Intrinsic anisotropy of the effective acoustic properties in metafluids made of two-dimensional cylinder arrays

2012 ◽  
Vol 376 (4) ◽  
pp. 637-642 ◽  
Author(s):  
Chunyin Qiu ◽  
Zhaofeng Ma ◽  
Jiuyang Lu ◽  
Zhengyou Liu
Keyword(s):  
Acoustic Properties ◽  
Two Dimensional ◽  
Cylinder Arrays ◽  
Intrinsic Anisotropy

SAXS of self-assembled nanocomposite films with oriented two-dimensional cylinder arrays: an advanced method of evaluation

2005 ◽  
Vol 38 (1) ◽  
pp. 78-86 ◽  
Author(s):  
Wilhelm Ruland ◽  
Bernd Smarsly
Keyword(s):  
Structural Parameters ◽  
Hexagonal Lattice ◽  
Preferred Orientation ◽  
Nanocomposite Films ◽  
Two Dimensional ◽  
Advanced Method ◽  
Cylinder Arrays ◽  
X Ray Scattering ◽  
Comparable Method ◽  
Method Of Evaluation

In a recent paper [Ruland & Smarsly (2002).J. Appl. Cryst.35, 624–633], an advanced method for the evaluation of the small-angle X-ray scattering (SAXS) from oriented lamellar systems was presented. In the present work, a comparable method is developed for the study of oriented cylinder arrays. Basic differences between the two methods are found in the way in which the preferred orientation affects the intensity distribution. The method is applied to the SAXS of SiO2-surfactant nanocomposite films which contain highly oriented arrays of cylinders. It is shown that up to eight structural parameters can be obtained by this method which characterize size, imperfection and preferred orientation of the two-dimensional hexagonal lattice formed by the cylinders, the radius and the polydispersity of the cylinders, and the interface boundary.

scholarly journals Deficiency of Standard Effective-Medium Approximation for Ellipsometry of Layers of Nanoparticles

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
E. G. Bortchagovsky ◽  
A. Dejneka ◽  
L. Jastrabik ◽  
V. Z. Lozovski ◽  
T. O. Mishakova
Keyword(s):  
Gold Nanoparticles ◽  
Effective Medium ◽  
Effective Medium Approximation ◽  
Two Dimensional ◽  
Effective Parameters ◽  
Correct Description ◽  
Interparticle Interactions ◽  
Standard Models ◽  
Intrinsic Anisotropy ◽  
Green Function Approach

Correct description of optical properties of layers of disordered interacting nanoparticles is the problem. Contrary to volumes of nanocomposites, when standard models of effective-medium approximations (EMA) work well, two-dimensional case of layers has intrinsic anisotropy, which influences interparticle interactions. The deficiency of standard Maxwell-Garnett model in the application to the ellipsometry of layers of gold nanoparticles is demonstrated. It demands the modification of EMA models and one way of this is considered in this paper. Contrary to existing 2D models with phenomenological parameters, the proposed Green function approach uses the same number of parameters as standard 3D EMA models for explicit calculations of effective parameters of layers of disordered nanoparticles.

The mechanical and acoustic properties of two-dimensional pentamode metamaterials with different structural parameters

2016 ◽  
Vol 109 (13) ◽  
pp. 131904 ◽  
Author(s):  
Xuan Cai ◽  
Lei Wang ◽  
Zhigao Zhao ◽  
Aiguo Zhao ◽  
Xiangdong Zhang ◽  
...  
Keyword(s):  
Structural Parameters ◽  
Acoustic Properties ◽  
Two Dimensional

scholarly journals Three-dimensional Floquet stability analysis of the wake in cylinder arrays

2007 ◽  
Vol 592 ◽  
pp. 79-88 ◽  
Author(s):  
N. K.-R. KEVLAHAN
Keyword(s):  
Reasonable Agreement ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Instability Mechanism ◽  
Cylinder Arrays ◽  
Spatial Periodicity ◽  
Wake Instability ◽  
Mode A ◽  
Three Dimensional Simulations

Three-dimensional stability of the periodic wake of tightly packed rotated and inline cylinder arrays is investigated for 60 ≤ Re ≤ 270. Results are compared with existing numerical and experimental studies for an isolated cylinder. Numerical Floquet analysis shows that the two-dimensional wakes of the rotated and inline arrays with spacing P/D = 1.5 become unstable at Rec = 64 ± 0.5 and Rec = 132 ± 1 respectively. Two-dimensional vortex shedding flow is unlikely in practice for such flows. The dominant spanwise wavelength is λ/D = 0.9 ± 0.1 for the rotated array at Re = 100 and λ/D = 3.0 ± 0.1 for the inline array at Re = 200. Three-dimensional simulations show excellent agreement with the Floquet analysis for the rotated case, and reasonable agreement for the inline case. The instability mechanism appears to be similar to Mode A for an isolated cylinder, although the structure of the three-dimensional vorticity is different due to the spatial periodicity of the flow. Unlike the isolated cylinder, both array flows are unstable as λ → ∞ (like a thin shear layer). This is the first investigation of three-dimensional wake instability in cylinder arrays, a problem of significant practical and theoretical interest.

Acoustic Properties of Fluidlike Metamaterials Based on Sonic Crystals

2007 ◽  
Author(s):  
Daniel Torrent ◽  
Jose´ Sa´nchez-Dehesa
Keyword(s):  
Phase Diagram ◽  
Viscous Fluid ◽  
Elastic Cylinder ◽  
Acoustic Properties ◽  
Effective Density ◽  
Two Dimensional ◽  
Solid Cylinder ◽  
Effective Parameters ◽  
Acoustic Parameters ◽  
Sonic Crystals

A homogenization method is used to get the effective parameters of two-dimensional clusters of solid cylinders embedded in a non viscous fluid or gas. The full elasticity is employed to describe the properties of cylinders. Asymptotic relations are derived and employed to formulate a method of homogenization based on the scattering properties of the cluster. Exact formulas for the effective parameters (i.e., effective sound velocity and effective density) are obtained as a function of the location of each cylinder, its physical parameters, and the embedded medium. Results of several solid-fluid composites will be reported. Also, phase-diagrams of fluid-like metamaterials based on sonic crystal will be analyzed. It is concluded that the method provides a tool to design acoustic metamaterials with prefixed refractive properties. The long wavelength behavior (homogenization) of two dimensional sonic crystals (periodic arrangements of two dimensional sound scatters) has been widely studied in the last years [1–9] due to its possible use as refractive acoustic devices. In a previous paper [2] the authors develop a theory to obtain the effective acoustic parameters of a cluster of fluid cylinder embedded in a non viscous fluid or gas, both for ordered and disordered case. The application of this theory to solid cylinder-fluid medium is only possible when the cylinder is rigid, that is, the sound does not propagates inside the cylinder. When it happens, elasticity must be taken into account, and a solid cylinder, in principle, cannot be considered a fluid cylinder with similar parameters. Here, the theory will be completed for the case of an elastic cylinder, and it will be discussed under what conditions an elastic cylinder can be considered a fluid cylinder, and which ones are the acoustic parameters of this fluid cylinder. It will be shown also that the effective parameters of clusters of elastic cylinders can lead to an effective medium with an effective speed of sound both higher and lower than that of the surrounding medium, and a phase diagram to analyze and predict this behavior will be given. Finally, a method to obtain a relative acoustic impedance equal to one (zero surface reflectance) will be discussed, and also a phase diagram to obtain it will be given.

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