Joabson Nogueira de Carvalho

In this paper, a compact matryoshka DGS using dielectric resonator (DR) is proposed. Despite the use of dielectric resonators to obtain band-stop frequency response not being a new idea, the proposed compact matryoshka DGS is an original contribution, since only recently the matryoshka geometry was used in DGS applications. Furthermore, a numerical analysis of the positioning of the DR is presented, which makes it possible to determine the region of the DGS for which the minimum resonant frequency is reached, and the resonant frequency range that can be obtained. To the best of the authors’ knowledge, this numerical analysis is an unpublished result, even more so, for the matryoshka DGS. The matryoshka geometry was described, including initial design equations. To verify the expected characteristics (miniaturization, selectivity, and resonant frequency tunability), two compact matryoshka DGSs (DGS1 and DGS2) were designed using a high permittivity ceramic (MCT-115) as DR. The obtained numerical and experimental results showed good agreement, and the initial design equations proved to be applicable, which allows new dimensions to be determined for other resonant frequencies, according to the application requirements. Resonant frequencies ranging from the maximum value to 33% (DGS1) and 27% (DGS2) were achieved, depending on the DR position. Considering λ ₀ the wavelength in free space, corresponding to the resonant frequency, DGS1 and DGS2 achieved an occupied area of 0.04λ ₀ ×0.04λ ₀ , and 0.05λ ₀ ×0.05λ ₀ , respectively, a good miniaturization. The proposed compact matryoshka DGS may be especially attractive for applications that require a very selective band-stop frequency response. If a wider band-stop is required, the proposed DGS can be cascaded.

This paper presents the characterization of dielectric properties (dielectric permittivity and dielectric loss factor) of Tommy Atkins mango (Mangifera indica L), a fruit produced in several regions of Brazil, of great economic importance. The fruits were characterized according to their maturation index, by probe method, and identified by the yellowish tone in their bark. The results allowed correlating the dielectric characteristics of the fruit with the physicochemical transformations that occurred in the maturation process of the mango Tommy. It was also verified a greater variation in the frequencies below 1 GHz, with the maturation indicated by the dielectric signature on the fifth day after the harvest. From these results, we can observe the use of electromagnetic materials and techniques in the solution and optimization of processes in agriculture can improve the quality of products consumed or suggesting best practices to the productive sector.

With the growing diffusion of the Internet of Things concept and the advances in low-power electronics, the RFID (Radio Frequency Identification) technology has gained attention in various fields, from entertainment to medicine, for example. Its sensing and signal processing capability allows us to highlight this technology as one of the main solutions in reducing cost and complexity in such applications. This work presents the design and test of a flexible RFID tag operating in the American UHF frequency of 915 MHz, for human body motion detection. Through the analysis of the Received Signal Strength Indicator (RSSI) variation with time and its Fast Fourier Transform (FFT) it was possible to ensure the tag's applicability.

Due to the recent miniaturization of wireless devices, the use of wearable antennas is steadily increasing. A wearable antenna is intended to be a part of the clothing used for communication purposes. In this way, a lower visual cost may be achieved. Recently, biologically inspired design, a kind of design by cross-domain analogy is a promising paradigm for innovation as well as low visual cost. The shapes of the plants are structures optimized by nature with the primary goal of light energy capture, transforming it into chemical energy. In this case, they have similar behavior to that of parabolic reflectors; this enables microwave engineers design innovative antennas using bio-inspired concepts. One of the advantages of using bio-inspired plant shapes is the design of antennas with great perimeters in compact structures. Thus, we have small antennas operating in low frequencies. This chapter presents the recent development in bio-inspired wearable antennas, easily integrated to the clothes and accessories used by the body, built in denim, low-cost flexible dielectric, and polyamide flexible dielectric, that is flexible with high resistance to twists and temperatures, for wireless body area network (WBAN) applications, operating in cellular mobile (2G, 3G, and 4G) and wireless local area network (2.4 and 5 GHz) protocols.

Neste trabalho, os parâmetros de espalhamento de uma junção de guias-de-onda de dimensões diferentes são determinados como função da frequência de excitação e o número de modos presentes em cada lado da estrutura [...].

Este artigo apresenta o protótipo de um secador por microondas automático, para obtenção de curvas de secagem de produtos agrícolas. [...].

Neste trabalho é apresentado um procedimento para o cálculo de circuitos em microfita, tendo como exemplo o projeto de dois filtros passa-baixas, um com resposta tipo Chebyshev e o outro Butterworth [...].

A perda média de penetração, PMP, é um parâmetro de propagação muito útil ao se estimar o nível de potência após um obstáculo.

Neste trabalho é apresentada a caracterização experimental de circuitos em microfita através da utilização de detectores de micro-ondas no lugar dos usuais medidores de potência [...].