Dynamic magnetic characteristics of a composite polymeric material based on carbonyl iron

Abstract

Keywords: wicrowave absorbing materials and coatings, composite materials, magnetic permeability and dielectric permittivity spectra, reflection coefficient, microwave range.Nowadays microwave radiation is used not only in special means: consumer devices of high-frequency radio electronics move actively ahead, including mobile telephones, computers, and photo-and videocameras. Due to mastering of gigahertz frequencies, miniaturization, small weight, and high speed of modern hardware is provided. Active mastering of the microwave range has aggravated the need for magnetic materials absorbing electromagnetic radiation. Such materials are required to reduce harmful influence on biological objects, to provide electromagnetic compatibility of units and blocks of high-frequency devices, and to construct anechoic chambers. Magnetic elastomers representing composite microwave materials put on metal surfaces whose main components are ferri-and ferromagnetic fillers are used as absorbers [1].Carbonyl iron is one of the perspective materials for manufacturing absorbing coatings [2]. The frequency band of natural ferromagnetic resonance (NFMR) in the presence of the domain structure lies generally in the limits from 2πf 1 = γH a to 2πf 2 = γ(H a + 4πМ S ) [3]. The anisotropy field of carbonyl iron is H a ≈ 500 Oe, its saturation magnetization is M S ≈ 1.7⋅10 3 G, and γ/2π = 2.8 GHz/kOe, that is, the NFMR frequency band lies in the limits from f 1 ≈ 1.4 GHz to f 2 ≈ 61 GHz.Samples of composite materials consisting of P-10 grade carbonyl iron powders in polyethylene matrix were fabricated. Powders of the given iron grade have bulbous structure with average particle sizes of ~3.5 μm. The thickness of the examined plane samples was 1 mm, and the volume iron contents were 50 and 15%.To measure the magnetic permeability (μ = μ′ -iμ″) and the dielectric permittivity (ε = ε′ -iε″) spectra, a Universal Broadband Radiospectrometer was used based on an E8363В Vector Circuit Analyzer of the Agilent Technologies. Measurements were performed in the frequency range 10 MHz -20 GHz. A coaxial waveguide, an irregular microstrip resonator [4], and a set of rectangular multimode volume resonators were used as measuring cells [5].Since various experimental techniques have different systematic and random measurement errors, permeability and permittivity values measured by the corresponding methods at the ends of the examined frequency range differed. In this regard, the experimental magnetic spectra of the composites were processed by the method suggested in [6,7]. To match the frequency dependences of the imaginary and real permeability components, the Cramers-Kronig relations and independent measurements of the initial static permeability µ 0 of the materials were used. Here µ 0 values, equal to 10.7 and 4.0 for composites with iron contents of 50 and 15%, respectively, were measured for toroidal samples at a frequency of 1 kHz using an LCR meter of digital Е7-8. Figures 1 and 2 show the magnetic permeability spectra of the composites. It can b...

Electromagnetic Waves Absorbing Characteristics of Composite Material Containing Carbonyl Iron Particles

“…The rather narrow operating frequency band is disadvantage of such RAC. It is shown in [5] [6] that double-layer RAC is more broadband and has less reflection coefficient than singlelayer RAC [1]- [3] [7]- [10]. The first layer of such RAC is an absorbing layer.…”

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

“…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.…”

“…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.…”

“…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].…”