Gun safe as a faraday cage


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battlecry
February 29, 2008, 10:28 PM
Locked my cel phone and home wireless phone inside the safe. Dialed them and I could hear them both from outside the safe :eek:

I had a feeling the door gap could pass RF or microwaves but finding out was a letdown. I am going to order some 3M embossed EMI tape to place around the door and report back. Hopefully I can make it an OK place to store some radios and such.

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Dave P
February 29, 2008, 10:36 PM
Uh, why??

Huge gaps around the door will let in a lot of energy. And unless you want to strip off the paint at the joints (to get low impedances) , the tape won't help much IMO.

TexasRifleman
February 29, 2008, 10:37 PM
You worried about an EMP or something?

I've heard, though never tested it, that a microwave oven makes a decent Faraday cage.

battlecry
February 29, 2008, 10:41 PM
My cell phone works inside my microwave oven :confused:

Makes you wonder.

41magsnub
February 29, 2008, 10:47 PM
My cell phone works inside my microwave oven

May I ask how you tested that? Does it work while it is running?:neener:

DoubleTapDrew
February 29, 2008, 10:48 PM
Why are you concerned about RF frequencies getting inside? Would an EMP from a nuke or something permanately damage electronics or do they shut down until the pulse passes then work again? I've always wondered that. If they are permantely damaged it's not like there will be any radio broadcasting going on anyway.
Seems like there would be better options than a gun safe for protecting against that. Some people use tinfoil hats :p

musher
February 29, 2008, 10:48 PM
Don't you need to ground the safe to make it work?

GhostlyKarliion
February 29, 2008, 10:51 PM
the key component to a faraday cage is that it's grounded and has no pass through holes larger than the desired frequency, a solid metal box will work fine, as long as it's grounded.

try getting a small sheet metal screw and driving it into an inconspicous part of the safe, wrap a copper wire around it and either get a plug from wally-world to wire the ground to (please make sure you stick it in the ground, the single hole below the other two) or just stick the other end of the wire in the ground socket in a plug, odds are that the safe isn't grounded anywhere.

also, instead of using tape for the door, you could install cut pieces of metal around the door openings, but your safe shouldn't be leaving any light passage holes anyway.

strat81
February 29, 2008, 10:57 PM
Did someone mention tinfoil hats?
http://www.tfhp.org/images/tinfoil-hat.jpg

Deacon Blues
February 29, 2008, 11:00 PM
Are you worried about the FBI spying on you? I find it highly unlikely that anyone is listening through my wife's cell phone, but I don't like the idea of enabling it through inaction. My microwave oven does work, although surprisingly a steel ammo can does not. :scrutiny: You could always construct a metal sleeve of some sort for the phone.

Snagglepuss
February 29, 2008, 11:01 PM
I thought an EMP only damaged electronics that were in use. If the radio is off, not plugged in or without batteries, there would be no damage. This is just what I thought, not what I know.

Cesiumsponge
February 29, 2008, 11:07 PM
Needs to have a very good RF/earth ground if you want to protect something I assume is quite valuable. You'd probably want to stake your own dedicated ground in the backyard with a network of 8' copper pipes driven into the ground. Consult some ham radio guys on how to make a good, dedicated ground.

Devices that aren't powered can still be damaged. The pulse creates incredibly high energy densities and it'll induce high voltages in anything wanting to be a receptive antenna. Considering semiconductors in general operate at voltages of 12VDC or lower, it wouldn't take much to damage them.

benEzra
February 29, 2008, 11:29 PM
I thought an EMP only damaged electronics that were in use. If the radio is off, not plugged in or without batteries, there would be no damage. This is just what I thought, not what I know.
No, EMP fries things by the induced current pulse. The pulse usually isn't big in absolute terms, but is big enough to fry transistors on a microchip, and whether it is turned on or off is irrelevant.

You may be thinking about power surges, which are transient overvoltage conditions in your wall AC that can fry something that's plugged in and turned on. But that's not EMP.

