Faraday cages are enclosures that shield against the entry or escape of electromagnetic fields.
These devices become useful in several circumstances.
For example, if you want to prevent your phone from being surveilled or the NSA from listening in on your conservations, then owning a Faraday cage is something that can help you take protective measures.
In this blog, we’ll take a closer look at what Faraday cages are and how you may utilize them in your life.
1. What is a Faraday cage?
A Faraday cage, or a Faraday shield, is a protective enclosure that prevents certain types of electromagnetic radiation from entering or exiting.
The cage was first invented in the 19th century, and it has both practical and personal applications.
For example, hospitals regularly use Faraday cages, but you can even see them in kitchens.
While not all cages are of the same quality, they generally follow the same principles.
We’ll discuss how these devices work below.
2. How does a Faraday cage work?
A Faraday cage is a container or shield that blocks out electromagnetic radiation from across the electromagnetic spectrum.
This includes radio waves and microwaves.
It operates on the principle that, when an electromagnetic field hits something that conducts electricity, the charges will remain on the exterior of the conductor rather than traveling inside.
So, if the cage is constructed of a material that can conduct electricity, it will prevent certain electromagnetic radiation from passing through.
This includes constant (static) electric fields and changing (non-static) electric fields.
3. Who invented the Faraday cage?
British scientist Michael Faraday invented the Faraday cage in the 19th century.
He did this by building on the work from Benjamin Franklin.
In 1755, Franklin realized that if he lowered a cork ball on a silk thread into a metal can with an electric charge running through it, then it was not electrified when lowered to the bottom of the can.
In 1836, Faraday furthered this research when he built a 12-foot cube with a wooden frame on four glass supports.
He lined the cube’s paper walls with metal foil, and then he stepped inside, using an electrostatic generator to plaster the room with electricity.
The inventor lived there for two days and confirmed what he suspected — electricity is a force and not a material liquid that flowed through wires like water through a pipe (as had been thought at the time).
Faraday is also known for the Faraday law of induction.
4. What are Faraday cages made of?
Faraday cages can be made of any material that can conduct electricity.
Common materials include wire mesh, metallic sheets, or coils of water.
Something as simple as aluminum foil can provide the sheathing for the cage.
The exterior of your cage is your conductor, so it can be extremely thin (like foil).
However, the thicker you make it, the more protection you will have against electric fields.
In terms of shape, Faraday cages can be any shape, including a box, sphere, or cylinder.
They also come in a range of sizes, which means you can have a portable cage if necessary.
5. What are some examples?
Do you want to make a simple, makeshift Faraday cage?
Take your phone, wrap it in plastic, and then surround it with aluminum foil.
Voila! You now have a makeshift Faraday cage.
You can also look at the microwave in your kitchen as an example.
A microwave keeps microwaves (see where they got the name?) trapped inside the machine.
This is how your food is heated.
Finally, a much larger example is an MRI scanner used in hospitals.
They use Faraday cages to prevent radio signals from entering the room and interfering with the equipment.
To perform a simple Faraday cage test on your at-home microwave, follow these steps:
Call your cell phone and make sure that it rings.
Next, take your cell phone and put it in a microwave. The microwave should be turned off at all times!
Call the cell phone from another phone. Does it ring?
Next, open the microwave door and dial your house phone number on the cell phone. As soon as you hit ‘send,’ shut the microwave door quickly. Does your house phone ring?
Finally, wrap the cell phone in aluminum foil. Call the cell phone again? Does it ring?
6. Is a car a Faraday cage?
When you hear the type of materials that are used to make a Faraday cage, you may wonder, “What about my car?”
Cars aren’t perfect examples of Faraday cages.
While the exterior would likely keep you safe from electrical charges, you are still able to get a signal on your phone.
This indicates that electromagnetic radiation can get in and out.
7. Does a Faraday cage need to be grounded?
“Grounding” a Faraday cage means providing a way for the electrical charge from the cage’s exterior to exit.
This is an important element for safety, but it’s not necessary for its operation.
If you don’t ground your cage, then it means that the electrical charge will remain in its exterior.
If you were to touch it, then it could allow the charge to pass into you, and this would be very dangerous.
If you ground your Faraday cage, then you allow the electrical charge to exit.
Cars, for example, have a natural grounder in the form of rubber tires.
If the car was to be hit by a lightning strike, then the charge could pass from the metal exterior of the car into the rubber tires and then into the ground, which would ultimately remove the charge from the car.
In your Faraday cage, you may have a wire to ground it and help eliminate the charge.
8. Are Faraday cages illegal?
In general, Faraday cages are not illegal (including in the US).
