Novel 2D antenna can be sprayed onto flexible materials

The promise of wearables, functional fabrics, the Internet of Things and their ‘next-generation’ technological cohort seems tantalizingly within reach. But their arrival is being delayed by the difficulty of seamlessly integrating connection technology – namely, antennas – with shape-shifting and flexible ‘things’.

A breakthrough by researchers in Drexel University's College of Engineering could now make installing an antenna as easy as applying some bug spray. In a paper in Science Advances, the researchers report on a method for spraying invisibly thin antennas, made from a type of two-dimensional, metallic material called MXene, that perform as well as the antennas currently used in mobile devices, wireless routers and portable transducers.

"This is a very exciting finding because there is a lot of potential for this type of technology," said Kapil Dandekar, a professor of electrical and computer engineering who directs the Drexel Wireless Systems Lab and is a co-author of the paper. "The ability to spray an antenna on a flexible substrate or make it optically transparent means that we could have a lot of new places to set up networks – there are new applications and new ways of collecting data that we can't even imagine at the moment."

The researchers, from the College's Department of Materials Science and Engineering, report that the MXene titanium carbide can be dissolved in water to create an ink or paint. The exceptional conductivity of the material allows it to transmit and direct radio waves, even when it's applied as a very thin coating.

"We found that even transparent antennas with thicknesses of tens of nanometers were able to communicate efficiently," said Asia Sarycheva, a doctoral candidate in the A.J. Drexel Nanomaterials Institute and the Department of Materials Science and Engineering. "By increasing the thickness up to 8µm, the performance of MXene antenna achieved 98% of its predicted maximum value."

Preserving transmission quality in a form this thin is significant because it would allow antennas to be easily embedded – literally, sprayed on – in a wide variety of objects and surfaces without adding additional weight or circuitry or requiring a certain level of rigidity.

"This technology could enable the truly seamless integration of antennas with everyday objects, which will be critical for the emerging Internet of Things," Dandekar said. "Researchers have done a lot of work with non-traditional materials trying to figure out where manufacturing technology meets system needs, but this technology could make it a lot easier to answer some of the difficult questions we've been working on for years."

Initial testing of the sprayed antennas suggest they can perform with the same range of quality as current antennas, which are made from familiar metals like gold, silver, copper and aluminum but are much thicker than MXene antennas. Making antennas smaller and lighter has long been a goal of materials scientists and electrical engineers, so this discovery is a sizeable step forward both in terms of reducing the footprint of antennas and broadening their application.

"Current fabrication methods of metals cannot make antennas thin enough and applicable to any surface, in spite of decades of research and development to improve the performance of metal antennas," said Yury Gogotsi, professor of materials science and engineering and director of the A.J. Drexel Nanomaterials Institute, who initiated and led the project. "We were looking for two-dimensional nanomaterials, which have sheet thickness about hundred thousand times thinner than a human hair – just a few atoms across – and can self-assemble into conductive films upon deposition on any surface. Therefore, we selected MXene, which is a two-dimensional titanium carbide material that is stronger than metals and is metallically conductive, as a candidate for ultra-thin antennas."

Drexel researchers discovered the family of MXene materials in 2011 and have been gaining an understanding of their properties, and considering their possible applications, ever since. The layered two-dimensional material, which is made by wet chemical processing, has already shown potential for use in energy storage devices, electromagnetic shielding, water filtration, chemical sensing, structural reinforcement and gas separation.

MXene materials have drawn comparisons with other promising two-dimensional materials like graphene, which won the Nobel Prize in Physics in 2010 and has also been explored as a material for printable antennas. In the paper, the Drexel researchers put the spray-on antennas up against a variety of antennas made from other nanomaterials, including graphene, silver ink and carbon nanotubes. The MXene antennas were 50 times better than graphene and 300 times better than silver ink antennas in terms of preserving the quality of radio wave transmission.

"The MXene antenna not only outperformed the macro and micro world of metal antennas, we went beyond the performance of available nanomaterial antennas, while keeping the antenna thickness very low," said Babak Anasori, a research assistant professor in the A.J. Drexel Nanomaterials Institute. "The thinnest antenna was as thin as 62nm – about 1000 times thinner than a sheet of paper – and it was almost transparent. Unlike other nanomaterial fabrication methods that require additives, called binders, and extra steps of heating to sinter the nanoparticles together, we made antennas in a single step by airbrush spraying our water-based MXene ink."

The group initially tested the spray-on application of the antenna ink on both a rough substrate – cellulose paper – and a smooth one – polyethylene terephthalate sheets. The next step will be to look for the best ways to apply the MXene antenna to a wide variety of other surfaces, from glass to yarn and skin.

"Further research on using materials from the MXene family in wireless communication may enable fully transparent electronics and greatly improved wearable devices that will support the active lifestyles we are living," Anasori said.

This story is adapted from material from Drexel University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.