Enrique A. Navarro

Analysis of the finite difference time domain technique to solve the Schrödinger equation for quantum devices

An extension of the finite difference time domain is applied to solve the Schrodinger equation. A systematic analysis of stability and convergence of this technique is carried out in this article. The numerical scheme used to solve the Schrodinger equation differs from the scheme found in electromagnetics. Also, the unit cell employed to model quantum devices is different from the Yee cell used by the electrical engineering community. A bound for the time step is derived to ensure stability. Several numerical experiments in quantum structures demonstrate the accuracy of a second order, comparable to the analysis of electromagnetic devices with the Yee cell.

Finite difference time domain Simulation of the Earth-ionosphere resonant cavity: Schumann resonances

This paper presents a numerical approach to study the electrical properties of the Earths atmosphere. The finite-difference time-domain (FDTD) technique is applied to model the Earths atmosphere in order to determine Schumann resonant frequencies of the Earth. Three-dimensional spherical coordinates are employed and the conductivity profile of the atmosphere versus height is introduced. Periodic boundary conditions are implemented in order to exploit the symmetry in rotation of the Earth and decrease computational requirements dramatically. For the first time, very accurate FDTD results are obtained, not only for the fundamental mode but also for higher order modes of Schumann resonances. The proposed method constitutes a useful tool to obtain Schumann resonant frequencies, therefore to validate electrical models for the terrestrial atmosphere, or atmospheres of other celestial bodies.

FDTD analysis of E-sectoral horn antennas for broad-band applications

The finite-difference time-domain (FDTD) method is applied to study the performance of E-plane sectoral horn antennas designed for broad-band applications. These antennas (proposed for 6-18 GHz phased arrays) have a large bandwidth, and they are easily array integrated. These antennas have a highly complicated geometry that is modeled using a polygonal approximation in the curved boundaries. Perfect matched layers (PMLs) combined with first-order absorbing boundaries are employed to simulate the free-space environment in the FDTD mesh.

A polarizer rotator system for three-dimensional oblique incidence

A numerical model to analyze a system formed by the cascade connection of slanted strip grating plates to rotate the polarization plane of a linearly polarized wave is presented. A variant of the Generalized Scattering Matrix Theory is formulated in terms of E-type and H-type modes. These modes enable as to study three-dimensional oblique incidence upon the polarizer rotator system. A simulation program was implemented allowing the design and optimization of these systems. General criteria of design are presented, and a four-plates 60/spl deg/ polarizer rotator is designed in the 7-18 GHz band; a prototype was manufactured and tested. Comparison between the theoretical results and measurements are given, and a good agreement is found. >

Multilayer and conformal antennas using synthetic dielectric substrates

Multilayer antennas - for example, stacked patches - often employ low permittivity substrates, such as foams. These foams, however, tend to be fragile, difficult to glue, and difficult to bend. In a previous contribution, the authors described how a Duroid substrate may be drilled in order to obtain a low permittivity synthetic dielectric. This paper shows, by means of both practical and numerical experiments, the results of using such a substrate in a range of multilayer antennas.

Some considerations on the accuracy of the nonuniform FDTD method and its application to waveguide analysis when combined with the perfectly matched layer technique

The accuracy of the finite-difference time-domain (FDTD) technique is measured with respect to the meshs cell dimensions. The accuracy of the FDTD technique is investigated for those applications that demand the use of nonuniform meshes. The results of simulations suggest that second-order accuracy can be achieved. These simulations are carried out using different boundary conditions. It is observed that the choice of boundary conditions plays a large role in the accuracy that is achieved with the FDTD method. The perfectly matched layer (PML) technique is found to be well suited to waveguide analysis because of its wide bandwidth, and the ease with which it can be implemented with a nonuniform mesh. We apply the nonuniform FDTD method, in combination with the PML technique, to analyze a narrow iris in waveguide.

