Cassio Goncalves Do Rego

An innovative formulation, intended by the authors, for the calculation and analysis of ground-reflection of ray paths under conditions of horizontally variable refractivity, is introduced in this letter. The deduced formulation is incorporated within a modified Ray Tracing (RT) technique that considers atmospheric refractivity effect in radiopropagation modeling. Canonical tests were carried out, where the proposed analytical solution was applied to predict coverage in a long-distance scenario that assumed different configurations of horizontally stratified refractivity changes along the investigated environment. The results achieved were confronted with the numerical solution of the Split-Step Fourier Parabolic Equation (SSPE) at 10 GHz. It was possible to observe that the results obtained from a modified RT with horizontally variable refractive and the SSPE method have a similar behavior when estimating the received power. These innovations contribute to the development of algorithms for modeling and analyzing wireless networks in more realistic environments.

Scanning microwave impedance microscopy (sMIM) has become a powerful tool for nanoscale characterization, utilizing microwave frequencies to probe the material properties of diverse systems with remarkable spatial resolution. This review offers an in-depth analysis of the foundational principles, technological advancements, and broad applications of sMIM. By harnessing near-field microwave interactions between a sharp metallic probe and the sample, sMIM enables simultaneous acquisition of both real (resistive) and imaginary (capacitive) components of the reflected signal, providing detailed insights into the local permittivity and conductivity of materials at the nanoscale. We address critical challenges, including impedance matching, probe–sample interactions, and the influence of environmental factors such as surface water layers and meniscus formation on resolution and contrast. Recent advancements in finite element modeling and the application of lumped-element circuit models have further enhanced the precision of signal interpretation, enabling more accurate analysis of complex systems. This review highlights sMIM’s wide-ranging applications, from material science and semiconductor diagnostics to biological systems, showcasing its ability to perform non-destructive, high-resolution imaging down to the single-digit nanometer scale. These capabilities position sMIM as an indispensable tool for advancing future innovations in nanotechnology and related fields.

This paper discusses a polarimetric measurement campaign conducted in two distinct environments, with data collected at the Federal University of Minas Gerais (UFMG) in Brazil. The study investigates millimeter wave propagation through vegetation at a frequency of 36.6 GHz in two scenarios: the Central Square of UFMG and a forested area within the campus. In the first scenario, measurements were conducted along a main street with varying degrees of vegetation obstruction, focusing on analysing fast fading. For the fast-fading analysis, Rayleigh, Rice, and m-Nakagami distributions were considered. Results from the first scenario indicate that the m-Nakagami distribution provides the best fit for both vertical and horizontal polarisations, surpassing traditional models such as Rayleigh and Rice. In the second scenario, measurements were taken within a forested area, and the study was undertaken to analyse fast fading and excess loss. Considering the excess loss study, measurements were compared with three traditional models (CCIR, Weissberger, and COST 235). Excess loss analysis showed that traditional excess loss propagation models tend to exhibit a minimum RMS error of 10.6 dB for vertical polarisation and 15 dB for horizontal polarisation (Weissberger model), whereas the proposed model demonstrated improved accuracy over log-distance models, particularly for vertical polarisation, presenting an RMS error of 5.8 dB, and for the horizontal polarisation a RMS error of 10.2 dB, at least 4.8 dB smaller than the Weissberger model. Considering the fast fading analysis, the m-Nakagami distribution tends to provide better results in both polarisation. These findings underscore the importance of accurate propagation models tailored to specific environmental conditions, such as vegetation, to enhance the reliability of future 5G evolution and 6G microwave communication systems.

In this article, a comprehensive analysis of the approach known as Split-Step Wavelet Parabolic Equation (SSW-PE) in modeling radio wave propagation is presented. The SSW-PE introduces innovations, such as the application of narrow-angle and wideangle approaches, referred to as NAPE and WAPE, respectively. Furthermore, the SSW-PE demonstrates the incorporation of refractivity variations, modifications in terrain modeling for better representation, and considerations of surface boundary conditions. In addition to its innovative aspects, this study aims to provide a complete guide for effectively replicating the algorithm, thereby promoting the advancement of propagation studies using wavelets. The effectiveness and applicability of this approach are validated through comparative studies with well-established solutions, including the Discrete Mixed Fourier Transform (DMFT) version of the Split-Step Parabolic Equation (SSPE) method. Comparisons with measurements from real propagation cases are also conducted. Statistical analysis confirms the innovative potential of the SSW-PE algorithm, which also offers computational efficiency for rapid and consistent simulations. Thus, this article contributes to a comprehensive and innovative analysis, providing tangible resources for the research community interested in expanding this methodology.

