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Electromagnetic environment and EMC (The Importance of EMC testing)

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2011-01-12 00:00

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Abstract: This paper introduces the technical coverage of electromagnetic compatibility. Several important technical branches such as interference spectrum distribution, intentional electromagnetic interference (IEMI), natural electromagnetic interference and electromagnetic pulse are introduced with emphasis. In particular, the importance of research on intentional electromagnetic interference, and the latest technological developments internationally.
　　1. Preamble

　　With the development of science and technology, the quality of human life is improving day by day. Informatization and automation are rapidly entering ordinary households, and more and more electronic and electrical equipment are used in households, resulting in the deterioration of the electromagnetic environment. The so-called electromagnetic environment (ElectromagneticEnvironment), refers to the transmission medium is generally refers to the types of transmission lines, cables and space transmission medium. Electromagnetic fields or electrical signals include various types of electrical signals, electromagnetic waves. The frequency ranges from close to direct current, low frequency to microwave, millimeter wave, and submillimeter wave; the signal forms are various, including pulsed and connected waves. Some are also modulated by various modulation methods. These electromagnetic waves and electrical signals are generated by thousands or even millions of signal sources. There are many types of radiation sources, and they are complex and changeable. Signal densities can exceed millions of pulses per second. These electromagnetic signals can directly affect the human body, resulting in the so-called biological effects of electromagnetic waves. It can also affect the work of various electrical appliances and electronic equipment, reducing their working performance and even destroying their normal work.
　　2. Spectrum distribution of electromagnetic interference (EMC electromagnetic compatibility test content) The
　　electromagnetic environment of the information society is extremely complex, and the EMC electromagnetic compatibility test is becoming more and more complicated. Electromagnetic interference is distributed throughout the electromagnetic spectrum. If divided according to the frequency spectrum of the most common interference, it can be roughly divided into the following frequency bands:
　　1. Power frequency interference: the frequency is about 50-60Hz, mainly the electromagnetic field radiation generated by the transmission and distribution system and the electric traction system;
　　2. Very low frequency interference: interference radiation below 30KHz, electromagnetic pulses generated by lightning, nuclear explosions and earthquakes, the energy of which is mainly distributed in this frequency band; 3. Long wave signal
　　interference: frequency range 10KHz ~ 300KHz. Including high-voltage DC transmission harmonic interference, AC transmission harmonic interference and AC electric railway harmonic interference, etc.;
　　4. Radio frequency and video interference: the frequency spectrum is 300KHz to 300MHz. Industrial medical equipment (ISM), power line corona discharge, spark discharge of high voltage equipment and electric traction system, internal combustion engine, electric motor, household appliances, lighting appliances, etc. are all in this range; 5. Microwave interference: frequency from 300MHz to 300GHz,
　　including High frequency, ultra high frequency, extremely high frequency interference;
　　6. Nuclear electromagnetic pulse interference: the frequency ranges from KHz to close to DC, and the range is very wide.
　　3. Intentional Electromagnetic Interference (IEMI)
　　In recent years, the term Intentional Electromagnetic Interference (IEMI) has appeared. It refers to all kinds of electromagnetic interference released by terrorists, criminals, and hackers to disrupt the normal operation of electronic and electrical equipment. Hacking activities and may be a little different, but the consequences are the same. Recently, the scientific and technological community has attached great importance to the study and assessment of the threat of intentional electromagnetic interference to human life.
　　In February 1999, at the EMC Electromagnetic Compatibility Testing Conference in Zurich, a symposium on IEMI was held. Everyone agreed to define IEMI as: maliciously producing electromagnetic energy for terrorist and criminal purposes, generating noise and signals to electrical and electronic systems and equipment, thereby disrupting, interrupting, or destroying these systems and equipment. There is no explicit mention of hacking in this definition, but hacking of "entertainment" systems for commercial gain is illegal in most countries.
　　The threat of IEMI is real. The threat of terrorist activities to the world is increasing, and IEMI is a new means of terror. Attacks can be carried out covertly and through many physical barriers (such as walls, national borders, etc.). my country's satellite TV broadcasting has been interfered and interrupted several times, which belongs to IEMI.
