Negative Magnetic Permeability Research Articles

Propagation of a localized wavepacket in a metamaterial with a negative index of refraction

Propagation properties of electromagnetic waves in a medium with a negative index of refraction are investigated. A model of a physical signal that combines simultaneously qualities of both a spatially-localized beam and a wavepacket was used as the incident wave. Such a choice was necessary because of the strong frequency dispersion of metamaterials in the spectral region with a negative index of refraction. An approximate analytical solution was derived that describes the propagation dynamics of such a signal through a slab made of material showing simultaneously a negative dielectric permittivity and magnetic permeability.

Magnetic dipole based systems for probing optical magnetism

Recent advances in plasmonic-based metamaterials show that the magnetic component of an optical field can be strongly affected by the material’s properties and geometry of metallic nanostructures, leading to such interesting effects as negative magnetic permeability and magnetic resonance in the optical range. To probe such effects experimentally, systems containing Eu3+ ions can be used as spectroscopic tools. The study of the magnetic dipole-related transition at ∼590nm in comparison with the electric dipole-related transition at ∼615nm can reveal information on the relative distribution of magnetic and electric fields as well as effective permeability and permittivity. We report the development of such systems, demonstrating very high emission efficiency, and the first experimental results.

Quasi-guided electromagnetic beam propagation in one-dimensional photonic crystal with a left-handed metamaterial

We show that due to consecutive phase front conjugation in one-dimensional photonic crystals consisting of layers of conventional right-handed dielectrics and left-handed metamaterials with simultaneously negative dielectric permittivity and magnetic permeability, the wide two-dimensional electromagnetic beams can exhibit quasi-guided propagation completely restoring its initial transverse structure over each period of photonic crystal. We find the conditions of quasi-guided beam propagation for both transverse electric and transverse magnetic polarization and corresponding dispersion relations for such a waveguide. We also demonstrate that waveguide modes can be forward as well as backward at different values of permittivity and permeability of the left-handed layers.

Three-dimensional photonic metamaterials at optical frequencies

Metamaterials are artificially structured media with unit cells much smaller than the wavelength of light. They have proved to possess novel electromagnetic properties, such as negative magnetic permeability and negative refractive index. This enables applications such as negative refraction, superlensing and invisibility cloaking. Although the physical properties can already be demonstrated in two-dimensional (2D) metamaterials, the practical applications require 3D bulk-like structures. This prerequisite has been achieved in the gigahertz range for microwave applications owing to the ease of fabrication by simply stacking printed circuit boards. In the optical domain, such an elegant method has been the missing building block towards the realization of 3D metamaterials. Here, we present a general method to manufacture 3D optical (infrared) metamaterials using a layer-by-layer technique. Specifically, we introduce a fabrication process involving planarization, lateral alignment and stacking. We demonstrate stacked metamaterials, investigate the interaction between adjacent stacked layers and analyse the optical properties of stacked metamaterials with respect to an increasing number of layers.

Magnetic excitation of magnetic resonance in metamaterials at far-infrared frequencies

The authors experimentally demonstrated magnetically excited magnetic resonances with negative magnetic permeability in a metamaterial composed of an array of silver rod pairs. In transmission spectroscopy of the metamaterial, by employing oblique incidence, an incident-magnetic-field-dependent absorption feature was clearly observed at 18THz. The experimental results directly prove that the rod pair structure interacted with the magnetic field of the incident light, producing magnetic resonance. The experimental results were in good agreement with a numerical simulation suggesting that the value of μRe of the silver rod pair array changes from −0.29 to 2.26 at resonance.

Simultaneous negative permittivity and permeability in a coherent atomic vapour

A new quantum optical mechanism to realize simultaneously negative electric permittivity and magnetic permeability is suggested. In order to obtain a negative permeability, we choose a proper atomic configuration that can dramatically enhance the contribution of the magnetic-dipole allowed transition via the atomic phase coherence. It is shown that the atomic system chosen with proper optical parameters can give rise to striking electromagnetic responses (leading to a negative refractive index) and that the atomic vapour becomes a left-handed medium in an optical frequency band. Differing from the previous schemes of artificial composite metamaterials (based on classical electromagnetic theory) to achieve the left-handed materials, which consist of anisotropic millimetre-scale composite structure units, the left-handed atomic vapour presented here is isotropic and homogeneous at the atomic-scale level. Such an advantage may be valuable in realizing the superlens (and hence perfect image) with left-handed atomic vapour.

