Everybody knows phenomena induced by electromagnetic fields such as TV and radio interferences caused by another electrical appliance such as a hair dryer, electric shaver, mixer, vacuum cleaner, etc when watching television or listening to the radio.
To shield against the electromagnetic emissions, there must be a barrier of an electrical conductive material to:
* Protect sensitive components from incoming EMI: "immunity"
* Avoid excessive emissions of EMI toward other sensitive equipments: "emission".
Starting from a unique cause there are several apparent results:
* Conductivity or insulation
* Electromagnetic interference
* Radio frequency interference.
The unique cause: Matter is made of electrical charged particles: electrons have a negative charge and protons a positive one. For each atom, negative and positive charges are balanced but according to the materials, some electrons can be more or less tightly held and can be more or less easily moved: the material is more or less conductive or, in other words, more or less insulating.