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.

In this paper, we obtain the Complex Natural Resonances of an object from the backscattered response in the frequency domain with a novel rational function approximation method based on both Vector Fitting and Cauchy methods. We determine the system order and an initial set of poles, which are used as a basis for a rational function approximation. The results from the simulations and experiments show an improvement in the reconstructed signals and the accuracy of the CNRs calculated, with an increased tolerance to the critical Signal-to-Noise Ratio. This is being used in the problem of GPR landmine humanitarian detection in Colombia.

We present in this paper the preliminary empirical model of the attenuation produced by nine vegetation types with diverse heights and climate conditions in Colombia. Measurements were performed in co and cross-polarization. Five frequency bands with the following central frequencies were considered: 150 MHz, 360 MHz, 580 MHz, 850 MHz, and 3600 MHz. As expected, a comparison between measurements and calculations with the Fitted International Telecommunication Union (FITU) attenuation model shows a strong dependence of the attenuation with the type of vegetation and its spatial distribution. FITU model shows a good agreement with measurements in coniferous forest and citrus plantation. On the other hand, the model presents more than 10 dBs of underestimation for some native species in the propagation losses for the highest measured frequency bands, while, for balsa, the model presents more than 10 dBs of overestimation. Based on these results, an adaptation of the existing attenuation model for propagation through vegetation, in special the FITU model, is proposed for Colombian conditions.

This paper presents a study on the identification of main parameters involved in the on-object gain penalty for RFID Tags when are used over front glass of vehicles. We assess four variables with relevant importance over this penalty: Glass type, polarized film, polarization of the electromagnetic wave, and the tag type. The assessment is performed using experimental tests based in the Design of Experiment technique. From the results, a simplified model to determine the on-object gain penalty is developed. Keywords.- ANOVA, DOE, Glass, On-object gain penalty, Penalty factor, Polarized film, RFID, Tag. RESUMEN Este documento presenta un estudio sobre la identificación de los principales parámetros que intervienen en el factor de penalidad para Tags RFID cuando son instalados sobre el vidrio frontal de los vehículos. Evaluamos las cuatro variables con importancia relevante sobre este factor de penalidad: Tipo de vidrio, película polarizada, la polarización de la onda electromagnética, y el tipo de tag. La evaluación se realiza mediante pruebas experimentales basadas en la técnica de Diseño Experimental. A partir de los resultados, se logra obtener un modelo simplificado para determinar el factor de penalidad de acuerdo a las variables analizadas. Palabras clave.- ANOVA, DOE, Factor de penalidad, Película polarizada, Penalidad de ganancia en objetos, RFID, TAG, Vidrio.