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Old 08-01-2012, 05:46 AM
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Quote:
Originally Posted by bobsmith View Post
two words: skin effect.
I would be very interested to hear how a faraday cage countering charges to a M field relates to "skin effect".

I always considered skin effect a problem associated with the "flow" of high frequency current. Not one associated with adjustement of electrons and magnetic field. I can't seem to find anything correlating skin effect and faraday cage.
Old 08-01-2012, 07:19 AM
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millenniumfly wrote: Consider these alternatives to mylar bags (from thesurvivalmom.com):

1.Tech Protect Bags – The owners of this company recommend nesting Faraday containers. NESTING GOOD, OTHERWISE SKETCHY
2.A metal garbage can MAYBE
3.Ammo cans MAYBE
4.An old microwave (mixed reviews on this one) NO
5.Heavy duty aluminum foil wrapped around individual items, wrapped in plastic, and then again with aluminum foil. YES
6.A tool box SKETCHY, PROBABLY NOT
7.Gun safe NO
8.A cardboard box or other container that has been “Faraday-ized” WHATEVER THAT MEANS
9.Holiday popcorn tins MAYBE

The very best conductors, in an affordable price range, are copper and aluminum. Steel isn't near as conductible as they are but that can be offset by using thicker layers.

Further, something like an ammo can, made of steel, could work because the metal is thick enough; however, it must have a conductive seal and no "cracks" through which an EMP could travel.

Same with a gun safe. The metal sides are thick enough, but are there cracks through which EMP can travel?

Further, is there a goldenrod in that safe? If so, you might do nothing more than conduct EMP though the wire into the safe. Not what you want.
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Old 08-01-2012, 12:17 PM
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I have one of my HF Ham Radios sealed in a "Faraday Cage". The container is a large Ammo Can that has had the rubber seal ring removed from the lid and replaced with crumpled aluminum foil in it's place.

The inside of the ammo can is lined with thick corrigated cardboard hot glued against the walls and the floor of the can and the inside of the lid. Then, foam padding cut from a camping sleeping mat is cut to tightly fit inside, providing even thicker protection from any inside contents to touch the metal walls, floor or lid.

The HF Radio, Mike, Power Cord, G5RV Wire Antenna and the Radio Manual all fit inside. Another piece of the foam padding (camping mat) is placed on top to insire that even if the ammo can is tipped over or even inverted, nothing inside can come in contact with the metal of the ammo can.

Finally, One surface of the outside wall of the ammo can and of the lid were sanded down to expose bare metal and a braided metal " grounding strap" was soldered to both surfaces to insure good complete conductivity between the lid and the ammo can. The aluminum foil gasket is about 1/2" thick before the lid is snapped tightly (and I do mean it's tight!). It smashes down and I have some extra foil sheeting folded up inside the can in a ziplock baggie to be able to replace the foil with new foil when needed after the Ammo Can Faraday Cage has been opened.

If my Ammo Can Faraday Cage works like I think it will, I will be able to open it after an event, pull out my radio equipment, throw the G5RV Antenna up in a tree and connect it to the radio, hook the radio to a 12 volt battery and start collecting informtion as well as passing information along to other radios that were also protected.

If nothing ever happens EMP-wise, my HF Radio is still well protected from lifes bumps.

While this is not a "Nested" Faraday Cage Set Up, is it good enough? Opinions?

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Old 08-02-2012, 12:57 PM
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This might help some one trying to make a faraday cage.

http://www.endtimesreport.com/faraday_cages.html
Old 08-02-2012, 02:36 PM
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Quote:
Originally Posted by goose3 View Post
I'd expect that to work. I'm presuming the lid to the jar is plastic.
It is plastic, so I also wrapped the area of the lid and somewhat below it with aluminum foil too. Then I carefully slide it off the top of the jar when I want to get inside. I can't say the wrapping over the lid comes in total contact with the foil that is wrapped around the jar, but I hope it's good enough.

Would this peanut jar idea work if I didn't have the plastic cap wrapped too? I'm assuming not.
Old 08-02-2012, 04:18 PM
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Why bother for portable electronics?

We've already seen test results for those, they aren't affected unless connected to long wire runs.

Handheld radios with 'rubber duck' antennas came through just fine.

As did nearly every vehicle tested.
Old 08-02-2012, 06:00 PM
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Quote:
Originally Posted by ncbill View Post
Why bother for portable electronics?

We've already seen test results for those, they aren't affected unless connected to long wire runs.

