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Cheng-wei Qiu - One of the best experts on this subject based on the ideXlab platform.

  • on the constitutive relations of g chiral media and the possibility to realize negative index media
    Microwave and Optical Technology Letters, 2006
    Co-Authors: SaÏd Zouhdi, Cheng-wei Qiu, Hai-ying Yao, M S Leong
    Abstract:

    Gyro-chiral (G-chiral) media of different constitutive relations are studied as potential materials to realize the negative-index material (NIM). G-chiral media are believed to have advantages over chiral media: negative refractive index and Backward Waves can be achieved without requiring the permittivity and permeability to be quite small at working frequency. The gyrotropic parameters favor the realization of NIM far off the resonances of the permittivity and permeability. The possibility of obtaining Backward Waves and negative refractive index under Post's and Tellegen's relations are discussed. Moreover, the mapping and comparison of G-chiral media of these two relations have been studied. It is found that the Tellegen's relations are more suitable to describing the G-chiral media so as to realize NIM by this kind of medium. Therefore, this paper not only provides an alternative way to achieve NIM from the G-chiral medium but also discusses the constitutive relation's effects on Backward wave propagation and refractive indices. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48:2534–2538, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21981

  • properties of faraday chiral media green dyadics and negative refraction
    Physical Review B, 2006
    Co-Authors: Hai-ying Yao, Cheng-wei Qiu, SaÏd Zouhdi
    Abstract:

    Selected properties of generalized Faraday chiral media are thoroughly studied in this paper where Green’s dyadics are formulated for unbounded and layered structures, and the possibility of negative refractive index, the Backward eigenWaves, and quantum vacuum are also investigated. After a general representation of the Green’s dyadics is obtained, the scattering coefficients of the Green’s dyadics are determined from the boundary conditions at each interface and are expressed in a greatly compact form of recurrence matrices. In the formulation of the Green’s dyadics and their scattering coefficients, three cases are considered, i.e., the current source is immersed in i the intermediate, ii the first, and iii the last regions, respectively. We present here layered dyadic Green’s functions for generalized Faraday chiral media. This kind of Faraday chiral media can also be manipulated to achieve negative refraction and possible Backward wave propagation is presented as well. As compared to the existing results, the present work mainly contributes: 1 the exact representation of the dyadic Green’s functions, with irrotational part extracted out, for the gyrotropic Faraday chiral medium in multilayered geometry; 2 the general DGFs and scattering coefficients which can be reduced to either layered chiroferrite, chiroplasma or other simpler cases; and 3 negative refractive index and Backward Waves achieved with less restriction and more advantages compared to chiral media.

Bernd Eber - One of the best experts on this subject based on the ideXlab platform.

  • wave reflections assessed with a novel method for pulse wave separation are associated with end organ damage and clinical outcomes
    Hypertension, 2012
    Co-Authors: Thomas Weber, Siegfried Wassertheurer, M Rammer, Anton Haiden, Bernhard Hametner, Bernd Eber
    Abstract:

    We recently developed a novel method for assessment of arterial wave reflections (ARCSolver method): based on adopted Windkessel methods, flow curves are estimated from pressure waveforms, and wave separation analysis is performed, yielding the amplitudes of the forward and Backward Waves. The aim of this study was to investigate their clinical correlates and prognostic impact. In 725 patients (417 men; mean age, 64 years) undergoing coronary angiography, we determined wave reflections from radial tonometry and transfer function-derived aortic waveforms using pulse wave analysis, as well as wave separation analysis. Measures of pulsatile arterial function were statistically significant, although moderately associated with markers of cardiac load and subclinic cardiac, renal, and aortic end-organ damage. After a median follow-up duration of 1399 days, 139 patients reached the combined cardiovascular end point (death, myocardial infarction, stroke, coronary, cerebrovascular, and peripheral revascularization). In univariate analysis, the relative risk of the combined end point increased with increasing levels of incident pressure wave height, augmented pressure, and forward and Backward wave amplitude (hazard ratio for 1 SD was 1.302, 1.236, 1.226, and 1.276; P

  • wave reflections assessed with a novel method for pulse wave separation are associated with end organ damage and clinical outcomes
    Hypertension, 2012
    Co-Authors: Thomas Weber, Siegfried Wassertheurer, M Rammer, Anton Haiden, Bernhard Hametner, Bernd Eber
    Abstract:

