We present in this paper a field-grade method for the determination of the electric permittivity of the explosives used in Improvised Explosive Devices (IED) found in Colombia. The paper presents a direct simplified method used to calculate the permittivity of dielectric materials. The efficiency of the direct method is analyzed using computer simulations of known low-loss and lossy materials. Additionally, the field deployable system and measurement setup are explained and their performance for field measurements is compared against reference measurements performed by a vector network analyzer in the frequency range from 0.3 GHz to 3 GHz. Finally, the measurements of complex permittivity of improvised explosives made of Ammonium Nitrate- Fuel Oil (ANFO) are presented.

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.

This article derives design guidelines for radar absorbing materials (RAM) integrating connected, fishnet-like, resistive frequency selective surfaces (R-FSSs). While R-FSSs have been long used in the radar signature and electromagnetic interferences reduction, nevertheless the configuration where all the unit-cells are physically connected has not been yet thoroughly investigated for this aim. Indeed, the fishnet-like arrangement can guarantee extraordinary key advantages in terms of RAMs fabrication, especially for large production scales. Therefore, this article, by resorting to significant test-cases, aims at deriving practical design procedures to realize advantageous connections among adjacent FSS unit-cells. Specifically, the effects on the overall FSS impedance behavior of the geometrical variations in the unit-cell connections are deeply explored. To ensure the broad applicability of the presented guidelines, the study has been carried out by recurring to an equivalent circuit analysis, based on the transmission line theory, and on accurate full-wave simulations. To prove the practical significance of the developed guidelines, two prototypes of the same RAM based on a resistive and connected FSS have been fabricated. Both in a small flat panel and in a large-scale conformal arrangement, the electromagnetic reflection was drastically reduced in the band between 6 and 18 GHz, while significantly simplifying the fabrication process. In conclusion, the proposed research exhibits promising potential to enable an efficient large-scale fabrication for RAMs, by addressing the difficulties associated with the design of connected unit-cells.

The complex permittivity of different types of soils in the ultrahigh frequency (UHF) is studied in this letter. A new model, whose inputs are the low-frequency conductivity and the volumetric water content, is proposed to estimate the complex permittivity of soils in UHF. The model is compared with complex-permittivity values of each soil in the UHF range, which are determined from two-port S-parameters measurements of a coaxial probe designed for material characterization. Results show that the model is in a good agreement with the measurements despite some differences in soils with high resistivity. The soil samples used in this study include locations where humanitarian demining operations are being conducted.

This paper presents a method for the maximization of the energy radiated by a Vircator at a given band of frequencies. The research focuses on axially extracted Vircators. The methodology carried out uses a combination of analytic and numerical techniques. The solution presented is useful in cases where the Vircator is available and drastic changes could be burdensome. Results are validated by numerical simulations.

We present a new technique for the design and test of coaxial switched oscillators (SWOs). In this paper (Part I of a two-part paper), we concentrate on the electrostatic design of coaxial SWOs. We introduce a new design for the electrodes, which have been conceived as conformal surfaces in a geometrically convenient curvilinear space where Laplace equation is solvable. Analytical solution of the electrostatic fields is presented, discussed, and validated using numerical simulation. A prototype of an SWO based on this design is built and validated using experimental data.