7 Textile Antennas
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7.3 Materials and Fabrication There are various ways metals can be included in textiles to achieve electrically conductive paths or patches. A trade-off between flexibility or drapability and conductivity remains. Conductive polymers can be included in textiles as alternatives to metals. Three categories to produce conductive textiles exist. Conductive fibres The first method uses conductive fibres that can be included into textile by textile manufacturing processes such as weaving, knitting, or embroidering [27]. Different conductive fibres exist. Metal fibres can be directly integrated in a monofilament structure or twisted with non-conductive fibres into a multifilament thread [28]. Alternatively, non-conductive fibres can be coated with conductive polymers or metals, or filled with metal powders or carbon [29, 30]. Commercially available conductive textiles at the time of editing include Shieldit Super by lessemf.com (nickel–copper-plated woven polyester) with sheet resistance 0.5 / [31], Flectron by Laird (copper-plated woven nylon) with sheet resistance 0.07 / [32], MedTex Balingen by Shieldex (silver-plated nylon knit) with sheet resistance 0.6 / [33], and Eeontex 170NW-PI-15 by Eeonyx (conductive polymer-coated polyester non-woven) with sheet resistance 15 / . Conductive ink Printing is a simple way of producing conductive structures on various substrates [34]. Ink is enriched with a conductive material and applied by screen printing or inkjet printing onto textile. Examples of conductive inks are carbon nanotubes [35], polymers [36, 37], or metallic nanoparticles [38, 39]. Conductive ink can be protected with a breathable thermoplastic to ensure stable performance after several washing cycles [40]. Miscellanious Thin films of most materials become bendable and thus can be integrated into textiles. For example, copper tape can be adhered to textiles without affecting the bendability [41]. Circuitry on flexible plastic substrates can be woven into textiles [42]. Santas et al. compare three different antennas produced according to the abovementioned categories [43], see Fig. 7.6. The antenna patches are 34 mm long and
Fig. 7.6 Three textile patch antennas with different materials. From left to right copper tape, woven copper threads and conductive spray. Courtesy of Santas et al. [43]