Entity

Time filter

Source Type


Hou Q.,Shandong University | Yan K.,Shandong University | Fan R.,Shandong University | Zhang K.,Grirem Advanced Materials Co. | And 3 more authors.
Materials Chemistry and Physics | Year: 2016

The radio frequency permittivity and permeability spectra of Fe-Si-Ni/epoxy magnetic composite materials were investigated in detail. A relaxation frequency dispersion of permittivity has been observed for the composites below percolation threshold, and tunable negative permittivity due to the plasma oscillation of delocalized electrons in interconnected Fe-Si-Ni has been obtained in the composites above but still near percolation threshold. The realization of negative permittivity in Fe-Si-Ni/epoxy composites can be applied for the electromagnetic shielding materials. © 2015 Elsevier B.V. Source


Chen M.,Shandong University | Gao M.,Shandong University | Dang F.,Shandong University | Wang N.,University of Electronic Science and Technology of China | And 3 more authors.
Ceramics International | Year: 2016

FeNiMo/Al2O3 composites with different FeNiMo content were prepared by hot-pressing sintering. Interestingly, simultaneous negative permittivity and permeability were realized in FeNiMo/Al2O3 composites with 30% FeNiMo content in the frequency range of 860MHz to 1GHz and in the frequency range of 890MHz to 1GHz for composites with 40% FeNiMo content. Experimental results and theoretical simulations indicate that the negative permeability is caused by the domain wall resonance and gyromagnetic spin resonance, while the negative permittivity is attributed to the plasma oscillation of conduction electrons and LC resonance. The negative permittivity of the FeNiMo/Al2O3 composite induced by the plasma oscillation of conduction electrons was analyzed using the Drude model. The fitting results indicated that the plasma frequency of the composites was 8.99GHz. © 2016 Elsevier Ltd and Techna Group S.r.l. Source


Chen M.,Shandong University | Fan R.-H.,Shandong University | Gao M.,Shandong University | Gao M.,Happiness | And 4 more authors.
Journal of Magnetism and Magnetic Materials | Year: 2015

The physical properties of conductor-insulator composites often take dramatic changes near the percolation threshold (fc), leading to interesting applications, such as double negative material. This phenomenon also will be enlarged by increasing the differences between the properties of the constitutive phases. In this paper, the Fe50Ni50/Al2O3 magnetic cermets with different Fe50Ni50 volume contents (10%, 20%, 30%, 40%) were prepared via hot-pressing sintering. The permittivity of Fe50Ni50/Al2O3 composites has been studied in the radio frequency range. The results indicate that when the Fe50Ni50 content is below fc, the reactance of the composites takes a negative value, which indicates a capacitive character. The metallic Fe50Ni50 grains are isolated in the insulating ceramic matrix, leading to an in-sulator-like dielectric property. When the volume fraction of Fe50Ni50 reaches 40% which is above fc, the composites manifest an inductive character. In this case, the negative permittivity has been obtained over the whole test frequency range due to the percolation phenomenon, which makes Fe50Ni50/Al2O3 composites as promising candidates for double negative materials. © 2014 Elsevier B.V. All rights reserved. Source


Wang X.-A.,Shandong University | Shi Z.-C.,Shandong University | Chen M.,Shandong University | Fan R.-H.,Shandong University | And 4 more authors.
Journal of the American Ceramic Society | Year: 2014

Cobalt/alumina composites with three-dimensional cobalt networks hosted in porous alumina matrix were prepared by a facile impregnation process under low temperature. The effects of composition and microstructure on their electromagnetic properties were investigated. A percolation phenomenon appeared with cobalt content increasing, and an interesting feature of negative permittivity was obtained in the percolative composites due to the appearance of equivalent inductances, while the composites were equivalent to circuit models composed of capacitance and resistance with Co content below the percolation threshold. Meanwhile, negative permeability was obtained in the frequency range of 500 MHz-1 GHz. Further investigations showed that the electromagnetic properties of the composites could be changed significantly when the cobalt particles networks turned into sheet structure. That was to say, the electromagnetic properties of metal-ceramic composites could be tailored by their compositions and microstructures, which make it available for microwave-absorbing materials, attenuation ceramics and microwave dielectrics, etc. © 2014 The American Ceramic Society. Source


Yan K.-L.,Shandong University | Fan R.-H.,Shandong University | Chen M.,Shandong University | Sun K.,Shandong University | And 5 more authors.
Rare Metals | Year: 2015

The nano-graphite sheet/alumina composites were prepared in situ by a facile impregnation-reduction process. The microstructure of the composites was analyzed by X-ray diffraction (XRD), and the final phase composition after reduction is Al2O3, metal Fe and graphite crystal. Scanning electron microscopy (SEM) images show that the particle size of Fe is about 20 nm, and the lamellae thickness of the graphite is about 30 nm. Then, the dielectric properties and conductive mechanism of the composites were investigated experimentally in the frequency range of 0.01–1.00 GHz by impedance analyzer. The results show that the real part of permittivity of composites increases with Fe3+ concentration, which is due to the increase in interfacial polarization between Fe and Al2O3 and the three-dimensional network of lamellar graphite formation. Therefore, tunable microtopography and electrical parameters of nano-graphite sheet/alumina composites can be realized by changing Fe3+ concentration. © 2015 The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg Source

Discover hidden collaborations