Faraday Cage Principle Glass
To understand how the Faraday Cage Principle relates to glass, we must first understand the Faraday Cage Principle.
A Faraday Cage is an enclosure made from a conducting material or mesh. It shields the inside of the enclosure from electrical fields.
When an electrical charge hits the Faraday Cage, it is redistributed along the exterior walls rather than penetrating the walls. In this way, the contents of the cage are shielded from the electrical field. The Cage works even if there are devices with electrical charge inside it.
The Faraday Cage is so called after Michael Faraday who built one in 1836 after observing this behaviour.
The Faraday Cage can have a number of uses, for example:
Protection from lightening – eg, when cars and aeroplanes are hit by lightening, the interior is shielded from the electrical field.
A Microwave oven which contains microwaves inside the enclosure.
Co-axel cable which is wrapped in a conductive material to shield the data inside.
In some cases, the Faraday Cage is also used to shield electro magnetic radiation. To do this, the wavelength of the radiation must be larger than the holes in the material forming the cage. As materials are different and so are the wavelengths, the effectiveness of the shield will depend on the availability of suitable materials and the wavelengths being prevented.
In the car example above, the Faraday Cage only applies to electrical fields and not electro magnetic fields, therefore, a mobile phone can work inside a car.
The choice of material for a Faraday Cage therefore depends on intended use. In highly secure environments, a high degree of shielding may be required. RF protection is the blocking of radio frequency electromagnetic radiation. It is required to protect data from a magnetic pulse. Shielding can also be used to stop external forces from penetrating places where sensitive data is stored and therefore the data is kept secure.
So how does this relate to glass?
In an environment which is designed as a Faraday Cage it is sometimes necessary to have windows. Special glass has been developed to act as a conductor or as an RF shield. It is important to use such glass to maintain the integrity of the Cage.
Pilkington Glass has developed such a glass called Datastop or K Glass. It is normal glass which has a special coating applied to it containing the shielding.