Handheld radios with 'rubber duck' antennas came through just fine.

As did nearly every vehicle tested.
Bill, try this experiment. Gather your favorite electronics together. One piece at a time, set off a 50kv spark one inch away from the piece. How many pieces weren't affected this time?
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Old 08-02-2012, 08:48 PM
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Quote:
Originally Posted by ncbill View Post
Why bother for portable electronics?

We've already seen test results for those, they aren't affected unless connected to long wire runs.

Handheld radios with 'rubber duck' antennas came through just fine.

As did nearly every vehicle tested.
What testing was this? AFAIK there is no testing machine that can replicate the EMP that theoretically can be generated by a HEMP device designed to emit massive amounts of Gamma Rays. They have large devices that can test whole airplanes and even warships but they produce an EMP more along the lines that were created by Operation Fishbowl in the '60's and some of the Soviet Cold War tests. Since then they have devised how to significantly improve the Gamma output.
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Old 08-02-2012, 08:57 PM
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Quote:
Originally Posted by Writer's Block View Post
Keep in mind a big part of the needs in a Faraday cage is that nothing inside touches the conductive surface outside either. Electricity and such travel THROUGH materials as easily as over them. You need something totally non-conductive that the object in the bag is completely sealed in to have even a hope of a foil bag working.

No, that is incorrect. The cage is made of a conductor, so the whole cage is always at the same potential. No insulation is needed on the inside of the cage -- there is no voltage to insulate against.
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Old 08-02-2012, 09:52 PM
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Quote:
Originally Posted by g211 View Post
No, that is incorrect. The cage is made of a conductor, so the whole cage is always at the same potential. No insulation is needed on the inside of the cage -- there is no voltage to insulate against.
Well, I would correct this slightly to say that under gausses law "there is no e field inside a continuous conductive shell".
Old 08-02-2012, 10:00 PM
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Oh, just an aside.

My LDS mylar will block cell phones. Without even being sealed.
Old 08-02-2012, 10:03 PM
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Originally Posted by MadPrepper View Post
Oh, just an aside.

My LDS mylar will block cell phones. Without even being sealed.
Mine won't when I try it near a tower. hmm
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Old 08-02-2012, 10:06 PM
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OK,

For the last time. Put your item in a zip lock bag. Wrap that bag in aluminum foil. Put that into another ziploc bag. Even a laptop will fit into one or two gallon bags covering and overlapping each end. Now add a second layer of foil around that.

You now have a double layered faraday cage.

OK. So you have a big bucks 17" laptop. Use a Kitchen garbage bag and the extra-wide foil from Sam's. It will work just fine.

Hay, I'm going to do that right now and cook my laptop in the M-Wave oven of two minutes. It is 11:06 now. Look for my next post at 11:08 plus time for Windows to boot up.
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Old 08-02-2012, 10:15 PM
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Quote:
Originally Posted by MTShawn View Post
Mine won't when I try it near a tower. hmm
No, I didn't try it more than on the coffee table. I know it's not a Faraday cage.

Just relating the fact that if I were ever trapped inside a 7 mil LDS 1 gallon mylar bag, I would not be able to phone for help!
Old 08-02-2012, 11:04 PM
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Quote:
Originally Posted by millenniumfly View Post
Consider these alternatives to mylar bags (from thesurvivalmom.com):
1.Tech Protect Bags – The owners of this company recommend nesting Faraday containers.
2.A metal garbage can
3.Ammo cans
4.An old microwave (mixed reviews on this one)
5.Heavy duty aluminum foil wrapped around individual items, wrapped in plastic, and then again with aluminum foil.
6.A tool box
7.Gun safe
8.A cardboard box or other container that has been “Faraday-ized”
9.Holiday popcorn tins
None of which can be relied upon to actually work.

Tech protect sells ESD bags at about 10 times their actual cost and claims they meet mill specs but those specs are for ESD protection, not EMP protection and these bags can't even stop a cell phone signal - which they used moments earlier in their video to prove that a microwave doesn't work; yes, they appear to protect against momentarily microwaving the phone (which would likely have been damaged if it wasn't in the center of the bag) but there are many differences between this and EMP and the bag is damaged in the process.

Popcorn tins normally have paint where the lid fits over the can; you might actually get some protection if you strip the paint off.

Aluminum foil may actually provide some protection but only if you crimp the seams properly which most instructions do not show. Aluminum has an oxide layer which interferes with electrical contact. Also, device should be insulated from the foil and not with a wimpy piece of plastic, either. Foil is very easily damaged.

