The shape of an antenna can make a big difference in its performance. Researchers at the Johns Hopkins Applied Physics Laboratory have used shape memory alloy to construct an antenna that changes shape depending on the signals it is receiving. Nitinol, a common shape memory alloy made from nickel and titanium, is an obvious choice, but it’s not obvious how you’d make a shape-changing antenna out of nitinol wire. That changed when a mechanical engineer found a way to 3D print the substance. You can find a paper about the research online from Applied Engineering Materials.
In practice, the antenna is a double spiral made of nitinol. A channel contains a copper wire that can heat the antenna and, therefore, change its shape. Having a powered wire in the antenna can cause problems, so special designs route the signal away from the heating element. It looks like the antenna can assume a flat configuration or a spiral conic configuration.
Printing nitinol requires selective laser melting with argon gas, so you probably aren’t printing an antenna with your Ender 3 anytime soon. The process also required post processing and forming over a metal fixture, so there’s a bit to making it work.
We’ve seen liquid metal antennas that use a similar trick. We are always surprised we don’t see more nitinol in the wild.
Mighty Morphin’, maybe?
I remember when nitinol was going to change everything. Not as much as graphene, but still.
Nope, it just changes itself :-)
Uses are probably limited because it’s so hideously expensive as an industrial feedstock, but it does find its way into many things.
after things cooled down, nitinol returned to normal ;-)
Nitinol is pretty lossy stuff, electrically. I can’t imagine it would make a great antenna.
HF current travels on the outside if the wire (skin effect). Coating the nitinol with a thin layer of silver or gold will solve the resistance problem.
The authors already wrote about this in their supplementary material: https://pubs.acs.org/doi/10.1021/acsaenm.4c00488. Radiation resistance is the predominant factor of an antenna, not the ohmic losses of nitinol (which is not that lossy due to skin effect and the ability to make the antenna not wire thin like traditional nitinol uses – it is quite conductive!). Up to 12GHz in the supplementary, the change in antenna relative gain is just 0.1dBi when compared to copper. For a 5dBi antenna, not an issue at all when other aspects of antenna design have a greater effect on the realized gain. For ~100GHz when the skin effect becomes more significant, what Wim Ton said is an easy engineering solution, but an unnecessary complexity for <Ka bands unless you need every fractional percentage of realized gain. The demonstrated antenna actually worked quite well for what it was modeled and designed for for the validation test in the paper!
It’s not just about the gain for the antenna: there’s also the noise factor. The noise temperature of an antenna’s independent of its gain, because you’re surrounded by the thermal bath: it doesn’t matter if you collect the noise with high gain from a small patch of sky or low gain from a wide patch of sky. Same power. Except when an antenna’s lossy it adds power, period.
In most cases it’s not a big deal, you can live with an extra 20-30K noise temperature, especially in typical comms situations.
Can be confusing though because a lot of times people just pay attention to gain as the only defining characteristics of an antenna.
Well, there’s something called the super-elastic signal stick that seems to work pretty well at VHF and UHF.