Sixtigers
March 1, 2008, 12:16 AM
The last couple of posts were spot on. A strong enough EMP burst ruins your electronics by inducing huge (comparitively) voltages across solid-state microcircuitry--basically, anything with chips. Standard solid state stuff--resistors, capacitors, chokes/coils, etc...and most transistors are large enough that the voltages involved don't do any damage. Microcircuitry, however, or 'chips'--that's a different story. A microchip is basically anywhere from four to several million transistors--little teeny-tiny transistors, microscopic in size. Ever walk across a carpet, then touch a doorknob? That shock you feel is on the average of about 50,000 volts. Very little amperage (thank heavens!), but very high voltages. An EMP burst generates these same differences in electrical potential (or 'voltage')That voltage blows big craters (well, microscopic craters, actually...but you get my drift) in the "world of teeny-tiny transistors", or microcircuitry. If you put an ESD damaged chipset underneath a microscope and observe the damaged area, that's exactly what it looks like. Like bombs went off in microcircuitry land.

These damaged chips can no longer function. Unfortunately, it does not matter whether or not your solid-state device is plugged in or not, or powered up or not--the EMP burst travels through the air. Thankfully, it's usually fairly localized. However, if an EMP burst takes out a power plant or telecommunications facility, the fact that your personal electronics may function does you no good, without power or access. And that's the true danger of an EMP burst.

I don't know if a solid-steel, grounded box would work as a faraday cage. The most important thing is the grounding--that cannot be overemphasized. When these guys tell you to hook it up to house ground, by all means--do it. But NOT through a household 115V AC socket's ground connection. If you want a successful cage, you need to connect to your house's actual grounding point, and you need to do it with some serious cable. I'm looking at the cabling we use for our cages here at work, and for our ESD benches, and the grounding cable is composed of stranded copper line (think automobile battery cables, only where the individual strands are the same gauge as the wire in clotheshangers) approximately 1/2" thick, 3/4" in some instances. The copper rod pounded in behind the shop is about 12 feet long, and provides our ground.

Our (I'm a military contractor) faraday cages are made out of copper cloth. I'm not an engineer, and don't quote me, but I'm fairly sure that a solid-steel cage isn't as effective as a grid--something to do with induced voltages across a grid draining more effectively than what is, effectively, a big friggin' antenna. Key factor: Grounding.

Not sure why you'd want to save your cell phone, anyway. In the event of an EMP, I'm thinking cellular communications won't be viable. An extra computer/ECU for your car, a hand calculator (or two), maybe hand-held talkies/CBs and shortwave trunk scanners...that kind of thing, sure.

The gentleman that are pointing out that your 'cage' must be grounded

atblis
March 1, 2008, 12:38 AM
Just wrap your phone radio in Aluminum foil. Grounding isn't needed.

DoubleTapDrew
March 1, 2008, 12:49 AM
An extra computer/ECU for your car
That's a dang good idea. However if you were the only working car on the road I think you wouldn't want to be anywhere near it if you ever plan on dropping below 60mph

Dravur
March 1, 2008, 01:09 AM
my dog in my safe, cuz it is spying on my from the chip in his head. The FBI put it there.

If you have an EMP pulse in your neighborhood, you might have some other problems....

Thin Black Line
March 1, 2008, 07:34 AM
If you're close enough for EMP to fry your electronics, you'll probably also be
close enough to the blast to feel some of the heat and experience the
subsequent fall-out to not worry about listening to the radio afterward.

TexasRifleman
March 1, 2008, 09:36 AM
you'll probably also be
close enough to the blast to feel some of the heat a

One of the fears during the Cold War was a space based detonation of a nuke for just this reason.

A 120km altitude detonation could have an EMP range as far as 1000km

brickeyee
March 1, 2008, 09:42 AM
It does not take much metal to attenuate an EMP pulse.
0.060 aluminum does a good job for the fast rise time pulses.

The biggest problem is holes and joints in the 'skin'.
The magnetic portion of the pulse can produce a large voltage across any joint that is not suitable bonded (and the bond needs to work at the frequencies of interest, think many 100s of MHz).
Opening must be less than 1/10 of the wavelength for the same frequencies.

The most common way to protect equipment is to use a nuclear event detector (NED, just a phototransistor in a metal can) to immediately crowbar the power supplies.
With no power and a decent enclosure electronics survives rather well.

Long conductors (think power lines) are harder to protect.
They can couple very large voltages and currents from the pulse, and fuses are often way to slow (milliseconds) to respond to the pulse (nanoseconds) before damage is done to transformers and other devices with insulation.


As for range and blast proximity, the ideal way to create a destructive EMP pulse would be to set off a nuke at the edge of the atmosphere above the target.
Even places slightly past actual line of sight from the detonation will get slammed by the pulse.
Set one off over the middle of the US and you could disrupt things from coast to coast with no other damage on the ground.

