Multiple Layer Faraday Cage Shielding For Better EMP Protection

ByKen J. Last Updated
30 Comments

It’s pretty common knowledge to use a galvanized trash can (and lid) as a poor man’s Faraday cage. I’ve written about it a few times here on the blog (as well as other EMP related articles). However is a galvanized trash can good enough to actually protect electronic equipment from EMP? I decided to do a simple test on this, and another test utilizing multiple layers of protection. Here’s what I found…

  1. It is my opinion that a single galvanized trash can is not good enough Faraday protection from EMP.
  2. Two layers (nesting) appears to be sufficient attenuation to potentially mitigate EMP.

Okay let me get into it a little bit… My research has indicated that most EMI (electromagnetic interference) attenuation that you might expect from a galvanized trash can with a tight fitting lid is about 40 dB. Maybe 50 dB with a very well sealed lid. That’s not bad. But that’s not great either. Especially if we’re talking about an electro magnetic pulse ranging from 10 KV to 50 KV per square meter!

Technical Note: EMP energy is mostly between 100 KHz and 1 GHz.

The U.S. military requires a minimum EMP hardening of 80 dB in the plane wave field from 10 MHz to 1.5 GHz in accordance with MIL-STD-125-1 and -2. There are other related MIL standards too, one of which is also mentioned below (graph).

My EMP Faraday Testing Method

I do not have any fancy test equipment / analyzers to measure EMI / RF (outside and inside the Faraday cage). However, I do have an iPhone. Common mid-band frequencies used for cell phone carriers (4G LTE) range from 1Ghz – 2.6 Ghz. This will work for my general layman tests…

I know that today’s cell phones are very very good at pulling in weak signals, so if I could get that signal totally blocked, I would feel pretty good about that Faraday method…

The phone was slipped into a Ziploc bag (electrically insulating) and then placed inside a galvanized trash can (lined with cardboard) and with tight fitting lid. I used Mrs. J’s phone to call myself. It rang right through.

Next I decided to try some ‘Christmas Tins’ that I had purchased awhile ago for this test (while forced to visit a ‘Hobby Lobby’ store with Mrs. J). They were on sale :=)

The lid seal edges were painted so I had to use heavy duty aluminum foil to make a good electrical conducting seal. Here’s what I found out… The phone rang through the sealed tin. However, after nesting two of them (each insulated from each other in a Ziploc), there was no ringy dingy. It worked! Two layers did the trick.

Are the results of nested Faraday enclosures approaching 80 dB? Yes I believe that may be an approximation. I do know there are variables in design, materials, and other factors – and I don’t want to get down into the weeds with all that. Instead, I’m pointing out the probability that a typical sealed metal enclosure like a galvanized trash can is likely not enough protection from EMP by itself.

Use Aluminum Foil To Nest 2 Layers Of Protection

Easier to do with smaller devices such as handheld 2-way radios, portable radios, etc..

So you already have a galvanized trash can for a poor man’s Faraday cage. You may get approximately twice the protection (EMI / RF attenuation) if you insulate (e.g. Ziploc bag) the device itself, wrap it in heavy duty Aluminum foil, and Ziploc it again – before you place it inside the can with the other stuff.

The photo up top shows two foil wrapped Baofeng radios and its charger – insulated in a Ziploc bag – which in turn goes into the galvanized trash can ‘Faraday cage’. Two layers of EMP protection.

Even without a galvanized can, simply do what I just described, but with at least two foil layers insulated from each other for similar protection.

I always have one of these around here:
Kirkland Signature Heavy Duty Foil 18″ X 500′
(view on amzn)

Conclusions

Relying solely on a galvanized trash can for EMP protection may not be enough at approximately 40dB attenuation.

Multiple layers of shielding / protection may increase overall EMI attenuation (EMP protection).

Multi-layer shielding such as wrapped aluminum foil inside galvanized trashcan may help to meet MIL spec (Insulate contents and layers from each other).

