Kind Of Artificial Materials Research Articles

Structures, principles, and properties of metamaterial perfect absorbers.

Metamaterials are a kind of artificial material with special properties, showing huge potential for applications in fields such as infrared measurement, solar cells, optical sensors, and optical stealth. A metamaterial perfect absorber (MPA) is designed based on a metamaterial, featuring strong absorption, small volume, light weight, ultra-bandwidth, tunability and other characteristics. This paper introduces the absorption mechanism of MPAs from microwave to optical wave band, and four directions of absorber design are elaborated. Equivalent impedance matching, plasma resonance and interference effect are the main absorption mechanisms of MPA. Multiband perfect absorption, ultra-wideband and ultra-narrowband perfect absorption, polarization and angle insensitive absorption, and dynamically controllable tunable absorption are the main design aspects. Among them, the proposal of a dynamically tunable absorber realizes the dynamic absorption. Finally, the problems and challenges of metamaterial perfect absorber design are discussed.

Theoretical and Experimental Study of the Vibration Dynamics of a 3D-Printed Sandwich Beam With an Hourglass Lattice Truss Core

3D printing (also known as additive manufacturing) has been developed for more than 30 years. The applications of 3D printing have been increasingly extended to a variety of engineering fields in recent years. The sandwich material with a high strength and overall low density is a kind of artificial material that has been extensively used in various industrial and daily life applications. This paper presents a comprehensive vibration analysis and passive control technique for a cantilevered sandwich beam with an hourglass lattice truss core fabricated with 3D printing technology. The governing equation of the beam is established by using a homogenized model and the Hamilton's principle, from which the natural frequencies are determined. The theoretical model is verified by the results from the existing literature and the finite element analysis. The frequency response of the sandwich beam measured experimentally further validates the proposed model. Subsequently, a non-linear energy sink (NES) is proposed for being employed to passively suppress the vibration of the sandwich beam. A parametric study based on the theoretical model confirms the viability of using NES to effectively control the vibration of the sandwich beam. This work presents a good demonstration of using 3D printing technology for fabricating sandwich beams with a complicated lattice core. More importantly, some guidelines regarding the dynamic analysis of sandwich beams are provided. In addition, the analytical method presented in this work provides a potential means to theoretically explore the advantages of using sandwich beams for energy harvesting in the future.

Marginal presence of plastic in nests of yellow–legged gulls (Larus michahellis) in the southeastern Bay of Biscay

Nest entanglement and consumption of plastics can be a cause of mortality in chicks of various seabird species. As plastic debris may be chosen as a source of nesting material, evaluation of its presence and contribution to nest building in seabird colonies is important. Here, we determined the contribution of anthropogenic debris to nest construction by a yellow–legged gull Larus michahellis population that largely depends on refuse tips to forage. Two colonies within the southeastern Bay of Biscay, Spain, were sampled in 2019. One of the colonies was in Getaria, where no debris was found in nests, and the second was in Ulia, where 40 % of the nests had some kind of artificial material. In all cases, however, this debris comprised less than 5 % of the nests’ area. Among the studied nests, we found one had a piece of fabric, five had pieces of rope, and 20 had pieces of flexible plastic packaging. These results contrast with other seabird species that face problems of conservation due to the increasing use of plastic for nesting. With the low prevalence of artificial debris (chiefly plastic) in nests found in this study, mortality due to debris entanglement or ingestion is unlikely.

A Compact Vivaldi Antenna With Artificial Material Lens and Sidelobe Suppressor for GPR Applications

A novel compact Vivaldi Antenna (CVA) for short-pulse ground penetrating radar (GPR) systems is presented. Artificial materials lens (AML) and sidelobe suppressor (SSR) are loaded to improve GPR Antenna’s radiation capability in the aperture and the flanks of the CVA. The simulation and experimental results indicate that the proposed CVA has a −10 dB impedance bandwidth of 100% (0.7-2.1 GHz) and a −3 dB gain bandwidth of 70.9% (1.0-2.1 GHz). Within the operating bandwidth of the CVA, AML primarily enhances the CVA’s high-frequency gain (1.4-2.1GHz), while the SSR primarily enhances the CVA’s low-frequency gain (0.7-1.4 GHz). Moreover, the CVA loaded with two kinds of artificial materials (AMs) has an average gain of 1 dB and 2 dB in the low-frequency and high-frequency parts, respectively. In addition, the transmission response with small ringing in time domain makes the proposed CVA suitable for short-pulse GPR systems. AML and SSR effectively enhance the gain of the CVA with a compact and space-saving loading method, which provides a new idea to enhance the gain of the CVA by artificial material.

