1,721,118 research outputs found
Progetto, realizzazione e caratterizzazione sperimentale di superstrati a band-gap elettromagnetico per l’incremento della direttività di antenne planari
No full textThree-dimensional Electromagnetic
Band-Gap (EBG) materials have been designed, by
using an in-house Fourier Modal Method (FMM)
code, to be employed as directivity-enhancing superstrates
for planar antennas. Alumina-woodpile
samples have been fabricated. Experimental results
have been collected, for the transmission properties
of EBG cavities, and comparisons have been performed
with FMM, with good agreement. The performances
of a woodpile-covered patch antenna have
been measured; the superstrate has been positioned
at different distances from the antenna and its orientation
has been varied; comparisons with the commercial
software HFSS show a good agreement. The
main effect of the EBG on the antenna performances
is an enhancement of about 10 dB in maximum gain
Simulation of electromagnetic scattering in a Through-Wall Environment
No full textIn the modelling of electromagnetic scattering in a Through-the-Wall environment large domains made by walls, and sparse targets are involved. Approximated models based on ray-tracing techniques are mostly employed to reduce computer times, although a more accurate response that takes account of all the interactions between walls and targets may be obtained with full-wave methods. In this work, the Cylindrical Wave Approach is employed, as full-wave technique for the modelling of Through-the-wall scenarios. The technique is mainly analytical, as targets with circular cross-section are modelled through expansions into cylindrical waves. However, through suitable rules, it is possible to approximate targets with cross-section of arbitrary shape through an arrangement of smaller circular cross-section cylinders. This may be applied, for example, to the modelling of pieces of furniture, as wall as to introduce further walls in the simulation domain
THE ANALYSIS OF NEUTRON-INDUCED TRANSMUTATION AND ACTIVATION IN NUCLEAR MATERIALS
No full textTHE ANALYSIS OF NEUTRON-INDUCED TRANSMUTATION AND ACTIVATION IN NUCLEAR MATERIAL
Scattering and Transmission of Pulsed Electromagnetic Waves with the CWA
No full textgeneral approach to solve the scattering of
pulsed fields is presented. The whole spectrum of the source
field is considered, expressed as the product of a space
spectrum and a frequency spectrum. Space spectrum is
relevant to the spatial nature of the incident field, as a plane
wave or a line source, whereas the frequency one deals with
shape of the excitation pulse in the time-doma in. The
formulat ion is applied to the Cylindrical Wave Approach, a
method to solve the scattering by buried circular cross-section
cylinders. This scattering technique, formulated for a
monochromatic excitation, is based on spectral integrals to
define cylindrical waves as used basis functions ofthe scattered
fields. The Cylindrical Wave Approach is extended to a pulsed
source applying an iterative method
Use of a Set of Wearable Dielectric Scatterers to Improve Electromagnetic Transmission for a Body Power Transfer System
No full textIn this paper we present an accurate analytical solution of the scattering of a plane-wave by dielectric cylinders placed above a multilayered medium. An analytical approach is used to solve the scattered field by the cylinders in each medium through expansions into cylindrical waves, expressed through plane-wave spectra. The multilayer models a biological tissue consisting of skin, fat and muscle covered by a cotton textile. Several numerical examples are presented considering the electrical parameters of the biological and textile tissues at the millimeter frequency range (24 GHz). The results show that it is possible to obtain an intensification of the electric field in the underlying tissues in case of TM polarization of the incident wave, finding an interesting application for the charging of implantable or wearable devices
Mode Filters for Oversized Rectangular Waveguides: A Modal Approach
No full textA semi-analytical approach, relying on the mode-matching method and the resonator technique, is proposed. It is conceived to evaluate the performance of mode filters, based on corrugations partially filled with an absorbing material, in the case of oversized rectangular waveguides. The mathematical formulation allows an accurate and fast computation of the scattering parameters, through closed-form expression of the surface integrals and some matrix algebra. The theoretical model is implemented in a code that is benchmarked against a finite-element method to elucidate its advantages with respect to volumetric solvers. After giving an insight on the physical mechanisms ruling the performance of these devices, the modal method is used to run the particle swarm optimization algorithm for different types of devices, taking advantage of the reduced computation time of the developed tool. © 1963-2012 IEEE
The cylindrical wave approach for the electromagnetic scattering by targets behind a wall
No full textAn overview of the cylindrical wave approach in the modeling of through-wall radar problems with targets hidden behind a dielectric wall is reported. The cylindrical wave approach is a technique for the solution of the two-dimensional scattering by buried circular cross-section cylinders in a semi-analytical way, through expansion of the scattered fields into cylindrical waves. In a through-wall radar application, the scattering environment is made by a dielectric layer between two semi-infinite half-spaces filled by air. For this layout, two possible implementations of the cylindrical wave approach have been developed in the case of plane-wave excitation. The first was an iterative scheme with multiple-reflection scattered fields, and the second was a fast and non-iterative solution, through suitable basis functions (i.e., reflected and transmitted cylindrical waves). Such waves take into account all the interactions of the source field with the interfaces bounding the dielectric layers and the targets. The non-iterative approach was also extended for excitation from the radiated field by a line source. A final system was derived for the computation of the scattered field by PEC or dielectric targets. Numerical results show the potentialities of the cylindrical wave approach in the modeling of through-wall radar, in particular in the evaluation of the scattered fields by human targets in a building’s interior, modeled with a two-dimensional approach
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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