Four-dimensional differential-form formalism is applied to define the duality transformation between electromagnetic fields and sources. The class of linear media invariant in any non-trivial duality transformation is labeled as that of self-dual media. It is shown that the medium dyadic of a self-dual medium, which represents a mapping between the two electromagnetic field two-forms, satisfies a quadratic algebraic equation. Further, it is shown that fields and sources in a self-dual medium can be decomposed in two uncoupled sets each self-dual with respect to a duality transformation. Also, for each of the decomposed fields the original medium can be replaced by a simpler effective medium. Splitting the electromagnetic problem in two self-dual parts can be used to simplify the solution process because differential equations for fields are reduced to those with second-order scalar operators. This is applied to find plane-wave solutions for the general self-dual medium.
Weak signal detection and localization are basic and important problems in radar systems. Radar performance can be improved by increasing the receiver output signal-to-noise ratio (SNR). Localizing the received signal is an important task in the detection of signal in noise. Distorting the localization of the received signal can leads to incorrect target range measurements. In this paper an algorithm is described for extracting and localizing an RF radar pulse from a noisy background. The algorithm combines two powerful tools: the wavelet packet analysis and higher-order-statistics (HOS). The use of the proposed technique makes detection and localization of RF radar pulses possible in very low signal-to-noise ratio conditions, which leads to a reduction of the required microwave power or alternatively extending the detection range of radar systems.
The inductive effect of near-end crosstalk for a category five unshielded, twisted-pair cable has been verified using the electromagnetic topology simulation method. Crosstalk reduction and its dependency on such parameters as driving signals, circuit configuration and impedance, are studied. The simulation results are consistent with analytical analysis. Results show that the straight- through, differential-generator, twisted-pair receptor model is the most effective configuration to control the near-end crosstalk level. This is due to the influences from both the neutralizing mutual inductance and the single current generator. The simulation results also show that electromagnetic topology-based predictions are valid only for cables that are electrically short. Simulations are carried out using a compaction scheme with a single equivalent circuit. As a result, the unshielded, twisted-pair cable portion of the circuit can be combined with a larger network for analyzing the overall response of the entire network system.
This paper is concerned with the diffraction of an electromagnetic wave by a perfectly conducting half-plane in a homogeneous bi-isotropic medium (asymptotically). Similar analysis in a source-free field is done in S. Asghar and A. Lakhtakia (1994), Planewave diffraction by a perfectly conducting half-plane in a homogeneous bi-isotropic medium. Int. J. Appl. Electromagnetics in materials, 5, (1994), 181-188. In this paper attention is focused on the wave coming from a line source. The objective is to study the scattering of an electromagnetic wave from the boundary of a half-plane and thereby to provide a theoretical framework for the line source diffraction asymptotical ly. In far field approximation it is shown that an incident wave coming from a line source behaves like a plane wave. The scattered field is calculated by using the Fourier transform and the Wiener-Hopf techniques. The scattered field in the far zone is determined by using contour integration.
In this paper, a fast method is presented to model the forward propagation above Gaussian rough surfaces and taking into account atmospheric refraction. The method is based on the Discrete Mixed Fourier Transform (DMFT) solved by the Parabolic Wave Equation, in which the Ament boundary condition with shadowing effect is used at grazing angle. In this model, for a bistatic configuration, the surface height PDF of the illuminated points is derived and it is introduced in the boundary condition. Examples demonstrate the capacities of the method to compute propagation factor above rough surfaces following Gaussian statistics and Gaussian height correlation and the proposed method is validated by comparison to a Monte Carlo approach.
The complete set of dyadic Green's functions (DGFs) for an electrically gyrotropic medium is obtained using a new formulation technique, which consists of a matrix method with dyadic decomposition in the k-domain. The analytic expressions for DGFs are represented in a unique form in terms of characteristic field vectors that exist in an electrically gyrotropic medium. It is shown that the dyadic decomposition greatly facilitates the calculation of an inverse operation, which is crucial in derivation of Green's functions. The DGFs found here can be used to solve electromagnetic problems involving the ionosphere and new types of anisotropic materials such as ceramics and advanced composites.