FDTD characterization of evanescent modes-multimode analysis of waveguide discontinuities

In this paper, a finite-difference time-domain numerical dispersion relation for evanescent waves is derived, and its impact on the modeling accuracy is studied. The numerical evanescent constant is found to differ from the analytical one. As a result, a correction must be used to compute discontinuity parameters. This influences the reference plane chosen for the analysis of propagating modes. Moreover, on calculating multimode transmission and reflection coefficients, the dispersion for evanescent higher order modes is determinant. The dispersive relation is derived, discussed, and used to correct the evanescent constants for the multimode analysis of a waveguide discontinuity.

Yagi-Like Printed Antennas for Wireless Sensor Networks

In this work, two alternative printed antennas for wireless sensor networks applications in the ISM band are presented. The antennas are based on the well- known Yagi-Uda antenna and the principal difference between them is on the printed dipole design; in only one face of the substrate or in both faces. The design has been performed by using an in house developed code based on FDTD algorithm. In the design process, we have focused on the optimization of the bandwidth and the directivity. Finally, some prototypes with different number of dipoles have been fabricated and measured. The good agreement between simulated and experimental results demonstrates the validity of the simulations. The radiation parameters show the potentiality of these antennas for increasing the distance of communication in wireless networks.

Subjective symptoms related to GSM radiation from mobile phone base stations: a cross-sectional study

Objectives We performed a re-analysis of the data from Navarro et al (2003) in which health symptoms related to microwave exposure from mobile phone base stations (BSs) were explored, including data obtained in a retrospective inquiry about fear of exposure from BSs. Design Cross-sectional study. Setting La Ñora (Murcia), Spain. Participants Participants with known illness in 2003 were subsequently disregarded: 88 participants instead of 101 (in 2003) were analysed. Since weather circumstances can influence exposure, we restricted data to measurements made under similar weather conditions. Outcomes and methods A statistical method indifferent to the assumption of normality was employed: namely, binary logistic regression for modelling a binary response (eg, suffering fatigue (1) or not (0)), and so exposure was introduced as a predictor variable. This analysis was carried out on a regular basis and bootstrapping (95% percentile method) was used to provide more accurate CIs. Results The symptoms most related to exposure were lack of appetite (OR=1.58, 95% CI 1.23 to 2.03); lack of concentration (OR=1.54, 95% CI 1.25 to 1.89); irritability (OR=1.51, 95% CI 1.23 to 1.85); and trouble sleeping (OR=1.49, 95% CI 1.20 to 1.84). Changes in –2 log likelihood showed similar results. Concerns about the BSs were strongly related with trouble sleeping (OR =3.12, 95% CI 1.10 to 8.86). The exposure variable remained statistically significant in the multivariate analysis. The bootstrapped values were similar to asymptotic CIs. Conclusions This study confirms our preliminary results. We observed that the incidence of most of the symptoms was related to exposure levels—independently of the demographic variables and some possible risk factors. Concerns about adverse effects from exposure, despite being strongly related with sleep disturbances, do not influence the direct association between exposure and sleep.

Determination of the effective permittivity of dielectric mixtures with the transmission line matrix method

In this article, the effective permittivity of two-phase dielectric mixtures is calculated by applying the transmission line matrix (TLM) method. Two slightly different TLM algorithms are considered: a hybrid approach, which combines the TLM method with a subgriding technique based on dual capacitor circuits, to allow a refined description of the material, and a standard or pure TLM approach, which uses a mesh size smaller than the typical dimension of insertions in order to appropriately describe details of the geometry. A study of the statistical distribution of permittivity for insertions in random positions is also presented, showing that the effective permittivity of the mixture tends to concentrate around the mean value as insertions reduce in size. Both TLM techniques are applied to dielectric mixtures in two-dimensional situations. When the concentration of insertions is small, the results are in close agreement with prediction formulae while for higher concentration values, deviations are observed, although basically the results fall within the range predicted by theoretical bounds. Numerical results obtained using the two TLM approaches present a similar qualitative behavior; nevertheless, a clear difference is observed between them. The study of special periodic situations with coated insertions allows us to identify the pure TLM results as more accurate than those of the hybrid approach and also explains why homogeneous distributions provide numerical values close to the theoretical limits. The effects of shape on permittivity are also modeled and deviations to the Wiener bounds are discussed in detail, using two- and three-dimensional examples in practical situations.