OPTIMIZATION OF BROADBAND MICROWAVE ABSORBER USING GENETIC ALGORITHM

2020 ◽  
Vol 65 (6) ◽  
pp. 90-97
Author(s):  
Hai Pham Van ◽  
Tu Vu Minh ◽  
Van Mai Ngoc ◽  
Dien Pham Van ◽  
Cuong Tran Manh
Keyword(s):  
Genetic Algorithm ◽  
Absorption Spectrum ◽  
Digital Technology ◽  
Optical Loss ◽  
Wide Frequency Range ◽  
Simple Random Sample ◽  
Work Demands ◽  
Unit Cells ◽  
Enormous Number ◽  
Conventional Unit

In recent years, scientists have been focusing on coding metamaterials absorbers to take full advantage of digital technology. This technology is mostly based on the fact that the absorption spectrum of a full-sized metamaterial varies with the different number and position of the defect elements in conventional unit cells (UCs) in it. However, both of their traditional methods namely simple random sample and combination of fundamental meta-block struggle with the enormous number of possible configurations especially when the number of UCs increases. In this article, we represent 5 configurations with different numbers of UCs, 2x2, 3x3, 4x4, 5x5, and 6x6 UCs, all of which maintain average absorption higher than 90% over a 10 GHz wide frequency range of interest between 17 GHz and 27 GHz. These results are obtained by using a genetic algorithm to generate configurations with higher optical loss through the process. Comparing to the conventional methods' result, our approach has achieved a significant improvement in the absorption spectrum. Furthermore, our methods could be applied to more structures with different sizes and numbers of UCs, thus provided a reliable tool to design practical metamaterials that serve the real work demands.

The intrinsic group–subgroup structures of the Diamond and Gyroid minimal surfaces in their conventional unit cells

2022 ◽  
Vol 78 (1) ◽  
Author(s):  
Martin Cramer Pedersen ◽  
Vanessa Robins ◽  
Stephen T. Hyde
Keyword(s):  
Minimal Surfaces ◽  
Subgroup Lattice ◽  
Unit Cells ◽  
Lattice Graphs ◽  
Conventional Unit

The intrinsic, hyperbolic crystallography of the Diamond and Gyroid minimal surfaces in their conventional unit cells is introduced and analysed. Tables are constructed of symmetry subgroups commensurate with the translational symmetries of the surfaces as well as group–subgroup lattice graphs.

Study on the effects of Ga-2N high co-doping and preferred orientation on the stability, bandgap and absorption spectrum of ZnO

2017 ◽  
Vol 31 (14) ◽  
pp. 1750107
Author(s):  
Qing-Yu Hou ◽  
Wen-Cai Li ◽  
Ling-Feng Qu ◽  
Chun-Wang Zhao
Keyword(s):  
Absorption Spectrum ◽  
Absorption Spectra ◽  
Theoretical Calculations ◽  
Co Doping ◽  
Unit Cells ◽  
Neighboring Site ◽  
Doped Zno ◽  
The Stability ◽  
Formation Energies ◽  
Co Doped

Currently, the stability and visible light properties of Ga-2N co-doped ZnO systems have been studied extensively by experimental analysis and theoretical calculations. However, previous theoretical calculations arbitrarily assigned Ga- and 2N-doped sites in ZnO. In addition, the most stable and possible doping orientations of doped systems have not been fully and systematically considered. Therefore, in this paper, the electron structure and absorption spectra of the unit cells of doped and pure systems were calculated by first-principles plane-wave ultrasoft pseudopotential with the GGA[Formula: see text]U method. Calculations were performed for pure ZnO, Ga-2N supercells heavily co-doped with Zn[Formula: see text]Ga[Formula: see text]O[Formula: see text]N[Formula: see text] ([Formula: see text], [Formula: see text]) under different co-doping orientations and conditions, and the Zn[Formula: see text]GaN2O[Formula: see text] interstitial model. The results indicated that under different orientations and constant Ga-2N co-doping concentrations, the systems co-doped with Ga-N atoms vertically oriented to the [Formula: see text]-axis and with another N atom located in the nearest-neighboring site exhibited higher stability over the others, thus lowering formation energy and facilitating doping. Moreover, Ga-interstitial- and 2N-co-doped ZnO systems easily formed chemical compounds. Increasing co-doping concentration while the co-doping method remained constant decreased doped system volume and lowered formation energies. Meantime, co-doped systems were more stable and doping was facilitated. The bandgap was also narrower and red shifting of the absorption spectrum was more significant. These results agreed with previously reported experimental results. In addition, the absorption spectra of Ga-interstitial- and 2N-co-doped ZnO both blue shifted in the UV region compared with that of the pure ZnO system.

scholarly journals MODELING OF PACKING DENSITY OF THE SIMPLEST HEXAGONAL LATTICE. I

2021 ◽  
pp. 39-52
Author(s):  
D.V. Fomin ◽  
Keyword(s):  
Packing Density ◽  
Hexagonal Lattice ◽  
Hexagonal Crystal ◽  
Crystal Lattices ◽  
Unit Cells ◽  
Overlapping Spheres ◽  
Conventional Unit

The article deals with the primitive and conventional unit cells of the cubic and densely packed hexagonal crystal lattices. The author analyzes the methods used for determining the spatial packing density and the distance between particles in a crystal. The spherical and cubic models of packing of equal-sized non-overlapping spheres are also considered. A comparative assess-ment of their effectiveness based on practical calculations is presented.

