A.J.M. Soares

Analysis of microstrip antennas on circular-cylindrical substrates with a dielectric overlay

The use of dyadic Greens functions and the moment method is explored for the solution of microstrip antenna problems on circular cylindrical substrates. The dyadic Greens functions of the electric type are obtained for a medium consisting of three cylindrical dielectric layers concentric with a perfectly conducting cylinder, and integral equations are developed for the evaluation of the electromagnetic fields. The effect of a dielectric overlay on the resonant frequency of a cylindrical-rectangular microstrip antenna is analyzed. The patch is directly fed by means of a microstripline printed along the cylinder axial direction. The results show that the effect of the dielectric overlay is substantial when its relative permittivity and thickness are increased, such that this effect has to be very carefully considered in the design of microstrip antennas. >

Microstrip antenna on a circular cylindrical substrate with a dielectric cover

The dyadic Greens function formalism and the method of moments were used to analyze a microstrip patch on a circular cylindrical substrate with a dielectric cover. The patch is fed on the side by means of a microstripline running parallel to the cylinder axis. The results showed a strong influence of the cover on the resonant frequency of the antenna.<<ETX>>

Effect of a dielectric cover in a microstripline on a circular cylindrical substrate

The effect of the dielectric cover on the effective dielectric constant of microstriplines on cylindrical substrates is investigated. The analysis is developed using dyadic Greens functions in a layered cylindrical medium. The effective dielectric constant is obtained by imposing the condition that the tangential electric field component is zero on the metal strip. The dielectric cover is shown to have an appreciable effect on the effective dielectric constant.<<ETX>>

Analysis and experimental results of wire antennas on a finite conductor ground plane

This paper shows the finite difference time domain method (FDTD) applied to analysis of wire antennas on a ground plane. The approach was validated with construction and tests of a monopole Yagi-Uda antenna above a finite conductor plane whose feeder was folded. The theoretical and measured results, for 820 to 850 MHz, show the validation of the approach.

Surface wave excitation on a microstrip ring antenna

A theoretical analysis of surface wave excitation in microstrip ring antennas is presented. The problem is formulated using dyadic Greens functions with the space and surface wave fields obtained separately. The radiation efficiency is calculated for the TM/sub 11/, TM/sub 12/, and TM/sub 13/ modes. It is shown that the efficiency of the TM/sub 13/ mode has a maximum for a specified dielectric substrate. In addition, the efficiency of the TM/sub 11/, TM/sub 12/ and TM/sub 13/ modes approaches zero for increasing values of dielectric substrate thickness. The results shown here are of particular importance for the design of these antennas.<<ETX>>

Ophthalmologic Manifestations of Wolfram Syndrome: Report of 14 Cases

Purpose: The aim of this study was to describe ophthalmological abnormalities in 14 cases of Wolfram syndrome belonging to 9 different families. Methods: Patients were submitted to a complete ophthalmological, neurological, otorhinolaryngological, urological, and genetic evaluation. Results: Our sample comprised 14 Caucasian patients belonging to 9 different families. Their ages ranged from 10 to 38 years. The mean duration of known disease was 11.3 ± 8.7 years. Genetic confirmation was obtained in 7 families. There was a parental consanguinity history in 2 families. Five families were homozygous for a mutation of exon 8 of the WFS1 gene (Chr. 4), and 2 patients were heterozygous. Diabetes mellitus was the first manifestation in all except 1 patient. The mean age at diagnosis was 8.7 years (range 3–22). None had diabetic retinopathy. The mean age at diagnosis of optic atrophy was 11.1 years (range 8–35). The best-corrected visual acuity ranged from counting fingers to 20/50. Conclusions: Association of optic atrophy with insulin-dependent diabetes mellitus should raise the suspicion of Wolfram syndrome.

New pediatric risk factors for amblyopia: strabismic versus refractive

Purpose: To assess the role of risk factors for amblyopia, such as family history and neonatal background, for the prediction of either strabismic amblyopia or refractive amblyopia. Methods: In this retrospective case-control model, the study population included all children born at the Hospital de Braga during 1997-2012 (3 to 18 years old) with ophthalmologic consultation in 2014. Data collection was performed from the clinical database and through telephone questionnaire surveys. Results: A total of 298 (50%) controls and 298 (50%) cases (120 [40.3%] strabismic amblyopia and 178 [59.7%] refractive amblyopia) were analyzed. A significantly lower birthweight was detected in patients with strabismic amblyopia (mean 2,961 g [95% confidence interval (CI) 2,827-3,096]) compared to controls (mean 3,198 g [95% CI 3,125-3,271]) (p = 0.002). Five-minute Apgar was significantly lower in patients with strabismic amblyopia (mean 9.57 [95% CI 9.37-9.77]) than in controls (mean 9.83 [95% CI 9.77-9.90]) (p = 0.004) or patients with refractive amblyopia (mean 9.79 [95% CI 9.69-9.89]) (p = 0.031). Family history of either amblyopia or strabismus was associated with amblyopia (χ2 [2, n = 562] = 12.66; p = 0.002; Cramer V = 0.150; χ2 [2, n = 561] = 11.0; p = 0.004; Cramer V = 0.140), but was significantly more associated with strabismic amblyopia (p = 0.0023 and p = 0.0032) than with refractive amblyopia (p = 0.48 and p = 0.015, respectively). Multinomial logistic regression model explained 50.8% of the variance in amblyopia development. Low 5-minute Apgar had a relevant odds ratio (OR) for either strabismic amblyopia (OR 3.44; p = 0.066) or refractive amblyopia (OR 3.30; p = 0.077). Conclusions: This division in amblyopia subtypes gives a new perspective of the risk factors for amblyopia, with family history and some obstetrician/neonatal outcomes appearing to be more relevant in strabismic amblyopia. Educating health care providers to recognize these risk factors can result in an early ophthalmologic referral.

Analysis and tests of the new cylindrical dipole antenna structure with a bazooka balun

In this paper, a new cylindrical dipole antenna structure is analyzed using the finite-difference time-domain (FDTD) method developed for solving Maxwells equations with the body of revolution (BOR) technique. A two-dimensional finite difference lattice is used to study the efficiency of a bazooka balun type, connected at the bottom of the cylindrical dipole antenna. A good agreement of the experimental and theoretical result from this new structure is shown, with the FDTD calculation design at a center frequency of 800 MHz. We conclude that the result demonstrated in this paper shows the great efficiency of the FDTD algorithm for such complex structures analysis.