Tuning the LC-Parameters of Metamaterial Unit Cells Using Genetic Algorithm

2016 ◽  
Author(s):  
Sadiq Ahmed ◽  
Madhukar Chandra ◽  
Husam Al-Behadili
Keyword(s):  
Genetic Algorithm ◽  
Unit Cells

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.

Measurement and Reduction of Radiation Damage in Frozen Hydrated Crystalline Specimens

1978 ◽  
Vol 36 (3) ◽  
pp. 70-77 ◽  
Author(s):  
R.M. Glaeser ◽  
S.B. Hayward
Keyword(s):  
Diffraction Pattern ◽  
Structural Information ◽  
Structural Disorder ◽  
Structural Features ◽  
Biological Macromolecules ◽  
Diffraction Intensity ◽  
Object Structure ◽  
Specimen Material ◽  
Unit Cells ◽  
Identical Unit

Highly ordered or crystalline biological macromolecules become severely damaged and structurally disordered after a brief electron exposure. Evidence that damage and structural disorder are occurring is clearly given by the fading and eventual disappearance of the specimen's electron diffraction pattern. The fading and disappearance of sharp diffraction spots implies a corresponding disappearance of periodic structural features in the specimen. By the same token, there is a oneto- one correspondence between the disappearance of the crystalline diffraction pattern and the disappearance of reproducible structural information that can be observed in the images of identical unit cells of the object structure. The electron exposures that result in a significant decrease in the diffraction intensity will depend somewhat upon the resolution (Bragg spacing) involved, and can vary considerably with the chemical makeup and composition of the specimen material.

Electron microscopy of niobium and tantalum hydrides

1978 ◽  
Vol 36 (1) ◽  
pp. 644-645
Author(s):  
T. Schober
Keyword(s):  
Electron Microscopy ◽  
Heat Storage ◽  
Measurement Techniques ◽  
Metal Hydrides ◽  
Detailed Understanding ◽  
Storage Devices ◽  
Unit Cells ◽  
Endothermic Reactions ◽  
Hydrogen Reactions ◽  
New Phase

Nb, Ta and V are prototype substances for the study of the endothermic reactions of H with metals. Such metal-hydrogen reactions have gained increased importance due to the application of metal-hydrides in hydrogen- und heat storage devices. Electron microscopy and diffraction were demonstrated to be excellent methods in the study of hydride morphologies and structures (1). - Figures 1 and 2 show the NbH and TaH phase diagrams (2,3,4). EM techniques have contributed substantially to the elucidation of the structures and domain configurations of phases β, ζ and ε (1,4). Precision length measurement techniques of distances in reciprocal space (5) recently led to a detailed understanding of the distortions of the unit cells of phases ζ and ε (4). In the same work (4) the existence of the new phase η was shown. It is stable near -68 °C. The sequence of transitions is thus below 70 %.

Crystal Structure Analysis of Cu-Zr Alloys by Convergent Beam Diffraction

1981 ◽  
Vol 39 ◽  
pp. 354-355
Author(s):  
A. F. Marshall ◽  
J. W. Steeds ◽  
D. Bouchet ◽  
S. L. Shinde ◽  
R. G. Walmsley
Keyword(s):  
Crystal Structure ◽  
Point Group ◽  
Intermetallic Phase ◽  
Three Dimensional ◽  
Crystal Structure Analysis ◽  
Ion Milling ◽  
Composition And Structure ◽  
Unit Cells ◽  
Sputter Deposited ◽  
Convergent Beam

Convergent beam electron diffraction is a powerful technique for determining the crystal structure of a material in TEM. In this paper we have applied it to the study of the intermetallic phases in the Cu-rich end of the Cu-Zr system. These phases are highly ordered. Their composition and structure has been previously studied by microprobe and x-ray diffraction with sometimes conflicting results.The crystalline phases were obtained by annealing amorphous sputter-deposited Cu-Zr. Specimens were thinned for TEM by ion milling and observed in a Philips EM 400. Due to the large unit cells involved, a small convergence angle of diffraction was used; however, the three-dimensional lattice and symmetry information of convergent beam microdiffraction patterns is still present. The results are as follows:1) 21 at% Zr in Cu: annealed at 500°C for 5 hours. An intermetallic phase, Cu3.6Zr (21.7% Zr), space group P6/m has been proposed near this composition (2). The major phase of our annealed material was hexagonal with a point group determined as 6/m.

