Search

Double‐negative refractive index materials have attracted sustained experimental and theoretical interest because they can display a range of surprising optical phenomena, including negative Doppler shifts and perfect lensing. Double‐negative indexes have been achieved experimentally in engineered metamaterials; however, these materials become increasingly challenging to fabricate at shorter wavelengths, and at optical wavelengths only 2D negative index materials have been achieved. Here, it is shown that a double‐negative index can occur in a natural material, near narrow optical transitions of dielectric crystals stoichiometric in a rare‐earth ion. Optical measurements of two candidate materials, the magnetically‐ordered erbium crystals, ErCl3 ·6H2O and 7LiErF4, which have ultra‐narrow optical linewidths of 3 GHz and 250 MHz, respectively, in the telecom band are presented. It is shown that the spectral density of 7LiErF4 is sufficient to achieve a negative index at 1530 nm. This material can enable the exploration of negative refractive index effects at optical wavelengths in a truly 3D, natural medium. [ABSTRACT FROM AUTHOR]

In present communication, a new Aurivillius family compound K2Bi4Ti4WO18 was synthesized, and the impact of swift heavy ion (SHI), Ni+11 irradiation on its surface and dielectric properties has been studied in detail. The phase formation in this complex oxide, and crystallization to B2cb symmetry was confirmed by the X-ray diffraction. However, post irradiation the XRD, SEM and AFM studies shows the surface amorphization, in agreement with the theoretical calculations. Furthermore, the effect of irradiation was also observed in the bulk dielectric properties as the system transform to a phase with negative dielectric constant above 350 K in the radio frequencies. This transition is in correlation with significant change in other dielectric parameters such enhancement in AC conductivity, a helical Nyquist plot and multiple dielectric relaxations. This conspicuous changes in the dielectric response post irradiation is attributed to the SHI induced defect formation, modification of energy barriers and their consequences on the electronic structure. Thus, current study suggests that the dielectric properties of Aurivillius K2Bi4Ti4WO18 could be tailored by ion irradiation and opens a new possibility of tuning functional properties.

A major challenge for negative‐index acoustic metamaterials is increasing their operational frequency to the MHz range in water for applications such as biomedical ultrasound. Herein, a novel technology to realize acoustic metamaterials in water using microstructured silicon chips as unit cells that incorporate silicon nitride membranes and Helmholtz resonators with dimensions below 100 μm fabricated using clean‐room microfabrication technology is presented. The silicon chip unit‐cells are then assembled to form periodic structures that result in a negative‐index metamaterial. Finite‐element method (FEM) simulations of the metamaterial show a negative‐index branch in the dispersion relation in the 0.25–0.35 MHz range. The metamaterial is characterized experimentally using laser‐doppler vibrometry, showing opposite phase and group velocities, a signature of negative‐index materials, and is in close agreement with FEM simulations. The experimental measurements also show that the magnitude of phase and group velocities increase as the frequency increases within the negative‐index band, confirming the negative‐index behavior of the material. Acoustic indices from –1 to –5 are reached with respect to water in the 0.25–0.35 MHz range. The use of silicon technology microfabrication to produce acoustic metamaterials for operation in water opens a new road to reach frequencies relevant for biomedical ultrasound applications. [ABSTRACT FROM AUTHOR]

We have designed a photonic crystal flat lens with negative index operating at λ = 1.55 μ m for silicon photonics. It focuses an incident plane wave while it collimates the wave emitted by a point source. Its focal length is 4 λ , and it is 4.4 λ thick. Thus, it acts as a convex lens. It consists of a graded photonic crystal and its operating frequency is set in the second band of photonic crystals, so that the effective index is negative. It also operates in the first band, where it also focuses a plane wave and collimates a point source wave. In both cases, the resolution is subwavelength. It is at the wavelength scale and it has been designed so as it can be fabricated via the silicon-on-insulator CMOS technology. This compact photonic integrated circuit is for optical communications applications, optical interconnects, sensing and lab-on-chip. [ABSTRACT FROM AUTHOR]

