EMC absorber

EMC absorber material is a material that can effectively absorb electromagnetic waves. It can be used in the EMC design of electronic products to eliminate electromagnetic interference and reduce electromagnetic radiation. EMC absorber material usually consists of one or more kinds of electromagnetic wave absorbers and a base material, where the electromagnetic wave absorber is the key to absorbing electromagnetic waves. Common EMC absorber materials include soft magnetic materials, nano-absorbing materials, porous absorbers, etc.

EMC absorber includes two aspects of requirements:

1. On the one hand, it refers to the equipment in the normal operation of the environment where the electromagnetic interference can not exceed a certain limit value (EMI);
2. On the other hand, it means that the apparatus has a certain degree of immunity to electromagnetic interference present in the environment, that is, electromagnetic sensitivity (EMS).

With the development of modern science and technology, electromagnetic wave radiation on the environment is increasing. In the airport, aircraft flights can not take off due to electromagnetic interference and are missed; in hospitals, cell phones often interfere with the normal work of various electronic medical instruments. Therefore, the management of electromagnetic pollution, looking for a material that can resist and weaken electromagnetic wave radiation – EMC absorber materials, has become a major issue of materials science.

Electromagnetic radiation through the thermal effect, non-thermal effect, and cumulative effect on the human body caused by direct and indirect harm. Research confirms that ferrite wave-absorbing material has the best performance, it has the characteristics of a high absorption band, high absorption rate, and thin matching thickness. The application of this material in electronic equipment can absorb the leaked electromagnetic radiation and can achieve the purpose of eliminating electromagnetic interference. According to the law of electromagnetic wave propagation in the medium from low magnetic orientation to high magnetic permeability direction, the use of high permeability ferrite to guide electromagnetic waves, through resonance, a large number of absorption of electromagnetic wave radiation energy, and then through the coupling of electromagnetic wave energy into thermal energy.

EMC absorber materials are designed with two issues in mind.

1. Electromagnetic waves encounter the surface of the absorbing material, as far as possible completely through the surface, to reduce reflection;
2. The electromagnetic wave into the absorbing material inside, to make the electromagnetic wave energy loss as much as possible.

In the increasingly important stealth and electromagnetic compatibility (EMC) technology, the role and status of EMC absorber materials are very prominent, and have become modern military electronic countermeasures and “secret weapons”, its engineering applications are mainly in the following areas.

1. Stealth technology

In aircraft, missiles, tanks, ships, warehouses, and other weapons and equipment and military facilities coated with absorbent materials, you can absorb reconnaissance waves, and attenuate the reflected signal, so as to break through the enemy’s radar defense zone, which is a powerful means of anti-radar reconnaissance, reduce the weapon system suffered infrared-guided missiles and laser weapons attack a method.

2. Improve the electromagnetic compatibility performance of the aircraft

False signals generated by the reflection of electromagnetic waves from the aircraft fuselage may lead to false interception or false tracking of highly sensitive airborne radar; when several radars on an aircraft or a ship work at the same time, the crosstalk between radar transceiver antennas is sometimes very serious, and the jamming machine on board or on the ship will also interfere with the radar or communication equipment that comes with it. In order to reduce such interference, foreign countries commonly used to absorb the material excellent magnetic shielding to improve the performance of the radar or communications equipment. Such as in the radar or communications equipment body, antenna, and all around the interference coated with absorbent materials, they can make them more sensitive and more accurate detection of enemy targets. In radar parabolic antenna opening on the surrounding wall coated with absorbing material, can reduce the secondary flap to the main flap interference and increase the distance of the role of the transmitting antenna, and the receiving antenna to reduce the false target reflection of interference; in the satellite communication system application EMC absorber material, will avoid interference between communication lines, improve the sensitivity of the on-board communication machine and ground station, thereby improving the quality of communication.