However, the United Kingdom has prohibited the use of jamming devices to block signals from a phone.
For example, a bar in the U.K. got in trouble when they used a Faraday cage to stop customers from looking at their phones in 2016.
They created a cage by installing copper wire mesh into the ceiling of the bar and metal foils into the walls.
9. Do Faraday cages block Wi-Fi?
Yes, you can create a Faraday cage around your Internet router, and this will block electromagnetic radiation – and thus access to the internet.
10. Would a Faraday cage protect from an EMP?
EMP stands for electromagnetic pulse.
It can occur naturally from solar flares or due to weapons.
It is designed to neutralize electronic equipment using a powerful electric field to create short-circuits in such equipment.
You can use Faraday cages to prevent these attacks.
However, because EMPs have very strong electric fields, you would need to have a cage that is as watertight as possible.
It should be of a thick and conductive material with no holes.
11. Can you make your own cage?
Believe it or not, a metal file cabinet requires just a few tweaks to become a Faraday cage.
You can find directions on transforming your filing cabinet into a simple Faraday cage here.
In addition to the cabinet, you’ll require some other modest materials.
If you want to build a cage from scratch, follow these instructions:
Measure out an 8 x 16-inch rectangle of screen metal mesh
Cut out the rectangle with heavy-duty scissors
Measure and cut five 8-inch lengths of wood strips
Carefully unroll the metal mesh rectangle so that it lays flat
Begin stapling the metal mesh to the wood strips
Staple the first strip at the end of the mesh
Staple the second strip 5.5 inches away from the first strip, again lengthwise on the mesh
Staple the third strip 2.5 inches from the second strip
Staple the fourth strip 5.5 inches from the third strip
Staple the fifth strip at the far end of the mesh
The wood strips are braces, so, after stapling them into place, fold the mesh at each strip to form a rectangular box
12. What design elements should you consider?
When making your own cage, you should consider the following design elements for the best results.
To ground your Faraday cage, you’ll need to feed a cable through it.
However, having gaps in your cage allows for penetration by outside electromagnetic fields.
Whether EM radiation can penetrate depends on the size of the hole as well as the thickness of the conductor.
The general rule of thumb is that the opening in the Faraday cage should be smaller than 1/10th of the wavelength that should be blocked.
For example, to block EM fields with frequencies of 10 GHz and lower, the hole size of the cage should be smaller than 3 mm.
Accessing a Faraday cage by opening a lid or door creates the real possibility of a break in continuity.
Even if one side is conducting, the charge may not redistribute properly.
This is normally not much of an issue, but as the size of the cage increases, it can become a larger concern.
If a conducting layer is resistive, then the charge is redistributed more slowly.
This can mean that electromagnetic fields are not fully canceled.
13. When should you use a Faraday cage?
Faraday cages have a variety of applications and uses.
We’ll name the most common uses below.
It’s very likely that this device already exists in your kitchen in the form of a microwave oven.
Its metal shell prevents microwaves inside the oven from leaking into the environment.
EMI shielding for electronic equipment
Some electronic equipment will need to be protected from electromagnetic radiation coming from other electronic units present in the environment.
For example, coaxial cables used for television generally consist of a copper braided shield underneath the PVC jacket that acts as a Faraday cage.
This cage protects the internal conductors from external electrical noise and prevents any radio frequency leakage.
Protective gear for electricians and linemen
There is a protective suit worn by individuals in hazardous environments that is nothing but a type of Faraday cage.
The suits are designed to protect workers from being electrocuted while working near high voltage power lines.
As noted above, Faraday cages are used in MRI scanning rooms to prevent eternal radio frequency signals from causing any distortion to the data coming from the patient.
The protective metal compartment of a car or airplane acts as a Faraday cage to protect its passengers from external electric charges such as lightning.
In the lab, Faraday cages can be incredibly useful to reduce noise (particularly power line noise, which exists everywhere).
14. What can penetrate a Faraday cage?
Faraday cages shield the interior from an external charge or electromagnetic radiation to a large degree (especially with a thick conductor).
That said, these devices cannot block stable or slow varying magnetic fields.
For example, a compass will still work with a Faraday cage because the Earth’s magnetic field can penetrate it.
15. Can you buy a Faraday cage?
Yes, Faraday cages of varying sizes for various uses are available for purchase.
Typically, they come as small as a bag for a smartphone or as large as a tent to park your car in.
So, what do you think?
Are you ready to build a Faraday cage?
For some people, making this device is just a cool experiment, but for others, it can be a life-saver.
Many are drawn to it because of how much it allows you to protect yourself in any given situation.
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