Quasiperiodic Structures Research Articles

Hollow-core photonic quasicrystal fiber with high birefringence and ultra-low nonlinearity

A hollow-core fiber based on photonic quasicrystal arrays is theoretically proposed for high-quality light wave propagation with high polarization maintaining performance and low nonlinearity. This fiber, called hollow-core photonic quasicrystal fiber (HC-PQF), can simultaneously realize a high birefringence that reaches 1.345 × 10−2 and a small nonlinear coefficient of 1.63 × 10−3 W−1·km−1 at a communication wavelength of 1.55 μm due to the air-filled core and unique quasiperiodic fiber structure. To further demonstrate the controllability of the nonlinear coefficient and the application of sensor and polarization-maintaining fiber, the nonlinearity is investigated by filling different inert gases in the fiber core while the birefringence keeps a high order of 10−2. In the wavelength range λ ∈ [1.53 μm, 1.57 μm], the dispersion is near zero and flattened. The HC-PQF is expected to be used for applications in optical communication, high power pulse transmission, polarization beam splitters, etc.

Propagation of the electromagnetic waves in one-dimensional asymmetric photonic comb-like structure based on Fibonacci chains of grafted resonators

We study the band structure and the transmission coefficient properties of electromagnetic waves in one-dimensional quasi-periodic Fibonacci structure. Our structure is composed of periodic waveguides in which the resonators having different lengths and depend on each other following a Fibonacci sequence grafted onto N equidistant sites. This study shows that comb-like structures of the Fibonacci type can exhibit localized bands with higher amplitude in the transmission spectrum. The variation between the resonator lengths give rise to new created gaps in the passbands, called flat bands. This structure can be used in the electromagnetic telecommunications field, in the design of new filter, multichannel and even for multiplexing and other engineering devices.

Metamaterial Control of Hybrid Multifunctional High-Tc Superconducting Photonic Crystals for 1D Quasi-periodic Structure Potential Applications

Abstract In the present work, electromagnetic wave properties of the Fibonacci one-dimention photonic crystal (1DPC) structure consisting of double negative materials incorporated high Tc superconductor are theoretically investigated. It is found that the quasi-periodic structure created a photonic band gap as a periodic structure. We have calculated the transmittance spectra and noticed a wide band gap which can be controlled in it by the thickness of metamaterial, superconductor layer and incidence angle.Photonic band gap became more noticeable by increasing the thickness of the metamaterial and superconductor layers. The structure was affected by changing the incident angle and the band gap width increase with a noticeable shift to short wavelength region. Additionally, the photonic band gap shifted to longer wavelength value with increasing the operating tempeature. Furthermore, we have studied the pressure effects and we found the change in the location and width of photonic band gap.

Bifurcation analysis of ion-acoustic waves in an adiabatic trapped electron and warm ion plasma

Bifurcation analysis of ion-acoustic waves in complex plasmas in the presence of adiabatic trapped electrons and warm ions is studied. Using bifurcation theory of dynamical structure, the Hamiltonian system inculpated electrostatic potential is derived. Effects of physical parameters, such as T and , are shown on the analytical solitary wave solution. The numerical results show that parameters T and affect significantly on nonlinear electrostatic solitary waves. By adding an external periodic perturbation to unperturbed Hamiltonian system, we investigate quasiperiodic structure of the perturbed Hamiltonian system.

ВЛИЯНИЕ ТАЙФУНА VONGFONG 2014 г. НА ИОНОСФЕРУ И ГЕОМАГНИТНОЕ ПОЛЕ ПО ДАННЫМ СПУТНИКОВ SWARM: 2. ГЕОМАГНИТНЫЕ ВОЗМУЩЕНИЯ

Strong meteorological disturbances in the atmosphere, accompanied by the generation of waves and turbulence, can affect ionospheric plasma and geomagnetic field. To search for these effects, we have analyzed electromagnetic measurement data from low-orbit Swarm satellites during flights over the typhoon Vongfong 2014. We have found that there are “magnetic ripples” in the upper ionosphere that are transverse to the main geomagnetic field fluctuations of small amplitude (0.5–1.5 nT) with a predominant period of about 10 s caused by small-scale longitudinal currents. Presumably, these quasiperiodic fluctuations are produced by the satellite’s passage through the quasiperiodic ionospheric structure with a characteristic scale of ~70 km induced by the interaction of acoustic waves excited by the typhoon with the E-layer of the ionosphere. In one of the flights over the typhoon, a burst of high-frequency noise (~0.3 Hz) was observed, which can be associated with the excitation of the ionospheric Alfven resonator by atmospheric turbulence.

