This article discusses the effect of geometry on the surface plasmon resonances. The static dielectric polarizability of a sphere suffers a singularity when its permittivity relative to the surroundings is -2. This well-known resonance condition is changed when the shape of the particle is no longer a sphere. In this article the character of the resonances is studied,with a particular emphasis on a two-layer sphere.
Higher integration and smaller layout size, two major trends in today's industry, lead to more prominent electromagnetic coupling with direct applications in the RF/microwave area such as directional couplers, filters, multiplexers, shifters, delay lines, etc. In the present work, an efficient hybrid-mode method is presented for a rigorous characterization of the coupling in multilayer bilateral microwave circuits including anisotropy effects. Various types of planar configurations were considered including microstrip, finline and coplanar structures, but the proposed approach can easily be extended to any form of coupled lines. To fully characterize bilateral multilayer circuits in millimetre wave region with an arbitrary number of conductors, closed forms of dyadic Green's functions were determined in the spectral domain, with use of the Galerkin technique. The computed results show good agreement with data available in the literature. Furthermore, two original configurations based on three line bilateral couplers were computed and validated using neural network models.
This paper presents electromagnetic energy absorption in the homogeneous and layered human body models due to body-worn UWB antennas, at frequencies of 3, 6 and 8 GHz. Typical small planar UWB antennas are used in this study: printed UWB disc monopole and UWB slot antenna. Distances of 2, 5 and 10mm (reactive near-field region) between antennas and human body were chosen, approximating realistic scenarios of operation in Wireless Body Area Networks. To approximate different parts of the human body, or body variations among different users, we compare results obtained for the planar homogeneous (muscle) model with those for three-layer body models (skin, fat and muscle), with different thicknesses of the skin (0.5- 2mm) and fat (1-9mm) tissue. For these body models we investigate the electromagnetic energy absorption mechanism by examining the peak 1-g SAR and peak SAR (without mass averaging). Based on our results we present and discuss new finding concerning the general electromagnetic energy absorption mechanism in human tissues under reactive near-fields exposure conditions.
The general dispersion relation for a nonreciprocal electrically gyrotropic or a gyroelectric medium is derived in two distinct forms by using three different methods. One of them is a new method which can be used when the stratification of the layers is in the z-direction. The wave numbers corresponding to each dispersion relation are obtained in closed form. It is shown that there exist two types of waves, type I and type II, in a gyroelectric medium. The wave propagation is investigated and the polarization of the waves, resonances and cut off conditions are obtained for the principle waves. The general wave propagation regions are identified using resonances and cut off conditions. These regions are then used to construct the Clemmow-Mually-Allis (CMA) diagram. The conditions showing the frequency bands for which wave can propagate in each region are tabulated for the first time. The results presented in this paper can be used in the development of nonreciprocal devices and in ionospheric problems including radiation and scattering applications.
A novel, potential and efficient microwave direct contact hyperthermia applicator referred to as water-loaded box-horn for therapeutic heating of bio-medium is designed and developed at 915 and 2450MHz. Also, theoretical expressions for fields in bio-medium as produced by a direct contact box-horn applicator have been derived using plane wave spectral technique. The box-horn is a special type of dual mode horn antenna which supports TE10- and TE30- modes. Therefore, the aperture field distribution over the H-plane of the box-horn is nearly uniform which prevents steep temperature gradients in the heating medium. Water-loading of the box-horn provides a better impedance match to the bio-medium and hence better coupling of microwave energy into bio-medium. Also, it reduces the size of box-horn applicator considerably. The SAR distributions in bio-medium in direct contact with water-loaded box-horn have been computed theoretically with the developed analytical model and measured experimentally with the help of Agilent/HP vector network analyzer (8714 ET) at 915 and 2450MHz. The theoretical and experimental results for SAR are in nearly in agreement with each other. It is investigated that higher penetration depth, lower power absorption coefficient and higher half-power width/depth or lower resolution in heating medium are found for box-horn designed at 915MHz in comparison to those for box-horn designed at 2450MHz.
The guided modes in a left-handed material (LHM) asymmetric slab waveguide are studied in this paper. Dispersion properties of electromagnetic guided waves are discussed by introducing three normalized parameters. The guidance conditions of guided modes in waveguide are determined by using a graphical method. Then we put emphasis on the surface wave modes with respect to different waveguide parameters and structures. The power flux in LHM asymmetric waveguide according to the Poynting vector is investigated in the end.
