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 farther away from the source of interference (far-field conditions), regardless of the nature of the interference source, it can
be regarded as a plane electromagnetic field.
At this time, the electric and magnetic fields are not negligible.
For aluminum plates, shielding of electric field waves is very effective in the entire frequency range; shielding of plane waves, Shielding performance is also
possible over the entire frequency range (0.5mm aluminum plate shielding effectiveness is at least greater than 120dB over the entire frequency range);
For the shielding of magnetic field waves, the shielding performance of the low frequency band (less than 100KHz) is poor, greater than 1MHz, and the shielding
performance is obviously increased.
2. Use aluminum plate or copper plate, mainly to shield electromagnetic waves above 100KHz. As for any special benefits, there may be other considerations
(personal opinion), Since the magnetic permeability of the aluminum plate or the copper plate is low, the shielding effect on the low frequency magnetic field
3. The magnetic permeability of the aluminum plate or the copper plate is very low. If the space is covered by the aluminum shield, the magnetic permeability
is low, and its function as a bypass is small, that is, the material with low magnetic permeability cannot be effectively shunted. The magnetic circuit causes its
shielding effectiveness against the magnetic field to decrease.
So, in order to obtain a closed space with better shielding effectiveness, it is necessary to use a large magnetic permeability steel plate to improve the shielding.
Thus, when the external magnetic field passes through the space, most of the magnetic field is guided away by the high magnetic permeability steel plate
(bypass), so that the space is relatively clean.
4. The shielding cover made of aluminum plate is not as good as the steel plate because the magnetic permeability of aluminum is not as good as that of steel
and other ferromagnetic materials.
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Shirley N.//SMC Editor