Faraday Cage/Box for EMP or CME

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Project by BoardSMITH posted 09-18-2014 12:43 PM 1785 views 3 times favorited 12 comments Add to Favorites Watch

I have never seen a project like this here on LJ so I thought I would contribute.

This is a simple 3/4” plywood box like anyone can make. What makes it different is the exterior covering. First we used heavy duty aluminum foil to wrap the entire box and provide for an interrupted skin of foil then followed that up with a covering of aluminum screen wire. Both coverings were tucked into grooves cut into the underside of the box and lid and are held in place by screen window/door flexible splines. The groove keeps the external coverings from coming inside the box. I was very careful to ensure that nothing penetrated the skin to the interior of the box. Had something penetrated to the interior, the box would have been worthless.

As a test once the box was complete, I placed my smart phone inside the box and closed it with the latches I installed. The phone didn’t ring which makes the box secure against EMP’s and CME’s. I realize that aluminum foil is very thin but the accepted electrical theory is that all it takes to protect electronics inside the box is a skin of electrical conductive material. Both the foil and screen wire provide that conductivity.

What is an EMP or a CME? (Electro Magnetic Pulse – Coronal Mass Ejection or Solar Storm) Both are high energy electrical fields produced by various means. An EMP is produced when a nuclear device is exploded and will disrupt and/or destroy electronic circuits. It has been determined that an EMP explosion about 400 miles over the USA will cripple most if not all electronic devices in the entire country.

A CME is a high energy blast produced by the sun and is what causes the Northern Lights. We have been hit four times this year so far and one blast which missed us was enough to rival the 1859 event. A CME can be as harmful as an EMP and we are far more likely to be hit with a CME that an EMP.

In this box will be placed a solar generator which I want to protect. An EMP or a CME would destroy the circuitry and make the generator a 100 pound boat anchor. The box will stay closed and will only be opened monthly to top off the batteries inside. I have another box for the solar panels and another to protect any electronic components I find to be vital.

-- David

12 comments so far

View kimosawboy's profile


164 posts in 2391 days

#1 posted 09-18-2014 02:43 PM

I don’t think you are going to have reliable contact at higher frequencies with just a ’’lap joint’’ for your seam. Not being an expert by any means , that is definitely your weak spot. You might want to look at a way to overlap your seams or use a conductive gasket of sorts!!
Looks great otherwise.

View BoardSMITH's profile


121 posts in 1683 days

#2 posted 09-18-2014 04:29 PM

If you are speaking of the joint between the lid and the rest of the box, the contact point is solid enough around the perimeter to make the box look unbroken to the frequencies. In all reality, the wire screen is there as more of a protection to keep the layers of foil unbroken. If it will keep out the UHF signal from a cell phone then the research I have read says that is enough to make is safe.

-- David

View Dark_Lightning's profile


2619 posts in 2529 days

#3 posted 09-18-2014 05:09 PM

That’s good, but unless you measure the bond resistance at the closure interface and ensure that it is less than the industry-accepted standard of 2.5 milliohms or less, you may still have leakage. I’d recommend a thicker metal, too, as the foil can easily be torn. The cell phone experiment only proves that there is enough attenuation of a low power cell phone signal to not excite the receiver. A badly placed tree that drips water can also block the signal, if it is in the line of sight to the cell phone. A large enough EMP can fry the foil right off the box, BTW. Also, you should drive a copper ground rod into the soil and attach it to the box for the best grounding. Every shielded room I’ve ever built was double clad- metal inside and outside, using steel, since the electromagnetic pulse can couple through the foil and destroy your equipment.

-- Random Orbital Nailer

View BoardSMITH's profile


121 posts in 1683 days

#4 posted 09-18-2014 05:38 PM

EMP bags use a thin copper mesh and are tested to 1mm volts without being grounded. Maybe the foil will be fried but at least I made an attempt.

The aluminum wire covers the foil so that should slow down any tears.

-- David

View The Box Whisperer's profile

The Box Whisperer

678 posts in 1490 days

#5 posted 09-18-2014 10:05 PM

Awesome dude. Well done.

-- "despite you best efforts and your confidence that your smarter and faster than a saw blade at 10k rpm…. your not …." - Charles Neil

View Matt's profile


182 posts in 838 days

#6 posted 09-19-2014 12:36 AM

I sincerely hope you never get to test its true effectiveness. We all need to take responsibility and prepare for the things we each deem likely, starting with basics (shelter, food, water) and going up from there. To be doing this you must be a well prepared dude!

Nice job.
(Keep some desacant in that box too!)

-- I do this for fun.

View BoardSMITH's profile


121 posts in 1683 days

#7 posted 09-19-2014 01:31 AM

The Box Whisperer; Matt – Thanks guys for the kind words. I really hope we don’t get the opportunity to test its effectiveness. At the very least, I hope to avoid the grief we had to endure last winter when the power was out for several days due to a severe ice storm.

The idea for the box came to me one night as I was laying in the bed just before going to sleep. Trial and error while making the first helped the next two go much smoother. Being able to use the woodworking skill set I have and having the right tools was also a major plus.

-- David

View missionworks's profile


63 posts in 2652 days

#8 posted 09-19-2014 11:47 AM

A very scary reality that more people should know about. We need to work on hardening the electrical grid.

-- MW |

View jaykaypur's profile


3996 posts in 1828 days

#9 posted 09-19-2014 12:34 PM

We all need one of these! Good job.

-- Use it up, Wear it out --------------- Make it do, Or do without!

View SuperCubber's profile


833 posts in 1704 days

#10 posted 09-21-2014 12:03 PM

Cool project!

-- Joe | Spartanburg, SC | "To give anything less than your best is to sacrafice the gift." - Steve Prefontaine

View sval229's profile


65 posts in 2962 days

#11 posted 11-09-2014 11:19 AM

If a CME fries everyone else’s phones who you gonna’ call?

View ScottKaye's profile


467 posts in 1373 days

#12 posted 11-09-2014 12:47 PM

ghost busters?

-- "Nothing happens until you build it"

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