Tunable dual-band nearly perfect absorption based on a compound metallic grating

Traditional metallic gratings and novel metamaterials are two basic kinds of candidates for perfect absorption. Comparatively speaking, metallic grating is the preferred choice for the same absorption effect because it is structurally simpler and more convenient to fabricate. However, to date, most of the perfect absorption effects achieved based on metamaterials are also available using an metallic grating except the tunable dual(multi)-band perfect absorption. To fill this gap, in this paper, by adding subgrooves on the rear surface as well as inside the grating slits to a free-standing metallic grating, tunable dual-band perfect absorption is also obtained for the first time. The grooves inside the slits is to tune the frequency of the Cavity Mode(CM) resonance which enhances the transmission and suppresses the reflectance simultaneously. The grooves on the rear surface give rise to the phase resonance which not only suppresses the transmission but also reinforces the reflectance depression effect. Thus, when the phase resonance and the frequency tunable CM resonance occur together, transmission and reflection can be suppressed simultaneously, dual-band nearly perfect absorption with tunable frequencies is obtained. To our knowledge, this perfect absorption phenomenon is achieved for the first time in a designed metallic grating structure.     

Effects of symmetrical and asymmetrical bumps on plasmonic behavior in a metallic grating

The influence was investigated of symmetrical and asymmetrical bumps on plasmonic behavior in a metallic grating. Compared with the resonant peaks of a smooth-slit grating, the peaks of odd (even) modes exhibit a blue-shift (red-shift) and the transmission properties are tunable by the size of bumps when the bumps are laid symmetrically. However, the peaks of all modes only exhibit a red-shift when the grating is engraved with a bump and a cut in the same slit (namely bend slit), and the bend slit can achieve the properties of a straight slit. Additionally, it is found that the dips in transmission spectrum can be adjusted by altering the size of the bumps if the bumps are set asymmetrically. Fabry–Pérot-like resonance, field interference and phase resonance mechanisms have been suggested for the physical origins of these observations.     

Origin of the positional offset of FP-like enhanced transmission peaks in a one-dimensional gold grating

General transmission characteristics of a one-dimensional optically thick gold grating were investigated as functions of the grating structural parameters (period, slit width and grating thickness) in the spectral range from 0.4 μm to 9.9 μm. The positions (resonant wavelengths) of the Fabry–Perot (FP)-like enhanced transmission (ET) peaks depend not only on the grating’s period and thickness, but also on the slit width. These numerically calculated FP-like resonant positions are different from the simple FP predictions. The physical origin of these positional offsets is ascribed to the additional phases produced by the special ‘reflecting planes’, which are caused by oscillating dipoles located at the entrances and exits of the slits. For a particular order of FP-like resonance, the additional phase is found to be independent of the refractive index of the surrounding, but dependent on the grating’s structural parameters.     

Broadband extraordinary optical transmission of sub-wavelength metallic grating with parabolic wall

We present a novel periodic sub-wavelength metallic grating with parabolic walls fabricated on the silica substrate. With finite difference time domain (FDTD) simulation, we find that the grating not only can realize broadband transmission in the visible range with TM-polarized incidence, but also can achieve higher transmission efficiency with TE-polarized light incidence. The transmission properties of the proposed grating strongly depend on the geometric parameters including the period, the thickness, the entrance width, and the exit width. The transmission spectra can be manipulated by tuning the parameters of the parabolic-wall grating. Transmission line theorem and the interaction between the surface plasmon waves on the slit walls are introduced to explain broadband extraordinary optical transmission of the grating proposed in this paper.     

Optical transmission through double-layer compound metallic gratings with subwavelength slits

Optical transmission through a double-layer compound metallic grating (DCMG) composed of two identical compound metallic gratings (CMGs) with two subwavelength slits filled with different dielectrics inside each period is investigated by using the finite-difference time-domain method. The results show that the transmission properties of the DCMG are dependent on both the separation G between the two metallic layers and the phase configurations of the electromagnetic waves at the exits of adjacent slits of each layer. When a suitable separation (G?～?300?nm) is chosen, for the DCMG a notable transmission peak emerges at a certain wavelength, at which phase resonance appears for the corresponding CMG, while the transmission spectra of the corresponding double-layer simple metallic gratings (DSMGs) with the separation (G?～?300?nm) exhibit unexpected transmission suppression in a broad spectral region. When G?>?340?nm, the intensity of the transmission around the wavelength for the DCMG gradually decreases down to almost zero as G increases, while the high transmission is nearly maintained for the corresponding DSMGs.     

