Theoretical results on the plane electromagnetic wave diffraction from a structure as a strip periodic grating on a paramagnetic layer, the permeability of which possesses negative real part in the microwave band, are obtained using analytical regularization based on the solution to the Riemann-Hilbert problem. The effect of the resonant transmission accompanied by extremely high absorption is thoroughly studied across the frequency band of the surface waves of the paramagnetic layer placed in the biasing magnetic field. This effect is caused by the surface waves of the layer excited resonantly by the plane incident wave with the diffraction grating present. The resonant frequency is electronically tuned by the biasing magnetic field.
In this paper, a metal-clad planar optical waveguide biosensor with five layer structure is studied theoretically for the detection of Pseudomonas and Pseudomonas-like bacteria. Using a very simple boundary matching technique, we derive the mode equation and other necessary formulae for the proposed biosensor and analyse its performance under different conditions related to its constituents. The numerical results presented in this paper leads to a significant optimization of the important design parameters to sense micro-scale biological objects. Also, we compare our computed results with the results given for a biosensor with four layer structure. In addition, we discuss the importance and need of the inclusion of the thickness of an affinity layer as fifth layer in the four layer structure of the metal clad planar waveguide.
This paper mainly deals with the optical properties of biological tissues that are measured using laser reflectometry method. The result is compared with the phantom and simulation values to get accurate result. The surface Backscattering was determined by laser reflectometry. The tissue equivalent phantom would be prepared with the help of white paraffin wax mixed with various colour pigments in multiple proportions. A familiar Monte Carlo Simulation is used for the analysis of the optical properties of the tissue. The normalized backscattered intensity (NBI) signals from the tissue surface, measured by the output probes after digitization are used to reconstruct the reflectance images of tissues in various layers below the skin surface. This method was useful to trace the abnormal in the tissue.
The microwave signal attenuation caused by dust is one of the major problems in utilizing microwave bands for terrestrial and space communication especially at desert and semi desert area. This paper presents a mathematical model developed to characterize the microwave signal attenuation due to dust. This model enables a convenient calculation of the microwave signal path attenuation which relates attenuation to visibility, frequency, particle size and complex permittivity. The predicted values from the mathematical model, which are compared with the measured values observed by the author in Sudan show relatively optimistic agreement.
The electromagnetic field produced by a horizontal electric dipole over a double negative (DNG) medium half space is discussed, and the analytical expressions of the field which are convenient for calculation are derived. It can be concluded that the dipole on the configuration composed of the double positive (DPS) medium and the DNG medium half space can effectively excite the surface wave. The propagation wave number of the surface wave is less than that in both of the mediums, so that this kind of surface wave is a slow wave. Considered both the mediums are lossless, the amplitude of the surface wave decreases with the radial distance as ρ1/2. The total field shows complicated interference because of the superposition of three kinds of wave modes.
The relationship of permittivity tensor of anisotropic medium in principal coordinate system and laboratory coordinate system is given. The characteristic of permittivity tensor of uniaxial anisotropic medium in the laboratory coordinate system is discussed. The transverse permittivity of an anisotropic plate are reconstructed in laboratory coordinate system based on the resonance and polarization characteristics of back scattering radar cross section (RCS) in wide band. Then, a new scheme of reconstructing the principal axis direction for a uniaxial sample plate is proposed, subject to the principal axis is unknown. The back scattering characteristics of a sample plate are discussed when the electromagnetic (EM) wave of different polarization is incident perpendicularity to the sample plate. Three sample plates, which are cut perpendicularly to the x', y', and z' axis in the laboratory coordinate system, are required. A numerical reconstruction example is given to demonstrate the availability of presented scheme.
