Building Your Own EMP Faraday Cage

[ttabs]

I should post a pic of my 'other' faraday cage.  It's a metal garbage can grounded out and lined with a foam military sleeping mat.  It only holds a few items so I went with the cabinet idea.   

I just ordered up 40' of copper weave on ebay.  I'm going to use that stuff around the doors and such.  Been too busy to do more with the cage idea for now but April is coming.  That's the mud season as I call it when the snow starts to melt and all the snowmobiling is over and done. 

If you guys are going to use ammo cans as a cage, be sure to replace the rubber lid gasket with a copper weave material.  Grounding the can is optional. 

[White Tiger]

As far as the cage function, you can test it to some degree with a cell phone. Turn on your phone, drop it in the Faraday cage, and then call it. If it doesn't ring, the cage is blocking it. If it does ring, back to the drawing board....

Excellent continuity test ray - I did the test 5 times and the cage/case (without alterations) did NOT block the signal 4 out of 5 times.

The only time the signal seemed to be blocked was when the case was placed on the concrete floor of my garage. When I stacked two cases, the phone rang consistently...so, back to the drawing board....

...maybe I will try ttabs idea of copper mesh, next?

[gil]

The phone test is a good one, but failing the test does not mean that your Faraday case is insufficient..  I remember seeing a test on a video where a guy puts a phone in a microwave oven, protected by a Faraday bag. The phone still rang when called but was not damaged by the microwave. Of course the phone was toasted without the bag...

I am going to test my KX3 Faraday box tonight with my phone... Stay tuned...

Gil.

[White Tiger]

I guess it would get back to the power generation frequencies and those utilized for communications...

Looking forward to your assessment of your KX3 test!

[gil]

It's not a test of the KX3, but a test of the cookie tin can I use as a Faraday box. I put my phone in it, inside a plastic bag. It does not ring! When I take it out of the can, it takes a few seconds to show a signal. The lid is electrically connected to the can, so there is no leakage.. So, test successful!

Gil.

[White Tiger]

It's not a test of the KX3, but a test of the cookie tin can I use as a Faraday box. I put my phone in it, inside a plastic bag. It does not ring! When I take it out of the can, it takes a few seconds to show a signal. The lid is electrically connected to the can, so there is no leakage.. So, test successful!

Gil.

Gil, very cool! I wonder if your method of electrically connecting the lid to the base would work for my case, or should I use the copper mesh ttabs suggested?

[Geek]

I read an article once about Faraday cages that indicated that any Faraday cage reduces a portion of the energy.  Therefore a Faraday cage inside a Faraday cage is a good idea.  I don't know if this is correct, but placing a cookie tin in a cardboard box, that goes in a galvanized trash can, may work where either the cookie tin or the trash can was insufficient.

[Frosty]

I read an article once about Faraday cages that indicated that any Faraday cage reduces a portion of the energy.  Therefore a Faraday cage inside a Faraday cage is a good idea. 

Nested cages, that's what I do as recommended by the futurescience site ttabs already mentioned.  Foil, bag, foil, bag, etc.  Then throw the individual packages in a big cardboard box lined with more foil at the end, and put it on the shelf.  Got a 1000w Honda gennie stored that way.   Hard to remove items from it, but they're just spares.  By my reading, there's not really a "protected" versus "vulnerable" distinction, each item's sensitivity varies as will the pulse strength.  All you can do is attenuate the amount the item receives and hope it's below the failure threshold of the individual item.

[Tadpoe62]

Here's a question guys, I just purchased a 40' shipping container in which to store some of my "supplies".  Couldn't I ground that and perhaps construct a commo room in there that would protect my equipment?

[Geek]

The problem as I understand it is that any opening defeats the Faraday Cage effect, so you need to seal all openings and seams.  If your idea was to store the entire room and you seal up the openings on your way out, you should get some protection.  If you expect to operate the room, go in and out, or have openings for antennas, etc. you're not going to get a benefit.

