Electromagnetic Compatibility Technology Introduction (Interference Spectrum Distribution, IEMI, Natural Electromagnetic Interference)

Introduce electromagnetic compatibility technology coverage. Focuses on several important technical branches such as interference spectrum distribution, intentional electromagnetic interference (IEMI), natural electromagnetic interference, and electromagnetic pulse. In particular, the importance of intentional electromagnetic interference research and the latest international technological developments.

With the development of science and technology, the quality of human life has been increasing. Informatization, automation, and rapid access to ordinary homes and households are increasing the use of electronic and electrical equipment, leading to the deterioration of the electromagnetic environment. The so-called electromagnetic environment (ElectromagneTICEnvironment), refers to the transmission medium is generally refers to the type of transmission line, cable and space transmission media. Electromagnetic fields or electrical signals include various types of electrical signals and electromagnetic waves. The frequency ranges from near DC and low frequencies up to microwaves, millimeter waves, and sub-millimeter waves; the signals come in various forms, including pulsed and linked waves. Some are also modulated by various modulation methods. These electromagnetic waves and electrical signals are generated by thousands, even millions, of signal sources. The types of radiation sources are numerous and complex. The signal density can exceed one million pulses per second. These electromagnetic signals can directly affect the human body and produce so-called electromagnetic wave biological effects. It can also have an impact on the operation of various electrical and electronic devices, which can degrade their performance and even destroy their normal operation.

The electromagnetic environment of the information society is extremely complex, and EMC electromagnetic compatibility testing is increasingly complex. Electromagnetic interference is distributed throughout the electromagnetic spectrum. If divided by the most common interference spectrum, it can be roughly divided into the following frequency bands:

1. Power frequency interference: The frequency is about 50 ~ 60Hz, which is mainly the electromagnetic field radiation generated by the transmission, distribution system and electric traction system;

2. VLF interference: electromagnetic radiation pulses, lightning, nuclear explosions and earthquakes below 30KHz are mainly distributed in this frequency band;

3. Long-wave signal interference: The frequency range is 10KHz to 300KHz. Including harmonic interference of HVDC transmission, harmonic interference of AC transmission and harmonic interference of AC electric railway, etc.;

4. RF and video interference: The frequency spectrum is between 300KHz and 300MHz. Spark discharges in industrial medical equipment (ISM), power line corona discharge, high voltage equipment, and electric traction systems, as well as internal combustion engines, electric motors, household appliances, and lighting appliances, are all in this area;

5. Microwave interference: frequency from 300MHz ~ 300GHz, including high frequency, ultra-high frequency, very high frequency interference;

6. Nuclear electromagnetic pulse interference: The frequency is from KHz to near DC and the range is very wide.

In recent years, the term intentional electromagnetic interference (IEMI) has emerged. It refers to terrorists, criminals, and all kinds of electromagnetic interference released by hackers to destroy the normal operation of electronic and electrical equipment. Hackers' activities may be somewhat 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, a seminar on IEMI was held at the EMC EMC Testing Conference in Zurich. Everyone agrees to define IEMI as: for the purpose of terror and crime, maliciously manufacture electromagnetic energy, generate noise and signals on electrical and electronic systems and equipment, and thus disrupt, interrupt, or destroy these systems and equipment. There is no explicit reference to hackers in this definition, but in most countries, attacks on the "entertainment" system for commercial interests are illegal.

The threat of IEMI does exist. The threat to the world from terrorist activities is increasing. IEMI is a new method of terror. Attacks can be hidden, passing through many physical obstacles (walls, borders, etc.). China’s satellite TV broadcasts are interfered with and interrupted several times, which is IEMI.

From the point of view of the signal type, the electromagnetic interference in the electromagnetic environment can be divided into two major categories, one is broadband and the other is narrow-band. From the perspective 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 (usually less than 1 with respect to the center frequency bandwidth), and is radiated at intervals of a certain time (generally on the order of microseconds). The device most likely to be affected is approximately 0.3 to 3 GHz. Of course, the performance of equipment outside this frequency range can also be affected, especially with a resonant system. This kind of electromagnetic radiation may also have modulation. This radiation is generally called high power microwave radiation (HPM). The term also includes radiation other than microwaves.

Broadband emissions are generally pulses in the time domain and are repetitive. The energy of broadband radiation is distributed over a wide frequency band. For example, ultra-wideband pulses (UWB) typically have a rise time of 0.1 nanoseconds and a fall time of about 1 nanosecond. Therefore, the energy is distributed over a very wide spectrum.

The energy of the narrow-band interference signal is concentrated on a single frequency, and it is easy to generate a field strength of several hundred kilovolts per meter. It can cause permanent damage to the device. In contrast, the energy of broadband electromagnetic interference is distributed at various frequencies, so the field strength is relatively weak. Precisely because its energy is distributed over many frequencies, many frequencies may be affected by a system, and this interference is mostly repetitive, lasting for a few seconds or even several minutes, adding to the risk of equipment damage. possibility.

The above interference, like other interferences handled by electromagnetic compatibility, can enter the electronic equipment through radiation, and can also enter the equipment through wires and cables. For radiated interference, EMC electromagnetic compatibility test radiation that appears to be higher than 100 MHz is most concerned. This kind of radiation can easily penetrate unprotected walls, enter the interior of buildings, and couple to machinery and equipment. And the antenna in this band can be made very small. Tests conducted in accordance with IEC Standard 61000-4-3 indicate that general commercial equipment is easily affected at field strengths of 3 to 10V/m (80MHz to 2.5GHz). Of course, the program of the equipment is different and the degree of interference is different.