The notions of negative refraction and negative index, introduced by V. Veselago more than 50 years ago, have appeared beyond the frontiers of macroscopic electromagnetism and purely formal during 30 years, until the work of J. Pendry in the late 1990s. Since then, the negative index materials and the metamaterials displayed extraordinary properties and spectacular effects which have tested the domain of validity of macroscopic electromagnetism. In this article, several of these properties and phenomena are reviewed. First, mechanisms underlying the negative index and negative refraction are briefly presented. Then, it is shown that the frame of the time-harmonic Maxwell’s equations cannot describe the behavior of electromagnetic waves in the situations of the perfect flat lens and corner reflector due to the presence of essential spectrum at the perfect $-1$ index frequency. More generally, it is shown that simple corner structures filled with frequency dispersive permittivity have a whole interval of essential spectrum associated with an analog of “black hole” phenomenon. Finally, arguments are provided to support that, in passive media, the imaginary part of the magnetic permeability can take positive and negative values. These arguments are notably based on the exact expression, for all frequency and wave vector, of the spatially-dispersive effective permittivity tensor of a multilayered structure.

Abstract This article concerns the Cauchy problem for the fractional semilinear pseudo-parabolic equation. Through the Green’s function method, we prove the pointwise convergence rate of the solution. Furthermore, using this precise pointwise structure, we introduce a Sobolev space condition with negative index on the initial data and give the nonlinear critical index for blowing up.

This article concerns the Cauchy problem for the fractional semilinear pseudo-parabolic equation. Through the Green's function method, we prove the pointwise convergence rate of the solution. Furthermore, using this precise pointwise structure, we introduce a Sobolev space condition with negative index on the initial data and give the nonlinear critical index for blowing up. [ABSTRACT FROM AUTHOR]

This paper introduces a 3-D spherical spiral expansion of the split ring resonator (SRR) commonly used to achieve negative permeability. The spherical spiral unit cell is shown to produce negative permeability over a much wider bandwidth than the traditional SRRs, and also to be capable of producing wideband negative permittivity or a double-negative response, depending on the orientation of the unit cell with respect to the incident electric field. The current structures leading to this phenomenon are discussed. Simulated and measured results are presented. [ABSTRACT FROM AUTHOR]

A new, compact planar wideband negative index metamaterial based on a modified split ring resonator (SRR) is studied to enhance performance of ultrawideband antenna. A compact, metamaterial (MTM)-inspired microstrip antenna is presented for microwave imaging system (MIS) application. Two layers of left-handed metamaterial array (2 x 4) of the unit cell are placed on the radiating patch and the ground plane, respectively. Each left-handed metamaterial (LHM) unit cell was constructed by modifying a square split ring resonator (SRR), resulting in negative permeability and permittivity with a stable negative refractive index. The results shows that it has a significant impact on the performance of conventional patch antenna in terms of transmission co-efficient, efficiency and low loss. Compared to antenna without LHM, it is shown that the bandwidth is significantly broadened up to a few megahertz and becomes more convergent leading to the achievement of desired properties for ultra-wideband (UWB) applications leading to microwave imaging. The proposed MTM antenna structure is fabricated on commercially-available, flame-retardant material of size 26 x 22 x 1.6 mm³ with 4.6 dielectric constants, due to its low cost and convenience for making multilayer printed circuit boards (PCBs). The antenna achieves 3.1 GHz to 10.71 GHz of impedance bandwidth (-10 dB), which covers the full UWB band. The use of double-layer negative index MTM unit cells enhances UWB performance, and the improved radiation efficiency, nearly directional radiation pattern, acceptable gain, stable surface current and negative refractive index make this MTM antenna a suitable candidate for UWB applications. [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, a negative index metamaterial with two components analysis for C- and X-band operations has been presented. The proposed metamaterial is designed on the epoxy resin composite with woven glass fiber and this epoxy resin formation processes are also explained step by step in this study. The unit cell structure has two arrows and a metal arm is connected to the two arrows that look like a double arrow shaped metamaterial. A Finite Integration technique based CST Microwave Studio is used to figure out the scattering parameters and the designed structure is investigated in the both x-axis and z-axis directions. The proposed metamaterial exhibited negative refractive index characteristics with wide bandwidth in S-, C-, and X-band for x-axis wave propagations. Besides, microwave spectrum in C- and X-band for z-axis electromagnetic wave transmissions. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1092-1096, 2017 [ABSTRACT FROM AUTHOR]

