Electromagnetic shielding is designed to prevent electromagnetic wave leakage to the outside or entry from the outside by blocking its transmission path and reflecting nearly 100% of waves. The most effective material for electromagnetic wave shielding is metal.
On the other hand, radio-wave absorbent materials absorb and eliminate radio waves entering through the materials by converting them into heat energy.
Based on their absorption pattern, radio-wave absorbent materials are classified into the absorption type with larger transmission attenuation and the matching type that utilizes multipath reflection between the metal surface and the absorbent.
Radio-wave absorbent materials have the following functions: [1] A function utilizing ohm loss from the resistive element; [2] A function utilizing dielectric loss from the dielectric substance; [3] A function utilizing magnetic loss from the magnetic body; [4] A combination of any of the above three functions.

[1] is an absorption type whereby metal powders or carbon powders are dispersed in an appropriate medium. This would be suitable for an anechoic chamber. However, it requires the thickness of 1/4 wavelength or more in order to exert sufficient absorption capacity.
The matching type of [3] is designed to attenuate radio waves by placing a magnetic material in the high-field area in front of the metal backing plate used to generate standing waves.
The absorption type is also available with [3].This type is designed to absorb permeable waves by magnetic loss. Carbonyl iron and special ferrite magnetic powders are used as the magnetic substance.

Single-layer radio-wave absorbent paints and double-layer broadband radio-wave absorbent paints are available as the ferrite radio-wave absorbent.Radio waves are absorbed by the single-layer type by coating the metal surface with the resin mixed or dispersed with ferrite powders and carbon black or metal powders.These paints are used for the marine vessels radar.

As shown in [Fig.1], the double-layer radio-wave absorbent paints are comprised of two layers: the metamorphic layer and the absorbing layer that absorbs electromagnetic energy on the metal plate. They are compatible with electromagnetic waves in a broad spectrum. The film thickness of approximately 1.3 mm can deliver sufficient performance by using the composition of epoxy, ferrite, and brass fiber for the absorbing layer. A metamorphic layer uses silicate non-organic pigments besides the ferrite in order to improve performance, including the mechanical property and the permeation preventing capacity of the paint film. Modifying the mixture ratio of these can change the broadband absorption characteristics.