Paint-On Carbon Nanotube Antennas Found to be Comparable to Copper in Efficiency

June 11, 2019 by Scott McMahan

For wireless applications, carbon nanotube antennas are as efficient as copper, according to researchers at Rice University's Brown School of Engineering. Carbon nanotube film antennas are also tougher, more bendable and can spread onto devices like paint.

The Rice lab of biomedical and chemical engineer Matteo Pasquali experimented with antennas made of "shear-aligned" nanotube films.

The researchers determined that not only were the conductive films able to match the performance of frequently used copper films, they could also be made thinner to better pickup higher frequencies.

The results detailing their latest findings related to carbon nanotube fibers were published in Applied Physics Letters.

The shear-aligned antennas were tested at the National Institute of Standards and Technology (NIST) facility in Boulder, Colorado.

Lead author Amram Bengio performed the testing, carried out the research, and wrote the paper while earning his doctorate in Pasquali's lab. Bengio has since established a company to develop the material further. (See image above of Rice University alumnus Amram Bengio holding a flexible nanotube film antenna. Photo by Jeff Fitlow)

At the target frequencies of 5GHz, 10GHz, and 14GHz, the antennas easily met the performance of their metal counterparts, he noted. "We were going up to frequencies that aren't even used in Wi-Fi and Bluetooth networks today, but will be used in the upcoming 5G generation of antennas," he said.

Bengio pointed out that other researchers have contended that nanotube-based antennas and their intrinsic properties have kept them from complying with the "classical relationship between radiation efficiency and frequency," but the Rice experiments with more refined films proved them wrong, allowing one-to-one comparisons.

Making the films required dissolving the nanotubes, most of them single-walled and up to 8 microns long, in an acid-based solution.

When spread across a surface, the shear force generated causes the nanotubes to self-align, a phenomenon the Pasquali lab applied in previous studies.

Bengio said that although gas-phase deposition is generally employed as a batch process for trace deposition of metals, fluid-phase processing lends itself to more scalable, continuous antenna fabrication.

The test films measured about the size of a glass slide and were between 1 and 7 microns thick. Strongly attractive van der Waals forces hold the nanotubes together. These forces give the material mechanically far more robust than those of copper.

The researchers said the new antennas could be suited for applications such as 5G networks and aircraft, especially unmanned aerial vehicles, for which weight is an issue

In addition, the antennas have the potential for use in IoT applications and could be used as wireless telemetry portals for downhole oil and gas exploration.

"There are limits because of the physics of how an electromagnetic wave propagates through space," Bengio said. "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."

"This is a great example of how collaboration with national labs greatly expands the reach of university groups," Pasquali said. "We could never have done this work without the intellectual involvement and experimental capabilities of the NIST team."

Pasquali is the A.J. Hartsook Professor of Chemical and Biomolecular Engineering and serves as a professor of chemistry and of materials science and nanoengineering. Bengio is the founder and CEO of Wootz, L.L.C.

Support for the research came from the Department of Defense, the Air Force Office of Scientific Research, and a National Defense Science and Engineering Graduate Fellowship.