The local well-posedness for the Cauchy problem of the liquid crystals system in the critical Besov space $$\dot B_{p,1}^{n/p - 1}\left( {{\mathbb{R}^n}} \right) \times \dot B_{p,1}^{n/p}\left( {{\mathbb{R}^n}} \right)$$ with n < p < 2 n is established by using the heat semigroup theory and the Littlewood-Paley theory. The global well-posedness for the system is obtained with small initial datum by using the fixed point theorem. The blow-up results for strong solutions to the system are also analysed. [ABSTRACT FROM AUTHOR]

We elucidate the role of the mode coupling of the Mie resonances in all-dielectric metamaterials to ensure a negative effective index at terahertz frequencies. We perform a study as a function of the lattice period and of the frequency overlapping of the modes of resonance. We show that negative effective refractive index requires sufficiently strong mode coupling and that for even more strong mode coupling, the first two modes of Mie resonances are degenerate; the effective refractive index is then undetermined. We also show that it is possible to obtain near-zero, or even null, effective index with a judicious adjustment of the mode coupling. Further, we discuss the mode coupling effect with hybridization in metamaterials.

Metasurfaces and metamaterials have been explored extensively in recent years for their ability to enable a variety of innovative microwave devices. However, because their exotic properties often arise from resonant structures, the large field enhancements under high-power microwave illumination can lead to dielectric breakdown and damage to the device. In order to develop metasurfaces and metamaterials capable of being utilized in high-power microwave applications, this paper investigates techniques for reducing the maximum field enhancement factor (MFEF) in several types of structures from the literature. Starting with a simple Sievenpiper metasurface, this paper evaluates the dependence of MFEF on the structure design parameters. For more complex metasurface geometries, a genetic algorithm is demonstrated that can evolve structures that have minimal MFEF. In addition, negative-index and low-index metamaterials are evaluated for field enhancement. By optimizing for low loss and by operating in the resonance tails, metamaterials with low MFEF can be realized for high-power applications. To illustrate this, a quad-beam focusing metamaterial lens is presented with an MFEF less than 5 over the entire operating band. [ABSTRACT FROM PUBLISHER]

In this paper, a miniaturized microstrip patch antenna using a negative index metamaterial with modified split-ring resonator (SRR) unit cells is proposed for ultrawideband (UWB) applications. The new design of metamaterial based microstrip patch antenna has been optimized to provide an improved bandwidth and multiple frequency operations. All the antenna performance parameters are presented in response-graphs. Also it is mentioned that the physical dimensions of the metamaterial based patch antenna are very small, which is convenient to modern communication. A 130% bandwidth, covering the frequency band of 2.9-13.5 GHz, (for return loss less than or equal -- 10 dB) is achieved, which allow the antenna to operate in the Federal Communication Commission (FCC) band. In addition, the antenna has a good radiation pattern in the ultrawide band spectrum, and it is nearly omnidirectional. [ABSTRACT FROM AUTHOR]

A new, compact planar wideband negative index metamaterial based on a modified split ring resonator (SRR) is studied to enhance performance of ultrawideband antenna. A compact, metamaterial (MTM)-inspired microstrip antenna is presented for microwave imaging system (MIS) application. Two layers of left-handed metamaterial array (2 × 4) of the unit cell are placed on the radiating patch and the ground plane, respectively. Each left-handed metamaterial (LHM) unit cell was constructed by modifying a square split ring resonator (SRR), resulting in negative permeability and permittivity with a stable negative refractive index. The results shows that it has a significant impact on the performance of conventional patch antenna in terms of transmission co-efficient, efficiency and low loss. Compared to antenna without LHM, it is shown that the bandwidth is significantly broadened up to a few megahertz and becomes more convergent leading to the achievement of desired properties for ultra-wideband (UWB) applications leading to microwave imaging. The proposed MTM antenna structure is fabricated on commercially-available, flame-retardant material of size 26 × 22 × 1.6 mm3 with 4.6 dielectric constants, due to its low cost and convenience for making multilayer printed circuit boards (PCBs). The antenna achieves 3.1 GHz to 10.71 GHz of impedance bandwidth (−10 dB), which covers the full UWB band. The use of double-layer negative index MTM unit cells enhances UWB performance, and the improved radiation efficiency, nearly directional radiation pattern, acceptable gain, stable surface current and negative refractive index make this MTM antenna a suitable candidate for UWB applications.

