We developed two-step solution-phase reactions to form hybrid materials of Mn3O4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn3O4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn3O4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn3O4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn3O4 nanoparticles grown atop. The Mn3O4/RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

Mn3O4-Graphene Hybrid as a High Capacity Anode Material for Lithium Ion Batteries

Here, we analyze the transverse-magnetic (TM) wave interaction with a pair of slabs, one being an epsilon-negative (ENG) layer in which the real part of permittivity is assumed to be negative while its permeability has positive real part, and the other being a mu-negative (MNG) layer that has the real part of its permeability negative but its permittivity has positive real part. Although the wave interaction with each slab by itself has predictable features, we show that the juxtaposition and pairing of such ENG and MNG slabs may, under certain conditions, lead to some unusual features, such as resonance, complete tunneling, zero reflection and transparency. The field distributions inside and outside such paired slabs are analyzed, and the Poynting vector distributions in such structures are studied. Using equivalent transmission-line models, we obtain the conditions for the resonance, complete tunneling and transparency, and we justify and explain the field behavior in these resonant paired structures. Salient features of the tunneling conditions, such as the roles of material parameters, slab thicknesses, dissipation, and angle of incidence are discussed. The analogy and correspondence between the ENG-MNG pair and the pair of a slab of conventional material juxtaposed with a "double-negative" medium is also discussed. Finally, a conceptual idea for a potential application of such a "matched" lossless ENG-MNG pair in "ideal" image displacement and image reconstruction is proposed.

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Pairing an epsilon-negative slab with a mu-negative slab: resonance, tunneling and transparency

Metamaterials (MTMs), which are formed by embedding inclusions and material components in host media to achieve composite media that may be engineered to have qualitatively new physically realizable response functions that do not occur or may not be easily available in nature, have raised a great deal of interest in recent years. In this paper, we highlight a large variety of the physical effects associated with double- and single-negative MTMs and some of their very interesting potential applications. The potential ability to engineer materials with desired electric and magnetic properties to achieve unusual physical effects offers a great deal of excitement and promise to the scientific and engineering community. While some of the applications we will discuss have already come to fruition, there are many more yet to be explored.

/pdf/a-positive-future-for-double-negative-metamaterials-1f2x06674u.pdf

A positive future for double-negative metamaterials

A rectangular waveguide filled with anisotropic uniaxial metamaterial with transversal negative effective permeability is investigated both theoretically and experimentally. It is shown that such a waveguide supports propagation of the backward wave below the cutoff frequency, thus, it can be considered as a dual of the ordinary waveguide. The transversal dimension of this waveguide can be arbitrarily smaller than half of a wavelength in the filling material, provided that the transversal permeability is negative. This peculiar behavior may be used for fabrication of miniaturized rectangular waveguides. Several experimental miniaturized waveguides loaded with double ring resonators in 7 GHz frequency band have been designed, fabricated and tested. The measured results revealed backward-wave passband located below the cutoff frequency. Furthermore, it was experimentally shown that the increase of the physical length of the waveguide caused the decrease of the electrical length. This is a direct proof of the backward-wave propagation since the phase of the backward wave increases along the waveguide.

