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"Stealth" Plasma Antennas
eldavojohn writes "There's a new antenna that consists of plasma and essentially vanishes when you turn it off. While it may seem to not have many uses in the commercial world, it is very important to military personnel who risk detection or for anybody wishing to avoid signal jamming."
How does having the antenna "disappear" effect it's ability to circumvent jamming? The article is apparently being slashdotted as I type this, so I'm just curious.
I got a catholic block.
When I submitted this story, I submitted the story from PhysOrg and I'm not sure why they changed the link. That poor blog didn't stand a chance. I guess they must do that to more randomly distribute their news sources or make it look like they aren't playing host to some PhysOrg worker trying to generate more traffic. Oh well, enjoy a usable link anyhow.
My work here is dung.
I read this in new scientist years ago:
http://www.newscientist.com/article/mg16422141.000-now-you-see-it---.html
(Sorry ham radio nerd humor.)
Disguise it as a stealth-plasma flagpole and proudly fly a red-white-and-blue flaming sheet-o-plasma flag! Has the added advantage of shocking the hell out of any pot-smoking hippies who try to burn it!
Give a man a fish and you have fed him for today. Teach a man to fish, and he'll say "WHERE'S MY FISH, YOU IDIOT?"
'Stealth' Antenna Made Of Gas, Impervious To Jamming Submitted by News Account on 12 November 2007 - 2:58pm. Physics
A new antenna made of plasma (a gas heated to the point that the electrons are ripped free of atoms and molecules) works just like conventional metal antennas, except that it vanishes when you turn it off.
That's important on the battlefield and in other applications where antennas need to be kept out of sight. In addition, unlike metal antennas, the electrical characteristics of a plasma antenna can be rapidly adjusted to counteract signal jamming attempts.
Plasma antennas behave much like solid metal antennas because electrons flow freely in the hot gas, just as they do in metal conductors. But plasmas only exist when the gasses they're made of are very hot. The moment the energy source heating a plasma antenna is shut off, the plasma turns back into a plain old (non conductive) gas. As far as radio signals and antenna detectors go, the antenna effectively disappears when the plasma cools down.
This prototype plasma antenna is stealthy, versatile, and jam-resistant. Credit: T. R. Anderson and I. Alexeff
The antenna design being presented at next week's APS Division of Plasma Physics meeting in Orlando consists of gas-filled tubes reminiscent of neon bulbs. The physicists presenting the design propose that an array of many small plasma elements could lead to a highly versatile antenna that could be reconfigured simply by turning on or off various elements.
- T. R. Anderson and I. Alexeff 2007 APS Division of Plasma Physics annual meeting November 12, 2007
Letter To Iran
In a normal antenna, electrons in the metal slosh up and down, accelerated by the electromagnetic fields that it's receiving (or transmitting). In this case, I could use the same description: electrons slosh up and down, driven by the EM fields.
The idea that this could lead to a reconfigurable antenna is a bit farfetched, as it would require that the driving bias electrodes be able to totally float at RF frequencies. Just like a neon sign, or a fluorescent light, you're going to have to keep a large voltage across these to get them to light, so it'll be tricky to use it as a receiving antenna in particular.
Take a look at another project, Talking Lights. This uses conventional fluorescent lights (hey, a plasma!) with a modified ballast to transmit data at serial-link speeds.
The "jam-resistance" doesn't make any sense. If it can receive signals, it can receive signals, period. At the point of the antenna, the desired signal and the jamming signal have already been mixed. The antenna itself can't help you out. (Clever frequency-hopping or other schemes can, though.)
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Microcontroller kits for the digital generation.
Back in my university days I had the pleasure of being taught by a physicist turned engineer who was actually working on one of these things. The trouble with traditional antennas is their giant radar footprint and traditionally they solved this problem by flopping the antennas up and down when they needed to send signals. Not the most graceful solution so they started looking for alternatives. We had one of the prototypes of these things in the plasma instrumentation lab and it was pretty adept at sending some small signals. The great thing about them is their tunability. Just like any kind of woodwind instrument if you change the length of the tube (imagine a giant piston that's got plasma in it) you change the resonant frequency. My lecturer referred to it as playing the plasma trombone. Good to see these things finally making their way through to practical uses. I was always hoping my crazy lecturer's tinkerings would be used someday.
The Refined Geek - Technology, Finance, Space and everything in between
Yes - and no :)
The gas is hot, but at very low pressure. So the amount of energy transmitted to the glass container surrounding it is minimal, and could be further reduced by active cooling. So the second your incomings are detected and the antenna shuts down it becomes invisible to both the RF and infrared seeker.
I'm aging rapidly, I bought a new game and had no idea if my machine was good for it.
Metallic antennas are excited by EM radiation (radio waves) of a proper wavelength. In turn, the antenna will re-radiate (transmit) a tiny bit of that energy, although very weakly, which can be detected. This is totally passive, which is how it is possible to build a passive repeater by simply running a wire between two directional antennas. It is also the general principal of how RFID tags work.
The stealth of this antenna is that it is non-metallic and will not react to EMF when switched off. It has nothing to do with how big the antenna is, or what color it is, or whether or not it emits light, which are all things people have been speculating about.
Dan East
Better known as 318230.
Install a listening device in an embassy meeting room. Records many weeks of conversations. Does not broadcast. Also has a radio receiver.
Prior to an electrical storm, drop a package on the roof using a rapid-descent parachute. It looks like a chimney or AC unit, with a large pole on top that functions as a lightening rod. The box sends a signal to the inside recorder that tells it to broadcast a burst of encrypted data to the box then when lightening hits the pole, it becomes a plasma attenna that can broadcast the data over a long distance. Oh, and the electricity from the lightening powers the whole operation. Then the box self-destructs on the roof.
Seth
$5 / month hosted VPS on linux = awesome!
As far as the micro fractures thing? That's not quite correct. What you get is a build up of internal stresses. This weakens the glass, and reduces it's ability to handle thermal and mechanical shocks. I may be mistaken, but I believe this is related to the coefficient of thermal expansion - basically as the outside of the glass cools it contracts. This leaves the cooled glass pushing against the pressure of the still molten glass, and once completely cooled, that stress remains.
That's all pretty much a non-issue though. Controlled cooling in an annealing oven takes care of it well enough.