Nanotube coating makes coaxial cables 50% lighter

"Our cable meets military standards, but we're able to supply the strength and flexibility without the bulk," says Francesca Mirri. (Credit: iStockphoto)

Common coaxial cables could be 50 percent lighter with a new nanotube-based outer conductor.

The coating would replace the tin-coated copper braid that currently transmits signals and shields the cable from electromagnetic interference. The metal braid is the heaviest component in modern coaxial data cables.

“This is one of the few cases where you can have your cake and eat it, too. We obtained better processing and improved performance.”

Researchers say replacing the outer conductor with the new flexible coating would benefit airplanes and spacecraft, in which the weight and strength of data-carrying cables are significant factors in performance.

Scientists made three versions of the new cable by varying the carbon-nanotube thickness of the coating and found that the thickest, about 90 microns—approximately the width of the average human hair—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.

“Current coaxial cables have to use a thick metal braid to meet the mechanical requirements and appropriate conductance,” says Francesca Mirri, a research scientist at Rice University. “Our cable meets military standards, but we’re able to supply the strength and flexibility without the bulk.”

Coaxial cables consist of four elements: a conductive copper core, an electrically insulating polymer sheath, an outer conductor, and a polymer jacket.

coaxial cable infographic
(Credit: Pasquali Lab/Rice University)

Researchers replaced only the outer conductor by coating sheathed cores with a solution of carbon nanotubes in chlorosulfonic acid. Compared with earlier attempts to use carbon nanotubes in cables, this method yields a more uniform conductor and has higher throughput, says Matteo Pasquali, professor of chemical and biomolecular engineering and professor of materials science and nanoengineering and of chemistry.

“This is one of the few cases where you can have your cake and eat it, too. We obtained better processing and improved performance.”

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Replacing the braided metal conductor with the nanotube coating eliminated 97 percent of the component’s mass, Mirri says.

The lab is working on a method to scale up production and is drawing on its experience in producing high-performance, nanotube-based fibers.

“It’s a very similar process,” Mirri says. “We just need to substitute the exit of the fiber extrusion setup with a wire-coating die. These are high-throughput processes currently used in the polymer industry to make a lot of commercial products. The Air Force seems very interested in this technology, and we are currently working on a Small Business Innovation Research project with the Air Force Research Laboratory to see how far we can take it.”

Other researchers from Rice and from the National Institute of Standards and Technology, Oak Ridge National Laboratory, and the University of Maryland are coauthors of the study that is published in the journal ACS Applied Materials and Interfaces.

The Air Force Office of Scientific Research, the Air Force Research Laboratories, the Robert A. Welch Foundation, NIST, the National Science Foundation, and a NASA Space Technology Research Fellowship supported the work.

Source: Rice University