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What is a Faraday Cage?

What is a Faraday Cage? Who was Michael Faraday? In this article, I review what a "faraday cage" is and what products we use in static control as faraday cages.

1. What is a Faraday Cage?

Answer: A Faraday Cage is any assemblage that utilizes conductive materials so that inner and outer surfaces of a container cannot transmit electrostatic discharges (ESD) between each other.

• The Faraday Cage Principle in Bags
• The Faraday Cage Principle in Garments

The principle is at work when lightning strikes the lightning rod of a building and travels to the ground so that it does not strike the people or the electronics inside the building.

NYC Lightning! by Frank Hazebroek licensed from 500px

Michael Faraday is often credited as being the first to discover electrostatic induction. Remarkably, he had no formal education but studied in the Royal Institute in London beginning in 1813 as an assistant at the age of 20 after impressing chemist Humphrey Davy with his notes from Davy’s lectures. From this point forward, Faraday spent much of his life at the Royal Institute performing numerous experiments on magnetism and electricity.

The principle of the “Faraday Cage” is based on the 1843 “Ice Pail Experiment” by Michael Faraday. At this time, Faraday was interested in how electromagnetic fields were created. Faraday believed correctly, contrary to popular opinion at this time, that there were not many types of electricity, but instead that the changing values of current and voltage produce different groups of phenomena.

I have far more confidence in the one man who works mentally and bodily at a matter than in the six who merely talk about it. – Michael Faraday

In the “Ice Pail Experiment” he lowered a positively charged ball into an electrically isolated conducting metal ice pail. (It was isolated by being placed on top of a wooden stool. Wood is an inductor.) Through electrostatic induction, the positive charge on the ball (without touching the ice pail) was transmitted from the ball to the outer surface of the ice pail. This proved electrostatic induction.

In the ice pail experiment, a charged ball is lowered into an ice pail isolated from ground by sitting on a wooden stool. Charge is then recorded on the surface of the ice pail.

What happens is that the negative and positive electrons inside the ice pail’s conducting metal separate: the negative electrons move to the inside of the ice pail towards the positive charge, and the positive electrons move to the outside surface of the ice pail.

Next, Faraday discharged the electrostatic energy from the ball to the ice pail by touching it to the ice pail. Then he removed the ball. There was no charge recorded on the ball, but the positive charge still existed on the exterior of the ice pail. This proved that charges only exist on the exterior of a charged conductor.

The corollary for the principle of the Faraday Cage is that the charge has no influence on anything enclosed within the conductor.

2. Static Shielding Bags

Diagram of 8100 Series "Metal-In" Static Shielding Bag Layers

Static Shielding Bags are static dissipative on their outer and inner touching layers but contain an aluminum layer sandwiched between these layers to stop ESD.

Aluminum is conductive and is what stops electrostatic discharges (ESD) from entering the bag.

Since the bag could hold a charge, it is best practice to place the bag on an anti static mat that is grounded for several seconds before handling the contents of the bag yourself. This gives any charge on the bag time to discharge to ground.

3. Static Shielding Smocks

ESD Smock and Lab Coat Fabric

ESD Smocks similarly use black carbon woven into them to stop electrostatic discharges on our clothes and skin from discharging onto electronics we are handling.

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