Since Maxwell established the electromagnetic theory, Herzig discovered electromagnetic waves more than a hundred years, electromagnetic energy has been fully utilized. Especially in today's scientifically developed, radio, television, communications, navigation, radar, telemetry and remote control and computers and other fields have developed rapidly, creating enormous material wealth for mankind, especially the explosive development of information and network technology, so that the world's dialogue distance and time suddenly shortened, the world's outlook has been refreshed, and the dream of the global village will become a reality. However, along with the utilization of electromagnetic energy, also brings the generation of electromagnetic interference. Electromagnetic fields used for meta-use invade sensitive electronic equipment in the form of fields and currents (voltages) by means of radiation and conduction, making it impossible for them to work normally. Moreover, as in the case of ecological pollution, with the development of science and technology. Electromagnetic environmental pollution is also becoming more and more serious. It not only jeopardizes the safety and reliability of electronic products, but also adversely affects human beings and ecology. Of course, this kind of pollution will not be stagnant and accumulation of electromagnetic energy, once the source of electromagnetic harassment to stop working, the interference that is also disappeared.
The continuous deterioration of the electromagnetic environment has caused the world's industrialized countries to pay attention to, especially since the 1970s, a lot of theoretical research and experimental work. And then proposed how to make electronic equipment or systems in the electromagnetic environment in which they are located, can be normal operation, and other equipment or systems working in the environment does not lead to intolerable electromagnetic interference of the new topic. This is called electromagnetic compatibility.
Electromagnetic compatibility is an emerging interdisciplinary and comprehensive application of the discipline. As a fringe technology, it is based on the basic theory of electrical and meta-wire electrical technology, and involves many new technology areas, such as microwave technology, microelectronics technology, computer technology, communications and network technology, and new materials and so on. Electromagnetic compatibility technology research in a wide range, almost all modern industrial fields, such as electric power, communications, transportation, aerospace, military, computers and medical care must be solved electromagnetic compatibility problems. The hot content of the research are:
The characteristics of the electromagnetic interference source and its transmission characteristics;
The hazardous effect of electromagnetic interference;
Electromagnetic interference suppression technology;
Electromagnetic spectrum utilization and management;
Electromagnetic compatibility standards and norms;
Electromagnetic compatibility measurement and testing technology;
Electromagnetic leakage and electrostatic discharge.
Electromagnetic leakage and electrostatic discharge.
Electromagnetic compatibility is again a practical engineering that emphasizes both technology and management. Carrying out such engineering requires a lot of human and financial resources. International Organization for Standardization has been and is developing EMC related standards and norms. China's start in this regard, although late, but the development is rapid. With the development of market economy, China to participate in the world technology market competition, import and export of electronic products must pass the EMC inspection. Therefore, China's government and relevant departments are increasingly concerned about the EMC problem, and constantly develop the relevant mandatory implementation of standards. Various departments and military branches have also begun to study and establish different sizes of EMC laboratories and testing centers. Various forms of technical seminars and exchanges to promote the popularization, promotion and application of EMC technology. China's 98 years of legislation mandatory for six types of imported electronic products (computers, monitors, printers, switching power supplies, televisions and stereos) and communication terminal products to implement EMC testing. 99 years of the State Quality Supervision Bureau issued the "EMC Certification Management Measures". China's Institute of Standardization of Electronic Technology EMC test laboratory by the U.S. Federal Communications Commission through the FCC accreditation. From February 16, 2000 onwards, exported to the United States of America's information technology equipment and transmitting and receiving equipment, the data issued by the laboratory will be directly accepted by the United States. At present, the country is also being validated and acceptance of formal EMC certification bodies and laboratories.
Product EMC testing is to achieve electromagnetic compatibility indispensable technical means, the mandatory implementation of electromagnetic compatibility standards, is to ensure product quality and improve market competitiveness of the prerequisite.
Second, the basic concepts of electromagnetic compatibility
On the EMC concepts, definitions and terms, in 1995 the promulgation of the national standard GB/T4365 "Electromagnetic compatibility terminology" has a detailed description. Here are only a few of the main concepts to make some auxiliary instructions.
1. Electromagnetic environment (Electromagnetic Environment)
Refers to the existence of a given place in the sum of all electromagnetic phenomena.
The given place is space. All electromagnetic phenomena include all of time and all of the spectrum.
