EMP vs Faraday cage
This is a discussion on EMP vs Faraday cage within the Bushcraft - Primitive Skills - Survival Skills - Camping forums, part of the Related Topics category; This subject seems difficult to find definitive answers. I understand that an EMP can fry unprotected electronic circuitry, I'd like to know effective ways to ...
March 14th, 2014 11:49 PM
EMP vs Faraday cage
This subject seems difficult to find definitive answers. I understand that an EMP can fry unprotected electronic circuitry, I'd like to know effective ways to protect it.
It seems logical not to put emphasis on delicate items that would need shielding. My food will be unaffected, along with knife, gun, water, etc, however most vehicles won't work, small engines (without points) including generators, radios/comm, electronic locks on gun safes, even my digital watch, and forget about cell phones completely. These high-end flashlights may even fail?
Granted its best not to depend on modern technology, but it is hard to avoid. It seems to me that some sort of Faraday cage would be a good idea to use and store sensitive devices. It seems to be pretty cheap to do at some level. I really don't want to be on the same technological level as a caveman!
I've read that a microwave oven makes a perfect Faraday cage? Ok, so if it is, would it need to be plugged in, IOW's grounded?
How about those aluminum attaché cases we often store pistols in? Grounded or not? Seals up well enough?
What if the contents inside touch the "shielding", or should they be wrapped in something non-metallic??
Pickup truck tool box? Gun safe?
Do any of these seal up well enough?
If sealing is very important, what if you stored the aluminum attaches inside a truck tool box?
I thought I read somewhere that cars were supposed to be one day manufactured to be EMP proof? Of course a GPS would fry, and we should all rely on a magnetic compass, but will that magnetized compass be affected?
I think there is a lot of questions about this, simply because we have never experienced an EMP of mega-scale proportions. Certainly we've learned things from smaller scale trials, but what are the hard and fast rules on protecting against it at the home level?
Mrs PPKheat, not happy right now with the notion of sleeping under chicken wire decor'.
I would consider but this EMP stuff could really compound survivability efforts.
March 15th, 2014 12:14 AM
I'm also interested in this. I just finished reading One Second After and it got me thinking. Although I don't have anything I'd really like to protect. A radio would be nice but what good is it without the other end working. I decided it would be better to spend time learning about non EMP effected energy sources like hit or miss engines
March 15th, 2014 01:05 AM
I'll bite, because I'm an Electromagnetic Compatibility (EMC) engineer, and part of my job is testing/hardening devices against EMP.
Let's get some misconceptions out of the way first.
The media/popular culture has massively overstated the effects of EMP. See this report for practical effects of EMP on vehicles.
You are not looking at the stone age for the conceivable future. Massive inconvenience? Possibly. Not stone age. You're kidding yourself if you think that an EMP is a credible threat that could reduce our society back to primitive origins. Yeah, you would need to be prepared for some time without power and some looting, but not the stone age for the conceivable future.
EMP's effects on various electronics are going to depend on how well the coupling path into said circuitry is tuned to the frequencies of the EMP. Just like your radio, if you don't have an effective antenna, you're not going to receive the signal. In this case, it's unwanted so that's a good thing, but the same principles apply. Your watch's dimensions are so small that most likely, it's going to survive. There is no multiple GHz frequency content to traditional understandings of EMP waveforms. Crash course in antennas: higher frequency signals need/use smaller antennas. This is why EMP couples effectively to power distribution networks. Mains feeders make good antennas.
If there is any advance notice, you can probably save a significant portion of what's in your house by simply disconnecting your electrical mains. Might take some time for the utilities to get the juice back on, but your stuff will be protected from conducted coupling through the power distribution network.
RE Fariday Cages:
The shielding effectiveness of any enclosure is directly related to the largest hole in said enclosure. A hole is anywhere, and I mean anywhere, seams, screw holes, etc. If you need to calculate a rule of thumb for how much leakage a given aperture has, its shielding effectiveness in dB is 20*log10(lambda/2L) where lambda is the wavelength in question and L is the longest dimension of the aperture. Wavelength of consideration is most easily calculated by considering traditional Mil-STD EMP waveforms, which have rise times on the order of 3 nanoseconds. Using the rule of thumb that bandwidth = 0.35/rise time, and applying some conservatism, you need to be concerned about attenuating frequencies up to 300 MHz. C = Lambda*F, rearrange, and you find that your wavelength is 1 meter.
So, let's say that you want 80 dB of shielding effectiveness, (factor of 10,000, bringing your typical expected 50 kV/m EMP down to 50 V/m, which most cell phones can produce in close proximity with ease). 20*log10(1/2L) means that you need to keep apertures TINY. On the order 0f 0.05 mm.
