Alfonso Salinas

Parallel 3D-TLM algorithm for simulation of the Earth-ionosphere cavity

A parallel 3D algorithm for solving time-domain electromagnetic problems with arbitrary geometries is presented. The technique employed is the Transmission Line Modeling (TLM) method implemented in Shared Memory (SM) environments. The benchmarking performed reveals that the maximum speedup depends on the memory size of the problem as well as multiple hardware factors, like the disposition of CPUs, cache, or memory. A maximum speedup of 15 has been measured for the largest problem. In certain circumstances of low memory requirements, superlinear speedup is achieved using our algorithm. The model is employed to model the Earth-ionosphere cavity, thus enabling a study of the natural electromagnetic phenomena that occur in it. The algorithm allows complete 3D simulations of the cavity with a resolution of 10km, within a reasonable timescale.

Shumann resonances and electromagnetic transparence in the atmosphere of Titan

Abstract Among the multiple questions that the CASSINI/HUYGENS mission tries to answer is the likelihood of electric discharges in Titans atmosphere. The instruments “Huygens Atmospheric Structure Instrument” and “Radio and Plasma Wave Science” will probe the electromagnetic emissions during the Huygens descent and Cassini flybys, respectively. Although no lightning was observed during Voyagers encounters with Titan in 1980 and 1981, this does not exclude the existence of lightning phenomena. Recent investigations show that lightning discharges could occur in the lower atmosphere, such as the detection of methane condensation clouds in the troposphere and the theoretical prediction of an electric field that would be sufficient enough to cause lightning. We present a numerical model of Titans atmosphere with the aim of calculating the resonance frequencies and the atmospheric transparency to electromagnetic waves. The detection and measurement of these resonances, Schumann frequencies, by the Huygens probe, would show the existence of electric activity connected with lightning discharges in the atmosphere. As it happens with the Schumann frequencies of Earth, losses associated with the electric conductivity will make these frequencies to be lower than the theoretically predicted, the fundamental one being located between 11 and 15 Hz. An analytical study shows that the strong losses associated with the high conductivity make it impossible that an electromagnetic wave generated near the surface with a frequency of 10 MHz or lower reaches the outer part of Titans atmosphere. Therefore the detection of electromagnetic waves coming from Titans lower atmosphere by the RPWS instrument is very unlikely.

Time domain simulation of electromagnetic cloaking structures with TLM method

The increasing interest in invisible cloaks has been prompted in part by the availability of powerful computational resources which permit numerical studies of such a phenomenon. These are usually carried out with commercial software. We report here a full time domain simulation of cloaking structures with the Transmission Line Modeling (TLM) method. We first develop a new condensed TLM node to model metamaterials in two dimensional situations; various results are then presented, with special emphasis on what is not easily achievable using commercial software.

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.

A simple and rapid phosphorimetric method for the determination of the fungicide fuberidazole in water samples

The applicability of heavy-atom induced room-temperature phosphorescence to determine pesticides in real samples is demonstrated in this work. Thus a new, simple, rapid and selective phosphorimetric method for fuberidazole determination is proposed. The phosphorescence signals are a consequence of intermolecular protection when analytes are found exclusively in the presence of heavy atom salts and sodium sulphite when used as an oxygen scavenger to minimize RTP quenching, so protective media (such as cyclodextrines, micellar media, etc) are not necessary to use for obtaining phosphorescence in solution. The determination was performed in 0.4 M KI and 8 mM sodium sulphite at a measurement temperature of 20°C. The phosphorescence intensity was measured at 515 nm exciting at 308 nm. Phosphorescence was easily and rapidly obtained, showing a linear concentration range between 0 and 25 ng mL−1 with a detection limit of 95 ng L−1. The method has been successfully applied to the analysis of fuberidazole in water.

Full 3-D TLM simulations of the Earth-ionosphere cavity : Effect of conductivity on the Schumann resonances

Schumann resonances can be found in planetary atmospheres, inside the cavity formed by the conducting surface of the planet and the lower ionosphere. They are a powerful tool to investigate both th ...

Extremely low frequency band station for natural electromagnetic noise measurement

A new permanent ELF measurement station has been deployed in Sierra Nevada, Spain. It is composed of two magnetometers, oriented NS and EW, respectively. At 10 Hz, their sensitivity is 19 μV/pT and the signal-to-noise ratio (SNR) is 28 dB for a time-varying signal of 1 pT, the expected field amplitude in Sierra Nevada. The station operates for frequencies below 24 Hz. The magnetometers, together with their corresponding electronics, have been specifically designed to achieve such an SNR for small signals. They are based on high-resolution search coils with ferromagnetic core and 106 turns, operating in limited geometry configuration. Different system noise sources are considered, and a study of the SNR is also included. Finally, some initial Schumann resonance measurements are presented in order to validate the performance of the measurement station, including 1 h length spectra, daily variations of resonance amplitudes and frequencies for the different seasons, and a 3 day spectrogram.

Application of the Monopulse Technique to a Planar Array of Nonlinearly Loaded Straight-Wire Coupled Antennas

The radiation and reception characteristics of a planar array of straight-wire coupled antennas are analyzed by a numerical method in the time domain. The numerical method allows us to calculate some significant magnitudes in an array of coupled wire antennas, such as the frequency dependence of the self- and mutual impedances between antennas. The antennas are fed by a time-varying Gaussian pulse, and they are loaded with various nonlinear elements to exert some control over the radiation field. The results are used to show how the monopulse technique with the slope pattern promises a much higher accuracy of angle measurement for a target.

A generalized dynamic symmetrical condensed TLM node for the modeling of time-varying electromagnetic media

A new transmission line matrix (TLM) formulation in terms of magnetic flux pulses is presented for the numerical modeling of time-varying electromagnetic media. After redefining the Thevenin theorem in terms of magnetic flux and electric charge, this conceptually new approach is used to develop a dynamic generalized TLM node for the modeling of electromagnetic-wave propagation through time-varying media. Different specific implementations of the generalized node show the successful behavior of the node proposed in this paper.

Importance of the singular constitutive parameters of cylindrical cloaks: illustration on the anticloak concept

Two-dimensional electromagnetic cloaking devices with infinite optic constants at the inner boundary are investigated. Numerical simulations of this class of ideal cloak, performed with the transmission line modeling method, confirm the fundamental importance of such extreme values in the efficiency of the cloak in some situations. This is illustrated by using the concept of the anticloak, which was shown to be capable of defeating the non-ideal cloak. We numerically show that the presence of a layer with extreme constitutive parameters renders the anticloak unable to produce its effect. Furthermore, we propose a simple theoretical model that leads to the same conclusion if the cloak is slightly dissipative.