    We recently developed a novel method for assessment of arterial wave reflections (ARCSolver method): based on adopted Windkessel methods, flow curves are estimated from pressure waveforms, and wave separation analysis is performed, yielding the amplitudes of the forward and Backward Waves. The aim of this study was to investigate their clinical correlates and prognostic impact. In 725 patients (417 men; mean age, 64 years) undergoing coronary angiography, we determined wave reflections from radial tonometry and transfer function-derived aortic waveforms using pulse wave analysis, as well as wave separation analysis. Measures of pulsatile arterial function were statistically significant, although moderately associated with markers of cardiac load and subclinic cardiac, renal, and aortic end-organ damage. After a median follow-up duration of 1399 days, 139 patients reached the combined cardiovascular end point (death, myocardial infarction, stroke, coronary, cerebrovascular, and peripheral revascularization). In univariate analysis, the relative risk of the combined end point increased with increasing levels of incident pressure wave height, augmented pressure, and forward and Backward wave amplitude (hazard ratio for 1 SD was 1.302, 1.236, 1.226, and 1.276; P<0.01 for all, respectively). In multivariate analysis, Backward wave amplitude was the most consistent predictor of the combined end point. Of note, its predictive value was independent of brachial systolic, diastolic, and mean blood pressures and was superior to brachial pulse pressure. In conclusion, the amplitude of the reflected wave, as assessed with a novel method for wave separation, is associated with hypertensive end organ damage and is an independent predictor of cardiovascular events in high-risk patients.

Levent Sevgi - One of the best experts on this subject based on the ideXlab platform.

  • petool matlab based one way and two way split step parabolic equation tool for radiowave propagation over variable terrain
    Computer Physics Communications, 2011
    Co-Authors: Ozlem Ozgun, Mustafa Kuzuoglu, Gokhan Apaydin, Levent Sevgi
    Abstract:

    Abstract A MATLAB-based one-way and two-way split-step parabolic equation software tool (PETOOL) has been developed with a user-friendly graphical user interface (GUI) for the analysis and visualization of radio-wave propagation over variable terrain and through homogeneous and inhomogeneous atmosphere. The tool has a unique feature over existing one-way parabolic equation (PE)-based codes, because it utilizes the two-way split-step parabolic equation (SSPE) approach with wide-angle propagator, which is a recursive forward–Backward algorithm to incorporate both forward and Backward Waves into the solution in the presence of variable terrain. First, the formulation of the classical one-way SSPE and the relatively-novel two-way SSPE is presented, with particular emphasis on their capabilities and the limitations. Next, the structure and the GUI capabilities of the PETOOL software tool are discussed in detail. The calibration of PETOOL is performed and demonstrated via analytical comparisons and/or representative canonical tests performed against the Geometric Optic (GO) + Uniform Theory of Diffraction (UTD). The tool can be used for research and/or educational purposes to investigate the effects of a variety of user-defined terrain and range-dependent refractivity profiles in electromagnetic wave propagation. Program summary Program title: PETOOL (Parabolic Equation Toolbox) Catalogue identifier: AEJS_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEJS_v1_0.html Program obtainable from: CPC Program Library, Queenʼs University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 143 349 No. of bytes in distributed program, including test data, etc.: 23 280 251 Distribution format: tar.gz Programming language: MATLAB (MathWorks Inc.) 2010a. Partial Differential Toolbox and Curve Fitting Toolbox required Computer: PC Operating system: Windows XP and Vista Classification: 10 Nature of problem: Simulation of radio-wave propagation over variable terrain on the Earthʼs surface, and through homogeneous and inhomogeneous atmosphere. Solution method: The program implements one-way and two-way Split-Step Parabolic Equation (SSPE) algorithm, with wide-angle propagator. The SSPE is, in general, an initial-value problem starting from a reference range (typically from an antenna), and marching out in range by obtaining the field along the vertical direction at each range step, through the use of step-by-step Fourier transformations. The two-way algorithm incorporates the Backward-propagating Waves into the standard one-way SSPE by utilizing an iterative forward–Backward scheme for modeling multipath effects over a staircase-approximated terrain. Unusual features: This is the first software package implementing a recursive forward–Backward SSPE algorithm to account for the multipath effects during radio-wave propagation, and enabling the user to easily analyze and visualize the results of the two-way propagation with GUI capabilities. Running time: Problem dependent. Typically, it is about 1.5 ms (for conducting ground) and 4 ms (for lossy ground) per range step for a vertical field profile of vector length 1500, on Intel Core 2 Duo 1.6 GHz with 2 GB RAM under Windows Vista.