　　4. General characteristics of IEMI
　　From the perspective of signal types, electromagnetic interference in the electromagnetic environment can be divided into two categories, one is broadband and the other is narrow frequency. From the point of view of the way of energy transmission, there are also two ways, one is radiation and the other is conduction. The narrow-band attack signal waveform is almost a single frequency (generally the frequency bandwidth relative to the center frequency is less than 1), and it radiates within a certain time interval (generally on the order of microseconds). The frequencies of the devices most likely to be affected are roughly between 0.3 and 3GHz. Of course, the performance of equipment outside this frequency range can also be affected, especially in systems with resonance. Such electromagnetic radiation may also be modulated. This radiation is generally referred to as high-power microwave radiation (HPM). The term also includes radiation other than microwaves.
　　Broadband transmissions are generally pulses in the time domain and are repetitive. The energy of broadband radiation is distributed over a very wide frequency band. For example, ultra-wideband pulses (UWB) generally have a rise time of 0.1 nanoseconds and a fall time of about 1 nanosecond. The energy is thus distributed over a very broad frequency spectrum.
　　The energy of the narrow-band interference signal is concentrated in a single frequency, which can easily generate field strengths of hundreds of kilovolts per meter. Can cause permanent damage to equipment. On the contrary, the energy of broadband electromagnetic interference is distributed in various frequencies, so the field strength is relatively weak. It is precisely because its energy is distributed on many frequencies, for a system, many frequencies may be affected, and this kind of interference is mostly repetitive, lasting for several seconds or even several minutes, which increases the risk of equipment damage. possibility.
　　The above interference, like other interferences dealt with by EMC, can enter electronic equipment through radiation, and can also enter equipment through wires and cables. For radiation interference, it seems that the EMC electromagnetic compatibility test radiation with a frequency higher than 100MHz is the most concerned by people. This radiation can easily penetrate undefended walls, enter the interior of buildings, and couple to machinery and equipment. And the antenna in this frequency band can be made very small. Tests done according to IEC standard 61000-4-3 show that general commercial equipment is easily affected when the field strength is 3~10V/m (80MHz~2.5GHz). Of course, the program of the equipment is different, and the degree of interference is also different.
　　For the EMC electromagnetic compatibility test content of broadband radiation, IEC uses the electrostatic discharge test (61000-4-2), which generates a peak electric field up to 1KV/m near the arc of electrostatic discharge. This peak has a rise time of 0.7 nanoseconds and a fall time of about 30 nanoseconds. This simulates the situation of electromagnetic interference radiation.
　　Five, naturally occurring electromagnetic interference
　　In principle, all electrical and electronic equipment may generate electromagnetic interference. But some are severe, and some are milder. Some of the main equipment and devices that generate electromagnetic interference signals are roughly as follows.
　　1.输电线电晕杂波。关于输电线的已有许多实测数据，基于这些数据，可以求得计算电晕杂波的实用公式。然而关于这种杂波的发生机理、发射及传播特性还不完全清楚，在这方面的理论仍需继续探讨。
　　2.汽车杂波。汽车杂波是产生甚高频（VHF）至特高频（UHF）频段城市杂波的主要原因。根据其强度和特性的测定结果，也可采取相应措施，使广播和电视的质量基本不受影响。但最近由于电子设备用于汽车控制，移动通信设备的广泛应用，这个问题又被重新提出。斯坦福研究所（SRI）对点火系统发射杂波的主要部件－点火栓、配电器接点等进行了改进，使处于30MHz~500MHz频段的杂波降低了13~20分贝。此外还有人求出6引擎发动机各点火栓的脉冲杂波振幅分布。对配电器的情况，若电极间隙从0.27mm~2.39mm，则杂波可下降10分贝。若在负荷电极上增加银接点，或用多发合金覆盖，也可降低杂波。点火系统以外的汽车电装置也能发出杂波，其特性正在测试研究中。
　　3.接触杂波。大体可分为接触器自身杂波及导体开合时放电而引起的杂波。继电器和电机触点、整流子电刷间的开合所产生的放电杂波在人为杂波中占相当大的比例。
　　4.电气机车杂波。电气机车运行时，导电、弓架与触线间的放电也是人为杂波的根源之一。如果导电弓架的电流通路用滤波材料包围起来并采用一些辅助措施，可将杂波降低20分贝，但至今尚未找到防止杂波的绝对有效的方法。
　　5.工业科学医疗用射频设备（ISM）杂波。ISM设备是把50Hz交流通过射频振荡变为射频的变频装置、用于工业感应和电介质加热、医疗电热法和外科手术工具以及超声波发生器、微波炉等。虽然ISM设备本身有屏蔽，但有缝隙、孔油、管线进出和接地不良等，仍将有电磁场泄漏形成干扰。
　　6. Urban clutter. Since urban clutter has a close relationship with social activities, it always changes with the times. In Japan, urban clutter EMC electromagnetic compatibility tests are regularly carried out every year. There are also many scholars and experts in Europe and the United States who collect clutter EMC electromagnetic compatibility test data. This work has also begun in our country. The source, degree and characteristics of urban clutter are changing at any time, and its testing methods and statistical processing methods still need to be further explored.