3. RFID antenna anti-metal isolation application

This application mainly uses a class of high channel rate, low loss type absorbing material with high channel rate characteristics. When used, the EMC absorber sheet is inserted between the 13.56MHz return antenna and the metal substrate to increase the inductive magnetic field through the absorbing material itself and reduce the chance of passing through the metal plate, thus reducing the inductive eddy currents generated in the metal plate and thus reducing the loss of inductive magnetic field. At the same time, because of the insertion of the EMC absorber sheet, the measured parasitic capacitance will be reduced, the frequency shift will be reduced, and the resonant frequency of the card reader will be consistent, so as to improve the reading distance, of course, the degree of improvement depends on the excellent degree of wave-absorbing material characteristics.

4. Security Protection

Due to the application of high-power radar, communication machines, microwave heating, and other equipment, the prevention of electromagnetic radiation or leakage, and protection of the operator’s health is a new and complex subject, and absorbing materials can achieve this purpose. In addition, today’s household appliances commonly have electromagnetic radiation problems, which can also be effectively suppressed through the rational use of EMC absorber materials and their components.

5. Microwave dark room

The absorbers decorated a wall space called a microwave dark room. In the darkroom can form an equivalent non-reflective free space (noiseless area), reflected back from around the electromagnetic waves then the direct electromagnetic energy is much smaller, and can be negligible. Microwave dark room is mainly used for radar or communication antennae, missiles, aircraft, spacecraft, satellites, and other characteristics of impedance and coupling degree of measurement, astronauts with back shoulder antenna directional map measurement and spacecraft installation, testing, and adjustment, which can eliminate outside interference and improve the measurement accuracy and efficiency (indoor all-weather work), but also to keep the secret.

Definition

Electromagnetic compatibility (EMC) is the ability of the equipment or system to operate in its electromagnetic environment and not produce intolerable electromagnetic interference with any equipment in its environment. Therefore, an EMC absorber includes two requirements: on the one hand, the electromagnetic interference generated by the equipment to the environment during normal operation cannot exceed a certain limit; on the other hand, the appliance has a certain degree of resistance to the electromagnetic interference in the environment of the equipment, that is, electromagnetic sensitivity.

EMC（Electromagnetic Compatibility）
In the International Electrotechnical Commission standard IEC, electromagnetic compatibility is defined as the system or equipment working normally in the electromagnetic environment without causing interference to other systems and equipment.

Figure 1 Concept atlas of EMC

EMC absorber includes EMI (electromagnetic interference) and EMS (electromagnetic tolerance), which is the electromagnetic noise generated by the machine itself against other systems; and EMS refers to the machine performing the function independent of the surrounding electromagnetic environment.
Electromagnetic compatibility (electromagnetic compatibility) of various electrical or electronic equipment in the common space of the complex electromagnetic environment, with the specified safety factor to meet the design requirements of the normal working capacity. Also called electromagnetic compatibility. Its meanings include ① electronic systems or equipment in the electromagnetic environment; ② electronic systems or equipment in the natural electromagnetic environment in accordance with the design requirements. If extended to the influence of electromagnetic fields on the ecological environment, the subject of electromagnetic compatibility can be called environmental electromagnetism.
The research of electromagnetic compatibility is gradually developed with the needs of electronic technology to high frequency, high speed, high precision, high reliability, high sensitivity, high density (miniaturization, large-scale integration), high power, small signal application, complexity, and other aspects. Especially after the extensive use of modern electronic technology in artificial earth satellites, missiles, computers, communication equipment, and submarines, the electromagnetic compatibility problem is made more prominent.

All kinds of operating power equipment use electromagnetic conduction, electromagnetic induction, and electromagnetic radiation to ways and influence each other, which will cause interference, influence, and harm to the operating equipment and personnel under certain conditions.

In the 1980s the rise of electromagnetic compatibility EMC absorber discipline for the purpose of research and solving this problem, mainly to study and solve the interference of the generation, propagation, receiving, and inhibition mechanism and the corresponding measurement and measurement technology, and on this basis according to the technical economy most reasonable principle, the interference level, anti-interference level, and inhibition measures to make clear provisions, make equipment in the same electromagnetic environment are compatible, at the same time not to any entity in the environment cannot allow electromagnetic disturbance.

The testing and testing institutions for electromagnetic compatibility (including electromagnetic interference and electromagnetic tolerance) include Suzhou Electrical Appliance Research Institute, the Aerospace Environmental reliability test Center, the environmental reliability and electromagnetic compatibility test Center, and other laboratories.