Ammo cans, trash cans, tool boxes, and gun safes do not have highly conductive gasketing required for effectiveness and most of these, except the trash can, have painted surfaces where contact should be made and the trash can has a loose fitting lid.

And, no, the mylar/aluminum laminated food storage bags can't be trusted, either.
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Old 08-02-2012, 11:07 PM
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Quote:
Originally Posted by 9111315 View Post
OK,

For the last time. Put your item in a zip lock bag. Wrap that bag in aluminum foil. Put that into another ziploc bag. Even a laptop will fit into one or two gallon bags covering and overlapping each end. Now add a second layer of foil around that.

You now have a double layered faraday cage.
No, you don't.

Quote:
OK. So you have a big bucks 17" laptop. Use a Kitchen garbage bag and the extra-wide foil from Sam's. It will work just fine.

Hay, I'm going to do that right now and cook my laptop in the M-Wave oven of two minutes. It is 11:06 now. Look for my next post at 11:08 plus time for Windows to boot up.
It is an hour later, no post.
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Old 08-02-2012, 11:52 PM
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Quote:
Originally Posted by Writer's Block View Post
Which is directly related to the thickness of the "skin" as well as the material that skin is made of. AND the frequency in querstion general rule of thumb, the higher the frequency, the shallower the penetrationAs well, the skin effect does NOT account for 100% of the current, i agree and in the case of EMP generated current, a little could be all you need for damage. i continue to agreeThe skin effect means the majority of the current is on the surface, decreasing as you penetrate the radius of the conductor...it does not mean all of it remain on the surface. never claimed it did, actually i didnt make any claims, i just stated a term, but if i were to make a claim i simply would ahve said that the current distribution is not uniform throught the thickness of a conductor in many casesThe skin effect MIGHT protect you if you were touching the outside of the object when it became charged, but it won't after.
huh? the skin effect is seen in ac, not dc, so i dont quite understand what you mean.
Old 08-02-2012, 11:53 PM
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Quote:
Originally Posted by Robot View Post
I would be very interested to hear how a faraday cage countering charges to a M field relates to "skin effect".

I always considered skin effect a problem associated with the "flow" of high frequency current. Not one associated with adjustement of electrons and magnetic field. I can't seem to find anything correlating skin effect and faraday cage.
AFIK your understanding is correct.
Old 08-03-2012, 12:31 AM
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Originally Posted by ncbill View Post

As did nearly every vehicle tested.
Nope, the EMP commission testing of the vehicles was done by gradually increasing the intensity of the pulses until the vehicle malfunctioned, then the testing stopped. So many of the vehicles were never exposed to full strength EMP to determine whether or not they would be permanently damaged. Indeed, since they were reportedly financially responsible for the vehicles borrowed from other agencies, they were going out of their way not to do any permanent damage. 29 out of the 37 cars and 13 of 18 trucks tested malfunctioned. Most vehicles were not even tested to stall as the tests stopped when non-critical systems malfunctioned.
Quote:
We tested a sample of 37 cars in an EMP simulation laboratory, with automobile vin-
tages ranging from 1986 through 2002. Automobiles of these vintages include extensive
electronics and represent a significant fraction of automobiles on the road today. The
testing was conducted by exposing running and nonrunning automobiles to sequentially
increasing EMP field intensities. If anomalous response (either temporary or permanent)
was observed, the testing of that particular automobile was stopped. If no anomalous
response was observed, the testing was continued up to the field intensity limits of the
simulation capability (approximately 50 kV/m).
In addition, it was expected that while many of the vehicles might have otherwise survived, the malfunctions could result in auto accidents.
Quote:
The ultimate result of automobile EMP exposure could be trig-
gered crashes that damage many more vehicles than are damaged by the EMP, the conse-
quent loss of life, and multiple injuries.
It did appear that vehicles were not damaged if they were not running.
Old 08-04-2012, 01:08 PM
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Quote:
Originally Posted by technoprepper View Post
Aluminum foil may actually provide some protection but only if you crimp the seams properly which most instructions do not show. Aluminum has an oxide layer which interferes with electrical contact. Also, device should be insulated from the foil and not with a wimpy piece of plastic, either. Foil is very easily damaged.
Yeah, I noticed that about the aluminum foil I'm using. I hold it up to a light and can see little tiny pinprick holes in it. But would that really keep it from working as intended against EMP? I mean, wouldn't the pulse current just jump from the foil where it's solid right over the pin holes since the distance would be so short?
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