How to do a good job in electromagnetic shielding of cabinet room. Therefore, all the above measures are closely connected with the special grounding of the computer room. Realize the normal work of the system's positive electromagnetic shielding, and give the computer room staff a green, safe and electromagnetic interference-free space. So that the computer room forms a clean and safe space like a "metal" house. Electromagnetic interference can be completely solved. Occurrence and Harm of Electromagnetic Shielding Magnetism in Sina Weibo 1 Computer Room A large amount of electrostatic charge will accumulate on the surface of components during the use of computers. The most typical thing is that after the display is used, touching the display screen with hands will produce serious electrostatic discharge. About the definition of electrostatic discharge, this is the electrostatic discharge phenomenon when the charge on the display screen and the charge of different symbols on me are neutralized. I won't describe it here. Interested readers can consult the materials themselves. Because the electrostatic discharge process is electromagnetic radiation with random and instantaneous changes in potential and current, electromagnetic radiation can be generated whether it is corona discharge with small discharge energy electromagnetic shielding or spark discharge with large discharge energy. As I mentioned earlier, the computer itself contains a large number of circuits and components with high electromagnetic sensitivity. Therefore, if you encounter electrostatic discharge during use (the consequences of ESP are unpredictable), the harm of electrostatic discharge to the computer can be divided into hard damage and soft damage. Hard damage means that components with high electromagnetic sensitivity, such as graphics card and CPU memory, can't work normally or even be completely scrapped because of the power of ESP. The damage degree of hard damage caused by electrostatic discharge mainly depends on the energy of electrostatic discharge and the electrostatic sensitivity of components, and is also related to the mutual position of electromagnetic shielding between hazard sources and sensitive devices. Soft damage refers to the electromagnetic interference caused by electrostatic discharge (electromagnetic pulse frequency spectrum can reach Mhz Ghz), which leads to storage errors and bit displacement in the memory, thus leading to hidden errors such as crash, illegal operation, file loss, bad track on the hard disk, which is more difficult to find than hard damage. 2. How to do electromagnetic shielding? Therefore, there is no need to modify the circuit. Electromagnetic shielding is one of the important means to solve the problem of electromagnetic compatibility. Most EMC problems can be solved by electromagnetic shielding. The biggest advantage of using electromagnetic shielding to solve the electromagnetic interference problem is that it will not affect the normal work of the circuit. The effectiveness of selecting shielding materials is measured by shielding effectiveness. Shielding efficiency is the ratio of the field strength E 1 at a certain position in space without shielding to the field strength E2 at that position with shielding. Therefore, decibels are usually used to represent the shielding effectiveness and the attenuation level of electromagnetic waves by the shielding body. Shielding for electromagnetic compatibility purposes can usually attenuate the intensity of electromagnetic waves to 1% to1million. At this time, the definition formula of shielding effectiveness is SE = 20lg E 1/ E2 dB. Only the shielding effectiveness of shielding materials can be tested by this definition formula. It is necessary to know which characteristic parameters of the material are related to the shielding effectiveness of the data. Not sure what electromagnetic shielding data should be used as a shield. Determine what material is used to make the shield. The practical formula for representing data shielding effectiveness in engineering is: SE = A+R dB. The calculation formula of electromagnetic wave propagation in shielding materials is: A=3.34t f μ r σ r dB t = the thickness of data. σ r = conductivity of data, μ r = permeability of data. Specific data, these are all known f = frequency of shielding electromagnetic waves. When electromagnetic waves are incident on the interface of different media, the calculation formula is: R=20lg ZW/ZS dB electromagnetic shielding type. Zs= characteristic impedance of shielding material. Zw= wave impedance of electromagnetic wave. The wave impedance of electromagnetic wave is defined as the ratio of electric field component to magnetic field component: Zw = E/H is close to the radiation source (:λ /2 π is called the far-field region), and the wave impedance is only related to the electric field wave propagation medium, and its value is equal to the characteristic impedance of the medium. The calculation method of shielding material impedance of 377Ω air is | zs | = 3.68 10- electromagnetic shielding 7μ r/σ r ω σ r = relative