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Sensors, Volume 21, Issue 17 (September-1 2021) – 309 articles

Cover Story (view full-size image): Research on bioactive natural products aims to both protect against dangerous biotoxicity and promote pharmacological innovation in drug discovery. Optical biosensors are characterized by high sensitivity, specificity, and rapid and cost-effective responses that meet environmental and health protection requirements. Of particular interest is the application of innovative optical biosensors to monitor aquatic biotoxins in the context of increasing harmful algal blooms. Simultaneously, technological advances in these analytical devices are helping to identify bioactive compounds of clinical interest. This article reviews advances in optical biosensors designed to improve the detection of aquatic biotoxins and accelerate the screening of novel natural products with biomedical applications. View this paper.
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18 pages, 4682 KiB  
Article
Individual’s Social Perception of Virtual Avatars Embodied with Their Habitual Facial Expressions and Facial Appearance
by Sung Park, Si Pyoung Kim and Mincheol Whang
Sensors 2021, 21(17), 5986; https://doi.org/10.3390/s21175986 - 6 Sep 2021
Cited by 30 | Viewed by 6370
Abstract
With the prevalence of virtual avatars and the recent emergence of metaverse technology, there has been an increase in users who express their identity through an avatar. The research community focused on improving the realistic expressions and non-verbal communication channels of virtual characters [...] Read more.
With the prevalence of virtual avatars and the recent emergence of metaverse technology, there has been an increase in users who express their identity through an avatar. The research community focused on improving the realistic expressions and non-verbal communication channels of virtual characters to create a more customized experience. However, there is a lack in the understanding of how avatars can embody a user’s signature expressions (i.e., user’s habitual facial expressions and facial appearance) that would provide an individualized experience. Our study focused on identifying elements that may affect the user’s social perception (similarity, familiarity, attraction, liking, and involvement) of customized virtual avatars engineered considering the user’s facial characteristics. We evaluated the participant’s subjective appraisal of avatars that embodied the participant’s habitual facial expressions or facial appearance. Results indicated that participants felt that the avatar that embodied their habitual expressions was more similar to them than the avatar that did not. Furthermore, participants felt that the avatar that embodied their appearance was more familiar than the avatar that did not. Designers should be mindful about how people perceive individuated virtual avatars in order to accurately represent the user’s identity and help users relate to their avatar. Full article
(This article belongs to the Special Issue Emotion Intelligence Based on Smart Sensing)
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23 pages, 3507 KiB  
Article
Investigation of Deformation Pattern and Movement Law of the Huge-Thick Conglomerate Stratum by a Large-Scale 3D Model Test with Distributed Optical Fiber Sensor Monitoring
by Qiang Yuan, Jing Chai, Yuzhu Zhang, Yongliang Liu and Yiwei Ren
Sensors 2021, 21(17), 5985; https://doi.org/10.3390/s21175985 - 6 Sep 2021
Cited by 1 | Viewed by 2203
Abstract
Mining activities under the circumstances of huge-thick stratum occurrence commonly result in dynamic response of the working face. It is crucial to understand the rock failure and movement of the huge-thick stratum in order to prevent dynamic hazards. This paper introduces distributed optical [...] Read more.
Mining activities under the circumstances of huge-thick stratum occurrence commonly result in dynamic response of the working face. It is crucial to understand the rock failure and movement of the huge-thick stratum in order to prevent dynamic hazards. This paper introduces distributed optical fiber sensor (DOFS) monitoring into a large-scale model test to investigate the deformation pattern and movement law of the huge-thick conglomerate (HTC); the monitoring results are verified by numerical simulation. The results indicate that DOFS monitoring captures the spatiotemporal evolution of zoning development in the overburden deformation. The deformation field of HTC is illustrated, and there exists a strain basin that can be used to estimate the movement law of HTC. The average strain variability Ex, a new homogenization index for characterizing the overburden deformation, is proposed to describe the broken rules of the HTC. The numerical simulation proves the feasibility of the DOFS monitoring method and the correctness of the deformation pattern and movement law. This study provides efficient methods for DOFS monitoring utilization to investigate mining engineering problems and could be beneficial for unearthing the mechanisms of deep ground rock deformation. Full article
(This article belongs to the Section Optical Sensors)
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16 pages, 5112 KiB  
Article
A Novel Machine Learning-Based Methodology for Tool Wear Prediction Using Acoustic Emission Signals
by Juan Luis Ferrando Chacón, Telmo Fernández de Barrena, Ander García, Mikel Sáez de Buruaga, Xabier Badiola and Javier Vicente
Sensors 2021, 21(17), 5984; https://doi.org/10.3390/s21175984 - 6 Sep 2021
Cited by 30 | Viewed by 4364
Abstract
There is an increasing trend in the industry of knowing in real-time the condition of their assets. In particular, tool wear is a critical aspect, which requires real-time monitoring to reduce costs and scrap in machining processes. Traditionally, for the purpose of predicting [...] Read more.