2. Electromagnetic Compatibility (Electromagnetic Compatibiiity-EMC)
The ability of a device or system to function properly in its electromagnetic environment without causing intolerable electromagnetic disturbances to anything in that environment.
The concept of EMC, as a discipline, can be translated as "electromagnetic compatibility", while the electromagnetic compatibility of a device or system can be called "electromagnetic compatibility".
As can be seen from the definition, EMC includes two aspects of the meaning of the device or system generated by the electromagnetic emission, does not affect the function of other equipment or systems; and the equipment or system's ability to resist interference, but also enough to make the function of the equipment or system is not affected by other interference. This leads to two other concepts - electromagnetic interference and electromagnetic sensitivity.
3. Electromagnetic Interference (Electromagnetic Interference-EMI)
Electromagnetic harassment caused by equipment, transmission channels or system performance degradation.
The so-called electromagnetic harassment (Electmmagnetic Disturbance) is any electromagnetic phenomenon that may cause a reduction in the performance of a device, equipment or system, or a damaging effect on living or meta-living matter. It may be electromagnetic noise, unwanted signals or changes in the propagation medium itself, which may cause equipment or system degradation or damage, but not necessarily form the consequences. Electromagnetic interference, on the other hand, is a consequence caused by electromagnetic harassment. EMI is composed of three components: the interference source, the coupled channel and the receiver. Often called the three elements of interference.
According to the path of interference propagation, electromagnetic interference can be divided into radiated interference and conducted interference.
Radiated interference (Radiated Interference) is propagated through space and with the characteristics and laws of electromagnetic waves. But not any device can radiate electromagnetic waves.
Conducted Interference (Conducted Interference) is interference that propagates along a conductor. Therefore, the propagation of conducted interference requires a complete circuit connection between the interference source and the receiver.
4. Electromagnetic Sensitivity (Electmmagnetic SuseeptibilkrEMS)
In the presence of electromagnetic harassment, the device, equipment or system can not be avoided the ability to reduce performance. High sensitivity and low immunity. In fact, the two are two aspects of a problem, that is, from different perspectives to reflect the anti-interference ability of the device, equipment or system. To level to indicate that the sensitivity level (just started to appear when the level of performance degradation) the smaller, that is, the higher the sensitivity, the lower the degree of immunity; and the higher the level of immunity, that is, the higher the degree of immunity, the lower the degree of sensitivity.
Electromagnetic sensitivity is also divided into radiated sensitivity and conducted sensitivity.
Third, the harm of electromagnetic interference
People often say that radio frequency interference (Radio Frequency Interference-RFI) refers to the interference of the range of meta-wire electrical broadcasting. 1934 held in Paris, the International Special Committee on Radio Interference (CISPR), is the first time to start the electromagnetic interference and its control technology of the world. Organized research. Today, as mankind enters the information society, electromagnetic wave as a resource has been widely used in information technology products, such as automobiles, communications, computers, home appliances and other products in the wide frequency range of OHz~400GHz, and a large number of people in the society and family. Accompanying electromagnetic interference is radiated or conducted from very low frequency (VLF) to microwave bands to the operating sub-equipment or system and the surrounding environment in a pervasive manner. To the equipment or system as well as ecological hazards of various kinds. Now on several areas of electromagnetic harassment phenomenon is briefly introduced.
(a) electromagnetic interference of information technology equipment can not be ignored
Information technology equipment (Informatbn Technohgy Equipmem-ITE) refers to equipment used for the following purposes:
Receive data from external sources (eg, through the keyboard, the data line input);
Received data for some processing;
The data received. some processing of the received data;
Providing data output.
In the past, it was often assumed that computers were digital systems characterized by logic and were not greatly affected by their own and external electromagnetic interference. Although in the system design and engineering realization, but also consciously or unconsciously to prevent and eliminate a variety of interference, however, mentioned the mastery and use of EMC technology to recognize and study, its awareness is still lacking. However, with the development of microelectronics technology, computers have towards high speed, high sensitivity, high integration and multi-functional direction, the system is a complex device containing a variety of components and many subsystems of low-voltage transmission of information. High speed and high density, will make the system radiation aggravation, low voltage, high sensitivity will make the system's immunity to reduce. Therefore, due to the interference of the electromagnetic environment and the system within the mutual interference, a serious threat to the stability, reliability and security of computer and digital system work. Such as compatible machines often crash phenomenon is a typical example.
