Ali Abdolali

COMBINATION OF MLS, GA & CG FOR THE REDUCTION OF RCS OF MULTILAYERED CYLINDRICAL STRUCTURES COMPOSED OF DISPERSIVE METAMATERIALS

In this paper the electromagnetic wave scattering from multilayered cylindrical structures is studied for a normally incident plane wave with linear (TE or TM), circular and elliptical polarizations. The cylindrical layers may be composed of any combination of dispersive common materials and metamaterials. The addition theorems for the cylindrical waves are used for the EM wave analysis. The objective of this study is to decrease or increase the Radar Cross Section (RCS) in an ultra wide band width. The optimization is based on the Method of Least Squares (MLS), employing a novel combination of the Genetic Algorithm (GA) and Conjugate Gradient (CG), where the global search for the minimization point is performed by GA and the local search is done by CG, which greatly speeds up the search algorithm. The behaviors of various combinations of common materials and metamaterials for reduction of RCS are studied. Furthermore, the procedures for selection of correct signs for metamaterial parameters, namely e, µ, k and η are presented.

Design and Optimization of Planar Multilayer Antireflection Metamaterial Coatings at Ku Band Under Circularly Polarized Oblique Plane Wave Incidence

In this paper, planar multilayered antireflection coatings composed of isotropic and dispersive common materials and metamaterials (DPS, DNG, ENG, and MNG) are designed and optimized at Ku band under circularly polarized oblique plane wave incidence by a full-wave method and combination of the method of least squares (MLS), genetic algorithm (GA) and conjugate gradients (CG). The body on which the coating is applied may be selected as PEC, plexiglas, or any other material. As a result a new class of radar absorbing materials (RAM) are obtained, which may be effectively used for antireflection coatings. Furthermore, guidelines are presented for the selection of correct signs for the real and imaginary parts of propagation constant k and intrinsic impedance η.

Realization of the Perfect Electromagnetic Conductor Circular Cylinder Using Anisotropic Media

In this paper, an analytical solution is investigated for the two-dimensional problem of electromagnetic scattering of a line source from a perfect electromagnetic conductor (PEMC) circular cylinder coated with an anisotropic media. In the anisotropic region, the relative permittivity and permeability tensors, when referred to principal axes (ρ, φ, z), are biaxial and diagonal. It is demonstrated that the relations of electromagnetic field vectors in anisotropic medium is equal to a PEMC boundary conditions when the parameters of the anisotropic region are chosen in an appropriate manner. Therefore, this region can act as a PEMC cylinder.

A NEW THREE-DIMENSIONAL CONICAL GROUND- PLANE CLOAK WITH HOMOGENEOUS MATERIALS

A new three dimensional conical ground plane electromag- netic cloak is proposed and designed based on the coordinate transfor- mation of Maxwells equations. Material parameters of the conical invisible cloak are derived which have simple form and lesser inhomo- geneity compared with other 3-dimensional cloaks. Because of conve- nient form of the constitutive tensors of the conical cloak, we propose a new strategy for homogeneous approximation of the materials of the cloaks. Numerical simulations conflrm that approximation with eight slices, is more than enough and this cloak can hide any object on the ground as well as inhomogeneous ones.

Highly sensitive miniaturized bio-sensor using 2-layer double split ring resonators

THz biosensors are used to detect the presence of materials in Biomedical Science, especially thin DNA strands, therefore needs considerably high sensitivity. In this paper, we introduce a new structure made up of Metamaterials, which is used for identification of very thin analytes according to their dielectric constants. Procedures for lowering the resonant frequency and increasing the sensitivity of the sensor, simultaneously, are presented. High sensitivity of (Δf_r/f_r = 2.73% for Δε_r = 1), in average, is reported and 10 nm thick DNA (ε_r = 3.2) was detected due to miniaturization techniques.

Cylindrical metasurfaces for exotic electromagnetic wave manipulations

We present closed-boundary cylindrical metasurfaces for the manipulation of electromagnetic waves. We suggest a systematic analytical approach for the analysis and synthesis of such metasurfaces. Moreover, we demonstrate a conceptual synthesis example i.e., an electromagnetic illusion device and suggest other applications using the proposed approach. The suggested approach paves the way for more complex and interesting wave manipulations.