Metamaterials for ballistic electrons

This article presents a metamaterial for ballistic electrons, which consists of a quantum barrier formed in a semiconductor with negative effective electron mass. This barrier is the analog of a metamaterial for electromagnetic waves in media with negative electrical permittivity and magnetic permeability. Besides applications similar to those of optical metamaterials, a nanosized slab of a metamaterial for ballistic electrons, sandwiched between quantum wells of positive effective mass materials, reveals unexpected conduction properties, e.g., single or multiple room temperature negative differential conductance regions at very low voltages and with considerable peak-to-valley ratios, while the traversal time of ballistic electrons can be tuned to larger or smaller values than in the absence of the metamaterial slab. Thus, slow and fast electrons, analogous to slow and fast light, occur in metamaterials for ballistic electrons.

Magnetostatic properties of amorphous and nanostructured Fe73.5Si13.5B9Cu1Nb3 wires

We present the results of experimental investigations of magnetostatic properties of Fe-based amorphous wires with diameter about 100μm. The samples were annealed at different conditions. The as-quenched sample had a weak increase (about 5%) of the magnetization with magnetic field decrease – the negative differential magnetic permeability could be observed in its hysteresis loops. The coercive force was about 0.2Oe. The conventional annealing decreased the value of the saturation field down to 5Oe without change of the coercive force value. When the annealing was accompanied with torsion stress the coercive force became less than 50mOe. After the current annealing any peculiarities disappeared in magnetization in a weak magnetic field.

Negative permeability in a Λ-type three-level atomic vapor

A new approach is suggested to realize negative magnetic permeability that follows directly from quantum mechanics. It is shown that a Delta-type three-level atomic system with proper atomic para ...

Negative refraction and sub-wavelength focusing in the visible range using transparent metallo-dielectric stacks

We numerically demonstrate negative refraction of the Poynting vector and sub-wavelength focusing in the visible part of the spectrum using a transparent multilayer, metallo-dielectric photonic band gap structure. Our results reveal that in the wavelength regime of interest evanescent waves are not transmitted by the structure, and that the main underlying physical mechanisms for sub-wavelength focusing are resonance tunneling, field localization, and propagation effects. These structures offer several advantages: tunability and high transmittance (50% or better) across the visible and near IR ranges; large object-image distances, with image planes located beyond the range where the evanescent waves have decayed. From a practical point of view, our findings point to a simpler way to fabricate a material that exhibits negative refraction and maintains high transparency across a broad wavelength range. Transparent metallo-dielectric stacks also provide an opportunity to expand the exploration of wave propagation phenomena in metals, both in the linear and nonlinear regimes.

Large-area magnetic metamaterials via compact interference lithography

Magnetic metamaterials with magnetic-dipole resonances around 1.2-mum wavelength are fabricated using an extremely compact and robust version of two- or three-beam interference lithography for 1D and 2D structures, respectively. Our approach employs a single laser beam at 532- nm wavelength impinging onto a suitably shaped dielectric object (roof-top prism or pyramid) - bringing the complexity of fabricating magnetic metamaterials down to that of evaporating usual dielectric/metallic coatings.The measured optical spectra agree well with theory; the retrieval reveals a negative magnetic permeability. Importantly, the large-scale sample homogeneity is explicitly demonstrated by optical experiments.

Dielectric, magnetic and optical properties of nanocomposites

Nanocomposites are media made of nanoparticles embedded in a matrix. Depending on the nanoparticle types and shapes, nanocomposites can have different properties. I discuss here dielectric and magnetic composites at low, as well as, high frequencies. At low frequencies, dielectric and magnetic properties can be enhanced by using elongated nanoparticles. At high frequencies various photonic, plasmonic and polaritonic effects can occur in nanocomposites, in particular in those with periodic arrangement of nanoparticles. The negative refraction can be achieved in nanocomposites with simultaneously negative dielectric function and magnetic permeability.

Wide band negative magnetic permeability materials (NMPM) with composite metalsemiconductor structures based on the Drude model, and applications to negative-refractive index (NIM)

Composite structures based on metal open rings and thin wires are well established, for obtaining efficient negative index materials (NIM), acting as metamaterials in the long wavelength regime. The main losses are due both to metal absorption and to the inner electric resistance of metals; to overcome this latter loss we propose a new metal-semiconductor structure dimensioned by direct synthesis method, which offers an almost perfect Drude-like effective magnetic permeability. The choice of particular semiconductor components allows to get a negative resistance for the current induced by the electromagnetic field, which cancels that of the metal but puts a limit to the spectral response of the metamaterial. We consider some parasite effects, such as bianisotropy and incorrect values of structural parameters, to see limitations and features of this new NIM technology.

