Cable shielding materials are widely used, and this article focuses on several common cable shielding materials, their use in their respective different categories of fields, and precautions.
1. Application of semi-conductive polymer materials
One is that we usually call the resistivity within a certain range with a certain level of shielding performance of the material called semi-conductive polymer material, the standard of classification is the conductivity principle of the internal material, the material itself has conductive properties is called the structural type, and the way of filler to achieve shielding interference is called the composite type.
Whether it is structural or composite semi-conductive polymer materials, it is the most important shielding material used in the cable structure, because semi-conductive polymer materials can not only shield electromagnetic interference, but also have a strong resistance to other natural damage, especially the ability to resist lightning strikes can make it widely used in special application scenarios such as aircraft cables. The manufacturing process of semi-conductive polymer materials is more complex and the cost is larger, therefore, semi-conductive polymer materials have the need for high costSecond, the application of wire braiding
The second is wire braiding, which mainly refers to the use of metal wire as the main material to form a shielding net to achieve anti-magnetic interference of cable shielding materials. HDMI2 is required in shielding1. In USB4 and other cables, the metal wires used in the braided shielding materials are mostly copper-clad aluminum wires, and this material selection method is mainly to improve the shielding performance of the cable.
Generally speaking, the effect of multi-layer weaving is better than that of single-layer weaving, and the coverage area is inversely proportional to the weaving angle, which means that to improve the shielding performance, the weaving angle should be reduced and the coverage area increased.
3. Shielding applications of low-frequency and high-frequency cables
The proportion of low-frequency cable manufacturing is the highest, and if the cable of different frequencies encounters multiple grounding points, it will produce more noise current, which is not conducive to the realization of a good anti-interference effect of the entire shielding layer. If the shielding method of single-point grounding is to be adopted, it is necessary to ensure that the current can be offset by itself in the shield, so as to ensure that the interference current remains in the shield, so as to effectively avoid electromagnetic interference. Due to the influence of the external grounding method of the application component, the shielding method inside some cables often adopts the two-point grounding method, which is mainly because the two-point grounding shielding method can export the current returned by the magnetic field inside the cable, thereby reducing the intensity of current interference.
The problem of stray capacitance is generally more likely to occur in high-frequency cables, which seriously affects the normal current transmission in high-frequency cables, and the single-point grounding and two-point grounding methods cannot effectively solve this problem, therefore, the shielding mode of multi-point grounding should be used in high-frequency cables. In the high-frequency cable, the interference current inside the line has a variety of frequencies and the characteristics of surface concentration, which directly leads to the doubling of the interference effect, which is not conducive to the normal operation of the whole line, and the multi-point grounding mode can reduce the impedance in the shielding layer, reduce the interference of noise current, and thus improve the overall shielding effect.
Fourth, the shielding application of data cables
The shielding layer of the data cable is mainly made of non-magnetic materials such as copper and aluminum, generally braided copper mesh (aluminum-magnesium woven mesh) or copper poke (aluminum, etc.), and their thickness is very thin, far less than the skin depth of the metal material on the frequency of use. It should be noted that one end of it must be connected with the signal of the circuit, because the effect of the shielding layer is not mainly due to the reflection and absorption of the electric field and magnetic field of the metal body itself, but due to the grounding of the shielding layer, the different forms of grounding will directly affect the shielding effect, and the future trend of electromagnetic shielding materials will develop in the direction of higher shielding efficiency, wider shielding frequency and better comprehensive performance.