Comment by venusenvy47 10 months ago
I'm a little disappointed this IEEE article doesn't give any technical details. As an EE, I'd like to know what they are using for the antenna wire conductor. The quote from the article says it's a transparent conductor, which I've never heard of.
“I don’t think the idea for using transparent conductive materials as an antenna existed before"
The touch screen on your laptop/phone are definitely made with "transparent' conductors. These range from ITO and Silver Nanotubes on LCDs to patterned aluminum mesh (Samsung's OCTA is On Cell Touch AMOLED) and semi-transparent cathode (~10nm Ag/Mg ground current return layer) on OLEDs.
Those electrodes are literally used as capacitive antennas to detect the position of your fingers and they range from about 300ohm/sq to 1ohm/sq. Depending on the capacitive coupling they range from GHz to 100kHz bandwidths.
I was trying to understand if "transparent" was literally a property of the metal, of if it just means "so thin that you can't see it".
That depends. For ITO it can be quite transparent (80-90%), if you do a good job of matching the index of refraction (otherwise you get weird yellowish reflections and blue transmission). For the nanotubes and metal mesh, it looks fairly neutral (grey >90% transmission), if they do a good job darkening the metal so it doesn't reflect. The OLED meshes are only 2-3um wide and actually aligned with the display sub-pixels (to allow their light through) and their reflections are blocked by circular polarizing films which help make the display black as well.
Just for clarification, the reason that ITO can be transparent even though it is conducting is due to a fairly novel effect where the bandgap of the material is just wide enough to allow most visible light (red-blue) through while still allowing electron conduction (degenerate bands due to Sn doping?). It's pretty cool. Most conductors (metals) have conduction bands that reflect visible light (though they might let X-rays or IR through). Most transparent materials (eg. glass, water) are insulators which have wide band gaps, but no conduction carriers (electrons or holes).
One counter example is Ruby (chromium doped sapphire) which looks red. If you heat it up the bandgap narrows and you it turns dark/black because only IR can get through, while if you cool it in LN2 they will turn light pink as the bandgap width increases!
You're almost certainly peering through transparent conductors right now as you read this comment: https://en.wikipedia.org/wiki/Transparent_conducting_film
The rest of the design is just the usual microwave antenna black magic, but with a different propagation velocity plugged in.