Carbon nanotube film antennas show promise for 5G

Metal-free antennas made of thin, strong, flexible carbon nanotube films are as efficient as common copper antennas, according to a new study. (Credit: Jeff Fitlow/Rice)

Antennas made of carbon nanotube films are just as efficient as copper for wireless applications—and are tougher, more flexible, and easily painted onto devices—researchers say.

When engineers tested antennas made of “shear-aligned” nanotube films, they discovered that not only were the conductive films able to match the performance of commonly used copper films, they could also make them thinner to better handle higher frequencies.

The results, which appear in Applied Physics Letters advance the lab’s previous work on antennas based on carbon nanotube fibers.

Lead author Amram Bengio, who carried out the research and wrote the paper while earning his doctorate in the lab of Matteo Pasquali, a chemical and biomolecular engineer at Rice University, tested the antennas at the National Institute of Standards and Technology (NIST) facility in Boulder, Colorado.

“We were going up to frequencies that…will be used in the upcoming 5G generation of antennas.”

At the target frequencies of 5, 10, and 14 gigahertz, the antennas easily held their own with their metal counterparts, Bengio says. “We were going up to frequencies that aren’t even used in WiFi and Bluetooth networks today, but will be used in the upcoming 5G generation of antennas,” he says.

Other researchers have argued nanotube-based antennas and their inherent properties have kept them from adhering to the “classical relationship between radiation efficiency and frequency,” Bengio notes, but experiments with more refined films have proved them wrong, allowing for the one-to-one comparisons.

To make the films, the Rice lab dissolved nanotubes, most of them single-walled and up to 8 microns long, in an acid-based solution. When spread onto a surface, the shear force produced prompts the nanotubes to self-align, a phenomenon the Pasquali lab has applied in other studies.

Bengio says that although gas-phase deposition is widely employed as a batch process for trace deposition of metals, the fluid-phase processing method lends itself to more scalable, continuous antenna manufacturing.

The test films were about the size of a glass slide, and between 1 and 7 microns thick. Strongly attractive van der Waals forces, which give the material mechanical properties far better than those of copper, hold the nanotubes together.

The new antennas could be suitable for 5G networks but also for aircraft, especially unmanned aerial vehicles, for which weight is a consideration; as wireless telemetry portals for downhole oil and gas exploration; and for future “internet of things” applications, the researchers say.

“There are limits because of the physics of how an electromagnetic wave propagates through space,” Bengio says. “We’re not changing anything in that regard. What we are changing is the fact that the material from which all these antennas will be made is substantially lighter, stronger and more resistant to a wider variety of adverse environmental conditions than copper.”

Coauthors are from Rice, NIST, and UCLA. Pasquali is a professor of chemical and biomolecular engineering, professor of chemistry and of materials science and nanoengineering. Bengio has founded Wootz, LLC, a company to further develop the material.

The Air Force Office of Scientific Research, the Department of Defense, and a National Defense Science and Engineering graduate fellowship supported the work.

Source: Rice University