In this paper, a microstrip inset-fed patch antenna covered by plasma sheath is simulated by using the (FD)²TD algorithm. Expressions of calculating the coefficients in the electric field update equation for cold plasma are presented in detail. Computational examples illustrate that the resonant frequency of the patch antenna covered by plasma sheath is changed. The curves presented in this paper may be useful when introducing appropriate corrections in the design of the microstrip patch antennas in the plasma environment.

A scattering model for rice canopy based on Monte Carlo simulations is applied to interpret RADARSAT data and to predict the temporal response of rice growth. The model takes into account the coherent wave interactions among vegetative elements which usually occur in clusters with closely spaced elements. The model was also used to analyze the structural effect of rice fields on the scattering returns. Simulation results show a significant difference in L-band backscattering returns from rice fields with different structures, and are consistent with empirical observations from JERS-1 Campaign. Taking the ratio of HH over VV can help eliminating ambiguities in this inverse scattering problem.

The conventional form of the electric-field integral equation (EFIE), unlike the magnetic-field integral equation, cannot be solved accurately with the method of moments using pulse basis functions and point matching. A new form of the EFIE is derived whose kernel has no greater singularity than that of the free-space Green's function. This low-order-singularity form of the EFIE, the LEFIE, is solved numerically for perfectly electrically conducting bodies of revolution (BORs) using pulse basis functions and point-matching. Derivatives of the current are approximated with finite differences using a quadratic Lagrangian interpolation polynomial. Such a simple solution of the LEFIE is contingent, however, upon the vanishing of a linear integral that appears when the original EFIE is transformed to obtain the LEFIE. This generally restricts the applicability of the LEFIE to smooth closed scatterers. Bistatic scattering calculations performed for a prolate spheroid demonstrate that results comparable in accuracy to those of the conventionally solved EFIE can be obtained with the LEFIE using pulse basis functions and point matching provided a higher density of points is used close to the ends of the BOR.

The purpose of this paper is a rigorous error estimation of the Method of Auxiliary Sources (MAS), when the latter is applied to electromagnetic scattering from a circular, coated, perfectly conducting cylinder, assumed to satisfy the Standard Impedance Boundary Condition (SIBC). The MAS matrix is inverted analytically, via eigenvalue analysis, and an exact expression for the discretization error in the boundary condition is derived. Furthermore, an analytical formula for the condition number of the linear system is also extracted, in addition to an asymptotic estimate for large scatterers, explaining the irregular behavior of the computational error resulting from numerical matrix inversion. Finally, the optimal location of the auxiliary sources is determined, on the grounds of error minimization.

The surface integral equation method is applied for the electromagnetic analysis of general metallic and dielectric structures of arbitrary shape. The method is based on the EFIE-CFIE-PMCHWT integral equation formulation with Galerkins type discretization. The numerical implementation is divided into three independent steps: First, the electric and magnetic field integral equations are presented and discretized individually in each non-metallic subdomain with the RWG basis and testing functions. Next the linearly dependent and zero unknowns are removed from the discretized system by enforcing the electromagnetic boundary conditions on interfaces and at junctions. Finally, the extra equations are removed by applying the wanted integral equation formulation, and the reduced system is solved. The division into these three steps has two advantages. Firstly, it greatly simplifies the treatment of composite ob jects with multiple metallic and dielectric regions and junctions since the boundary conditions are separated from the discretization and integral equation formulation. In particular, no special junction basis functions or special testing procedures at junctions are needed. Secondly, the separation of the integral equation formulation from the two previous steps makes it easy to modify the procedure for other formulations. The method is validated by numerical examples.

