Optimization Design of Electromagnetic Nihility Nanoparticles

Nihility material is a medium whose relative permittivity and permeability tend to zero simultaneously.In this work,comparing with the scattering properties of perfect nihility nanoparticles(made from nihility material),we provide an optimization design of electromagnetic nihility nanoparticles,which is a coated hybrid nanosphere constituted by commutative ε-negative(ENG) and μ-negative(MNG) media.Compared to a single ENG or MNG nanosphere,it is found that the total and back scattering spectra of coated hybrid nanospheres are much closer to those of perfect nihility nanospheres.Moreover,it is observed that the scattered electromagnetic field distribution of coated hybrid nanospheres is identical to that of perfect nihility nanospheres.These results indicate that the combination of commutative ENG and MNG media can constitute a composite structure which gives the closest approximation of electromagnetic scattering of perfect nihility nanospheres in a wide frequency range.     

Nonlinear optical and magneto-optical effects in non-spherical magnetic granular composite

The magnetization-induced nonlinear optical and nonlinear magneto-optical properties in a magnetic metal-insulator composite are studied based on a tensor effective medium approximation with shape factor and Taylor-expansion method. There is a weakly nonlinear relation between electric displacement D and electric field E in the composite. The results of our studies on the effective dielectric tensor and the nonlinear susceptibility tensor in a magnetic nanocomposite are surveyed. It is shown that such a metal-insulator composite exhibits the enhancements of optical and magneto-optical nonlinearity. The frequencies at which the enhancements occur, and the amplitude of the enhancement factors depend on the concentration and shape of the magnetic grains.     

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.     

A Fractal Model for Effective Thermal Conductivity of Isotropic Porous Silica Low-k Materials

We establish a new model based on fractal theory and cubic spline interpolation to study the effective thermal conductivity of isotropic porous silica low-k materials. A 3D fractal model is introduced to describe the structure of the silica xerogel and silica hybrid materials （such as methylsilsesquioxane, MSQ）. Combined with fractal structure, a more suitable medium approximation is developed to study the isotropic porous silica xerogel and MSQ materials. Cubic spline interpolation for fitting discrete predictions from the fractal model is used to obtain the continuous function of the effective thermal conductivity versus porosity. Compared with other common models, the effective thermal conductivity predicted by our model presents better agreement with the experimental data for all porosity. These results indicate that the proposed model is valid.     

Effective medium parameters for 1D photonic crystal containing single-negative material layers using the envelope function approach

Nonlinear wave propagation in a 1D photonic crystal containing single-negative layers is investigated using the multiple-scale method. In this approach, the electric field is decomposed into a slowly varying envelope function and a fast Bloch-like function to obtain the analytic expressions of the effective parameters of an equivalent medium. The periodic structure has an equivalent left-handed medium for the envelope function. Gap soliton formation is discussed and compared with that associated with the Bragg gap.     

Stopband Phenomena in the Passband of Left-Handed Metamaterials

Stopband phenomena are reported in the passband of left-handed metamaterials. The samples with linear defect are designed by removing one layer of split ring resonators （SRRs）. It is shown that the left-handed transmission peaks have a distinct transform with the relative deviation of the SRRs centre from the wire centre 8, from a single left-handed peak, double left-handed peaks with different magnitude to no transmission peak, i.e. left-handed properties of metamaterials disappear. Numerical simulation shows that the change of 8 makes the effective permeability shift at a frequency range, where stopband occurs. It is thought that the stopband in left-handed passband is due to the symmetry breaking between SRRs and wires in the metamaterials.     

Optimal Acoustic Attenuation of Weakly Compressible Media Permeated with Air Bubbles

Based on fuzzy logic （FL） and genetic algorithm （GA）, we present an optimization method to obtain the optimal acoustic attenuation of a longitudinal acoustic wave propagating in a weakly compressible medium permeated with air bubbles. In the optimization, the parameters of the size distribution of bubbles in the medium are optimized for providing uniformly high acoustic attenuation in the frequency band of interest. Compared with other traditional optimization methods, the unique advantage of the present method is that it can locate the global optimum quickly and effectively in need of knowing the mathematical model precisely. As illustrated by a numerical simulation, the method is effective and essential in enhancing the acoustic attenuation of such a medium in an optimal manner. The bubbly medium with optimized structural parameters can effectively attenuate longitudinal waves at intermediate frequencies with an acoustic attenuation approximating a constant value of lO（dB/cm）. Such bubbly media with optimal acoustic attenuations may be applied to design acoustic absorbent by controlling broader attenuation band and higher efficiency.     