conductivity f= incident electromagnetic wave frequency Hz μ r= relative permeability. & gt From the above formula. Some qualitative conclusions are given below. In order to facilitate the design, the shielding effectiveness of various shielding materials can be calculated. Electric field wave and magnetic field wave should be considered separately; When designing near-field shielding. > using good information from magnetic permeability; When electromagnetic shielding is used to shield electric field waves of data with good conductivity. When shielding magnetic field waves. The same shielding material. Shielding efficiency makes the shielding efficiency of different electric field waves the highest, for different electromagnetic waves. The shielding efficiency of magnetic field wave is the lowest, that is to say, electric field wave is the easiest to shield and magnetic field wave is the most difficult to shield; On the whole. The higher the shielding efficiency; The better the data conductivity and electromagnetic shielding. When shielding electric field waves. When shielding the magnetic field source, the shielding body should be as close as possible to the radiation source. Shielding as far away from the magnetic field source as possible; There is a situation that needs special attention. For example, this is a magnetic wave below 1kHz. This kind of magnetic field wave is generally generated by a strong current radiation source. Power lines, high-power transformers, etc. that transmit large current. For this low-frequency magnetic field, only data with high permeability can be used for shielding, and the commonly used data is permalloy containing about 80% nickel. Electromagnetic leakage of holes and its countermeasures are generally in addition to low-frequency electromagnetic shielding magnetic field. The rare case is the shielding body made of metal, and most metal data can provide shielding efficiency above 100dB. But in fact. Not so high shielding efficiency, or even almost no shielding efficiency. This is because many designers don't understand the key of electromagnetic shielding. First of all. In static electricity, the electromagnetic shielding you need to know has nothing to do with whether the shield is grounded or not. This is different from the shielding of electrostatic field. As long as the shielding layer is grounded, the electrostatic field can be effectively shielded. However, electromagnetic shielding has nothing to do with whether the shield is grounded or not, so it is necessary to make clear that electromagnetic shielding has two key points. In other words, the whole shield must be a complete and continuous conductor. Another point is that no conductor can pass through the chassis. For an actual chassis, one is to ensure the continuity of shielding. These two points are very difficult to achieve. The first is electromagnetic shielding. At the same time, it will not affect other performances (aesthetics, maintainability and reliability) of the chassis. A practical chassis will have many holes and gaps: vents, display ports, openings for installing various adjusting rods, gaps for combining different components, etc. The main content of shielding design is how to properly handle these holes. Secondly. So that the shielding effectiveness of the shielding body is reduced by dozens of times. Proper handling of these cables is one of the important contents in shielding design (the harm of conductors passing through the shielding body is sometimes greater than that of holes). There will always be cables coming in and out of the chassis, and at least one power cord. These cables will greatly damage the shielding layer. When electromagnetic waves are incident on a hole. Its radiation efficiency is the highest (regardless of the width of the hole), that is, when the length of the hole reaches λ /2, it acts as a dipole antenna (figure 1. All the energy that excites holes can radiate in. For holes in data with electromagnetic shielding thickness of 0. In the worst case (polarization direction causing the largest leakage), the formula for calculating the shielding effectiveness (in fact, the shielding effectiveness may be greater) is: in the far-field region. Se =100-20lgl-20lgf+20lg [1+2.3lgl/h] db if L ≥λ /2 SE = 0 dB, each quantity in the formula: L = the length of the slot (mm H = the width of the slot (mm f = the frequency of the incident electromagnetic wave (. In the near field, the electromagnetic shielding leakage of holes is larger than that in the far field (shielding efficiency is low), and the calculation formula of electromagnetic shielding of holes is: if ZC >；; 7.9/d f se = 48+20lgzc-20lgf+20lg [1+2.3lgl/h] ifzc GB 2887-89 computer hiding technical conditions > and GB50 174-93 computer room design specifications > and other related requirements. Prevent step voltage and static electricity. Form a good grounding network. 10 shielding data and measures are connected to the ground wire. The metal fixing feet of the electrostatic floor are connected to the equipotential bus through a special grounding branch of 6 square meters.