(2) when the frequency of the interference electromagnetic wave is low, to use high permeability materials, so that the magnetic line of force is limited to the shielding body inside, to prevent the diffusion of the shielded space to go.
(3) in some occasions, if the requirements of high frequency and low frequency electromagnetic fields have a good shielding effect, often using different metal materials to form a multi-layer shielding body.
Many people do not understand the principle of electromagnetic shielding, think that as long as the metal to make a box, and then ground the box, will be able to play the role of electromagnetic shielding. Under the guidance of this concept results in failure. Because, electromagnetic shielding and shielding body grounding and no relationship. Really affect the shielding effectiveness of the shielding body only two factors: one is the entire surface of the shielding body must be conductive continuity, the other is that there can be no direct penetration of the shielding body of the conductor. Shielding body has a lot of conductive discontinuity, the most important category is the shielding body of different parts of the combination of the formation of non-conductive gaps. These non-conductive gaps create electromagnetic leakage, just as a fluid would leak from a gap on a container. One way to address this leakage is to fill the gaps with a conductive elastomeric material to eliminate the non-conductive spots. This is the same as filling a gap in a fluid container with rubber. This elastic conductive filler material is the electromagnetic sealing liner. In much of the literature will be electromagnetic shielding body analogous to a liquid sealed container, it seems that only when the conductive elastic material will be sealed to the gap to the degree of watertight to prevent electromagnetic wave leakage. In reality this is inaccurate. The reason is that whether or not a gap or hole will leak electromagnetic waves depends on the size of the gap or hole relative to the wavelength of the electromagnetic wave. When the wavelength is much larger than the size of the opening, and does not produce significant leakage. Figure Title: electromagnetic shielding box electromagnetic shielding mechanism: a. When electromagnetic waves reach the surface of the shielding body, due to the discontinuity of the impedance at the air-metal interface, the reflection of the incident wave. This reflection does not require the shielding material must have a certain thickness, only requires the discontinuity in the interface;
b, not reflected off the surface and into the shielding body of energy, in the body of the forward propagation of the process, by the shielding material attenuation. Also known as absorption;
c, in the shielding body has not been attenuated out of the remaining energy, to the other surface of the material, encountered the metal - air impedance discontinuity in the interface, will form a reflection again, and return to the shielding body. This reflection in the two metal interfaces may have multiple reflections. In conclusion, the attenuation of electromagnetic by electromagnetic shielding body is mainly based on the reflection of electromagnetic wave and the absorption of electromagnetic wave. There are now many national and international standards on the limits of radiated and conducted emissions from products. Some of them also specify minimum sensitivity requirements for various types of interference. Often, there are different standards for different types of electronic equipment. While meeting these standards is necessary for a product to be successful in the marketplace, compliance is voluntary.
However, some countries give specifications rather than standards, so compliance is mandatory in order to sell products in these countries. Some norms not only specify standards but also give the authorities the power to confiscate non-conforming products. Applications . 3C products such as laptops, GPS, ADSL and cell phones can generate noise due to high-frequency electromagnetic interference, which affects the quality of communication. In addition, if the human body is exposed to strong electromagnetic fields for a long time, it may be susceptible to cancerous lesions. Therefore, anti-electromagnetic interference is a must-have process.
Conductive paint EMI conductive paint spraying technology with high conductivity, high electromagnetic shielding efficiency, spraying operation is simple (with the same surface spraying operation only to be sprayed on a thin layer of conductive paint in the plastic shell) and other characteristics, widely used in communications products (cell phones), computers (laptops), portable electronics, consumer electronics, network hardware (servers, etc.), medical equipment, home electronics and aerospace and defense and other electronic products. Electronic products and aerospace and defense and other electronic equipment EMI shielding. It is suitable for shielding of various plastic products (PC, PC+ABS, ABS, etc.).