Juan Hinojosa

S-parameter broadband measurements on-coplanar and fast extraction of the substrate intrinsic properties

A broadband technique for determining the electromagnetic properties of isotropic thin-film materials, which uses a coplanar line, is presented. Complex permittivity and permeability are computed from S-parameter measurements of a coplanar cell propagating the dominant mode. Measured /spl epsi//sub /spl tau// and /spl mu//sub /spl tau// data for several materials are presented between 0.05 GHz and 40 GHz. This technique shows a good agreement between measured and predicted data.

S-parameter broad-band measurements on-microstrip and fast extraction of the substrate intrinsic properties

A broad-band technique for determining the electromagnetic properties of isotropic film-shaped materials, which uses a microstrip line, is presented. Complex permittivity and permeability are computed from analytical equations and S-parameter measurements of microstrip cells propagating the dominant mode. Measured /spl epsiv//sub r/ and /spl mu//sub r/ data for several materials are presented between 0.05 GHz and 40 GHz. This technique shows a good agreement between measured and predicted data.

Novel Compact Wide-Band EBG Structure Based on Tapered 1-D Koch Fractal Patterns

This letter presents a novel electromagnetic band-gap (EBG) structure in microstrip technology based on nonuniform one-dimensional (1-D) Koch fractal patterns whose dimensions and period are modulated by a tapering function that significantly improves the width of the band-gap. This wide band-gap is achieved by maintaining the radius-to-period (r/a) ratio of the Koch fractal patterns larger than 0.5 in the whole structure. In the passband region, an improved flat response is obtained by tapering the dimensions of the Koch fractal patterns etched in the ground plane, together with the width of the microstrip line, with a Kaiser distribution that also modulates the periodicity of the fractals. A major consequence of this modulation of the periodicity of the pattern is that this structure is much more compact than a uniform conventional one.

Empirical model generation techniques for planar microwave components using electromagnetic linear regression models

Accurate and efficient empirical model generation techniques of microwave devices, for a large range of geometric and material parameters opportunely chosen, are presented. The empirical models are based on multiple linear regression approach, which compensates the error between an initial inaccurate empirical model and an electromagnetic (EM) full-wave solver (or measurement data). The aim of these techniques is to generate accurate empirical models, which are computationally very efficient with respect to any EM technique. These simple models could be integrated in a toolbox of any commercially available computed-aided design tools for RF/microwave circuits. Comparisons with artificial neural networks and linear-regression-based models are listed and discussed for the dispersion of a microstrip transmission line propagating the quasi-TEM mode and a microwave tunable phase shifter propagating the even mode.

Dielectric constant tunability at microwave frequencies and pyroelectric behavior of lead-free submicrometer-structured (Bi 0.5 Na 0.5 ) 1¿x Ba x TiO 3 ferroelectric ceramics

In this article, we show that the dielectric constant of lead-free ferroelectric ceramics based on the solid solution (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3, with compositions at or near the morphotropic phase boundary (MPB), can be tuned by a local applied electric field. Two compositions have been studied, one at the MPB, with x = 0.06 (BNBT6), and another one nearer the BNT side of the phase diagram, with x = 0.04 (BNBT4). The tunability of the dielectric constant is measured at microwave frequencies between 100 MHz and 3 GHz by a nonresonant method and simultaneously applying a dc electric field. As expected, the tunability is higher for the composition at the MPB (BNBT6), reaching a maximum value of 60% for an electric field of 900 V/cm, compared with the composition below this boundary (BNBT4), which saturates at 40% for an electric field of 640 V/cm. The high tunability in both cases is attributed to the fine grain and high density of the samples, which have a submicrometer homogeneous grain structure with grain size of the order of a few hundred nanometers. Such properties make these ceramics attractive for microwave tunable devices. Finally, we have tested these ceramics for their application as infrared pyroelectric detectors and we have found that the pyroelectric figure of merit is comparable to traditional lead-containing pyroelectrics.

