Composite Microwave‐Absorbing Materials with Magnetic Constituents: State‐of‐the‐Art and Possible Ways for Improving their Parameters

The rapid progress of wireless technologies and telecommunications requires the development of microwave‐absorbing materials (also known as radio‐absorbing materials or radar‐absorbing materials), since electromagnetic radiation threatens human health and interferes with the operation of electronic devices. Microwave‐absorbing materials are also used to conceal “sensitive” targets, in particular, specific military equipment. This review considers the current state of composite microwave‐absorbing materials engineering, focusing on the materials containing magnetic components. The mechanisms of magnetic absorption and methods for measuring complex permittivity and permeability are described. Two types of ferrites (spinels, hexaferrites) having different natural ferromagnetic resonance frequencies are analyzed. It is pointed out that in the hexagonal structure, cationic substitutions substantially influence the magnitude of crystallographic anisotropy field and may both increase and decrease the ferromagnetic resonance frequency. Such ferrites can be used for microwave‐absorbing materials operating at frequencies up to tens and even 100 GHz. A review describes methods for ferromagnetic nanoparticles synthesis and shows their influence on the microwave absorption through the size and shape of nanoparticles. Examples of various microwave‐absorbing materials are presented, their characteristics are given. From the analysis of literature publications, the directions for future research are formulated, and ways for improving the properties of microwave‐absorbing materials are outlined.