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Search Results: 1 - 10 of 300133 matches for " Joaquim J. Barroso "
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Experimental Study on Split-Ring Resonators with Different Slit Widths  [PDF]
Pedro J. Castro, Joaquim J. Barroso, Joaquim P. Leite Neto
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2013, DOI: 10.4236/jemaa.2013.59058

Metamaterial one-dimensional periodic structures are composed of split-ring resonators, which can display electric permittivity and magnetic permeability simultaneously negative, are studied experimentally. In the present study, each resonator is made up of two concentric circular copper rings patterned on a substrate of kapton, with slits diametrically opposite each other and with the line of the splits along the longitudinal direction of the periodic array containing seven split rings evenly spaced. The experiments consist in inserting the metamaterial slab into a square waveguide of side length 6 mm, corresponding to a cutoff frequency of 25 GHz. Transmission bands due to magnetic and electrical responses are identified for slits with aperture widths of 1 mm and 2 mm, centered at 5.67 and 6.12 GHz frequencies, respectively, values well below the 25 GHz frequency cutoff, so characterizing a medium with negative permeability and

The sinusoid as the longitudinal profile in backward-wave oscillators of large cross sectional area
Leite Neto, Joaquim P.;Barroso, Joaquim J.;
Brazilian Journal of Physics , 2004, DOI: 10.1590/S0103-97332004000800013
Abstract: high-power generation in backward-wave oscillators (bwo) of large section requires that the beam electrons flowing close to the corrugated wall interact efficiently with surface waves supported by a periodic structure. such waves are described by the superposition of slow-wave space harmonics of the operating mode. the present paper reports on design tools for bwos operating in symmetric tm modes since these modes are able to perturb the axial velocity and electron density on rectilinear beams confined by an external magnetic field in slow-wave systems. here we investigate whether a cylindrical guide with sinusoidally rippled wall can provide strong coupling between the guide surface waves and mildly relativistic (~ 500 kev) electron beams in the 8-9 ghz frequency range for bwos of large diameter (d ~ 3l). for this purpose, the characteristic equation of a sinusoidally corrugated structure is derived on the basis of the rayleigh-fourier method, whereby the field solution is represented by a single expansion of tm eigenmodes. from the dispersion diagrams thus obtained we infer the appropriate periodic length and ripple amplitude of the guiding structure that optimize the beam-wave interaction.
Modeling and Analysis of Ladder-Network Transmission Lines with Capacitive and Inductive Lumped Elements  [PDF]
Ana Flávia G. Greco, Joaquim J. Barroso, José O. Rossi
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2013, DOI: 10.4236/jemaa.2013.55034
Abstract: This paper examines the properties of wave propagation in transmission lines with periodic LC and CL cells, taking into account ohmic losses in resistors connected in series to lumped capacitors and inductors. First order time differential equations are derived for current and charge, thus allowing analysis of transient regimes of the lines being excited by a pulse of arbitrary shape. In particular we examine the propagation characteristics of periodic lines in which identical unit cells are repeated periodically and also discuss the interpretation of positive and negative phase velocities associated with the LC and CL topologies. Loss effects on the propagation bandwidths of both lines are also discussed, and it is shown that in the left-handed transmission line (CL configuration) the phase advance of the crest of the transmitted signal with respect to the source signal is due to the intrinsic dispersive nature of the CL line which, in contrast to the LC line, is highly dispersive at low propagation factors.
Retrieval Approach for Determination of Forward and Backward Wave Impedances of Bianisotropic Metamaterials
Ugur Cem Hasar;Joaquim J. Barroso
PIER , 2011, DOI: 10.2528/PIER10112303
Abstract: A simple approach is proposed for retrieving the forward and backward wave impedances of lossless and lossy bianisotropic metamaterials. Compared with other methods in the literature, its main advantage is that forward and backward wave impedances can be uniquely and noniteratively extracted. It has been validated for both lossless and lossy bianisotropic metamaterials by performing a numerical analysis. The proposed approach can be applied for checking whether the metamaterial structure shows the bianisotropic property by monitoring forward and backward wave impedances, since the forward and backward wave impedances of a metamaterial structure depend on different polarizations of the incident wave.
Simulation of Inhomogeneous Columns of Beads under Vertical Vibration
Marcus V. Carneiro,Joaquim J. Barroso,Elbert E. N. Macau
Mathematical Problems in Engineering , 2009, DOI: 10.1155/2009/345947
Abstract: We present results from computational experiments of one-dimensional inhomogeneous granular column. With characteristic properties lying between those of liquids and solids, this class of material consists of assemblies of solid particles which interact via mechanical forces (contact and friction) and are maintained together by a gravitational field. The system is composed of a vertical column of spherical beads driven by a sinusoidally vibrating plate. Results for 10 bead experiments show the fluidization and condensation phenomena, both dependent on the amplitude and frequency of the driving plate. Some scaling properties arising from the dynamics of the beads are also shown.
