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Magnetic absorbing material (MAM) sheet was fabricated by calendaring carbonyl iron flakes into acrylonitrile-butadiene rubber. The complex permittivity and permeability of the sample were measured within 0.3–18 GHz. The calculated reflection loss (RL) and surface wave attenuation constants of the MAM are shown to be effectively manipulated by the layer thickness and electromagnetic (EM) parameters, respectively. It is found that the thickness of MAM should be suitable so as to realize good microwave wave absorption and surface wave attenuation performances in wide frequency range. In view of this goal, there also exist consistency requirements in EM parameters of MAM, i.e., a proper permittivity and high permeability. Furthermore, the measured RL and monostatic radar cross section reduction of a slab coated with the fabricated MAM sheet are in good agreement with the theoretical calculation. The present results provide a pathway to the development of MAM with high-efficiency absorption on both incidence EM waves and surface waves in the gigahertz range. [ABSTRACT FROM AUTHOR]

Monodomain NiCuZn ferrites were investigated for use in the design of a high-efficiency terrestrial digital multimedia broadcasting antenna with reduced physical dimensions. The results show that the reported monodomain design is effective. Specifically, monodomain ferrite with 1 wt% Co2O3 doping has a high miniaturization factor (~14) and very low loss factors (tan $\delta _{{\mu }} = 0.017$ and tan $\delta _{{\varepsilon }} = 0.012$ , respectively). It also reveals equivalent permeability and permittivity ( $\mu ^\prime = 14.05$ and $\varepsilon ^\prime = 14.12$ , respectively) at the frequency of 200 MHz, implicating the convenient impendence match in the antenna application and consequent miniaturization. The magnetic spectra of the monodomain samples were studied with a numerical fitting method to obtain guidelines for preparing high-quality materials. The results indicate that it is necessary to lower relaxation frequency $\omega _{{{\text{r}}}}$ and maintain the other dispersion parameters as moderate to achieve a high real part of permeability and low tan $\delta _{{\mu }}$ . Furthermore, we demonstrate that appropriate Co2O3 doping is a feasible way to adjust the dispersion parameters. [ABSTRACT FROM AUTHOR]

The electromagnetic and microwave absorption properties of polymer-based Ba3Co2Fe24O41/P(VDF-TrFE) composites were investigated. The effective complex permeability and permittivity of the two-phase composites can be manipulated by either varying the Ba3Co2Fe24O41 content or applying the dc magnetic field (Hdc). The composite containing 90 wt% Co2Z obtains a maximum reflection loss (RL) due to a proper impedance match and relatively high magnetic loss. In addition, it is found that the position of RL peak was tuned from 5.5 to 7 GHz with Hdc up to 50 mT, whereas the intensity obtains a remarkable enhancement of 67% at 15 mT. These results reveal great potential for the applications of ferroelectric–ferromagnetic composites with tunable microwave absorption. [ABSTRACT FROM PUBLISHER]

Mg1–xCuxFe2O4 ferrites for electromagnetic interference suppression were systematically investigated in crystallographic structure, morphologies, and magnetic and dielectric spectra over a frequency range of 10–1000 MHz. Findings indicated that the Mg1–xCuxFe2O4 ferrites with $x$ = 0–0.6 showed a single-phase cubic spinel structure, but the sample structure with $x = 0.8$ transforms into a tetragonal phase. Moreover, the substitution of Cu was shown to lower the sintering temperature and enhance densification of the ferrites, resulting in increased saturation magnetization (67%) and decreased coercivity (88%). More importantly, the complex permeability and permittivity of Mg–Cu ferrites could be tailored with Cu content, leading to an enhanced magnetic loss and permeability. The magnetic loss tangent of the Mg0.4Cu0.6Fe2O4 ferrite sintered at 1150 °C was significantly increased by 56% at $f>300$ MHz. [ABSTRACT FROM AUTHOR]

Abstract: Polystyrene coated Fe–Co–Zr alloy flakes have been prepared from gas atomized powders and styrene monomer by high energy ball milling. The effective complex permittivity and complex permeability of flakes/paraffin composites within 3.95–12GHz were measured to assess the application potential of these products used as microwave absorbers. It is found that both the real and imaginary parts of complex permittivity substantially decrease with the increasing amount of reactant styrene. For the complex permeability, the real part of polystyrene coated samples is larger than those of the as-milled sample in high frequencies, however, the imaginary part exhibits a decline while resonance frequency shifts to high values. The calculated reflection loss curve suggests that a proper thickness of coating can redound to improve the absorbing performance of polystyrene coated Fe–Co–Zr alloy flakes in high frequency range. [Copyright &y& Elsevier]

The microwave absorbing properties of multiferroic particulate composites consisting of Co 2 Z hexaferrite and BaTiO 3 (BT) were investigated over a frequency range of 2–18 GHz. The effective complex permeability and permittivity of Co 2 Z–BT composites are shown to be effectively manipulated by varying the weight ratio of the two phases, which consequently demonstrates a strong tunability in the optimal working frequency and minimum reflection loss (RL). For the optimal Co 2 Z–10BT composite, the RL peak at a thickness of 2.0 mm was enhanced by 97.8% in comparison with that of the single phase Co 2 Z hexaferrite. Moreover, the impedance-matched RL characteristics below 10 GHz show a substantial improvement in both thickness and bandwidth with increasing BT content. This work clearly shows the potential to tune the impedance matching and microwave absorption performances of multiferroic composites. [ABSTRACT FROM AUTHOR]

• We calculate the relative permittivity chart to guide the design of specific materials with particular microwave absorption (MA) properties. • Design composites are prepared and characterized to realize the temperature-insensitive MA properties. • The temperature-insensitive and enhanced MA properties are believed to be the cooperative effect of dielectric loss and impedance matching. • Prepared meta-structure can realize a reflection loss less than −5 dB at 8.2–18.0 GHz in the temperature range of 25–1100 °C. Developing high-temperature microwave absorption (MA) materials remains a challenge in the field of radar stealth. Here, we propose a design concept of meta-structure for temperature-insensitive and broadband MA. The three-phase TiB 2 /Al 2 O 3 /MgAl 2 O 4 composites are prepared to realize the temperature-insensitive MA properties, which is ascribed to the interaction of different components in terms of the electrical conductivity, dipolar polarization and interfacial polarization as temperature increases. On this basis, we design and fabricate a three-layer meta-structure composed of the SiO 2 ceramics as environmental adaptation layer, the patch-type and flat composites as MA layers. Compared with flat composites, the meta-structure can optimize its effective permittivity, thereby realizing enhanced MA properties at elevated temperatures. This meta-structure can realize a reflection loss (RL) less than −5 dB at 8.2–18.0 GHz in the temperature range of 25 °C to 1100 °C. The experiment matches well with the simulation. The temperature-insensitive and enhanced MA properties are attributed to the consequence of the combination of traditional absorbing materials and metamaterial structures. [ABSTRACT FROM AUTHOR]