Printing low-cost, flexible radio-frequency antennas with graphene ink

Graphene can now be printed on materials like paper and plastic to create ubiquitous uses such as in RFID tags, wireless sensors, and wearable electronics
May 24, 2015

These scanning electron microscope images show graphene ink after it was deposited and dried (a) and then compressed (b)k, which makes the graphene nanoflakes more dense, so it improves its electrical conductivity (credit: Xianjun Huang, et al./University of Manchester)

The first low-cost, flexible, environmentally friendly radio-frequency antenna using compressed graphene ink has been printed by researchers from the University of Manchester and BGT Materials Limited. Potential uses of the new process include radio-frequency identification (RFID) tags, wireless sensors, wearable electronics, and printing on materials like paper and plastic.

Commercial RFID tags are currently made from metals like silver (very expensive) or aluminum or copper (both prone to being oxidized).

Graphene conductive ink avoids those problems and can be used to print circuits and other electronic components, but the ink contains one or more polymeric, epoxy, siloxane, and resin binders. These are required to form a continuous (unbroken) conductive film. The problem is that these binders are insulators, so they reduce the conductivity of the connection. Also, applying the binder material requires annealing, a high-heat process (similar to how soldering with a resin binder works), which would destroy materials like paper or plastic.

Printing graphene ink on paper

So the researchers developed a new process:

1. Graphene flakes are mixed with a solvent and the ink it dried and deposited on the desired surface (paper, in the case of the experiment). (This is shown in step a in the illustration above.)

2. The flakes are compressed (step b above) with a roller (similar to using a roller to compress asphalt when making a road). That step increases the graphene’s conductivity by more than 50 times.

Graphene printed on paper (credit: Xianjun Huang et al./Applied Physics Letters)

The researchers tested their compressed graphene laminate by printing a graphene antenna onto a piece of paper. The material radiated radio-frequency power effectively, said Xianjun Huang, the first author of the paper and a PhD candidate in the Microwave and Communications Group in the School of Electrical and Electronic Engineering.

The researchers plan to further develop graphene-enabled RFID tags, as well as sensors and wearable electronics. They present their results in the journal Applied Physics Letters from AIP Publishing.

Abstract of Binder-free highly conductive graphene laminate for low cost printed radio frequency applications

In this paper we demonstrate realization of printable RFID antenna by low temperature processing of graphene ink. The required ultra-low resistance is achieved by rolling compression of binder-free graphene laminate. With compression, the conductivity of graphene laminate is increased by more than 50 times compared to that of as-deposited one. Graphene laminate with conductivity of 4.3×104 S/m and sheet resistance of 3.8.