Faraday Cage/Box for EMP and CME Protection

[DWSmith]

I have never seen a project like this here on NCWW 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.

Questions and comments are appreciated.

 

[Mike Davis]

Once you have that filled and positioned will you attach a strong ground wire to dissipate the electrical charge?

 

[ehpoole]

Just a couple of points to make:

1) Only the utility and satellite operators need any protection from CMEs -- to build up harmful charges from a CME requires miles of strung up cable as it is the Earth's magnetic fields interacting with those cables that builds up a harmful charge. Which is probably a good thing since your box would need to be magnetically shielded to yield any protection from a CME here on Earth. In space it is a different matter as satellites can be harmed from both the snapping of a Earth's magnetic fields as well as the build up of charged particles on the satellite's exterior.

Not that CMEs should not be of concern to us for other reasons -- consider all the utilities we have come to depend upon that are delivered via either satellites or that involve miles of wiring between yourself and the provider (internet, telephone, cable a TV, power -- possibly even natural gas pipelines). Now imagine life without any of those things for many years!

2) The degree of protection afforded by aluminum foil and screen will vary by frequency. They'll afford considerable protection from MF to SHF frequencies and above, but are considerably less effective at lower frequencies which have a much greater probability of penetration. An EMP is a broadband energy (RF and magnetic radiation) source, so the degree of protection will depend upon how the energy is distributed throughout that spectrum. Regardless of RF frequency, the aluminum will offer little protection against sources of magnetic interference (which can accompany EMP depending upon source or location) as the aluminum used is much too thin to sustain the eddy currents necessary to resist a magnetic field (ELF). Steel or iron do a better job at inhibiting magnetic fields when using thin sheet metal, while aluminum (copper, etc.) is adequate for the higher RF frequencies (MF+). Ideally one could combine both when using thinner sheet metals, but beware of galvanic processes degrading the two metals.

For reference, your cellphone is in the realm of UHF (300MHz to 3GHz) as most cellphones today fall between 850MHz to 1.9GHz depending upon carrier and band.

For real EMP protection the various pieces and edges of sheet metal, and especially the lid to body interface need very robust electrical bonding to one another. Try to imagine 1,000A of RF energy interacting with the sheet metal and developing high voltage potentials on certain areas depending upon the wavelength the energy is focused in or at which your box is most resonant, poor contact will result in the thin aluminum foil being burned through, creating potential paths to the interior. Also keep in mind that you really want cold welded or better connections as the oxides of aluminum are electrically insulating, which reduces the conductive effectiveness of contact points at high RF energies. The screen can provide effective shielding for wavelengths that can not penetrate the openings (less than microwave), but its effective connection to the underlying aluminum foil is likely very poor due to oxides and limited mechanical electrical bonding (i.e. cold or hot welded or soldered).
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That all said, I really do hope we never end up needing such in our lifetimes, but you never know until after the fact.

 

[red]

Very interesting.

Red

 

[Glennbear]

On a similar related note which came to mind after reading Ethan's post I offer the following: Most of us are aware of the importance of grounding the electrical circuitry and machines in our shops but I daresay few are aware of the concept of bonding. Prior to retirement I spent some years as a college pool manager and one of the things I was responsible for was maintaining electrical bonding of all metal fixtures, ladders, diving boards, bleachers etc. in the pool area including periodic testing by a certified testing company. My prior training kicked in a few years ago when I was in the shop during a storm standing close to the metal overhead door when lightening struck nearby and there was a loud crack as stray current bridged the gap over the weatherstrip between the bottom of the door and the floor slab. I now have the door and frame bonded to the shop ground rod via the sub panel. Had I been touching the door during the afore mentioned incident I do not think the result would have been pretty. :no:

 

[DWSmith]

Mike - I have been researching this subject for many, many months and have read and researched what is needed or not. Most agree, the skin effect of the foil does not require a ground. If I did ground the box it would have to be to a ground rod and not to the electrical ground or water pipe ground.

ehpoole - Interesting read. As I said above, I have studied this subject for many months. In the book "A Nation Forsaken", the author reports experts who say a devastating CME is not an "if" but a "when". The 1859 Compton event would have crippled the current electrical grid and would have brought this country to a halt. The resulting chaos and anarchy will be devastating. Our enemies have researched EMP bombs for years and it will only take a cheap SCUD launched from a rusty freighter to take our society down to the 1700's. Will my boxes work, may be and maybe not. But I know this, something is better than nothing. I am not willing to do nothing.

