G. Gerosa

Electromagnetic scattering by an object in relativistic translational motion

An exact relativistic solution to the problem of electromagnetic wave scattering by uniformly translating bodies can be performed by applying Lorentz field transforming formulae to plane wave spectra representing impinging and scattered fields. An application to the two-dimensional problem of a monochromatic plane wave scattering for the case of one cylinder in the presence of a plane interface has been carried out. By virtue of a peculiar notation for electromagnetic vector fields used throughout the paper, the application of Lorentz formulae to plane waves and to plane-wave expandable fields can be easily expressed by altering propagation parameters (amplitude, frequency and direction).

Electromagnetic wave scattering by a perfectly conducting wedge in uniform translational motion

The exact relativistic solution to the problem of electromagnetic wave scattering by a perfectly conducting wedge in uniform translational motion is obtained on the ground of the Frame Hopping Method; a field representation in terms of plane-wave spectra allows us to apply Special Relativity covariance relations in terms of simple alteration rules for the wave parameters of the spectral components. Numerical simulations based on the analytic evaluation of Doppler frequency spectra, as measured by a fixed observer, are presented.

ELECTROMAGNETIC RADIATION FROM MOVING FRACTAL SOURCES: A PLANE-WAVE SPECTRAL APPROACH

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.

Stepped leaky-wave antennas for microwave and millimeter wave applications

This work presents the complete general features of a recently proposed class of leaky-wave antennas, derived from stepped rectangular-section waveguides with radiating slits. Based on very favorable topological features, straightforward but extremely effective design procedures are shown to be possible for achieving sophisticated radiation properties. Furthermore, new possibilities are considered as concerns in both the use of linear arrays to scan in two dimensions, and in the introduction of dielectric parts to improve the angular pointing range and to also protect the radiating elements. The analysis of all these properties illustrates very attractive characteristics and perspectives for this type of antenna which can profitably find applications both at microwaves and at millimeter waves.RésuméCet article présente les propriétés générates completes d’une classe d’antennes à onde de fuite récemment proposée, déduites des guides rectangulaires à sections en échelons avec fentes rayonnantes. Des caracteristiques topologiques favorables conduisent à des mprietesthodes simples mais efficaces pour obtenir les propri étés de rayonnement. En outre, des nouvelles possibilites concernent I’usage de réseaux rectilignes pour balayage bidimensionnel et l’introduction de portions diélectriques pour améliorer I’étendue de pointage angulaire et pour protéger les éléments rayonnants. L’analyse de ces propriétés illustre les caractéristiques et les possibilités intéressantes de ce type d’antenne qui peut trouver des applications dans les bandes hyperfréquences et millimétriques.

Experimental investigation on NRD-guide dual-mode filters

New interesting possibilities of implementation of high-performance dual-mode filters are analyzed by considering the non-radiative dielectric (NRD) waveguide components. The excitation and coupling of dual modes are investigated for NRD circular- and square-section dielectric resonators, and the influence of different perturbation techniques, such as tuning screws or cuts, is discussed. Various promising topologies of NRD-guide dual-mode filters are then suggested and tested to implement both classical and elliptic configurations.<<ETX>>

A convenient transmission-line formulation for wave propagation in typical ferrite structures

In this work, a simple and practical distributed-circuit model is rigorously carried out for schematizing wave propagation in transversely magnetized ferrites. Through this suitable transmission-line formalism, a very advantageous extension of the transverse resonance technique is also proved possible. Thus, a strong simplification is achieved as regards the electromagnetic analysis of a variety of important nonreciprocal devices employing waveguides partially filled with ferrite slabs. The relevant characteristic eigenvalue equations are easily obtained, the mismatching effects of longitudinal discontinuities are also simply quantifiable, and the procedures for deriving the Greens functions are directly applicable, making use of the network formalism.

Necrosis evolution during high-temperature hyperthermia through implanted heat sources

A nonstationary model for high-temperature hyperthermic treatments is developed. The aim of this model is to describe the thermal propagation within a living tissue and to quantify its clinical effects as it regards the physiological status (necrosis) of a neoplastic body. Particular attention is turned to the description of the necrotic transition induced by heating. This leads to the introduction of a necrosis field and to an effective-medium approximation for the corresponding physiological status (vascularization, necrosis, etc.) of the exposed tissue. The resulting nonlinear, nonstationary model is applied to a multilayered spherical structure with a temperature-regulated implant, and to a clinical case of a solid liver tumor. Clinical data on the spatial extent of the necrotized region are in good agreement with model predictions.

Characterization of the resonant and coupling parameters of dielectric resonators of NRD-guide filtering devices

The design of millimeter-wave filtering devices using dielectric resonators of various shapes in nonradiative dielectric (NRD) waveguides is considered. By developing different approximate and rigorous theoretical methods, the resonant and coupling properties (frequencies, field configuration, unloaded and loaded quality factors, scattering parameters, etc.) are modeled and implemented in an adaptive code. Experimental comparison through suitable measurements are performed to validate the theoretical and numerical results.<<ETX>>

A boundary-element-method formulation for the electromagnetic coupling between dielectric waveguides and resonators

The Boundary Element Method has been applied to evaluate the electromagnetic coupling between dielectric waveguides and resonators. A two-dimensional integral-equation formulation has been developed, using dyadic Greens functions. A numerical solution as a function of electromagnetic and geometrical quantities has been obtained for the scattering parameters of a filtering device, consisting of a “Non-Radiative Dielectric” waveguide and a “pillbox” resonator.

Theoretical and Experimental Investigation on Rectangular Resonators in Nrd Waveguide

A systematic study of Non-Radiative Dielectric (NRD) rectangular resonators is carried out, both theoretically and experimentally. Different numerical methods have been used and compared in order to obtain the set of resonant frequencies for the modes excitable in NRDstructures. Measurements have been performed in typical configurations for basic filter applications.