Internal interference refers to the mutual interference between various components of the electronic equipment, including the following:

1. Interference caused by leakage through the distributed capacitance and insulation resistance of the working power supply; (related to the working frequency)
2. Interference caused by the impedance coupling of the signals through the ground wire, the power supply, and the transmission wires, or the mutual feeling between the wires;
3. The interference caused by the heating of some components inside the equipment or the system, affecting the stability of the components themselves or other components;
4. Interference caused by the magnetic field and electric field generated by high-power and high-voltage components affecting other components through coupling.

External interference refers to the interference of factors other than the electronic equipment or system to the line, equipment, or system, including the following:

1. External high voltage and power supply interfere with electronic lines, equipment, or systems through insulation leakage;
2. External high-power equipment generates a strong magnetic field in space, which interferes with electronic lines, equipment, or systems through mutual inductive coupling;
3. Interference of spatial electromagnetic waves to electronic lines or systems;
4. The temperature of the working environment is unstable, causing interference caused by the parameter change of electronic lines, equipment, or internal components of the system;
5. The interference is caused by the equipment with power supplied by the industrial power grid and by the power grid voltage passing through the power supply transformer.

Rapid development in electromagnetic compatibility technology

From the surface of the earth to the satellite activities of nearly thousands of kilometers of space everywhere there are electromagnetic waves, electricity, and magnetism always affect people’s life and production, the wide application of electromagnetic energy so that the development of industrial technology with each passing day. Electromagnetic energy in creating great wealth for human beings, but also brings a certain harm, known as electromagnetic pollution, the study of electromagnetic pollution is an important branch of environmental protection. In the past, people called the interference of radio communication devices electromagnetic interference, which indicates that the device is invaded by external interference. In fact, it also causes harm to other external devices, that is, it becomes a source of interference. Therefore, it is necessary to study the interference and interference of the device at the same time and pay attention to the compatibility of the organization inside the device and between the device in the middle time. With the development of science and technology, the increasingly widely adopted microelectronics technology and the gradual realization of electrification have formed a complex electromagnetic environment. The continuous research and solution of the problems of the interrelationship between equipment and systems in the electromagnetic environment have promoted the rapid development of electromagnetic compatibility technology.

EMC absorber design requirements

In the electromagnetic compatibility design requirements:

1. Clear the electromagnetic compatibility indicators of the system. The EMC absorber design includes the electromagnetic interference environment where the system can work normally and the allowable indicators for the system to interfere with other systems.
2. On the basis of understanding the interference sources, interference objects, and interference channels of the system, these indicators are assigned to each subsystem, subsystems, circuits, components, and devices through theoretical analysis.
3. According to the actual situation, take corresponding measures to inhibit the interference source, eliminate the interference way, and improve the anti-interference ability of the circuit.
4. Through the experiment to verify whether the original index requirements, if not, further measures will be taken, cycle many times, until the original index is reached.

EMI Source

There are two types: natural and artificial. Natural interference sources mainly include various phenomena in the atmosphere, such as thunder, snow, rainstorm, hailstorm, and sandstorm noise. Natural interference sources also include cosmic noise from the sun and outer space, such as solar noise, interstellar noise, galactic noise, etc. Human interference sources are diverse, such as various signal transmitters, oscillators, motors, switches, relays, neon lights, fluorescent lamps, engine ignition systems, electric bells, electric heaters, arc welding machines, high-speed logic circuits, door circuits, silicon control inverter, gas rectifier, corona discharge, various industrial, scientific and medical high-frequency equipment, urban noise, electrical railway noise and nuclear electromagnetic pulse produced by a nuclear explosion, etc.

EMI propagation route

It can be divided into two kinds: conduction interference and radiation interference. The interference propagating along the conductor is called conduction interference, and its propagation modes include electrical, magnetic, and electromagnetic coupling. The electromagnetic interference propagating in space in the form of electromagnetic waves is called radiation interference, and its propagation mode includes near-field field induction coupling and a far-field radiation coupling platform. In addition, conduction interference and radiation interference may exist at the same time, thus forming compound interference.