Numerically Efficient Techniques for Electromagnetic Scattering Calculations in the Frequency Domain

Questo lavoro di tesi si prefigge lo scopo di sviluppare algoritmi numerici nel dominio della frequenza al fine di superare alcuni dei limiti che caratterizzano le tecniche convenzionali di analisi elettromagnetica. In particolare, nel primo capitolo, è riportata una formulazione MoM la quale, impiegando espressioni analitiche per il campo elettromagnetico radiato da un dipolo elettricamente corto, riesce ad evitare l’utilizzo di equazioni a potenziali misti e di conseguenza i relativi problemi a bassa frequenza e il trattamento della singolarità proprio della funzione di Green. Nel terzo capitolo verrà introdotto l’algoritmo di tipo Dipole Moment e la sua applicazione alla risoluzione di problemi di scattering elettromagnetico. In particolare verrà dimostrato che la suddetta tecnica permette di risolvere agevolmente problemi caratterizzati da perdite e spessori finiti senza incorrere in matrici numericamente mal condizionate. La soluzione di problemi di tipo multiscala, i quali coinvolgono contemporaneamente oggetti sia piccoli che grandi rispetto alla lunghezza d’onda, risulta spesso fortemente onerosa dal punto di vista computazionale costringendo a sacrificare l’accuratezza del risultato finale a causa delle limitate risorse di calcolo a disposizione. Al fine di superare i problemi precedentemente citati, nell’ultima parte dell’elaborato verrà introdotta una tecnica ibrida che combina il metodo Dipole Moment con un nuovo algoritmo ricorsivo nel dominio della frequenza, il RUFD. Tale metodo si è infatti dimostrato essere vantaggioso sia in termini di tempo che di occupazione di memoria rispetto ai principali solutori elettromagnetici disponibili in commercio

The Dipole Moment (DM) and Recursive Update in Frequency Domain (RUFD) Methods: Two Novel Techniques in Computational Electromagnetics

In this paper, we begin by introducing a novel concept for formulating electromagnetic simulation problems that is based on the use of the Dipole Moment (DM) approach, which has several desirable features. First, it circumvents the need to deal with the singularity that is inherently encountered during the process of evaluating the matrix elements in the conventional Method of Moments (MoM) formulation based on the Green's function approach. Second, it handles both dielectric and conducting materials, be they lossy or lossless, in a universal manner, without employing different starting points for the formulation. This enables us to handle inhomogeneous problems in a convenient manner using a single formulation. Third, it does not suffer from the so-called “low-frequency breakdown” problem in the conventional MoM formulation, which is presently handled by using special basis functions, such as the loop-star. Fourth, it enables us to hybridize with finite methods to solve multi-scale problems in a convenient manner

Low-Sar Hexa-Band Antenna For Mobile Applications

In this work, we describe a hexa-band mobile phone antenna with a metallic backing, designed for SAR reduction. The proposed antenna has a simple structure comprising of two radiating strips and a coupling strip which serves to enhance the bandwidth at high frequency. The antenna has been designed to cover multiple bands, namely LTE Band 13 (747-787 MHz); DCS 1800 (1710-1880MHz); PCS 1900 (1850-1990MHz); WCDMA (1920-2170MHz); LTE Band 40 (2300-2400 MHz); and Band 41 (2496-2690MHz). The designed antenna only occupies a small area of 15×29.5 mm2 on the system circuit board. By adjusting the shape, location and size of the backing, the SAR is effectively reduced over all of the bands, while the efficiency of the antenna is preserved. Thus, the antenna is an excellent candidate for incorporation into smart phones for next generation wireless systems

Numerical Analysis of the Electric Field Distribution within Complex Cell Structures

This paper shows the importance of using realistic cell shapes with the proper geometry and orientation to study the mechanism of direct cellular effects from RF exposure. For this purpose, the electric field distribution is computed, using the FDTD technique, in realistic cell models exposed to a linearly polarized plane wave of frequencies 900 MHz and 2.45 GHz. Furthermore, an insight on the mutual interactions between erythrocyte cell models shows that polarizing effects significantly affect the values of field intensity within the cell. © 2008 EuMA

Efficient Analysis Of Scattering By Strip Gratings

Plane wave scattering by a perfectly conducting strip grating is considered. A methodology for the computation of the induced currents is proposed, which utilizes the knowledge of the current induced in the center region of a truncated finite grating with only a moderate number of strips

Efficient modeling of conformal Frequency Selective Surfaces using the characteristic basis function method

The paper presents a numerically efficient and accurate technique for the analysis of large, finite and conformal Frequency Selective Surfaces (FSSs) that are not amenable to analysis by using conventional methods applicable to infinite, planar and doubly-periodic FSSs. The proposed technique begins by employing the Characteristic Basis Functions (CBFs) to describe the currents induced on the elements. The reaction integrals needed to derive the reduced matrix elements are either computed in the spatial domain or in the spectral domain, depending on their separation distance, so as to make the process numerically efficient. © 2013 IEICE

Volume Integral Equation Analysis of Thin Dielectric Sheet Using Sinusoidal Macro-Basis Functions

In this letter, we present an improvement over the conventional thin dielectric sheet (TDS) formulation for the analysis of thin dielectric sheets. Our focus is to address the problem of scattering from thin penetrable scatterers by developing a volumetric formulation based on the use of macro-basis functions. The electric fields produced by the source basis functions are derived directly, bypassing the summation of scalar and vector potentials. The latter results in a considerable time advantage in comparison to the conventional method of moments (MoM) solution of the volume electric field integral equation (V-EFIE), while the accuracy remains comparable. In contrast to the TDS formulation, both tangential and normal currents are employed so that problems with high and low permittivity, as well as those involving grazing incident angles, can be accurately analyzed. Several examples are reported that show excellent agreement with conventional techniques and demonstrate the effectiveness of the new approac