John J. Pantoja

On the Electromagnetic Susceptibility of Hot Wire-Based Electroexplosive Devices to RF Sources

We present an analysis of the thermal response of a hot-wire electroexplosive device (EED) excited with different transient signals. First-order and second-order analytical models to calculate the thermal response of an EED are assessed taking as reference numerical simulations obtained using ANSYS. For the early-time response, when the time is much smaller than the thermal constant of the EED, the best approach corresponds to a first-order differential model in which the thermal capacitance is calculated with short-pulse excitations. A linear simplification to calculate the maximum temperature due to short excitations is also shown to be adequate. On the other hand, the most appropriate model for the late-time response is a second-order model. The models are used to assess the electromagnetic susceptibility of a wired EED for different electromagnetic pulsed environments. Radiated signals produced by a mesoband radiator, two types of radars, and a hyperband radiator are considered. The radar signal proved to be the most disturbing source because of its highest duty cycle and its flat spectral response around a specific frequency. Even the temperature firing threshold can be exceeded with the radiated field produced by a radar of 200 kW of output power located at a distance of 5 m.

Nonfatal lightning injuries in Colombia: Case reports

Lightning accidents involving several fatalities and injuries are reported every year in the world. Colombia, a country with a high keraunic level, reports frequently lightning fatalities involving several injury mechanisms. However, there are also some fortunate cases where the victims have survived without disabling traumas. Two nonfatal events in which lightning strikes persons are reported. In both cases it is observed that some metal objects such as necklaces or buckle belts saved the life and integrity of the victims. Moreover, both the relative localization and the comprehensive description of the cases scenarios involving visual consequences in the victims skin are presented. The analysis of such accidents could be of interest to protect persons against indirect lightning currents.

Characterization, Modeling, and Statistical Analysis of the Electromagnetic Response of Inert Improvised Explosive Devices

The experimental characterization of the electromagnetic (EM) response of a set of inert improvised explosive devices (IEDs) is presented in this paper. The characterization is based on measurements of gain and input impedance of the firing circuits of inert IEDs in the range of 200 MHz to 2 GHz. First, a theoretical model to predict the average gain is developed. A comparison between the measurement results and theoretical predictions is presented. Then, the power delivered to a hot wire-based electro-explosive device connected to the inert IED is calculated for each measured case and it is statistically analyzed. The effects on the IED response of different characteristics of the coupling, such as the IEDs elements, the incident field polarization, and the impedance mismatch, are also studied. In addition, the statistical performance of the induced power and current are determined and compared with the results of a numerical model based on Monte Carlo simulations. It is demonstrated that both approaches, a theoretical model based on an equivalent antenna and Monte Carlo simulations, can be used to describe the average EM response of the firing circuit of IEDs.

On the Differential Input Impedance of an Electro-Explosive Device

In this paper, a model for the input impedance of a hot-wire electro-explosive device (EED) based on differential-mode measurements is proposed. The model represents the EED using three transmission line segments in cascade. The characteristics of each segment are estimated according to data reported in the literature and to measurements of the differential-mode input impedance of actual EEDs in the ultrahigh frequency range. The experimental procedure and model are presented in detail. In addition, the impedance measurements and the predictions of the proposed model are compared with previous results reported in the literature.

Selection and adjustment of propagation models to compute the electric field strength for exposure assessment purposes in urban environment

This work deals with the selection of the best suited propagation models for computing electric field strength for exposure level assessment in urban environments in Colombia. The selection is based on the comparison of numerical results obtained using a well known commercial tool and measurements performed in the bands assigned in Colombia to the Digital Television Broadcasting (470 MHz-698 MHz) and Digital Radio Trunking (806 MHz-898 MHz).

Antenna array assessment for RF energy harvesting

This paper presents experimental results of an antenna array for energy harvesting. An array of five high monopoles was implemented and its radiofrequency receiving properties were measured. Experimental results show that the main contribution of the radiofrequency power captured by the array is given in the FM band.

On the backscattering from RFID tags installed on vehicular glasses

This paper discusses the application of power budget link in RFID systems with tags installed on vehicular windshield with polarized films. The performance of three tags on glasses with polarizing films and a circular polarized antenna is studied using full wave simulations and measurements. It is found that the mismatch effect due to the change impedance of the RFID antenna when the tag is placed on the windshield presents the main contribution in the budget losses and is the main responsible of the reading range reduction.

High power electromagnetics applied to humanitarian demining in Colombia

This paper summarizes the main findings of a long-term research to explore the use of high power electromagnetics in humanitarian demining. A neutralization method based on remote detonation of electrically-activated improvised explosive devices (IED) was developed. A general overview of the problem is given considering all the components from the source of power to the port of interest in the IED. Different types of radiation systems are analyzed and the most adequate for this application are identified. Experimental results that validate the neutralization method are presented.

Susceptibility frequency regions of deterministic loads connected to circuits with arbitrary characteristics

In this paper, the parameters that determine the resonance frequency bands of circuits with arbitrary elements are studied. Antenna theory is used to analyze the radiated electromagnetic susceptibility of an arbitrary circuit with a deterministic susceptible load. From the gain and the transmission coefficient between the circuit and the load, two parameters to describe the complete circuit behavior are proposed. Then, these parameters are expressed in terms of variables of a Norton equivalent circuit and the independent variables that determine the frequency response of the circuit are deduced. From this analysis, it is possible to relate the frequency ranges in which the susceptibility to radiated disturbances increases.

Optimization of a Vircator using a novel evolutionary algorithm designed to reducing the number of evaluations

This paper presents an optimization of a virtual cathode oscillator (Vircator) with axial extraction using a novel evolutionary algorithm (EA) thought to reduce the number of evaluations. The EA was tested on a Vircator optimization with two objective functions to maximize the radiated energy and to tune the resonance frequency at 5GHz. The simulations were made on CST Particle Studio. The EA was programed in Matlab. The proposed EA is an effort to reduce the computational time used to optimize problems where the objective function should be obtained using computational simulation. At the end, the algorithm identified a zone into the search space where the optimal solution can be found. Results are accord with a previous Vircator optimization using NSGA-II.