The knowledge of the electromagnetic constitutive properties of materials is crucial in many applications. Free-space methods are widely used for this purpose, despite their inherent practical difficulties. This paper describes an affordable free-space experimental setup for the characterization of flat samples in 1–6 GHz in a non-anechoic environment. The extracted properties are obtained from the calibrated Scattering Parameters, using a frequency-by-frequency solution or a multi-frequency reconstruction. For the first, we describe how the Time-Domain Gating can be implemented and used for filtering the signals. For the latter, a weighting factor is introduced to balance the reflection and transmission data, allowing one to have a more favorable configuration. The different role of transmission and reflection measurements on the achievable results is analyzed with regard to experimental uncertainties and different noise scenarios. Results from the two strategies are analyzed and compared. Good agreement between simulation, measurement and literature is obtained. According to the reported results for dielectric materials, there is no need of filtering the data by a Time-Domain Gating in case of the multi-frequency approach. Experimental results for Polymethylmethacrylate (PMMA) and Polytetrafluorethylene (PTFE) samples validate both the setup and the processing.

Resumo A educação profissional técnica é responsável pela preparação de grande parte dos profissionais qualificados que atuam nas profissões técnicas da cadeia produtiva e na prestação de serviços. Neste artigo é feita uma revisão sobre algumas características da educação profissional técnica, especialmente na modalidade integrada ao ensino médio. Adicionalmente, é analisado como o modelo de aprendizagem experimental de Kolb pode ser aplicado para a melhoria do processo de ensino-aprendizagem. Neste contexto, é apresentado e discutido como o ensino técnico integrado e o perfil dos alunos podem desafiar a aplicação do referido modelo. São usados dados experimentais de dois cursos do Instituto Federal de Educação, Ciência e Tecnologia de Minas Gerais (IFMG) - campus Ibirité para embasar parte da discussão. Por fim, são apresentadas propostas de melhorias, considerando a realidade dos alunos e as características do curso.

This paper describes a prototype of a free-space transmission setup for dielectric parameters estimation. The transmitter and receiver, both configurable by software and working in the range 0.85–1.55 GHz, are not synchronized, as they use different clocks. An estimation of the dielectric permittivity of a planar sample was obtained by comparing our measurements with a numerical model. A parametric study with different variables was conceived in order to find the best fit between measurements and simulations. Customized techniques were applied to deal with noise and inconsistencies found in the measurements. The genetic algorithm was used to adjust the constants that minimized the error between simulated and experimental data. Results for a reference sample of polymethylmethacrylate are presented and discussed. Although the accuracy of the proposed approach in recovering the dielectric parameters of the sample was relatively low, the simplicity and cost-effectiveness of this setup make it interesting for scenarios where a rough characterization of the material is sufficient.

This paper describes the integrated use of two design strategies for controlling the permittivity and permeability of a transformation electromagnetics two-dimensional cloak. This hybrid process permits more freedom in the choice of the constitutive properties, which could simplify the implementation with metamaterials. Because simplicity of materials and scattering performance are inherently conflicting characteristics, a multi-objective genetic algorithm is applied to optimize them. According to the presented results for a transverse-magnetic layered cloak, it is possible to have a good performance in terms of scattering even with an approximated reduced set of parameters with unitary axial permeability.

A singular coordinate transformation leads to extreme materials in a transformation-based cloak. If a non-singular transformation is used, the perfect invisibility is lost. The invisibility is also influenced by the homogenization process. In this paper, we investigate these two influences in 2-D circular cylindrical cloaks, obtained from different non-singular mappings. Considering a further deterministic optimization, we also conclude that it is better to use a non-singular cloak based on a mapping scale up to 20%, since it has lower scattering and simpler materials when compared with cloaks based on other mappings.

Este artigo descreve algumas das estratégias adotadas e os resultados obtidos na disciplina Circuitos Digitais e Microcontroladores, do curso técnico concomitante em Mecatrônica do Instituto Federal de Educação, Ciência e Tecnologia de Minas Gerais campus Ibirité, durante o primeiro semestre de 2022. Essa disciplina, em particular, por ter uma ementa extensa, significativa carga horária prática e ter ocorrido presencialmente após um ano de ensino remoto emergencial, representou uma oportunidade para a adoção de estratégias de aprendizagem experimental.