Yehuda Leviatan

On the use of wavelet expansions in the method of moments (EM scattering)

An approach which incorporates the theory of wavelet transforms in method-of-moments solutions for electromagnetic wave interaction problems is presented. The unknown field or response is expressed as a twofold summation of shifted and dilated forms of a properly chosen basis function, which is often referred to as the mother wavelet. The wavelet expansion can adaptively fit itself to the various length scales associated with the scatterer by distributing the localized functions near the discontinuities and the more spatially diffused ones over the smooth expanses of the scatterer. The approach is thus best suited for the analysis of scatterers which contain a broad spectrum of length scales ranging from a subwavelength to several wavelengths. Using a Galerkin method and subsequently applying a threshold procedure, the moment-method matrix is rendered sparsely populated. The structure of the matrix reveals the localized scale-fitting distribution long before the matrix equation is solved. The performance of the proposed discretization scheme is illustrated by a numerical study of electromagnetic coupling through a double-slot aperture. >

Single-Post Inductive Obstacle in Rectangular Waveguide

A rapidly converging moment solution for electromagnetic scattering by a single inductive post in a rectangular waveguide is obtained. The numerical results show good agreement with Marcuvitzs data as far as this data goes. Furthermore, Marcuvitzs curves are extended to cover data for large posts. This new data should aflow one to design a simply constructed new type of narrow bandpass filter, namely, a filter consisting of large single posts. The successful use of this straightforward moment solution in solving the single-post problem suggests that this technique should prove useful in solving a variety of microwave discontinuities such as those involving thin or thick irises and posts of arbitrary shape.

A selectively coated photonic crystal fiber based surface plasmon resonance sensor

We propose a novel design for a photonic crystal fiber based surface plasmonic resonance sensor. The sensor consists of selectively metal-coated air holes containing analyte channels, which enhance the phase matching between the plasmonic mode and the core-guided mode. Good refractive index sensitivity as high as 5500 nm/RIU (refractive index unit) can be achieved in the proposed structure. Compared with the entirely coated structure, the selectively coated sensor design demonstrates narrower resonance spectral width. Moreover, the greater resonance depth can improve the sensing performance in terms of signal to noise ratio (SNR). The improvements in spectral width and SNR can both contribute to a better detection limit for this refractive index sensor.

Analysis of electromagnetic scattering from dielectric cylinders using a multifilament current model

A moment solution is presented for the problem of transverse magnetic (TM) scattering from homogeneous dielectric cylinders. The moment solution uses fictitious filamentary currents to simulate both the field scattered by the cylinder and the field inside the cylinder and in turn point-matches the continuity conditions for the tangential components of the electric and magnetic fields across the cylinder surface. The procedure is simple to execute and is general in that cylinders of arbitrary shape and complex permittivity can be handled effectively. Metallic cylinders are treated as reduced cases of the general procedure. Results are given and compared with available analytic solutions, which demonstrate the very good performance of the procedure.

Generalized formulations for electromagnetic scattering from perfectly conducting and homogeneous material bodies-theory and numerical solution

A generalized E-field formulation for three-dimensional scattering from perfectly conducting bodies and generalized coupled operator equations for three-dimensional scattering from material bodies are introduced. A fictitious electric current flowing on a mathematical surface enclosed inside the body is used to simulate the scattered field, and, in the material case, a fictitious electric current flowing on a mathematical surface enclosing the body is used to simulate the diffracted field inside the body. Application of the respective boundary conditions lead to operator equations to be solved for the unknown fictitious currents, which facilitates calculation of the fields in the various regions, using the magnetic vector potential integral. The existence and uniqueness of the solution are discussed. These alternative operator equations are solvable using the method of moments. The numerical solution is simple to execute, rapidly converging, and general in that bodies of smooth but otherwise arbitrary surface, both lossless and lossy, can be handled effectively. Comparison of the results with available analytic solutions demonstrates the accuracy of the moment procedure. >

Novel method of UWB antenna optimization for specified input signal forms by means of genetic algorithm

A novel optimization procedure for the design of antennas for ultrawideband (UWB) wireless communication systems is presented. The optimization is based on the time-domain characteristics of the antenna. The optimization procedure was applied to a simplified version of the volcano smoke antenna proposed by Kraus. However, any other type of UWB antenna can be treated with the same technique. Our optimization procedure aims at finding an antenna not only with low VSWR but also a low-dispersion one which will ensure high correlation between the time-domain transmitting antenna input signal and the receiving antenna output signal. In pulse communications systems, usually an input signal form suited to a particular purpose is used. Hence, we strive to design the best antenna for a given input signal form. The optimization technique adopted here makes use of genetic algorithm (GA) search concepts. The electromagnetic analysis of the antenna is done by means of a finite-difference time-domain method using the commercially available CST Microwave Studio software

Multiband Flat-Plate Inverted-F Antenna for Wi-Fi/WiMAX Operation

A printed multiband flat-plate inverted-F antenna (IFA) is presented. The antenna is complexly structured and can operate as an internal laptop antenna over multiple Wi-Fi and WiMAX frequency bands. The antenna was studied by means of numerical simulations. The predicted achievable -10 dB return loss bandwidth of the antenna is confirmed and demonstrated by experimental measurements.

Analytic continuation considerations when using generalized formulations for scattering problems

A generalized operator equation has been developed for a simple scattering problem for which a closed-form solution exists. The operator equation has been solved numerically via the method of moments using spatially impulsive fictitious sources as expansion functions together with a simple point-matching testing procedure. The study focused on the convergence and accuracy of the solution and examined how they are dependent on the location and distance of the fictitious sources relative to the area containing the singularities of the actual field simulated by these sources. As expected, it was found that when the actual field simulated by the fictitious impulsive sources has singularities lying between the physical boundary and the closed surface over which the sources are placed, the impulsive expansion does not yield a uniformly convergent solution. In this case, instabilities are encountered as the number of sources increases, in the sense that a small improvement of the boundary error requires a considerable change in the currents. The moment matrix is then difficult to invert and easily susceptible to large round-off errors. Conversely, if the actual field has no singularities lying between the physical boundary and the closed surface over which the sources are placed, the impulsive expansion does yield a uniformly convergent solution to any degree of precision. >

Analysis of Inductive Dielectric Posts in Rectangular Waveguide

A rapidly converging moment solution for the complete analysis of homogeneous dielectric posts of the inductive type in rectangular waveguide is presented. The moment method approach uses filamentary currents to simulate both the field scattered by the post and the field inside the post and in turn point-matches the continuity conditions for the tangential components of the electric and magnetic fields across the post surface. The procedure is simple to execute and is general in that inductive posts of arbitrary smooth shape, size, location, and number, Iossless as well as lossy, can be handled effectively. Data are given and compared with the few cases for which approximate results are available. The technique is further appfied to other situations where no experimental data or other analytic results are available.

Multiple-Post Inductive Obstacles in Rectangular Waveguide

A complete analysis of multiple-post inductive obstacles in rectangular waveguide is presented. A moment method solution with exponential ( e/sup jnTheta/) expansion and weighting functions is used in a Galerkin solution. Post currents are expressed as a Fourier series. As many Fourier series terms (e/sup jn Theta/) as desired may be included. All higher order (cutoff) mode interactions between posts are taken into account. The solution is rapid and accurate, and errors maybe controlled (specified). Data are given for the triple-post obstacle and for a two-element filter.