Compact cross-dispersion device based on a prism and a plane transmission grating

This paper presents a cross-dispersion prism-grating device using a plane transmission grating attached directly to a prism, which is different from traditional cross-dispersion grating-prism systems that are based on the reflection grating. Unlike conventional direct-vision grism or constant-dispersion grism in which both the prism and grating have the same dispersion direction, for this device the dispersion directions of the prism and grating are different. The analytical expressions for the cross-dispersion of this device are derived in detail and the formulas of the footprint of the dispersed spectra are given. The numerical results and ray-tracing simulations by ZEMAX are shown. The device provides a compact, small-sized and broadband cross-dispersion device used for the medium resolution spectrometer.     

Analysis of the transmission characteristics of an internal reflection microstructure grating

The transmission characteristics of an internal reflection grating primarily integrated into light-emitting diodes are numerically calculated and optimized by using rigorous coupled-wave analysis (RCWA). The obvious polarization effect of the near field distribution is demonstrated. To easily analyze the transmittance performance of the internal reflection grating, simple methods involving scalar diffraction theory and effective medium theory are used. The validity of both methods is quantitatively evaluated by comparing the transmittance results obtained using the simple methods and RCWA. The limitation of both simple methods mainly depends on the grating structure parameters, such as the normalized period and normalized groove depth. Generally, when the dimensions of the normalized period is more than twofold wavelengths of incident light, the scalar treatment can be used to calculate precisely the transmittance of the optical element within 5% error. Also, the validity of the scalar theory is slightly influenced by the change in incident angle. The effective medium theory is accurate for evaluating the transmittance within 1% error when higher-order diffraction waves other than zeroth-order waves do not propagate.     

Plasmonic-induced transparency in a metallic stub with two cuts and transmission line model

We investigate a metal–insulator–metal (MIM) structure, which is composed of a bus MIM waveguide and a stub modified by two cuts. A transmission line (TL) model is proposed to depict the propagation characteristics of surface plasmon polaritons (SPPs). The finite element method is conducted to calculate the transmission spectrum of SPPs. Plasmonic-induced transparency spectral response can be achieved when different cuts are introduced. Under different parameters, theoretical results based on the TL model match with the simulation results very well. It is believed that our findings provide a smart way to design MIM-based plasmonic sensors and slow light devices.     

Characteristics of a long-period fiber grating with reduced cladding for refractive index sensing

The sensitivity to surrounding refractive index (SRI) of a long-period fiber grating (LPFG) can be effectively improved by decreasing the cladding radius. When the cladding is reduced, a three-layer model is necessary to evaluate the effective refractive index (ERI) of the core mode. A variation of SRI can induce a greater resonant wavelength shift when the core mode is coupled to a higher-order cladding mode. However, as the cladding is reduced further, the highest-order cladding mode would be cut off, i.e. the number of cladding modes that a given fiber structure can support would be less; thus, the higher-order cladding modes that can be used for higher sensitivity are limited. Hence, the implementation of high sensitivity for SRI sensing with cladding-reduced LPFGs is dependent on the proper combination of cladding radius and cladding mode order. Based on the vector coupled-mode theory, the transmission spectrum and sensitivity are numerically analyzed with respect to the cladding radius, which shows that the SRI sensitivity of the HE₁₂ mode with cladding radius a ₂?=?20?µm is 32 times as high as that with a ₂?=?62.5?µm and the SRI resolution is available to the order of 10^?7.     

Ferromagnetic resonance in metallic glasses: study of fracture,stress and thermal stability

Effects of fracture, stress and isothermal annealing of Fe-Ni based metallic glasses have been investigated using the ferromagnetic resonance technique.fmr linewidth is quite sensitive to changes in the magnetic and structural order in metallic glasses, andfmr lineshape seems to provide useful qualitative information on the mechanical state of these systems. Our observations are compared with recent work of Baianu and co-workers.     

