Resistance type, dielectric type, and magnetic dielectric type electromagnetic wave absorbers

Resistive absorberIncluding conductive carbon black, graphite, carbon fiber, and silicon carbide, it has a high dielectric loss tangent and relies on the electronic polarization or interface polarization attenuation of the medium to absorb electromagnetic waves.

Dielectric absorbers mainly absorb electromagnetic waves through dielectric polarization relaxation losses, including barium titanate ferroelectric ceramics, silicon nitride, iron nitride, etc. Nano Si/C/N absorbers composed of silicon carbide, silicon nitride, and free carbon exhibit strong absorption properties in the centimeter and millimeter wavelength bands.

Magnetic medium type absorberIncluding ferrite, ultrafine metal powder, and carbonyl iron powder. The losses of ferrite absorbers can be divided into hysteresis losses, eddy current losses, and residual losses. The main mechanism of absorbing electromagnetic wave energy is natural resonance phenomenon, but the disadvantages are high specific gravity and narrow frequency band. Ultrafine metal powder refers to metal powder with particle size below 10um. Metal nano powder has good attenuation performance for high-frequency and even optical frequency electromagnetic waves.

In addition, new types of absorbers are developing rapidly, such as nano stealth materials, chiral absorbers, polycrystalline iron fibers, conductive polymers, Schiff base absorbers, plasma stealth, etc.

For wave absorbers, they can be divided into uniform distribution, layered distribution, spherical distribution and distribution along open porous foam according to their composition characteristics.

1) Uniform distribution: The absorber is distributed in a point like pattern within the absorber.

2) Layered distribution: The composition and distribution of adjacent surfaces or layers exhibit abrupt changes.

3) Spherical distribution: The absorber is distributed along the surface of the spherical transparent material.

4) Distribution along the open porous foam: the wave absorber is distributed along the inner wall of the complex cavity composed of many open hollow tubular holes.

According to the type of structure, it can be divided into coating type absorbing materials and structural type absorbing materials.

of whichCoating type absorbing materialIt can be divided into absorption type, interference type, and resonance type.

Structural absorbing materials can be divided into laminated structure absorbing materials, sandwich structure absorbing materials, and frequency selective surface absorbing materials.