The same shielding body has different shielding performances for different properties of electromagnetic waves. Therefore, when considering electromagnetic shielding performance, it is necessary to have a basic understanding of the types of electromagnetic waves. There are many ways to classify electromagnetic waves, but when designing shields, electromagnetic waves are based on their wave impedance. The wave impedance ZW, which is divided into electric field wave, magnetic field wave, and plane wave electromagnetic wave, is defined as the ratio of the electric field component E to the magnetic field component H in the electromagnetic wave: ZW = E / H.
The wave impedance of electromagnetic waves is related to the nature of the radiation source of electromagnetic waves, the distance from the observation point to the radiation source, and the propagation medium in which the electromagnetic waves are located. When it is close to the radiation source, the wave impedance depends on the characteristics of the radiation source. If the radiation source is high current and low voltage (the impedance of the radiation source is low), the wave impedance of the generated electromagnetic wave is less than 377, which is called a magnetic field wave.
If the radiation source is high voltage and small current (the impedance of the radiation source is relatively high), the wave impedance of the generated electromagnetic wave is greater than 377. When the electric field wave is far away from the radiation source, the wave impedance is only related to the electric field wave propagation medium. The value is equal to the characteristic impedance of the medium, which is 377Ω for air. The wave impedance of electric field waves decreases as the propagation distance increases, and the wave impedance of magnetic field waves increases as the propagation distance increases.
Shielded room performance indicators: (Meet national GB12190-90, national confidentiality BMB3-1999, GJBz-20219-94 standard C)
Magnetic field: 14KHz≥80dB? 200KHz≥85dB
Plane wave: 50mHz—1GHz≥110dB
Application scope: Information confidentiality of the core departments of party and government agencies; national defense security, EMC testing, radar navigation, post and telecommunications, scientific research institutes, and industrial and commercial enterprises involving information technology confidentiality and other fields.