A Faraday cage works by three mechanisms: (1) the conductive layer reflects incoming fields, (2) the conductor absorbs incoming energy, and (3) the cage acts to create opposing fields. Field cancelation occurs when the free carriers in the conductive material rapidly realign to oppose the incident electric field.
Yes, as long as the holes are small with respect to the wavelength of the incident electromagnetic wave.
Yes, there are many conductive enclosures that can be used, including ammo cans, metal garbage cans, anti-static bags, and even old microwave ovens. Anti-static bags are readily available to protect electronic components against electrostatic discharge. The Prepared Prepper's Cookbook: Over 170 Pages of Food Storage Tips, and Recipes From Preppers All Over America! Does anyone know if you can use packing peanuts to insulate and keep the contents of the cage from contact with the exterior walls? Question about gaps: If I use an ammo can with a rubber gasket to make the ammo can (and radio equipment) waterproof, having to repeatedly re-seal the can with conductive tape seems like a real pain.
I read on another blog that an old microwave oven (old plugged of course) could be used for small items. I have several 30 gallon metal trashcans setup in a similar manner, except I don’t use any coffin locks, or anything else on the lid since its already tight fitting. An EMP is not a continuous event, it is a burst of energy that is released, the damage is done, and then it’s gone, unless it is caused by a solar storm which could last for several hours or even days. As stated in the article, a solar storm is not likely to produce effects that will hurt small electronic items, unless they are connected to an external long wiring system, which could include the electrical grid, your landline telephone, your local cable TV provider, all of which contain long enough antennas to induce large voltages onto the system, and into connected devices.
The Carrington Event of 1859 cause problems with telegraph offices because the telegraph wires between the offices acted as a large antenna system, which collected the energy and delivered it to the devices connected to it. If vulnerable equipment is not in the protected enclosure during the event, then it could be subject to damage.
The truth is that no one knows for sure what will work without knowing the exact characteristics of electromagnetic pulse and that is impossible to know in advance. I know that lightning isn’t RF or an EMP but it is a huge energy source and I predict EMP will be just as unpredictable.
As a EE I think that this article was spot on; although perhaps a little more complex in the description of the physics than it would have to be . I dont think you all got my point, You have explained what an EMP does and how long it lasts, but you, me and everyone here does NOT know when one will happen.
What you keep in your Faraday cage always are the spare electronic parts for your car or truck, your spare ham radio, your extra laptop computer, etc. If you have a set of 2 way radios that work ok in your area, and you are happy with them, then buy a second set and put them in the cage. I keep hand held wallis talkies for communication on the farm and with my neighbors Ina faraday box. But go ahead and use the garbage cans, the ammo cans, the aluminum foil packets, the coffee cans, etc.
It’s good that you do such important work with things for a living because if you had to interact with people you would be out of a job.
As somebody else in the radio field, I am going to have chime in to state that your information is not correct, either here or your improved explanation below.
Some articles I’ve read refer to super EMP devices, nuclear devices designed for maximum magnetic yield. If it does happen, I figure it at least gives me a fighting chance, and if I do have a break-in, chances are that the burglars will overlook that antique.
You’re absolutely right about the multiple layer effects working better than a thick conductor.
I have a lead lined ammo box , that was originally used to transport radioactive pharmaceuticals in for small stuff .
Instead of thinking of a faraday cage like you would an umbrella in a rainstorm, think of it instead like a sponge you are standing under. That is perhaps the best analogy I can come up with for how a faraday cage is supposed to work. I’ve had to harden communications sites, some of the most vulnerable equipment to emp, to survive direct lightning strikes. Electromagnetic pulses occur at various frequencies depending on how they’re caused, and you need various strategies to protect your electronics. You don’t need a Faraday cage to protect small electronics from EMPs caused by lightning or solar flares. The components inside the cage must be electrically isolated from the conductive material of the cage; wrap them in a towel or a rubber material, or set them on an old mouse pad. You may use a wire mesh to build your cage, as long as the mesh is smaller than 1 millimeter. Faraday cages are not necessary to protect small electronics from solar coronal mass ejections (solar flares) or lightning, because they occur at low frequencies (long wavelengths) which can’t couple energy into small circuits, unless long wires are entering the system. Lightning strikes and solar flares create EMPs at frequencies ranging from 3 Hz to 30 KHz, which is far too low a frequency to couple directly with your small electronics.