Prolonged length of stay in hospitalized internal medicine patients

BACKGROUND Targeting patients with prolonged hospitalizations may represent an effective strategy for reducing average hospital length of stay (LOS). OBJECTIVE We sought to characterize predictors of prolonged hospitalization among internal medicine patients in an effort to guide future improvement efforts. DESIGN We conducted a retrospective cohort study using administrative data of internal medicine patients from all hospitals of the Spanish Public Health Service between January 1st, 2005 and December 31st, 2013. Multivariable logistic regression was performed to assess the association between sociodemographic and clinical variables and prolonged LOS, defined as >30days. KEY RESULTS Of 5,275,139 discharges, 166,470 (3.2%) had a prolonged LOS. Prolonged hospitalizations accounted for 17.4% of total inpatient days and contributed 0.5days to an average LOS of 9.8days during the study period. Prolonged hospitalizations were associated with younger age (odds ratio [OR]: 0.97 per 10-year increase in age, 95% confidence interval [CI]: 0.96-0.98) and male gender (OR 0.88 IC95% 0.87-0.89). Compared to patients without prolonged LOS, prolonged LOS patients were more likely to require a palliative care consult (OR: 2.48, 95% CI: 2.39-2.58), surgery (OR: 6.9 95% CI: 6.8-7.0); and be discharged to a post-acute-care facility (OR: 2.91, 95% CI: 2.86-2.95). CONCLUSIONS Prolonged hospitalizations in a small proportion of patients were an important contributor to overall LOS and particularly affected complex hospital stays who were not discharged home.

A Novel Low-Pass Filter Based on Rounded Posts Designed by an Alternative Full-Wave Analysis Technique

A new low-pass waveguide filter topology is proposed based on capacitive posts using rounded shapes. The new structure is designed using a technique that benefits from a full-wave integral equation simulation tool for arbitrarily shaped capacitive microwave circuits. This integral equation method enables one to apply an efficient filter design technique employing iris geometries other than rectangular discontinuities, such as the one based on rounded posts proposed in this work. A prototype using circular posts has been manufactured and measured obtaining excellent results as compared with predictions, thus demonstrating the practical feasibility of the new proposed filtering structure. A new filter using elliptic capacitive posts was compared in terms of multipactor risk against similar filters based on traditional rectangular windows and on rectangular posts. Simulation results indicate that the new proposed concept using rounded shapes leads to geometries that can double multipactor thresholds as compared with traditional filters.

Optimization-Oriented Design of RF/Microwave Circuits Using Inverse-Linear-Input Neuro-Fuzzy-Output Space Mapping With Two Different Dimensionality Simulators

In this paper, an efficient optimization technique aligning three-dimensional (3-D) electromagnetic simulator responses with two-dimensional (2-D) electromagnetic simulator responses around space mapped solution, for the electromagnetic design of radiofrequency and microwave 3-D circuits is presented. The interface between 2-D and 3-D electromagnetic simulators is obtained from an inverse linear input space-mapping approach and an output modeling process based on a fuzzy logic technique. It is shown that the technique provides a highly accurate estimation of the 3-D design parameter space of the 3-D radiofrequency and microwave circuits to be designed, for initially fixed design specifications. Designs of first-order, second-order and sixth-order C-band 3-D evanescent rectangular waveguide bandpass filters with dielectric posts show the performance of our approach.

Substrate Integrated Waveguide (SIW) With Koch Fractal Electromagnetic Bandgap Structures (KFEBG) for Bandpass Filter Design

High-performance bandpass filters (BPFs) based on substrate integrated waveguide (SIW) and half mode SIW (HMSIW) with Koch fractal electromagnetic bandgap (KFEBG) patterns etched on the waveguide surface are proposed. These BPFs are designed using a new methodology. The BPF responses are improved by applying a chirped and tapered technique to the KFEBG patterns which exhibit a radius-to-period ratio r/a ≥ 0.5. Simulation results and experimental verification are presented. Good values for insertion losses and stopband rejection are achieved.

Accurate and reusable macromodeling technique using a fuzzy-logic approach

An approach for applying fuzzy logic for accurate analog circuit macromodel sizing is presented. In our proposed method, multiple adaptive neuro-fuzzy inference systems (MANFIS) are trained to predict the performance characteristics (gain, bandwidth) of a fully differential telescopic transconductance amplifier (OTA). The neuro-fuzzy computed characteristic values are in excellent agreement and one order of magnitude faster than those obtained from device level SPICE simulations. This technique allows the generation of accurate, efficient and reusable models of analog circuits. It is demonstrated and compared with other classical techniques like polynomial regression or artificial neural network approaches.