The Dyadic Green's function is in general viewed as a generalized, or distribution function. A commonly used procedure to evaluate its volume integral is the principal-volume method, in which an infinitesimal volume around the singularity is excluded from the integration volume. In this paper, we develop a general analytical technique to evaluate the integral of the dyadic Green's function without the need to specify an exclusion volume. The newly derived expressions accurately integrate the singularity and can be used for integration over any shape of spatial discretization cell. We derive explicit expressions for the integral of the 3D dyadic Green's function over a sphere and over a general rectangular block. Similar expressions are obtained for the 2D dyadic Green's function over a cylinder and over a general rectangular cell. It is shown that using the integration technique described in this paper for spherical/circular cells, simple analytical expressions can be derived, and these expressions are exactly the same as those obtained using the principal-volume method. Furthermore, the analytical expressions for the integral of the dyadic Green's function are valid regardless of the location of the observation point, both inside and outside the integration domain. Because the expressions only involve surface integrals/line integrals, their evaluation can be performed very efficiently with a high degree of accuracy. We compare our expressions against the equivalent volume approximation for a wide range of frequencies and cell sizes. These comparisons clearly show the efficiency and accuracy of our technique. It is also shown that the cubic cell (3D) and the square cell (2D) can be approximated with an equivalent spherical cell and circular cell, respectively, over a wide range of frequencies. The approximation can be performed analytically, and the results can be written as the value of the dyadic Green's function at the center multiplying a "geometric factor". We describe analytical procedures to derive the corresponding geometric factors.

Temperature increase analysis has been performed with consideration to the anatomical model of the human head exposed to a cellular phone operating at 900 MHz. Four different numerical methods, in particular an implicit method based on the Alternating Direction Implicit technique (ADI), were applied to solve the Bio-Heat Equation (BHE), their advantages and limitations were compared using a canonical case. The tests performed on the latest have shown that the implicit approach is well adapted to solve this type of equations. The rise of temperature in the human head exposed to the RF emission of a mobile phone with a radiated power of 250 mW at 900 MHz was analyzed. In addition the influence of the presence of the telephone kit close to the head was discussed. The influence of different thermal parameters such as the thermal conductivity and the blood perfusion coefficient on the rise of temperature has been analyzed. The simulation carried out showed that the maximum temperature increase in the internal tissues linked to SAR deposition does not exceed 0.1ºC. We recorded a temperature difference of 1.6ºC in the skin due to the presence of a switched off cellular phone, which has been confirmed by the experimental measurements performed.

The propagation characteristics of an elliptical step-index fiber with a conducting helical winding on the core-cladding boundary are investigated analytically and compared with those of a circular step index fiber with a conducting radial winding. Our optical waveguides are unconventional: in view of the existence of helical conducting windings on the core-cladding boundaries. Appropriate coordinate systems, circular cylindrical and elliptic cylindrical, are chosen for the circular and elliptical fibers. Applying the boundary conditions as modified by the presence of conducting helical windings, the characteristic equations are obtained for both the fibers. Dispersion curves are also obtained for two special values of the helical pitch angle ψ, namely, for ψ = 0º and ψ = π/2 for each fiber and the results have been compared. It is found that the introduction of the helical winding has two main effects on the characteristics of both types of fibers. These are: (1) The helix introduces band gaps and (2) has the effect of splitting a mode into a pair of adjacent modes In the case of the elliptical helically clad waveguide we find two band gaps for V < 30 whereas for circular guide we have only one band gap in the same range of V-values, V being the normalized frequency parameter.

The radiation properties of an axially slotted circular or elliptical antenna coated with metamaterials are investigated. The fields inside and outside the dielectric coating are expressed in terms of Mathieu functions. The boundary conditions at various surfaces are enforced to obtain the unknown field expansion coefficients. Numerical results are presented graphically for the radiation pattern, aperture conductance and antenna gain for the TM case. It was found that slotted antenna coated with metamaterials has more directive beam with lower sidelobes compared to coated with conventional dielectric material.

Using a commercial software, simulations are done on the radiation of a dipole antenna embedded in metamaterial substrates. Metamaterials under consideration are composed of a periodic collection of rods, or of both rods and rings. The S-parameters of these metamaterials in a waveguide are analyzed and compared with their equivalent plasma or resonant structure. Farfield radiation is optimized by analytic method and is simulated numerically. The metamaterial is shown to improve the directivity.

The paper focuses on λ/4 monopole antennas located in a meta-material that exhibits simultaneously negative values of effective permeability and permittivity within a microwave frequency band, as well as our experimental study in an anechoic chamber. The experimental results show that the electromagnetic waves radiated by the monopole are negatively refracted at the interface between the meta-material and the air at certain directions. In addition, the radiation pattern of the monopole in the meta-material is directional while it is non-directional without the meta-material.