Computer processing of high-resolution images of periodic specimens

1986 ◽  
Vol 44 ◽  
pp. 2-5
Author(s):  
W. Chiu ◽  
M.F. Schmid ◽  
T.-W. Jeng
Keyword(s):  
High Resolution ◽  
Fourier Transforms ◽  
Complex Structure ◽  
Distribution Functions ◽  
Multiple Image ◽  
Cryo Electron Microscopy ◽  
Structure Factors ◽  
Unit Cells ◽  
High Resolution Images ◽  
Phase Probability Distribution

Cryo-electron microscopy has been developed to the point where one can image thin protein crystals to 3.5 Å resolution. In our study of the crotoxin complex crystal, we can confirm this structural resolution from optical diffractograms of the low dose images. To retrieve high resolution phases from images, we have to include as many unit cells as possible in order to detect the weak signals in the Fourier transforms of the image. Hayward and Stroud proposed to superimpose multiple image areas by combining phase probability distribution functions for each reflection. The reliability of their phase determination was evaluated in terms of a crystallographic “figure of merit”. Grant and co-workers used a different procedure to enhance the signals from multiple image areas by vector summation of the complex structure factors in reciprocal space.

Correlation averaging of two-dimensional crystals: basic strategy and refinements

1986 ◽  
Vol 44 ◽  
pp. 136-139
Author(s):  
W. Baumeister ◽  
R. Rachel ◽  
R. Guckenberger ◽  
R. Hegerl
Keyword(s):  
Low Dose ◽  
Signal To Noise Ratio ◽  
Real Space ◽  
Fourier Domain ◽  
Two Dimensional ◽  
Signal To Noise ◽  
Unit Cells ◽  
Lateral Displacements ◽  
Established Technique ◽  
Crystalline Array

IntroductionCorrelation averaging (CAV) is meanwhile an established technique in image processing of two-dimensional crystals /1,2/. The basic idea is to detect the real positions of unit cells in a crystalline array by means of correlation functions and to average them by real space superposition of the aligned motifs. The signal-to-noise ratio improves in proportion to the number of motifs included in the average. Unlike filtering in the Fourier domain, CAV corrects for lateral displacements of the unit cells; thus it avoids the loss of resolution entailed by these distortions in the conventional approach. Here we report on some variants of the method, aimed at retrieving a maximum of information from images with very low signal-to-noise ratios (low dose microscopy of unstained or lightly stained specimens) while keeping the procedure economical.

TEM observations of surface-step and hole-edge faceting in acid-etched and annealed MgO thin foils

1993 ◽  
Vol 51 ◽  
pp. 1134-1135
Author(s):  
Simon King ◽  
C. Barry Carter
Keyword(s):  
Marked Contrast ◽  
Aqua Regia ◽  
Surface Step ◽  
Smoke Particle ◽  
Hole Edge ◽  
Thin Foils ◽  
Surface Steps ◽  
Unit Cells ◽  
Reflection Electron Microscopy ◽  
Similar Preparation

Surface-steps formed during the cleavage of MgO on {100} planes, the smaller steps of which may be of atomic height, have been observed in Reflection-Electron Microscopy investigations to be accurately aligned along <001> directions. Steps of atomic height also have been identified on MgO smoke-particle platelets; these steps may be curved or straight, with the straight steps showing evidence for faceting along <001>. Reference also is made to faceting along <011> and <012> directions. Straight steps ∼2 unit cells high, with edges along <100> also have been imaged by High-Resolution Profile-Imaging at the peripheries of MgO smoke microcubes. After etching in aqua-regia and annealing in air, however, high densities of “large” steps several unit cells high, as well as numerous holes, are formed. It is faceting in these foils that is reported here.As can be seen in fig 1, obvious faceting of the surface-step traces is extremely rare in these foils, in marked contrast to substrates such as LaAlO3 and SrTiO3, on which surface-step traces facet readily after a similar preparation treatment.

Bayesian removal of noise for increased sensitivity in vector pattern recognition lattice imaging of interfaces

1993 ◽  
Vol 51 ◽  
pp. 994-995
Author(s):  
L. Fei ◽  
P. Fraundorf
Keyword(s):  
Pattern Recognition ◽  
Perfect Crystal ◽  
Unit Cell ◽  
Ion Milling ◽  
Beam Radiation ◽  
Major Interest ◽  
Unit Cells ◽  
Mapping Process ◽  
Increased Sensitivity ◽  
Electron Microscopes

Interface structure is of major interest in microscopy. With high resolution transmission electron microscopes (TEMs) and scanning probe microscopes, it is possible to reveal structure of interfaces in unit cells, in some cases with atomic resolution. A. Ourmazd et al. proposed quantifying such observations by using vector pattern recognition to map chemical composition changes across the interface in TEM images with unit cell resolution. The sensitivity of the mapping process, however, is limited by the repeatability of unit cell images of perfect crystal, and hence by the amount of delocalized noise, e.g. due to ion milling or beam radiation damage. Bayesian removal of noise, based on statistical inference, can be used to reduce the amount of non-periodic noise in images after acquisition. The basic principle of Bayesian phase-model background subtraction, according to our previous study, is that the optimum (rms error minimizing strategy) Fourier phases of the noise can be obtained provided the amplitudes of the noise is given, while the noise amplitude can often be estimated from the image itself.

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