REFERENCE:

From Department of Defense, MIL-STD-188-125-1, High Altitude Electromagnetic Pulse Protection For Ground Based Facilities Performing Critical Time-Urgent Missions,

Minimum HEMP Shielding Effectiveness Requirements

80dB shielding attenuation

MISSION DARKNESS
(Faraday store on amzn)

[ Read: Will EMP Destroy Anything Electronic NOT Plugged Into The Grid? ]

[ Read: What Items Do You Store In Your Own Faraday Cage? ]

30 Comments

  1. Cell phones work on a micro volt level of pulse voltage whereas EMP pulses are on the multimillion level of pulse voltage. This was a gallant effort of experimentation
    but there is no way to draw conclusions from this experiment. From Gausses law in physics only a continuously conductive (unbroken surface) can short out an emf field. Signal loss is not by attenuation either, the electric field component of a electromagnetic wave has to be shorted out for a Faraday shield to be effective, conductive layering does not help with the problem. I am sorry I know my comment will anger many but I am just trying to explain what happens in the real world.

    1. To ‘no joke’,

      I added an image at the end of article above, from Department of Defense, MIL-STD-188-125-1, High Altitude Electromagnetic Pulse Protection For Ground Based Facilities Performing Critical Time-Urgent Missions,

      Minimum HEMP Shielding Effectiveness Requirements

      As you can see, dB attenuation matters very much. This standard requires 80dB RF signal attenuation at ~ 1Ghz (see slope/graph for details of freq. vs attenuation).

      I have read test reports (using a sweep transmitter, test receiver, and recording analyzer) that a sealed galvanized trash may evidently result in ~ 40dB attenuation, though may be improved with conductive lid seal. This, combined with a sort of ‘insurance factor’ by way of multi-layering/shielding (exemplified above) may provide additional attenuation factor for a better margin of safety in this regard.

      1. You might want to ground your can to a cold water pipe…???

        Use the large 40mm ammo can. I leave the rubber gasket intact, but I use aluminum flashing bent in a “U” shape to make contact with the can and lid on all 4 sides. I line the can with heavy duty cardboard and wrap all items going the can with heavy duty tin foil….

        1. Additionally, don’t take any items after the first nuke blast out of the can. Chances are a second blast will follow after 3 days. I learned this from my nuclear weapons instructor in school….

        2. 21Bravo – Any Japanese citizen could have told you about the 3 day rule; it’s a good reminder though. I’ve often wondered if a labyrinth of underground water pipes might induct energy from an EMP, because of the wide area affected, and back-feed it into that which was grounded. Maybe No Joke has a solid understanding to share. I’d really like to know if I’m just over-thinking it. Microwave ovens too, urban legend, or settled science?

        3. Regarding microwave ovens… They operate at 2.4 GHz. They’re designed to keep that frequency ‘inside’. Poor results at other frequencies (EMP is fairly wideband).

      2. Re using 2 nested metal cans plus foil & ziplock bags – could you use 2 galvanized trash cans – one smaller inside the larger one? That would provide a much larger container to hold more sensitive items. Of course, still wrapping with the foil & ziplock bags as well.

  2. FWIW, there is a business in Berkeley, CA called TWP. They sell copper mesh. I bought a roll (it was NOT cheap) and constructed a Faraday Cage for my Honda generator. In hindsight, I would have been better off going solar. After reading ONE SECOND AFTER, the lightbulb went on over my head and I thought about the noise and the need for gasoline. Since in any kind of SHTF situation you will be dealing with desperate, stupid, and homicidal humans, I made a dubious choice. I did line an aluminum Army surplus equipment box with the remainder of the mesh and I use it to store FRS radios, a short wave set, night vision and other optics. Plan accordingly. Bleib ubrig.

    1. Dweezil – Regarding noise, we are seeing a new trend in generator theft. Crooks will fire up a junk lawnmower and roll it up next to your running generator, then steal your generator. It’s disorienting for the homeowner because the power just went out, but you still hear an engine running. That buys enough time to boost the generator and get down the road.

