Magnetic particle based absorbing materials in the frequency range of 8-12 GHz

Magnetic particle based absorbing materialsMost of them have high magnetic loss tangent angles, mainly relying on polarization attenuation such as hysteresis loss, domain wall resonance, and aftereffect loss to absorb electromagnetic waves. Common ones include ferrite, metal micro powder, polycrystalline iron fiber, etc.

Ferrite is one of the earliest and most mature absorbing materials, mainly including nickel zinc ferrite, manganese zinc ferrite, and barium ferrite. Its absorbing mechanism is natural resonance of magnetic domains. Ferrites are divided into spinel type, garnet type, and magnetic lead stone type. Among them, the hexagonal plate-like magnetic lead stone type has the best absorption performance. Due to its high magnetic anisotropy equivalent field and high natural resonance frequency, hexagonal plate-like magnetic lead stone ferrite exhibits excellent high-frequency absorption performance.

The hexagonal ferrite absorbing material prepared by Advanced Institute Technology has a maximum absorption of 16.5dB and a minimum absorption of 8dB in the frequency range of 8-12 GHz. A 2mm thick material with a surface density of 5kg/m2 was preparedFerrite absorbing materialIts absorption rate is greater than 10dB in the frequency band range of 8-18GHz.

In addition, due to the large specific surface area of nano ferrite particles, the surface atomic band structure is different from that in the body, resulting in high coercivity, which can cause absorption mechanisms such as hysteresis loss, interface polarization, and multiple scattering; At the same time, the size of nanoparticles is much smaller than the wavelength of electromagnetic waves, and their transmittance of electromagnetic waves is also much higher than that of ordinary particlesAbsorbing material.

Advanced Institute of Science and Technology research has found that the maximum reflectivity of ferrite samples with a particle size of 5 μ m is -17dB, and the bandwidth with reflectivity less than -10dB is 3.5GHz. The maximum reflectivity of ferrite samples with a particle size of 65nm is -28.5dB, and the bandwidth with reflectivity less than -10dB reaches 5GHz. Advanced Institute of Technology has studied the effect of Fe3O4 particle size on electromagnetic wave absorption efficiency in the frequency range of 1-1000MHz. The results show that the smaller the particle size of nanoscale Fe3O4, the higher its absorption efficiency.

Magnetic metal micro powder is a type of absorbing material that combines free electron absorption and magnetic loss. It mainly includes micro powders of cobalt, nickel, cobalt nickel alloys, iron nickel alloys, aluminum nickel alloys, and various organic modified metals. The famous F/A-18c/D "Bumblebee" stealth aircraft uses carbonyl based iron micro powder absorbing materials. Magnetic metal micro powder has high permeability and good temperature stability, but its anti-aging, acid and alkali resistance, spectrum characteristics and other properties are poor. Polycrystalline iron fibers have strong eddy current losses, hysteresis losses, and dielectric losses.

As a good conductor of polycrystalline iron fibers, when subjected to an external alternating electric field, the free electrons inside the fibers undergo oscillatory motion, generating oscillatory currents and converting some electromagnetic wave energy into thermal energy. The polycrystalline iron fiber absorbing coating developed by 3M Company in the United States can attenuate 30dB in the frequency range of 5-16GHz.

The composite of conductive polymers and magnetic particles takes into account both dielectric and magnetic loss absorption characteristics. Although some progress has been made, there are also some shortcomings. To develop conductive polymers with lightweight, strong absorption, wide bandwidth, adjustable electromagnetic parameters, and good comprehensive performanceMagnetic particle composite absorbing materialFurther research is needed in the following areas:

① Exploring the absorption mechanism of conductive polymer/magnetic particle composites by combining macro and micro perspectives;

② Selection and optimization of material size and type;

③ Preparation process and technology of composite absorbing materials.