274 research outputs found
Advanced image processing techniques for the discrimination of buried objects
No full textA numerical study for the
electromagnetic detection of buried objects is
presented. The whole GPR set-up is simulated
through an integral formulation solved by means
of the Method of Moments and a new
discrimination process based on the 2D-Wavelet
decomposition of computed electric field maps is
proposed. The new wavelet methodology proves
to be an effective tool for discrimination even in
presence of noise
Kinetic resolution of chiral racemic alcohols by BITIANP-ruthenium(II)-catalyzed hydrogenation
No full textChiral allylic secondary alcohols have been resolved efficiently by catalytic hydrogenation with ruthenium complexes derived from the new chiral atropisomeric (R)- and (S)-BITIANP. These catalytic sistems have been applied to the resolution of NCS-382, a selective antagonist of the γ-hydroxybutyric acid (GHB) receptors. NCS-382 may play a role as a central neuromodulator and possesses several neuropharmacological properties that can be investigated in detail only if both entomer and distomer are available in bulk. Copyright (C) 2000 John Wiley and Sons, Ltd
Analysis and Design of Low Frequency Microstrip Antennas
No full textMicrostrip antennas are adapted in a number of applications, being their use generally
limited 10 the high frequency range [1-2]. However, their versatility has solicited the
investigation on the suitability of printed microstrip antemas for low-frequency
applicationr, typically requiring other antenna configurations [3], by v i a e of a
considerable reduction on the value of the work frequency attained by means of a
double substrate of ferradcchic and ferrimagnetic material, rerpectivsly. In faet, high
values of permittivity and permeability allow the usc of the proposed antenna down to
the MHz range.
Moreover, the possibility of varying the permcability of the femtc through a simple dc
bias [4-51 represents a versatile fcahlre in l a " of Nnability ( a d selectivity), e.g. with
respect to clas~icall oop antennas.
The design of the proposed antenna calls for a careful simulation of both the rubswtes
as concems their frequency-dependent behavior and the anisotropy of the ferrite. In
particular, a Debye model is adopted for the ferroelcchiic material (barium or strontium
titanate), being the relevant values derived from experimental data [6-71, while a
c l a ~ ~ i cPaoll der tensor form is considered for the permeability of the ferrite substrate
material.
The solution of the problem is achievcd by means of an analysis method based on a
three-dimensional (3-D) finite-element method (FEM) [X-91, with a nodal-based
approach in terms of magnetic vector and electric scalar potentials. In the frequency
range of interest, the magnetic field is the quantiry of major interest, and second-order
tetrahedral elements are considered. The results, validatcd through a commercial code,
demonstrate the feasibility of the antenna as source or receiver of low-frequency EM
fields
SPICE Model Extraction for Signal Integrity Analysis of Unshielded Twisted Pairs from Full Wave Simulation
No full textImproved SPICE-like macromodels are
proposed to model unshielded twisted pairs (UTPs). The
equivalent SPICE circuits of UTPs cable are obtained by
applying suitable extraction techniques based on the Vector
Fitting procedure to the scattering matrix representation of
the cable. The proposed SPICE models are suitable to
analyze the transmission properties of UTPs taking into
account frequency-dependent losses, proximity effect, and
radiation losses. The characterization of the UTPs cable by
the scattering matrix is here performed by a three
dimensional full-wave numerical tool based on the Finite
Integration technique. The proposed extraction procedures
are absolutely general and can be also applied to measured
scattering parameters. The UTPs SPICE models are
validated by comparing the results with those provided by
the full-wave simulation and by measurements
Modeling Interconnects Discontinuities in the Wavelet Domain
No full textThe extraction of equivalents of lumped discontinuities in common printed circuit boards (PCBs) is
a key topic in the study of wave propagation of high-speed signals along interconnects, since these
irregularities pose several signal integrity (SI) and electromagnetic interference (EMI) problems. In
the past, much research has focused on modeling such discontinuities by means of appropriate lumped
equivalent circuits, suitable to be used in transient circuit simulators, either starting from reasonable
physical observations or simply applying fitting techniques on full-wave numerical data [1]. In this
paper a novel technique is presented for the extraction of two-port equivalents in the wavelet-domain,
which has been proved to be an efficient and powerful tool for the analysis of transmission lines and
interconnects [2]. The wavelet-transformed scattering parameters of the discontinuities are included in
a wavelet equivalent of TEM wave propagation paths along the PCB in order to obtain an overall
equivalent of the whole structure under investigation
New extraction procedure of shielded cable SPICE macro-model for the prediction of signal integrity and conducted immunity
No full textAn improved extraction procedure is here proposed to carry out shielded cable macro-model suitable to be implemented in any SPICE based circuit simulator. The proposed procedure permits to account frequency-dependent losses as skin effect, and frequency-dependent behaviour of the transfer impedance. The shielded cable is modelled by a four-port network with lumped time-constant parameters obtained by applying the proposed improved fitting technique. The proposed macro-model is validated by comparing the results with those obtained by measurements
Efficient computation of the shielding effectiveness of metallic enclosures loaded with conductors
No full textThe effects of conducting loads on the shielding effectiveness of rectangular metallic enclosures is investigated through an efficient formulation based on the method of moments. As expected, the analysis shows that the classical shielding effectiveness is a very tricky figure of merit which is seriously affected by the possible presence of loads inside the enclosure, especially in the frequency range above the first resonant frequency of the enclosure. Comparisons with rigorous fall-wave results obtained through commercial software confirm the validity of the proposed technique and its high efficiency
Extraction of Discontinuity Models in the Wavelet Domain
No full textA novel wavelet-based technique is presented for the extraction of two-port equivalents of common printed circuit board (PCB) discontinuities. The wavelet-transformed scattering parameters of the discontinuity can be included in a wavelet equivalent of TEM wave propagation paths along the PCB in order to obtain an overall equivalent of the Whole structure under analysi
Finite-difference time-domain study on the influence of the conductor catenary in the simulation of lightning surges
No full textWhen accounting for the catenary shape, overhead power lines are non-uniform structures. Usually, the impact caused by the catenary on the transmission properties of the line is neglected. Hence, the line is simulated as uniform considering a constant equivalent height. In this paper, we investigate the impact of the catenary on induced overvoltages caused by direct and indirect lightning strokes. Employing a recently proposed implicit finite-difference time-domain code, we assess that the catenary may have a severe impact on the correct computation of the overvoltages. Finally, we outline the accuracy limits of the EMTP-RV software in conjunction with the LIOV module through an in-depth comparison
Electromagnetic Shielding
No full textThe definitive reference on electromagnetic shielding materials, configurations, approaches, and analyses. This reference provides a comprehensive survey of options for the reduction of the electromagnetic field levels in prescribed areas. After an introduction and an overview of available materials, it discusses figures of merit for shielding configurations, the shielding effectiveness of stratified media, numerical methods for shielding analyses, apertures in planar metal screens, enclosures, and cable shielding. Up to date and comprehensive, Electromagnetic Shielding: Explores new and innovative techniques in electromagnetic shielding. Presents a critical approach to electromagnetic shielding that highlights the limits of formulations based on plane-wave sources. Analyzes aspects not normally considered in electromagnetic shielding, such as the effects of the content of the shielding enclosures. Includes references at the end of each chapter to facilitate further study. The last three chapters discuss frequency-selective shielding, shielding design procedures, and uncommon ways of shielding-areas ripe for further research. This is an authoritative, hands-on resource for practicing telecommunications and electrical engineers, as well as researchers in industry and academia who are involved in the design and analysis of electromagnetic shielding structures. © 2008 John Wiley & Sons, Inc
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