Calculation of High Frequency Complex Permeability of Carbonyl Iron Flakes in a Nonmagnetic Matrix

The carbonyl iron flakes are fabricated by high-energy ball milling. The effective permeability is measured and calculated for the composite consisting of flakes embedded in a nonmagnetic matrix. The magnetic flakes with a shape anisotropy and random spatial distribution of normal direction are considered to calculate the complex permeability of magnetic flake materials. Its analytical model is derived from the Landau-Lifshitz-Gilbert equation and Bruggeman ＇s effective medium theory. The calculated results agree well with the experiment.     

Focusing of a Flat Left-Handed Metamaterial Lens in a Heterogeneous and Lossy Medium

For applications such as near-field target detection and tumor hyperthermia with a fiat left-handed metamaterial （LHM） lens, a microwave will be focused in the heterogeneous and lossy medium. Different from the focusing of a fiat LHM lens in vacuum as reported in most previous studies, the medium loss and heterogeneity will affect the focusing performance of the LHM lens. Numerical simulations indicate that the medium loss will degrade the focusing resolution, while the heterogeneity of random variability within ±30% will affect the focusing resolution to a limited extent. Both the loss and heterogeneity of the medium will shift the focal point away from the image plane. When focusing in a medium with different permittivity values, an LHM lens will also have different focusing resolutions due to different electric thicknesses.     

A Method of Analyzing Transmission Losses in Left-Handed Metamaterials

A method of analyzing transmission loss in left-handed metamaterials （LHMs） is proposed. As a demonstration of this method, transmission loss of LHMs composed of split-ring resonators （SRR） and conducting wires is studied. By means of retrieving and analyzing the effective constitutive parameters, different transmission losses as well as their origins are studied. The results show that the left-handed bandwidth is narrowed because of high loss caused by the non-zero high imaginary parts of the effective permeability and permittivity. In the effective left-handed band, the radiation loss is very low and can be neglected, and the transmission losses are the sum of the substrate loss and the ohmic loss. Moreover, when the dielectric loss tangent of the substrate is greater than 0.003, the substrate loss is higher than the ohmic loss.     

Lamellar model of the left-handed metamaterials composed of metallic split-ring resonators and wires

Left-handed materials composed of split ring resonators (SRRs) and wires are investigated in the viewpoint of lamellar composite with epsilon-negative (ENG) and mu-negative (MNG) materials staked alternatively. Several configurations of the SRR-wire metamaterial are numerically simulated to confirm its left-handed response as an analogy to the ENG-MNG lamellar model.     

Ground state of alkaline-earth fermionic atoms in one-dimensional optical lattices

The properties of the wave transmission in the lossy single-negative (SNG) metamaterials are experimentally investigated. The model structure of lossy epsilon-negative (ENG) monolayer and SNG bilayer consisting of a lossy ENG material and a mu-negative (MNG) are considered in this work. Simulation and experimental results show that the transmittance of the lossy SNG materials can be enhanced by two approaches, increasing dissipation coefficient and increasing the thickness of the lossy SNG. The lossy ENG material is physically fabricated by using composite right- and left-handed transmission lines grafted with radiation unit cell. The experimental results are in very good agreement with the previous theoretical analysis.     

Effects of losses on the transmission and reflection in the single-negative materials

In this work, we investigate the angular dependence of transmission and reflection in the single-negative (SNG) materials. We consider a model structure of a SNG bilayer which consists of the epsilon-negative (ENG) and mu-negative (MNG) layers. The wave transmission and reflection properties due to the losses from the ENG and MNG materials are specifically investigated. With the presence of losses in the ENG and MNG materials, some unusual wave properties will be explored and numerically demonstrated.     

