Abstract A numerical model based on the finite-difference time-domain (FDTD) method is developed for calculating discharge currents and fields produced due air ionization between two electrodes. Electric conductivity σ of the ionized channel between two electrodes is calculated using non-linear equations, i.e., σ is obtained using functions of time. The functions for calculating σ are adapted and proposed in this work for each stage of the plasma formation and disrupting processes. The proposed numerical model is validated by making comparisons among the obtained FDTD results and experimental data published in literature. In order to perform the validation procedures, an experimental setup from literature is numerically reproduced using the proposed FDTD methodology.

Abstract Semi-analytical equations are developed for aiding the process of designing terahertz graphene-based rectangular dipole antennas lying on glass substrates. It directly provides the dipole length required for obtaining resonance at a desired frequency since antenna width and graphene chemical potential are known. By using the finite-difference time-domain (FDTD) method, a large number of computational simulations were performed considering several combinations of antenna dimensions and chemical potential values. The simulation results were used along with graphene electrostatic scaling law combined with the least squares method to optimize the formulation coefficients. With the optimized coefficients, we obtain very satisfying accuracy levels. In the frequency range from 0.5 THz to 3.0 THz, the average relative absolute error is 1.50%, with maximum relative absolute error of 6.77%.

Abstract The Amazon region has high lightning occurrence rates, with many lightning hot spots. Different rivers cross the Amazon rainforests and the people that live there use these rivers as roads to go from one place to another. Every year, lightning deaths are reported in the Brazilian Amazon region. In 2018, a lightning discharge struck a small riverboat, which killed 4 people and injured 5 in the North region of Brazil. In this study, we investigate lightning fatalities in Amazon rivers and compute electric field distribution in a small riverboat due to a lightning strike using the finite-difference time-domain (FDTD) method. The results show that the electric field produced inside the boat is large enough to cause air breakdown. Additionally, we propose a cost-effective method to improve lightning safety for people that use small boats in the Amazon region.

Abstract In this paper, a finite-difference time-domain (FDTD) formulation, based on the exponential matrix and on thin material sheet methods is developed for modeling subcellular thin graphene sheets. This formulation is validated by reproducing graphene frequency selective surfaces (FSS) known from literature. Then, we propose in this work a smart graphene FSS device. Smartness is obtained by means of a unity cell formed by a graphene ring with a graphene sheet placed in its aperture. By properly regulating the chemical potentials of the graphene elements, two frequency- tunable modus operandi are obtained: single- or dual-band rejection modes. When the device operates in its dual-band rejection mode, either of the rejection bands can be shifted individually in the frequency spectrum. Additionally, both rejection bands can also be reconfigured simultaneously.

Abstract Partial discharge (PD) monitoring is widely used in rotating machines to evaluate the condition of stator winding insulation, but its practice on a large scale requires the development of intelligent systems that automatically process these measurement data. In this paper, it is proposed a methodology of automatic PD classification in hydro-generator stator windings using neural networks. The database is formed from online PD measurements in hydro-generators in a real setting. Noise filtering techniques are applied to these data. Then, based on the concept of image projection, novel features are extracted from the filtered samples. These features are used as inputs for training several neural networks. The best performance network, obtained using statistical procedures, presents a recognition rate of 98%.

Abstract It is shown that proper representation of transmitting and receiving antennas in indoor environments are decisive for accurate prediction of electromagnetic power transfer parameters using the standard 3D-FDTD method. With the standard Yee method, it is not always possible to precisely describe all the geometrical details of electrically small antennas. A new approach for description of the discone antenna in uniform 3D-FDTD lattice is presented. The calculations are validated by comparing FDTD results with the polyhedral beam-tracing method and experimental data.

Abstract A methodology based on spectral analysis for localization of multiple partial discharges in dielectric region of hydro-generator coils is proposed. This pinpointing of multiple discharges aims to provide means for performing diagnosis of insulating regions of the coil. A numerical model of the structure was developed by using the finite-difference time-domain method (FDTD-3D) to solve Maxwell’s equations. Transient voltage associated with partial discharges that occurs at different positions of the coil is calculated at specific point and its spectrum is used to perform the diagnosis. In 90% of simulations, accurate estimates of simultaneous discharges location were obtained. Physical phenomena allowing the development of the methodology are assessed numerically and experimentally. Finally, a localized artificial PD injection schema is proposed and used for validating our numerical results and physical analysis.

Abstract In order to measure electrical signals produced by partial discharges in hydrogenerators stator windings, capacitive couplers are regularly used. They are electrically connected to the windings and therefore, require undesired insulation intrusion. For avoiding such an intrusion, a microstrip directional coupler is used, which is experimentally and numerically investigated in this work. This electromagnetic field sensor is analyzed initially via computer simulation using the finite-difference time-domain method. This numerical analysis is fulfilled considering the coupler placed over a stator bar. Experimental high-voltage tests with generator windings were also performed. We compare the results of the measurements obtained by using various sensors and show that the microstrip directional coupler has some important advantages over traditional capacitive sensors such as complete conductive insulation from the windings and the capacity of detecting shorter PD pulses due to their wider bandwidth.

the aim of this work is to present a new methodology, based on vector and geometrical techniques, for determining the position of an intruder in a residence (3D problem). Initially, modifications in the electromagnetic responses of the environment, caused by movements of the trespasser, are detected. It is worth mentioning that slight movements are detected by high frequency components of the used pulse. The differences between the signals (before and after any movement) are used to define a sphere and ellipsoids, which are used for estimating the position of the invader. In this work, multiple radars are used in a cooperative manner. The multiple estimates obtained are used to determine a mean position and its standard deviation, introducing the concept of sphere of estimates. The electromagnetic simulations were performed by using the FDTD method. Results were obtained for single and double floor residences.