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Microwaves

Is A Microwave A Faraday Cage? (Explained & Solved!)

Antonio Forde
Updated: June 2, 2024
6 min read

A microwave is an electric oven that heats and cooks food by exposing it to microwave-frequency electromagnetic radiation. People use this to heat their foods quickly, and some are curious if microwaves can classify as an example of Faraday cages.

This article will show you what a faraday cage is and if a microwave is considered a faraday cage.

Is a Microwave a Faraday Cage?

Simply put, Faraday Cages disperse electrostatic charge around their perimeter. As a result, they act as a barrier to anything within them.

In this regard, they are a hollow conductor in which the electromagnetic charge remains only on the cage’s external surface. But, as with many things, the reality is a little more complicated.

Microwave ovens are another common application for Faraday Cages. However, unlike other applications, they are designed to reverse and keep the microwave radiation within the oven. You can see a portion of the cage on the microwave oven’s transparent window.

Microwaves nowadays are not built and designed as a Faraday cage, but rather a 1/4 wave choke that effectively attenuates 2.4 GHz but not other frequencies.

What Exactly Is a Faraday Cage?

According to the Magnetic Field Laboratory at Florida State University, A Faraday cage is a protective enclosure that prevents particular electromagnetic radiation from entering or exiting. The cage was invented in the nineteenth century and had a variety of practical and entertaining applications.

We use Faraday cages regularly in places like hospitals and even your kitchen. Some Faraday cages are superior to others, but they all operate on the same principles. How does a Faraday cage function?

A Faraday cage is a container or shield that blocks electromagnetic radiation from all parts of the electromagnetic spectrum, including radio waves and microwaves.

When an electromagnetic field collides with something that can conduct electricity, the charges remain on the conductor’s exterior rather than traveling inside.

In a practical sense, this means that a cage made of electrically conductive material will prevent specific electromagnetic radiation from passing through. This cage holds constant (or static) electric fields and changing (or non-static) electric fields. Now that we learned some information about it let us know who invented this Faraday cage.

The Faraday cage was invented in the nineteenth century by British scientist Michael Faraday, also known for the Faraday law of induction. He built on the work of American scientist Benjamin Franklin from the previous century.

According to the National Archives, Franklin discovered in 1755 that when he lowered a cork ball on a silk thread into a metal can with an electric charge running through it, the cork ball would not electrify it when lowered into the bottom of the can.

Faraday later moved into the theater at The Royal Institution in London, where he worked in the basement. According to The Guardian. He constructed a 12-foot cube with a wooden frame supported by four glass supports inside the theater. He used metal foil to line the cube’s paper walls.

Then, apparently, he went inside, used an electrostatic generator to flood the room with electricity, and spent nearly two days there. Inside the box, Faraday discovered what he had suspected all along: electricity is a force, not a material liquid that flows through wires like water through a pipe, as was previously thought, according to The Royal Institution.

According to Florida State University, Faraday’s electroscope detected no electricity inside the “cage”; only the metal foil surrounding the room conducted electricity, demonstrating the concept of a Faraday cage.

A Faraday cage is from any material that conducts electricity. This cage could be wire mesh, metallic sheets, or wire coils. They can be any shape, such as a box, sphere, or cylinder, and any size, ranging from extremely small to extremely large.

According to Florida State University, the cage’s exterior can be as simple as aluminum foil. The outer covering, or conductor, can be as thin as foil, but thickening it will provide additional protection from more powerful electric fields.

Conductors, in essence, have a reservoir of free-moving electrons that allow them to conduct electricity. When there is no electrical charge present, the conductor has roughly the same number of commingling positive and negative particles throughout it.

As a result, the rest of the cage’s material is relatively free of negatively charged electrons, giving it a positive charge. Electrons repel if the approaching object will charge negatively, but the net effect is the same, just reversed.

This process is known as electrostatic induction. It produces an electrical field opposite to that of the external object.

You will know the effectiveness of a faraday cage by its design, size, and construction materials. They will shield their interiors if the conductor is thick enough and the holes in the mesh are smaller than the wavelength of the radiation in question if they are of mesh construction.

Even though Faraday’s cages and shields are incredible, they are far from perfect. They do not, on the whole, provide complete protection against electromagnetic waves.

Longer wavelengths, such as radio waves, are typically attenuated or blocked by the cage, whereas near-field high-powered frequency transmissions, such as HF RFID, can usually penetrate the shield.

Is a Microwave a Good Faraday Cage?

There are some examples of Faraday cages that we use these days. Faraday cages can be quite complex or very simple, ranging from a shoebox to an entire building. Wrapping your phone in plastic and then wrapping it in aluminum foil, for example, creates a makeshift Faraday cage.

On a larger scale, Faraday cages are used in medical settings to prevent radio signals from entering the room and interfering with the equipment, according to MRI scanner manufacturers EEP.

If you have a microwave in your kitchen, it acts as a Faraday cage, trapping microwaves inside the machine so that they heat your food and do not escape. However, the question is, is it a good Faraday cage?

In 2013, Nick Trefethen of the University of Oxford became interested in Faraday cages after discovering a lack of a thorough mathematical analysis of the cages in the scientific literature.

According to him, the shielding in microwave oven doors is typically a solid sheet of metal with holes punched in it – essentially a Faraday cage with thick wires.

Thinner wires would improve visibility inside the oven, but microwave designers do not use them, which appears to be consistent with the team’s findings.

Trefethen also points out that microwave ovens, despite their thick wires, are not perfect Faraday cages. That is because if you put your mobile phone – which communicates via microwaves – into an oven and call it, it will almost certainly ring.

A microwave oven has a frequency of 2.45 GHz (gigahertz) and a wavelength of 4.82 inches. Because the holes in a microwave oven’s screen mesh are small in comparison to the wavelength of the microwave, little radiation can escape.

Mesh screens are also installed on the sides of the oven cavity to protect the oven light while allowing it to shine into the cavity and the other to allow ventilation.

To some extent, an old microwave oven could be repurposed as an EMP Faraday cage (electromagnetic pulse). Its design is similar to a basic Faraday cage (with a possible frequency/wavelength caveat). A Faraday cage is a closed enclosure made of conducting material or a mesh made of such material.

The very design of a microwave oven is to enclose microwave electromagnetic radiation and prevent it from escaping. The inverse will also be true – they will be unable to enter.

Consider a Faraday cage to be a reflector. An electromagnetic wave reflector. It reflects waves are coming in from the outside and the waves coming out from the inside.

A microwave may partially protect your electronic devices during an EMP, but only to a point. A microwave oven’s design protects at a wavelength of 2.45 GHz. Because an EMP is broad-spectrum, there may be pulse radiation energy from other frequencies that attenuates to protect your devices if used as a Faraday cage.

Sources:

Let’s Talk Science

Interesting Engineering

Physics World

Live Science

Written by
Antonio Forde
I'm the head-writer @ Ask The Home Geek (or, in plain English, I'm the guy writing & editing the majority of the content here). Current learning project: Korean.
Have any questions? Write us a message.
Antonio Forde
I'm the head-writer @ Ask The Home Geek (or, in plain English, I'm the guy writing & editing the majority of the content here). Current learning project: Korean.