OMGWTFBBQ
March 1, 2008, 09:57 AM
If you need a cheap Faraday cage for small stuff, just take an ammo can and coat the inside with Plastikote truck bed liner or something else that will serve as an insulating barrier, hell, you don't even need to get that fancy, it should do for radio equipment and such.

MaterDei
March 1, 2008, 09:58 AM
If you can remove the antennae on your phones, that will help.

hqmhqm
March 1, 2008, 10:04 AM
I don't understand why grounding the cage makes any difference at all to what is inside. Is it voltage difference across the components inside that kills them, and the faraday cage is a shield that makes a uniform voltage over it's surface. It should not matter too much what the "absolute" voltage level is. It's like when those guys work on live power lines, as long as they are the same voltage as the line, there is no voltage difference, and hence no damaging currents. In fact in that case you don't want to ground the guy, you want him to float up to the voltage he is working on.

sacp81170a
March 1, 2008, 10:05 AM
When these guys tell you to hook it up to house ground, by all means--do it. But NOT through a household 115V AC socket's ground connection. If you want a successful cage, you need to connect to your house's actual grounding point, and you need to do it with some serious cable.

I ground radio and computer equipment the old fashioned way, through the plumbing. Water supply lines(especially copper) are great and you can get grounding straps for them at most hardware stores. Alternatively, you can buy a copper sheathed steel grounding rod about 8 feet long at Lowe's, pound it into the ground until only a couple inches are sticking out and ground to that. The advantage of using your home's plumbing is that condensation on the pipes makes even better contact with earth than a dry grounding rod. When we put the grounding grid in for my server room, they installed a drip system to keep the ground moist and provide reliable contact.

If you need a cheap Faraday cage for small stuff, just take an ammo can and coat the inside with Plastikote truck bed liner or something else that will serve as an insulating barrier, hell, you don't even need to get that fancy, it should do for radio equipment and such.

Good for shielding M6 blasting caps from RF when onboard aircraft, too. ;)

RoadkingLarry
March 1, 2008, 10:05 AM
Nuke 'em from high orbit, it's the only way to be sure!

230RN
March 1, 2008, 10:07 AM
This is a test of moderator response time, right?

QuakKillz
March 1, 2008, 10:19 AM
http://www.glumbert.com/media/highpower

armabill
March 1, 2008, 10:20 AM
Line your safe with 1" thick sheets of lead and coat the outside with 1/2" of tin foil.

This will protect the inside from all EMP's and from Superman.

Chipperman
March 1, 2008, 10:27 AM
This is a test of moderator response time, right?

Invalid test. They always sleep in on Saturday morning.

Dave B
March 1, 2008, 10:32 AM
This is slightly off topic, but how could I store a small GPS and hand held radio aboard a boat to protect them from a lightning strike? Maybe that ammo can with the rubberized liner? I've had that happen, and all electronics get fried.

Snagglepuss
March 1, 2008, 10:37 AM
Thanks for clearing up my question about on or off electronics being damaged. Obviously we have some very, very intelligent folks in our midst.

XD Fan
March 1, 2008, 10:38 AM
This is slightly off topic,

Isn't the whole thread? Interesting discussion, but is this gun related? (sincere question, not being a smart aleck)

Pat-inCO
March 1, 2008, 10:38 AM
I don't understand why grounding the cage makes any difference at all to what is inside.
Because without the ground, the "cage" is nothing more than one side of a capacitor (which passes changing voltages).

FieroCDSP
March 1, 2008, 11:07 AM
I don't understand why grounding the cage makes any difference at all to what is inside. Is it voltage difference across the components inside that kills them, and the faraday cage is a shield that makes a uniform voltage over it's surface.

An EMP is a different form of "electricity" from line voltage.. When it hits something, it has to have somewhere to go. Now, since it's free-floating electrons that are disorganized, they will naturally attach themselves to anything metal in an attempt to sort themselves out and to flow to the nearest ground. The issue with frying electronics is that the circuits cannot dissipate the energy fast enough, it builds up in the weaker portions, and cooks silicon.

To protect against that kind of power, you need a surface to "recieve" the energy, and a massive ground to send the now-organized energy somewhere at a rate faster than it can build up to a damaging level.
Copper fabric is the ideal affordable conductor. A wide surface area with a high conductivity collects a large amount of energy in a short amount of time. Copper conducts better than steel, especially painted or coated steel.