INFLUENCE OF THE VONGFONG 2014 HURRICANE ON THE IONOSPHERE AND GEOMAGNETIC FIELD AS DETECTED BY SWARM SATELLITES: 2. GEOMAGNETIC DISTURBANCES

Strong meteorological disturbances in the atmosphere, accompanied by the generation of waves and turbulence, can affect ionospheric plasma and geomagnetic field. To search for these effects, we have analyzed electromagnetic measurement data from low-orbit Swarm satellites during flights over the typhoon Vongfong 2014. We have found that there are “magnetic ripples” in the upper ionosphere that are transverse to the main geomagnetic field fluctuations of small amplitude (0.5–1.5 nT) with a predominant period of about 10 s caused by small-scale longitudinal currents. Presumably, these quasiperiodic fluctuations are produced by the satellite’s passage through the quasiperiodic ionospheric structure with a characteristic scale of ~70 km induced by the interaction of acoustic waves excited by the typhoon with the E-layer of the ionosphere. In one of the flights over the typhoon, a burst of high-frequency noise (~0.3 Hz) was observed, which can be associated with the excitation of the ionospheric Alfven resonator by atmospheric turbulence.

Numerical modeling of nonlinear dynamic and static compression of the metal mesh

Simulation of elastoplastic compression of a symmetric fragment of a bundle of woven steel grids was carried out. The simulation was carried out under static and dynamic loading modes in ANSYS and ANSYS LS-DYNA computing systems. A porous mesh package is formed by overlaying the layers on top of each other while maintaining the directions of wires. Such a packet has a quasiperiodic structure; therefore, a certain symmetric fragment can be distinguished. The compression was carried out by a pair of absolutely rigid plates moving symmetrically towards each other. In the calculations, a multilinear plasticity model with isotropic hardening was used. The diagram of static deformation of the material was used which was obtained experimentally. The calculations were carried out according to the algorithm of a perfect symmetric contact of bodies without friction and with friction. The dynamic loading of a fragment of the mesh packet was carried out at a constant speed. The characteristics of the pulse and the loading rate correspond to those observed in previous experimental studies. The dynamic strain diagram was assumed to be similar to a static one with an increased yield strength. Calculations showed that in all loading modes there is a high level of internal stresses, and complex inhomogeneous stress-strain state. We investigated two factors that could cause differences in the behavior of the curves of deformation of a porous medium - the finite length of the acting pulse and the differences in the dynamic and static compression diagrams of the initial mesh material. The main influence on the dynamic behavior of a fragment of a porous packet of a steel mesh is exerted by the dynamic properties of the wire material. The strain curves of the porous fragment qualitatively change in accordance with the behavior observed in static and dynamic experiments. The final duration of the loading pulse and the friction between the wires for this type of mesh do not have a significant effect. The numerical dependences of the relative area of the normal and lateral through sections of the symmetric fragment of the grid packet on the compression deformation are obtained.

Dodecagonal bilayer graphene quasicrystal and its approximants

Dodecagonal bilayer graphene quasicrystal has 12-fold rotational order but lacks translational symmetry which prevents the application of band theory. In this paper, we study the electronic and optical properties of graphene quasicrystal with large-scale tight-binding calculations involving more than ten million atoms. We propose a series of periodic approximants which reproduce accurately the properties of quasicrystal within a finite unit cell. By utilizing the band-unfolding method on the smallest approximant with only 2702 atoms, the effective band structure of graphene quasicrystal is derived. The features, such as the emergence of new Dirac points (especially the mirrored ones), the band gap at M point and the Fermi velocity are all in agreement with recent experiments. The properties of quasicrystal states are identified in the Landau level spectrum and optical excitations. Importantly, our results show that the lattice mismatch is the dominant factor determining the accuracy of layered approximants. The proposed approximants can be used directly for other layered materials in honeycomb lattice, and the design principles can be applied for any quasi-periodic incommensurate structures.

