First of all, let's understand a phenomenon. When electronic equipment is working, it neither wants to be interfered by external electromagnetic waves, nor does it want to radiate electromagnetic waves to interfere with external equipment, as well as radiation hazards to human body. Therefore, it is necessary to block the propagation path of electromagnetic waves. This is electromagnetic shielding.
According to Maxwell's electromagnetic theory, electromagnetic waves are composed of mutually perpendicular electric and magnetic fields. The changing electric field is converted into magnetic field, and the changing magnetic field is converted into electric field. They alternate, and the energy travels forward. Therefore, electromagnetic shielding should be divided into two aspects: electric field shielding and magnetic field shielding.
The electric field shielding is based on the Faraday cage effect. When the electric field hits the surface of the metal cage, part of it is reflected, and the other part generates induced charges on the metal surface. These induced charges form skin current, and energy is consumed. It can be understood that part of the conductive layer is attenuated, so the electric field is shielded for the internal space. If the conductor is not completely enclosed, for example, there are some holes or gaps, the skin current formed by the induced charge will flow along the surface of the conductor. When the gap is encountered, the current will enter the inner cavity of the conductor along the gap, and an electric field will be formed inside, which will weaken the shielding effect. Therefore, the coating of conductive paint needs to be as comprehensive as possible.
Magnetic field shielding requires materials with high permeability to block the transmission path. Generally speaking, the shielding effect of low-frequency electromagnetic wave is greater than that of high-frequency electromagnetic wave and electric field.
After understanding the above principle, let's see how conductive paint can play a shielding role. If the shell of an electronic product is plastic, the external electromagnetic radiation will penetrate the non-conductive plastic shell without blocking. In the same way, it generates relatively large electromagnetic radiation and will penetrate its shell without any barrier. After the conductive paint is sprayed, a conductive film of metal can be formed on its surface. According to the above theory, it can play a shielding role.
Conductive paint is divided into pure silver and silver copper with high conductivity suitable for shielding electric field and nickel conductive paint with magnetism suitable for shielding magnetic field interference with slightly poor conductivity. (NX-101 pure silver conductive paint) Silver is relatively expensive, suitable for high-end products and military applications; (NX-202 silver conductive paint) The application scope of silver copper is very wide; (NX-401 nickel conductive paint) Nickel is mainly suitable for low-frequency interference and shielding magnetic field interference.
Another little knowledge:
The electromagnetic shielding effectiveness is expressed by SE (shielding effectiveness), SE=- 20 lg (E out/E in), in dB decibels. The shielding effectiveness of 100 decibels is only 1/100000 electromagnetic energy leakage.
Therefore, the shielding effectiveness of conductive paint is less than 100dB, and it will reach 80dB!