TO remove the energy at a high rate of speed, you need a large ground wire and a large ground. THe copper pipe array is a nice idea. To work effectively, though, you'll have to split the ground wire into equal lengths to each ground rod to provide equal "pull" and distribution.

At least, this is what makes sense to me. YMMV :D

sacp81170a
March 1, 2008, 12:52 PM
Isn't the whole thread? Interesting discussion, but is this gun related? (sincere question, not being a smart aleck)

Actually, to get it kinda sorta back OT, I was thinking of getting one of those fancy Nikon Laser IRT scopes. If I hadn't chanced on this thread I would probably have stored it in the old gun safe and assumed it was safe from lighting strikes and whatnot (even though a lighting strike is a low probability event and an EMP is even lower). Knowing that I'd be spending that much money on an electronic device and assuming it would be good to go in the safe, I think I'm gonna be adding a ground in the near future.

Eric F
March 1, 2008, 01:35 PM
ok if you are close enough to get effects of an emp from a nuke your not gonna last long enough to try your protected electronics out. Oh your cell phone only works if the towers work which are not protected.

Would some one call a moderator please?

Acera
March 1, 2008, 07:44 PM
As I was reading through this thread, I was wondering if anyone was going to post like Eric F did. Who cares if your cell phone is undamaged if all the equipment in the country is fried, lol. It still would not work. You probably would not feel the blast from a space based detionation, your stuff just quits working. Suposedly that will be the first bomb to go off in WWIII.

bogie
March 1, 2008, 07:49 PM
Be awful damn nice if some of y'all put as much effort into contacting opinion makers, such as congresscritters, civic leaders, school administrators, etc., etc., as you do into the tinfoil hat conspiracy crap.

Awful damn nice.

As it is, next to damn useless. 60,000 users, and they wanna pway widda wenolds wrap... awww... isn't that precious...

Snagglepuss
March 1, 2008, 07:57 PM
Thank God my guns will still work. Opps, my laser cannon will be in operable however.:p

Cesiumsponge
March 1, 2008, 08:11 PM
This is slightly off topic, but how could I store a small GPS and hand held radio aboard a boat to protect them from a lightning strike? Maybe that ammo can with the rubberized liner? I've had that happen, and all electronics get fried.

That thin rubber layer doesn't protect against lightning strikes. High voltage arcs right through most materials, not to mention rubber is usually doped with carbon to make it black. This becomes conductive at very high voltages. The dielectric strength of rubber isn't that great compared to other materials out there.

bogie, the invention and development of Faraday cages (Michael Faraday) dates back almost 200 years and well established electrical principle. This isn't some tinfoil conspiracy. That, and people that gave more technical responses in this thread are likely engineers and science majors. Be awfully damn nice that people like that come in and correct misconceptions people have about the physical world. Maybe we'd be better off with people running around believing everything they read on the errornet instead?

Eric F
March 1, 2008, 08:12 PM
Hey my point was if you are close enough to get the EMP the rads you just got will make you so sick you wouldnt really want to make calls or you just got turned into anything from energy to ash to jello

Dumpster Baby
March 1, 2008, 09:08 PM
Just wrap your phone radio in Aluminum foil. Grounding isn't needed.

100% correct. Take the batteries out of any SHTF electronics you want to preserve, and wrap in a couple of layers of aluminum foil, with no holes or gaps anywhere.

EAdams
March 1, 2008, 09:28 PM
This thread is definitely not gun related, but it did teach me that I can check the radiation shielding in my microwave by placing my cell phone inside and trying to call it!

-v-
March 1, 2008, 09:36 PM
Remember fellas, EMP is also made by random occurrences like lightening strikes, or that step-down transformer on the telephone pole outside your house overheating and exploding (Seen this happen a few times, actually). Be a real shame if the EMP from a transformer exploding damaged that nice $2,000 NVG Gen2+ scope or EOTech that is attached to your AR-15, now wouldn't it?

NukemJim
March 1, 2008, 10:00 PM
ok if you are close enough to get effects of an emp from a nuke your not gonna last long enough to try your protected electronics out.

Hey my point was if you are close enough to get the EMP the rads you just got will make you so sick you wouldnt really want to make calls or you just got turned into anything from energy to ash to jello


Uhmm guys you might want to do a little reading prior to posting.

