Metal powder absorbing materials have the characteristics of high microwave permeability and good temperature stability (the Curie temperature is as high as 770K). There are two main types of metal powder absorbing materials: one is carbonyl metal powder absorbing material; the other is magnetic metal powder absorbing material obtained by evaporation, reduction, organic alkoxide and other processes. Metal carbonyl powder includes carbonyl iron, carbonyl nickel, and carbonyl cobalt. The particle size is generally (0.5-20) μm, of which carbonyl iron powder is the most commonly used one. Another type of magnetic metal powder includes Co, Ni, CoNi, FeNi, etc., and their electromagnetic parameters are closely related to their composition and particle size.
Research results show that metal ultrafine powders (or films) have excellent attenuation properties for electromagnetic waves, especially high-frequency and even light-wave frequency ranges, but the absorption mechanism is still unclear. It is generally believed that the absorption of electromagnetic wave energy is determined by three effects: electron scattering caused by the thermal vibration of the lattice electric field, electron scattering caused by impurities and lattice defects, and the interaction between electrons and electrons. Magnetic metal powder is an absorbent with large electrical loss and magnetic loss. In addition to the source and dielectric loss, the electrical loss of this series of coatings also has conduction loss; its magnetic loss is not only derived from residual loss, but also eddy current Loss, which makes the magnetic metal powder coatings have a strong surface effect. The movement of atoms and electrons intensifies under the electromagnetic field radiation, which promotes magnetization and converts electromagnetic energy into heat energy, which can well absorb electromagnetic waves (including visible light and infrared light). Therefore, it is one of the ideal materials for millimeter wave stealth and visible light-infrared stealth.
The disadvantages of metal micro-powder absorbing materials are: poor oxidation resistance, acid and alkali resistance, far inferior to ferrite; large dielectric constant and poor spectral characteristics, poor low-frequency absorption performance; relatively dense (ρ< 8.0g/cm 3) Big