Spectral analysis and structural response of periodic and quasi-periodic beams

Periodic structures have found a big interest in engineering applications because they introduce frequency band effects, due to the impedance mismatch generated by periodic discontinuities in the geometry, material, or boundary conditions, which can improve the vibroacoustic performances. However, the presence of defects or irregularity in the structure leads to a partial lost of regular periodicity (called quasi-periodic structure) that can have a noticeable impact on the vibrational and/or acoustic behavior of the elastic structure. The irregularity can be tailored to have impact on dynamical behavior. In the present paper, numerical studies on the vibrational analysis of one-dimensional finite, periodic, and quasi-periodic structures are presented. The contents deal with the finite element models of beams focused on the spectral analysis and the damped forced responses. The quasi-periodicity is defined by invoking the Fibonacci sequence for building the assigned variations (geometry and material) along the span of finite element model. Similarly, the same span is used as a super unit cell with Floquet–Bloch conditions waves for analyzing the infinite periodic systems. Considering both longitudinal and flexural elastic waves, the frequency ranges corresponding to band gaps are investigated. The wave characteristics in quasi-periodic beams, present some elements of novelty and could be considered for designing structural filters and controlling the properties of elastic waves.

Numerical investigations and experimental measurements on the structural dynamic behaviour of quasi-periodic meta-materials

Abstract The periodic structures have various applications in vibroacoustic engineering fields since they introduce frequency band effects due to the periodic discontinuities in the geometrical or material configurations: this can lead to increased performances. This paper is focused on the analysis of quasi-periodic structures: instead of using strictly repeated patterns, a certain degree of irregularity is introduced. Quasi-periodic lattices are defined as assemblies of two different elements in two directions. The assembly follows a Thue-Morse Morphism sequence which results in asymmetry in both directions. Numerical studies and experimental measurements on two-dimensional periodic and quasi-periodic lattices are thus performed. First validations are carried out by comparing the quasi-periodic lattice modelled by using finite element model with a prototype manufactured by laser machine. The wave characteristics in quasi-periodic lattice introduce elements of novelty for designing wider frequency stop bands in low frequency ranges.

Phasonic Spectroscopy of a Quantum Gas in a Quasicrystalline Lattice.

Phasonic degrees of freedom are unique to quasiperiodic structures and play a central role in poorly understood properties of quasicrystals from excitation spectra to wave function statistics to electronic transport. However, phasons are challenging to access dynamically in the solid state due to their complex long-range character and the effects of disorder and strain. We report phasonic spectroscopy of a quantum gas in a one-dimensional quasicrystalline optical lattice. We observe that strong phasonic driving produces a nonperturbative high-harmonic plateau strikingly different from the effects of standard dipolar driving. Tuning the potential from crystalline to quasicrystalline, we identify spectroscopic signatures of quasiperiodicity and interactions and map the emergence of a multifractal energy spectrum, opening a path to direct imaging of the Hofstadter butterfly.

Realization of Multi-Modulation Schemes for Wireless Communication by Time-Domain Digital Coding Metasurface

Metasurfaces are well-designed artificial periodic or quasiperiodic structures to achieve customized electromagnetic responses. Based on the time-domain digital coding metasurface (TDCM) with dynamic reflection or transmission characteristics, one can realize direct information modulation on the metasurface, which has been used in wireless communications. In comparison with the classical architectures of wireless communication systems, the TDCM has advantages for simple architecture, easy manufacture, and low cost. However, the wireless communication systems based on the TDCM are still limited by low conversion efficiency, spectrum pollution, and hard to implement high-order modulation schemes. To solve these limitations, we propose a new route to achieve multi-modulation schemes in wireless communications by regulating the reflection phases of the TDCM in a nonlinear way. By carefully designing the regulation voltages applied to the diodes on TDCM, arbitrary constellation diagrams are successfully synthesized. The novel systems can implement various modulation schemes such as quadrature phase shift keying (QPSK), 8PSK, and 16QAM with good communication quality, high stability, and free scheme switching. The presented method may find important applications in modern wireless communication technologies.