　　7. Others. The above mainly introduces the status quo and existing problems of several kinds of man-made clutter. In addition, such as electrostatic discharge and abnormal operation of radio stations are sometimes harmful. Moreover, almost all kinds of clutter and mixed waves generated by transients are propagating on the power lines of almost all machinery and equipment, which will cause malfunctions of the machines. The problem is exacerbated with the widespread adoption of digital circuits. In addition, unexplained interference was also found to exist. The micro switch of the automatic boiler igniter in the food industry also has poor contact, so it is necessary to accelerate research to find out the cause of these clutter.
　　6. Nuclear electromagnetic pulse
　　Everyone knows that there are three major effects of nuclear explosions: shock waves, thermal radiation (light radiation) and radioactive contamination. In fact, there is a fourth effect of nuclear weapons - Electromagnetic Pulse (Electromagnetic Pulse), referred to as EMP. If the hydrogen bomb is exploded at a high altitude outside the atmosphere, there will be no shock wave or thermal radiation due to the lack of air, and the radioactive dust will weaken with the square of the distance and then be absorbed by the atmosphere, so it will be very weak when it reaches the ground. Harmless to people. However, a nuclear explosion at an altitude of more than 100 kilometers can generate a strong electromagnetic pulse (50~100kV/m) in an area of several million square kilometers. One of the third-generation nuclear weapons currently being developed by the United States, Russia and other countries is the nuclear electromagnetic pulse bomb. Here the electromagnetic pulse effect of the nuclear explosion is highlighted. If the energy released by general nuclear weapons in the form of electromagnetic pulses only accounts for 3/1010 to 3/105 of the total energy released by nuclear bombs, nuclear electromagnetic pulse bombs can increase this value to 40. The consequence of EMP is to destroy electrical and electronic equipment without harming people, just the opposite of the neutron bomb. EMP can enable the enemy to command, control, communicate and intelligence (Command, Control, Communication&Intelligence, abbreviated as C3I) The system was damaged and paralyzed, the power grid was disconnected, metal pipelines and underground cable communication networks were all affected, and it fell into a world of no power, no communication, and no computer. Just because they do not kill people, this makes nuclear weapons "routineized", thus increasing the danger of nuclear war.
　　7. Summary
　　Since the 1980s, electronic equipment has undergone fundamental changes, and integrated circuits have replaced transistors, which has greatly reduced the ability to withstand damage (high voltage and high current breakdown and burnout). The current of an integrated circuit is one-thousandth of that of a transistor, one-millionth or even one-thousandth of that of a tube. Nuclear electromagnetic pulse has become a lethal threat to electronic equipment. The higher the level of microelectronics technology, the worse the invulnerability of electronic equipment. No wonder some Russian military aircraft and radio stations now use ultra-small electronic tubes instead of transistors and integrated circuits. There are many national field radios that are still assembled with discrete components.

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