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In this article, we will explore what a Faraday cage is, examples of a Faraday cage, how a Faraday cage works, its applications and uses, as well as the history behind the Faraday cage. We will also cover what types of packaging create a “Faraday cage” and the effect this has on electronic components.
“a conductive barrier against ESD e.g. static shielding bag, conductive box, etc.”
So, what exactly is a “Faraday cage”? A “Faraday cage”, otherwise known as a Faraday shield, is a sealed enclosure formed by materials which are electrically conductive. They offer a conductive barrier against electrostatic discharges (ESD). The outer layer of a Faraday cage blocks external static and non-static electromagnetic fields protecting the item or electronic device inside the packaging.
A Faraday cage is needed to protect various electronic components and devices (i.e. motherboards, microchips, PCBs, etc.) from electrostatic discharges. Using any closed shape, these cages can be produced from either a conductive material or a non-conductive material and then coated or wrapped in a conductive substance. Occasionally, a fine metallic mesh will be used to make the Faraday shield. These protect a wide range of static sensitive electronic components and devices from electrostatic discharges (ESD).
A “Faraday cage” can also occur in our daily life. One example of a “Faraday cage” or “Faraday shield” is an aircraft being struct by lightning. This occurs frequently but does not harm the passengers or the plane. The metal body of the aircraft protects the interior.
Another example of a “Faraday cage” is a car. A car may also be a safe place during a thunderstorm. The chassis of a car can protect the people inside of a vehicle with its metal framed structure. The electrical charge travels over the metal surface of a car into the ground. This means that people inside a vehicle remain unaffected by lighting as long as the windows are shut.
A Faraday cage does exactly what electric fields in conductors do: they cancel an electromagnetic field by creating a second one in the opposite direction.
Metals (a type of conductor) have negatively charged electrons within them. Without electrical charge, the conductor will have the same amount of positive and negative electrons.
When an electrically charged external object comes into proximity to the conductor (for example an electrically charged balloon and an aluminium can), the electrons disperse. Any electrons with an opposite charge to the external object are drawn to that object, but any electrons with the same charge are repulsed and move away from the object.
The positive and negative electrons then land up on the opposite sides of the conductor, the following process is a redistribution of charges. As a result, an opposing electrical field cancels out the field of the external object. The opposing field shields the interior from exterior static charges, therefore protecting the object inside.
To sum up, a Faraday cage works in the same way as a conductor. The cage will distribute charges around the cage’s exterior and will cancel out radiation or charges from within the cage’s interior. If you would like to learn more about static electricity and electrostatic discharge, please head over to our ‘what is electrostatic discharge (ESD)?‘ article.
There are various applications and industries that use a Faraday cage, including science labs, hospitals, telecommunications and packaging for electronics to name a few.
Anti-static packaging can create a “Faraday cage” effect that channels any electrostatic discharge (ESD) outside the packaging container. The diverting of the charges protects the contents within (e.g. static sensitive electronic components like printed circuit boards or microchips).
ESD control products that create a “Faraday cage” or “shielding” include: static shielding bags, conductive totes and Corstat coated fibreboard products.
In the electronics manufacturing industry where electronic components and devices are manufactured and assembled, it is important to utilise ESD protective packaging when transporting or storing static sensitive electronic items outside of an ESD protected area (EPA).
There are several types of ESD packaging materials that offer shielding properties (“Faraday cage”). A commonly used packaging material is a static shielding bag.
Static shielding bags, or metal shield bags, have several layers: a static dissipative outer and inner surface layer, a static dissipative polyethylene innermost layer and an aluminium vapour deposited sheet intermediary layer. The polyester dielectric works with the metal layer to provide a Faraday cage effect, the metal layer preventing penetration from damaging electrostatic fields. The specially processed polyethylene keeps tribocharging to a minimum.
Corstat coated fibreboard products are another type of packaging option which provides “Faraday cage” protection. The material used for this packaging is simply a carbon coating which allows the creation of the “Faraday cage”. There are a wide range of Corstat coated fibreboard products to select from including Corstat transit packs, Corstat inplant handlers and Corstat bin boxes to name a few.
However, please bear in mind that simply using a conductive material will not create a “Faraday cage” or provide “shielding”. This is because the structural design of the packaging also plays an important part.
As well as anti-static packaging, Faraday cages can also be found in science laboratories where they are used in experiments or used to help with product development.
Faraday cages are also commonly found in hospitals, particularly in MRI scanning rooms. These rooms must be shielded to stop stray electromagnetic fields from impacting and changing a patient’s diagnostic image.
The “Faraday cage” phenomenon is named after the British scientist, Michael Faraday. Faraday made important observations, such as electrical conductors – when charged – only charge on the surface.
In 1836, Micheal Faraday made the first Faraday cage. He built a large box and lined it with wire mesh, charging the mesh with an electrostatic generator. He tested his invention by zapping the box from the outside with static electricity while he stood inside it. By using an electroscope inside of the room, it indicated that there was no static charge present just as he predicted. The static charge only entered the surface of the wire mesh.
Although the “Faraday cage” was technically invented by Michael Faraday, it was Benjamin Franklin who was the first to contribute to the discovery of Faraday cages.
It was in 1755 when Franklin electrified a silver can and lowered an uncharged cork ball connected to a silk thread (non-conductive) into it. He did this until the cork touched the bottom of the can.
He realised that when he lowered the cork ball into the can, the can had no effect on the cork ball. However, when he retracted the cork ball and hung it near the edge of the can, he noticed that the cork ball was instantly attracted to the electrified surface.
The experiment which really elevated the idea though was Faraday’s famous ice pail experiment. Following on from Franklin’s idea, Faraday used a metal ice pail where he lowered a charged brass ball into it to study how charges placed themselves when a charged item was brought inside the pail.
The results were the same as Franklin’s – the electric charge inside the conductive shell drives an equal charge and the charge then stays entirely on the surface. The ice pail experiment was the first measurable experiment on electrostatic charge, which later resulted in the invention of the Faraday cage.
The conductivity of any metal is suitable to enable the carriers to realign and cancel the external fields. The best type of conductor is silver; however this type of metal can be very costly and so you may not want to use it solely as a conductive material.
Grounding a Faraday cage means to link it to an Earth-referenced source of charge. Although, this is somewhat ineffective on the field levels seen inside of the cage. The act of grounding helps to keep the Faraday cage from being electrically charged, but realistically this is the purpose of a cage anyway. In addition, an ungrounded Faraday cage will protect the contents just as well as a grounded Faraday cage.
The conductive layer does not need to be thick, it can actually be quite thin for it to work. This is because the current flows mainly on the surface of a conductor. The conductive layer needs to be greater than its surface depth to give excellent shielding where the absorption loss is large.
Packaging that creates a “Faraday cage” can help to reduce or even eliminate electrostatic damage to static sensitive products or electronic components.
If you think you could benefit from using packaging with “Faraday cage” shielding, please don’t hesitate to get in touch with us on 01793 511000 or sales@bondline.co.uk.
Bondline Electronics Ltd supply a wide range of anti static packaging products. Browse our complete anti static bag range or take a look at our available Corstat products.
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