[White Tiger]

The problem as I understand it is that any opening defeats the Faraday Cage effect, so you need to seal all openings and seams.  If your idea was to store the entire room and you seal up the openings on your way out, you should get some protection.  If you expect to operate the room, go in and out, or have openings for antennas, etc. you're not going to get a benefit.

ah yes, but if you set up spares inside the "EMP shack"(40' shipping container) and had the antenna EMP blocking connectors that WA4STO posted earlier - i believe this shack would be sealed during and after any event - the coax might compromised - but that is what the spare coax inside the shack is for...

[Geek]

I was actually concerned not just about the antenna, but the fact that there has to be a hole someplace for the antenna to pass in and out of the container.  It seems to me that the hole is a problem for getting proper Faraday cage benefits.

[White Tiger]

I was actually concerned not just about the antenna, but the fact that there has to be a hole someplace for the antenna to pass in and out of the container.  It seems to me that the hole is a problem for getting proper Faraday cage benefits.

since its a field effect - a hole won't necessarily matter, depends on how far away from a right angle it is. The stronger the current/surge the further out you go from the two opposing metal walls. The repelling force comes from the similar charge on the same structure - running into itself at right angles. Cranking up the charge would actually spread the effect further away from the fulcrum point of the angled wall.

[Geek]

I was actually concerned not just about the antenna, but the fact that there has to be a hole someplace for the antenna to pass in and out of the container.  It seems to me that the hole is a problem for getting proper Faraday cage benefits.

since its a field effect - a hole won't necessarily matter, depends on how far away from a right angle it is. The stronger the current/surge the further out you go from the two opposing metal walls. The repelling force comes from the similar charge on the same structure - running into itself at right angles. Cranking up the charge would actually spread the effect further away from the fulcrum point of the angled wall.

Are you saying that a stronger charge would be less likely to make it through the hole in the wall?  What about a weaker charge?  With a CME you might be faced with highly variable EMP effect spread over a period of time.

I don't follow the point about right angles either.  Are you saying that it is better to have any gaps closer to a corner or further away from a corner?

[White Tiger]

I was actually concerned not just about the antenna, but the fact that there has to be a hole someplace for the antenna to pass in and out of the container.  It seems to me that the hole is a problem for getting proper Faraday cage benefits.

since its a field effect - a hole won't necessarily matter, depends on how far away from a right angle it is. The stronger the current/surge the further out you go from the two opposing metal walls. The repelling force comes from the similar charge on the same structure - running into itself at right angles. Cranking up the charge would actually spread the effect further away from the fulcrum point of the angled wall.

Are you saying that a stronger charge would be less likely to make it through the hole in the wall?  What about a weaker charge?  With a CME you might be faced with highly variable EMP effect spread over a period of time.

I don't follow the point about right angles either.  Are you saying that it is better to have any gaps closer to a corner or further away from a corner?

Im certainly not an expert - but I was speaking to the concern regarding holes.

The Faraday Effect happens when you send a charge thru a metallic object. My familiarity of it comes from manufacturing - and it is best expressed by the way two magnets of similar charge repel one another regardless of the amount of mechanical force applied to overcome it.

In the example used - a shipping container - the thickness of the steel walls would come into play, but the entire cage is effected by the applied charge...the effect repels with the most intensity at the corners...as you move away from the corner/right angles, the effect diminishes...unless you crank up the voltage, which would cause the effect to intensify somewhat further away from the corner/right angle (again, depending on the thickness of the metal wall, the distance away from the corners, and the voltage applied).

The (similar/like) charge actually meets itself head on in a corner - creating a "void" in the electrical field....like trying to push those two magnets with same polarization together...nothing electro-magnetic will ever be forced into that corner...

When you paint electrostatically, this effect actually occurs on the inside of a channel at the point of the right angle. The paint is actually repulsed, leaving a void emanating from the angle point, out wards. That void is increased when the charge is turned up...

It's not holes so much as gaps, or a lack of contact surface (i.e., continuity).

I'll attach a picture of how it applies in my field - and how I think about the problem: