Faraday cages & EMPs; fact/fiction

[strantor]

I've started watching this show called Dommsday Preppers, you may have heard about it. A bunch of mo-rons on there, and the occasional intelligent person, but sometimes hard to differentiate between them. Anyways, these doomsday types seem obsessed with faraday cages, to protect from an EMP from a nuclear weapon, or from a solar flare. They say a bad solar flare or EMP from a nuclear explosion can take out the power grid, and anything electronic. I'm 90% sure that's correct in theory, but let me describe some of the finer details and mabe you can fill me in, if there's any truth or if it's all just farce. I know nothing about EMPs or faraday cages.

#1 - To keep your electronics safe, just wrap wire mesh around a box made of sticks and put the electronics inside.
I'm almost positive this is wrong. i've seen people make a faraday cage like this, put a walkie talkie inside, and you could still communicate with it.

#2 - "The more you spend on a faraday cage, the less likely it is to work." This guy said that he keeps replacement electronic devices in metal trash cans. The metal trash cans are a faraday cage. He "tested" the principle by putting a walkie talkie in a trash can, closing the lid, and then shorting out his truck battery across the handles with jumper cables. After a few seconds, (probably right before the battery exploded) he removed the cables, took out the radios, and since they worked, it "proves" his theory that the faraday cage did it's job.
I'm pretty sure that passing a few hundred amps of 12VDC through a conductive body in close proximity to a device is not the same as bombarding it with high energy electromagnetism.

#3 - (same guy as #2) - "When an EMP hits, you won't know that anything happened; you won't feel a thing, except that the keys in your pocket will get so hot that that you'll be scrambling to get them out"
This one I'm not too sure, but common sense makes me want to write it off. I know you can heat metal with induction, they have induction forges and I've seen them work. Basically an air core transformer, pumping tons of current into steel rod at high frequency. But I don't think an EMP or solar flare would have the same effect.

#4 - The best protection is to put your devices in a faraday cage, and then put that faraday cage inside another faraday cage.
This one actually sounds plausible to me, but like I said, I have no idea what I'm talking about.

#5 - being underground is better than being in a faraday cage
sound plausible to me.

There are more I can't think of ATM, think I will post them if I remember them.

 

[DerStrom8]

Hey strantor! I don't get to see you post here often, so it's good to see you

I saw one or two episodes of that show, and to be honest, I found it mildly amusing.

#1 - If constructed properly, a faraday cage will block signal to a walkie-talkie or radio and it will not operate. Theoretically, a faraday cage would prevent damage to sensitive electronics by grounding the EMP. However, it would have to be designed and built correctly, and well-grounded, in order to work.

#2 - That guy is completely clueless. Shorting a battery across the metal handles would not cause any damage to the walkie-talkie, even if the box was made of wood or plastic. It's a DC voltage and not powerful enough to create an EMP effect. If you're going to build a faraday cage, the cost has absolutely no effect. It's a simple device, and as long as you build it correctly, it'll work.

#3 - An EMP is generally just one pulse, which is not enough to cause heating through induction. It's also probably not even powerful enough. An EMP would really only cause damage to electronics that have devices such as FETs, which have very sensitive gates. Once again, he's clueless--he doesn't know what he's talking about.

#4 - if the first cage is constructed properly, you won't need a second one, but the second one will ensure your electronics are safe in case there are some faults in your first one. It's just one of those "just-in-case" things.

#5 - If you're still talking about a massive EMP, I think that's probably true--being underground would most likely be best, but putting your devices in a faraday cage would probably be enough. Really, the only thing in danger in the case of a giant EMP is your computer and similar electronics. Otherwise, you will probably not be harmed.

 

[strantor]

Thanks DerStrom, yeah I had a bit extra time today and got bored on my other forums, so I poked my head in here and decided to ask a handful of dumb questions. Thanks for that, I find the show amusing too. My made up statistic is that 90% of those people are idiots. the other 10% I identify with; they see a problem that hasn't happened yet, and they come up with logical preemptive solutions. Did you see the one with that pothead who moved all his stuff out into the back yard and put it inside a tent? He bought a HHO generator from some dude, and they were blowing holes in a soda can with it, saying "whoah... this is awesome... this will come in real handy for doomsday...."; It was full of non-value-added flashing LEDs and looked like a movie prop.

 

[DerStrom8]

Thanks DerStrom, yeah I had a bit extra time today and got bored on my other forums, so I poked my head in here and decided to ask a handful of dumb questions. Thanks for that, I find the show amusing too. My made up statistic is that 90% of those people are idiots. the other 10% I identify with; they see a problem that hasn't happened yet, and they come up with logical preemptive solutions. Did you see the one with that pothead who moved all his stuff out into the back yard and put it inside a tent? He bought a HHO generator from some dude, and they were blowing holes in a soda can with it, saying "whoah... this is awesome... this will come in real handy for doomsday...."; It was full of non-value-added flashing LEDs and looked like a movie prop.

Hahaha, no I didn't see that one I agree, about 90% of them are total fools. In most cases, they don't know what they're talking about, and their solutions hardly make any sense. It's a good laugh, anyway

 

[KJ6EAD]

Thanks for the marketing tip. I will soon be selling Faraday helmet liners made of gold plated silver wire mesh. My new and improved models offer several stylish ground bonding drag tethers that can be clipped to your tool/utility belt for unencumbered freedom of movement.

What media company produces the show?

