The necessity of electromagnetic shielding
With the development of modern electronic technology towards high frequency, high efficiency, high integration, high reliability and high precision, electromagnetic interference has become a prominent obstacle to the normal operation of systems and equipment. For example, the signal transmission cable, it will not only be subjected to interference from the outside world, but also produce a variety of electromagnetic interference on the outside space. Therefore, it is necessary to reduce or reduce the electromagnetic interference from the outside of the signal transmission cable and take electromagnetic shielding measures.
Electromagnetic shielding
When the high frequency circuit is working, it will radiate electromagnetic waves to the outside, causing interference to other nearby equipment; On the other hand, various electromagnetic waves in space will also cause interference in the inductive circuit. The role of electromagnetic shielding is to cut off the propagation path of electromagnetic waves, thus eliminating interference.
The purpose of electromagnetic shielding
Control the electromagnetic field of the internal radiation area, and do not let it go beyond a certain area. Control the interior to prevent external radiation from entering an area.
Traditional magnetic shielding material
There are many materials that can be used for electromagnetic shielding, and they have their own characteristics and advantages.
Electromagnetic pure iron, silicon steel and permalloy, as traditional magnetic shielding materials, have been widely used in the construction of large magnetic shielding rooms, electric motors, transformers and other magnetic shielding plates as well as the internal magnetic shielding plates for TV and computer cathode ray tubes, and have obtained satisfactory shielding efficiency. However, due to the magnetic properties affected by machining, sensitivity to stress, large weight and other shortcomings, the use of these materials has been limited.
Selection of electromagnetic shield material
For the large interference magnetic field on the shielding effect is not high requirements, can choose pure iron, silicon steel and other soft magnetic materials, these materials have high saturation magnetic induction, low permeability, not easy to be saturated magnetized, and the price is relatively cheap; For the case of weak interference magnetic field and high shielding effect requirements, ****** should be high permeability, especially high initial permeability of 1J79 Permalloy, Co based amorphous alloy and other materials.
For the situation between the two, 1J50 Permalloy, Fe-Ni-based amorphous alloy, Fe-based amorphous alloy and other materials can be selected. According to the actual situation, the combination of the above two or three materials should be a better choice.
Amorphous electromagnetic shielding material
The application of amorphous alloy in switching power supply, transformer, magnetic head and other magnetic devices has made amazing progress, as electromagnetic shielding material is a new field of application of amorphous alloy.
As a new material with superior properties to traditional materials, amorphous alloy mainly uses the magnetic bypass principle to guide the electromagnetic energy flow generated by the field source so that it does not enter the space protection zone. In 1976, it was first reported that amorphous soft magnetic alloy was used as magnetic shielding material abroad.
The application forms of amorphous alloys are mostly used as structural materials alone, and composite materials and shielding coatings are also involved by researchers, and there have been related patents
Amorphous alloys have been used in electromagnetic shielding chambers, precision measuring instruments, shielding coatings and other aspects with excellent performance, and have gradually replaced the use of traditional materials in some fields with strict requirements for shielding efficiency.
At present, amorphous alloys such as Fe-based, Fe-based nickel and cobalt alloys have better soft magnetic properties, and are most widely used by researchers.
The application of amorphous alloys in the field of electromagnetic shielding has also been researched and developed in China, both as structural materials and shielding coatings have been achieved
Structural shielding material
Fe-based amorphous
Some experts compared the magnetic shielding performance of iron based amorphous steel sheet and silicon steel sheet, the experiment selected 3% silicon steel sheet with different texture and magnetic domain shape and the cylindrical shielding device composed of iron based amorphous alloy ribbon, all the shielding devices were annealed without process. The magnetic shielding effect under an alternating magnetic field with a frequency of ****** up to 20kHz is measured.
The results show that not only the permeability but also the shape of the domain have an effect on the shielding effect. The Fe-based amorphous alloy without magnetic field annealing has a very high shielding effect on the high frequency magnetic field.
Fe-Ni based amorphous
Because the magnetic properties of traditional iron-nickel alloys are very sensitive to machining processes, researchers have used the bonding technology used in aviation technology to produce metal or fiber layer pressing to prepare a new composite material composed of aluminum and iron-nickel amorphous soft magnetic alloys. Members made of this material can be well shielded from the interference of AC electromagnetic fields from DC to 1000kHz, and the magnetic properties can vary within a large range by changing the thickness and number of layers. The magnetic properties of the material are not affected by machining processes such as cutting and drilling. The shielding efficiency can be improved by using amorphous ribbons of different thickness and changing the weight percentage of ferromagnetic powder.
Co-based amorphous
Co-based amorphous titanium alloy has a low saturation magnetic induction strength, magnetostriction coefficient is close to zero, has a very high initial permeability and very low high-frequency loss, but also has a high mechanical strength, good toughness and wear resistance, become the most widely used electromagnetic shielding material.
The researchers of the General Institute of Iron and Steel Research made a large shielding chamber (750×750×750m) with Co-based amorphous alloy for the Institute of Geophysics of the Chinese Academy of Sciences. The shielding factor of the shielding chamber reached 34.4, which achieved good shielding effect, light weight, simple structure and reduced the cost of the shielding chamber.
Electromagnetic shielding coating
In a variety of electromagnetic shielding materials, coatings with its simple process, no special equipment, no space and integration with the substrate and other advantages to become one of the leaders, is widely used in all kinds of electronic products, devices, systems of electromagnetic radiation protection.
At present, the commonly used shielding coatings are mainly composed of resins, diluents, additives and fillers, etc. The electromagnetic properties of the fillers directly affect the shielding properties of the prepared coatings, and the commonly used filler materials are mainly conductive copper, nickel and other metal and carbon materials.
In response to electromagnetic interference caused by high-frequency electromagnetic waves emitted by electronic devices such as computers, Japanese researchers have invented electromagnetic shielding materials that use sheet, short fiber and granular ferromagnetic amorphous alloys as fillers and organic polymers.
The shielding material has high shielding efficiency for electromagnetic waves in the MHz to GHz range, and for electromagnetic waves in the frequency range of 1MHz to 100MHz, the shielding efficiency reaches at least 30dB, or even more, and the material also has good adhesion and corrosion resistance.
In response to electromagnetic interference caused by high-frequency electromagnetic waves emitted by electronic devices such as computers, Japanese researchers have invented electromagnetic shielding materials that use sheet, short fiber and granular ferromagnetic crystal alloys as fillers and organic polymers.
The shielding material has a high shielding efficiency for electromagnetic waves in the range of MHz to GHz, and for electromagnetic waves in the frequency range of 1MHz to 100MH2, the shielding efficiency reaches 30dB or even more, and the material also has good adhesion and corrosion resistance.
Brief
The development of electromagnetic shielding materials not only involves human health problems, but more importantly is related to the security of national economic and military information, so the development of comprehensive, convenient and low-cost electromagnetic shielding materials has important social significance, and can bring good economic benefits.
The use of amorphous alloy materials in the form of fiber, ribbon and coating in the shielding structure is promising and effective, expanding the application range, improving the performance stability, and further reducing the production cost of amorphous alloy are problems that need to be further solved, and amorphous alloy will have a broader application prospect in the field of electromagnetic shielding.