At present, there are many kinds of absorbing materials, which can be roughly divided into the following categories:
1、 According to material forming process and bearing capacity
Absorbing materials can be divided into coating absorbing materials and structural absorbing materials.
2、 According to the principle of absorbing wave
1. The basic types of absorbing materials include absorbers with the same complex permeability and complex permittivity, broad-band absorbers with gradual impedance and thin-layer absorbers that attenuate surface current.
2. The interference absorbing material is to eliminate the interference by using the equal amplitude and opposite phase of the reflected waves on the surface and bottom of the absorbing layer.
3、 According to material loss mechanism
1. Resistance type loss, such absorption mechanism is related to the conductivity of the material, the higher the conductivity, the greater the macro current caused by carriers, which is conducive to the conversion of electromagnetic energy into heat energy. Such as silicon carbide, graphite, etc. belong to resistance type absorbing materials.
2. Dielectric loss, which is a kind of dielectric loss absorption mechanism related to electrode, is to convert electromagnetic energy into thermal energy consumption and dissipate it through the "friction" produced by repeated polarization of medium. Such as barium titanate is a dielectric type absorbing material.
3. This kind of absorption mechanism is a kind of magnetic loss related to the dynamic magnetization process of ferromagnetic medium, which can be refined into: hysteresis loss, damping loss, rotating magnetic eddy current, and post magnetic effect. The main sources are domain turn, domain wall displacement and natural resonance of magnetic domain which are similar to the hysteresis mechanism. For example, ferrite and hydroxy iron belong to magnetic loss absorbing materials.
4、 By study period
1. Traditional microwave absorbing materials, such as ferrite, barium titanate, metal powder, graphite, silicon carbide, conductive fiber and so on, belong to traditional microwave absorbing materials. Among them, ferrite absorbing materials and metal micro powder absorbing materials have more research and application and better performance.
2. New absorbing materials, including nano materials, chiral materials, conductive polymers, polycrystalline iron fibers and circuit simulation absorbing materials, have different absorbing mechanism from traditional absorbing materials. Among them, nano materials and polycrystalline iron fibers are two kinds of new wave absorbing materials.
5、 By material
1. Ferrite absorbing material, which is a kind of complex dielectric material, can absorb electromagnetic wave with polarization effect and magnetic loss effect. With the advantages of high absorptivity, thin coating and wide frequency band, it is widely used in various fields.
2. The particle size of metal powder is 0.5-20 μ M. Therefore, the materials have the advantages of high magnetic susceptibility and high magnetic conductivity in the field of microwave absorption. It mainly absorbs electromagnetic wave through hysteresis loss and eddy current loss. At present, the size of metal powder is usually 1-10 μ M.
3. The absorbing mechanism of polycrystalline iron fiber absorbing material is eddy current loss and hysteresis loss. In addition, it is a good conductor with strong dielectric loss absorption performance. Under the action of external alternating electric field, the electrons in the fiber vibrate and the electromagnetic energy part is transformed into heat energy. Polycrystalline iron fiber has unique shape anisotropy, which can achieve high absorption in a wide frequency band. The mass of polycrystalline iron fiber is 40% - 60% less than that of traditional metal powder materials, and overcomes the serious defects of most magnetic materials. Polycrystalline iron fiber absorbing material has the advantages of light weight, small area density (can be reduced to 1.5 ~ 2kg / m2), wide frequency band (4 ~ 18GHz), and the electromagnetic parameters of the material can be adjusted by adjusting the length, diameter, arrangement of the fiber and the content of dispersant.
4. Nano wave absorbing material refers to that the size of the material is nanometer (usually 1-100nm). The unique structure of nanomaterials makes them have the characteristics of tunneling effect, quantum effect, small size effect and interface effect. Jonah
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