In this article, a negative index metamaterial antenna is presented for ultrawideband (UWB) microwave imaging applications. Four left-handed (LH) metamaterial (MTM unit cells are located along one axis of the antenna as the radiating element. Each left-handed metamaterial unit cell assembles a modified split-ring resonator with a capacitance-loaded strip to obtain a design architecture that at a time shows both negative permittivity and negative permeability, which assures the stable negative refractive index to raise the antenna performance for microwave imaging. The antenna structure of dimension 16 × 21 × 1.6 mm3 is printed on low dielectric FR4 material with a slotted ground plane and a microstrip feed. Measured reflection coefficient illustrates that this antenna attains 114.5% bandwidth covering the frequency band of 3.4-12.5 GHz for a voltage standing wave ratio less than 2 with a maximum gain 5.16 dBi at 10.15 GHz. There is a stable harmony between simulation and measured results and improved nearly omnidirectional radiation characteristics within the operational frequency band. The stable surface current distribution, negative refractive index characteristic, considerable gain, and radiation property have made this proposed negative index metamaterial antenna distinguishable for UWB microwave imaging applications. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1352-1361, 2015 [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, a negative-index metamaterial prism based on a composite unit cell containing a split-ring resonator and a z-dipole is designed and simulated. The design approach combines simulations of a single unit cell to identify the appropriate cell design (yielding the desired negative-index behavior) together with subcell modeling (which simplifies the mesh representation of the resonator geometry and allows for a larger number of resonator cells to be handled). In addition to describing the methodology used to design a n = −1 refractive index prism, results including the effective-medium parameters, the far-field scattered patterns, and the near-zone field distributions corresponding to a normally incident plane-wave excitation of the prism are presented. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:537-540, 2015 [ABSTRACT FROM AUTHOR]

This study reports new shape of meta-material array structures having electric and magnetic resonances designed for terahertz (THz) frequency band. The proposed structures exhibit left handed meta-material propertiesin THz frequency band. The introduced meta-material split ring resonators in this paper are constructed using a single loop of conducting wire strip printed over a very thin low permittivity polyimide dielectric substrate. The effective parameters like permeability and negative index are extracted from the simulated complex scattering parameters using direct retrieval method. Unloaded Q-factor is calculated for proposed terahertz metamaterial resonators. The proposed arrays are tested by loading different dielectric samples in order to confirm the testing capability. Significant shift in the transmission is observed. The reported array structures are novel in terms of their left handed behavior in THz frequencies. High values of Q-factor reported here, are suitable for near field sensing applications. [ABSTRACT FROM AUTHOR]

In recent years, considerable research has been carried out relative to the electromagnetic (EM) propagation and refraction characteristics in metamaterials with emphasis on the origins of negative refractive index. Negative refractive index may be introduced in metamaterials via different methods; one such is the condition whereby the Poynting vector of the EM wave is in opposition to the group velocity in the material. Alternatively, negative refractive index also occurs when the group and phase velocities in the medium are in opposition. The latter phenomenon has been extensively investigated in the literature, including recent work involving chiral metamaterials with material dispersion up to the first order. This paper examines the possible emergence of negative refractive index in dispersive chiral metamaterials with material dispersion up to the second order. The motivation is to determine if using second- as opposed to first-order dispersion may lead to more practical negative index behavior. A spectral approach combined with a slowly time-varying phasor analysis is applied, leading to the analytic derivation of EM phase and group velocities, and the resulting phase and group velocities and the corresponding phase and group indices are evaluated by selecting somewhat arbitrary dispersive parameters. The results indicate the emergence of negative index (via negative phase indices along with positive group indices, as reported in the literature) or negative index material (NIM) behavior over information bandwidths in the low RF range. The second-order results are not significantly better than those for first-order results based on the theoretical analysis; however, greater parametric flexibility exists for the second-order system leading to the higher likelihood of achieving NIM over practical frequency bands. The velocities and indices computed using the Lorentzian and Condon models yield an NIM bandwidth around 200 - 400 Mrad/ sec, about 2 orders of magnitude higher than that for the parametric approach; more importantly, NIM is found not to occur in the first order when using practical models. [ABSTRACT FROM AUTHOR]