I'll post a few links for you

http://www.doh.wa.gov/ehp/rp/factsheets/factsheets-htm/fs41elecpuls.htm

http://www.johnstonsarchive.net/nuclear/hane.html

http://glasstone.blogspot.com/2006/03/emp-radiation-from-nuclear-space.html

NukemJim

Eric F
March 1, 2008, 10:49 PM
ok great so you light a 1.4 megaton nuke 250 miles in the air What else do you think will happen? if you say nothing I think you to be wrong. Much like every other prediction one person launches every one launches. Which leaves ground devices much shorter range. And from what I see any thing short of a nuke is for now fiction.
And this is all still very ungun related.
$2,000 NVG Gen2+ scope or EOTech that is attached to your AR-15, now wouldn't it? but this is not.........I think home owners would cover this. and if that were really the case there would be problems at my house all the time. The light infront of my house has blown out about 3 times a year for 5 years noe and I have yet to have any problems....must be low tech lighting around my block.

NukemJim
March 2, 2008, 09:10 AM
There are few so ignorant as those who will not read.:rolleyes:

NukemJim

nainc
March 2, 2008, 11:14 AM
Ummm...

What about the stuff outside the safe? Like cell towers, satellites, and everyone else's cell phone. Wouldn't that make the point of shielding your stuff kind of moot?

Im283
March 2, 2008, 11:36 AM
If I remember correctly Mythbusters did an episode on EMP's . They drove a car through a EMP burst. It killed the motor and major electronics on the car. But some of the smaller stuff still worked, can't remember exactly what but the wipers, windows, maybe the dome light still worked. The ignition was done.

What I want to know is will the keypad on my RSC still work if one of these happens?

battlecry
March 2, 2008, 12:01 PM
Not really, nainc. I want to use the safe to store 2 meter and other mobile ham radio equipment. The kind of stuff to use in RACES to restore communications and assist in emergency situations. The cell and wireless phones were used to test the RF isolation inside the safe. I was surprised to discover they still work inside the safe, microwave oven, and ammocan.

To those who want to use aluminum foil, I recommend that you first wrap the gear in bubblewrap or another convenient insulator before wrapping the mass in aluminum foil. Some case materials may be conductors and I believe you want whatever is inside the faraday cage to be insulated from the shield.

I still would like to make the safe an affective protection device. Will try some emi tape around the door gap. My safe is not grounded. Not so sure about the grounding strap; it also works as an antenna. I'll read your references.

Thanks for the advice, guys. Sorry if the post annoyed some.

Kindrox
March 2, 2008, 12:20 PM
If you want to stop all EMP/Radio signals, you have to be INSIDE a sealed metal container. Rubber strips/paint on an ammo can is not a sealed metal container.

We have "screen rooms" at work and you won't get a cell phone call inside one. Since that is what I know, I'll use the "screen" moniker.

For practical reasons, our screen rooms are a metal can inside a metal can, but theoretically you may or may not only need one for nuclear-induced EMP protection (I don't know).

For true protection I do know you need two. One stops electric fields, the second stops magnetic fields induced from the electric current flowing on the outer can.

Our screen rooms are on the order of $100k and are about 10' x 12'.

We do have smaller screen 'boxes' but you can typically still get a cell phone to receive a call in one. There is something about physical size which makes larger screen "containers" more effective.

If your screen container stops a cell call, you can probably consider yourself protected as I know it is no easy feat.

The screen room does not "need" to be grounded to work. It is only for safety, so that you large metal cage does not get electified and "grounded" through you. Screen rooms work on the principal that you cannot have any net charge (electrons) inside a sealed metal ball. No net charge means no EMP pulse of electrons.

230RN
March 2, 2008, 01:42 PM
Pet Picayune Peeve (PPP):

a high rate of speed

Speed is the first derivative of position.

A "high rate of speed" would imply the speed is changing, which is the second derivative, No? Meaning "acceleration?"


Actually, to get it kinda sorta back OT, I was thinking of getting one of those fancy Nikon Laser IRT scopes.

Aha! A raison d'etre for this thread. Protection for all them there electronical shooting aids.

I woulda never thought of that because I'm an old phart who doesn't trust them electronicimator gizzies to advise me how high over the Prairie Rat to hold at my eyeball-determined (not laser-determined) range to the aforesaid Prairie Rat.

And doesn't trust anememomitrators to tell me how far off to hold for the wind.

Prefer to use "Kentucky Windage" and "Kentucky Elevationage."

'Course, the Prairie Rats don't shoot back.

