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Has anyone any advice on building a Faraday cage for VHF - 20GHz or higher? Answered

Hi, I've found lots on the 'net about building Faraday cages, but most of these are a couple of years old and targeted at lower frequencies up to around around the 2.4GHz range. I'm looking at making a Faraday cage for a room, to shield against a recent phone tower upgrade with transmissions now in the 19GHz range. (I've seen some other towers, fortunately not near me, recently approved for transmissions at 38GHz.) From what I've read so far, I'd need about 20 layers of heavy duty alfoil to come close to getting effective shielding, or wire with holes less than 7.5mm wide, which is going to be pretty tricky. Just wondering if anyone's tackled this problem before and, if so, how?

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Downunder35m

3 years ago

Get or make conductive paint ;)
Once all is covered mount a grounding plate onto it and paint over it, connect a good ground and all should be fine.

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iceng

3 years ago

How much volume do you need to protect ?

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icengiceng

Answer 2 years ago

A large safe or a military safe closet.

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rickharris

3 years ago

Think microwave. The higher the frequency the smaller the holes. When the holes get closed up completely ALL frequencies are blocked. As said aluminium foil is cheap and will work fine.

On the other hand I can't find any conclusive evidence that such a sensitivity exists

http://www.livescience.com/52978-electromagnetic-h...

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powerup

3 years ago

It's to provide relief from sensitivity symptoms which are very debilitating. (I'm very sensitive.) All the towers in the area are receiving licences to transmit at 18-19GHz (some even higher). I'm struggling heaps healthwise even for short periods in town where these upgrades have been effected, and towers closest to my home are to be upgraded in the next couple of weeks. Hadn't thought about the foil insulating panels - thanks for that suggestion Quadrifoglio. (Not sure I'll tolerate the inner insulation material from a chemical perspective but worth checking out.) As for the lonely existence - I'm retro/living in the '80s. All my internet is cabled, use a corded phone, watch all my movies and TV streamed on the cabled internet and same for listening to the radio. :-)

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Quadrifogliopowerup

Answer 3 years ago

Except for the music, the 80’s were a good time, IMHO.

One “good” thing about the higher frequency RF is that it is more attenuated by walls. This chart only goes up to 5.0 GHz but it give you an idea of the frequencies and what happens as they increase http://www.l-com.com/content/wireless-frequency-overview-chart.pdf. People liked 900 MHz phones because they could go out way out into their yards and still get reception.

WiFi blocking wall paper http://www.brit.co/wifi-wallpaper/. If it keeps it from getting out, it keeps it from getting in.

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Josehf Murchison

3 years ago

What is it for?

If you want an EM free lab retired steel shipping containers work great.

Just have it grounded and when you close the door nothing gets in.

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Quadrifoglio

3 years ago

1.9 GHz and 3.8 GHz are cell phone frequencies and are normally attenuated by external walls. However, windows are a different story. Have you ever watched someone cozy up to a window for a better signal? A fitted frame with RF blocking film or fabric would be easy enough in a rented space.

My house is terrible (good?) for any external RF (cell phone, OTA TV) because it is wrapped in foil covered insulating panels behind the bricks. They are lightweight so I guess you could stand them up around your room and use foil tape on the joints and use an oversized removable one over the door. That still leaves you with the floor and ceiling. Also, from experience picking up OTA TV, RF bounces off everything; hills, towers, buildings, signs, and yes, even the airplanes taking off and landing at the airport.

A problem you will run into is figuring out what levels and signals you are trying to attenuate and if your efforts are effective. A spectrum analyzer could tell you but from what I have seen, they are very expensive. Maybe someone could suggest a more economical solution. This would also allow you to better evaluate the health risks.

It may be a pretty lonely existence in the room without WiFi, cell phone, TV, and other electronics. Although sleep and real books are good things.

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powerup

3 years ago

Pretty large one - my bedroom so I have at least one room I can spend large amounts of time in and not suffer from sensitivity symptoms. At a guess (haven't measured it up yet) 5x5x3m.

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powerup

3 years ago

Thanks heaps guys, particularly for all your information, Jack. I had gotten that far with my research, and was thinking maybe some aluminium insect screen (but might still need a couple of layers to make sure the hole size was small enough). Paint has a few issues for me - I'm in a rental property, but I'm also pretty chemically sensitive so unlikely paint would be a viable option. Was thinking I could try to find some strong painter's tape or something that won't mark the walls that I could put a lining of butcher's paper over the walls and ceiling first to protect them from marks, and then tape the screen over the top. Just one question re grounding - if someone is very sensitive even to low frequencies (ie. non-RFs from power points etc), I'm guessing I'd need to ground the faraday cage, even if I didn't use any of the points/light switches etc in the room, because there would still be power running from the mains to those points (unless I switched them off at the mains)? Am wondering even with grounding that might still be an issue unless I switch off at the mains (because powerpoints and light switches are grounded, but I feel those).

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Jack A Lopez

3 years ago

A perfect Faraday cage is easy to describe. It is simply a enclosed conductive surface. In this ideal case, the enclosing is perfect; i.e. no holes, and the conductivity is perfect too, allowing currents of arbitrary size to flow anywhere in this conducive surface, if they want to.

A practical Faraday cage is an approximation of the ideal, with good enclosing, and good conductivity, over the whole surface of the cage.

The trouble with making a Faraday cage for microwave frequencies is the size of the largest allowable holes must be very small. How small? Well, a rule of thumb is to say the holes must smaller than about 1/10 the wavelength of the radiation you are trying to block.

That is according to a discussion I found here:

https://www.quora.com/What-size-of-mesh-should-I-u...

And this rule of thumb seems believable, considering other things I have read about antennas and waveguides and such, physical shapes for guiding electromagnetic radiation.

The wavelength of 30 GHz radiation, using the formula you learned in physics class, (3.0e8 m/s)/(3.0e10 s^-1) = 1.0e-2 m = 1.0 centimeter =10 mm. So that suggests a maximum hole size of about 1/10 of that, or about 1mm.

So I guess that rules out poultry netting, a.k.a. chicken wire.

I think aluminum foil, or conductive fabric, would work, if you could find a way to do the seams so there's good conduction at the seams too.

Also maybe you want a door for this room also? The same problem with conduction at the seams, applies to edges around the door frame.

There are places that sell conductive fabric, conductive paint, for EM shielding, like,

http://lessemf.com/

LessEMF seem to know their stuff, but the shielding they sell seems kind of pricey. I shudder to think what it would actually cost to shield, for microwave frequencies, every wall of a room, and under the carpet too, as well as whatever kind of seal or gasket is needed for the door.