Principle of use of electromagnetic shielding film

Electromagnetic shielding is one of the effective methods widely used in electromagnetic compatibility engineering to suppress electromagnetic interference. The so-called shielding refers to a shield made of conductive and magnetic materials that confines electromagnetic waves within a certain range, suppressing or attenuating them when they couple or radiate from one side of the shield to the other.

Electromagnetic shielding filmThe film is mainly made of conductive materials (Ag, ITO, indium tin oxide, etc.), which can be plated on glass or other substrates such as plastic films. The main performance indicators of the material are transmittance and shielding effectiveness, that is, how much energy is shielded.

Sputtering gold plating is the process of using high-energy argon ions to impact a metal in a vacuum container, causing the metal to vaporize, and then forming a thin metal film on the surface of plastic fabrics and other materials. Sputtering gold plating can also be applied to various plastics. Compared with vacuum gold plating, the adhesion between the plated metal and plastic is generally stronger. However, the equipment cost is high, and there are also advantages and disadvantages of vacuum gold plating.

Metal melting is the process of instantly melting metal under high arc temperature, and then immediately blowing the melted metal into a mist with high-pressure air and spraying it onto the surface of plastic. After the metal Zn is melted at high temperature by arc, it is blown into extremely fine granular powder on the surface of plastic with high-speed airflow, forming a very thin metal layer with a thickness of about 50um and good conductivity. The bulk resistivity can reach below 10-2 Ω· cm, and the shielding effect is about 60-120dB. The disadvantage of the metal dissolution spray method is that the adhesion between the Zn coating and the plastic is poor, and the coating is prone to detachment, requiring a special dissolution spray device.

Paste metal foil composite shielding materialIt is to bond metal foil or composite metal foil with plastic sheet, thin film or thin film with adhesive first, and then press it into shape by laminating method, which can produce soft and hard shielding materials. Metal foil can be attached to the surface or between two layers of plastic. Its advantages are that the method is simple and easy to implement, the bonding strength is high, it is not easy to partially detach, and the conductivity is good.

Electromagnetic shielding principle

Electromagnetic shielding refers to the use of reflection, attenuation, etc. of shielding materials to prevent the electromagnetic energy generated by electromagnetic radiation sources from entering the shielded area. Usually, the shielding effectiveness SE (Shielding Efficiency, dB) of a shielding material at a certain point in space is expressed as: SE=20lg(E0/E)， E0 is the field strength at the point without shielding material, and E is the field strength at the point with shielding material. SE less than 30dB is considered a difference; 30-60dB is moderate and can be used for general industrial or commercial electronic devices; 60-90dB is considered good and can be used for shielding aerospace and military instruments and equipment; 90dB or above is preferred, used for demanding high-precision and high-sensitivity products. According to practical needs, for most electronic product shielding materials, an SE of at least 35dB or higher in the frequency range of 30-1000MHz is considered effective shielding.

S. According to A. Schelkunoff's electromagnetic shielding theory, when electromagnetic waves propagate to the surface of shielding materials, there are usually two different mechanisms for attenuation:

(1) Absorption loss that enters the shielding body without being reflected;

(2) Reflection loss on the incident surface;