Faraday Cage

What Is A Faraday Cage?

A Faraday Cage (Shield) can be described as an enclosure created by conducting materials that blocks external electric fields (both static and non-static).

These shields – cages can be used to protect different kinds of electronic equipment from electrostatic discharges. They can’t block magnetic fields like Earth’s magnetic field, but they can protect the interior from electromagnetic radiation coming from the outside.

The Invention of Faraday Cage

Michael Faraday invented the “cages” in 1836, and they were named after him, but Benjamin Franklin also made a great contribution to “Faraday Cage” development and application.

Faraday noticed that the conductor charge (on a charged conductor) did not influence anything that was enclosed within; the charge resided only on the exterior. Faraday constructed a room, coated the entire room with metal foil, and used an electrostatic generator to create high-voltage discharges that stroke the outside of his metal foil-coated room. He found no electric charge on the inside walls. Faraday used an electroscope to prove this.

In 1755, Benjamin Franklin discovered what we now call “A Faraday Cage”, in his own experiment. He used a cork ball and a can. The cork was suspended on a thread and put into the can through a small opening. Franklin found that the cork wasn’t attracted to the inside, although it did touch the bottom; when drawn out, the cork was not electrified. If it touched the outside, it would have been electrified.

How Does It Work?

An external electrical field leads to rearrangement of the charges, and this cancels the filed inside. Electric fields (applied externally) create forces on electrons in the conductor, creating a current, which will further result in charge rearrangement. The current will cease when the charges rearrange and the applied field inside is canceled.

Applications of the Faraday Cage

Safety against lightening: The cage protects the interior of the vehicle from the strong electric fields. Cars and aircraft act as Faraday cages / shields to protect people when the vehicle is struck by lightening.

Microwave: the microwaves inside the oven are trapped and used for cooking. The metal shell of the microwave acts as a Faraday cage.

Protections for electronic goods: Electronic equipment can be shielded and protected from stray electromagnetic fields by using coaxial cables that contain a conducting shell that acts as a Faraday cage.

Protective suits for linemen: linemen often wear protective suits that act as Faraday cages while working with high voltage power lines. These suits protect them from getting electrocuted.

MRI (Magnetic resonance imaging) scan rooms are good examples of a Faraday cage. External radio frequency signals are prevented from interfering with the data coming from the patient.

How to Build a Faraday Cage

Do you know that your fragile computer chips need protection from the Electro Magnetic Pulse (EMP)? To prevent them from getting disrupted by the EMP, we can build our own Faraday cages. There are also other numerous examples of the Faraday cage. Here is how to construct your own Faraday cage.

You will need:

- Two cardboard boxes – one cardboard box should fit tightly inside the other
- Aluminum foil
- 6 to 10 mm black polyethylene sheeting
- Grounding wire (wire that connects metal components in a circuit to the ground)
- An Alligator clip (also called spring clip / crocodile clip)
- Cellophane tape

• Place the smaller cardboard box inside the bigger one.
• Cover the external box completely with aluminum foil.
• Attach a grounding wire to the aluminum foil using the cellophane tape. Attach the crocodile clip to the end of the grounding wire.
• Wrap the covered box with the black polyethylene sheeting
• Use tape to prevent the foil from ripping
• Put the item into the smaller box

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