Mylar as a Faraday Cage?

[Tbald14]

I am thinking about putting a hand crank weather radio/Power supply in my BOB. To keep it protected from water i was going to put it in a sealed Mylar bag. Would this also serve as a basic Faraday cage?

 

[CathyInBlue]

The issue with the design of a faraday cage is two fold. First, the size of the holes in the mesh determines the highest frequency that will be blocked, the tighter the mesh, the higher the cut off frequency. With a continuous conductive film, that's not a real issue for mylar. Second, the gauge of the conductor used in the mesh (or film as the case may be) determines the magnitude of electric impulse the faraday cage can protect against. With a tight mesh of relatively thick gauge wire, a faraday cage can easily conduct away gargantuan currents from an EMP, nuclear blast, or solar CME. With a thin film, the magnitude of impulse from which a mylar based faraday cage would protect will be seriously degraded.

Does that mean that it would not protect from electrical attack X? No. It means that there are a larger span of intense attacks against which the mylar would break down and actually burn through due to inductive heating due to the currents flowing through the mylar film. If the mylar burns through and opens up holes in the film, those are just like the mesh of traditional faraday cages and see above. They would allow any remaining EMP to enter the mylar bag's interior and wreak its havoc.

The lesson is, if you're going to use mylar for EMP shielding, use as heavy a gauge of mylar as you can obtain and make it of a type that's thermally resilient so even with currents heating it up, it won't burn through.

 

[Valvestate]

What type of metallic film is actually on the mylar?

 

[CathyInBlue]

It's generally aluminum that is electricly "sputtered" onto a flat surface and then coated in the plastic film to make the metallic mylar film.

 

[pudly]

Aluminum foil is an easy/cheap way to upgrade that protection. As Cathy noted, it is still not the ideal protection.

Can anyone confirm the following? I heard/read somewhere that putting your vulnerable items in a metal filing cabinet (with some insulation so they don't touch the metal) should have the same effect. Seems like a very easy solution.

 

[churchmouse]

Aluminum foil is an easy/cheap way to upgrade that protection. As Cathy noted, it is still not the ideal protection.

Can anyone confirm the following? I heard/read somewhere that putting your vulnerable items in a metal filing cabinet (with some insulation so they don't touch the metal) should have the same effect. Seems like a very easy solution.

I have thought of this as well. We ran a wire to a ground rod on the outside and attached it to the cabinet. Not sure if this is a wasted effort when dealing with EMP's

 

[Exodus]

So what about all that food you've been storing in mylar bags if emp does hit? (Btw not directed at anyone, but everyone)

 

[ClydeB]

So what about all that food you've been storing in mylar bags if emp does hit? (Btw not directed at anyone, but everyone)

That's an interesting question. Obviously organic material isn't going to be shorted out by an EMP / CME event. But the bag itself? The melting point of Mylar is 254 degrees Celsius or 489.2 Fahrenheit.
http://usa.dupontteijinfilms.com/informationcenter/downloads/Physical_And_Thermal_Properties.pdf

I do not personally recall any mention of small quantities of metal getting hot enough to catch things on fire in any of the EMP and CME reading I have found. Only things like long distance power lines got hot enough to combust. The powerlines act as antenna's to catch the electrical currents generated by the EMP / CME event. So I wouldnt worry too much about Mylar unless you have it plugged into the electrical grid somehow.

If you want more info. I thought this pdf explains things with EMP fairly well. http://www.oecd.org/sti/futures/globalprospects/46891645.pdf

Now for those who want to use mylar as a faraday cage? I really do not know if your run of the mill mylar is up to that or not. There is a company called EMP Faraday Cages Bag Solutions For Electromagnetic Pulse Protection EMP that sells mylar looking bags (they say its not mylar) designed for EMP protection.

 

[CathyInBlue]

I would sooner store things in a 5 gal bucket lined first by aluminum foil with about a 2" overlap between sheets/segments, and then with 2" foam insulation. The thickness of aluminum foil will definitely be enough to handle any currents an EMP would induce in something that small.

 

[NathanJefferson]

I have thought of this as well. We ran a wire to a ground rod on the outside and attached it to the cabinet. Not sure if this is a wasted effort when dealing with EMP's

Winner, you need a nice ground to be complete.

But overall an EMP, even if severe would most likely not have much affect on items that aren't plugged in.

If you want an easy and cheap faraday, Get some metal shelves and wire them to a ground, then put anything you want to protect in metal ammo boxes. That would be more protection than you should ever need in a million billion years. (if you need more protection than that its not going to be the EMP that gets it!)

 

[churchmouse]

Winner, you need a nice ground to be complete.

But overall an EMP, even if severe would most likely not have much affect on items that aren't plugged in.

If you want an easy and cheap faraday, Get some metal shelves and wire them to a ground, then put anything you want to protect in metal ammo boxes. That would be more protection than you should ever need in a million billion years. (if you need more protection than that its not going to be the EMP that gets it!)

Thanks. I deal with electricity and things related on a daily basis and have found that a good ground will cure many of the issues. Seemed right to have a "Drain" on the cabinet.

 

[ThrottleJockey]

Hmm, for in home use an old defunct microwave acts as a good faraday cage and can be left plugged in for the ground.....In my bob, I have a small metal cookie tin with aluminum foil wrapped around the paper towel wrapped electronics. Don't really know how well it will work, but the same method keeps my prepass and my ezpass from being scanned at tollways and weight stations.

 

[ThrottleJockey]

Not sure if anyone's interested but I just saw these for free on CL and figured they may serve just this purpose....
copper screen