1. What is a shielded wire? Definition: The conductor wrapped around the conductor is called the shielding wire, and the wrapped conductor is called the shielding layer, which is generally a braided copper network or copper berth (aluminum). The shielding layer needs to be grounded, so that external interference signals can be imported into the earth by this layer.       The shielding layer of the shielded cable is mainly made of copper, aluminum and other non-magnetic materials, which is very thin. The effect of the shielding layer is not mainly due to the reflection and absorption of the electric field and magnetic field by the metal body itself, but due to the grounding of the shielding layer. The different forms of grounding will directly affect the shielding effect. Grounding methods for electric field and magnetic field shields are different. It can be ungrounded, single-ended grounded, or double-ended grounded. The role of the shielding wire: to avoid interference signal into the inner layer, conductor interference and reduce the loss of the transmitted signal. The shielding wire isolates the electromagnetic noise source from the sensitive equipment and cuts off the transmission path of the noise source. Shielding is divided into active shielding and passive shielding. The purpose of active shielding is to prevent the noise source from radiating outward. It is the shielding of noise source. The purpose of passive shielding is to prevent the sensitive equipment from being interfered with by noise sources. It is the shielding of sensitive equipment. Structure: (ordinary) insulation layer + shielding layer + wire; (Advanced) insulation layer + shielding layer + signal conductor + shielding grounding conductor Note: When selecting the shielding wire, the insulating layer of the shielding ground wire has the conductive function and can be conductive with the shielding layer (with a certain resistance).   2. Principle of shielded cables Shielding wiring system originated in Europe, it is outside of the common unshielded cabling system plus metal shielding layer, using metal shielding layer of reflection, absorption and skin effect, we can realize the function of preventing electromagnetic interference and electromagnetic radiation, shielding system balance principle of comprehensive utilization of the twisted pair and shielding layer shielding effect, thus has very good characteristics of electromagnetic compatibility (EMC).     Electromagnetic compatibility (EMC) refers to the ability of electronic devices or network systems to resist electromagnetic interference without generating excessive electromagnetic radiation. In other words, it is required that the equipment or network system can work normally in a relatively harsh electromagnetic environment, and at the same time can not radiate excessive electromagnetic waves to interfere with the normal work of other equipment and network around. The balance c...