来源：http://jnggsdz.com 发布时间：2019-06-04 17:21:23
The shielding performance of aluminium plate, steel plate and copper plate were compared.
1. What range of electromagnetic waves are usually shielded by aluminium plates?
2. What are the special advantages of using aluminium plates as mounting plates for major electrical components, such as filters in electrical cabinets?
3. We know that aluminium permeability is very low. If a space is sealed with an aluminium cover and there is no leakage, will the magnetic lines of the external magnetic field not pass through the enclosed space?
(1) For high voltage and low current sources, the electric field is dominant in the near field, and the magnetic field component can be neglected; (2) for low voltage and high current sources, the magnetic field is dominant in the near field, and the electric field component can be neglected; (3) for high frequency or far field conditions, regardless of the characteristics of the source itself, such as the far field condition. Anyway, it can be regarded as plane electromagnetic field. At this time, the electric and magnetic fields can not be neglected. For aluminium plate, the shielding efficiency of electric field wave in the whole frequency range is very good. The shielding efficiency of plane wave is acceptable in the whole frequency band (the shielding efficiency of 0.5 mm aluminum plate is at least more than 120 dB in the whole frequency band); for magnetic field wave shielding, the shielding efficiency of low frequency (less than 100 KHz) is poor, and when it is greater than 1 MHz, the shielding efficiency is significantly improved.
2. Aluminum or copper plates are mainly used to shield electromagnetic waves above 100KHz. As for special benefits, there may be other considerations.
3. The permeability of aluminium or copper sheets is very low. If the space is shielded by aluminium, it has almost no bypass function because of its low permeability. In order to obtain a better shielding efficiency of the enclosed space, it is necessary to use high permeability steel plate for progressive shielding. In this way, when the external magnetic field passes through the space, most of the magnetic field is transferred by high permeability steel plate (bypass), which makes the space cleaner.
4. The influence of shielding magnetic field made of aluminium sheet is not as good as that of steel sheet, because aluminium permeability is not as good as that of steel and other ferromagnetic materials. But in some occasions, it has been heard that aluminium sheet can be magnetically insulated, mainly referring to the characteristics of aluminium sheet. I also want to ask, because of the low permeability of aluminium, whether magnetic field wire can pass through aluminium sheet.
The first question is: What does "in some cases" mean? In many cases, it is impossible to distinguish whether the magnetic component is large or the radio component is the main component. This is the case above (3). In this case, I can make it simple (easy to understand). In fact, the shielding efficiency of materials to electromagnetic waves depends not only on the permeability of materials, but also on the shielding efficiency of plane waves.
In short, there are three factors affecting shielding efficiency. (2) Permeability of plane electromagnetic wave (3) frequency; conductivity of aluminium or copper is small, but larger than that of steel plate. A. For low frequency electromagnetic wave, steel plate has a good shielding effect on plane wave (the skin depth of steel plate is less than that of aluminum (copper). B. For plane waves with frequencies greater than 0.01MHz, aluminum or copper have good shielding effect. Moreover, in many cases, the frequency of electromagnetic wave is larger than this frequency range, so the shielding effect of aluminium plate is very good in many cases. In fact, who is better or worse depends basically on the frequency band of the electromagnetic wave you want to shield. Okay? Different materials have different frequencies of electromagnetic waves.
Second problem: Aluminum plate has low permeability and few magnetic field lines passing through it. You think, permeability, as the name implies, is the size of the permeability, the permeability of aluminium plate is very low, of course, the permeability of the poor, many magnetic lines through the aluminium plate, directly affect the closed internal space of aluminium, affect the internal space of the aluminium cover, in order to avoid the impact of magnetic shielding. However, if this is a steel plate, when the magnetic line contacts the steel plate, most of the magnetic line will be due to the high permeability of the steel plate, so as not to affect the internal space of the steel plate through the steel plate, to achieve shielding effect. Note: The above analysis only considers permeability. In other words, in the case of low frequencies dominated by electromagnetic waves.