Two solutions for UHF RFID tags for soil moisture sensing were designed and are described in this paper. In the first, two conventional tags (standard transponders) are employed: one, placed close to the soil surface, is the sensor tag, while the other, separated from the soil, is the reference for system calibration. By transmission power ramps, the tag’s turn-on power levels are measured and correlated with soil condition (dry or wet). In the second solution, the SL900A chip, which supports up to two external sensors and an internal temperature sensor, is used. An interdigital capacitive sensor was connected to the transponder chip and used for soil moisture measurement. In a novel design for an UHF RFID tag the sensor is placed below the soil surface, while the transponder and antenna are above the soil to improve communication. Both solutions are evaluated practically and results show the presence of water in soil can be remotely detected allowing for their application in landslide monitoring.

In this study, the analysis of a three‐coil wireless power transfer (WPT) system, which can be divided into source, communication and load circuits, is discussed in details. Among the three‐coil WPT systems features, it is demonstrated, for instance, that maximum efficiency ( ) and maximum power transferred to the load ( P _3MAX ) do not depend on the load resistance, neither on the mutual inductance between communication and load coils. In fact, it is shown that and P _3MAX depend only on source and communication circuits parameters. Practical results are also presented, showing good agreement with the developed theory and validating the proposed analysis.

This paper presents the development and analysis of a system for Brazilian Sign Language (Libras) recognition, which is composed of an instrumented glove and an acquisition system. The instrumented glove has five flex sensors, an inertial sensor, and two contact sensors (made with silver-coated fabric). For data acquisition, five volunteers performed gestures in Libras. In the proposed segmentation technique, the collected data were segmented into three periods (fixed amounts of signal samples): construction period, alphabet gesture, and relaxation period. The periods of alphabet gesture are submitted to segmentation, and the classifier was designed to recognize the 26 letters of alphabet. Different classifiers were employed to classify the gestures and analyze the system in different scenarios. For the classification in group of sensors, the highest performance obtained was an accuracy of 96.15% with Random Forest (RF) classifier.

Sign Language recognition systems aid communication among deaf people, hearing impaired people, and speakers. One of the types of signals that has seen increased studies and that can be used as input for these systems is surface electromyography (sEMG). This work presents the recognition of a set of alphabet gestures from Brazilian Sign Language (Libras) using sEMG acquired from an armband. Only sEMG signals were used as input. Signals from 12 subjects were acquired using a Myo^TM armband for the 26 signs of the Libras alphabet. Additionally, as the sEMG has several signal processing parameters, the influence of segmentation, feature extraction, and classification was considered at each step of the pattern recognition. In segmentation, window length and the presence of four levels of overlap rates were analyzed, as well as the contribution of each feature, the literature feature sets, and new feature sets proposed for different classifiers. We found that the overlap rate had a high influence on this task. Accuracies in the order of 99% were achieved for the following factors: segments of 1.75 s with a 12.5% overlap rate; the proposed set of four features; and random forest (RF) classifiers.

This work presents a comparative study between dimensionality reduction and feature selection to classification problem for six hand gestures by sEMG signal. The classified signals are wrist flexion, wrist extension, wrist flexion for the left, wrist extension to the right, forearm supination, and forearm pronation. An armband with eight channels was used to acquire the signals from 13 subjects (8 male and 5 female). Then, 29 features from time and frequency domain were extracted. Linear Discriminant Analysis (LDA), Quadratic Discriminant Analysis (QDA), and Support Vector Machine (SVM) were used as classifiers. Regarding the dimensionality reduction, Principal Component Analysis and LDA were applied in the signal; for feature selection, the feature combination for wrapper method step wise forward was used. The best scenario with dimensionality reduction was obtained with QDA classifier and 80 attributes from PCA, reaching accuracies of 84%. In the second scenario, with 112 attributes (8 features), a non-linear SVM (with Gaussian kernel) reached accuracies of 91%. Both methods presented similar performances among the accuracies for each class; however, dimensionality reduction approach presented less computational cost whilst has a lower accuracy compared with feature selection approach.

The condition for maximum power transfer of 2-coils wireless power transfer (WPT) system is derived from circuit analysis and discussed together with the respective WPT system efficiency (η). In the sequence, it is shown that a 4-coils WPT system (which can be divided in source, two communication and load circuits) without power losses at the two communication circuits (ideal 4-coils WPT system) presents, from maximum power transfer and efficiency point of view, a performance similar to those of a 2-coils WPT system. The exception is the influence of coupling coefficient (k): in 2-coils system η increases as k approaches one, while in ideal 4-coils WPT system η increases as k between the two communication coils approaches zero. In addition, realistic 4-coils WPT systems (with power losses at the two communication circuits) are also analyzed showing, for instance, that η presents a maximum as a function of k of the communication coils. In order to validate the presented theory, 4 coils were built, and a setup to perform 2-coils and 4-coils WPT systems has been carried out. Practical results show good agreement with the developed theory.