(ii) the electromagnetic leakage of information technology equipment threatens information security
Computer keyboards, displays, etc. will make the information radiation leak out. If the leakage is useful information, once intercepted by the enemy, will cause huge losses. The United States is the earliest use of electromagnetic radiation leakage to obtain information and pay attention to the prevention of information leakage of the country. The United States has been done in New York test, the radiation signal interception equipment "data scanner" installed in the car, from the southern end of Manhattan Battery Park, along Wall Street slow, along the way the Customs House, the Federal Reserve Bank, the World Trade Center, City Hall, the Police Department, the New York Telephone Department and the United Nations Headquarters and other units are working on the radiation signal monitoring computer. computers at work at the United Nations Headquarters. To my surprise, I found that New York was a vast repository of information. If the interceptor, is interested in it, he or she can obtain useful intelligence through techniques such as amplification, feature extraction, decryption, decoding, or information processing. According to information, today's interception technology is quite advanced, allowing clear screen images to be obtained within 1 kilometer. In the area of communications, on the other hand, leakage and interception tend to take place in the form of conducted waves. This is because the main forms of signal propagation in the field of communications are cables, fiber optic cables and radio waves. Therefore, in the network era, the leakage in the form of conduction is more serious. The United States had in the 1970s, a diver in the former Soviet Union territorial waters deep inside the Sea of Okhotsk 120 meters deep undersea military communications cables installed a 6-meter-long eavesdropping device, which recorded a large number of all the communication signals passing through the cable. Since no encryption measures were taken, a large amount of military communications information easily fell into the hands of the Americans. The United States is also very skillful in the technology of information leakage control. The U.S. National Security Agency and the U.S. Department of Defense from the twentieth century in the sixties on the development and gradual improvement of anti-electromagnetic leakage standards, is used for computers and information equipment to prevent information leakage of the research is called Tempest technology. IBM developed Tempest personal computers, printers, monitors and other products. IBM developed Tempest personal computers, printers, monitors and other products. In the network era, information leakage is considered the biggest threat to network security. Therefore, the prevention of information leakage is no longer only for the military field is meaningful, but in the economic field and all walks of life should be given sufficient attention.
(C) EMI phenomenon of airborne systems
We all know that the use of laptop computers, cell phones and listening to CDs are not allowed on airplanes. The reason for this is to avoid electromagnetic harassment from these devices. Once the electromagnetic harassment through the airplane cable coupled to the sensitive equipment on board, it may form interference, so that the equipment work instability, or even out of control. If these nuisances through the cabin windows to the outside radiation, so that the space of the electromagnetic environment more complex, and the fuselage has a large number of sensors and dozens of antennae, it will be due to interference and increase the possibility of the aircraft deviation from the route or cause other accidents. Originally, the aircraft design of electromagnetic compatibility, especially the requirements of immunity is very high.
Modern transportation increasingly relies on electronic systems. For the vehicle receiving, monitoring and positioning electronic control system, if the electromagnetic immunity is not enough, it is easy to space electromagnetic environment interference and can not work properly, or even out of control caused by the accident. Such as the failure of the protection of airbags, positioning errors and so on. Railroad turnout signal automatic control, if caused by electromagnetic interference caused by miscontrol, will bring unimaginable disaster to the train driving.
(D) electromagnetic interference in the field of microwave
Satellite ground stations and radar devices will be subject to such as: ultra-high-frequency band television signals, nuclear power signals and other interference. Such as the United States is developing a new generation of high-power emblem weapons, its frequency in the range of l ~ 100GHz, can be imagined, the strong microwave radiation will give the electronic equipment or systems as well as biological and bring how serious damage and killing.
Mobile phones are booming in our country, but the electromagnetic interference it generates brings a lot of trouble and panic to people with cell phones. At present, the country has no electromagnetic radiation health standards on cell phones, there is no cell phone electromagnetic radiation test method standards. But according to the preliminary detection and analysis of the relevant departments, that the electromagnetic radiation of the cell phone for the point frequency microwave radiation. Cell phone in the process of use, its electromagnetic radiation to cell phone and base station (network) to get in touch with the largest, after the first ring, radiation gradually decreases. Therefore, in the first few seconds after the cell phone is connected, it is best not to immediately put the phone against the ear to answer. Because the human brain and eyes are more sensitive to radiation, so as not to cause harm. Of course, during the call, the pitch of the voice, the size and speed of the sound will also make the radiation different. In addition, the different types of cell phones, antennas built-in or external, their radiation will be somewhat different.
