Views: 0 Author: Site Editor Publish Time: 2022-11-10 Origin: Site
shielded cable Shielding is the isolation of metal between two regions of space to control electric and magnetic fields and electromagnetic waves from one region to the other area to another area of induction and radiation. Specifically, it is the shielding of components, circuits, assemblies, cables or The whole system of interference sources surrounded by shielding to prevent the spread of interference electromagnetic field to the outside: shielding the receiving circuit, equipment or system.
The shield surrounds the receiving circuit, equipment or systemto prevent them from the influence of external electromagnetic fields. This is because the shield protects against interference from wires, cables,components, circuits or systems.
The shield absorbs energy (eddy current loss) and reflects energy (electromagnetic wave interface on the shield).
magnetic waves on the shield interface reflection) and offset energy (electromagnetic induction in the shield to produce reverse electromagnetic field, can offset part of the interference electromagnetic waves).
The role of the shield body, so the shield has the function of attenuating interference.
(1) When the frequency of the interfering electromagnetic field is high, the use of low resistivity of the metal material generated in the eddy current, the formation of external
The effect of shielding is achieved by using the eddy currents generated in the low resistivity metal material to create a counteracting effect on the incoming electromagnetic waves.
(2) When the frequency of interfering electromagnetic waves is low, to use high permeability materials, so that the magnetic lines of force are restricted to the shielding
inside the body to prevent diffusion to the shielded space.
(3) In some cases, if the requirement for both high-frequency and low-frequency electromagnetic field has a good shielding effect, often used. In some cases, if good shielding effect is required for both high frequency and low frequency electromagnetic fields, a multi-layer shield is often used with different metal materials.
Many people do not understand the principle of electromagnetic shielding, think that as long as the metal to make a box, and then ground the box,
The role of electromagnetic shielding can be played. The result is failure under this concept. Because, electromagnetic shielding and shielding body grounding and there is no relationship between shielding and grounding. Only two factors really affect the shielding effectiveness of the shield: one is the entire surface of the shield must be electrically conductive and continuous.
The other is that there must not be a conductor that directly penetrates the shield. There are many conductive discontinuities on the shield, the most
The main category is the combination of different parts of the shield body formed at the non-conductive gaps.
These non-conductive gaps produce electromagnetic leakage, as the fluid will leak from the gap on the container. One way to address this leakage is to fill the gaps with a conductive elastic material to eliminate the non-conductive points. to eliminate the non-conductive points. This is similar to the reasoning behind filling the gaps in a fluid container with rubber. This elastomeric conductive filling material is the electromagnetic seal liner
In many literature,the electromagnetic shield is compared to a liquid sealed container, and it seems that only when the gap is sealed with a conductive elastic material. It seems that only when the gaps are sealed with conductive elastic material to the extent that no water can leak can prevent electromagnetic wave leakage. In fact, this is inaccurate. Because
whether a gap or a hole is will leak electromagnetic waves depends on the size of the gap or hole relative to the wavelength of the electromagnetic waves. When the wavelength is much larger than the size of the opening, there is no significant leakage. does not produce significant leakage. Therefore, when the interference is at a higher frequency, which is a
shorter wavelength, it is necessary to use an electromagnetic sealing liner.
Specifically, when the frequency of interference exceeds 10 MHz, the use of electromagnetic sealing gaskets should be considered. Any material that is flexible and conductive can be used as an electromagnetic sealing liner. According to this principle, the electromagnetic sealing gasket is manufactured sealing gaskets are:
Conductive rubber: in the silicone rubber filled with 70 -80% of the total weight of metal particles, such as silver powder, copper powder, aluminum Powder, silver-plated copper powder, silver-plated aluminum powder, silver-plated glass balls, etc. This material retains part of the good elastic properties of silicone rubber, while
at the same time. It has good electrical conductivity.
Metal woven wire mesh: Beryllium copper wire, Monel wire or stainless steel wire woven into a long tubular strip, the shape is very similar to the shielding cable
shield. But its weaving method is different from the cable shield, the cable shield is woven with multiple wires, while this shield liner is woven from a single thread. To use an analogy, it is like the sleeve of a sweater. In order to enhance the gold the elasticity of the metal mesh. Sometimes a rubber core is added to the mesh.
Instead of saying what the shielded wire does, we should say what the shield does. Because the shield is the part of the wire that works. So, what is the role of the shielding layer?
1, first of all, the outermost layer of the general wire is the insulation layer, mostly made of rubber. If it is a high-voltage wire, the middle of the insulation layer will be added a layer of resin-like. The filler can help the wire play a good insulating effect. The shielded wire is the outermost layer plus a shielding layer that can shield the current.
2, second, the role of shielded wire has two main aspects. First, when the wire through the flow of electricity is very large, the magnetic field around the current will be shielded by the shielding layer in the wire. Second, the shield can play a good grounding protection function, when the wire is broken inside, leaking out of the current shielding, so as to play a protective effect of other components.
3, finally, shielding wire shielding interference with the ability of the signal is mainly related to the shielding layer, if you want to improve the role of the product, you need to buy this type of wire, choose the shielding layer of quality wire.
In practical applications, The purpose of shielding is to conduct the induced electromagnetic noise to earth as a return path for the noise signal, which is crucial. Failure to understand its meaning can mean ineffective shielding. The cable shield and its termination must be able to provide a low impedance ground path for electromagnetic noise. An ungrounded shielded cable will not work effectively, and any break in the ground path. Any break in the ground path or too many nodes will reduce the shielding performance of the cable by increasing the grounding impedance.