Frequency-Controlled Focusing Using Achromatic Metasurface

Structural, electronics and optical properties of sodium based fluoroperovskites NaXF3 (X = Ca, Mg, Sr and Zn): First principles calculations

The electronic structure, elastic, optical and thermodynamic properties of cubic perovskite NaBaF3 under high pressure were investigated using the ab initio calculations. The calculated lattice constant (a0) and bulk modulus (B0) at 0 GPa were determined to be 4.278 A and 53.555 GPa, respectively, which are consistent with previous reports. The elastic constants and bulk modulus at high pressure were calculated. According to Pugh’s crystal mechanical stability conditions, the phase transition point of NaBaF3 is found to be 68.8 GPa, which has not been reported by any previous paper. The band structure calculations reveal that cubic perovskite NaBaF3 is a direct band-gap material in the pressure range from 0 GPa to 60 GPa. The dielectric function ɛ(ω), absorption coefficient α(ω), reflectivity R(ω), transmittance T(ω), absorbance A(ω) and complex refractive index N(ω) at 0 GPa, 20 GPa, 40 GPa and 60 GPa were studied. It is found that the band gap increases with the increasing pressure, and the absorption spectra show blue shift. The Debye temperature at 300 K and the values of the relative volume, heat capacity, bulk modulus, thermal expansion coefficient, heat capacities, and relative Debye temperature with pressures and temperatures effect were investigated. Our results will provide theoretical guidance for the experimental investigations and industrial applications of NaBaF3 in future.

Electronic structure, elastic, optical and thermodynamic properties of cubic perovskite NaBaF3 with pressure effects: First-principles calculations

A flexible, dual-broadband, and polarization-insensitive coding metasurface is proposed to manipulate electromagnetic (EM) scattering in microwave frequency band. The 1 bit coding units “0” and “1” are formed by the Pancharatnam–Berry (PB) phase based on the same-sized meta-atoms with different orientations. The layout of the coding metasurface is obtained through genetic algorithm (GA). The simulation results indicate that the proposed coding metasurface in this communication can achieve more than 10 dB radar cross section (RCS) reduction in the range of 9.26–12.87 and 14.84–19.35 GHz in the planar case, which is attributed to the reorientation of the reflected energies into different directions by optimizing the coding sequence. The diffuse scattering performance in the dual-wideband is well maintained, while the coding metasurface is conformal on metallic cylinder with diverse curvature radii. Moreover, the scattering characteristics of conformal metasurfaces become better with the decrease of curvature radius under the case of the certain size of the flexible metasurface. A flexible coding metasurface prototype is prepared and measured. The experiment results coincide with the numerical simulation ones, demonstrating the outstanding capacity of RCS reduction. The proposed design has potential application value in the field of antenna and stealth of more complex objects. 

Combining Pancharatnam–Berry Phase and Conformal Coding Metasurface for Dual-Band RCS Reduction

The elastic, electronic, and optical properties of Cu 3 MTe 4 (M = Nb, Ta) are investigated for the first time using the density-functional formalism. The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. Different elastic moduli are calculated. The Born criteria for mechanicalstability are found to be fulfilled from the estimated values of the elastic moduli, C ij . The band structure and the electronic energy density of states (EDOS) are also determined. The band structure calculations show semiconducting behavior for both the compounds. The theoretically calculated values of the band gaps are found to be strongly dependent on the nature of the functional representing the exchange correlations. Technologically significant optical parameters (e.g., dielectric function, refractive index, absorption coefficient, optical conductivity, reflectivity, and loss function) have been determined. Important conclusions are drawn based on the theoretical findings.

Structural, elastic, electronic and optical properties of Cu3MTe4 (M = Nb, Ta) sulvanites — An ab initio study

First-principles calculation of the electronic structure, optical, elastic and thermodynamic properties of cubic perovskite LiBeF3

Optical meta-surface element is a kind of two-dimensional ultra-thin device based on the regular arrangement of single-layer or multi-layer sub-wavelength nanostructure array. It can realize the sudden operation of optical amplitude, phase, polarization, the wavelength in a subwavelength scale. In this paper, we design a Huygens meta-surface based on low loss all-dielectric, which can approach the phase control of the outgoing beam after the parallel beam incident on the meta-surface. By the single-layer dielectric nanostructure array, so called Huygens surface, the abnormal transmission without reflection and low loss meta-atoms are realized. Five different beam deflectors were design by these meta-atoms. The different performance of five beam deflectors were discussed, and the effect of wavelength for different beam deflector was investigated next. The highest efficiency of beam deflector is around 85%. The largest deflection angle is 13.248˚ for one polymer grating. These silicon-based beam deflection meta-surfaces may be applied as blazed grating in the monochromator r, precision measurement, and laser shaping.

Yiman Wu

Papers

Electronic structure, elastic, optical and thermodynamic properties of cubic perovskite NaBaF3 with pressure effects: First-principles calculations

First-principles calculation of the electronic structure, optical, elastic and thermodynamic properties of cubic perovskite LiBeF3

Design of high-efficiency all-dielectric polymer meta-surfaces beam deflection blazed grating