Радиопоглощающие и радиоэкранирующие характеристики феррит-полимерных композитов Mn-Zn феррит/П (ТФЭ-ВДФ)

The article discusses the electromagnetic absorbing and shielding properties of ferrite-polymer composites of the composition Mn-Zn ferrite/fluoroplast-42, obtained by pressing a mixture of powders with heating. The measurement of the complex magnetic and dielectric permittivity spectra, as well as the reflection coefficient spectra was carried out in the frequency range 0.1 - 7 GHz. Using the obtained spectra, a comprehensive analysis of the absorbing characteristics of the composites was carried out, and the factors responsible for the absorption were determined. Fitting of the composites magnetic permeability spectra show that the process of natural ferromagnetic resonance prevails over the resonance of domain walls, and a decrease in the concentration of ferrite inclusions leads to a significant shift in the frequency of natural ferromagnetic resonance to high frequencies. It was found that for composites with a thickness of 5 - 10 mm, compositions with a mass fraction of ferrite ≤ 0.4 show radio-absorbing properties, while compositions with a fraction of ≥ 0.6 show shielding properties.

Tuning the particle size, natural ferromagnetic resonance frequency and magnetic properties of ε-Fe2O3 nanoparticles prepared by a rapid sol–gel method

A fast method for the synthesis of ε-Fe2O3, yielding 100% pure material with a variable FMR frequency, is proposed.

Selective EHF absorber based on BaFe12O19 hexaferrite

The results of the study of the electromagnetic response of the hexagonal ferrite composite BaFe12O19 in the frequency range 34–250 GHz at room temperature are presented. At a frequency of 46.5 GHz a region of natural ferromagnetic resonance was found. The possibility of creating a selective EHF absorber based on the developed material is shown.

Effect of Annealing on the Magnetostatic and Microwave Electromagnetic Properties of Glass-Coated Fe-Rich Microwires

Glass-coated FeCuNbVSiB microwires was annealed in the temperature range of 380 °C to 600 °C. The microstructures and magnetostatic properties of the glass-coated microwires were characterized by X–ray diffraction (XRD), Vibrating Sample Magnetometer (VSM) respectively. Relative complex permeability and complex permittivity was measured by transmission/reflection (T/R) coaxial line method in the frequency range of 2-18 GHz for as-casted and annealed Fe-rich microwires samples. The measured results show that the coercive field of the Fe-rich microwires decrease to 1.54 Oe at 470 °C, and then increase rapidly with the increasing of the annealing temperature. The coercive field and saturation field of the microwire samples increased abruptly with the outgrowth of the Fe-B hard magnetic phase in the Fe-rich microwire samples. The imaginary part of permeability and the natural ferromagnetic resonance frequency decrease for the thermal treatment below 470 °C, and then increase with the annealing temperature up to 530 °C. The change of magnetostatic and microwave electromagnetic properties of the microwires samples with the annealing process come from the change of the anisotropy caused by the internal stress.

Metamaterials Fabricated of Amorphous Ferromagnetic Microwires: Negative Microwave Permeability

Microwave permeability of glass-coated ferromagnetic amorphous microwire exhibiting a weak negative magnetostriction has been studied. The diameter of the microwire was about 20 m and the diameter of the metal core was about 12 m. The microwire was wound to comprise a 7/3 washer-shaped composite sample with the volume fraction of magnetic constituent of about 10%. The permeability of the composite sample was measured in a coaxial line in the frequency range from 0.1 to 10 GHz. The composite was found to exhibit a negative permeability within the frequency range from approximately 0.7 to 1.5 GHz, with the permeability being as low as −0.4. Therefore, microwire-based composites, particularly, crossed arrays of microwires may be employed to develop metamaterials for microwave applications. In the composite, the negative microwave permeability is due to the natural ferromagnetic resonance and the negative microwave permittivity is due to the inherent inductance of the wire. Such metamaterials are advantageous in simple design, isotropic in-plane performance, and possible tunability of performance by external magnetic bias. However, for a feasible metamaterial fabricated from microwire arrays, the wires have to exhibit higher magnitude of the ferromagnetic resonance, higher quality factor, and higher resonance frequency.