arXiv subjects

E. Cojocaru

Publications and source records attributed to E. Cojocaru.

8 recordsLinked to original sources

arXiv2012

Backward waves in a grounded bilayer slab containing double-negative (DNG) and double-positive (DPS) metamaterials

Simple dispersion relations for the guided modes in a grounded DNG/DPS bilayer slab are given in terms of normalized parameters. Relations corresponding to the grounded single-layer DNG slab are refound as specific cases. Numerical examples are given showing dispersion curves of the lower order modes and the respective total normalized power carried on the propagation direction. Snapshots obtained by the finite-difference time-domain method are provided showing the electromagnetic field inside the grounded DNG/DPS bilayer slabs. Since an important characteristic of the guided modes in the slab containing a DNG layer is the existence of a turning point (TP) at which the power carried by each mode of order m>0 equals zero and changes the sign, we present implicit relations at the TP for the normalized parameters of the guided modes in the grounded DNG/DPS and DNG slabs. We show that a thin DPS layer coating on the grounded DNG slab produces a shift of the TP on the dispersion curve.

physics.optics↗

arXiv2011

Animations obtained by the finite-difference time-domain method showing the backward wave propagation in double-negative single-layer waveguides

The materials having negative permittivity and negative permeability, which are labeled as double-negative (DNG) materials, have attracted much attention because of their unusual physical properties, which are different from those of conventional double-positive (DPS) materials. Animations obtained by the finite-difference time-domain method (FDTD) are provided showing how a transient sinusoidal signal that starts at t=0 propagates in the DPS and DNG waveguides. Three types of waveguides are considered: a slab or grounded slab inside the cladding medium and a parallel-plate waveguide filled with the slab. Dispersion curves in terms of normalized parameters are also provided.

physics.optics↗

arXiv2010

Third-order triangular finite elements for waveguiding problems

Explicit relations of matrices for two-dimensional finite element method with third-order triangular elements are given. They are more simple than relations presented in other works and could be easily implemented in new algorithms for both isotropic and anisotropic materials. Numerical examples are given comparatively using second-order and third-order triangular elements for problems of wave propagation in rectangular waveguides which have analytic solutions.

math-ph↗

arXiv2009

Elemental matrices for the finite element method in electromagnetics with quadratic triangular elements

The finite element method has become a preeminent simulation technique in electromagnetics. For problems involving anisotropic media and metamaterials, proper algorithms should be developed. It has been proved that discretizing in quadratic triangular elements may lead to an improved accuracy. Here we present a collection of elemental matrices evaluated analytically for quadratic triangular elements. They could be useful for the finite element method in advanced electromagnetics.

math-ph↗

arXiv2009

Parabolic cylinder functions implemented in Matlab

Routines for computation of Weber's parabolic cylinder functions and their derivatives are implemented in Matlab for both moderate and great values of the argument. Standard, real solutions are considered. Tables of values are included.

math-ph↗

arXiv2008

Mathieu functions computational toolbox implemented in Matlab

The Mathieu functions are used to solve analytically some problems in elliptical cylinder coordinates. A computational toolbox was implemented in Matlab. Since the notation and normalization for Mathieu functions vary in the literature, we have included sufficient material to make this presentation self contained. Thus, all formulas required to get the Mathieu functions are given explicitly. Following the outlines in this presentation, the Mathieu functions could be readily implemented in other computer programs and used in different domains. Tables of numerical values are provided.

math-ph↗

arXiv2008

Mathieu functions approach to bidimensional scattering by dielectric elliptical cylinders

Two-dimensional scattering by homogeneous and layered dielectric elliptical cylinders is analyzed following an analytical approach using Mathieu functions. Closed-form relations for the expansion coefficients of the resulting electric field in the vicinity of the scatterer are provided. Numerical examples show the focalizing effect of dielectric elliptical cylinders illuminated normally to the axis. The influence of the confocal dielectric cover on the resulting scattered field is envisaged.

physics.comp-ph↗

arXiv2008

Elliptic Cylindrical Invisibility Cloak, a Semianalytical Approach Using Mathieu Functions

An elliptic cylindrical wave expansion method by using Mathieu functions is developed to obtain the scattering field for a two-dimensional elliptic cylindrical invisibility cloak. The cloak material parameters are obtained from the spatial transformation approach. A near-ideal model of the invisibility cloak is set up to solve the boundary problem at the inner boundary in the cloak shell. The proposed design provides a more practical cloak geometry when compared to previous designs of elliptic cylindrical cloaks.

physics.comp-ph↗