Aluminum sheet plate metal, which is costly and not tough enough, was not used for construction until the early 20th century = it was mainly used to decorate architectural details, and aluminum began to be used in roofs, waterproof boards, wallboards and spandrels. The first widespread use of aluminum in architecture was in the Empire State building. The utility model is made of a plurality of structural components such as an elevator steeple and a window, and a plurality of decorative components such as an elevator steeple.
As a material, aluminum also has excellent strength to weight ratio, which means that the exterior wall system made of aluminum can be smaller than steel plates. Contemporary aluminum alloys can also support the weight of heavy glass spans to maximize the building's ability to use natural sunlight. The metal and its alloy components are light, durable, corrosion-resistant and can be recycled indefinitely. According to statistics, roughly 75% of all aluminum products are still in use.
1. Within what range is aluminum plate normally used to shield electromagnetic waves?
2. What are the special advantages of using aluminum plates for the mounting plate of main electrical components such as filters in the electrical cabinet?
3. We know that the permeability of aluminum is relatively low. If a space is sealed with an aluminum cover without leakage of gaps, will the magnetic force lines of the external magnetic field not pass through the closed space?
1. First:
- For the interference source of high voltage and small current, the near-field is mainly electric field, and its magnetic field component can be ignored
- For the interference source with low voltage and high current, the near-field is mainly magnetic field, and its electric field component can be ignored
- For high frequency or 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 field and magnetic field can not be ignored. For aluminum plates, the shielding efficiency of electric field waves is very good in the whole frequency range; for plane wave shielding, the shielding efficiency in the whole frequency range is also acceptable, (the shielding efficiency of 0.5mm aluminum plate in the whole frequency range is at least greater than 120dB); for the shielding of magnetic field wave, the shielding efficiency in low frequency band (less than 100kHz) is poor, and the shielding efficiency increases significantly when it is greater than 1MHz.
2. Aluminum or copper plates are mainly used to shield electromagnetic waves above 100kHz. As for the special benefits, there may be other considerations (individually), because the permeability of aluminum or copper plates is low, the shielding effect for low-frequency magnetic fields is indigent.
3. The permeability of aluminum plates or copper plates is very low. If the space is covered with aluminum shield, it plays little role in bypass due to its low permeability, that is, the material with low permeability can not effectively shunt the magnetic circuit, resulting in the decline of its shielding efficiency to the magnetic field. Therefore, it is just the opposite to what you said. In order to obtain a closed space with better shielding efficiency, the steel plate with high permeability should be used to enhance the shielding. In this way, when the external magnetic field passes through space, most of the magnetic field is guided away by the steel plate with high permeability (bypass effect), so as to make the space cleaner.
4. The shielding effect of the shield made of aluminum plate on the magnetic field is not as good as that of steel plate, because the permeability of aluminum is not as good as that of ferromagnetic materials such as steel. However, on some occasions, it is heard that aluminum plates can isolate magnetism. What are the characteristics of aluminum plates? I also want to ask if aluminum has low permeability. Can the magnetic force line of the magnetic field pass through the aluminum plate?
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 whether the radio wave component is the main component. That is, the above situation (3). For this scenario, I may be straightforward (easy to understand). In fact, the shielding effectiveness of a material for electromagnetic waves depends not only on the permeability, but also on the conductivity in the case of plane waves.
In a word, there are three factors affecting shielding effectiveness (1) conductivity(2) Permeability (3) frequency of plane electromagnetic waves; although the permeability of aluminum or copper is very small, its conductivity is larger than that of steel plates. In this way: A. for low-frequency electromagnetic waves, steel plate has a good shielding effect on plane waves (the skin depth of steel plate is less than that of aluminum (copper)) B. for plane waves with frequency greater than 0.01mhz, aluminum or copper has good shielding effect. In many cases, the frequency of electromagnetic waves is greater than this frequency range, so the shielding effect of aluminum plate can be heard on many occasions. In fact, who is good and who is bad mainly depends on which band of electromagnetic waves you want to shield. See? For different materials, the frequency of electromagnetic wave shielded is different.
The second problem: the permeability of the aluminum plate is low, and there are few magnetic lines of force passing through the aluminum plate. Think about it. The permeability, as the name suggests, is the size of the magnetic conductivity. The permeability of aluminum plates is low. Of course, its magnetic conductivity is poor. Many magnetic lines of force directly pass through the aluminum plate, affecting the internal space of the aluminum enclosure and the internal space of the aluminum enclosure, so it can not play the effect of magnetic shielding. If it is a steel plate, when the magnetic force line touches the steel plate, due to the strong permeability of the steel plate, most of the magnetic force lines are guided away by the steel plate, so they will not pass through the steel plate and affect the internal space of the steel plate, so as to achieve the shielding effect. Note: the above analysis only considers the permeability. In other words, for the case of low frequency dominated by magnetic waves.