Resolving Phase Ambiguity in the Inverse Problem of Reflection-Only Measurement Methods
Ugur Cem Hasar;Joaquim J. Barroso;Cumali Sabah;Yunus Kaya
PIER , 2012, DOI: 10.2528/PIER12052311
Abstract: We have applied the phase unwrapping technique to resolve the phase ambiguity problem arising from complex expressions of scattering parameters, for reflection-only measurement configurations, since, at some instances, only one side of the sample under test is accessible for electromagnetic measurements. We considered two different measurement configurations for testing the applicability of the phase unwrapping technique as: 1) two identical samples with different lengths flushed by a short-circuit termination and 2) one sample shorted by a varying short-circuit termination. For each measurement configuration, the underlying expressions for the reflection scattering parameters are derived. For both cases, we evaluated the suitability of the phase unwrapping technique by considering a highly-dispersive medium (distilled water) as our test sample. We note that continuity of the real part of the complex wavelength is a key issue in the unwrapping technique for (one-port) reflection-only measurements.
Application of a Useful Uncertainty Analysis as a Metric Tool for Assessing the Performance of Electromagnetic Properties Retrieval Methods of Bianisotropic Metamaterials
Ugur Cem Hasar;Joaquim J. Barroso;Mehmet Ertugrul;Cumali Sabah;Bulent Cavusoglu
PIER , 2012, DOI: 10.2528/PIER12040802
Abstract: We applied a useful uncertainty model, ignored in most metamaterials retrieval studies, to monitor the accuracy of retrieved electromagnetic properties of bianisotropic metamaterial (MM) slabs composed of split-ring resonators and cut wires. Two different MM slab structures are considered to make the analysis complete. As uncertaintymaking factors, we took into consideration of uncertainties in scattering (-) parameters of bianisotropic MM slabs as well as the length of these slabs. The applied uncertainty model is based upon considering the effect of minute change (differential) in uncertainty factors on the retrieved electromagnetic properties of bianisotropic MM slabs. The significant results concluded from the analysis are: 1) any abrupt changes in the phase of -parameters of bianisotropic MM slabs remarkably influence the retrieved electromagnetic properties; 2) any small-scale loss (i.e., the loss of the substrate) in the bianisotropic MM slabs improves the accuracy of the retrieved electromagnetic properties of these slabs; and 3) precise knowledge of bianisotropic MM slab lengths are required for correct analysis of exotic properties of these slabs. The presented uncertainty analysis can be utilized as a metric tool for evaluating various retrieval methods of MM slabs in the literature.
Nanogap Transducer for Broadband Gravitational Wave Detection
Guilherme L. Pimentel,Odylio D. Aguiar,Michael E. Tobar,Joaquim J. Barroso,Rubens de M. Marinho
Physics , 2009,
Abstract: By changing from a resonant multimode paradigm to a free mass paradigm for transducers in resonant mass gravitational wave detection, an array of six spheres can achieve a sensitivity response curve competitive with interferometers, being as sensitive as GEO600 and TAMA300 in the 3 to 6 kHz band and more sensitive than LIGO for 50 percent of the 6 to 10 kHz band. We study how to assemble a klystron resonant cavity that has a 1 nm gap by understanding the stability of the forces applied at it (Casimir force, elastic force, weight). This approach has additional benefits. First, due to the relatively inexpensive nature of this technology (around US$ 1 million), it is accessible to a broader part of the world scientific community. Additionally, spherical resonant mass detectors have the ability to discern both the direction and polarization resolutions.
Retrieval of Effective Electromagnetic Parameters of Isotropic Metamaterials Using Reference-Plane Invariant Expressions
Ugur Cem Hasar;Joaquim J. Barroso;Cumali Sabah;Ibrahim Yucel Ozbek;Yunus Kaya;Deniz Dal;Tolga Aydin
PIER , 2012, DOI: 10.2528/PIER12072412
Abstract: Three different techniques are applied for accurate constitutive parameters determination of isotropic split-ring resonator (SRR) and SRR with a cut wire (Composite) metamaterial (MM) slabs. The first two techniques use explicit analytical calibration-dependent and calibration-invariant expressions while the third technique is based on Lorentz and Drude dispersion models. We have tested these techniques from simulated scattering (-) parameters of two classic SRR and Composite MM slabs with various level of losses and different calibration plane factors. From the comparison, we conclude that whereas the extracted complex permittivity of both slabs by the analytical techniques produces unphysical results at resonance regions, that by the dispersion model eliminates this shortcoming and retrieves physically accurate constitutive parameters over the whole analyzed frequency region. We argue that incorrect retrieval of complex permittivity by analytical methods comes from spatial dispersion effects due to the discreteness of conducting elements within MM slabs which largely vary simulated -parameters in the resonance regions where the slabs are highly spatially dispersive.
Experimental measurements and numerical simulation of permittivity and permeability of Teflon in X band
Adriano Luiz de Paula,Mirabel Cerqueira Rezende,Joaquim José Barroso
Journal of Aerospace Technology and Management , 2011,
Abstract: Recognizing the importance of an adequate characterization of radar absorbing materials, and consequently their development, the present study aims to contribute for the establishment and validation of experimental determination and numerical simulation of electromagnetic materials complex permittivity and permeability, using a Teflon sample. The present paper branches out into two related topics. The first one is concerned about the implementation of a computational modeling to predict the behavior of electromagnetic materials in confined environment by using electromagnetic three-dimensional simulation. The second topic re-examines the Nicolson-Ross-Weir mathematical model to retrieve the constitutive parameters (complex permittivity and permeability) of a homogeneous sample (Teflon ), from scattering coefficient measurements. The experimental and simulated results show a good convergence that guarantees the application of the used methodologies for the characterization of different radar absorbing materials samples.
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