 

[Phil S]

But I have to ask - if/when this happens, who are you going to call and thru what cell tower ?

 

[DWSmith]

Never said I intended to make a cell call. That isn't what I built the box for.

 

[Hmerkle]

David,
What is the "Solar Generator" you refer to that is going in the box?

I thought there was a simple inverter to use the solar energy and turn it into 110?
I wouldn't think that equipment would be very sensitive?

Obviously I am wrong - school us some more...

 

[DWSmith]

The generator is a Goal Zero solar generator using solar panels to collect energy and send it to storage batteries. There is an inverter built in which supplies the AC power. www.goalzero.com/yeti1250 Anything with a computer chip controlled circuit is at risk.

 

[ehpoole]

But I have to ask - if/when this happens, who are you going to call and thru what cell tower ?

Not so much cellphones, but radio operators with sustainable power sources, such as solar or hydroelectric, will be in an excellent position to maintain local, regional and even global communications. It just won't be as convenient to your average citizen since most will have to depend upon others to relay messages. For this reason alone we need HOAs to stop erecting absolute blocks to the mounting if typical HF and VHF antenna structures on private property. In such a scenario having a radio operator, if not several, in your neighborhood becomes a vital lifeline (including the means by which to make emergency contact with local authorities).

I fall somewhere between amused and irritated when an HOA has an absolute ban on antennas, but no similar restriction on large trampolines and similar structures which, to me, are at least as much of an eyesore if not more so as many types of antenna can be made nearly invisible to the average observer from any reasonable distance. It is a problem that is only getting worse with time as there are many markets today where it is next to impossible to avoid such covenants without having to go rural or very old, and often run down, suburban properties.

 

[Hmerkle]

The generator is a Goal Zero solar generator using solar panels to collect energy and send it to storage batteries. There is an inverter built in which supplies the AC power. www.goalzero.com/yeti1250 Anything with a computer chip controlled circuit is at risk.

O.K. so my next two possibly dumb questions are
1. Aren't there non-computer controlled units?
2. How far underground would the unit have to be to remain safe? (root cellar or bomb shelter?)

 

[DWSmith]

Radio operators are just as much of a target. That is, unless they have a spare radio in a protected place not connected to an outside source like an antenna which would serve as a lightning rod for any EMP or CME blast. Otherwise, their antenna hook-ups and plugs into an electrical system will make them vulnerable.

Hank - Definitely not dumb questions. 1. Honestly, I don't know. Not much in todays world that doesn't have a computer chip in it. 2. If I remember correctly, and I am sure I will be corrected if I don't, 6' of dirt covering might be enough. The next time you are up in this area give me a heads-up the day before and I will have one here for you to test drive.

 

[Hmerkle]

Radio operators are just as much of a target. That is, unless they have a spare radio in a protected place not connected to an outside source like an antenna which would serve as a lightning rod for any EMP or CME blast. Otherwise, their antenna hook-ups and plugs into an electrical system will make them vulnerable.

Hank - Definitely not dumb questions. 1. Honestly, I don't know. Not much in todays world that doesn't have a computer chip in it. 2. If I remember correctly, and I am sure I will be corrected if I don't, 6' of dirt covering might be enough. The next time you are up in this area give me a heads-up the day before and I will have one here for you to test drive.

O.K. (he says hesistently) you did mean test drive the generator not helping dig a 6' hole? (I know how you Seebees are! (Huck Finn learned his tricks from a Seebee!):rotflm:

 

[SubGuy]

I would suggest, having extensive experience in the EMP field, that the effectiveness of a scud and freighter would be quite negligible and very localized. Payload and efficiency is extremely limited.

 

[ehpoole]

Radio operators are just as much of a target. That is, unless they have a spare radio in a protected place not connected to an outside source like an antenna which would serve as a lightning rod for any EMP or CME blast. Otherwise, their antenna hook-ups and plugs into an electrical system will make them vulnerable.

