Researchers Develop Spray-on Antennas

While the advent of next gen electronics and IoT does seems closer that ever before, one of the prime reasons of their delayed launch, according to researchers at Drexel, is seamlessly integrating antennas in to flexible "things". A recent breakthrough by researchers at Drexel's College of Engineering, has led to the development of spray on antennas. This new technology could make installing an antenna as easy as applying some bug spray.

In a research paper published in Science Advances, the Drexel Engineering group talked about a method for spraying invisibly thin antennas, made from a type of two-dimensional, metallic material called MXene. The antennas perform as well as those being used in mobile devices, wireless routers and portable transducers. It's an exciting finding because there is a lot of potential for this type of technology, according to Kapil Dandekar, Ph.D., a professor of Electrical and Computer Engineering in the College of Engineering, who directs the Drexel Wireless Systems Lab, and was a co-author of the research. The ability to spray an antenna on a flexible substrate or make it optically transparent means that setting up networks will become alot easier, as you can spray on an antenna where ever it is required.

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 enables it to transmit and direct radio waves, even when it's applied in a very thin coating. The research group found that even transparent antennas with thicknesses of tens of nanometers were able to communicate efficiently. By increasing the thickness up to 8 microns, the MXene antenna achieved 98 percent of its predicted maximum performance value.

Preserving transmission quality in a form this thin is significant because it would allow antennas to easily be 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. 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 they have been working on for years.

Initial testing of the sprayed antennas suggest that 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 their footprint as well as broadening their application.

According to Yury Gogotsi, Ph.D., Distinguished University and Bach professor of Materials Science and Engineering in the College of Engineering, and Director of the A.J. Drexel Nanomaterials Institute, who initiated and led the project, the 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. They 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, 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 since then have been studying 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.

Naturally MXene materials have drawn comparisons to promising two-dimensional materials like graphene, which won the Nobel Prize in 2010 and has 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 these new materials, 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, they went beyond the performance of available nanomaterial antennas, while keeping the antenna thickness very low, according to Babak Anasori, Ph.D., a research Assistant Professor in A.J. Drexel Nanomaterials Institute. 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 require additives, called binders, and extra steps of heating to sinter the nanoparticles together, Drexel researchers made antennas in a single step by airbrush spraying the water-based MXene ink.

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 these antennas 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.