Shielded wire principle
The shielded wiring system originated from Europe. It is a metal shielding layer added to the outside of the ordinary unshielded wiring system, and the reflection, absorption and skin effect of the metal shielding layer are used to prevent electromagnetic interference and electromagnetic radiation.
The shielding system comprehensively utilizes the balance principle of the twisted pair and the shielding effect of the shielding layer, so it has very good electromagnetic compatibility (EMC) characteristics.
(Skin effect: refers to the fact that the distribution of current on the conductor cross-section tends to be distributed on the surface of the conductor as the frequency increases. The higher the frequency, the smaller the skin depth, that is, the higher the frequency, the weaker the penetration ability of electromagnetic waves)
Electromagnetic compatibility (EMC) means that electronic equipment or network systems have a certain ability to resist electromagnetic interference, and at the same time cannot generate excessive electromagnetic radiation.
That is to say, it is required that the device or network system can work normally in a relatively harsh electromagnetic environment, and at the same time cannot radiate excessive electromagnetic waves to interfere with the normal operation of other surrounding devices and networks.
The balanced characteristics of U/UTP (unshielded) cables are not only determined by the quality of the components themselves (eg twisted pairs), but are also affected by the surrounding environment.