Abnormal kinetics of domain structure in KTA single crystals

Single crystals of potassium titanyl phosphate (KTiOPO4, KTP) family (MTiOXO4, where M is K, Rb, or Cs, and X is P or As) with periodical domain structures have emerged as one of the key platforms for enabling nonlinear photonics applications. Potassium titanyl arsenate (KTiOAsO4, KTA) crystals possess nonlinear optical properties outperforming those of KTP. However, domain kinetics in KTA, being the crucial element for periodical poling, lacks comprehensive studies. We present the results of in situ imaging of domain kinetics in KTA with high temporal resolution. The analysis of a set of instantaneous domain structure images (kinetic map) has allowed reliable revealing of the slow and fast domain walls, similar to KTP. The mobility and the threshold fields for the domain walls have been estimated. The main stages of the domain structure evolution have been revealed. The original hatching stage representing the formation of quasiperiodic structure of the narrow stripe domains has been discovered. The relative input of the hatching stage has increased with external field. The obtained qualitative difference in the domain structure evolution, compared with KTP, has been attributed to a six times larger ratio of fast to slow wall mobility in KTA. This fact results in suppression of the undesirable broadening of the stripe domains thus making KTA crystals very attractive for periodical poling.

Combined zero degree structure beam dynamics and applications

The combined zero degree structure (KONUS) is a quasiperiodic structure. It was developed for the low-energy part of multigap drift tube linacs with H-type cavities. Their rf efficiency depends very much on a low electrical capacity of the drift tube structure, while in E-type structures like the Alvarez-DTL this is a minor effect. Therefore, instead of having quadrupole singlets integrated in voluminous drift tubes, KONUS allows one to develop a separated function drift tube linac (DTL) with a large voltage gain between two lenses. Very low beam injection energies can be realized, as the drift tube lengths can range down to around 10 mm. One KONUS period consists of a triplet lens, a rebuncher with a few gaps at a synchronous phase around $\ensuremath{-}35\ifmmode^\circ\else\textdegree\fi{}$, and the main multigap acceleration designed for a hypothetical zero degree synchronous particle. The longitudinal beam dynamics along this main acceleration section and the layout of the quadrupole triplet channel are explained in detail. Two examples for pulsed high current proton and heavy ion acceleration are included.

Experimental study on enhancement of supersonic twin-jet mixing by vortex generators

Experimental results on the mean flow evolution and the control of single and twin compressible jets at Mach 1.6 are presented. The jets issue from conical CD nozzles closely placed side-by-side resembling the twin nozzle configuration of supersonic aircrafts. The results are relevant to scenarios where turbulent jet mixing, supersonic core length, thermal radiation and acoustic loading are of concern. Experiments show that closely spaced twin jets grow, merge and interact near the inter-nozzle region that influences the characteristic decay and jet spread. Moreover, the deviation in centerline characteristic decay is more significant at off-design conditions. Vortex generators in the form of small metallic rectangular tabs mounted at the nozzle exit plane in different azimuthal orientations are used to control the mixing characteristics and the spread of these jets. Abrupt reduction in the core length and suppression of shock cell structure is achieved in over to under-expanded conditions. Furthermore, the orientation of vortex generators is found to significantly influence the development of jet flow field. The jet bifurcation and formation of daughter streams with distorted quasi-periodic shock cells structure are visualized using the schlieren technique. The underlying mechanisms for the observed effects and the behavior of daughter streams are discussed.

Observations of filaments at the TUMAN-3M tokamak

Some factors limiting an increase in the plasma pressure at the periphery of the tokamak plasmas can arise when the improved confinement is achieved in the H-mode. It happens when the edge localized modes (ELMs) develop in tokamak plasmas, and the factors mentioned above manifested themselves in the form of quasi-periodic filamentary structures, or filaments. The formation of such structures results in the occurrence of the anomalous energy and particle flows onto the first wall and divertor plates of tokamaks. Studies of the filaments were previously performed at tokamaks with divertor configuration using various plasma diagnostic methods, including the Doppler backscattering method. The paper presents the first observations of the filaments at the TUMAN-3M, which is the tokamak with limiter configuration. The filaments were studied using the Doppler backscattering method. Plasma was probed by the double-frequency microwave radiation of the O-wave in the frequency range of 27–37 GHz. The data were obtained in the H-mode regime initiated by the pulsed gas injection, in which the ELM-like events are observed. The poloidal velocity of the filaments and their radial localization were determined, and the radial and poloidal sizes of the filaments were also estimated.

