An enhanced algorithm for complex permittivity extraction at microwave frequencies

An efficient technique of complex permittivity extraction is employed to characterize low-loss conventional dielectric materials at microwave Ku-band. The computational approach eliminates mathematically the systematic errors of the experimental setup. This method needs two uncalibrated S-parameter measurements. The first is performed with a sample under test and the second is done with an empty rectangular waveguide. Three low-loss dielectric materials (Celotex, Plexiglas and Teflon) are characterized to validate experimentally the extraction method over the Ku-band frequencies [12-18] GHz. The average relative errors between the calibrated and uncalibrated results are then calculated and compared. The proposed method has been improved using the mobile average to the experimental results obtained from the uncalibrated measurements, therefore, the stability is then enhanced

A microwave method for complex permittivity extraction of thin materials

An improved microwave method to extract the complex permittivity of solid and liquid materials filled in a short-circuited waveguide is developed. The method determines accurately the dielectric constant of thin and moderate thick samples. It eliminates the problems arising from any position offset of the dielectric slab in transmission / reflection methods. The proposed method is iterative and the initial value is calculated by using the 7th approximation order of trigonometric terms in the exact reflection coefficient equation. This approach is applied to the simulated data of low loss and dissipative materials in limited frequency band

Determination of Distant Learner’s Sociological Profile Based on Fuzzy Logic and Naïve Bayes Techniques

The present article is elaborated in the context of e-learning softwares that provide assistance and functionalities to learners engaged in distance learning. Our contribution consists of a system that estimates a behavioral (sociological) profile for each student. This estimation is based on automatic analysis of students’ textual asynchronous conversations. In general, the automatic analysis of textual conversations is based on speech acts for classification and categorization of messages. This technique has several disadvantages like the absence of standardization of speech acts for determining social behaviors of learners. To overcome this, we propose a multi-agent system based on fuzzy logic reasoning and supervised learning technique for automatic classification and categorization of textual conversation. The determined profiles are proposed to teachers to provide them assistance during tutoring tasks. The objective of this article is to share our reflections around these issues by presenting our experience in the analysis of asynchronous online discussion forums. In this paper, we specifically propose (i) definitions for the used sociological profiles and (ii) introduce the architecture of the Multi-Agent System (MAS) that determines the profiles. The system was experimented with the students of the Master Program “Software Quality” in the Ibn Tofail University. The results obtained from this experience, presented and discussed in this paper, show that the proposed approach can be of interest

Design and characterization of a wideband metamaterial absorber for microwave applications

The metamaterial absorber’s new conception and simulation are presented in this paper. Two peaks of 97% and 99,8% are respectively shown by the absorption spectrum at the resonance frequencies 12,5 GHz and 14,5 GHz. Absorptivity is greater than 80% in the 6 GHz – 16 GHz frequency band and is sensitive to both polarization and incidence’s angles. Clearly this structure provides absorption more than 90% in the range frequency 11,9 GHz -15 GHz. The simulations’ results have revealed that the absorption characteristics can be controlled either by adding resistors to the metallic pattern or by changing its geometric or physical parameters. The proposed structure’s impedance is approximately equal to that of the free space at the resonance frequencies, which explains the perfect absorption’s obtention at these frequencies. A numerical comparison of our absorber with the four broadband perfect absorbers reported in the literature, leads to satisfactory Conclusion. This designed metamaterial absorber can be applied to antennas to improve their directivities