  • Two-way fourier split step algorithm over variable terrain with narrow and wide angle propagators
    2010 IEEE Antennas and Propagation Society International Symposium, 2010
    Co-Authors: Ozlem Ozgun, Mustafa Kuzuoglu, Gokhan Apaydin, Levent Sevgi
    Abstract:

    Helmholtz's wave equation can be approximated by means of two differential equations, corresponding to forward and Backward propagating Waves each of which is in parabolic wave equation (PWE) form. The standard PWE is very suitable for marching-type numerical solutions. The one-way Fourier split-step parabolic equation algorithm (SSPE) is highly effective in modeling electromagnetic (EM) wave propagation above the Earth's irregular surface through inhomogeneous atmosphere [1–4]. The two drawbacks of the standard PWE are: (i) It handles only the forward-propagating Waves, and cannot account for the backscattered ones. The forward Waves are usually adequate for typical long-range propagation scenarios. However, the Backward Waves become significant in the presence of obstacles that redirect the incoming wave. Hence, this necessitates the accurate estimation of the multipath effects to model the tropospheric wave propagation over terrain. (ii) It is a narrow-angle approximation, which consequently restricts the accuracy to propagation angles up to 10°-15° from the paraxial direction. To handle propagation angles beyond these values, wide-angle propagators have been introduced [5–6].

Ki Young Kim - One of the best experts on this subject based on the ideXlab platform.

  • fundamental guided electromagnetic dispersion characteristics in lossless dispersive metamaterial clad circular air hole waveguides
    arXiv: Optics, 2009
    Co-Authors: Ki Young Kim
    Abstract:

    The fundamental guided electromagnetic dispersion characteristics in lossless dispersive metamaterial clad circular air hole waveguides are investigated. Two operating guided modes are found to exist: circular waveguide and surface plasmon polariton modes that support fast and slow Waves, respectively. Hybrid mode classifications are also made in an empirical manner so that the guided modes can be sorted into either TM-like or TE-like modes in terms of their unique dispersion characteristics. Unusual dispersion characteristics, including multi-valued propagation constants at a single frequency, Backward Waves, and subwavelength guided propagations, are observed and discussed in relation to the air-hole radii and dielectric and magnetic constants of the metamaterial clad. A discussion comparing the extraordinary dispersion characteristics with those of other dielectric, plasmonic, and metamaterial waveguides is also included.

  • fundamental guided electromagnetic dispersion characteristics in lossless dispersive metamaterial clad circular air hole waveguides
    Journal of Optics, 2007
    Co-Authors: Ki Young Kim
    Abstract:

    The fundamental guided electromagnetic dispersion characteristics in lossless dispersive metamaterial clad circular air-hole waveguides are investigated. Two operating guided modes are found to exist: circular waveguide and surface plasmon polariton modes that support fast and slow Waves, respectively. Hybrid mode classifications are also made in an empirical manner so that the guided modes can be sorted into either transverse magnetic (TM)-like or transverse electric (TE)-like modes in terms of their unique dispersion characteristics. Unusual dispersion characteristics, including multi-valued propagation constants at a single frequency, Backward Waves, and subwavelength guided propagations, are observed and discussed in relation to the air-hole radii and dielectric and magnetic constants of the metamaterial clad. A discussion comparing the extraordinary dispersion characteristics with those of other dielectric, plasmonic, and metamaterial waveguides is also included.

Majeed A S Alkanhal - One of the best experts on this subject based on the ideXlab platform.

  • electromagnetic Waves in parallel plate uniaxial anisotropic chiral waveguides
    Optical Materials Express, 2014
    Co-Authors: Abdul Ghaffar, Majeed A S Alkanhal
    Abstract:

    Theoretical analysis of electromagnetic wave propagation in planar waveguides filled with uniaxial chiral anisotropic media is presented. The guide parallel plates are assumed to be perfect electric conductors. The material filling the waveguide is a generalized medium that incorporates chiral and metamaterials. The behavior of the field intensities, the dispersion curves, and the energy flux for three varieties of uniaxial chiral media are examined numerically. The results demonstrate the phenomena of Backward Waves in uniaxial anisotropic chiral media. The comparisons of the computed results of the presented general formulations with published results for some material cases confirm the accuracy of the presented analysis.