The Mirror: Mother of All Symmetries in Crystals

2020 ◽  
Vol 12 (3) ◽  
pp. 289-313
Author(s):  
Mohammad Abdul Wahab
Keyword(s):  
Mirror Symmetry ◽  
Point Group ◽  
Prima Facie ◽  
Fundamental Symmetry ◽  
Combination Scheme ◽  
Unit Cells ◽  
Diffraction Patterns ◽  
Group Symmetries ◽  
The Given ◽  
Conventional Unit

Mirror symmetry is found to be the only fundamental symmetry in crystalline solids because all other symmetries, such as rotation, inversion, rotoreflection, rotoinversion and translational periodicity can be easily derived from suitable combinations of mirrors. Similarly, the point group symmetries can also be derived from the same. The mirror combination scheme is found to work in accordance with the principle of Wigner-Seitz cells and Brillouin Zones (and not with the conventional unit cells as proposed by Bravais), where the zone boundaries of a Brillouin zone represent different sets of Bragg planes obtained from diffraction pattern of the given crystal, while the diffraction of given crystal takes place in terms of decreasing interplanar spacing in reciprocal space. Because the Wigner Seitz cells, the Brillouin zones and the diffraction patterns possess defined origin and exhibit spherical symmetry, they cannot have translational symmetry of any kind (microscopic or macroscopic). Results obtained on the basis of this concept help us to remove the existing ambiguities in crystallography and make the crystal structure determination simple. Further, prima facie the diffraction patterns are found to take care of the proposed 'systematic absences' arising due to the so called lattice centering, glide planes and screw axes without actually taking them into consideration. This newly and first discovered concept is expected to explain all other complicated or less understood issues related to crystallography.

scholarly journals Modulation of out-of-plane reflected waves by using acoustic metasurfaces with tapered corrugated holes

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Xiao-Shuang Li ◽  
Yan-Feng Wang ◽  
A-Li Chen ◽  
Yue-Sheng Wang
Keyword(s):  
Dimensional Space ◽  
Three Dimensional ◽  
Wide Frequency Range ◽  
Square Lattice ◽  
Reflected Waves ◽  
Incident Plane ◽  
Acoustic Focusing ◽  
Out Of Plane ◽  
Unit Cells ◽  
Circular Holes

Abstract In this paper, modulation of reflected wavefront out of the incident plane by a tunable acoustic metasurface is investigated based on the fully generalized Snell’s law in the three-dimensional space. The metasurface is constructed by a square lattice of circular holes with gradient annular bumps. The phase shift is tuned by changing the volume of water filled in the holes. The acoustic wave steering out of the incident plane and the out-of-plane acoustic focusing with the oblique incidence at the subwavelength scale are demonstrated numerically by selecting suitable distributions of water depth. The numerical results show that the wavefront of the reflected wave can be manipulated over a wide frequency range; and the gradient design of the unit cells can suppress the parasitic reflection. The present work is relevant to the practical design of novel acoustic devices.

An Automated Approach for Scheduling Bug Fix Tasks

2016 ◽  
Vol 26 (02) ◽  
pp. 239-271 ◽  
Author(s):  
Fernando de Castro Netto ◽  
Márcio de Oliveira Barros ◽  
Adriana C. F. Alvim
Keyword(s):  
Genetic Algorithm ◽  
Error Correction ◽  
End Users ◽  
Project Managers ◽  
Project Manager ◽  
Search Procedure ◽  
Software Projects ◽  
Time Required ◽  
Enormous Number ◽  
Bug Repositories

Software projects usually maintain bug repositories where both developers and end users can report and track the resolution of software defects. These defects should be fixed and new versions of the software incorporating the patches that solve them must be released. The project manager must schedule a set of error correction tasks with different priorities in order to minimize the time required to accomplish these tasks and guarantee that the more important issues have been fixed. This problem is recurrent for most software organizations and, given the enormous number of potential schedules, a tool that searches for good schedules may be helpful to project managers. In this work we propose a genetic algorithm using information captured from bug repositories to find near optimal schedules. We evaluated our approach using a subset of the Eclipse bug repository and the results suggested better schedules than the schedule followed by the developers and schedules proposed by a simpler search procedure.

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