Drexel University's Spray-On Antennas

Courtesy of the American Radio Relay League's weekly ARRL Letter, we learn of a new material for spraying antennas onto insulating substrates, with more features than simply spraying conductive paint.  The new material is called MXene (pronounced "Maxine") and is a new form of titanium carbide developed at Drexel University being described as a two dimensional conductor, like the better known graphene.  The MXene antennas were shown to be 50 times better than graphene and 300 times better than silver ink antennas.  The MXene form of titanium carbide is easily dissolved or suspended in water and then sprayed onto test substrates with an air brush. 

"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," said Drexel Wireless Systems Laboratory Director and engineering professor Kapil Dandekar, a co-author of the research published recently in Science Advances.

Wait.  "Optically transparent", as in "invisible"?

“The thinnest antenna was as thin as 62 nanometers — about thousand times thinner than a sheet of paper — and it was almost transparent. Unlike other nanomaterials fabrication methods, that requires 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 buzzword in radio design these days, like so much of engineering, is the Internet of Things (IoT) so naturally they talk about that market for printable, virtually invisible antennas, or printed antennas that work better than any current technology allows.  There's a belief that people will want antennas embedded into their clothes, possibly onto their skin, and many other parts of day to day life.

“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, PhD, a research assistant professor in A.J. Drexel Nanomaterials Institute.
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The group initially tested the spray-on application of the antenna ink on a rough substrate — cellulose paper — and a smooth one — polyethylene terephthalate sheets — the next step for their work will be looking at the best ways to apply it to a wide variety of 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.

Drexel researchers discovered the family of MXene materials in 2011, so they're not really a new discovery.  They've spent the last seven years gaining an understanding of their properties, and considering possible applications.  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.

Doctoral student Asia Sarycheva with an antenna printed onto a small square of plastic.

Nowhere in the Drexel or the ARRL articles do they mention the practical question of "how do you hook it up?"  For hams who need to keep a low profile due to Home Owners Associations, an invisible antenna might be just the thing.  Hang up a sheet of clear plastic with an antenna printed on it?  A clear plastic yagi antenna?   My experience with HOA people is they'll still complain.