  3. This is what I did to my main back up drive, kinda.
    plastic, alum foil, plastic, alum foil, plastic, alum foil, plastic bubble wrap.
    3 layers.
    In hopes it survives for a day I can utilize it again.
    It is a minor ass pain removing that all several times a year to update that drive.

  4. Was thinking of taking the huge ammo can I store electronics in.
    I removed the rubber seal, ground the paint off the necessary surfaces and replaced the old seal with aluminum.
    I was going to use aluminum screen material to make a kind of bag to put the ammo can inside, just never got around to it.

    1. I don’t know if this is right or not, I was told that a proper Faraday cage in reality resembles the depiction of an Tesseract, yes I’m horrible at explanations.
      A complete box within a box connected at the corners, no holes, solid sides.

      Not saying I’m right but somewhere in my head this makes sense.
      Also annoyingly difficult to construct and a space hog.

      For most, luck will be the factor if things work or not.
      Were you far enough away, deep enough below ground, on the other side of a mountain kinda thing.

      1. Horse, That is my hope. Mountains to the north and east, hills to the south and west. No target of any consequence within a hundred miles. Prevailing winds off the ocean.

  5. Several good points: Remove the paint at the lid. Aluminum tape at the lid. Nesting electronics with foil. EMP bags? Nested?

    Nearly all of my faraday cages are inside of a metal building. Maybe a little more protection–maybe not. Way too many variables for a non-scientist like me. Fragility of electronics will be variable. I’d suggest a multi-meter in faraday. If ya had to, a manual charge controller for solar/wind. In some ways, like Christmas morning: Some good news and some disappointments. It’s worth the effort, in case it works.

    1. Plainsmedic,

      Conductive adhesive backed copper foil tape is available and may give you a better “seal” for your faraday cage than aluminum tape. A fine sand paper on both surfaces apply tape and you’re ready. Are you sealing between the lid and can or applying it on the out side? I use a drum with a locking band and seal between the lid and barrel lip. Put on the locking band and I am good. I hope. : )

      I keep my cage in my basement. No or extremely bad cell signal so maybe that will give so additional attenuation. I think the multi layer approach is also a positive thing to do. I do worry that if/when such an event happens even the “prepped for emp” folks will have that Christmas morning time with good and bad news.

      1. Deep South,
        The aluminum tape I’m using is the stuff with a removeable paper on the back. Very sticky stuff and it does provide conductivity between the can/lid. Mostly use a side grinder with a brush to remove paint quickly. I use a lot of popcorn tins for things I need occasionally, ham radios, etc.

        I’m not an expert on CME/EMP, but I’ve read a LOT. The cell phone test is better than nothing, but it doesn’t cover the whole range of frequencies. Not sure what I can do about that, likely nothing. Like you, try my best and hope it works. Thought about trying to make faraday from a small metal building. Really looked at it. Just doesn’t seem feasible if using the building at all. Who knows?

  6. Don’t mean to sound ignorant, but what do we do with our large 100-watt solar panels to protect them from an EMP…don’t they have blocking diodes that would be susceptible? And won’t all cell phone towers and wifi equipment be destroyed?…making it pointless to protect phones, tablets, etc? Seems the only communications equipment that would be worth saving would be battery-operated ham radios…? Sorry, folks…just trying to learn the concepts

    1. YellowRose:
      Being one of limited knowledge of Solar, besides what I have set up. Yes the diodes could be toast.
      Most like myself have stored a limited number of 400 watt spare panels among other items.
      But honestly 95% of the stuff that uses power would be useless in a short time, except for the comm’s of course.
      As one the thinks more along the likes of zero power, I argue/suggest adapting a lifestyle conducive of the 1800’s. How did folks live 150 years ago, or how do billions of people live now without power?
      Tis not really that difficult once you start down that road.

