Electromagnetic coupling mechanism study

Jun 17, 2023

With the continuous development of science and technology and the continuous expansion of human activities, microelectronics technology, computer technology is applied to all aspects of social life, a large number of high technology content, complex internal structure of electrical and electronic products are widely used, so that it is increasingly informatization and electromagnetic sensitivity. The influence of complex electromagnetic environment on human beings has attracted more and more people's attention. Therefore, it is of great significance to study the coupling mechanism of electromagnetism.

I. Concept of electromagnetic environment

　　Electromagnetic environment refers to the sum of electromagnetic phenomena existing in space. A variety of man-made electromagnetic radiation and natural electromagnetic radiation constitute a complex electromagnetic environment, in which man-made electromagnetic radiation, including mobile phones, radio conversational machines, radio and television transmitters, satellites, radar, etc., lightning, static electricity, geomagnetic field, sunspot activity, cosmic rays, etc., constitute a natural source of electromagnetic radiation.

　　The formation of electromagnetic radiation effects requires the simultaneous presence of the following three elements:

　　Electromagnetic wave source, refers to the components, equipment, systems or natural phenomena that generate electromagnetic waves;

　　A coupling channel, meaning a channel or medium that couples or propagates energy from a wave source to a sensitive device and causes that device to respond;

　　Sensitive device, a device that responds to electromagnetic waves.

　　These three elements are usually referred to as the three elements of electromagnetic coupling.

Ⅱ. The coupling mode of electromagnetic radiation

　　(A) antenna coupling

　　All exposed to the electromagnetic field of the metal conductor can be considered as an antenna, "front door" coupling ("front-door" coupling) means that the electromagnetic pulse or microwave energy through the target on the antenna coupled to the electronic system. Therefore, according to the design characteristics of the antenna to calculate the coupling strength, when the electromagnetic wave frequency and antenna design frequency is equal, the coupling reaches the peak.

　　(B) hole and seam coupling

　　Generally, electronic equipment is encapsulated in a container composed of conducting material. Due to equipment cooling and ventilation, notches, cracks, and feed, signal transmission needs, the container can not be sealed, there are different types of holes and seams, which provides a coupling pathway for electromagnetic radiation. "Back-door" coupling ("back-door" coupling) is a high-energy electromagnetic pulse energy through the target on the hole, gap coupling into the system, interference or destruction of electronic equipment. When the wavelength is smaller than the size of the holes, electromagnetic waves will enter the shielding body without obstruction; when the wavelength is larger than the size of the holes, electromagnetic waves will be blocked; when there is the size and length of the electromagnetic wave comparable to the holes, electromagnetic wave coupling is very serious, will produce resonance.

　　Power line is exposed to the system outside the long line, vulnerable to electromagnetic energy attack, both to receive interference energy can also transmit interference energy. If there is a power line or signal transmission line from the shielding shell connected to the inside of the system, the received, induced current will propagate along the line into the shielding body. The general propagation is microwave pulse current, even if the current is not introduced from the lead of the transmission cable core, but is induced on the outer shield, through the transfer impedance will also be coupled to the core, directly into the electronic system. For microwave, shielded cable transfer impedance is also much larger than the RF, so microwave can be through the power line, the braided shield of the transmission line into the core.

　　(D) the skin effect of metal shells

　　Electromagnetic wave penetration of the metal shell is realized through the skin effect, electromagnetic waves in the material skinning depth as follows

　　Where f is the frequency of the electromagnetic wave, and respectively for the magnetic permeability and electrical conductivity of the metal shell material. For 2GHz microwave signals, it is in the copper (=5.5 × 107S/m) and aluminum (=3.2 × 107S/m) in the skinning depth of 1.52 and 2.82. For higher frequency microwave signals, the value of the skinning depth is smaller.

Ⅲ. the role of electromagnetic energy mechanism

　　Electromagnetic hazards on the impact of high-tech equipment, mainly through the energy of conduction coupling, radiation coupling occurs, the role of the mechanism can be summarized as follows four aspects:

　　(A) thermal effect

　　Electrostatic discharge and high-power electromagnetic pulse generated by the thermal effect is generally completed in nanoseconds or microseconds, is an adiabatic process. As an ignition source and detonation source, instantly cause flammable, explosive gas or electrical fireworks explosion, but also can make the system of microelectronic devices, electromagnetic sensitive circuits overheating, resulting in localized thermal damage, circuit performance deterioration or failure, and even lead to the stockpile of material combustion and explosion.

　　(B) radio frequency interference and "surge" effect

　　Electromagnetic radiation caused by radio frequency interference, information technology equipment caused by electrical noise, electromagnetic interference, so that it produces false action or functional failure. Strong electromagnetic pulse and its "surge" effect on the system will also cause hard damage, not only can make the device or the performance parameters of the circuit deterioration or failure, but also the formation of cumulative effects, buried potential hazards, so that the circuit or the use of equipment to reduce.

　　Electromagnetic hazards generated by the strong electric field (especially static field) can not only make the MOS circuit gate oxide layer breakdown or intermetallic dielectric breakdown, resulting in circuit failure, but also the formation of potential damage to the system self-testing instrumentation and sensitive devices affect the work.

　　(D) magnetic effect

　　Electrostatic discharge, lightning strikes, lightning and similar electromagnetic pulse caused by strong currents can produce a strong magnetic field, so that the electromagnetic energy is directly coupled to the internal system, interfering with the normal operation of electronic equipment.

　　References:

　　[1] Liu Shanghe, Wu Zhancheng:Electromagnetic environment and high-tech weaponry[J]. Modern Military,2001.

　　[2] Wu Xiong:Environmental Problems of Electric, Magnetic and Electromagnetic Fields[J]. Electric Power Environmental Protection,2007,(4).

　　[3] Gao Yan and Yu Bo: Characteristics of Complex Electromagnetic Environment[J]. Sichuan Journal of Military Engineering,2008,(1).

　　[4] Gao Bin, Tang Xiaobin: Complex Electromagnetic Environment Effects[J]. Journal of China Academy of Electronic Science,2008,(4).