Will Sprayable Antennas Give us “Smart” Everything?

It’s called the Internet of Things—the collection of health trackers, household gadgets, smart phones, next-generation appliances, and other technologies that connect to the internet and transmit information. The “IoT” is changing our world. And if the predictions of tech experts are right, we’re only in the early stages of that revolution.

Researchers from Drexel University developed a way to “spray paint” invisibly thin antennas from a type of two-dimensional material called MXene. Here, Drexel University’s Asia Sarycheva holds an RFID tag created with this technique.
Image Credit: A. J. Drexel Nanomaterials Institute – Kanit Hantanasirisakul.

“We are moving from an inert world to a ‘pulsating world,’ explained Georgia Tech’s Alain Louchez, managing director of the Center for the Development and Application of Internet of Things Technologies, in a recent interview with ITU News. “Why pulsating? Because everything in and around us will be able to send and receive data constantly. IoT will completely change the way we live, the way we work and the way we do business.”

Imagine stoplights that react to traffic in real time to minimize traffic jams, ingestible health monitors that communicate irregularities to patients and doctors, and a dumpster that alerts the city and schedules its own trash pickup when full.

Most of the technology exists to create this reality, but there’s a key component that still requires modernization—the antenna. In a recent issue of the journal Science Advances, a team from Drexel University led by Yury Gogotsi and Babak Anasori reports progress on this challenge and introduces an antenna far from the “rabbit ears” of the early radio and television era. This antenna is so thin and flexible that it can be can be sprayed directly onto a surface.

If you’re old enough to have fiddled around with a radio or television antenna, repositioning it until you got a clear signal, you probably know that antennas were integral to communication. That’s still true, although most antennas are hidden inside devices now. On the transmission side, antennas turn electrical signals into radio waves that are transmitted through space. On the receiving side, antennas capture radio waves and turn them back into electrical signals that devices can read.

Communication between devices requires radio frequency antennas. So, to add connectivity to things like clothes, ingestible monitors, and see-through objects, we need antennas that are tiny, flexible, transparent, and generally inconspicuous.

Scientists have tried miniaturizing existing antennas, but that hasn’t worked out very well. Traditional antennas made from metals like gold and aluminum don’t conduct electivity very well when you scale them down so much. Scientists have also tried making antennas from two-dimensional materials like graphene and carbon nanotubes, but prototypes haven’t conducted electricity very well either—it takes a lot of extra steps to get their performance up to par.

In this new research, Drexel scientists used a material from the MXene family (pronounced like “Maxine”) to produce sprayable antennas. MXenes are two-dimensional, sheet-like, metallic nanomaterials that were first synthesized in 2011 at Drexel University, explains Asia Sarycheva, a PhD student working with Gogotsi. MXenes conduct electricity well and are physically strong.

First, the team synthesized a solution of flakes of the MXene titanium carbide, Ti3C2, suspended in water. Using an air spray gun, they sprayed the solution into patterns on surfaces, creating stacked layers of very thin Ti3C2 films. In total, the patterns ranged from just 62 to 1400 nanometers thick—less than half the thickness of a strand of spider silk. The team also created slightly thicker antennas using the same solution but a different technique. Experimental tests showed that the material conducted electricity well, prompting the researchers to make and test three key devices:

  1. A dipole antenna (the most common kind of antenna) to explore the material’s ability to radiate radio waves; 
  2. A transmission line to explore how a signal travels through the material under different conditions; and 
  3. An RFID tag to explore the material’s ability to scatter incoming electromagnetic waves back to the sender.

The results are promising. The dipole antenna exhibited the highest performance-to-thickness ratio of any material so far. Tests of the transmission line showed that Ti3C2 antennas are very flexible and work when bent. The samples performed well in the Wi-Fi and Bluetooth frequency band as well as at the ultrahigh frequency of RFID.

The MXene antennas perform as well or better than the ones currently used in mobile devices and RFID tags.
Image Credit: A. J. Drexel Nanomaterials Institute – Kanit Hantanasirisakul.

When taken together, the outcomes indicate that MXene antennas perform as well as existing antennas in important areas. “Use of MXene may unlock flexible antennas, transparent antennas, and knittable antennas,” says Sarycheva. If MXene provides the key, a pulsating world may not be that far away, at least from the technological perspective.

IoT has other challenges—security, privacy, ethics, energy sources, and more. Concludes Louchez, “It will take time, but we believe the challenges will eventually be overcome, and, a little bit like electricity overhauled economy and society throughout the one hundred years following Edison’s light bulb patent, the Internet of Things will radically transform our lives in a way that we can now barely begin to fathom.”

Kendra Redmond

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