A NOVEL NON-COHERENT MICRO-DOPPLER IMAGING METHOD USING HYBRID OPTIMIZATION

Conventional radar imaging methods use coherent analysis which highlights the necessity of signal phase measurement setups and complex inverse algorithms. To mitigate these drawbacks, this paper proposes a novel phase-less imaging algorithm. A nonlinear over-determined system of equations based on signal Doppler shift is developed, and a new error function originated from least square method is introduced. To obtain the exact position of targets, hybrid optimization is applied to the achieved error function. Simulation results demonstrate that the proposed method is well capable of detecting the targets containing strong point scatterers, even with the distance of 1 cm. Also, the resolution of imaging algorithm for point scatterer circumstances is obtained in the order of millimeter. Concurrent with the priory imaging algorithms with the same imaging setups using proposed method reduces complexity and increases imaging swiftness.

A New Implementation of Frequency Selective Surface Cloak for Cylindrical Structures

The main purpose of this paper is to design, implement and measure a new sample of mantle cloak. A new method called mantle cloak is introduced by cloaking an object by a single, conformal meta-surface which can drastically suppress the scattering of the desired object. In this paper, a grid lattice is placed around a dielectric object as the cloaking structure. Previously, this FSS has been utilized for the cloaking of PEC object; but, when patch structure is placed around the dielectric it has inductive equivalent circuit with appropriate designing, it can be used for cloaking of dielectric cylinder. Numerical simulations of near field and far field of the designed structure are derived to prove the effectiveness of our meta-surface cloak. Also, measurement results of S11 and S21 related to cloaked structure and their comparison with single dielectric proves suitable performance of the designed cloak. The results show more than 20% bandwidth for this structure. This means that this structure is suitable for broadband operations.

Interaction of Electromagnetic Waves with a Moving Slab: Fundamental Dyadic Method

This paper concerns with the interaction of electromagnetic waves with a moving slab. Consider a homogeneous isotropic slab moving uniformly in an arbitrary direction surrounded by an isotropic medium (free space). In this paper a new simple and systematic method is proposed for analyzing re∞ection and transmission of obliquely incident electromagnetic waves by a moving slab based on the concept of propagators. In the previous works complex relations were arrived but using this novel method those complexities will not appear thus the method may be extended to more complex structures. In this method, flrst, electric and magnetic flelds are decomposed into their tangential and normal components then each constitutive dyadic is decomposed into a two-dimensional dyadic in transverse plane and two two-dimensional vectors in this plane. Substituting these dyadics into Maxwells equations gives a flrst order difierential equation which contains fundamental dyadic of the medium. From the solution of this equation, flelds inside the slab may be expressed in terms of flelds at the front surface of the slab and the propagator matrix which is an exponential function of fundamental dyadic. Using this method the up-going and down-going tangential electromagnetic flelds may be obtained at the same time. As a limiting case a slab with vanishing velocity is discussed using this method, and re∞ection and transmission coe-cients of this slab are derived, which ends in Fresnels equations. At last, several typical examples are provided to exemplify the applicability of the proposed method. Moreover, the results are compared with the method of Lorentz transformation. A good agreement is observed between the results which verifles the validity of the proposed method.

RECONSTRUCTING CONSTITUTIVE PARAMETERS OF INHOMOGENEOUS PLANAR LAYERED CHIRAL MEDIA BASED ON THE OPTIMIZATION APPROACH

This paper presents a frequency domain technique for reconstructing the constitutive parameters of inhomogeneous planar layered chiral media based on an optimization approach. The measured co- and cross-re∞ection and transmission coe-cients are used to extract proflles of electromagnetic parameters of the inhomogeneous chiral media. To identify the functions of constitutive parameters of the chiral media, Fourier series expansions and Genetic Algorithm (GA) are utilized. Since the optimization problem is highly non-linear, enhanced GA in which a fuzzy system is used for improving the speed and accuracy of GA. The performance and feasibility of the proposed reconstruction method is proven using two typical examples.