Nuclear EMP Shielding Advice Needed

[SlovakMan]

I've searched the Internet for many weeks and have also looked at all 49 threads on this site to no avail. I work for a state government agency that is concerned about potential effects of nuclear electromagnetic pulses (EMP) and solar coronal mass ejections (CME). The concerns are based on two respected and recent publications: 1) Severe Space Weather Events--Understanding Societal and Economic Impacts Workshop Report (see

http://www.nap.edu/catalog/12507.html

) and 2) High-Impact, Low-Frequency Event Risk to the North American Bulk Power System (see

http://www.nerc.com/files/HILF.pdf

) I recommend the second one especially to anyone involved in electric power transmission.

We feel we've got a handle on Faraday Cages to protect our equipment. However, a big concern is the functioning of vehicles after an EMP or CME. Constructing a fully shielded garage is a major and costly undertaking. Full protection is also difficult to achieve with everyday maintenance activities, e.g. constantly moving vehicles.

Can anyone provide some suggestions or advice on how to effectively shield & protect a single vehicle from EMP (the more severe problem) and CME??

We will only protect critical vehicles at designated locations. Ideally, the solution will also have portability, but we can live without that. Of course, every option would have to be grounded properly to drain off the magnetic fields. Probably would ground at all four corners of the vehicle. We'd like to achieve 60+ dB attenuation in the up to 3 GHz range. At least that's my understanding of requirements. The largest vehicle is 18 ft 4 in long, 6 ft 8 in wide, and 6 ft 7 in tall.

Some considerations we've had are:
== Silver or other metal fabric (difficult to electrically bond fabric sheets. also costly.)
== Metal plated plastic cages (difficult to electrically bond sections)
== RF shielded paints (enormously expensive, $90/liter)

FYI, I'm a Civil Engineer with some past electrical experiece including radar repair in the U.S. Air Force. I'm conversational, but not design savvy in electromagnetic work.

This problem has proven to be very challenging. Any ideas and suggestions would be most appreciated.

Mike (SlovakMan)

 

[biff44]

Not sure there is much you can do about it with today's vehicles! There are so many low voltage digital boards in a modern vehicle that some are sure to be fried in a nearby EMP. Solar mass ejections probably will not be a problem for a vehicle, as they need large wiring networks, like a power grid, to get received and cause trouble.

On the positive side of things, a modern vehicle already has a lot of surge suppression circuitry on every electronics board. This is because the DC voltage in a vehicle can jump around a lot, and can overvoltage very high if the voltage regulator ever fails. So, there is some built in protection.

If you guys are serious, the best way is to take a typical vehicle, shut it up in a shield room, and submit it to a simulated EMP, see what fails, and see if there is some add on (additional varistors, metal shielding, etc) that can be added on.

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[VEBill]

"...would have to be grounded properly to drain off the magnetic fields..."

Magnetic fields don't "drain" via ground. Electric charge can "drain" to ground, but not magnetic fields.


If this is just a few vehicles, and the assumption is that they'll be used post-EMP, then why not use mechanical diesel engines and simplify those few vehicles down to zero electronics and minimal (shielded) electrics (light bulbs, fuel solenoid). And have a few spares for those sitting on a shelf.

 

[Higgler]

Specialized mylar film tents to park them in, but add vessels of water/salt water inside the tent to act as attenuating low cost absorbers. If you don't have absorbers inside, the tent will resonate and be much harder to seal.

Disconnect and add RF loads to all antenna input connectors (sma, N, TNC, bnc) on the vehicle electronics. Or add failsafe switches to the electronics to disconnect antennas.

Add a second layer of mylar tent atop the vehicle, as in a car cover.

Ducting RF energy into water loads via antennas inside the tent can also help.

At lower frequencies (f<500 mHz), HFSS and CST could analyze the problem.

 

[biff44]

Do you mean metallized mylar films? Mylar itself will stop nothing. And how do you propose connecting it to earth ground, to stop it from becoming a huge antenna of its own?

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[VEBill]

Shields do not depend on earth ground to work. Airplanes and satellites can be protected from EMP, and wires to earth ground would be tremendously inconvenient in those cases.

 

[biff44]

This shield, a mylar tent roof, would heavily depend on earth ground. Only if the mylar went all around, including the entire floor, forming a faraday shield, would the earth ground not be important. A metalized mylar tent, flapping in the breeze, would need multiple connections to earth ground along each edge to make the somewhat conductive earth below the footprint of the tent a wall of the faraday cage. Yes/no?

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[VEBill]

If someone was planning to use the approach of a Faraday cage parking garage, then they might as well use metal construction and make it cover all six sides. The screened metal floor would probably be cheaper than the paperwork required to prove it wasn't necessary.

Shielded room are not cheap, but they're not THAT expensive that a government would even blink. Even for one large enough to park several trucks.

Beware the cycle limit on the door seals (typically finger-stock). Usage of doors on shielded rooms, and wear and tear on the finger stock, becomes an issue relatively quickly.

 

[Higgler]

I was thinking metallized mylar, and a metallic floor to drive the vehicle onto.


It might be cheapest to take a bulldozer, dig one large trough, keep the soil wet and permeated with salt water, (fresh water loss is 10 dB/inch at 2.45 ghz, salt water is much higher loss) and park the vehicles in the trough, then insulate them further with metallized mylar and cover the top with Aluminum supports and dirt. Then there's only two ends of the trough to fully seal (bulldozers and metal and salty soil).

quotes from Ground Penetrating Radar;
In some situations, penetration depth may be limited to a few feet or less within clays, whereas pipes residing in sandy soils could be detected at depths up to 30 feet.

 

[SlovakMan]

Thank you all for interesting and informative responses. After looking up several of your proposed ideas, and discussing them with co-workers, we've come up with another scheme. Brainstorming leads to interesting ideas.