Left-handed materials (LHM) are engineered structures that exhibit electromagnetic properties not found in nature. Real applications of LHM need substrates with low loss, wide bandwidth as well as stable mechanical characteristics. In this paper, we summarize some experimental as well as numerical results of left-handed materials with different configurations of rods and split-ring resonators (SRRs). Hot-press technics utilized in PC board manufacture are used to produce solid-state multi-layer left-handed materials. Either mechanical or electromagnetic characteristics of LH samples are notably improved.

We present a theoretical analysis of the radiation of an S-shaped split ring resonator (S-SRR) for the realization of a metamaterial exhibiting left-handed properties. It is shown that the structure is resonant due to its internal capacitances and inductances, which can be adjusted such that the electric plasma frequency and magnetic plasma frequency, both due to the S-SRR only, appear within the same frequency band. Using the same idea, we also present some extended S-shaped split-ring resonator structures with improved performance.

This paper presents a quasi-static analysis of a metamaterial consisting of a three-dimensional array of small tunable stacked split ring resonators (SSRRs). The resonance frequency of the proposed resonator structure can be controlled by adjusting the auxiliary lumped elements which are inserted between the split of each ring. In addition, the size of the ring resonator can be reduced to an order of 0.01λ that is one tenth that of the split ring resonator (SRR) by choosing the proper lumped elements. The analysis is based on the quasi-static Lorentz theory, and the generalized matrix representation of the macroscopic constitutive relations of the composite medium is calculated.

Two-dimensional isotropic metamaterials fabricated from cross split-ring resonators (CSRRs) are characterized and their constitutive relation tensors are studied in this paper. The effective constitutive parameters of the metamaterials are determined utilizing the quasi-static Lorentz theory and numerical method (i.e., the method of moments for solving the electric field integral equation). The induced current distributions of a single CSRR at the resonant frequency are presented. Moreover, the dependence of the resonant frequency on the dimensions of a single CSRR and the space distances of the CSRR array is also discussed. Reflection and transmission coefficients of a metamaterial slab versus frequency are finally discussed.

This paper focuses on the complex guided wave solutions of grounded slab made of metamaterials. Complex solutions of both TE and TM modes have been analyzed. It is found that they are distributed on the proper Riemann sheet. This property differs dramatically from that of a conventional grounded slab. A number of other distribution properties are studied analytically. Some numerical examples are given to verify the analytical results. It is important to take the peculiar complex solutions into account in the problems of microstrip and surface wave excitation.

Guided waves in a wire medium slab are studied. The wire medium is considered as a continuous medium described in terms of uniaxial permittivity dyadic. Nonlocal model of the wire medium, taking into account spatial dispersion, is used in the analysis. Different cases of an arrangement of the wires are considered. Analytic expressions for the fields in unbounded media and numerical solutions for eigenmodes spectrum in wire medium slab are obtained. Comparison of the results given by old (local) and new model of wire medium is presented.

The increasing interest in electromagnetic effects in double-negative (DNG) materials requires a formulation capable of a full analysis of wave propagation in such materials. We develop a novel technique for discretization of the Drude medium model and adopt multi-domain pseudospectral time-domain (PSTD) algorithm and well-posed PML formulation to analysis the plane wave scattering properties of a single circular cylinder and a periodic array of the circular cylinders fabricated from the Drude medium. The simulation results show accuracy of the proposed constitutive equation-discretization scheme.

^nullOptical surface plasmon resonance sensors have been known for a long time. In this paper, we discuss the use of metamaterials to construct a surface plasmon sensor which can be used at microwave frequencies. We review the conditions for the existence of surface plasmon and the use of the forward and backward surface waves. A sharp dip in the reflection coefficient occurs when the propagation constant of the incident wave along the surface is nearly equal to the propagation constant of the plasmon surface wave and may be used to probe bulk material characteristics or to determine metamaterial characteristics. Numerical examples are given to illustrate the basic characteristics.

Characteristics of surface wave modes on a grounded slab of negative permittivity and negative permeability parameters are investigated. It is shown that, unlike a slab with positive parameters, the dominant mode can have evanescent fields on both sides of the interface between the slab and the surrounding air. Detailed characteristics of such mode for various combinations of the slab parameters are given.