Comparison of shielding properties of aluminum plate, steel plate and copper plate

1. In what range is the aluminum plate usually used to shield electromagnetic waves? 2. In the electrical cabinet, the installation board of the main electrical components such as the filter, what special advantage does the use of aluminum plate have? 3. We know that aluminum has a low magnetic permeability ratio. If a space is sealed with a cover made of aluminum and does not leak any gaps, will the magnetic field lines of the external magnetic field not pass through this enclosed space? 1. First of all: (1) For high-voltage, low-current interference sources, the near field is dominated by electric fields, and its magnetic field component can be ignored; (2) For low-voltage, high-current interference sources, the near-field is dominated by magnetic fields, and its electric field The component can be ignored; (3) For higher frequencies or in places far away from the interference source (far-field conditions), regardless of the characteristics of the interference source itself, it can be regarded as a plane electromagnetic field. At this time, the electric and magnetic fields cannot be ignored. For aluminum plate, the shielding effect of electric field wave is very good in the whole frequency range; the shielding effect of plane wave is also good in the whole frequency range, (0.5mm aluminum plate has at least the shielding effect in the whole frequency range Greater than 120dB); shielding magnetic field waves, the shielding effectiveness of low frequency band (less than 100KHz) is poor, greater than 1MHz, the shielding effectiveness is significantly increased. 2. Use aluminum or copper plates, mainly to shield electromagnetic waves above 100KHz. As for any special benefits, there may be other considerations (personally think). Because aluminum or copper plates have low magnetic permeability, they are suitable for low-frequency magnetic fields. The shielding effect is very poor. 3. The magnetic permeability of aluminum or copper plates is very low. If the space is covered by an aluminum shielding cover, due to its low magnetic permeability, it plays little role in bypassing, that is, materials with low permeability cannot effectively shunt flow The magnetic circuit leads to a decrease in its shielding effectiveness against the magnetic field, so it is exactly the opposite of what you said. In order to obtain a closed space with better shielding effectiveness, it is necessary to improve the shielding with a steel plate with high permeability. In this way, when the external magnetic field passes through the space, most of the magnetic field is guided away by the steel plate with high permeability (bypass). Make the space cleaner. 4. The shielding cover made of aluminum plate is not as effective as steel plate in shielding the magnetic field, because the magnetic permeability of aluminum is not as good as that of ferromagnetic materials such as steel. However, in some occasions, someone said that aluminum plate can isolate magnetic field, which mainly refers to the characteristics of aluminum plate. What? I also want to ask, the magnetic permeability of aluminum is low, can the lines of force of the magnetic field pass through the aluminum plate? The first question: What do you mean by the so-called certain occasions, which are actually many actual situations? In many cases, it is not possible to simply distinguish whether the magnetic wave component is large or the radio wave component is the main component. This is the case (3) above. For this case, what I may say is simpler (to facilitate understanding). In fact, the shielding effectiveness of a certain material against electromagnetic waves not only depends on the magnetic permeability, but also for the case of plane waves. , Conductivity is also a factor that affects its shielding effectiveness. In short: there are three factors that affect shielding effectiveness (1) conductivity; (2) magnetic permeability (3) frequency of plane electromagnetic waves; although the permeability of aluminum or copper is very small, its conductivity is greater than that of steel , So: a. For low-frequency electromagnetic waves, the steel plate has a good shielding effect on plane waves (the skin depth of the steel plate is less than that of aluminum (copper)) b. For the plane wave with a frequency greater than 0.01MHz, the shielding effect of aluminum or copper Great. The frequency of electromagnetic waves in many occasions is greater than this frequency range, so in many occasions, you will hear that the shielding effect of aluminum plate is good. In fact, whoever is better depends on the frequency band of the electromagnetic wave you want to shield. do you understand? For different materials, the frequency of the electromagnetic wave shielded is different. The second problem: the magnetic permeability of the aluminum plate is low, and there are few lines of magnetic force passing through the aluminum plate. Think about it, magnetic permeability, as the name suggests, is the size of the magnetic permeability. The magnetic permeability of the aluminum plate is low. Of course, its magnetic permeability is poor. Many magnetic lines of force pass directly through the aluminum plate, which affects the inside of the aluminum enclosure. The space affects the internal space of the aluminum cover, and thus the magnetic shielding effect is not achieved. If it is a steel plate, when the magnetic line of force hits the steel plate, the magnetic permeability of the steel plate is strong, so that most of the magnetic line of force is led away by the steel plate, so that it will not pass through the steel plate to affect the internal space of the steel plate, and achieve the shielding effect. Note: The above analysis only considers the magnetic permeability. That is to say, for the case where low frequency is dominated by magnetic waves.