Electromagnetic transmission interference in two ways: one is the conduction of transmission, the other is radiation transmission. Conduction between the source of interference in the transmission of sensitive equipment and a complete circuit connection, the interference signal is passed along to the receiver is connected circuit occurs electromagnetic interference. 4g cell phone jammer
Radiative transfer is interfering signals in the form of interference by the media spread outward in the form of electromagnetic waves. Common radiation coupling in three ways: 1) an electromagnetic wave radiated from the antenna is received by another antenna accidentally called coupling antenna of the antenna; 2) sensing the electromagnetic field coupled via the wire, called the coupling field of lines. 3) high-frequency signal between the two conductors of equal and mutual inductive coupling formed, called inductive coupling line to line.
EMI generating mechanism 2
Interference with sensitive equipment from the perspective of interference coupled coupled conduction and radiation can be divided into two types of coupling.
● conductive coupling model
Conductive coupling principle can be divided according to their resistive coupling, capacitive coupling and inductive coupling three basic coupling.
● radiation coupled model
Radiation coupling is another way interfere with the coupling, in addition to intentional radiation emitted from external interference sources, there are a lot of unintentional radiators. Meanwhile, PCB board traces both the power lines, signal lines, clock lines, data lines or control lines, can play the effect of the antenna can radiate interference wave, but also play a role in the receiver. 4g cell phone jammer
3 Electromagnetic Interference Control Technology
① transmission channel suppression
● Filtering: in the design and selection should pay attention to the frequency characteristics of the filter, pressure resistance, rated current, impedance characteristics, shielding and reliability. Install the filter insertion loss characteristics is correct or not its great influence, and only install the proper location, proper installation methods, in order to play the expected interference filtering effect. Consider installing a filter should be installed at the location, the input and output side wiring must be shielded isolation, and high-frequency grounding and bonding methods. 4g cell phone jammer
● Shield: electromagnetic shielding can be divided according to the principle of electric field shielding, magnetic shielding and electromagnetic shielding three. Electric field shielding and electrostatic shielding contain alternating electric field shielding; contain low frequency magnetic shielding magnetic shielding and high frequency magnetic field shielding. Different types of electromagnetic shielding of the different requirements of the shield. In the actual shield, the electromagnetic shield structure depends on the effectiveness of the shield to a greater extent, i.e., the conductive continuity. The actual shielding body due to manufacturing, assembly, maintenance, cooling, observation and interface requirements are generally opened thereon shapes, different size apertures, the apertures of the shielding effectiveness of the shielding body plays an important role in the impact must therefore be taken to suppress electromagnetic apertures leak.
● Grounding: Grounding There are two safe ground and signal ground. Meanwhile, the ground will be the introduction of ground impedance and ground loop interference. Grounding techniques, including the choice of ground, circuit combination, grounding design and reasonable measures to suppress interference grounding applications.
● Lap: Lap is a low-impedance connection between the guide body, only good lap in order to make the circuit to complete its design features that make all kinds of interference suppression measures are to play a role. The method can be divided into the lap lap permanent and semi-permanent lap two kinds, and lap types are divided into direct and indirect lap lap.
● Wiring: Wiring is the key to a printed circuit board design of electromagnetic compatibility, you should choose a reasonable wire width, take the right cabling strategies, such as bold ground, close to the ground loop, reducing wire discontinuity, multi-laminates and so on.
② spatial separation
Spatial separation is an effective way to space radiation harassment and harassment inductive coupling suppression, harassment by increasing the spatial distance between the source and the receiver sensitive equipment, so harassment electromagnetic field strength reaches the sensitive equipment when the equipment has been attenuated below the acceptable threshold sensitivity , so as to suppress electromagnetic interference. By electromagnetic theory shows that the field strength in the near-zone induction field to 1 / r3 way decay, far-field radiation field intensity distribution is reduced by 1 / r way. Therefore, in order to meet the electromagnetic compatibility requirements of the system, each device as possible spatial distance between components of the system increases. In the device, the system wiring, limit minimum spacing parallel cable to reduce crosstalk. In PCB design, the provisions cited the minimum interval between the lines. In addition, the spatial separation is also included in the limited space of the case, the source of the radiation pattern of harassment azimuth adjustment, spatial orientation of the electric field vector and the magnetic field disturbance source vector control.
③ time separation
When the disturbance source is very strong, reliable and easy to use other methods of suppression, often using time-separated ways in which the useful signal in time to stop the harassment signal emitted by transport, or when strong harassment signal transmission, so vulnerable to harassment short of sensitive equipment when turned off, in order to avoid suffering damage. Time to separate control two forms, one is the active time separator for the useful signal and the interference signal occurs time periods to determine the relationship between the situation has; another is passive time separator, features appear in accordance with the useful signal interference signal so that a signal in which the rapid closure, does not overlap in time so as to achieve, not covered by the control request. 4g cell phone jammer
④ spectrum management
Planning division of the spectrum is allocated to the various bands of various radio services, the development of the band for a specific user. Develop national standards to prevent interference and, in some cases to ensure that the communication system to achieve the required communication performance basis. This includes the approval process of radio equipment, radio transmitters, receivers and other equipment minimum performance standard file type approval required.
⑤ electrical isolation
Electrical isolation is a reliable method to avoid circuit conduction disturbances, while also making a useful signal properly coupled transmission. Common forms of electrical isolation coupled with a mechanical coupling, electromagnetic coupling, optical coupling. DC / DC converter is a widely used electrical isolation device, it A DC voltage into another DC voltage, in order to prevent multiple devices share a common power supply causing interference resistance, application DC / DC converter a separate power supply and the brightest to ensure that the circuit from the power of signal interference.
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