EMP Protection

I'm sure someone here can explain it to me...

I've been reading about protection in event of a pulse bomb and how everything in the country would get wiped out including personal electronics. Umm...wouldn't wrapping by a good insulator like rubber be all one needs to protect my belongings? What if I kept all my survival stuff in a rubber room? All I'm hearing about are Faraday boxes/cages. Is that the only thing effective enough against widescale emp?

A Faraday Cage can protect any electronic from an EMP of any size. You'll only need to worry about things with chips in them like a GPS device or an iPod. Simple circuits aren't in danger so things like flashlights or a grill with an electric starter will be fine.

There are a lot of pricey gadgets out there now that have built in protection from EMPs. Most of them are either made for the military or private companies who can afford them.

EMP damage is pretty capricious. We have to run some classes of stuff we design through an EMP simulator. There's a raft of things you do by the book, but when you get in the chamber and start blowing stuff up, you find out that the weirdest stuff makes a difference.

It's not true that "you'll only need to worry about things with chips in them". In fact, a lot of times the semiconductors don't blow. A lot of stuff you read on the net is written by journalists that couldn't tell you one end of a diode from another.

It's true that semiconductor junctions are vulnerable to overvoltage induced by EMP, but only if the EMP can induce that voltage. This requires being hooked to some sort of external lead that intercepts enough magnetic flux or radio frequency energy. Mainly that ends up being the front ends of receivers, the finals of transmitters and the stuff in the input end of the power supply. The cases absorb a lot of the signal so unless you've got an ungodly long trace or crappily shielded backplane, you won't get enough to pop something. But comm circuits are in for it, as are unprotected power supplies.

It's a lot more likely you'll get a circuit upset that crashes the computer than anything else. Or you can get secondary damage - for example, if you have a switcher making 0.85V for a CPU from a 12V rail, and the EMP upsets the switcher causing it to jam with the top transistor on, then the CPU will eat 12V and blow. That's not because the EMP blew it. So when you're designing for EMP-proof-ness, you have to look at "if this goes bats--t in some way, does it blow up other stuff" on a section by section level.

As far as passives go, low voltage ceramic caps can pop. I've also seen a lot of motors, speaker coils and deflection yokes go in Navy tests at Patuxent. Probably more of that sort of thing than popped circuit boards, really.

Tranzorbs!

My main product is an intercom system used by a well known fast food restaraunt. These places are just sponges for the EMP-like effects generated during lightning storms. All the audio lines running out to the speakers "Can I take your order, please?" make for great antenna.

Tranzorb diodes connecting the audio lines to ground at the circuitboard take care of all but the worst storms. I'll still get an occasional board back that's been toasted, but never as bad as they were before the protection.

I think a slow leak to ground through those diodes may clear up background EM, slight fluxes and what not, but it cant stop a full scale EMP when it hits.

Those speaker lines running from mic to amp to speaker all over that building will go... and will probably be the first thing TO go.
Man, all those coils... excessive amounts of wire... more coils... oooh and an amplifier mixed into it... tasty! That would be quire the treat for an EMP to knock around.


Its true though, it really is difficult to determine exactly what an EMP would destroy and what it would leave behind.
If it has a coil... anything attached to that coil is a gonner.
If it has alot of wire... the wire is effectively an antenna at that point, say goodbye to whatever is using that wire.
If it has sensitive diodes, relay switches, Eprom's, EEproms, Inductors, filter chokes, etc... its good as dead.

A good copper cage is a nice trick, half inch spacing between strands of copper, in the form of a mesh such that there are as many turns of copper wire on the way up, as there are coming back down in the opposing spiral direction. Completley enclosed... and a small DC current running through the cage. It's similar to what is called degaussing... but it's not degaussing. You're just creating your own EM field around those objects... when the EM Pulse gets to that cage, it has to push through your EM field before it can induce it's own into whatever is inside. Chances are... most of the empulse will be soaked up into that copper mesh... at least in theory.

[EDIT]
Oh yeah, and if the EMP was powerful enough to make you feel dizzy... don't even bother checking your electronics, they're ALL dead if it was that strong... may be a flashlight made it...

[edit on 13-3-2007 by johnsky]

Originally posted by apc
Tranzorbs!

My main product is an intercom system used by a well known fast food restaraunt. These places are just sponges for the EMP-like effects generated during lightning storms. All the audio lines running out to the speakers "Can I take your order, please?" make for great antenna.

Tranzorb diodes connecting the audio lines to ground at the circuitboard take care of all but the worst storms. I'll still get an occasional board back that's been toasted, but never as bad as they were before the protection.

I use transorbs, gas tubes and zeners like putty when I'm doing a low-susceptibility design.

The trick is to keep the signal from squeezing around the protection, you have to route incoming leads through the box walls just so, or it can bypass your clamp by running in places you wouldn't believe.

johnsky: The EMPRESS has killed a couple of swabbies caught on deck. But the ship held up to it, mostly. So if you're shielded good enough, you can in fact have equipment survive a hit that kills the people. Albeit in this case the shield was the ship's hull, for the most part.

Originally posted by Tom Bedlam
johnsky: The EMPRESS has killed a couple of swabbies caught on deck. But the ship held up to it, mostly. So if you're shielded good enough, you can in fact have equipment survive a hit that kills the people. Albeit in this case the shield was the ship's hull, for the most part.

lol, yes, but I doubt many people have enough steel lying around to build a solid hull around their house. That would be an interesting sight...

"Hey bob, what the hell are you doing?"
"Protecting my house from EMP's"
"Okay... but where's the house?"
"Inside that upside down hull."
"... how do you get back in?"
"... ahh f***!"

Truthfully, I expect anything in a solid TEMPEST room to survive.

The SCIF will be the last vestige of technology.

On a more serious note, you could take the TEMPEST building spec and use it as a sort of guideline for building a house that would not only hold up to a pretty brisk EMP, but would also be very tough physically.

It really would be something eh?
An EMP shelter that doubles as a bomb shelter.

How would you make the foundation support all that excess weight?

Any SCIF is built that way. I'm pretty sure the SCIF building code requirements are online from somewhere or another.

Military blast hardened buildings with TEMPEST are even tougher, but you can't receive squat in "The Vault" here, and it's plain ol' SCIF level TEMPEST.

There's more to it than the building itself, you have to have isolators on the AC feed and bypasses on the wiring going in and out, what little of it you have. The less you have, the easier it is to pass that audit.

Whoa, thanks guys. Definitely got more than I bargained for.

So I guess that's a negative on the rubber room?

Correct me if I'm wrong, but isn't rubber an electrical insulator and has little to no insulation capabilities when it comes to Magnetic fields?

I'm guessing an independantly grounded copper casing would be one of the better EM shieldings you can have no?