A nuclear EMP, on the other hand, can damage electronic devices by coupling energy with their integrated circuits.
Because of the so-called skin effect, the conductive material can be very thin.A You can make your own Faraday cage by placing your electronics in a cardboard box and wrapping the box with heavy-duty aluminum foil, which is about 24 microns thick. In the video, I demonstrate a DIY Faraday cage made from a cardboard box and heavy duty aluminum foil. Place the items inside and isolate them from the container with a towel or rubberized material. Anti static bags offer some protection, and those certified to MIL-PRF-8170 or MIL-PRF-131 offer the most.
An EMP (electromagnetic pulse) can be created by space weather, like massive solar flares, as well as HEMP weapons.
In a nuclear war it is possible that the first nukes used would be HEMP weapons in an attempt to knock out defenses. As the EMP hits the faraday cage, the energy travels around the outer metal material but not through the insulator. Batteries should not be effected by an EMP but might be useful stored with your electronics for easy access.
If you have certain individual electronics you use regularly and want to add a level of protection, consider buying small faraday bags. This entry was posted in How To and tagged electromagnet pulse, electronics, emp, faraday cage, grid down, hemp weapon on November 6, 2013 by Michael.
Please note that all modern Lithium Ion batteries have management electronics built in, and thus be vulnerable to an EMP.
Legal NoticeThe contents of this website are provided for informational purposes only and should not be construed as professional, legal, or financial advice. Watch this video: - Is a steel garbage can a good Faraday cage to protect against EMP and Solar flares? A better precaution against solar events is to unplug electronics and use quality surge suppressors.
If the cage is made from something non-conductive, the free carriers are not mobile enough to realign and cancel the incident field.
The conductivity of nearly any metal is good enough to allow the carriers to easily realign to cancel external fields. Each has its own level of effectiveness as covered in my book, Disaster Preparedness for EMP Attacks and Solar Storms. They can be purchased in many different sizes, including some large enough to hold radio equipment. Engineers who work in electromagnetics often use “shield rooms” to conduct experiments because they do an excellent job of filtering out interfering signals, providing in excess of 100 dB of shielding.
There can be no conductive penetrations into the room, or it will seriously degrade the shielding. A steel trash can with a very tight fitting lid does a pretty good job of acting as a Faraday cage. I tested ammo cans for my book, and they didn’t do great because of the less than perfect seam going around them. Yes, your cell phone may get fried — but, as you said, the rest of the network may get fried, too. A ground provides a safe place to direct excess current from lightning strikes, power line surges or static discharge to protect your more delicate electronics. A high altitude nuke EMP will generate upwards of 25,000 volts per meter within a close distance and 5000 volts per meter out to around 1500 miles from zero. Some where around 200,000 volts per meter of wire at zero and 100,000 volts at the horizon. I don’t expect to have a serious auto accident, but that doesn’t mean I don’t buy coverage for it. I didn’t have time to talk about that in this article, but it is discussed in a youtube video that I did. You want do dump the energy ASAP, longer lines introduce delays and resistance to the energy moving away. These EMPs cause damage by driving voltage spikes into things that are plugged into your electrical outlets. The wavelengths involved range from several miles to 100,000 miles in length, so they can’t couple with the short wiring circuits in a cell phone, a thumb drive, or a radio.
These occur at frequencies of around 1 GHz, which corresponds to a wavelength of .3 meters, or about 1 foot. Modern ovens operate at a frequency of 2.45 GHz, and their built-in shielding will exclude all frequencies below that, including nuclear EMPs.
