Amir Boag

A multilevel matrix decomposition algorithm for analyzing scattering from large structures

A multilevel algorithm is presented for analyzing scattering from electrically large surfaces. The algorithm accelerates the iterative solution of integral equations that arise in computational electromagnetics. The algorithm permits a fast matrix-vector multiplication by decomposing the traditional method of moment matrix into a large number of blocks, with each describing the interaction between distant scatterers. The multiplication of each block by a trial solution vector is executed using a multilevel scheme that resembles a fast Fourier transform (FFT) and that only relies on well-known algebraic techniques. The computational complexity and the memory requirements of the proposed algorithm are O(N log/sup 2/ N).

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.

Design of electrically loaded wire antennas using genetic algorithms

A novel antenna design procedure based on genetic algorithm (GA) driven optimization is proposed and applied to the synthesis of wire antennas loaded with lumped components. Loading circuit parameters, locations of the loads along the antenna, as well as matching network parameters, are optimized simultaneously. A computational scheme based on the Sherman-Morrison-Woodbury formula for the fast evaluation of the antenna performances for many distinct loading configurations is developed. The GA iteratively guides a population of randomly selected design candidates toward the optimal solution. The success of the proposed procedure is demonstrated through its application to the design of efficient ultra-broadhanld antennas and their corresponding matching networks.

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. >

Highly Efficient and Broadband Wide-Angle Holography Using Patch-Dipole Nanoantenna Reflectarrays

We demonstrate wide-angle, broadband, and efficient reflection holography by utilizing coupled dipole-patch nanoantenna cells to impose an arbitrary phase profile on the reflected light. High-fidelity images were projected at angles of 45 and 20° with respect to the impinging light with efficiencies ranging between 40-50% over an optical bandwidth exceeding 180 nm. Excellent agreement with the theoretical predictions was found at a wide spectral range. The demonstration of such reflectarrays opens new avenues toward expanding the limits of large-angle holography.

Complex multipole beam approach to electromagnetic scattering problems

A novel approach to reducing the matrix size associated with the method of moments (MoM) solution of the problem of electromagnetic scattering from arbitrary shaped closed bodies is presented. The key step in this approach is to represent the scattered field in terms of a series of beams produced by multipole sources located in a complex space. On the scatterer boundary, the fields generated by these multipole sources resemble the Gabor basis functions. By utilizing the properties of the Gabor series, guidelines for selecting the orders as well as locations of the multipole sources are developed. It is shown that the present approach not only reduces the number of unknowns, but also generates a generalized impedance matrix with a banded structure and a low condition number. The accuracy of the proposed method is verified by comparing the numerical results with those derived by using the method of moments. >

Reconstruction of electrostatic force microscopy images

An efficient algorithm to restore the actual surface potential image from Kelvin probe force microscopy measurements of semiconductors is presented. The three-dimensional potential of the tip-sample system is calculated using an integral equation-based boundary element method combined with modeling the semiconductor by an equivalent dipole-layer and image-charge model. The derived point spread function of the measuring tip is then used to restore the actual surface potential from the measured image, using noise filtration and deconvolution algorithms. The model is then used to restore high-resolution Kelvin probe microscopy images of semiconductor surfaces.

Rotation-induced superstructure in slow-light waveguides with mode-degeneracy: optical gyroscopes with exponential sensitivity

We study wave propagation in a rotating slow-light structure with mode degeneracy. The rotation, in conjunction with the mode degeneracy, effectively induces superstructure that significantly modifies the structures dispersion relation. It is shown that a rotation-dependent stop band is formed in the center of the slow-light waveguide transmission curve. A light signal of frequency within this stop band that is excited in a finite-length section of such a waveguide decays exponentially with the rotation speed and with the coupled resonator optical waveguides total length or total number of degenerate microcavities. This effect can be used for optical gyroscopes with exponential-type sensitivity to rotation.

Analysis of TE scattering from dielectric cylinders using a multifilament magnetic current model

A moment solution is presented for the problem of transverse electric (TE) scattering from homogeneous dielectric cylinders. The moment solution uses fictitious filamentary magnetic 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. >

Nonuniform polar grid algorithm for fast field evaluation

A novel algorithm to efficiently compute time-harmonic fields produced by known two-dimensional source constellations is proposed. The algorithm relies on domain decomposition and comprises two steps to be repeated for each subdomain. In the first step, phase, and amplitude compensated fields, produced by currents residing within each subdomain are computed over a sparse set of points surrounding the observation domain. During the second step, total fields in the observer domain are evaluated by interpolation, phase and amplitude restoration and aggregation of subdomain fields. The proposed approach is applied to the fast iterative analysis of scattering phenomena using the method of moments.