We're looking into "simply" building a Faraday Cage around the vehicle and keeping it in there when not in use. All six sides of the cube would be covered. The design would follow the example of a sheilded design U.S. military communications shelter called an S-250. It uses 0.032-inch aluminum sheets connected together at all seams by alumium rivets, 1 inch on center. The overlap of the sheets has a conductive grease to promote conductivity. The four corners would be connected to multiple grounding rods buried in bentonite to provide the best earth ground for the cage.

There is still the problem of dis-similar metals and potential for (pun?) galvanic corrosion. Aluminum sheets connected to 2/0 copper wire, in turn connected to a copper-clad steel grounding rod. Any suggestions on these connections would be helpful. Probably cover the finished connections with silicone sealant to minimize galvanic interaction.

How to fabricate our own door that is still EMF tight is still an issue. Thoughts on this are welcome.

We're working out the actual design and cost estimate but that's our thinking right now. Comments and critiques are welcome. Much better to find problems in the design stage. Also, thoughts on how to make it better are especially welcome.

Oh yes, our state suffers from greatly reduced taxes and other revenues. Our agency has lost five people as a result of two years of 15% and 10% budget cuts. And other states have taken even worse hits.

 

[VEBill]

"Our agency has lost five people as a result of..." Nuclear attack? Yikes... ;-)


"The four corners would be connected to multiple grounding rods buried in bentonite to provide the best earth ground for the cage."

You may induce MORE currents onto the structure with four ground rods. Any local area EMP-induced ground currents would say, "Hey lookie, a better path through this metal building." The shield should still work (in simplified theory), but I don't see how *multiple* ground points could possibly help.

 

[Higgler]

I was just writing the same thing VE1BLL.

Who said grounding it was a good idea? That's something to look at more closely.

Having it connected to an RF load (the ground) would be good if the ground is very lossy (clay, salty marsh) but it's a bad idea if it's on sandy soil thats fairly lossless. As VE1BLL pointed out, you're making a larger antenna that will conduct more lower frequency energy.

Inside the Faraday cage, consider connecting the vehicle or not connecting the vehicle to the cage. Having the vehicle isolated by the tires will be good or bad,not sure at first glance.

Add some RF loading inside the Faraday cage either using water/salt water or Resistance card (standard automobile dark window tint and it's cheap).

 

[Higgler]

check out this metallized tent link. Good data on sealing performance. Can make any size tent to cover your vehicle.

http://www.marktek-inc.com/metallizedfabrics.htm

 

[biff44]

A big metal enclosure with 0.032 aluminum would do the trick if:
1) no wiring going into/out of the building, like AC power lines for lighting.
2) You would need to get a good electrical connection to the door.

It has been a while, but I do not think the frequency spectrum of the emp is that high, so you would not need microwave fingerstock. But you would want something that could handle high low frequency currents.

For safety concerns in a thunderstorm, the codes would probably require the metal building to be grounded for lightning. Not sure if that would hurt or help!

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[biff44]

According to this, you probably only have to worry about RF up to around 10 MHz (20 db down):

http://www.tscm.com/emp.pdf

So a good, high current, attachment between the door and the walls/floor every 4 meters (1 eigth wavelength) would probably work.

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[pstox]

You could always email a company and ask their suggestions. I know LBA Group has experience in large shielding projects.

http://www.lbagroup.com/technology/rf-electromagnetic-shielding.php

 

[passerbye]

Interesting responses here. One possibility to EMP or CME proof a vehicle is to simply keep spares with the vehicle, or nearby that are adequately shielded themselves. Don't worry about the entire vehicle unless it is packed with sensitive equipment. For most vehicles, protect spare electronic ignition and perhaps starter parts... a spare radio (or two-way walkie-talkie set) if important. A few alternate layers of complete foil wrapping and plastic bagging should do (called "skinning"). Alternately, I've an improvised Faraday cage on the cheap; a steel trash can thoroughly lined inside with rubber matting and a thin strip of aluminum screen mesh wedged into the opening. I'm NOT an engineer, but the better info I've found seems to indicate that grounding the cage is not needed and makes things worse. And no cords outside cage. The beauty of a can is that older computers, monitors, etc. can easily be added or removed as needed. Incidentally, if a solar or blast event occurs, there may be a residual hum for hours or days. Opening a cage to test the survival of an item could potentially expose it and all else to damage. For that reason, I have some small electronics that are merely wrapped (and safe) other places that can come out as needed and act as "guinea pigs."

From a cost standpoint, many kinds of spare emergency equipment and electronics COULD be ordered and securely stored for future use... being rotated out much like one's pantry. There is little loss and one could view it as relatively inexpensive insurance. Might make it an easier sell to those who are unaware or unconcerned about this potential problem. I would dare say that with all costs rising, it might be a good idea anyway. Oh, and consider batteries (unaffected) and a non-grid means of recharging if needed (solar?).

One site I visited suggested dismantling a small back-up home generator to protect the sensitive parts. Reasonable, but I have instead lined the inside of a cardboard box with continuous foil (double-sided tape to the rescue), rubber mat at the bottom and plastic bagging over the item. I can quickly use it for normal power outages and easily return it... and no one sees me using the foil which also avoids the mild embarrassment of looking eccentric. Foil thickness by the way seems to be relatively unimportant. Being hole-free could be.

I use an insulin pump, providing incentive to get educated on this topic. It is good to consider and stock what electronics and other items are critical should a Katrina-like event occur.

I want to add that I am merely condensing and passing on what I have found various places on the internet for my own use. Please try to confirm this info if you can by other means. I'd just want to see EVERYONE as ready for this as possible, while hoping it is never, ever needed.