This paper presents the results of profile inversion of multi-frequency electromagnetic scattered field data, measured by the Institute Fresnel, Marseille, France, from cylindrical objects, both for TM and TE illuminations. The reconstructions are obtained by applying the Multiplicative Regularized Contrast Source Inversion (MR-CSI) method. The results show that the MR-CSI method successfully performs 'blind' inversion of a wide class of scattered field data. Further, we also show that by inverting both TM and TE data simultaneously, a more accurate reconstructed image can be obtained.
Circularly symmetric patch antennas tuned by transversely magnetized lossy ferrite are studied. The circular and ring patch geometries printed on ferrite substrate or tuned by ferrite post and ferrite toroid are studied. Both saturated and partially magnetized ferrite are considered. Strong effects on the dispersive properties of modes propagating under the patch and in turn on the antenna resonant frequency and input impedance are observed when the ferrite losses are taken into account. The patch antennas resonance at a novel mode propagating in the traditionally assumed switch-off frequency range of negative effective permeability constitutes an essential original contribution of this work. In all cases the dynamic control of the patch resonant frequency through the DC-biasing field is investigated. The "perfect magnetic walls approximation" was employed in the analysis since it offers a valuable physical insight as well as simplified closed form expressions for the resonant conditions. These are used as engineering design formulas for an initial antenna design, which is in turn fine tuned with the aid of a numerical simulation-optimization scheme. The validity of the present method was verified through comparisons with published experimental results and numerical simulations.
Combined volume scattering with rough surface scattering effects in passive microwave remote sensing of wet snow is studied in this paper. The dense medium radiative transfer (DMRT) theory with quasicrystalline approximation (QCA) is used to describe the volume scattering model for densely distributed sticky coated dielectric particles. The Numerical Maxwell Model of 3D simulations (NMM3D) is used to simulate the rough surface bistatic scattering and emission, and the bistatic scattering coefficients and emissivity of the rough surfaces are utilized as the boundary conditions for the DMRT. Full multiple scattering solutions are calculated by solving the DMRT numerically. Wet snow model is adopted in this paper, the results are illustrated for a layer of wet snow over a moist rough ground at 18.7 GHz and 38.5GHz.
Abstract-Electromagnetic Interference (EMI) is becoming a crucial issue in the era of modern electronic systems. For EMI measurement, it is required to place a sensor to receive the radiation from the equipment in a suitable test environment. The performance of the sensor depends on its Antenna Factor, which is the ratio of the incident electric field on the antenna surface to the received voltage at the load end. Here, a Method of Moment-based numerical technique has been used to evaluate the performance of a sensor in different test environments with different wave impedances. The evaluation of the sensor has been performed in terms of the Antenna Factor. The results are presented for free space environment of impedance 377â„¦ and Gigahertz Transverse Electromagnetic (GTEM) Cell of characteristic impedance 50â„¦. The results show well agreement with experimental data.
In present paper, a novel and effective hyperthermia applicator utilizing an elliptically bent conformal array of longitudinal slots in narrow wall of rectangular waveguide is analyzed by two different approaches, viz., the vector potential method and Fresnel- Kirchhoff scalar diffraction field theory. The agreement between two theories is reasonably very good. This configuration is mainly intended as a specialized and very effective applicator for hyperthermia treatment of tumor within curved portions of human body such as abdomen, neck, chest etc. Each slot of the conformal array is excited by a coaxial line probe. It is proposed that the interior of the waveguide be filled with water to provide a good impedance match with the bio-medium. The contour distribution of specific absorption rate (SAR) in x-z plane, SAR distribution in y-direction and parameters such as penetration depth, power absorption coefficient, effective field size (EFS) due to the conformal array as well as single slot are evaluated and compared at 433 MHz. The results for contour SAR distribution at 433 MHz for elliptically bent conformal array are also compared with those for other array configurations such as circularly bent conformal array and planar array. The effect of change in phase and amplitude excitation of each slot of the array on SAR distribution is also examined. The results demonstrate that slotted waveguide conformal array offers marked improvement in SAR distribution and penetration depth over single slot. It also has better focusing ability as compared with planar array for controlled amplitude and phase excitations of the elements.
