Javier Leonardo Araque Quijano

A water-rich muscle-equivalent tissue-mimicking phantom within a polymeric matrix was experimentally evaluated through a multimodal characterization methodology to determine whether it reproduces the coupled dielectric–thermal behavior of hydrated biological tissue under exposure to electromagnetic waves. The material was analyzed using thermogravimetric analysis, microwave dielectric spectroscopy from 1.5 to 4.0 GHz, VIS–NIR spectroscopy between 350 and 1200 nm, and terahertz time-domain reflection. The thermogravimetric results confirmed dominant water content, with primary mass loss below 200 °C, establishing hydration as the governing factor of its thermal response. Next, the microwave dielectric measurements show that the phantom exhibits a relative permittivity of 37.4 and an electrical conductivity of 2.4 S/m. On the other hand, the VIS–NIR spectra show smooth broadband absorption with limited spatial variability, and principal component analysis reveals macroscopic optical homogeneity without structural spectral distortion. In the THz regime, strong broadband attenuation characteristic of water-rich matrices is observed, and reflection-mode measurements enable robust assessment of temporal stability through time- and frequency-domain signatures. Finally, a microwave thermal validation demonstrates stable behavior under low-power excitation, whereas under hyperthermia-level irradiation, a significant thermal drift of −3.985 °C/h was reached under non-adiabatic conditions, identifying hydration-mediated moisture redistribution as the principal limitation during prolonged high-power exposure. Collectively, these results demonstrate cross-regime dielectric–thermal consistency while explicitly defining the hydration-driven constraints governing long-term stability, providing a validated reference material for broadband electromagnetic and thermal biomedical experimentation.

The hypersonic flight regime is conventionally defined for Mach > 5; in these conditions, the flying object becomes enveloped in a plasma. This plasma is densest in thin surface layers, but, in typical situations of interest, it impacts electromagnetic wave propagation in an electrically large volume. We address this problem with a hybrid approach. We employ the equivalence theorem to separate the inhomogeneous plasma region from the surrounding free space via an equivalent (Huygens) surface and the Eikonal approximation to Maxwell equations in the large inhomogeneous region for obtaining equivalent currents on the separating surface. Then, we obtain the scattered field via (exact) free-space radiation of these surface equivalent currents. The method is extensively tested against reference results and then applied to a real-life reentry vehicle with full 3-D plasma computed via computational fluid dynamic (CFD) simulations. We address both scattering [radar cross section (RCS)] from the entire vehicle and radiation from the onboard antennas. From our results, significant radio link path losses can be associated with plasma spatial variations (gradients) and collisional losses to an extent that matches well the usually perceived blackout in crossing layers in the cutoff. Furthermore, we find good agreement with existing literature concerning significant alterations of the radar response (RCS) due to the plasma envelope.

Nonlinear effects in the radio front-end can degrade communication quality and system performance. In this paper we present a new design technique for reconfigurable antennas that minimizes the nonlinear distortion and maximizes power efficiency through the minimization of the coupling between the internal switching ports and the external feeding ports. As a nonlinear design and validation instance, we present the nonlinear characterization up to 50 GHz of a PIN diode commonly used as a switch for reconfigurable devices in the microwave band. Nonlinear models are extracted through X-parameter measurements supported by accurate calibration and de-embedding procedures. Nonlinear switch models are validated by S-parameter measurements in the low power signal regime and by harmonic measurements in the large-signal regime and are further used to predict the measured nonlinearities of a reconfigurable antenna. These models have the desired particularity of being integrated straightforwardly in the internal multi-port method formulation, which is used and extended to account for the power induced on the switching elements. A new figure of merit for the design of reconfigurable antennas is introduced—the power margin, that is, the power difference between the fed port and the switching elements, which combined with the nonlinear load models directly translates into nonlinearities and power-efficiency-related metrics. Therefore, beyond traditional antenna aspects such as port match, gain, and beam orientation, switch power criteria are included in the design methodology. Guidelines for the design of reconfigurable antennas and parasitic layers of minimum nonlinearity are provided as well as the inherent trade-offs. A particular antenna design suitable for 5G communications in the 3.5 GHz band is presented according to these guidelines, in which the specific switching states for a set of target performance metrics are obtained via a balancing of the available figures of merit with multi-objective separation criteria, which enables good control of the various design trade-offs. Average Error Vector Magnitude (EVM) and power efficiency improvement of 12 and 6 dB, respectively, are obtained with the application of this design approach. In summary, this paper introduces a new framework for the nonlinear modeling and design of reconfigurable antennas and provides a set of general-purpose tools applicable in cases beyond those used as examples and validation in this work. Additionally, the use of these models and guidelines is presented, demonstrating one of the most appealing advantages of the reconfigurable parasitic layer approach, their low nonlinearity.

We present the multi-physical analysis of the induction-corrosion process undergone by a buried pipe subject to electromagnetic induction from a nearby High Voltage Transmission Line (HVTL). The scenario analyzed models a typical situation found in Colombia by using realistic characteristics of the pipe, the HVTL, and environmental parameters such as soil resistivity. The results presented provide a quantitative view of the corrosion process and constitute a useful tool for the analysis and design of the increasingly common situation of pipelines running near HVTLs.

In this chapter the source reconstruction using equivalent currents is a mature technique with a number of interesting applications such as field transformation (NF-FF/NF-NF), electromagnetic diagnostics, design optimization, general source modeling, and antenna synthesis. Its formulation and numerical solution are based on the widely popular MoM and therefore inherits its well-known properties such as accuracy and flexibility and profits directly from advanced techniques developed around MoM such as low-frequency, large-scale, and multi-resolution solvers to mention some. It has been found that the DEqF provides robust results and the best accuracy in real-world situations both for diagnostics and for field transformations, while the simpler SEqFs could be of interest in order to reduce memory and time requirements when the loss in accuracy is acceptable, or when dealing with data from simulation.

This paper describes the design and validation by simulation of compact dual-port reconfigurable antennas (via switches) providing antenna diversity or port duplexing, which in turn are useful in advanced techniques such as cognitive radio (CR) and Multiple-Input Multiple-Output (MIMO). The design results from optimization of an initial structure using the Genetic Algorithm (GA) and evaluated via Method of Moments (MoM) electromagnetic simulation. The optimization process determines concurrently: antenna geometry, location, number and state of the switching devices. The starting point is a simple planar antenna that offers robustness, compactness and allows for an easy fabrication. The resulting devices operate over a band of 0.6 octaves and possess dimensions under 0.25λ0 × 0.25λ0 for the lowest frequency of operation.

This paper presents an investigation of a new technique for the accurate determination of the full sphere pattern of an antenna from truncated spherical near field measurements. The approach was first described and is based on determining a set of equivalent currents that radiate the same pattern in the known area and thus extrapolate the unknown fields in the truncated area. The study is performed on actual measured near-field data to investigate the effectiveness of the technique in realistic spherical near field antenna measurement scenarios.