Cesiumsponge
March 2, 2008, 02:32 PM
If I remember correctly Mythbusters did an episode on EMP's . They drove a car through a EMP burst. It killed the motor and major electronics on the car. But some of the smaller stuff still worked, can't remember exactly what but the wipers, windows, maybe the dome light still worked. The ignition was done.


Mythbusters is entertainment, not science.

another okie
March 2, 2008, 03:29 PM
I think that show was the one with the shaved head guy who claims to be a Navy Seal, not the one with the Hollywood stunt guys.

In either case, Cesiumsponge's description is correct.

ilbob
March 2, 2008, 04:37 PM
Grounding a Faraday cage does not improve its effectiveness with respect to EMP. that is a myth.

Any large piece of metal is commonly bonded to reduce the chances of some kind of ground fault resulting in a hot piece of metal someone might come in contact with.

Im283
March 4, 2008, 05:09 AM
whether Mythbusters is science or entertainment doesn't change the fact that there were still electronics on that car that worked.

I still would like to know about the RSC's keypad.

Cesiumsponge
March 4, 2008, 05:39 AM
whether Mythbusters is science or entertainment doesn't change the fact that there were still electronics on that car that worked.

If the test isn't scientific in nature, the results are dubious and not conclusive, nor scientifically sound. Cobbling something together that "may simulate EMP" is not the same as a device designed specifically with the impulse waveform and power levels to "simulate EMP".

Maybe of their tests are approximations and aren't entirely accurate. Many here have complained before about their Carlos Hathcock sniper scope shot and how their setup was flawed, making the results inconclusive.

RSC keypads aren't shielded...at least not consumer grade stuff. Induced voltages should be enough to short all those junctions on your silicon semiconductors.

Owens
March 4, 2008, 05:49 AM
Interesting discussion, even if somewhat off topic.

I always thought that a 'screen' room or Farady cage was in essence a big resonant choke, that formed a trap, routing RF energy to ground.

Ah, the joys of a mechanical lock!

mekender
March 4, 2008, 07:32 AM
if i remember correctly, the US DoD did a study on EMP shielding back in the 60s... what they determined then was that it was impractical to spend $10,000,000 on shielding that could be easily be negated by a $5000 nuclear weapon... it was more economical for them to use redundant backups that were located geographically far apart

Cesiumsponge
March 7, 2008, 01:11 AM
Just for reference, mil spec FF-L-2740A (https://portal.navfac.navy.mil/pls/portal/docs/PAGE/NAVFAC/NAVFAC_WW_PP/NAVFAC_NFESC_PP/LOCKS/PDF_FILES/ffl2740a.pdf)

test subjection subsections:

4.6.11 Electromagnetic pulse. The lock shall be installed in a Class 6 security file cabinet as decribed in federal specification AA-F-358. The installed lock shall be tested in 4 orientations at each field level: front-on, drawer closed; front-on, drawer open; side-on, drawer closed; side-on, drawer open. The lock shall withstand 10 pulses in each orientation. The lock shall be subjected to transient pulse illumination with electric field peaks within the range of 28 to 37 kV/m with a 1.5 to 3.0 ns risetime. After exposure at each field level, the lock shall operate normally.

4.6.12 Electrostatic discharge. The lock shall be mounted on the test stand described in 4.6.8.1. The lock dial shall be subjected to 5 electrostatic discharges of 250 kV. After exposure, the lock shall operate normally.

You can buy yourself a Kaba X-09 electronic lock that meets/exceeds FF-L-2740A, if you want to put one on your safe. I hope you have four figures to spend on the lock though.

mekender
March 7, 2008, 02:36 AM
problem is, an EPM can easily go above 1MV/m which would be way beyond what those were designed to protect against

Cesiumsponge
March 7, 2008, 10:07 PM
The field strength drops as the inverse cube of the distance. If you double the distance from the point source, the field strength drops by a factor of 8. If you're 10 times the distance, its 1000 times weaker, and if you're 100 times further, its 1 million times weaker. You weren't seeing megavolt induction in electronic gear when the effects of EMP were first seen. You would have to be very near to the source to see that type of electric field strength.

No gear is hardened to withstand MV/m field strength to my knowledge nor is it practically possible. You'd have to use exotic materials with high dielectric strength like strontium titanate or barium titanate which have physical properties making them impractical for use outside of capacitor plates. If you're detonating EMP weapons high up in the air, you're not going to see megavolts induced on gear on the ground.

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