Electromagnetic interface shielding is the most common application. Conductive fibres braided into a shield or sock offer superior performance against electromagnetic interference, and they present the following advantages ... 

K.H. Wong, S.J. Pickering, C.D. Rudd, Recycled carbon fibre reinforced polymer composite for electromagnetic interference shielding. Compos. A 41, 693-702 (2010)... 

Not only surface fibres are coated with metal (fig 2a), but also the nonwoven fabrics internal fibres (fig. 2b) and areas between fibres (fig. 2c). Similar crystallization are observable for zinc layers deposited on polypropylene film (fig. 3). A layer obtained in that manner characterises with large sp>eafic surface area, which disperses electromagnetic field and increases shielding coefficient SE at the same time. Cross-section of such compwsite is presented in Fig. 4. It comes to one s attention that metaUic layers on fibre surface are solid and uniform. Best composites characterise with SE 60 dB, which not only stems from low surface resistivity, but also from expanded surface of metaUic layers (fig. 5). 

Hughes Aircraft, Graphite fibre reinforced silica matrix composite, UK Pat. Appl. GB2208076 A. Chung DDL, Materials for electromagnetic interference shielding, J Mater Eng Performance 9(2), 2000. 

Properties affected Attraction of (especially) lightweight plastics (films, fibres, etc.) to each other and to other materials improved operation of high-speed machinery (e.g. for packaging) shielding equipment against electromagnetic interference reduction/elimination of spark hazard in handling electronics, chemcials. medical equipment. 

On the electrical side, a variety of fillers may be used to produce statically-conductive plastics (metal powders), shielding of electromagnetic interference (carbon fibres) or magnetic composites (powdered Al/Ni alloys or barium ferrite). 

Flakes and fibres are used as fillers in plastics to convert the inherent insulating polymeric material into electrically conductive composites. These composite materials have been studied and evaluated to create products to transmit electricity, to dissipate static charges built up by friction, or to provide electromagnetic interference (EMI) shielding. In this section, the focus is on recent developments in flake and fiber fillers that are used to provide EMI shielding for electronic devices that are found in homes, factories, offices, commercial establishments and transportation systems that ever increasingly rely on electronic broadcast systems for communications. 

Conductive polymer composites can be defined as insulating polymer matrices which have been blended with filler particles such as carbon black, metal flakes or powders, or other conductive materials to render them conductive. Although the majority of applications of polymers in the electrical and electronic areas are based on their ability to act as electrical insulators, many cases have arisen more recently when electrical conductivity is required. These applications include the dissipation of electrical charge from rubber and plastic parts and the shielding of plastic boxes from the effects of electromagnetic waves. Consequently, materials scientists have sought to combine the versatility of polymers with the electrical properties of metals. The method currently used to increase the electrical conductivity of plastics is to fill them with conductive additives such as metallic powders, metallic fibres, carbon black and intrinsically conducting polymers such as polypyrrole. 

Das, N.C., Khastgir, D., Chaki, T.K., Chakraborty, A., 2000. Electromagnetic interference shielding effectiveness of carbon black and carbon fibre filled EVA and NR based composites. Composites Part A-Applied Science and Manufacturing 31, 1069—1081. 

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