Negative permittivity derived from inductive characteristic in the percolating Cu/EP metacomposites

Abstract

Recently, increasing attention has been concentrated on negative permittivity with the development of the emerging metamaterials composed of periodic array structures. However, taking facile preparation into consideration, it is important to achieve negative permittivity behavior based on materials' intrinsic properties rather than their artificially periodic structures. In this paper, we proposed to fabricate the percolating copper/epoxy resin (Cu/EP) composites by a polymerization method to realize the negative permittivity behavior. When Cu content in the composites reached to 80 wt.%, the conductivity abruptly went up by three orders of magnitudes, suggesting a percolation behavior. Below the percolation threshold, the conductivity spectra conform to Jonscher's power law; when the Cu/EP composites reached to percolating state, the conductivity gradually reduced in 2 high frequency region due to the skin effect. It is indicated that the conductive mechanism changed from hopping conduction to electron conduction. In addition, the permittivity did not increase monotonously with the increase of Cu content in the vicinity of percolation threshold, due to the presence of leakage current. Meanwhile, the negative permittivity conforming to Drude model was observed above the percolation threshold. Further investigation revealed that there was a constitutive relationship between the permittivity and the reactance. When conductive fillers are slightly above the percolation threshold, the inductive characteristic derived from conductive percolating network leads to the negative permittivity. Such epsilon-negative materials can potentially be applied in novel electrical devices, such as high-power microwave filters, stacked capacitors, negative capacitance field effect transistors and coil-free resonators. In addition, the design strategy based on percolating composites provides an approach to epsilon-negative materials.

Hydrosoluble Graphene/Polyvinyl Alcohol Membranous Composites with Negative Permittivity Behavior

“…With the increase of graphene content, the connectivity of the graphene sheets increases, so it is inevitable to generate the leakage current especially when the graphene content is in the vicinity of percolation threshold. As is well known, the dielectric constant is related to the polarization of dipoles in materials 55. Absolutely, the leakage current is detrimental to the polarization of dipoles, so the permittivity in the GR/PVA composites with 18 wt% graphene got lessened.…”

“…According to the free electron gas theory, the positive and negative charges can separate from each other and generate a slight displacement; under the action of an alternating electric field, the electrons can give rise to a collective harmonic oscillation, which called plasma oscillation 55. It is indicated that the permittivity of conductive materials commonly presented negative values, when the test frequency is below the plasma oscillation frequency.…”

Conductive Ag Microspheres with Lychee-like Morphology on the Enhanced Microwave Absorption Properties of MWCNTs

“…The absorbing mechanism for Ag@MWCNT hybrids is demonstrated in Figure . The possible reason for the enhanced absorbing performance is as follows: (1) MWCNTs belong to the dielectric loss absorbing material, while conductive Ag had resistance loss characteristics . The combination of MWCNTs with Ag microspheres would generate synergy effect to collectively attenuate the energy of EM waves.…”

“…(5) Electron migration and electronic hopping between the Ag−Ag particles, MWCNTs−Ag particles, and MWCNTs−MWCNTs would be generated, which was helpful to transform EM energy into heat energy or other forms. Based on the above analysis, the deposited conductive Ag on the PS microspheres could increase the interfacial polarization and resistance loss, 42 which was quite meaningful to improve the absorption properties.…”

“…The possible reason for the enhanced absorbing performance is as follows: (1) MWCNTs belong to the dielectric loss absorbing material, while conductive Ag had resistance loss characteristics. 42 The combination of MWCNTs with Ag microspheres would generate synergy effect to collectively attenuate the energy of EM waves. (2) The deposition of Ag particles on the PS microspheres would generate much more heterogeneous interface to produce interfacial polarization, 40 which was vital to enhance the absorbing performance.…”