What are the classifications of absorbing materials? The following will answer for you: The absorber used in microwave anechoic chambers is often made into a wedge shape (golden tower shape), mainly composed of polyurethane foam type, non-woven fabric flame-retardant type, and silicate plate gold film assembly Type etc.
With the decrease of frequency (wavelength increase), the length of the absorber also increases greatly. The ordinary wedge-shaped absorber has an approximate relationship of L/λ≈1, so at 100MHz, the wedge length reaches 3000mm, which is not only difficult to achieve in technology, Moreover, the effective available space of the microwave anechoic chamber is greatly reduced.
Double or multilayer flat shape
This kind of absorber can work in a wide operating frequency range and can be made into any shape. For example, NEC Corporation of Japan disperses ferrite and short metal fibers evenly in a suitable organic polymer resin to make composite materials, and the working frequency band can be expanded by 40% to 50%. Its disadvantages are large thickness, complicated process and high cost.
Only coating-type absorbing materials can be used on the surface of the aircraft, which broaden the frequency band, and generally use composite coatings. For example, when the thickness of the lithium cadmium ferrite coating is 2.5mm～5mm, it can attenuate 8.5dB in the centimeter band; when the thickness of the spinel ferrite coating is 2.5mm, it can attenuate 24dB at 9GHz; the ferrite is chlorinated When the thickness of the butadiene rubber coating is 1.7mm～2.5mm, the attenuation is about 30dB at 5GHz～10GHz.
Incorporating microwave absorbing materials into engineering plastics makes them have both absorbing properties and load capacity, which is a direction for the development of microwave absorbing materials. Nowadays, in order to further improve the performance of absorbing materials, several complex absorbers with a combination of shapes have been developed abroad.