(v) EMI hazards to healthcare equipment or systems
Today, many medical devices utilize advanced electronics and information technology. How immunity of these devices is directly related to the safety of people's lives. For example, cardiac starters are often subjected to electromagnetic interference from computers, cell phones, etc., which changes their function. It is said that a pay by the bioelectricity control of the prosthesis, in the high-voltage line by electromagnetic interference after the person back car over. Therefore, the electromagnetic compatibility design of medical equipment is particularly important, the electromagnetic environment of the medical unit deserves attention.
In addition, lightning and electrostatic discharge hazards, also belongs to the category of electromagnetic hazards, the severity of its harm is more people have experienced and recognized.
Four, adhere to the electromagnetic compatibility design, to ensure product quality
The establishment of the EMC discipline and the development of a series of electromagnetic compatibility standards for us from the combination of theory and practice to achieve the electromagnetic compatibility of the product or system provides guidance.
The goal of EMC design is to pass EMC testing and certification.
The ultimate goal of EMC design is to enable our equipment or system to work normally and stably in a predetermined electromagnetic environment, and not to constitute an electromagnetic nuisance to anything in that electromagnetic environment, i.e., to achieve electromagnetic compatibility.
EMC design involves a lot of content. From the principle, to study
interference of the three elements (interference source, interference coupled channel and receiver) and
suppression of interference measures. In terms of technology, it is mainly how to use the three main techniques of filtering,
grounding and shielding.
The basic principles and methods of electromagnetic compatibility design, first of all, according to the product design of EMC requirements and the corresponding indicators, and then, according to the relevant standards and norms of electromagnetic compatibility, the design of the product electromagnetic compatibility indicators required to be broken down into component-level, circuit-level, module-level and product-level indicators, and then in accordance with the function of the level to be achieved at all levels of the requirements, the level of the hierarchical level of the design.
Electromagnetic compatibility design should consider a lot of issues, but according to, is how to improve the immunity of the equipment and prevent electromagnetic leakage. Usually take measures, on the one hand, the equipment or system itself should be selected to minimize interference with each other's equipment, circuits and components, and a reasonable layout. Then it is through the grounding, shielding and filtering technology, suppression and isolation of electromagnetic harassment. Different equipment or systems have different design methods and measures. The following specific talk about some rough understanding.
(a) Component selection and circuit analysis is the basis of EMC design
Take the computer as an example. It is mainly digital circuits, low-level signal transmission equipment. The digital integrated circuits used are both sources of interference, but also interference sensitive devices, represented by the memory MOS devices is a typical example. Memory instantaneous operation can produce a large current, coupled with the operating frequency of up to 100 megabytes or more, and thus prone to tampering, resulting in false operation or through the public **** resistance to interference with other circuits. But on the other hand, the MOS device itself is very poor immunity. Digital circuits transmit pulse signals, resulting in a wide range of radiation frequencies, such as clock generators, high-speed logic circuits, etc., will produce high-frequency interference and electromagnetic leakage, but also by communications, television and other frequency bands of electromagnetic harassment. Therefore, the design should consider the selection of anti-interference devices, reasonable determination of indicators and the use of grounding, shielding and other technologies.
(II) Electromagnetic compatibility design of the electric bead system
Whether it is information technology equipment or radio electronics, electrical products have to have a power supply. Power supply has an external power supply and internal power supply, the power supply is a typical and serious harm electromagnetic interference sources. Such as the impact of the power grid, the spike voltage can be as high as a thousand volts or more, will bring devastating damage to the equipment or system. In addition, the power supply trunk line is a variety of interference signals invade the path of the equipment. Therefore, the power supply system, especially switching power supply EMC design is an important part of the component-level design. Its measures are varied, such as power supply cables directly from the grid mains, the grid leads to the AC by the voltage regulator, low-pass filtering, isolation between the power transformer windings, shielding, and surge suppression and over-voltage and over-current protection, and so on.
(C) grounding system anti-interference design
Good grounding can protect the normal operation of equipment or systems and personal safety. Can eliminate a variety of electromagnetic interference and lightning strikes, etc.. So grounding design is very important, but also difficult subject. There are many types of grounding, such as logic ground, signal ground, shielding ground, protective ground, etc.. The grounding method can also be divided into single-point grounding, multi-point grounding, mixed grounding and suspended ground. The ideal ground should be zero potential, no potential difference between the grounding point. However, in reality, any "ground" or grounding wire has resistance. When a current passes through, there will be a voltage drop, so that the potential on the ground is not zero, and there will be ground voltage between the two grounding points. When the circuit is grounded at multiple points, well there is a signal connection, it will constitute a ground loop interference voltage. Therefore, the grounding technology is very careful, such as signal grounding and power grounding to be separated, complex circuits using multi-point grounding and public **** ground.
