Joaquim J. Barroso

Bio: Joaquim J. Barroso is an academic researcher from Instituto Tecnológico de Aeronáutica. The author has contributed to research in topics: Metamaterial & Gyrotron. The author has an hindex of 26, co-authored 255 publications receiving 2300 citations. Previous affiliations of Joaquim J. Barroso include Federal University of São Paulo & National Institute for Space Research.

Modified Nicolson-Ross-Weir (NRW) method to retrieve the constitutive parameters of low-loss materials

Abstract: The constitutive parameters of a Teflon sample of arbitrary thickness are retrieved from scattering parameters experimentally measured with a vector network analyzer and a waveguide system into which the test sample is inserted by filling the transverse section of the X-band waveguide. Based on the Nicolson-Ross-Weir (NRW) method and modified to eliminate the phase ambiguity inherent to the NRW procedure, the algorithm used is able to correctly retrieve over the frequency range considered (8.20 to 12.40 GHz) the permittivity and permeability without any divergence at half-wavelength resonant frequencies for either dielectric or magnetic materials.

Bouncing ball problem: stability of the periodic modes.

Abstract: Exploring all its ramifications, we give an overview of the simple yet fundamental bouncing ball problem, which consists of a ball bouncing vertically on a sinusoidally vibrating table under the action of gravity. The dynamics is modeled on the basis of a discrete map of difference equations, which numerically solved fully reveals a rich variety of nonlinear behaviors, encompassing irregular nonperiodic orbits, subharmonic and chaotic motions, chattering mechanisms, and also unbounded nonperiodic orbits. For periodic motions, the corresponding conditions for stability and bifurcation are determined from analytical considerations of a reduced map. Through numerical examples, it is shown that a slight change in the initial conditions makes the ball motion switch from periodic to chaotic orbits bounded by a velocity strip v=+/-Gamma(1-epsilon) , where Gamma is the nondimensionalized shaking acceleration and epsilon the coefficient of restitution which quantifies the amount of energy lost in the ball-table collision.

Stepwise technique for accurate and unique retrieval of electromagnetic properties of bianisotropic metamaterials

Abstract: Metamaterials (MMs) are artificial materials that have received attention recently because their built-in features create collective electromagnetic effects that are otherwise impossible, such as negative refraction, and because of their exotic electromagnetic applications, namely, perfect lens and invisibility cloaks. Depending on wave propagation characteristics, MMs possessing normally weak magneto-electric coupling coefficients start to exhibit stronger bianisotropic effects. Therefore, accurate electromagnetic characterization of these MMs is important. In this study, we adapt a stepwise method based on the Nicolson–Ross–Weir technique for accurate and unique retrieval of electromagnetic properties of bianisotropic MM slabs. For this goal, we have derived explicit expressions for unique retrieval of electromagnetic properties of these slabs and compared these expressions with those in the literature in the retrieval process. From the comparison, we note that derived expressions are appropriate for unique determination of electromagnetic properties of bianisotropic MM slabs. In the performance analysis of the stepwise method for different measurement scenarios, we considered different bianisotropic MM cell configurations (split-ring and Omega-shaped resonators as well as the same resonators with wire strips) and extracted their electromagnetic properties when measured/simulated scattering parameters have some thermal noise. We note that for most of the frequencies, the stepwise method retrieves correct electromagnetic properties even when a relatively higher normally distributed noise with zero mean value and with standard deviations of 0.015 is present. In addition to the influence of thermal noise on performance of the stepwise method, we also analyzed the effect of both increasing length slab and the frequency band on retrieved electromagnetic properties of the analyzed various bianisotropic MM slabs.

Retrieval of Permittivity and Permeability of Homogeneous Materials from Scattering Parameters

Abstract: On the basis of measured scattering parameters, we present a general assessment of the main problems with the Nicholson-Ross-Weir retrieval procedure: First, the inherent instability of the method for low-loss materials at frequencies corresponding to integer multiples of the transmitted wavelength in the sample; second, the multivalued solutions for the complex wavenumber when the electrical length of the sample exceeds a wavelenghth. It is shown that the presence of small perturbation or noise on the transmission coefficient T at around |T| ≈ 1 suffices to trigger the instability when retrieving the impedance of the sample. Unlike the ill-conditioned expression of the impedance, the product μe (refractive index squared) is stable to perturbation in T. For nonmagnetic materials (relative permeability μr = 1), therefore, the product μe reduces to the complex permittivity, which is then correctly retrieved without divergent ripples as shown by the extracted permittivity spectra in the X-band (8.2–12.4 GHz)...

