The antenna demonstrated abilities which would make it practical for use in radio-frequency identification (RFID) tags and wireless sensors, the researchers said. Furthermore, the antenna is flexible, environmentally friendly and could be mass-produced cheaply.
The study shows that printable graphene is now ready for commercial use in low-cost radio frequency applications, according to Zhirun Hu, a University of Manchester researcher in the School of Electrical and Electronic Engineering.
Kostya S. Novoselov, who coordinated the project, added:
Since graphene was first discovered in 2004, researchers have struggled to make practical use of its astounding electrical and mechanical properties.
One of the first commercial products manufactured from graphene was conductive ink, which can be used to print circuits and other electronic components. Graphene ink is generally low cost and mechanically flexible, advantages it has over other types of conductive ink, such as solutions made from metal nanoparticles.
To produce the ink, graphene flakes are mixed with a solvent, and sometimes a binder, such as ethyl cellulose is added to help the ink stick.
Graphene ink with binders usually conducts electricity better than binder-free ink, but only after the binder material, which is an insulator, is broken down in a high-heat process called annealing. Annealing, however, limits the surfaces onto which graphene ink can be printed because the high temperatures destroy materials like paper or plastic.
The University of Manchester researchers, in collaboration with graphene manufacturer BGT Materials Limited, found a way to increase the conductivity of graphene ink without resorting to a binder. They accomplished this by first printing and drying the ink, and then compressing it with a roller, similar to the way new pavement is compressed with a road roller.
Compressing the ink increased its conductivity by more than 50 times, and the resulting graphene laminate was also almost two times more conductive than previous graphene ink made with a binder.
The high conductivity of the compressed ink, which enabled efficient radio frequency radiation, was one of the most exciting aspects of the experiment, Hu said.
Antennas, Wireless Sensors, and Beyond
The researchers tested their compressed graphene laminate by printing a graphene antenna onto a piece of paper. The antenna measured approximately 14 centimeters long, and 3.5 millimeter across and radiated radio frequency power effectively, said Xianjun Huang, first author of the paper and PhD candidate in the Microwave and Communcations Group in the School of Electrical and Electronic Engineering.
Printing electronics onto cheap, flexible materials like paper and plastic could mean that wireless technology, like RFID tags that currently transmit identifying info on everything from cattle to car parts, could become even more widespread.
Most commercial RFID tags are made from metals like aluminium and copper, Huang said, costly materials with complicated fabrication processes that increase the cost.
The University of Manchester and BGT Materials Limited team has plans to further develop graphene enabled RFID tags, as well as sensors and wearable electronics.
Xianjun Huang, Ting Leng, Xiao Zhang, Jia Cing Chen, Kuo Hsin Chang, Andre K. Geim, Kostya S. Novoselov, and Zhirun Hu Binder-free Highly Conductive Graphene Laminate for Low Cost Printed Radio Frequency Applications Applied Physics Letters, May 19, 2015. DOI: 10.1063/1.4919935
Scanning electron microscope images show the graphene ink after it was deposited and dried (a) and after it was compressed (b). Compression makes the graphene nanoflakes more dense, which improves the electrical conductivity of the laminate. Credit: Xianjun Huang, et al./ University of Manchester