Formation of novel Si-fullerene compound materials using a high-density silicon-ion plasma

A Si-Ar plasma is produced using a RF discharge by an internal coil, which is accompanied by DC sputtering, for the purpose of forming novel Si-fullerene compound materials. According to the analysis of the fullerene-C₆₀ after Si-Ar plasma ion irradiation, mass peaks corresponding to Si-heterofullerenes (SiC₅₉, Si₂C₅₈ and Si₃C₅₇) are observed.It was also found that the method of introducing sublimated C₆₀ into the Si-Ar plasma using a C₆₀-oven resulted in an increase in the formation efficiency of SiC₅₉.     

Numerical study of shear banding evolution in bulk metallic glass composites

In this article, a systematic simulation was performed to demonstrate the detailed shear banding evolution in bulk metallic glass (BMG) composites subjected to the tension, and the relation between microstructures and tensile ductility was therefore elucidated. Free volume was adopted as an internal state variable to characterize the shear banding nucleation, growth and coalescence in BMG matrix with the help of free volume theory, which was incorporated into ABAQUS finite element method (FEM) code as a user material subroutine. The present numerical method was firstly verified by comparing with the corresponding experimental results, and then parameter analyses were conducted to discuss the impacts of particle volume fraction, particle shape, particle orientation and particle yielding strength on the enhancement efficiency of the tensile ductility of BMG composites.     

Inferring environmental transmission using phylodynamics: a case-study using simulated evolution of an enteric pathogen

Indirect (environmental) and direct (host–host) transmission pathways cannot easily be distinguished when they co-occur in epidemics, particularly when they occur on similar time scales. Phylodynamic reconstruction is a potential approach to this problem that combines epidemiological information (temporal, spatial information) with pathogen whole-genome sequencing data to infer transmission trees of epidemics. However, factors such as differences in mutation and transmission rates between host and non-host environments may obscure phylogenetic inference from these methods. In this study, we used a network-based transmission model that explicitly models pathogen evolution to simulate epidemics with both direct and indirect transmission. Epidemics were simulated according to factorial combinations of direct/indirect transmission proportions, host mutation rates and conditions of environmental pathogen growth. Transmission trees were then reconstructed using the phylodynamic approach SCOTTI (structured coalescent transmission tree inference) and evaluated. We found that although insufficient diversity sets a lower bound on when accurate phylodynamic inferences can be made, transmission routes and assumed pathogen lifestyle affected pathogen population structure and subsequently influenced both reconstruction success and the likelihood of direct versus indirect pathways being reconstructed. We conclude that prior knowledge of the likely ecology and population structure of pathogens in host and non-host environments is critical to fully using phylodynamic techniques.     

孪晶片层结构在室温轧制过程中的微观结构演变

研究了一种具有纳米孪晶片层结构的电解沉积铜的微观结构特征及其在室温轧制形变后的微观结构演变.结果表明,电解沉积制备的纯铜样品由柱状晶组成,柱状品内含有平行于样品沉积表面的纳米量级厚度的高密度孪晶片层结构,在孪晶界上缺陷很少,为共格孪晶界.形变后,孪晶片层的微观结构特征与片层厚度密切相关.粗大的孪品片层的形变行为以全位错运动为主,而细小的孪晶片层的形变行为以肖克莱(Shockley)位错在孪晶界上的滑移为主,从而导致几个纳米厚的超细孪晶片层消失.     

Interaction dynamics of Bragg grating solitons in a semilinear dual-core system with dispersive reflectivity

The interactions of quiescent Bragg grating (BG) solitons in a semilinear dual-core system, where one core is nonlinear and is equipped with a BG with dispersive reflectivity and the other core is linear are investigated. It has been previously shown that the model supports stable quiescent solitons which may or may not have sidelobes in their profiles. The interaction of in-phase solitons can lead to various outcomes such as generation of two moving solitons with equal or unequal velocities, merger of solitons into a quiescent one, generation of three solitons (one quiescent and two moving ones) and destruction of solitons. The presence of sidelobes can radically change the interaction dynamics, e.g. in-phase solitons can repel or form a temporary bound state which subsequently splits into two separating solitons. We have identified the outcome regions for in-phase interactions through systematic numerical simulations in the plane of dispersive reflectivity vs. frequency. We have also analysed the effect of initial separation on the outcomes of interactions. It is found that when sidelobes are present in solitons’ profiles, the outcomes of the interactions are strongly dependent on the initial separation.     