One thing I neglected to mention in the video is that LED bulbs are highly susceptible to EMP damage. Even they had some electronic components, but none of them are required to start and run the engine. It must be heavy duty foil, which is 24 microns thick, and I use two layers just to be sure.


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High Altitude Electromagnetic Weapons (HEMP weapons) are nuclear weapons that are detonated high in the atmosphere. As long as the conducting layer is greater than the skin depth, it will provide excellent shielding because the absorption loss will be large.
For example, if silver (the best conductor) is used in place of aluminum, the skin depth at 200 MHz is reduced to about 4.5 microns. A poor-man’s shield room can be made by lining a small closet with heavy-duty aluminum foil, covering all four walls, the floor, the ceiling, and the inside of the door.
I tested this as part of my book, and found that it varies greatly depending on the fit of the lid.
It would be fine sitting inside a Faraday cage as long as you’re not scrubbing your bare electronics against it. An EMP is a high frequency radiated event (not conducted like a bolt of lightning), so the goal is to simply shield the sensitive electronics from the high electromagnetic fields. EMP is a high energy radio wave, but radio waves are not current flow, otherwise they couldn’t go through air which is an insulator. I only have a couple walkie-talkies, a transistor radio and a couple flashlights in it, with no batteries in them. Check out disasterprepper videos (or my name) and you’ll find one on Faraday Cage testing. However, they do couple with long power lines and create huge voltage surges which are transmitted through power cables connected to the electrical grid, so if you have something plugged into the power outlet in your wall, it can be damaged. Very small gaps are OK, but to offer protection, they must be significantly smaller than the wavelength of the EMP; in the case of a nuclear EMP, the greatest gap you want is about 1 millimeter.
Add to the the fact that many modern flashlights have electronic circuits that control the output, and your flashlight is definitely an item you want to protect.
You might have the materials lying around in your garage right now – and if not the cost to build one is very low and can sometimes be done in less than 10 minutes. If the box is grounded to the earth (third prong in household wiring or to a metal rod stuck in the ground) it should work better, but this is not required.
The reader should seek his or her own legal or financial advice from a qualified professional. Arthur Bradley, author of Disaster Preparedness for EMP Attacks and Solar Storms, answers a few basic questions and perhaps debunks a few myths.
The enclosure itself can be conductive, or it can be made of a non-conductive material (such as cardboard or wood) and then wrapped in a conductive material (such as aluminum foil). The bottom line is that an ungrounded cage protects the contents from harmful electromagnetic fields as well as a grounded one. It resides in my basement and the electronic items in it don’t seem to care if it looks dated. I am not sure of your experience, but I say this as a NARTE certified EMC engineer who has worked in electromagnetics for 20 years. The best protection is to unplug your electronics, but use a surge protector in case you’re not there to unplug everything.
Electromagnetic pulses don’t hurt people directly, they just wipe out communications and infrastructure.
As an example, consider that for a frequency of 200 MHz, the skin depth of aluminum is only about 21 microns.
The results from testing three different types of bags are provided in Disaster Preparedness for EMP Attacks and Solar Storms.
When selecting an ESD bag, consider not only the shielding effectiveness but also the physical ruggedness of the bag.
Also, lay a piece of plywood or cardboard on the floor so that it can be walked on without damaging the aluminum foil. The author directs you to his book to find the effective shielding of the various recommended containers, but this is at pretty much the lower end of shielding effectiveness. I want to think I can get around when TSHTF happens without the dependence of a cellular device,Who are you going to call? In this context, a Faraday cage is a container made of conductive material that completely surrounds your electronics.
Therefore, wrapping a box in a couple of layers of heavy duty aluminum foil (typically about 24 microns thick) provides the necessary conductor thickness to protect against high-frequency radiated fields.
Rooms built in this way have been shown to offer more than 50 dB of shielding up to several hundred MHz.



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