Metamaterials电磁特性的数值仿真研究

利用HFSS软件，对电磁波在左手材料中的后向波传输、平板成像特性和近零折射率媒质的定向辐射特性进行了全波仿真研究，分别验证了左手材料与近零折射率媒质的上述特性。利用AnsoftDesigner软件，对去掉并联电感和去掉串联电容的、基于微带线的两种简化的左右手复合传输线构成的具有磁单负和电单负特性介质的电磁特性进行了仿真研究，验证了电磁波在匹配的MNG-ENG介质对结构的隧穿特性。     

Trapping of electromagnetic wave in single-negative metamaterial waveguides

We study the trapping properties of transverse magnetic (TM) waves in single-negative metamaterial waveguides including epsilon-negative (ENG) metamaterial and mu-negative (MNG) metamaterial. The relationship between effective refractive index and reduced core width is analyzed when the permittivities of ENG and MNG metamaterials are different, and the inflection on this curve can be regarded as the trapping point. Simulation results show that the properties in an ENG–MNG–ENG metamaterial waveguide are contrary to that in a MNG–ENG–MNG metamaterial waveguide. The sensitivity of trapping point to the change of permittivity makes the single-negative metamaterial waveguides to be an effective method to detect the permittivity variation and can be used as a new kind of waveguide sensor.     

Analysis of angle-dependent unusual transmission in lossy single-negative (SNG) materials

The properties of unusual transmission as a function of the dissipation factor in single-negative (SNG) materials are theoretically investigated. Using Drude-like expressions for the permittivity in epsilon-negative (ENG) material and the permeability in mu-negative (MNG) material, we investigate the angular dependence of unusual transmission for both transversal electric (TE) and transversal magnetic (TM) waves. Two model structures, a single ENG layer and an ENG–MNG bilayer, are examined. A very different dependence of the incident angle on the transmission is found for these two structures. A discussion of the effect of the polarization of incident waves is also given.     

Influence of absorption in the zero effective phase gap in one-dimensional photonic crystals containing single-negative materials

The transmission properties of one-dimensional (1D) photonic crystals containing two kinds of single-negative (ENG and MNG) material are investigated theoretically. A type of photonic gap with zero effective phases (zero-φ_eff) and the effects of absorption on the properties of the zero-φ_eff gap were shown. Specifically, it is demonstrated that strong absorption creates photon states inside the gap and this makes the band gap to be of zero width.     

Energy transport in a metamaterial subwavelength open-cavity resonator

We present a theoretical and experimental investigation into the energy transport in a conjugate matched bilayer consisting of ε-negative (ENG) and μ-negative (MNG) slabs. It is proved that the conjugated matched ENG/MNG bilayer is a subwavelength open-cavity resonator, in which the resonance frequency is determined by the complete tunneling condition, and the Q factor increases exponentially with the slab thickness. It is revealed that the wave is not evanescent inside the bilayer, but it is a hybrid of a traveling wave and a reactive standing wave. It is also manifested during the transient wave propagation that the reactive field energy stored inside the bilayer is provided by the incident wave.     

Optical Magnus effect in metamaterials fabricated from ferromagnetic microwires

In homogeneous negative phase velocity media, the Doppler and Cherenkov-Vavilov effects and the refraction and pressure of light are anomalous: they are inverse with respect to the corresponding effects in conventional media. Using the geometrical optics approximation, it is shown that the optical Magnus effect in inhomogeneous negative phase velocity media is also anomalous. The effect is demonstrated by considering a metamaterial consisting of parallel amorphous ferromagnetic microwires in a magnetic field. The metamaterial proves to be a left-handed one in the realistic region of the electromagnetic spectrum. The optical properties of such a left-handed medium can be controlled by the external magnetic field.     

Time-domain investigation of the tunneling modes in photonic heterostructure containing single-negative materials

We present a theoretical investigation into the energy transport and transient wave propagation in metamaterial tunneling structures consisting of ??-negative (ENG) and ??-negative (MNG) materials. It is proved that a conjugated matched ENG/MNG bilayer and a (zero-index-material doped) photonic crystal heterostructure can work as a sub-wavelength resonator at tunneling frequency. The tunneling modes need a certain time to achieve the steady state and the charge up characteristic time increases (nearly) exponentially with the thickness of the structures. Under the steady state, the wave in the single-negative-material structures is not evanescent, but a hybrid of a traveling wave and a reactive standing wave. The phase difference between the electric field and the magnetic field varies with the position and time. The investigation of transient wave propagation in the metamaterial tunneling structures will help us to understand the interaction process between wave and metamaterial and to design special functional apparatus.