Spray-on Antennas? I say “Spray-on Bunkum”
Thanks to John, who pointed out that this post was mangled. Fixed now.
I wasn’t going to mention this one, but Dave, Chris and Jeff over at The Amp Hour brought it up on their most recent podcast, but other than Jeff’s somewhat enthusiastic declaration that he thought it was BS, I don’t think they pulled it apart enough.
The topic is a recent video poasted under the auspices of Google’s new Solve for X program. Try watching it:
If you try googling for “spray on antennas”, you’ll find dozens and dozens of links to this video, or what amounts to a copied press release regarding this video. If you dig a little deeper, you’ll find lots of people complaining about how poor the presentation was. What is somewhat harder to find is any kind of a critical evaluation of the information (what little there is) on this antenna scheme. I’ll try to confine my comments to the latter.
It’s begins with a pitch, and not a modest one. We are told to imagine that we can send signals twice as far using no more power. Or the same distance with half the power. Or that we can get rid of cell towers. Or communicate from the depths of the ocean to outer space. And the key is some kind of nanotechnology. that Chamtech has developed for “spray on antennas”.
Following this pitch is a story: a story how “a business partner” who asked him develop a hidden antenna for Special Operations. He was then asked by “the government” to try his antenna technology, which was then tested by “a government team”, who found that this spray on antenna was “an order of magnitude better” than their best antenna.
I’m sorry, but that’s just bunk. Good antennas are efficient. A given antenna has a particular radiation resistance. For instance, a typical dipole antenna such as the antennas that many radio amateurs use might have a radiation resistance of around 70 ohms or so. But, of course, there are other bits of resistance in the antenna too. There is the ohmic resistance of the antenna, so-called “ground losses”, and “coil losses”. The antenna efficiency is just the ratio between the radiation resistance and the total resistance of the antenna.
But here’s the thing: at VHF+ frequencies, it’s just not that hard to make antennas with efficiencies that are 90% or higher. And that means that there is no “head room” to make an antenna which is “an order of magnitude more efficient”. It’s just basic math. You can’t get more energy out of an antenna than you put in, and existing antenna designs are already enormously efficient at radiating what you put in.
Beyond that, the geometry of antennas is important. You can’t generate an efficient one by just stringing a random conductor (or spraying one) higglety piggly all over the place. The length of the various elements change the feedpoint impedance and that must be matched carefully to the transmitter output impedance in order to be efficient. The idea that these nanocapacitors can “hold” electrons and then release them at their “happy place” is enough to make milk shoot out of my nose.
The “test” on the iPhone was comical: inside an Faraday cage (originally he said anechoic chamber, which I thought was an odd mistake for an RF engineer to make) he claimed that their technology improved the output power of the iPhone by “20 dBm”. I’m sorry, but I cry BS on this as well: dBm is the power ratio referenced to a 1mw signal. It doesn’t make any sense to say that there is a 20dBm improvement. An improvement of 20dB is a hundred fold increase in output power. Just where is this power supposed to be coming from? A typical cell phone has an output power of around 27dBm, or around 500mw. A 20dB improvement would raise that to 47dBm, which is about 50 watts. Bunkum.
Honestly Google, I know you have some pretty smart guys who know about RF: why did you let this guy use your forum to sell this complete nonsense? It doesn’t bode well for Solve For X if it can’t distinguish between “radical solutions” and “snake oil”.