Microstructural evolution and densification of Fe80P11C9 metallic glass under high pressure

Abstract

The structural evolution of Fe₈₀P₁₁C₉ metallic glass was investigated by X-ray diffraction with synchrotron radiation under high pressure up to 32 GPa at room temperature. The diffraction data, structure factor and pair distribution function show no indication of phase transition. The positions of the first sharp diffraction peak q₁ are increasing and scale with pressure. The nearest neighbour distance r₁ decreases with increasing pressure. After decompression, q₁ and r₁ do not revert to normal levels at ambient pressure. The results indicate that microstructural relaxation occurs during pressure progress. The annihilation of free volumes and reduction of voids in the amorphous matrix increase the packing density of amorphous alloys. The present study demonstrated that high pressure induces a ‘highly ordered’ glass state and densification of metallic glass.     

一种新型复合局域共振型声子晶体带隙特性

设计了一种新型复合局域共振型声子晶体,通过建立弹簧-质量块等效模型用于计算带隙的上下边界频率,同时结合有限元方法分析了该结构共振带隙的产生机理,根据带隙起止点频率处的位移模态研究了声子晶体的带隙特性。研究结果表明,该声子晶体结构在频率2 200 Hz附近产生三条完整带隙,其中一条是带宽达406.17 Hz的宽带隙。对于有限周期结构的声子晶体进行了传输特性仿真和隔声实验测试,在相同的频段内弹性波传播受到了阻碍。最后,对影响声子晶体带隙打开的几种因素进行分析,讨论了带隙上下边界调控机制。研究结果为声子晶体获得较宽的低频带隙提供了一种新的设计思路和方法。     

Mechanical properties and thermal stability of a Cu-based bulk metallic glass microalloyed with silicon

(Cu₄₂Zr₄₂Al₈Ag₈)_{100? x} Si _x (x?=?0?～?1) amorphous alloy rods of 2–6?mm diameter were prepared by Cu-mold drop casting. The thermal properties, microstructure evolution, and mechanical properties were studied by differential scanning calorimetry (DSC), X-ray diffractometry (XRD), transmission electron microscopy (TEM), hardness test, and compression test. The XRD result revealed that all as-quenched (Cu₄₂Zr₄₂Al₈Ag₈)_100?x Si _x alloy rods exhibited a broad diffraction pattern in the amorphous phase. The (Cu₄₂Zr₄₂Al₈Ag₈)_99.5Si_0.5 alloy was found to possess the highest glass forming ability (GFA) as well as the best thermal stability among all tested samples. In addition, both its hardness and yield strength were increased by the microalloyed Si content. The fracture strength and the plastic strain of (Cu₄₂Zr₄₂Al₈Ag₈)_99.5Si_0.5 amorphous alloy can reach 2000?MPa and 3.5 %.     

Micro flash butt welding of super duplex stainless steel with Zr-based metallic glass insert

Micro flash butt welding of super duplex stainless steel with Zr-based metallic glass insert was carried out. Zr₅₅Cu₃₀Ni₅Al₁₀ of Zr-based metallic glass with thickness of 50 μm and Zr metal with thickness of 500 μm were used as the insert materials. After welding, Zr-based metallic glass insert became much thinner than that of Zr metal insert. The supercooled liquid of Zr-based metallic glass insert at the interface was protruded outside of the specimen during welding. The formation of the protrusion discharged the oxide films on the butting surfaces and contact surface, resulting in metallurgical bonding through the fresh surfaces. The Fe-Zr metallic compounds were observed at the bonding interface for the Zr metal insert, but the metallic compound for Zr-based metallic glass insert was hardly observed. The micro flash butt welding of stainless steel with Zr-based metallic glass insert was successfully welded.     

Comparisons of buckling-to-weight behavior of cylindrical shells with composite and metallic stiffeners

The present research deals with the study of buckling pressure-to-weight ratio of cylindrical shells with laminated ring stiffeners. The research introduces a strain energy formulation for laminated rings, in which each ring stiffener may be treated individually and the geometrical dimensions and material properties of the stiffeners may be different from one another. In a parametric study, the impacts of various geometrical parameters of rings on the buckling pressure-to-weight ratio of shells for composite and metallic stiffeners are compared. The results show that the buckling-to-weight behavior of the shells with Steel stiffeners generally differs from the shells with stiffeners made of Aluminum, E-glass/epoxy, Graphite/epoxy, or Kevlar49/epoxy.