Composite radio-absorbing material based on carbonyl iron for millimeter wavelength range

Abstract

Keywords: radio-absorbing materials and coatings, composite materials, spectra of magnetic permeability and dielectric permittivity, reflection, absorption, and transmission coefficients, microwave range.Electromagnetic wave absorbers fabricated from radio-absorbing materials (RAM) are used in microwave technology to manufacture anechoic chambers, to protect personnel against the influence of microwave radiation, to manufacture matched loads for waveguide structures, and to mask radars [1]. Composite RAM whose matrix is formed by high-molecular polymer compounds and whose fillers are particles of ferro-or ferrimagnetic materials have found wide application [2]. These materials deposited on metal surfaces are effectively used as absorbers of electromagnetic waves.In [3][4][5][6] it was suggested to use carbonyl iron (FeC) powders for RAM in the microwave range. Investigations of the spectra of complex magnetic permeability ( i ′ ′′ μ = μ − μ ) and dielectric permittivity ( i ′ ′′ ε = ε − ε ) of composites with different filling factors at frequencies up to 18 GHz have demonstrated that these materials possess noticeable magnetic and dielectric losses and are promising for application as absorbers of electromagnetic waves in the microwave range. It has also been demonstrated that the two-layer RAM have smaller reflection coefficient and wider frequency band [4,6] in comparison with single-layer RAM [5]. They consist of a strongly absorbing layer deposited on the metal surface and a layer that matches the electromagnetic wave absorber with the free space having smaller values of the magnetic permeability and dielectric permittivity. The composite 0.94 mm thick comprising 50% (by volume) of P-10-grade carbonyl iron was an absorbing layer and the composite 2.2 mm thick comprising 15% of FeC was used in [6] as a matching layer. The frequency range in which the reflection coefficient was less than -10 dB extended from 2.9 to 16.8 GHz [6].It is well known [7] that the frequency range in which great magnetic losses are observed due to the phenomenon of natural ferromagnetic resonance in the presence of domain structure extends fromDue to the large value of iron saturation magnetization M S ≈ 1.7⋅10 3 G, this range extends from f 1 ≈ 1.4 GHz to f 2 ≈ 61 GHz. In calculations, γ/2π = 2.8 GHz/kOe and the anisotropy field H a ≈ 0.5 kOe were assigned. The above-mentioned estimates demonstrate that the composite materials based on carbonyl iron can have significant absorbing properties at frequencies of 20 GHz and higher. This work presents results of experimental investigations into the absorbing properties of composites comprising R-10-grade carbonyl iron powders in the polyethylene matrix for frequencies in the range 26-37 GHz. Samples with volume iron content of 15% (sample No. 1) and 50% (sample No. 2) were investigated.Measurements were performed using an R2-65 standing-wave ratio (SWR) meter with horn antennas 5 cm long and 2 ×1 cm 2 antenna aperture. To measure the transmission (T) and reflection coefficients (R) for a s...

Electromagnetic characteristics of double-layer composite materials on basis of carbonyl iron

“…% is absorbing layer, and matching layer has thickness 2.2 mm, concentration of carbonyl iron 15 %. Reflection coefficient is smaller than -10 dB in frequency band 2.9 -16.8 GHz [6,7].…”

Study of the Radio-Wave Absorbing Properties of a Lithium-Zinc Ferrite Based Composite

“…Measurements of the complex permeability and permittivity, and also of the reflection coefficient of the composite material were carried out on a universal wideband setup based on the PNA 8363В vector circuit analyzer (Agilent Technologies, USA) [17][18][19], belonging to the Center for Radiophysical Measurements, Diagnostics, and Research on the Parameters of Natural and Artificial Materials (Collective Use Center) of the National Research Tomsk State University, and certified as operational [20].…”

Radio Absorbing Material for Next-Generation Wireless Devices

“…The spheres are packed with carbonyl or ferrite iron. Once iron ball paint enters electric radiation, the ferrite or iron carbonyl molecules absorb it, which allows them to oscillate [16]. The molecular oscillations decay with heat release, and this is an important process for electromagnetic waves damping.…”