What is a Faraday cage, and can it help packaging?

1. What is a Faraday cage?
2. How do they work?
3. The history of the Faraday cage
4. Frequently asked questions
5. Applications and uses
6. GWP Conductive
7. Summary

How electricity flows through conductors is key to understanding how a Faraday cage works.

Metals contain negatively charged particles, or electrons. Without an electric charge, the conductor will have equal numbers of positive and negative particles.

When an external object with electrical charge approaches the conductor (the metal) the particles separate. Any electrons with an opposite charge to the external object are drawn to that object, but any electrons with the same charge are repelled and move away from the object.

The negative and positive particles then end up on the opposite sides of the conductor. The following process is a redistribution of charge that results in an opposing electric field that cancels the field of the external object.

The opposing field shields the interior from exterior static charges, therefore protecting the item inside.

In summary, a Faraday cage, being a conductor, works the same way. The cage will distribute charges around its exterior and cancel out radiation or charges from within the cage’s interior.

Although technically invented by Michael Faraday, Ben Franklin was the first to play a part in the discovery of Faraday cages.

Franklin’s experiment took place in 1755, where he electrified a silver can and lowered an uncharged cork ball attached to a silk thread (non-conductive).

He found that when he lowered the ball into the can, the can had no effect on the cork ball, but when he withdrew it and dangled it near the edge of the can, he observed that the cork was immediately drawn to the electrified surface.

Fast forward to 1836, Physicist Michael Faraday makes other observations, such as electrical conductors, which show that when charged, only the charge is on the surface.

He further tested and confirmed his findings by lining a room with metal foil and then charging the foil with an electrostatic generator. He then used an electroscope inside the room, which indicated there was no charge present, just as he expected. The charge only penetrated to the surface of the foil.

The experiment, which really elevated the idea, though, was his famous ice pail experiment.

In essence, the experiment was a follow-up to Franklin’s idea, in which he lowered a charged brass ball into a metal pail, usually used to hold ice. The results were the same as Franklin’s – the electric charge inside the conductive shell impels an equal charge, and the charge then resides entirely on the surface.

The ice pail experiment was the first precise quantitative experiment on electrostatic charge and later led to the invention of the Faraday cage.

There are a number of common questions asked when discussing Faraday cages and their performance.

Surprisingly, the conductive layer can be quite thin. This is because the current flows primarily on the skin of a conductor. The conductive layer must be thicker than its skin depth to provide excellent shielding where absorption loss is high.

The conductivity of any metal is sufficient to allow the carriers to realign and cancel the external fields. Silver is the best conductor, but you probably wouldn’t want to use it purely for the purpose of a conductive material, mainly due to the consideration of its price.

Grounding a cage means to connect it to an earth-referenced source of charge. This, however, has very little effect on the field levels seen inside the cage. Primarily, grounding helps to keep the cage from becoming charged, but realistically, this is the purpose of a cage anyway. In effect, an underground cage will protect the contents just as well as a grounded cage.

Faraday cages often go by other names. They can be called Faraday shields, radio frequency (RF) cages, or electromotive force (EMF) cages.

They are most often found in science labs, used in experiments or help with product development. They do have a wider range of uses, however.

Power utility linemen will wear suits that utilise the Faraday cage concept. This allows them to work on high-voltage power lines with a reduced risk of electrocution.

Hospitals also use this technology. An MRI scanning room will always enforce a ‘switch your mobile off’ sign, and you’ll often find that in those parts of the hospital, even the waiting rooms, you’ll either have no mobile signal or there will be interference with the signal.

This is because MRI scans rely on powerful magnetic fields to produce images of the human body. MRI rooms must be shielded to prevent stray electromagnetic fields from affecting a patient’s diagnostic image.

In addition, governments protect vital telecommunications equipment from lightning strikes and other interference by using Faraday shields.

As the UK’s leading designer and manufacturer of electrostatic discharge (ESD) safe and anti-static packaging, GWP Conductive offers a range of packaging, storage, and handling products that utilise Faraday cages.

The well-known Corstat coated fibreboard, for example, is effectively a carbon coating which allows the creation of the Faraday cage. Corriplast and SSI Schaefer products both have carbon impregnated directly into the Polypropylene material during manufacture.

It must be noted, however, that simply using a conductive material will not create a Faraday cage – the packaging’s structural design also plays a key role.

Despite this, a wide range of boxes, layer pads, dividers, totes, cases, foam inserts, and other materials-handling products is available. These are predominantly used to protect static-sensitive devices, tools, or components from harmful electromagnetic field exposure.

And if you can’t find a box, bin, or tote that exactly meets your application requirements, you can also specify fully bespoke designs and sizes.

If you think that packaging that creates a Faraday cage could reduce or eliminate damage to your products or components, please use the link below to get in touch.

Alternatively, you can see the full range of anti-static packaging products available by clicking here.