A wearable antenna may just be a spray away
US engineers believe a material called MXene could unlock the potential of smart, connected technology. Nick Carne reports.
Installing antennas could soon be as easy as “applying some bug spray” if US engineers are on the money.
In research published in the journal Science Advances, a team from Drexel University College of Engineering in Philadelphia, US, reports on a method for spraying invisibly thin antennas made from a two-dimensional metallic material called MXene, which, the researchers say, perform as well as those currently used in mobile devices, wireless routers and portable transducers.
If they really do, that would mean antennas could be embedded easily in a variety of objects and surfaces without adding weight or circuitry, or requiring a certain level of rigidity. And that would open up a range of exciting possibilities for functional fabrics, the Internet of Things – and more.
“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,” says co-author Kapil Dandekar, who directs the Drexel Wireless Systems Lab.
“There are new applications and new ways of collecting data that we can't even imagine at the moment.”
The hunt for a wearable antenna is not new. More than a decade ago a research paper introduced us to a glove and bracelet that detected when users interact with unobtrusively tagged objects, and more recently papers have, for example, addressed the challenges associated with flexible antenna integration or described a radio-enhanced garment composed of blended textile antennas.
The Drexel team has taken things a step further, however, coming up with a specific idea they believe stands up to pretty tough initial scrutiny and has real potential.
“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,” says Dandekar.
The key is the exceptional conductivity of MXene titanium carbide, which enables it to transmit and direct radio waves when applied in a very thin coating. It can even be dissolved in water to create an ink or paint.
Initial testing suggests sprayed antennas can perform with the same range of quality as those made from familiar metals such as gold, silver, copper and aluminum, which by necessity are larger and heavier.
MXene even topped other new materials. The MXene antennas were found to be 50 times better than ones made from graphene and 300 times better than ones constructed from silver ink, 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,” says Dandekar’s colleague Babak Anasori.
“The thinnest antenna was as thin as 62 nanometers – about 1000 times thinner than a sheet of paper – and it was almost transparent. Unlike other nanomaterials 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 a rough substrate of cellulose paper, and a smooth one of polyethylene terephthalate sheets. The next step will be to look at the best ways to apply it to a wide variety of other surfaces, from glass to yarn and even skin.
Drexel researchers discovered the family of MXene materials in 2011 and have been gaining an understanding of its properties, and considering their possible applications, ever since.
The layered two-dimensional material, which is made by wet chemical processing, has already shown potential in energy storage devices, electromagnetic shielding, water filtration, chemical sensing, structural reinforcement and gas separation.