Absorbing material is a kind of material which can absorb the electromagnetic wave energy projected on its surface. In engineering application, the requirements for absorbing materials are very high. In addition to high absorption rate of electromagnetic wave in a wide frequency band, it is also required to have the properties of light weight, temperature resistance, humidity resistance and corrosion resistance.
With the development of modern science and technology, the impact of electromagnetic radiation on the environment is increasing. In the airport, the flight cannot take off due to electromagnetic wave interference, and in the hospital, mobile phone often interferes with the normal work of various electronic diagnosis and treatment instruments. Therefore, it has become a major subject of material science to control electromagnetic pollution and find a material which can resist and weaken electromagnetic radiation.
Electromagnetic radiation causes direct and indirect harm to human body through thermal effect, non thermal effect and cumulative effect. The results show that the ferrite absorbing material has excellent properties, such as high absorption band, high absorptivity and thin matching thickness. The application of this material in electronic equipment can absorb the leakage of electromagnetic radiation, which can achieve the purpose of eliminating electromagnetic interference. According to the law of electromagnetic wave propagating from the direction of low magnetism to high permeability in medium, high permeability ferrite is used to guide electromagnetic wave. Through resonance, a large amount of radiation energy of electromagnetic wave is absorbed, and then the energy of electromagnetic wave is transformed into heat energy through coupling.
The loss mechanism of absorbing materials can be roughly divided into the following categories:
Resistance type loss
This kind of absorption mechanism is related to the electrical conductivity of the material, that is, the higher the conductivity, the greater the macro current caused by carriers (including the current caused by the change of electric field and eddy current caused by the change of magnetic field), which is conducive to the conversion of electromagnetic energy into heat energy.
2 dielectric loss
It is a kind of dielectric loss absorption mechanism related to the electrode, that is, the electromagnetic energy is converted into thermal energy consumption and dissipated through the "friction" effect produced by the repeated polarization of the medium. The process of dielectric polarization includes: electron cloud displacement polarization, polar medium electric moment turning polarization, ferroelectric domain turning polarization and wall displacement.
3 magnetic loss
This kind of absorption mechanism is a kind of magnetic loss related to the dynamic magnetization process of ferromagnetic medium. This kind of loss can be subdivided into: hysteresis loss, gyromagnetic eddy current, damping loss and magnetic aftereffect effect effect. Its main sources are domain turn, domain wall displacement and domain natural resonance, which are similar to the hysteresis mechanism. In addition, the microwave loss mechanism of nanomaterials is a hot spot in the analysis of microwave absorbing materials.
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