nonmetal 'stealth' antennas - Page 1
Forum section: electronics / rf-microwave

author: CopperCone
author_rank: Super Contributor
timestamp: August 16, 2017, 07:54:08 am
content: Assuming someone wants to design something that's stealthy, is it possible to make an antenna out of something like graphite, carbon fiber, or some kind of other electrically conductive material that has trouble showing up on a metal detector?Are there downsides to these implementations?I guess aluminum is used alot, but how about nonmetals?I guess a (non CIA) benefit might be environmental resistance, ease of application, etc.. something like patterning a bicycle with a fractal antenna comes to mind to prevent theft. (fast vacuum deposition of carbon on the frame etc)

author: tszaboo
author_rank: Super Contributor
timestamp: August 16, 2017, 07:57:40 am
content: I'm going to ask you, not to use this forum to design anything illegal or nefarious.

author: CopperCone
author_rank: Super Contributor
timestamp: August 16, 2017, 07:58:23 am
content: Quote from: NANDBlog on August 16, 2017, 07:57:40 amWould you rather have some people thinking its not possible? I am interested in bug detection not manufacture. Don't threaten me.gee, nothing showed up on my super sensitive metal detector on this plastic bottle. I won't bother checking for a energy harvesting bug with the non linear junction detector.Posts like this, on a public forum, just make me think 'yea i'm totally doing that, i don't want anyone to find any information on google'who you workin for lol?

author: Rerouter
author_rank: Super Contributor
timestamp: August 16, 2017, 08:30:10 am
content: He was not threatening you, he was asking nicely that we dont want illegal activities tied back to this forum. And bypassing metal detectors sounds like exactly that.The only comparable knowledge i can offer is on a shirt i embedded some I2C temp sensors on, with 10 micron copper didnt get picked up by a hand waver when i went to an expo.

author: CopperCone
author_rank: Super Contributor
timestamp: August 16, 2017, 08:53:23 am
content: Where is it illegal to RF physics of a non metal?North Korea maybe?thats just trying to scare people away from posting in this thread. its completely ridiculous. It has a chilling effect on the discussion. And it seems like someone is frustrated because their secret weapon is revealed (just a bit, I am not completely serious here).if its possible then people should be aware so countermeasures can be developed and used appropriately. Otherwise it can proliferate and used to gather data on a large scale unimpeded.And I also listed peaceful/non espionage applications.Copper and aluminum are popular choices for antennas. I don't think most metal detectors will pick them up in small amounts. (RFID tags I believe are just metalized).The problem with exotic materials like carbon is that maybe X-ray might have trouble picking it up (if automated to look for certain things), and that more sensitive metal detectors might also have trouble picking them up ( i believe stuff exists for nonferrous metals).Also, some people might have the illusion of safety scanning a plastic object for metal, and trust the plastic object, especially when a NLJD is not available (since they cost north of 5000$ typically)

author: dmills
author_rank: Super Contributor
timestamp: August 16, 2017, 10:19:18 am
content: An aerial has to be sufficiently conductive, but that is about the only requirement.Carbon fibre, sure, going to be a bit lossy, but if you can live with that (And you link budget will tell you), no problem.Metallised plastic? Also clearly possible and you could print matching caps by metallising the other side....Printed carbon (Like they use for switch contacts in cheap things), again somewhat lossy but I not see why not.One usually does not do these things because they are all inferior to other ways to skin the cat for most applications.Incidentally, Peter Wright tells a story in his (awful, don't bother) book "Spycatcher" about a cavity with a membrane and an attempt to use it as a microphone by hitting it with a LOT of microwave power from across the street and picking up the Doppler, no junction required.73 Dan.

author: tszaboo
author_rank: Super Contributor
timestamp: August 16, 2017, 10:31:13 am
content: Quote from: CopperCone on August 16, 2017, 07:58:23 amQuote from: CopperCone on August 16, 2017, 08:53:23 amWow, you have some mental health issues.