Many do have spare radios. However, much of what you would do to protect active equipment is not at all much different from what an operator with proper lightning protection (emphasis on "proper" as most do not). It is simply about offering a preferential path to ground to dissipate the charge while simultaneously ensuring proper bonding to ensure that all electrical services in the affected location are brought up to the same electrical potential in lockstep, thus preventing the build up of the differential potentials that are the cause of what most people would colloquially term "lightning damage". Lightning dissipates far more energy and in a much more localized manner (complete with a very generous EMP to boot) -- and anything short of an actual direct hit (through the roof and into your shelter) is preventable with proper measures. If you can discharge a moderate lightning strike to your antenna then you can deal with most other sources of induced current as well.

While EMPs are a valid concern for a radio operator, CMEs are of no concern aside from the damage they will do to their electric utility and unprotected equipment that may be plugged into that utility at that moment, along with the loss of most landline dependent communications (phone, internet, a TV, etc,) services and the loss of our satellites. I really do not think you realize just how substantial an antenna tower or dipole a radio operator would have to possess before the effects of a CME even began to exceed the normal static buildup such towers are already designed to dissipate, much less to exceed normal lightning protection practices. The effects of a CME are not so much RF as they are magnetic fields, specifically the snapping of Earth's magnetic field lines. For a transmission line (radio or otherwise) to be in a realm where a CME represented a danger to the operator as a consequence of their antenna(s) they would need to have *miles* of such transmission line strung up. The average amateur operator is in the upper 1% (if not a much smaller percentage) of operators if their entire antenna field includes anywhere near a mile if transmission line or feeders, most will have at most a few hundred feet -- even our towers max out at 200ft without FAA waivers, and very few have antennas anywhere near such heights.

But just as importantly, it is quite easy for the individual, should they choose, to mitigate personal losses due to a CME as they are well announced and we know with some considerable lead time (typically 2-3 days) when to expect the possible consequences from an unusually large CME. You will not know exactly how great or small the impact will be, nor the exact hour of its arrival, until it arrives due to difficulties with calculating the precise hour of arrival, but if you care to know, or watch a TV or the news, you will know that a large CME is coming well in advance and one can make any preparations one deems appropriate based upon that information.

The threat of CMEs to society is very real and a credible threat to our civilization, potentially crippling our technological society for a decade or more before we can recover, but in terms of the personal, it is a threat to the average citizen only by way of our wired utilities and their avenues into our home due to our utility companys' many miles of transmission lines strung literally from one end of this continent to the other, not from a CME interacting directly with the (much shorter runs of) wiring in one's own home or personal radio antenna(s).

I can't shed any light on recommended depths of holes, but I would imagine that it will differ considerably based upon soil type. Red clay, for example, has very high iron content and, as such, I would expect it to have far more shielding per unit of depth than, say, ordinary sand. A couple layers of ordinary red clay brick is enough to severely attenuate a 5GHz WiFi signal to uselessness in short order, and significantly weaken 2.4GHz a WiFi as well.

 

[ehpoole]

I would suggest, having extensive experience in the EMP field, that the effectiveness of a scud and freighter would be quite negligible and very localized. Payload and efficiency is extremely limited.

For a little EMP trivia, brush up on Starfish Prime (1962). If only it had been extremely limited, instead it far exceeded all prior expectations for EMP effects and literally scared everyone straight as nobody dared repeat those lessons hard learned. This is 1962, the very dawn of the Space Age, and yet we managed to inadvertently destroy 6 satellites, and likely several others that failed not long after, and wrecked havoc on large portions of Hawaii blowing out street lights and destroying portions of the telephone system.

Any nation with the technology to build a megaton-plus class thermonuclear bomb and launch it into the atmosphere on the back of a missile, could duplicate the effects today. Thankfully that rules out contemporary terrorist organizations, but there are nation states, some unfriendly, that have the necessary ingredients to repeat it.

 

[Bas]

I can't believe nobody posted Roger's pic yet....

 

[DWSmith]

I realize some will believe all this is a joke. It isn't.

 

[McRabbet]

Sapwood strikes again! Great pic from last century of Roger! Thanks, Bas -- and no, electrolysis is no joke, it really works well!