Dependence of the magnetic-resonance frequency on the cut-wire width of cut-wire pair medium

We investigated some magnetic metamaterials based on cut-wire pairs instead of split-ring resonators to quest for the possibility of a negative magnetic permeability. Several periodic structures of cut-wire pairs were designed and fabricated, and their transmission spectra were measured in the microwave-frequency regime. The width dependence of magnetic-resonance frequency was studied both theoretically and experimentally for the periodic structures of cut-wire pairs. It was found that, besides the length dependence, the magnetic-resonance frequency also depends significantly on the width of cut-wire pair. A simple equivalent-circuit model proposed by Zhou et al. [Opt. Lett. 31, 3620-3622 (2006)] was employed to elucidate this interesting phenomenon and to simulate the width dependence. In the simulation the magnetic and the electric energies of the cut-wire pair were directly calculated to obtain the magnetic-resonance frequency. The theoretical results are in good agreement with the experimental ones. It reveals that there is a rather easy way to manipulate the magnetic-resonance frequency of magnetic-magnetic metamaterials.

Experimental demonstration of negative magnetic permeability in the far-infrared frequency regime

Using transmission and reflection measurements in a five layer micrometer-scale split-ring resonator (SRR) system, fabricated by a photolithography procedure, the authors demonstrate the occurrence of a negative magnetic permeability regime in that system at ∼6THz. The transmission and reflection were measured using oblique incidence, resulting to a magnetic field component perpendicular to the SRR plane, which excites the resonant circular currents constituting the magnetic resonance.

Effective properties of split-ring resonator metamaterials using measured scattering parameters: Effect of gap orientation

This paper presents experimental S-parameter data (amplitude and phase) in the 8–26GHz range for split-ring resonator (SRR) metamaterial samples exhibiting electric (E) and/or magnetic (H) resonances at 10.4GHz depending on the orientation of the gaps of the SRRs with respect to the E and H fields. Use of a thru, reflect, line (TRL) calibrated focused plane wave, free space microwave system permits inversion of the complex permittivity, permeability, and refractive index of planar metamaterial samples from measurement of the reflected and transmitted S parameters of the system. Samples were prepared by patterning concentric SRRs on a dielectric substrate. Three different orientations of the SRR have been used in the experimental study; (i) SRRparallel—gaps in the split rings parallel to the incident E field to realize a dielectric resonance; (ii) SRRrandom—randomly oriented gaps to realize simultaneous dielectric and magnetic resonances; and (iii) SRRperpendicular—gap oriented perpendicular to the E-field to realize a strong magnetic resonance. The experimentally extracted material properties show very good agreement with numerical simulations of effective properties giving rise to a negative magnetic permeability. A second resonance at 23GHz clearly establishes a passband between 10.4 and 23GHz for all samples. The extraction of effective properties from measured S parameters is a useful development in metamaterials research and the study of random orientations of gaps with respect to the E field is an interesting design for metamaterials that may lead to negative index behavior with further optimization.

Negative refractive index in artificial metamaterials

We discuss optical constants in artificial metamaterials showing negative magnetic permeability and electric permittivity and suggest a simple formula for the refractive index of a general optical medium. Using the effective-field theory, we calculate the effective permeability and the refractive index of nanofabricated media composed of pairs of identical gold nanopillars with magnetic response in the visible spectrum.

Artificial dielectric medium possessing simultaneously negative permittivity and magnetic permeability

An artificial dielectric medium comprising two sublattices of spherical particles made of a high-dielectric-constant (high-e) material, which are embedded into a low-e dielectric matrix, are considered. Particles belonging to different sublattices have different diameters. It is shown that the properties of this composite structure are equivalent to those of an isotropic medium possessing a negative refractive index (n 200 can be made of a ferroelectric material.

Wave scattering by metamaterial wedges and interfaces

AbstractWe outline specific features of numerical simulations of metamaterial wedges and interfaces. We study the effect of different positioning of a grid in the Yee method, which is necessary to obtain consistent convergence in modelling of interfaces with metamaterials characterized by negative dielectric permittivity and negative magnetic permeability. We demonstrate however that, in the framework of the continuous‐medium approximation, wave scattering on the wedge may result in a resonant excitation of waves with infinitely large spatial frequencies, leading to non‐convergence of the simulation results that depend on the discretization step. Copyright © 2006 John Wiley & Sons, Ltd.

Negative index materials using simple short wire pairs

Negative refraction is currently achieved by a combination of artificial ``electric atoms'' (metallic wires with negative electrical permittivity $\ensuremath{\epsilon}$) and artificial ``magnetic atoms'' (split-ring resonators with negative magnetic permeability $\ensuremath{\mu}$). Both $\ensuremath{\epsilon}$ and $\ensuremath{\mu}$ must be negative at the same frequency, which is not easy to achieve at higher than THz frequencies. We introduce improved and simplified structures made of periodic arrays of pairs of short metal wires and continuous wires that offer a potentially simpler approach to building negative index materials. Using simulations and microwave experiments, we have investigated the negative index $n$ properties of short wire-pair structures. We have measured experimentally both the transmittance and the reflectance properties and found unambiguously that $nl0$. The same is true for $\ensuremath{\epsilon}$ and $\ensuremath{\mu}$. Our results show that short wire-pair arrays can be used very effectively in producing materials with negative refractive indices.