 

[strantor]

Thanks for the marketing tip. I will soon be selling Faraday helmet liners made of gold plated silver wire mesh. My new and improved models offer several stylish ground bonding drag tethers that can be clipped to your tool/utility belt for unencumbered freedom of movement.

What media company produces the show?

National Geographic. If you want a business partner, I can make a helluva EMP-immune perpetual motion generator.

 

[strantor]

Oh I just remebered one, they said that an automobile functions as a faraday cage. Really? Then how can I talk on my cell phone while inside of it?

 

[DerStrom8]

Oh I just remebered one, they said that an automobile functions as a faraday cage. Really? Then how can I talk on my cell phone while inside of it?

That's a very good question. It's not exactly true that it functions as an actual faraday cage. I imagine they were only referring to an automobile's ability to channel lightning strikes around the outside, and similar events. However, the windows and other places not covered by metal leave enough space for the radio waves to enter the car. A real faraday cage is completely surrounded by metal or metal mesh that cancels out (or grounds) the EM waves. A car leaves a lot of gaps.

 

[crutschow]

The theory is that an EMI or RF signal will be attenuated by a gap in a metal enclosure when the gap is less than 1/2 the wavelength of the signal. Thus the gap due to car windows will readily pass cell phone and FM radio signals but will attenuate AM radio signals.

You can also notice this effect in metal frame buildings where cell phones and FM radios will work but an AM radio often won't.

 

[strantor]

The theory is that an EMI or RF signal will be attenuated by a gap in a metal enclosure when the gap is less than 1/2 the wavelength of the signal. Thus the gap due to car windows will readily pass cell phone and FM radio signals but will attenuate AM radio signals.

You can also notice this effect in metal frame buildings where cell phones and FM radios will work but an AM radio often won't.

so what's the wavelength of an emp or a solar flare supposed to be? Or is it even known?

 

[crutschow]

The wavelength of these events can vary widely. EMP from a nuclear burst can be in the X-ray region so that's pretty difficult to shield against. Solar flairs have a wide frequency range range with significant radiation in the GHz region. For example there can be high radiation in the 10.7cm band (2695 MHz).

 

[strantor]

The wavelength of these events can vary widely. EMP from a nuclear burst can be in the X-ray region so that's pretty difficult to shield against. Solar flairs have a wide frequency range range with significant radiation in the GHz region. For example there can be high radiation in the 10.7cm band (2695 MHz).

Alright, so...

Faraday cages are usually designed so that the largest mesh openings have a diameter of 1/10 of the shortest wavelength [https://outreach.atnf.csiro.au/visiting/parkes/pkswebcamdetails.html]

for 2695MHz the wavelength is 4.4" and the mesh would need to be .44"

oh, and x-rays..

X-radiation (composed of X-rays) is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers,

getting a mesh that's 1/10th of .01nanometers is going to be impossible. Even if you made a box out of plate steel, and welded it shut with your precious electronics inside, the radiation would probably still get through imperfections in the weld, or maybe through the steel itself. So I guess this is why X-ray is used for looking through human bodies. Does this make the construction of a faraday cage for protection against nuclear EMP totally pointless? That would take the cake if so...

 

[KJ6EAD]

Find yourself an old mine that's flooded. The deeper the mine and the more rusty or salty the water, the better. Get a waterproof container for your electronics and just enough lead to sink it. Attach a 50' rope, a float and a retrieval line. Throw it in. Come back after the apocalypse and enjoy.

 

[strantor]

Lol, yeah use the radio to listen to the stations that don't exist. Maybe plug it into the socket that doesn't work.

 

[JimB]

getting a mesh that's 1/10th of .01nanometers is going to be impossible.

Correct.

Even if you made a box out of plate steel, and welded it shut with your precious electronics inside, the radiation would probably still get through imperfections in the weld, or maybe through the steel itself.
So I guess this is why X-ray is used for looking through human bodies.

X-rays are also used to examining welds on critical structures such as things which have to contain high pressures like gas pipelines, nuclear reactors.
And also where you have to keep the high pressure out, such as the hull of a submarine.

Does this make the construction of a faraday cage for protection against nuclear EMP totally pointless?

No, the x-rays will be attenuated as they pass through the steel.
The thicker the steel, the more the attenuation.

Materials which are more dense, such as lead, provide even more attenuation.
Which is why radioactive sources are stored in lead containers.

On a practical level, if you want to protect something from EMP, wrap it completely in alumininium foil and put it in a metal box with a close fitting lid (like a biscuit tin).
If that is not sufficient protection, you have far bigger problems than just EMP!

JimB

 

[Sceadwian]

By the way, there is no practical way to shield the power grid from solar flares, however over the coming years with the power industry is going to have plenty of practice dealing with them as we're just starting towards the peak of a solar cycle, the last peak solar cycle didn't have technology even a fraction of what we have today.

 

[Mosaic]

For lower frequencies the common microwave is a good example of a faraday cage containing EM Power. In addition to wrapping stuff in foil which I do to eliminate ESD when transporting raw circuits is also grounding the foil somehow. I guess with foil u can make a faraday room by wallpapering everything with foil and grounding it.

 

[strantor]

Now we're getting into foil hat territory

 

[tcmtech]

Now we're getting into foil hat territory

I prefer mine to be made with Mu metal as the first layer followed by aluminum, copper, iron, lead, and a wig.

Its full spectrum protection so nothin's gettin in or out!

 

[nsaspook]

How about **broken link removed**
https://www.youtube.com/watch?v=lQPGJSIq3ys

And it's home to: https://stargate.wikia.com/wiki/Stargate_Command