One of the most interesting and peculiar phenomena of Quantum Mechanics is the interference (I ) induced by the electrons. Strangely enough, though the electrons are real particles, they often behave just like waves. From the point of view of the classical mechanics the I induced by the electrons is unexplainable, however it is solved mathematically using the formalism of quantum mechanics and applying Schrödinger's equation. The quantum solution of the problem is clear and elegant, especially from a mathematical point of view, however it still leaves some perplexities as to understand how exactly the phenomenon happens. We will make a hypothesis trying to understand the undulation phenomenon of the electron: it is really a strange and mysterious phenomenon. Maybe if we consider that the electron, just as the baryons and the mesons, might be made of smaller particles (saving the integrity of the unity of the negative electrical charge and the other Laws of Conservation), we could understand more easily how a single electron can go through two close holes at the same time. Analogously we could better understand another very particular quantum phenomenon carried out mainly by electrons, that is the tunnel effect. In this case, though the particle does not have enough energy to go through the potential barrier, though it does not have any material possibility to pass through a layer which does not have any hole, after several "attempts" the particle will manage to pass through the barrier anyway, as it had dug a tunnel, or as it had managed to find a "breach" in the wall. In this phenomenon too, though we can explain it from a mathematical point of view, using the equations of the quantum mechanics, it is still not clear how actually the electron manages to have an undulation behaviour.
A method is proposed for analysis of arbitrarily loaded lossy and dispersive nonuniform single or coupled transmission lines. In this method, the transmission lines are subdivided to several uniform sections, at first. Then the voltage and current distributions are obtained using second order step-by-step numerical integration (second order finite difference method). The accuracy of the method is studied using analysis of some special types of single and coupled transmission lines.
In this article, we propose to apply the Gabor expansion to describe magnetic and electric currents given on a regular curved interface in dimension 2. From this description, we show that the computation of the current radiation can be performed by the introduction of a new kind of gaussian beams. We call them the conformal gaussian beams. Their analytic formulation is obtained using an asymptotic evaluation of the radiation integrals. Their properties are discussed and an application example is presented.
Active microwave imaging is explored as an imaging modality for early detection of breast cancer. When exposed to microwaves, breast tumor exhibits electrical properties that are significantly different from that of healthy breast tissues. The two approaches of active microwave imaging - confocal microwave technique with measured reflected signals and microwave tomographic imaging with measured scattered signals are addressed here. Normal and malignant breast tissue samples of same person are sub jected to study within 30 minutes of mastectomy. Corn syrup is used as coupling medium, as its dielectric parameters show good match with that of the normal breast tissue samples. As bandwidth of the transmitter is an important aspect in the time domain confocal microwave imaging approach, wideband bowtie antenna having 2:1 VSWR bandwidth of 46% is designed for the transmission and reception of microwave signals. Same antenna is used for microwave tomographic imaging too at the frequency of 3000 MHz. Experimentally obtained time domain results are substantiated by finite difference time domain (FDTD) analysis. 2-D tomographic images are reconstructed with the collected scattered data using distorted Born iterative method. Variations of dielectric permittivity in breast samples are distinguishable from the obtained permittivity profiles.
The open-sleeve antenna is analyzed using the method of moment. Emphasis is given to the analysis of the VSWR of the antenna. The multi-band characteristic of the sleeve antenna are investigated. The 1st and the 3rd frequency bands come from the driven dipole, and the 2nd frequency band is due to the length of parasitic elements and the distance between the driven element and the parasitic elements. Some useful results are presented and discussed in this paper.
An analytical solution for the radiation by a prolate hemispheroidal dielectric resonator antenna (DRA) over an infinite ground plane excited by a rectangular slot is presented. The dyadic Green's functions pertaining to a magnetic-current source are used in a form convenient for numerical computations. The dyadic Green's functions are then employed to formulate the electromagnetic fields radiated by the DRA. The electromagnetic far field is expressed analytically in a compact form. The far field patterns for different design parameters are computed and plotted.