author: SparkFly
author_rank: Regular Contributor
timestamp: August 16, 2017, 12:18:00 pm
content: Perhaps not quite what you are thinking of, but an example of a 'stealthy' non metal antenna would be a plasma antenna. Because of theplasma frequency, the antenna is effectively invisible to radio waves greater than this frequency. Plasma frequency is given by:Where ?pe= plasma frequency, ne= density of electrons, e = electric charge, m*= effective mass of the electron, ?0= permittivity of free space.Further reading can be found in Plasma Antennas, T. Anderson. I highly recommend this book.

author: alanb
author_rank: Frequent Contributor
timestamp: August 16, 2017, 02:35:19 pm
content: Quote from: dmills on August 16, 2017, 10:19:18 amI haven't read Spycatcher but this may be what he was r4efering to.https://en.wikipedia.org/wiki/The_Thing_(listening_device)

author: dmills
author_rank: Super Contributor
timestamp: August 16, 2017, 03:37:21 pm
content: That looks right.For such a poor IMHO book. its publication sure did cause a **MASSIVE** fuss.Regards, Dan.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 16, 2017, 07:39:42 pm
content: Relevant,http://hamwaves.com/dielectric.rod/en/index.htmlTim

author: CopperCone
author_rank: Super Contributor
timestamp: August 16, 2017, 08:12:30 pm
content: the good thing about 'the thing' was that you need to illuminate it with CW microwave. This means you can just hook up a SA to a broad band antenna and detect it. I think it required fairly powerful irradiation.

author: cdev
author_rank: Super Contributor
timestamp: August 16, 2017, 08:20:37 pm
content: That actually happened at the US Embassy in Moscow in the 1950s and it is historic, part of our electronics heritage.The Russians turned the seal into a sensitive but passive listening device that modulated microwave radiation beamed at it. It was only picked up by chance, they easily could have missed it.Stalin was a truly evil man, BTW. No shades of grey there.Quote from: dmills onTodayat 04:19:18

author: CopperCone
author_rank: Super Contributor
timestamp: August 16, 2017, 08:26:48 pm
content: all of those guys were. starve india, gas people, burn cities, drop nukes, work people to death... the world went nuts for a few decades

author: hermit
author_rank: Frequent Contributor
timestamp: August 16, 2017, 11:29:51 pm
content: Depending on the application the best way might to be to simply make it look like something else or cover it. A piece of carbon fiber that looks like an antenna will still draw attention. The wire holding the picture on the wall? Not so much.

author: cdev
author_rank: Super Contributor
timestamp: August 16, 2017, 11:56:49 pm
content: People are still being worked to death. You can even see them from space.But I am getting off point.Please, it bothers me when people attempt to discuss things like evading metal detectors here.Just my $0.02

author: cdev
author_rank: Super Contributor
timestamp: August 17, 2017, 12:02:00 am
content: In North Korea, since you brought it up, its illegal to teach anything like electronics to a very large percentage of the population. Their education is quite limited to what they will need in the dangerous professions they are limited to. Mining, manual labor, farming using themselves as draught animals. They have to live in very limited areas of the mountains, where there typically is no electricity too. So what do they need electronics for, right?Keep some perspective.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 17, 2017, 12:13:52 am
content: People have used various non-metallic objects as antennas from time to time over the years, from theproverbial "piece of string" (they soaked it in brine), to trees.The one thing they all have in common is poor efficiency.Ashermitsays, there are a lot of metallic things in any room-----why not use one of them as an antenna?

author: CopperCone
author_rank: Super Contributor
timestamp: August 17, 2017, 05:05:04 pm
content: that sounds almost like a survival technique, to use salt water to make an antenna. Perhaps if stranded on a damaged ship.

author: Howardlong
author_rank: Super Contributor
timestamp: August 17, 2017, 05:13:52 pm
content: Quote from: T3sl4co1l on August 16, 2017, 07:39:42 pmI was thinking about dielectric horns as the classic solution, where the Er of the dielectric makes it act like a lens in much the same way as refractive index of glass works with optics, but I do like that dielectric rod!