So no, you don't want to use a microwave. What you do want to do is pick out some supplies that you know will keep electronically speaking, head out to Home Depot, and buy some aluminum flashing, plywood, and LOTS of screws. Build yourself a box and shield it inside and out with flashing, making sure to overlap all seams by a good 6 inches and secure the flashing at least every inch with screws at overlap points. The overlap produces LOTS of capacitance which helps to short out the field above and beyond what a simple straight-walled enclosure could provide.
Pile your stuff inside, seal it up, and don't open it unless you need to add other stuff or check on how your supplies are holding up.
Alternately, if you have lots of $$$ lying around, buy yourself one of these to store your supplies in.
Universal Shielding | RF Shielded Room, Solid Wall Rooms, Shielded Enclosures
For fun reference and further reading, Google MIL-STD-461 RS105 and read away. You can get an idea of how the military tests for EMP, what the waveforms look like, and lots of other stuff.
March 15th, 2014 08:36 AM
Thanks for your input, and feel free to add more. This is exactly what I wanted is some definitive answers, there are too many misconceptions.
Originally Posted by ZacMan1987
Please check back later on this, I have some more questions about the points you made. I'm not questioning you whatsoever, but I do want to learn more.
March 15th, 2014 09:59 AM
Below are two links that I found in the past and seemed helpful and credible. The biggest practical issues for me were: Would I actually use something like this every single day to make it worthwhile? (things don't tend to go wrong on schedule); What would I want to save?; Would it even matter if nothing else worked? Any tool is only valuable if it is there (or being used) when needed.
What I personally determined is that some things that could be helpful but not used daily (e.g., EOTech holographic sight and spare batteries, night vision goggles, portable radio with batteries, a GPS, and thumb drives with personal information and videos) might be worthwhile, while things like a mobile phone or computer would probably have less immediate value and would be less likely to be in storage when needed. So, FWIW.
I guess that I'm limited to one video per post, so I'll post the second video next -
March 15th, 2014 09:59 AM
Here's the second video -
March 15th, 2014 10:06 AM
Just wrap everything in tin foil.
I have put this comment back because I deleted it in error thinking that it was an off topic yuk yuk comment and I was informed that it was not.
I carry a gun, because a Cop is too heavy.
Second Amendment: The difference between politicians and rulers.
U.S. Army, Retired
NRA Benefactor Life Member
March 15th, 2014 10:10 AM
Would disconnecting the mains require actually disconnect ing the wire or simply throwing the breakers ? Additionally what type of things ( batteries etc) would be affected that we would not suspect.
We have different gifts, each according to the grace God has given to each of us.
March 15th, 2014 12:05 PM
I can't really add a whole lot here, other than to say that if you are prepared for a long-term disaster, you'll be prepared for an EMP.
You can literally spend tens of thousands of dollars on hardened equipment or functioning faraday cages. IMO, whatever electronics I have aren't worth that kind of $$ to protect.
"I eat steak primarily. That's pretty much what my diet consists of. Sometimes I supplement that with other steaks." -Jocko Willink
March 15th, 2014 12:20 PM
Electro magnetics is the one field that I always wanted to learn some basics on. The degaussing of ships and the whole eddy current thing in nukes. Trouble is early on I realized I wasn't smart enough to understand magnetics. My hat is tipped to you sir.
March 15th, 2014 03:37 PM
Please respect the OP. This thread is not posted in Humor/Off Topic. Any comments that are just posted for a "yuk-yuk" will be deleted.
Add...or ask something relevant or constructive or just move on.
Two off topic comments have been removed from this thread already.
Liberty Over Tyranny Μολὼν λαβέ
March 15th, 2014 03:46 PM
I would think that a set of two way type radios would also be something that you would want to protect so that at least some close range communication would still be possible if cell phones were kaputt.
Liberty Over Tyranny Μολὼν λαβέ
March 15th, 2014 04:48 PM
P.S. I made an order of magnitude mistake in my calculations. The previous aperture size quoted would reduce the field inside of the box to 5 V/m, not 50. Pretty much anything out there should be able to survive a 5 V/m transient field.
March 15th, 2014 05:00 PM
Very credible information taken in a scientific way. Watch this if you're interested in how to create a good shielded enclosure for your stuff.
Originally Posted by cn262
March 15th, 2014 05:15 PM
This guy not so much. FM radio is going to provide an optimistic value for shielding effectiveness because its frequency content is lower than that of an EMP, and plus, the dynamic range of an FM radio is only about 50 dB with a GREAT signal. So aside from not knowing exactly how much attenuation you actually get, an FM radio could give you a good feeling when you're still exposed.
Originally Posted by cn262
That, and come on...sunglasses? I don't think the government can do retinal scans through youtube yet...
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