A miniaturized antenna employing a negative index metamaterial with modified split-ring resonator (SRR) and capacitance-loaded strip (CLS) unit cells is presented for Ultra wideband (UWB) microwave imaging applications. Four left-handed (LH) metamaterial (MTM) unit cells are located along one axis of the antenna as the radiating element. Each left-handed metamaterial unit cell combines a modified split-ring resonator (SRR) with a capacitance-loaded strip (CLS) to obtain a design architecture that simultaneously exhibits both negative permittivity and negative permeability, which ensures a stable negative refractive index to improve the antenna performance for microwave imaging. The antenna structure, with dimension of 16 x 21 x 1.6 mm³, is printed on a low dielectric FR4 material with a slotted ground plane and a microstrip feed. The measured reflection coefficient demonstrates that this antenna attains 114.5% bandwidth covering the frequency band of 3.4-12.5 GHz for a voltage standing wave ratio of less than 2 with a maximum gain of 5.16 dBi at 10.15 GHz. There is a stable harmony between the simulated and measured results that indicate improved nearly omni-directional radiation characteristics within the operational frequency band. The stable surface current distribution, negative refractive index characteristic, considerable gain and radiation properties make this proposed negative index metamaterial antenna optimal for UWB microwave imaging applications. [ABSTRACT FROM AUTHOR]

One way to obtain materials with a negative index is to achieve media with doubly negative constitutive parameters. We show that the double negativity required for perfect (non-dissipative) media is not necessary for real passive (lossy) metamaterials, for which single negativity of one of the two constitutive parameters may be sufficient. The analysis is presented through original diagrammatic representations involving both the real and imaginary parts of the dynamic constitutive parameters for isotropic media. A valid demonstration for acoustic and electromagnetic metamaterials is supported by considering an actual soft 3D locally-resonant ultrasonic metafluid having a negative acoustic index while being a single-negative medium. The crucial role of the imaginary parts of the constitutive parameters is then discussed through its impact on the figure of merit. Finally, the analysis is extended to an example of an electromagnetic negative-index metamaterial exhibiting both single and double negativity. [ABSTRACT FROM AUTHOR]

Metamaterials intrigue many exciting applications in the broad electromagnetic spectrum ranging from microwave to optics. However, many of the envisaged applications still remain in theory, largely because of the intrinsic loss and dispersion associated with passive metamaterials. Incorporating active devices or media into conventional passive metamaterial structures for loss compensation, as well as dispersion control, is very attractive and may finally enable many desired applications. In addition, because of the added design degree of freedom in active metamaterials, new and rich physical phenomena and insights can be discovered. In this paper, we review the recent progress in the realm of active, gain-assisted metamaterials. Physical limitations on loss and bandwidth of metamaterials are firstly discussed. Recent experimental efforts in transmission-line and volumetric metamaterials with net gain in the microwave and optical regime are then examined. The idea of utilizing non-Foster active devices to reduce the dispersion and achieve broad bandwidth is also presented. Finally, one of the important issues of active metamaterial design, stability, is briefly discussed. [ABSTRACT FROM AUTHOR]