The technology of adaptive antennas is rapidly growing during the last years. It is true that switched beam antennas, the simplest type of smart antennas, may provide substantial benefits when implemented in a cellular mobile telephony system. The performance of a six-beam switched parasitic planar array, in terms of bit error rate (BER) measurement, is presented in this paper. The switched parasitic planar array is designed with the aid of genetic algorithms method. The antenna system is evaluated in a radio environment where interfering signals are present. The results obtained from the simulation are compared with respect to the ones when an omni directional antenna is used instead of the switched beam array, revealing that the performance of such a telecommunication system can be improved.
Artificial boundary conditions, which can be identified as Robin boundary conditions positioned at a complex space coordinate, are introduced in order to obtain pertinent approximations for the Green's functions in grounded layered media. These artificial boundary conditions include perfectly matched layers backed by perfectly electric or magnetic conductors. As a first result, we obtain analytical expressions for the differences of Green's functions sub ject to different boundary conditions. Since weighted sums of Green's functions are again Green's functions, the need arises to solve an optimization problem, in the sense of obtaining the optimal weighted mixture of Green's functions, as compared to the exact Green's function. Comprehensive eigenexpansions for the Green's functions are given in the general case, and a few examples illustrate the goodness of fit between the approximate Green's functions and the exact Green's function.
A Nyström method with edge condition (EC) is developed for electromagnetic scattering by two-dimensional (2D) open structures. Since EC correctly describes the edge behavior of currents on the scatterers, the use of it in Nystr Ìˆom method can dramatically coarsen the discretization near the edges. In the implementation of the scheme, we derive the closed-form expressions for the singular or near- singular integrations of Hankel functions multiplied by the polynomials with or without EC. This allows us to control the numerical errors efficiently by approximating the Hankel functions with more series terms and selecting higher-order polynomials to represent the currents in the local correction. The numerical results illustrate that the solutions with the use of EC converge much faster than without the use of EC. Also, EC is more essential in TM polarization than in TE polarization due to the singular behavior of current near edges.
The limited-memory quasi-Newton optimization method with simple bounds has been applied to develop a novel fully threedimensional (3-D) magnetotelluric (MT) inversion technique. This nonlinear inversion is based on iterative minimization of a classical Tikhonov-type regularized penalty functional. But instead of the usual model space of log resistivities, the approach iterates in a model space with simple bounds imposed on the conductivities of the 3-D target. The method requires storage that is proportional to ncpÃ—N, where the N is the number of conductivities to be recovered and ncp is the number of the correction pairs (practically, only a few). This is much less than requirements imposed by other Newton type methods (that usually require storage proportional to NÃ—M, or NÃ—N, where M is the number of data to be inverted). Using an adjoint method to calculate the gradients of the misfit drastically accelerates the inversion. The inversion also involves all four entries of the MTimp edance matrix. The integral equation forward modelling code x3d by Avdeev et al. [1, 2] is employed as an engine for this inversion. Convergence, performance and accuracy of the inversion are demonstrated on a 3D MTsyn thetic, but realistic, example.
In this paper a new technique for the evaluation of the Green's functions of filament sources in layered media, is presented. The technique is based on the annihilation of the asymptotic and singular behaviors of a spectral Green's function. The remaining function, after annihilation, is treated using a two levels discrete complex image method (DCIM). The application of the proposed technique, provides a complete analytical expression for the spatial Green's function, in terms of the iterative value of the propagation constant. This expression consists of the annihilating functions and a number of complex images. In order to validate the proposed technique, microstrip lines and slotlines are analyzed and the obtained results are found to agree very well with those obtained using a commercial software.
In this paper, we introduce a first order accurate resonance model based on a second order Padé approximation of the reflection coefficient of a narrowband antenna. The resonance model is characterized by its Q factor, given by the frequency derivative of the reflection coefficient. The Bode-Fano matching theory is used to determine the bandwidth of the resonance model and it is shown that it also determines the bandwidth of the antenna for sufficiently narrow bandwidths. The bandwidth is expressed in the Q factor of the resonance model and the threshold limit on the reflection coefficient. Spherical vector modes are used to illustrate the results. Finally, we demonstrate the fundamental difficulty of finding a simple relation between the Q of the resonance model, and the classical Q defined as the quotient between the stored and radiated energies, even though there is usually a close resemblance between these entities for many real antennas.