Effective Constitutive Parameters Retrieval Method for Bianisotropic Metamaterials Using Waveguide Measurements

Abstract: An effective method for extraction of electromagnetic properties of bianisotropic biaxial omega-type metamaterial (MM) slabs from waveguide measurements is presented. The method relies on measurements of S-parameters of two MM slab configurations (transverse and longitudinal) to extract electromagnetic properties endowed with strong bianisotropic coupling. An uncertainty analysis is performed for examining the effect of geometrical parameters of the longitudinal configuration on its resonance characteristic. For verification of the proposed method, constitutive parameters of a polyethylene sample are extracted at the $X$ -band (8.2–12.4 GHz). Then, the method is applied for extraction of electromagnetic properties of an MM slab (square split-ring resonators over FR4 substrate) using simulated and measured S-parameters for the two configurations at the $X$ -band. It is noted that extracted electromagnetic properties obtained from measured S-parameters are in good agreement with those obtained from simulated S-parameters except for a small frequency shift and magnitude change, which could arise from fabrication tolerances, air gaps present between MM cells, and local irregular surface of the longitudinal configuration. For completeness, it is analyzed whether extracted properties satisfy the locality conditions.

Physics, Astrophysics and Cosmology with Gravitational Waves

Abstract: Gravitational wave detectors are already operating at interesting sensitivity levels, and they have an upgrade path that should result in secure detections by 2014. We review the physics of gravitational waves, how they interact with detectors (bars and interferometers), and how these detectors operate. We study the most likely sources of gravitational waves and review the data analysis methods that are used to extract their signals from detector noise. Then we consider the consequences of gravitational wave detections and observations for physics, astrophysics, and cosmology.

Enhanced sensitivity of the LIGO gravitational wave detector by using squeezed states of light

Abstract: Nearly a century after Einstein first predicted the existence of gravitational waves, a global network of Earth-based gravitational wave observatories1, 2, 3, 4 is seeking to directly detect this faint radiation using precision laser interferometry. Photon shot noise, due to the quantum nature of light, imposes a fundamental limit on the attometre-level sensitivity of the kilometre-scale Michelson interferometers deployed for this task. Here, we inject squeezed states to improve the performance of one of the detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) beyond the quantum noise limit, most notably in the frequency region down to 150 Hz, critically important for several astrophysical sources, with no deterioration of performance observed at any frequency. With the injection of squeezed states, this LIGO detector demonstrated the best broadband sensitivity to gravitational waves ever achieved, with important implications for observing the gravitational-wave Universe with unprecedented sensitivity.

A regularity statistic for medical data analysis

Abstract: A new statistic has been developed to quantify the amount of regularity in data. This statistic, ApEn (approximate entropy), appears to have potential application throughout medicine, notably in electrocardiogram and related heart rate data analyses and in the analysis of endocrine hormone release pulsatility. The focus of this article is ApEn. We commence with a simple example of what we are trying to discern. We then discuss exact regularity statistics and practical difficulties of using them in data analysis. The mathematic formula development for ApEn concludes the Solution section. We next discuss the two key input requirements, followed by an account of a pilot study successfully applying ApEn to neonatal heart rate analysis. We conclude with the important topic of ApEn as a relative (not absolute) measure, potential applications, and some caveats about appropriate usage of ApEn. Appendix A provides example ApEn and entropy computations to develop intuition about these measures. Appendix B contains a Fortran program for computing ApEn. This article can be read from at least three viewpoints. The practitioner who wishes to use a "black box" to measure regularity should concentrate on the exact formula, choices for the two input variables, potential applications, and caveats about appropriate usage. The physician who wishes to apply ApEn to heart rate analysis should particularly note the pilot study discussion. The more mathematically inclined reader will benefit from discussions of the relative (comparative) property of ApEn and from Appendix A.