Potential Application of 205-MHz Stratosphere–Troposphere Wind Profiling Radar in Ionospheric Studies: Preliminary Results

A state-of-the-art 205-MHz wind profiling radar designed for measuring both the horizontal and vertical wind components from 315 m to beyond 20 km has been installed at the Cochin University of Science and Technology (CUSAT), India (10.04°N, 76.33°E, dip angle ~7.1°N). Subsequently, the radar was operated with special configuration to probe the ionosphere. After a series of experiments, the radar was successfully configured to receive ionospheric reflections from about 90 to 500 km range covering the E and F layers, with high resolution (45 m for the 90-110 km region). The received echoes are identified as signatures of field-aligned irregularities (FAIs) of the E and F regions of the ionosphere. The E region echoes were observed at an altitude range of 90-110 km. Both continuous and quasi-periodic structures were identified. Further analysis from the spectrum shows that the E region FAIs are Type 2 in nature. The night time spread-F observed so far is of either bottom type or bottom side in nature. This letter portrays the scope of employing 200 MHz range of very high frequency (VHF) band for ionospheric observations, and the technical details and the initial results of the experiment conducted with this stratosphere-troposphere (ST) Radar.

Phononic crystal based tunable and nonreciprocal ultrasonic metamaterials

Phononic crystals with asymmetric scatterers is an ideal platform to control the transmission of acoustic waves. These asymmetric scatterers has been used for nonreciprocal ultrasonic wave propagation in a fluidic medium due to the differential dissipation induced by the scatterers. The non-reciprocity of the wave-propagation depends significantly on the surface properties and the orientation of these individual scatterers. These quasi-periodic phononic structures with asymmetric scatterers can be used to modulate the propagation of the acoustic waves for an active acoustic insulator to a conductive behavior. The dispersion of the ultrasonic wave through the phononic crystal can be used to focus, beam-steer or filter the acoustic wave propagation as well as realize acoustical cavity for multifunctional applications. The localization of sound wave due to these orientation of the asymmetric scatterers has also been observed experimentally.

Efficiency enhancement in Si solar cell using 1D quasi-periodic antireflection coating

In order to enhance the efficiency of thin-film Si solar cell, two well-known Fibonacci and Thue–Morse sequences of 1D quasi-periodic structures have been considered to achieve a broadband (300–1100 nm) planar antireflection coating, in this article. As almost non-absorbing materials in the solar spectrum, TiO2 and SiO2 with optimized thicknesses are considered to eliminate the reflections in the front side of the solar cell. An optimized bilayer antireflection coating with thicknesses of 54.4 nm and 85.6 nm respectively for the TiO2 and SiO2 layers has been obtained. Considering material dispersion and solar power spectrum (AM1.5), maximum efficiency enhancements of 42.78%, 46.15%, and 50% have been achieved for the 3 µm thin-film Si solar cell using the FC(3,1) structure which correspond to the cells without any recombination, with bulk recombination, and with bulk and surface recombinations, respectively. The proposed quasi-periodic multilayer antireflection structures have been investigated and optimized using the TMM and FDTD methods. The electrical characteristic of the design is studied by the drift–diffusion method after extracting the electron–hole pair generation. Also, the stability of the performance of the proposed ARC against induced roughness in practice has been investigated and discussed.

Optical, IR and THz screens based on layered metal-dielectric-semiconductor structures

In this work, we consider multilayer coatings of metal-dielectric-semiconductor nanosized layers located on a transparent substrate and described on the basis of the Drude–Lorentz model that serve as multiband screen filters for different frequency ranges. Structures with several layers and quasi-periodic structures are investigated. A method of the approximate synthesis of band gap structures with two layers per period and three layers per period is proposed. For three layers, the difference in plasma frequencies allows one to extend the bands. It is shown that semiconductor layers made of narrow-band crystal materials like InSb are promising for THz-band structures with the ability to adjust the ranges by doping.