Dynamic multifunctional control of terahertz beam based on graphene coding metamaterial

Terahertz (THz) waves have aroused tremendous research interest due to its some unique features and widespread applications in broadband communication, military radar, non-destructive detection, biomedical, security check, etc. With the development of THz applications, dynamic control beam of THz wave with wide bandwidth and multifunction has become a key issue in the field THz technology. The metamaterial with a kind of artificial material provides an approach to controlling the terahertz beam. However, the characteristics of metamaterials based on the equivalent medium parameters are limited by the structural configuration, which usually causes disadvantageous problems including the real-time dynamic control, narrow bandwidth, modulating efficiency, complicated design, etc. The coding metamaterial based digital elements provide an approach to wideband and flexible control terahertz wave by different sequences. However, the THz waves are still hard to tune in dynamic ways due to the limitation of material properties and processing capability. Graphene with a new two-dimensional material has excellent photoelectric properties such as tunable band gap, flexibly dynamic performance, and low material loss. Therefore, the graphene with coding metamaterial can offer a new way of dynamically controlling beam. In this paper, we design a 1 bit coding metamaterial based on graphene ribbon, which can be expected to realize multi-modulation to the number of beams, frequency and amplitude of THz wavers. The mechanism of controlling electromagnetic wave by coding metamaterial can be explained by the reflective array antenna. And the characteristics of the proposed metamaterial based on the graphene ribbon and the far-field scattering of coding metamaterial are simulated using the CST Microwave Studio. A composite structure which consists of gold metal, polyimide, silicon, silicon dioxide, graphene ribbon is designed and characterized in the THz range. The simulation results show that by gating different graphene ribbons, the coding state (digital element) on each column can be independently controlled as well, thus the ‘0’ and ‘1’ digital elements with a phase difference of 180° in a certain frequency range can be realized, and then the coding sequence on metamaterials is dynamically modulated. Full-wave simulation results also show that different-sequence coding metamaterials can achieve the control of the number of scattering THz beams, from one, double, multi scattering in a wide frequency range (from 1.7 to 2.2 THz). For coding sequence ‘010101...’ realized by gating different voltages on coding elements ‘0’ and ‘1’, the frequency at which double scattering beams are produced, presents shift. For the coding metamaterial of periodic sequence of 000000 or 111111 with different voltage for different graphene ribbon, which can be expected to realize amplitude modulation from -12 dB to -23 dB of THz beam steering at f1=1 THz. Therefore, this graphene coding metamaterial can control the THz beam flexibly and may offer widespread applications in stealth, imaging, and broadband communication of THz frequencies.

Strain Engineering for Phosphorene: The Potential Application as a Photocatalyst

Phosphorene has been attracted intense interest due to its unexpected high carrier mobility and distinguished anisotropic optoelectronic and electronic properties. In this work, we unraveled strain engineered phosphorene as a photocatalyst in the application of water splitting hydrogen production based on density functional theory calculations. Lattice dynamic calculations demonstrated the stability for such kind of artificial materials under different strains. The phosphorene lattice is unstable under compression strains and could be crashed. Whereas, phosphorene lattice shows very good stability under tensile strains. Further guarantee of the stability of phosphorene in liquid water is studied by ab initio molecular dynamics simulations. Tunable band gap from 1.54 eV at ambient condition to 1.82 eV under tensile strains for phosphorene is evaluated using parameter-free hybrid functional calculations. Appropriate band gaps and band edge alignments at certain pH demonstrate the potential application of phosphorene as a sufficiently efficient photocatalyst for visible light water splitting. We found that the strained phosphorene exhibits significantly improved photocatalytic properties under visible-light irradiation by calculating optical absorption spectra. Negative splitting energy of absorbed H2O indicates the water splitting on phosphorene is energy favorable both without and with strains.

Electron interactions and Dirac fermions in graphene-Ge2Sb2Te5 superlattices

Graphene based superlattices have been attracted worldwide interest due to the combined properties of the graphene Dirac cone feature and all kinds of advanced functional materials. In this work, we proposed a novel series of graphene-Ge2Sb2Te5 superlattices based on the density functional theory calculations. We demonstrated the stability in terms of energy and lattice dynamics for such kind of artificial materials. The analysis of the electronic structures unravels the gap opening nature at Dirac cone of the insert graphene layer. The Dirac fermions in the graphene layers are strongly affected by the electron spin orbital coupling in the Ge2Sb2Te5 layers. The present results show the possible application in phase-change data storage of such kind of superlattice materials, where the Ge2Sb2Te5 layers exhibit as the phase-change data storage media and the graphene layer works as the electrode, probe, and heat conductor.

Topological Insulating inGeTe/Sb2Te3Phase-Change Superlattice

$\mathrm{GeTe}/{\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ superlattice phase-change memory devices demonstrated greatly improved performance over that of ${\mathrm{Ge}}_{2}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{5}$, a prototype record media for phase-change random access memory. In this work, we show that this type of $\mathrm{GeTe}/{\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ superlattice exhibits topological insulating behavior on the basis of ab initio calculations. The analysis of the band structures and parities as well as ${Z}_{2}$ topological invariants unravels the topological insulating nature in these artificial materials. Furthermore, the topological insulating character remains in the $\mathrm{GeTe}/{\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ superlattice under small compressive strains, whereas it is not observed as more ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ building blocks introduced in the superlattice. The present results show that multifunctional data storages may be achieved in the $\mathrm{GeTe}/{\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ superlattice. Such kinds of artificial materials can be used in phase-change random access memory, spintronics, and quantum computing.

RELAXATION PROCESSES OF CARRIERS IN AMORPHOUS SEMICONDUCTOR SUPERLATTICES WITH MODULATEDLY DISTRIBUTED RECOMBINATION CENTERS

We propose a continuous-time-random-walk model for a medium with moduiatedly distributed recombination centers to describe dynamical recombination processes of carriers in amorphous semiconductor superlattices. The survival probabilities of carriers are obtained in cases of different types of time distribution functions. Analysis of the results yields informations on the influences of the periodic potential wells and of the modulated doping on the macroscopic transport properties in this kind of artificial materials.