X. F. Zhang

Microstructure and microwave absorption properties of carbon-coated iron nanocapsules

Carbon-coated Fe [Fe(C)] nanocapsules were synthesized by a modified arc-discharge method, and their microstructure and electromagnetic (EM) properties (2–18 GHz) were investigated by means of transmission electron microscopy, Raman spectroscopy and a network analyser. The reflection loss R of less than −20 dB was obtained in the frequency range 3.2–18 GHz. A minimum reflection loss of −43.5 dB was reached at 9.6 GHz with an absorber thickness of 3.1 mm. The in-depth study of relative complex permittivity and permeability reveals that the excellent microwave absorption properties are a consequence of a proper EM match in microstructure, a strong natural resonance, as well as multi-polarization mechanisms, etc.

Enhanced microwave absorption in Ni/polyaniline nanocomposites by dual dielectric relaxations

Ni/polyaniline (PANi) nanocomposites were prepared by chemical polymerization, and electromagnetic characteristics were then studied at 2–18GHz. The permittivity of the Ni/PANi nanocomposite presents dual dielectric relaxations with increasing content of PANi to over 15.6wt%, which is ascribed to a cooperative consequence of the core/shell interfaces and the dielectric PANi shells. Additionally, the permeability presents a strong natural resonance around 2–8GHz, which is dominant among microwave magnetic loss. The proper matching of the permittivity and the permeability contributes to enhanced microwave absorption.

Multidielectric polarizations in the core/shell Co/graphite nanoparticles

Hybrid core/shell Co/graphite nanoparticles synthesized by an arc-discharge method exhibit an enhanced dielectric loss property in the frequency range of 2–18 GHz. Complex permittivity expressed by Debye dipolar polarization approximate show that three kinds of dielectric polarizations coexist in this hybrid system. Combined with theoretical simulation, we further clarified that the dielectric polarizations are ascribed to the high defective graphite shells, and additional interfacial polarizations arising from the special core/shell architecture.

Influence of alloy components on electromagnetic characteristics of core/shell-type Fe–Ni nanoparticles

Fe–Ni alloy nanoparticles with various alloy components were fabricated by a direct current arc-discharge method. By dispersing the nanoparticles homogeneously into a paraffin matrix, the complex permittivity (er=er′+ier″) and permeability (μr=μr′+iμr″) of the nanoparticles have been investigated in the frequency range of 2–18 GHz and the effects of alloy components on the electromagnetic parameters were discussed. It is found that the permittivities of the nanoparticles are lower than those of the microscale counterparts and almost independent of frequency. The magnetic loss is attributed to natural resonance and the resonance peak shifts to high frequency range with the increase in Fe content. Better microwave absorption performances can be obtained by adjusting the composition and tailoring the core/shell structures to balance the electromagnetic parameters. The calculated results indicate that the Fe–Ni nanoparticles with 49 wt % Ni exhibit excellent electromagnetic wave (EMW) absorption properties (r...

Transform between the permeability and permittivity in the close-packed Ni nanoparticles

We report an anomalously electromagnetic resonance in a simple Ni nanoparticle/paraffin system. The resonance, caused by the near-field interaction of nanoparticles, appears at ∼16 GHz as decreasing the interparticle distance down to ∼11 nm. It is associated with an unusual energy transfer from the permeability to permittivity, resulting in the enhanced dielectric and weakened magnetic attenuations. These experimental results can be well modeled by a numerical simulation, evidencing the enhanced electrical filed distribution as decreasing the interaction distance. This study enables us to first realize the permeability-to-permittivity transform of electromagnetic wave in nanocomposites.

Model for Prediction of Shear Strength with Respect to Degree of Saturation

A new prediction model for unsaturated soil shear strength parameters with respect to degree of saturation is presented in this paper. Details of the model formulation and the determination of model parameters are described and reported. Introducing shear strength parameters of saturated soil, the model can be used in practice engineering involving both unsaturated soils and saturated soils. Moreover, more soil engineering characteristics can be captured in the new model compared with previous analogous models. The validity of this model is verified through a number of shear strength data available in the published literature. To verify the model against Yunnan red clay from China, a series of constant-water content triaxial tests have been carried out on both saturated and unsaturated specimens. Details of the experimental program and results are presented in this paper.