With the explosion in cell phones, WiFi, Bluetooth, and other radio technologies, the demand for antennas is increasing. Everything is getting smaller and even wearable, so traditional antennas are less practical than ever. You’ve probably seen PCB antennas on things like ESP8266s, but Drexel University researchers are now studying using titanium carbide — known as MXene — to build thin, light, and even transparent antennas that outperform copper antennas. Bucking the trend for 3D printing, these antennas are sprayed like ink or paint onto a surface.
A traditional antenna that uses metal carries most of the current at the skin (something we’ve discussed before). For example, at WiFi frequencies, a copper antenna’s skin depth is about 1.33 micrometers. That means that antennas have to be at least thick enough to carry current at that depth from all surfaces –practically 5 micrometers is about the thinnest you can reasonably go. That doesn’t sound like a lot, but when you are trying to make something thin and flexible, it is pretty thick. Using MXene, the researchers made antennas as thin as 100 nanometers thick — that’s 10% of a micrometer and only 2% of a conventional antenna.
There are other materials that wind up in thin antennas, but they all have challenges either because they are not very conductive or are difficult to fabricate. MXene is a fairly new family of materials developed at Drexel University. To produce it you start with MAX which is a combination of titanium, aluminum, and carbon. The aluminum is removed in a process that requires acid and stirring for 24 hours, lithium chloride, and a centrifuge. The hydrofluoric acid is nasty to work with, but not beyond the reach of a careful home lab. You can see a Drexel video about making MXene, below. The researchers sprayed the antennas on a thin plastic substrate.
The only thing that looked tricky to us, was that thin flakes of the specific MXene used degrade in the air due to oxidation. That means production needs argon gas and the final product has to be laminated with something to protect it from the air, so that’s going to add thickness in a practical device.
Of course, PCB antennas are nothing new. But if you read the paper, you’ll see these antennas can readily outperform conventional thin antennas.