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Carbon nanotube coating avoids need for metal braid shielding

28 January 2016

Common coaxial cables could be made 50 percent lighter with a new nanotube-based outer conductor developed by Rice University scientists.

A coating of carbon nanotubes, seen through a clear jacket, replaces a braided metal outer conductor in an otherwise standard coaxial data cable (photo: Jeff Fitlow/Rice University)

The Rice lab of Professor Matteo Pasquali has developed a coating that could replace the tin-coated copper braid that transmits the signal and shields the cable from electromagnetic interference. The metal braid is the heaviest component in modern coaxial data cables.

Replacing the outer conductor with Rice's flexible, high-performance coating would benefit aircraft and spacecraft, in which the weight and strength of data-carrying cables are significant factors affecting performance.

Rice research scientist Francesca Mirri, lead author of a paper published in the journal, ACS Applied Materials and Interfaces, made three versions of the new cable by varying the carbon-nanotube thickness of the coating.

She found that the thickest - about 90 microns - met military-grade standards for shielding and was also the most robust; it handled 10,000 bending cycles with no detrimental effect on the cable performance.

Coaxial cables consist of four elements: a conductive copper core, an electrically insulating polymer sheath, an outer conductor and a polymer jacket. The Rice lab replaced only the outer conductor by coating sheathed cores with a solution of carbon nanotubes in chlorosulphonic acid.

Compared with earlier attempts to use carbon nanotubes in cables, this method yields a more uniform conductor and has higher throughput. "This is one of the few cases where you can have your cake and eat it, too," says Pasquali. "We obtained better processing and improved performance."

Replacing the braided metal conductor with the nanotube coating eliminated 97 percent of the component's mass.  The lab is now working on a method to scale up production, drawing on its experience of producing high-performance nanotube-based fibres.

"It's a very similar process," Mirri said. "We just need to substitute the exit of the fibre extrusion set-up with a wire-coating die. These are high-throughput processes currently used in the polymer industry to make a lot of commercial products."

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