Waveguide miniaturization using uniaxial negative permeability metamaterial

Recent theoretical studies have shown that circular patch antennas loaded by an inhomogeneous substrate partially filled with a mu-negative (MNG) metamaterial may in principle support a resonant radiating mode, even if the total size of the radiator is significantly smaller than the wavelength of operation. In those theoretical analyses, MNG metamaterials have been assumed as continuous, isotropic and readily available materials, characterized by a proper dispersion in frequency and by inherent ohmic losses. The fabrication of such compact antennas, however, would require the major effort of designing proper subwavelength inclusions that realize the MNG behavior of the substrate, and consequently a careful design of their geometry, location and orientation. The fabrication of a fully isotropic MNG sample to reside underneath the sub-wavelength patch, moreover, may be challenging with the current technological limitations. In this paper, we first show that the proposed sub-wavelength radiator may operate even when the fabricated MNG sample is not isotropic, due to the specific polarization of the magnetic field in the MNG region. Then, we propose a complete design of the magnetic inclusions, presenting full-wave numerical simulations of the structure, which effectively supports the expected resonant mode, despite the small size of the antenna. The comparisons among analytical results of the patch loaded by: (a) the ideal MNG sample applying a simple cavity model; (b) full-wave numerical simulations of the same antenna considering the presence of the feed; and (c) full-wave numerical simulations of the antenna loaded by the proposed magnetic inclusions, show how our design effectively simulate the presence of an MNG sample, allowing the realistic design of a sub-wavelength metamaterial patch antenna with satisfactory matching and radiating features. This may open up new venues in the realization of efficient metamaterial radiating components for practical purposes.

Design of Miniaturized Metamaterial Patch Antennas With $\mu$ -Negative Loading

A simple one-dimensional meta-material which exhibits negative permeability within a finite frequency band is proposed in this paper. Instead of recently introduced split-ring resonators, this structure comprises an array of the capacitively loaded small loop antennas. Due to resonant behaviour of the antenna current, intensity of the magnetic field of the incoming plane wave may be locally decreased yielding a stop-band with negative effective permeability. Theoretical analysis was verified by measurements of the transmission coefficient of experimental structures in free space and in rectangular waveguide, in 10 GHz frequency band. The developed structure was also combined with previously reported negative permittivity wire structure and left-handed (backward wave) properties were observed.

Capacitively Loaded Loop as Basic Element of Negative Permeability Meta-material

This paper reports design of a very low-cost (less than 2000 USD) chemical vapour deposition (CVD) reactor for graphene synthesis, based on readily available off-the-shelf components. The reactor i...

https://www.tandfonline.com/doi/pdf/10.1080/00051144.2018.1528691

Low-cost synthesis of high-quality graphene in do-it-yourself CVD reactor

The experimental investigation of recently proposed nanophotonic devices and metamaterials based on the plasmonic nanospheres is rather difficult and expensive using the present technology of nano-fabrication. Here, we propose the idea of scaled experiments in the RF regime, based on the spherical resonators that behave similarly to the plasmonic nanospheres. Two different designs, based on well-known Best's four-arm spherical resonator and on Stuart's spherical resonator were tested experimentally in 500 MHz and 1 GHz bands. It was found possible to construct the linear chains of the resonators and to demonstrate both the backward-wave propagation and the forward-wave propagation, which is consistent with already published theoretical predictions.

Spherical resonators acting as rf replicas of plasmonic nanospheres

The fact that field distribution inside four-arm spherical helix, previously used for design of small antennas, resembles distribution inside ENG sphere is used for experimental investigation of electromagnetic properties of a chain of plasmonic nanospheres by scaled experiments in RF and microwave regime

Investigation of Electromagnetic Properties of a Chain of Plasmonic Nanospheres by Scaled Experiments in Radiofrequency and Microwave Regime

This paper presents an update on recently introduced low-cost CVD reactor for graphene synthesis in metamaterial research. Apart from previously reported synthesis of single-layer graphene, it has been shown possible to produce large area multi-layer graphene, as well. Raman spectroscopy revealed high quality and good repeatability of synthesized samples. Synthesized multi-layer graphene may find application in absorbers and non-linear metasurfaces that apply recently demonstrated phenomena such as four-wave mixing and phase conjugation.

Zoran Eres

Papers

Capacitively Loaded Loop as Basic Element of Negative Permeability Meta-material

Low-cost synthesis of high-quality graphene in do-it-yourself CVD reactor

Spherical resonators acting as rf replicas of plasmonic nanospheres

Investigation of Electromagnetic Properties of a Chain of Plasmonic Nanospheres by Scaled Experiments in Radiofrequency and Microwave Regime

Low-cost multi-layer graphene for linear/non-linear metasurface applications