Ferromagnetic materials and good metal conductor materials are commonly used shielding materials. The die-cutting of conductive shielding materials is suitable for low-frequency shielding of magnetic fields below 1 kHz. The principle of operation is to use magnetic permeability of ferromagnetic materials to guide magnetic lines of force through high-penetration materials and reduce magnetic flux density in nearby spaces to achieve magnetic shielding. Commonly used ferromagnetic materials are pure iron, silicon steel, permalloy (iron-nickel alloy), etc. The electromagnetic shielding effect of permalloy is much better than the other ones. Permalloy has three main components, namely 78% Ni, 65% Ni and 50% Ni, of which 78% Ni Permalloy has a much higher magnetic permeability than the other two, reaching the order of 3 × 10 ~ 1.2 × 10. Permalloy versus stress It is sensitive, and the magnetic properties are extremely related to heat treatment. The materials used are not heat treated, so it is necessary to understand and master the heat treatment process. The newly emerged iron-cobalt (FeCo) alloy [51, iron aluminum alloy [ 51 is also a soft magnetic alloy material that can be used for shielding of low frequency magnetic fields.
Due to the low electrical conductivity of ferromagnetic materials, it is not suitable for the shielding of high-frequency electromagnetic fields. The good conductors of metal have high conductivity and are suitable for shielding of high and low frequency electromagnetic fields and electrostatic fields. Conductivity in electromagnetic shielding becomes the main basis for selecting shielding materials. Table 2 shows the electrical conductivity and magnetic permeability of some metals. The most commonly used materials are steel plates, galvanized steel sheets, copper sheets, aluminum sheets and the like. The metal shielding material also has excellent mechanical properties, but its disadvantages such as high density, easy corrosion, and difficulty in processing are obvious, and the limitations are large.
Surface coating film shielding material
Such materials are used to adhere a conductive layer to the surface of an insulator such as plastic to achieve the purpose of shielding, and belong to a shielding material mainly based on reflection loss. Common preparation methods include electroless gold plating, vacuum spraying, sputtering, metal spraying, and metal foil. Such surface conductive film shielding materials generally have the advantages of good electrical conductivity and obvious shielding effect, and the disadvantage is that the surface conductive film has low adhesion, is easy to be peeled off, and the secondary processing performance is poor.
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