The feasibility of remote teaching as an alternative to face-to-face classes during the period of social isolation caused by the Covid-19 pandemic encountered many difficulties in accessing the Internet in remote regions, and even in urban areas of the country. This work presents a study of Internet access capabilities using the cell phone network for video-class sessions in environments similar to those that could be used by students in remote areas and with weak cell phone signals, in particular indigenous communities. The work seeks to answer three research questions related to data consumption, monetary cost and quality of user experience (QoE) per video lesson session. Measurement experiments with real devices show that the cost per video session is proportional to the QoE of the users, as well as to the conditions of the wireless access network. The results show an 80% reduction in cost per video session while maintaining the median QoE on the Mean Opinion Score (MOS) scale.

In this paper, we demonstrated a highly sensitive microwave-based resonator sensor capable of detecting variations in an aqueous medium of up to 0.94 mg/dL. In the presented device, the intrinsic resonant response (resonant amplitude, resonant frequency, and quality factor) is capacitively perturbed in reaction to the sample presence. To achieve higher sensitivity, the sample under testing generally is placed on the resonator surface, where the electric field is highly concentrated at the operating frequency. Thus, demonstrating excellent results in terms of sensitivity and reproducibility.

This paper presents a radiopropagation algorithm based on a Ray Tracing (RT) technique that combines a modified multipath model for constant refractivity gradient profiles and the Uniform Theory of Diffraction (UTD). A novel formulation is proposed by the authors for calculation and ground-reflection analysis of ray paths depending on atmospheric refractivity. The algorithm introduced herein was evaluated in a mixed scenario and in two more realistic case studies, under conditions of constant refractivity gradient and lossy terrain profiles. Pathloss results are obtained and compared with Parabolic Equation (PE) numerical solution results at 2.0 GHz, 3.5 GHz and 5.4 GHz. In such conditions, the modified radiopropagation multipath algorithm with atmospheric refractivity introduced herein showed satisfactory results.

In this work a closed time-domain formulation was developed to analyze offset IRA (Impulse Radiating Antennas) satellite dishes responses. Such antennas present more complex geometry than reflector parabolic antennas fed at the focus. For this reason, the formulation studied here has more extensive expressions. At first, expressions for the field radiated by the offset reflector in the frequency domain were revised. They were obtained by approximations of geometric optics (GO) and the aperture method. Following, the inverse Laplace transform was applied to those expressions, which allowed obtaining radiation expressions in the time domain, which were used to determine a unit step temporal response.

In this work, we analyzed numerically a multiscale nanosystem based on sMIM on TBG. Spontaneous formation of a water-meniscus by the approximation between the tip-sample concentrates the microwave fields, reaching resolutions of up to 1nm.

The system capable of harvesting RF energy from the environment through an antenna and converting it into direct current energy to deliver to a load is known as rectenna. The rectifier circuit is an important part of the rectenna and its modeling is arduous since it employs a non-linear device working at extremely low power levels. In addition, there are some losses in the system. Thus, the design of a high-efficient rectifier is a great challenge. In this work, several rectifier topologies are optimized, using the Genetic Algorithm, in order to achieve the highest efficiency and output voltage. An analysis of the influence of the variables on the output of these rectifiers was also performed. The topologies under investigation were optimized for-15 dBm input power and 2.45 GHz operating frequency, in accordance with the most suitable band for energy harvesting. Under these conditions, the Monodiode Series topology presents the best performance. When the input power is-15 dBm, it presents an output voltage of 402 mV and an efficiency of 51.3%. At that power level, the achieved efficiency is higher than that found in the literature.