ABSTRACT

274Regardless of the long lasting extensive theoretical and experimental work on creating effective microwave absorbers, there is an ongoing interest in obtaining such absorbers with tailored properties suitable for a variety of applications in the respective frequency range. Our study is aimed at studying some chemical, crystal, crystallographic, and structural characteristics of absorption-active fillers and their influence on the interaction of thus reinforced elastomeric composite materials with microwaves.

We have selected different kinds of ferrites for our research: magnetite, barium, and strontium-substituted and non-substituted hexaferrites having a high field of intrinsic magnetic anisotropy. The presence of a filler with high field of intrinsic magnetic anisotropy in a composite leads to qualitative changes in the frequency spectra of the real and imaginary parts of permittivity and permeability. Another result is significantly improved interaction of the composite with electromagnetic waves. The natural ferromagnetic resonance (NFMR) is an extremely important feature of used ferrite fillers, which manifests itself in the decimeter and the centimeter band of electromagnetic waves spectrum. Depending on their crystal composition, ferrites having various NFMR in predetermined areas of the frequency spectrum can be selected, so that interaction and absorption of microwaves is efficient in a certain frequency range.

In order to obtain broadband microwave absorbers, we have also studied some combinations of the used ferrites with carbon-containing fillers of high dielectric losses, such as graphite, carbon black, and activated carbon.

Various types of rubber have been used as a polymer matrix such as natural, acrylonitrile butadiene, chloroprene, butadiene, and styrene-butadiene rubber. It has been found that when the polymer matrix contains polar functional groups and bonds capable of altering its magnetic susceptibility, its chemical nature has a statistically significant impact on the degree of the composites interaction with electromagnetic waves.

The analysis of the obtained experimental results allows the conclusion that acrylonitrile butadiene rubber suits best as a polymeric matrix for composites required to interact effectively with microwaves. This, to a great extent, is due to the nitrile group present in its macromolecule.

We have developed and optimized voluminous and thin-film microwave absorbers, such with a concentration gradient, inclusive, and determined their microwave characteristics.