The finite-difference time-domain (FDTD) method is used to obtain numerical solutions of infinite periodic structures without resorting to the complex frequency-domain analysis, which is required in traditional frequency-domain techniques. The field transformation method is successfully used to model periodic structures with oblique incident waves/scan angles. Maxwell's equations are transformed so that only a single period of the infinite periodic structure is modeled in FDTD by using periodic boundary conditions (PBCs). When modeling periodic structures with the transformed fields, the standard Mur second-order absorbing boundary condition cannot be used directly to absorb the outgoing waves. This paper presents a new implementation of Mur's second-order absorbing boundary condition (ABC) with the transformed fields in the FDTD method. For designs that require multi-parametric studies, Mur's ABCs are efficient and sufficient boundary conditions. If more accurate results are needed, the perfectly matched layer (PML) ABC can be used with the parameters obtained from the Mur solution.
We consider possible magnetic symmetries of two-dimensional square lattices with circular ferrite rods magnetized by a uniform dc magnetic field. These structures can be used as tunable and nonreciprocal photonic crystals. Classification of eigenmodes in such crystals is defined on the basis of magnetic group theory and the theory of (co)representations. Some general electromagnetic properties of the magnetic crystals such as change in the basic domain of the Brillouin zone, change of symmetry in limiting cases, bidirectionality and nonreciprocity, symmetry relations for the waves and lifting of eigenwave degeneracies by dc magnetic field are also discussed.
A novel approach based on spatiotemporal differential- operators is developed here for broadband, velocity-dependent scattering. Unlike the spectral-domain representations, the new method facilitates a compact formulation for scattering by arbitrary excitation signals, in the presence of moving objects. In free space (vacuum), relativistically exact formulas are developed. After developing the general theory, analysis of relativistically exact free-space scattering by cylinders, and a half-plane, are examined. For cylinders the analysis shows that in the far field pulses are located on circles in the co-moving reference-frame where the ob ject is at-rest. In other reference frames this feature is valid only as an approximation. These results apply also to the diffractive part of the half-plane scattered field. The geometrical-optics contribution is associated with plane-waves and obeys the appropriate transformations. The various zones for these fields in an arbitrary reference-frame are analyzed.
Due to the proximity of mobile phones to users' heads and resulting interrogations on potential health effects, as well as to the development of promising medical applications of electromagnetic waves such as non-invasive RF Hyperthermia treatments, near-field interactions between antennas and lossy scatterers, such as human beings, have been a topic of growing interest over the last decade. More generally, for various kinds of radiating sources and targets, much scientific effort has been done to answer the following question in particular configurations: what is the minimal/maximal power that can be absorbed in a lossy ob ject located in the reactive field region of an antenna? The aim of this paper is to propose a general and analytical solution to this problem, applicable to any source-scatterer system. To this purpose, a method, allowing to describe power deposition mechanisms in near-field regions, is introduced. This approach is based on an equivalent junction/circuit model which is shown here to result from an appropriate modal expansion of the radiated field. The dual interpretation of this model in terms of localized circuit and lumped junction is used to demonstrate how trends and bounds in power absorption phenomena can be derived. Firstly, the analogy with the microwave circuit theory provides the concepts of available power and load factor for electromagnetic fields, which allow to highlight the parameters influencing power dissipation and to analyze consequent trends. Secondly, the junction matrix formalism is used to obtain analytical lower and upper bounds of the power absorbed in a lossy object, located in the near field region of any radiating source. Those bounds give a clearer insight of the relationship between the total radiated power due to the antenna and the minimal or maximal power potentially dissipated in any scatterer exposed to such a radiated field. An example of bounds in a simple source-load configuration is finally provided, showing the link, to be further investigated, between the near-zone electric-field pattern of the antenna and the total dissipated power. This example also suggests that the power dissipated in a given object can be rapidly increased or reduced as the modal complexity of the source increases.
In this work the solution to the problem of electromagnetic radiation from (pre-)fractal antennas is performed by means of Plane- Wave field representation based on closed-form Fourier transforms of the self-similar current patterns. The generalization to the case of uniformly translating antennas is then accomplished through the Frame-Hopping Method by exploiting special-relativistic covariance properties of Plane-Wave spectra.