Electromagnetic compatibility
1. Electromagnetic compatibility
Electromagnetic compatibility (emc) is a new and interdisciplinary comprehensive application discipline. As a fringe technology, it is based on the basic theory of electrical and radio technology and involves many new technology fields, such as microwave technology, microelectronics technology, computer technology, communication and network technology and new materials. Electromagnetic compatibility (emc) technology has a wide range of research, almost all modern industrial fields, such as power, communications, transportation, aerospace, military, computer and medical treatment must solve the emc problem. The purpose of electromagnetic compatibility research is as follows.
(1) ensure the normal operation of the internal circuit of the drive power, without interference, and achieve the expected function.
(2) reduce the electromagnetic energy radiation from the drive power, so that the electromagnetic interference intensity generated by the drive power is lower than the specified limit value.
(3) reduce the influence of external electromagnetic energy on the drive power, and improve the anti-interference ability of the drive power.
The hot topics of driving power research are as follows.
(1) characteristics of electromagnetic interference source and its transmission characteristics.
(2) harmful effects of electromagnetic interference.
(3) electromagnetic interference suppression technology.
(4) utilization and management of electromagnetic spectrum.
(5) electromagnetic compatibility standards and specifications.
(6) electromagnetic compatibility measurement and testing technology.
(7) electromagnetic leakage and electrostatic discharge, etc.
For the drive power manufacturers, the purpose of emc research is to achieve the drive power through the CE certification and network access test of the relevant institutions, gain market access, improve the reliability of the drive power, and reduce online accidents. In view of the fact that obtaining CE certification has become an access condition for driving power products to enter the overseas market, and emc test content is gradually added to the network access test of various communication products in China, the significance of emc research is self-evident.
Electromagnetic compatibility of driving power supply is studied under the conditions of given time, space and spectrum resources:
(1) the compatibility and non-interference of each circuit module in the drive power supply can work normally;
(2) compatibility between the drive power and different devices.

Emc can be divided into electromagnetic interference (EMI) and electromagnetic sensitivity (EMS).
(1) EMI: electromagnetic interference, that is, the driving power supply in a certain environment should not produce more electromagnetic energy than required by the corresponding standards during normal operation.
(2) EMS: electromagnetic sensitivity, that is, when the drive power in a certain environment is in normal operation, the drive power can withstand the electromagnetic energy interference within the range specified by the corresponding standard, or the drive power is not sensitive to the electromagnetic energy within a certain range, and can maintain normal operation according to the design performance.
Emc is a practical engineering that attaches equal importance to technology and management. The international organization for standardization has started to formulate standards and norms related to electromagnetic compatibility. With the development of market economy, if our country wants to participate in the world technology market competition, the import and export electronic products must pass the electromagnetic compatibility test. Therefore, the Chinese government and relevant departments pay more and more attention to the electromagnetic compatibility problem, and continuously develop relevant mandatory implementation standards. Various departments and services and arms have also started to research and establish emc test rooms and test centers of different sizes, which has promoted the popularization, promotion and application of emc technology. In 1998, China has legislated compulsory emc testing on 6 types of imported electronic products (computer, display, printer, driving power, TV and audio) and communication terminal products. In 1999, the state administration of quality supervision issued the administrative measures for emc certification. The emc test room of standardization institute of electronic technology in China has been certified by FCC. As of February 16, 2000, information technology equipment and transmitting and receiving equipment exported to the United States, data issued by the test room will be directly accepted by the United States. Emc testing of products is an indispensable technical means to realize emc. Mandatory implementation of emc standards is a prerequisite for ensuring product quality and improving market competitiveness.
The English name for electromagnetic compatibility ElectroMagneticCompatibility, EMC for short. Electromagnetic compatibility refers to the coexistence of devices (subsystems, systems) in a common electromagnetic environment that can perform their respective functions together. There are two meanings here, namely, the electromagnetic radiation generated by its work should be limited to a certain level; In addition, it should have a certain anti - jamming ability. In other words, on the one hand, the electromagnetic interference generated by electrical and electronic instruments does not affect any other instrument or system; On the other hand, even if other instruments, systems of electromagnetic interference, electrical, electronic instruments also have the normal operation of disturbance resistance. The biggest purpose of emc is to ensure the normal working electromagnetic environment when multiple different devices are used in the same environment. Electromagnetic compatibility technology involves a frequency range of 0 ~ 400GHz. In addition to traditional facilities, research objects involve electromagnetic environment from chip level to various ships, space shuttle, intercontinental missiles and even the whole earth.
Electromagnetic compatibility (emc), also known as environmental electromagnetics, initially considered only radio frequency interference with radio broadcasts. However, nowadays, there are more and more electronic products, more and more power transmitted by various electronic devices, more and more sensitivity of electronic device system, and more and more ability to receive weak signals. At the same time, the frequency band of electronic products is also getting wider, smaller and smaller, and the mutual influence is also getting bigger and bigger. Therefore, electromagnetic interference is no longer limited to radiation, but also consider the electromagnetic interference caused by induction, coupling and conduction, such as electromagnetic radiation exposure to biological hazards, static electricity, lightning also belong to the category of electromagnetic compatibility. The three elements of emc are interference source, coupling path and sensitive body.
Electromagnetic compatibility solutions mainly include shielding, grounding and filtering, but there is an inevitable connection between these three or other solutions. Any EMC problem is dealt with around three elements: reducing the interference source, cutting off or weakening the transmission path, and improving the disturbance rejection capability of the equipment. In general, a reasonable EMC design is the most cost-effective way to eliminate most rf interference, that is, to limit electromagnetic energy to where it is needed. Clock spread spectrum technology can be used or appropriately slow down the rising edge of the signal to reduce the interference intensity of the clock signal. In addition, electromagnetic interference intensity can be controlled in the selection of components and the reduction of antenna effect (such as strictly controlling the length of the line and the area of the signal loop). Through the necessary layout, wiring and shielding, grounding measures to improve the anti-interference ability of equipment. In the three-factor countermeasures, cutting off the propagation path of interference is the most important link. The following measures can be taken on the single board to cut off the coupling path or reduce the coupling.
(1) corresponding conduction coupling: filter capacitor, filter, common mode coil, isolation transformer, etc.
(2) corresponding radiation coupling: vertical wiring of adjacent layers, addition of shielded ground wire, rational layout of magnetic components, 3W rule, correct layer distribution, inner layer of strong radiation capacity or sensitive signals, use of I/O twisted pair, signal with strong radiation capacity away from handle bars, plate edge gaps, etc. From the product EMC design countermeasures, means to be divided, usually used only grounding, shielding, filtering three kinds.