(D) printed circuit board EMC design
Components, circuits and ground caused by the harassment will be reflected in the printed circuit board. Therefore, the printed circuit board EMC engineering design is very critical. Printed circuit board wiring should be reasonable, such as the use of multi-layer boards, power lines and ground lines close to the clock line, signal lines and ground lines close to the minister, in order to reduce the circuit work caused by internal noise. Strict implementation of printed circuit board process standards and specifications, analog and digital circuits, layered layout, in order to achieve mutual compatibility between the various circuits on the board.
In addition, it is worth noting that in the EMC design, must not ignore the protection of electrostatic discharge (ESD).ESD protection of the key, one is to prevent the generation and accumulation of electrostatic nuclei, and then is to block the ESD effect occurs. Block phi electric methods and measures are many, not to be repeated here.
Fifth, master and use of EMC test technology
EMC design and EMC testing is complementary to each other, the good and bad EMC design is to be measured by EMC testing. Only in the product EMC design and development of the whole process, EMC compatibility prediction and assessment, in order to early detection of possible electromagnetic interference, and take the necessary suppression and protection measures, so as to ensure that the system of electromagnetic compatibility. Otherwise, when the product is finalized or the system is built and then found to be incompatible with the problem, it is necessary to spend a lot of money on manpower and material resources to modify the design or use remedial measures. However, it is often difficult to completely solve the problem, and bring a lot of trouble to the use of the system.
EMC testing, including test methods, measuring instruments and test sites, test methods based on various standards, measuring instruments based on the frequency domain, the test site is a prerequisite for EMC testing, but also an important factor in measuring the level of EMC work. EMC testing by the site has a great impact on, in particular, to the emission of electromagnetic radiation, radiation reception and radiation sensitivity testing on the site of the most stringent requirements. The most stringent requirements. At present, domestic and foreign commonly used test sites are: open field, semi-electrical dark room, shielded room and transverse electromagnetic wave chamber.
As the EMC test laboratory there are two types of laboratories: one is validated by the EMC authority and quality system certification and has the legal testing qualifications of the comprehensive design and testing laboratories. Or testing center. It includes conducted interference, conducted sensitivity and electrostatic discharge sensitivity test shielding room, radiation sensitivity test anechoic shielding room, there are used for radiated emissions test of the open field and fully equipped with test and control instruments and equipment. To establish such a complete set of laboratories need to invest millions or even tens of millions of yuan. At present, there are several domestic has been built or are investing in the construction.
Another type is based on the actual needs of the unit and the financial situation and the establishment of the EMC laboratory with certain test functions. Than the large-scale integrated laboratory, this type of test laboratory is small, low cost. Mainly for pre-compatibility testing and EMC evaluation. That is, in order to make the product before the final EMC certification, with the means of self-testing and evaluation. If there is a shortage, you can also make full use of the results of the community, internal and external cooperation, mutual comparison and exchange, in order to save money, improve the design, and constantly improve the product of the purpose of electromagnetic compatibility.
In terms of testing instruments, the spectrum analyzer as the core of the automatic detection system can quickly and accurately provide EMC-related parameters. The new EMC scanner combined with spectrum analyzer realizes the visualization of electromagnetic radiation. It can carry out all-round three-dimensional testing of individual components of the system, PCB boards, the whole machine and cables, etc., showing the real electromagnetic radiation situation.
EMC testing must be performed in accordance with the test methods given in the EMC standards and specifications, and the limit values specified in the standards are used as a basis for judgment. For pre-compatibility testing, although it is not possible to guarantee that the product passes all the items of the standard test, but at least it can eliminate the vast majority of electromagnetic interference, thus improving the credibility of the product. And it can point out how you can improve the design and suppress EMI emissions.
VI. Conclusion
EMC as a multidisciplinary high-tech, with its important role in the quality assurance system is gradually recognized. Adhere to the electromagnetic compatibility design, improve the implementation of EMC standards awareness. Eliminate electromagnetic interference, realize electromagnetic compatibility, fundamentally improve product quality and reliability.
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