In this paper, the characteristics of thunderstorms in Zibo City were analyzed. The thunderstorms could be divided into cold-front thunderstorm, upper trough (shear line) type thunderstorm and cold-vortex thunderstorm. We also screened out the atmosphere parameters that were highly correlated to the occurrence of thunder/ lightning. They were treated as the predictors. Each possible influencing factor was analyzed on the lightning day correspondingly. Their threshold values were also determined. Among them, the parameter that had the highest neutralizing capacity was treated as negative index. For different type of thunderstorm weather, the negative index was different. The application of negative indexes was also discussed. We hope to provide a valuable basis for the accurate forecasting of thunder/lightning. [ABSTRACT FROM AUTHOR]

Abstract: Nanostructures made of two layers of metallic triangular nanoprisms arranged in hexagonal lattice separated by a dielectric layer are theoretically analyzed as chiral metamaterial slabs. Transmitted and reflected electromagnetic field of normally incident circular polarized plane waves are computed using a tri-dimensional (3D) finite-difference time domain (FDTD) algorithm. Chirality and effective constitutive parameters are calculated using the modified S-parameter retrieval method for chiral metamaterials. Different hybridized plasmon modes are induced by the left and right circularly polarized light leading to a chiral behavior of the asymmetric type metamaterials. Negative refractive index due to chirality is obtained in the near infrared range of the spectrum for either left or right polarization. [Copyright &y& Elsevier]

Thanks to Victor Veselago for his hypothesis of negative index of refraction, meta-materials - engineered composites - can be designed to have properties difficult or impossible to find in nature: they can have both electrical permittivity (ϵ) and magnetic permeability (μ) simultaneously negative. The metamaterials - henceforth negative-index materials (NIMs) - owe their properties to subwavelength structure rather than to their chemical composition. The tailored electromagnetic response of the NIMs has had a dramatic impact on classical optics: they are becoming known to have changed many basic notions related with electromagnetism. The present article is focused on gathering and reviewing fundamental characteristics of plasmon propagation in coaxial cables fabricated of the right-handed medium (RHM) (with ϵ > 0, μ > 0) and the left-handed medium (LHM) (with ϵ < 0, μ < 0) in alternate shells starting from the innermost cable. Such structures as conceived here may pave the way to some interesting effects in relation to, for example, optical science exploiting the cylindrical symmetry of coaxial waveguides that make it possible to perform all major functions of an optical fiber communication system in which the light is born, manipulated, and transmitted without ever leaving the fiber environment, with precise control over the polarization rotation and pulse broadening. This review also covers briefly the nomenclature, classification, potential applications, and the limitations (related, for example, to the inherent losses) of the NIMs and their impact on classical electrodynamics in general, and in designing the cloaking devices in particular. A recent surge in efforts on invisibility and the cloaking devices seems to have spoiled the researchers worldwide: proposals include not only a way to hide an object without having to wrap the cloak around it, but also to replace a given object with another, thus adding to the deception even further! All this is attributed as much to the fundamental as to the practical advances made in the fabrication and characterization of NIMs. The article concludes briefly addressing the anticipated implications of plasmon observation in the multicoaxial cables and suggesting future dimensions worth adding to the problem. The background provided is believed to make less formidable the task of future writers of reviews in this field. [ABSTRACT FROM AUTHOR]

Abstract: Metal–dielectric–metal films perforated with triangular nanoholes arranged in a hexagonal array are theoretically analyzed as metamaterial slabs. Effective constitutive parameters are calculated using three-dimensional (3D) finite-difference time domain (FDTD) simulations and S-parameter retrieval method. Nanoholes side length and dielectric spacer thickness determine the magnitude and frequency of the hybridized plasmon modes resonances leading to negative effective permeability and plasmon modes inversion. Fundamental and second order asymmetric modes resonances lead to a double negative refractive index in the near infrared and a single negative refractive index in the visible range of the spectrum. [Copyright &y& Elsevier]

In this paper we obtain some sharp ${L}^{p} - {L}^{q} $ estimates and the restricted weak-type endpoint estimates for the multiplier operator of negative order associated with conic surfaces in ${ \mathbb{R} }^{3} $ which have finite type degeneracy. [ABSTRACT FROM PUBLISHER]