Electromagnetic waves can act with electronic components to produce an interference phenomenon called EMI (Electromagnetic Interference). For example, the common "snowflake" on a TV screen indicates that the received signal is being interfered with.
Shielding is the isolation of metal between the two space regions to control the electric field, magnetic field and electromagnetic waves from one region to another region of induction and radiation. Specifically, it is the shielding body will be meta-components, circuits, assemblies, cables or the entire system of the source of interference surrounded, to prevent the interference electromagnetic field to the outside world; with the shielding body will be the receiving circuits, equipment or systems surrounded, to prevent them from being affected by the external electromagnetic field. Because the shielding body from the wires, cables, components, circuits or systems, such as external interference electromagnetic waves and internal electromagnetic waves are playing the role of absorbing energy (eddy current loss), reflecting energy (electromagnetic waves in the shielding body on the interface of the reflection) and offsetting energy (electromagnetic induction in the shielding layer on the generation of the reverse electromagnetic field, which can be offset in part of the interference electromagnetic waves), so shielding has the function of attenuating the interference. (1) When the frequency of the interference electromagnetic field is high, the use of low resistivity of the eddy currents generated in the metal material, the formation of foreign electromagnetic wave offsetting effect, so as to achieve the effect of shielding. (2) When the frequency of the interfering electromagnetic wave is low, use materials with high permeability so that the magnetic lines of force are confined inside the shielding body and prevented from spreading to the shielded space. (3) in some occasions, if the requirements of high frequency and low frequency electromagnetic fields have 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, 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, there is no significant leakage.
Mechanism of electromagnetic shielding. a. When the electromagnetic wave reaches 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 that the shielding material must have a certain thickness, only the discontinuity in the interface; b, not reflected off the surface and into the shielding body of energy, in the body of the process of forward propagation, the shielding material is attenuated. Also known as absorption; c, in the shielding body has not yet attenuated the remaining energy, transmitted to the other surface of the material, meet the metal - air impedance discontinuity in the interface, will form a reflection again, and re-return to the shielding body. This reflection in the two metal interfaces may have multiple reflections. In short, the attenuation of electromagnetism by an electromagnetic shield is mainly based on the reflection of electromagnetic waves and the absorption of electromagnetic waves.
There are now many national and international standards on the limits of radiated and conducted emissions from products. Some 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 with these standards is voluntary.
However, some countries give specifications rather than standards, so compliance is mandatory to sell a product in those countries. Some norms not only set standards, but also give 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 (the same as the surface paint operation only to spray 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. Suitable for shielding of various plastic products (PC, PC+ABS, ABS, etc.). Spraying conductive paint to solve the problem of doing metal shielding cover by space constraints, operations, cost pressures, because of its conductive paint spraying operation is extremely simple to do the plastic metallization, and by more and more attention and promotion. Gradually replaced the previous paste tin foil, copper paper, do metal shielding process.
Shenzhen Xin Sheng Feng Technology Co., Ltd. specializes in the production of conductive silver paste, conductive paint, conductive powder. Factory in Baoan, Shenzhen, Guangdong Province, Xixiang Gushu all the way to 537, plant area of 5000 square meters, specializing in the production of research and development of various specifications of conductive paint,
as well as supporting the conductive paint spray processing one-stop service.
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