An objective of the present study is to make a physical insight into the radiation properties of an L-shaped wire antenna. More specifically, the study is focused on the effects of the antenna geometry over the characteristic radiation pattern of an L-shaped wire antenna. Regarding the basic equations for the radiated field, three main regions according to the length-height ratio of an L-shaped wire antenna have been determined. The said regions depict the geometrical boundaries where the L-shaped wire antenna loses its characteristic monopoletype radiation pattern. In this sense and relating to the aspect ratio of the L-shaped antenna, the said radiation properties can be easily varied in order to achieve a half isotropic radiation pattern or even, a patch-type radiation pattern. Thus, the method described herein demonstrates that simple modifications applied to the geometry of a basic structure, allow obtaining radiation properties associated to more complex structures.
A model of the ring waveguide of a fixed cross-section and variable distribution of the surface impedance of waveguide's wall has been considered. For a class of circular hodographs of surface impedance the analytical solution of the corresponding boundary-value problem has been obtained. This solution has been used for simulating a 'cycle slipping' phenomenon, known from the observations of VLF signals propagating over long paths in the earth-ionosphere waveguide, with the goal of clarifying the cause for its initiation. Numerical experiments have shown that this phenomenon, in the context of the model in question, is a consequence of the interconversion of two dominant waveguide modes in circumstances where their propagation constants are close.
In this paper, a novel algorithm for computing Physical Optics (PO) integrals is introduced. In this method, the integration problem is converted to an inverse problem by Levin's integration algorithm. Furthermore, the singularities, that are possible to occur in the applications of Levin's method, are handled by employing trapezoidal rule together with Levin's method. Finally, the computational accuracy of this new method is checked for some radar cross section (RCS) estimation problems performed on flat, singly-curved and doubly-curved PEC plates which are modeled by 8-noded isoparametric quadrilaterals. The results are compared with those obtained by analytical and brute force integration.
A hybrid technique based on finite-difference frequency domain (FDFD) and particle swarm optimization (PSO) techniques is proposed to reconstruct the angular crack width and its position in the conductor and ability to detect the crack width, position, and its depth in single and multilayer dielectric objects. FDFD is formulated to calculate the scattered field after illuminating the object by a microwave transmitter. Two-dimensional model for the object is used. Computer simulations have been performed by means of a numerical program; results show the capabilities of the proposed approach. This paper presents a computational approach to the two dimensional inverse scattering problem based on FDFD method and PSO technique to determine the crack position, width and depth. By using the scattered field, the specifications of the crack are reconstructed.
A systematic method for the diagnosis of planar antenna arrays from far field radiation pattern using neural networks is presented. Two types of neural networks, Radial basis function (RBF) and Probabilistic neural network (PNN) are considered for the performance comparison. Deviation pattern is used as input to the neural network to determine the location of the faulty element and error in excitation.
The shimming method used for producing high field homogeneity of the open permanent main magnet for magnetic resonance imaging (MRI) is researched in this paper. The central shimming method based on integer programming is proposed, which fulfills the combination of optimal theory and the practical manual shimming. The formulation of shimming is solved by using Lingo software and the numerical analysis method is used to compute the contribution of small shim arrays. The homogeneity of imaging region is eventually advanced nearly by 50%.The validity of the method is validated by using simulation test of shimming. The efficiency of shimming is improved through experiment corporated with the manufacturing enterprise.
Perfect electromagnetic conductor (PEMC) is a medium where certain linear combinations of electromagnetic fields are required to vanish. Since PMC has found important applications in antenna design, one may expect that PEMC will also have potential for similar applications; therefore it is important to investigate its radiation properties. In this paper, dyadic Green functions in integral forms have been derived for a structure with a dielectric layer on a PEMC plane. Whereas electric and magnetic dyadic Green functions is required to satisfy the dyadic mixed boundary condition on PEMC surface, a new classification of the electric and magnetic dyadic Green functions has been introduced based on parameter M of PEMC boundary. This classification is general and contains classes of dyadic Green functions which satisfy Dirichlet and Neumann boundary conditions.
In classical antenna books, the field radiated by a filamentary antenna is calculated integrating the electrical current induced over the wires as if it was a primary (impressed) source. This is no technically incorrect, but is not rigorous. In this paper some formal steps are added to the classical procedure to do it more rigorous.
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