      1. @NRP – we don’t have to go all the way back to the 1800’s for examples. My grandparents homesteaded in west ND before the turn of the 20th century and their area was not electrified till late. When I was a kid in the 1960’s my grandmother still lived the same way; she cooked (fabulously, I might add) on her wood stove and used kerosene lanterns. The bedrooms had down comforters that she had made atop rope beds my grandfather had built and there was no running water, but a pitcher and basin on the dresser and we used the outhouse. So glad I had those experiences which seemed normal at the time, even though we came from the thoroughly “modern” suburbs with all the conveniences to visit her. She was one tough cookie but had a beautiful, happy and comfortable home. All of us cousin kids had wonderful memories of her and that house.

  7. NRP & Blue: Thanks for the reply…we don’t have the ability to store 400-watt panels, so I’m guessing we’d have to go the “living without power” route eventually…might be an idea for an article from Ken…”what to store for use in a total no power world”… :)

  8. YellowRose:
    Actually the new 400s are the same size,approx as the 100s.
    As far as lifestyle without power is the underlying factor of most of MSB.
    Search the articles, you’ll find hundreds on the subject.
    Heck even I strongly suggest doing “Lights Out” weekends where as you spend the entire weekend or longer using zero electrical equipment at all. Also no piped in or out plumbing, etc.
    Also no Pre made fires, Propane stoves and the like.
    Again think 150 years ago.
    If you have not read “Lights Out” and/or “One Second After” you should do so.
    Ken has a good list of reading materials here, check them out.
    One last thing….
    There are a LOT of GREAT folks that hang out here on MSB, Please do not be worried about asking questions. Please remember, we all started out at the beginning on the journey called Preparedness/Lifestyle.

  9. NRP & Blue: Thanks so much! We have considered doing a “Lights Out” weekend ! We have all of the equipment, as we used to camp a lot. I have read tons of books…including all of the Forstchen books…some sobering stuff! I began the journey many years ago, but it seems to have gotten more serious lately, so I am paying extra close attention to all the great MSB folks…I have been monitoring this blog for almost a year, and have learned so much…and am continuing to learn more on a daily basis…I’m grateful for the information, and always thankful for new and caring folks in my life~

    1. YellowRose,
      From what I’ve read, solar panels themselves might survive just fine. The charge controllers and invertors are the fragile components. I’ve got a few panels stashed in a metal building. Will they still work? No one really knows. Different ideas from differing sources. Yes, I have some replacements for charge controllers/invertors in faraday. I can only hope we can cobble something together that will function. Put a spare multi-meter in faraday. Maybe, and it’s a big maybe, ……………..?

      1. I have several multi-meters put away in 3 different places in hopes at least two make it.
        Analog hurt my eyes.
        As for solar panels I have 6 100w in their cardboard boxes on the basement floor.
        So, in the basement about 4′ below ground level but nothing special above to protect.

      2. Imow – Every so often I agree with you. My preference is a DVOM, and I have a stack of them still boxed and put back. But I started with a Simpson when I was a wee-tot making crystal-tuned receivers, now you made me want one again. In addition, bulk packs of cutting/grinding/sanding wheels, true cobalt drill bits, various size soldering irons with pounds of solder, spare tools and a a few dozen spare batteries for whichever cordless power tool platform you subscribe to; Makita for me; but Milwaukee has surpassed them.

        1. I somehow think you cheated and got rock bottom prices from your workplace.

  10. I don’t think anyone knows for certain what the result of a nuke EMP would actually be like in regards to ‘killing’ electronics en mass. I’ve done the cell phone test using a microwave, a 40mm ammo can lined with cardboard, and even simple mylar bags used for food storage. In all three experiments the cell phone did not ring! I do have a small supply of EMP-proof bags, but we just don’t know for sure how protected we actually would be. I have a Pelican case containing a complete portable HF ham radio setup. Nestled in layers of foam, I have been thinking of putting each component in mylar and hope for the best. My main station is unprotected as is the mobile radio in the truck.

  11. Whydah,
    Yep, it’s an interesting problem. Especially with the radios. Ya need ’em to use and ya need ’em protected. Only answer I’ve come up with is similar to your solution. Keep one of ’em in faraday at all times. Heck, I can only use one at a time anyway, so… 73

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