For EMC electromagnetic compatibility testing of broadband radiation, the IEC uses an electrostatic discharge test (61000-4-2) to generate a peak electric field of up to 1 KV/m near an electrostatic discharge arc. The peak rise time is 0.7 nanoseconds and the fall time is about 30 nanoseconds. This simulates electromagnetic interference radiation.

In principle, all electrical and electronic equipment may generate electromagnetic interference. However, some are serious and some are weak. Some of the major devices and devices that generate electromagnetic interference signals are as follows.

1. Power line corona clutter. There are many measured data on transmission lines. Based on these data, a practical formula for calculating corona clutter can be obtained. However, the mechanism of occurrence, emission and propagation of this type of clutter are still not fully understood, and the theory in this area still needs further discussion.

2. Car clutter. Car clutter is the main cause of urban clutter in the VHF to UHF (UHF) frequency bands. According to the measurement results of its strength and characteristics, corresponding measures can also be taken to make the quality of radio and television basically unaffected. However, recently, due to the widespread use of electronic equipment for vehicle control and mobile communication equipment, this issue has been revisited. The Stanford Research Institute (SRI) has improved the main components of the ignition system to emit clutter, such as ignition plugs and distributor contacts, and has reduced clutter in the 30-MHz to 500-MHz frequency band by 13-20 dB. In addition, it has been found that the pulsed clutter amplitude distribution of the six engine engine ignition plugs. In the case of distributors, if the electrode gap is from 0.27mm to 2.39mm, the clutter can drop by 10dB. If the silver contact is added to the load electrode, or covered with multiple alloys, the clutter can also be reduced. Car electrical equipment outside the ignition system can also emit clutter, and its characteristics are being tested.

3. Contact with clutter. It can be roughly divided into the clutter of the contactor itself and the clutter caused by the discharge of the conductor during opening and closing. The discharge clutter generated by the opening and closing of relays and motor contacts and commutator brushes accounts for a significant proportion of human clutter.

4. Electric locomotive clutter. When the electric locomotive is in operation, the discharge between the electric conduction, the arch and the contact line is also one of the sources of human clutter. If the current path of the pantograph is surrounded by filter material and some auxiliary measures are taken, the clutter can be reduced by 20 dB, but no absolute effective method of preventing clutter has been found yet.

5. Industrial Science Medical Radio Frequency Equipment (ISM) Clutter. The ISM equipment is a frequency conversion device that converts 50 Hz AC to RF through radio frequency oscillation, industrial induction and dielectric heating, medical electrothermal and surgical tools, and ultrasonic generators, microwave ovens, and the like. Although the ISM equipment itself is shielded, but there are gaps, hole oil, pipeline in and out of the ground and other bad, there will still be electromagnetic field leakage to form interference.

6. Urban clutter. Because urban clutter has a close relationship with social activities, it always changes from time to time. Every year in Japan, urban clutter EMC testing is conducted regularly. Many scholars and experts in Europe and the United States also collect clutter EMC electromagnetic compatibility test data. Our country’s work has also begun. The causes, degree and characteristics of urban clutter are changing at any time. The test methods and statistical processing methods have yet to be further explored.

7. Others. The above mainly introduces the status quo and existing problems of several kinds of artificial clutter. In addition, abnormal actions such as electrostatic discharge and radio stations are sometimes harmful. Moreover, almost all the equipment and equipment on the power line have a variety of clutter and wave propagation of the transient, which will cause the machine to malfunction. With the widespread adoption of digital circuits, the problem is even more serious. In addition, unexplained disturbances are also found. The micro-switches of the automated boiler igniters in the food industry also have poor contact conditions, so it is also necessary to speed up the research to ascertain the cause of these clutters.

Everybody knows three major effects at the time of a nuclear explosion: shock waves, thermal radiation (light radiation), and radioactive contamination. In fact, there is a fourth effect of nuclear weapons - electromagnetic pulse (ElectromagneTIcPulse), referred to as EMP. If the hydrogen bomb is exploded at a high altitude outside the atmosphere, there will be no shock wave and no heat radiation because there is no air, and the radioactive dust decreases with the square of the distance, and then it is absorbed by the atmosphere, so it is very weak when reaching the ground. It is harmless to people. However, conducting nuclear explosions at altitudes above 100 kilometers can generate strong electromagnetic pulses (50 to 100 kV/m) over a few million square kilometers. One of the third-generation nuclear weapons currently under development in the United States, Russia, and other countries is the nuclear electromagnetic pulse bomb. This highlights the electromagnetic pulse effect of a nuclear explosion. If the average nuclear weapon releases energy in the form of electromagnetic pulses, it only accounts for 3/1010 to 3/105 of the total released energy of nuclear bombs, while the nuclear electromagnetic pulse bomb can increase this value to 40. The consequence of EMP is the destruction of electrical and electronic equipment without harming humans, just as opposed to neutron bombs. EMP can cause enemy command, control, communication & intelligence (C3I) systems to be destroyed, power grids disconnected, metal pipelines and underground cable communication networks, etc., and fall into no power, no Three worlds without communication, without computers. It is precisely because of the lack of killing and wounding that it "normalizes" nuclear weapons, thereby increasing the danger of nuclear war.

Since the 1980s, electronic equipment has undergone fundamental changes, and integrated circuits have replaced transistors, which has greatly reduced the ability to withstand destruction (high-voltage, high-current breakdown burn-out). The current of an integrated circuit is one thousandth of a transistor, which is one millionth or even one-thousandth of an electron tube. Nuclear electromagnetic pulses have become a threat to electronic devices. The higher the level of microelectronics technology, the worse the destruction resistance of electronic devices. It is no wonder that some Russian military aircraft now use wireless radios instead of transistors and integrated circuits. There are many national field radio stations that are still assembled using discrete components.

(Editor: admin)

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