There is an increasing trend in the industry of knowing in real-time the condition of their assets. In particular, tool wear is a critical aspect, which requires real-time monitoring to reduce costs and scrap in machining processes. Traditionally, for the purpose of predicting tool wear conditions in machining, mathematical models have been developed to extract the information from the signal of sensors attached to the machines. To reduce the complexity of developing physical models, where an in-depth knowledge of the system being modelled is required, the current trend is to use machine-learning (ML) models based on data from the tool wear. The acoustic emission (AE) technique has been widely used to capture data from and understand the real-time condition of industrial assets such as cutting tools. However, AE signal interpretation and processing is rather complex. One of the most common features extracted from AE signals to predict the tool wear is the counts parameter, defined as the number of times that the amplitude of the signal exceeds a predefined threshold. A recurrent problem of this feature is to define the adequate threshold to obtain consistent wear prediction. Additionally, AE signal bandwidth is rather wide, and the selection of the optimum frequencies band for feature extraction has been pointed out as critical and complex by many authors. To overcome these problems, this paper proposes a methodology that applies multi-threshold count feature extraction at multiresolution level using wavelet packet transform, which extracts a redundant and non-optimal feature map from the AE signal. Next, recursive feature elimination is performed to reduce and optimize the vast number of predicting features generated in the previous step, and random forests regression provides the estimated tool wear. The methodology presented was tested using data captured when turning 19NiMoCr6 steel under pre-established cutting conditions. The results obtained were compared with several ML algorithms such as k-nearest neighbors, support vector machines, artificial neural networks and decision trees. Experimental results show that the proposed method can reduce the predicted root mean squared error by 36.53%. Full article
(This article belongs to the Special Issue Structural Health Monitoring with Acoustic Emission Sensors)
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12 pages, 1151 KiB  
Article
EMG Based Analysis of Gait Symmetry in Healthy Children
by Kristina Daunoraviciene, Jurgita Ziziene, Jolanta Pauk, Giedre Juskeniene and Juozas Raistenskis
Sensors 2021, 21(17), 5983; https://doi.org/10.3390/s21175983 - 6 Sep 2021
Cited by 8 | Viewed by 3343
Abstract
The purpose of this study was to examine the changes in muscular activity between the left and right lower legs during gait in healthy children throughout temporal parameters of EMG and symmetry index (SI). A total of 17 healthy children (age: [...] Read more.
The purpose of this study was to examine the changes in muscular activity between the left and right lower legs during gait in healthy children throughout temporal parameters of EMG and symmetry index (SI). A total of 17 healthy children (age: 8.06 ± 1.92 years) participated in this study. Five muscles on both legs were examined via the Vicon 8-camera motion analysis system synchronized with a Trigno EMG Wireless system and a Bertec force plate; onset–offset intervals were analyzed. The highest occurrence frequency of the primary activation modality was found in the stance phase. In the swing phase, onset–offset showed only a few meaningful signs of side asymmetry. The knee flexors demonstrated significant differences between the sides (p < 0.05) in terms of onset–offset intervals: biceps femoris in stance, single support, and pre-swing phases, with SI values = −6.45%, −14.29%, and −17.14%, respectively; semitendinosus in single support phase, with SI = −12.90%; lateral gastrocnemius in swing phase, with SI = −13.33%; and medial gastrocnemius in stance and single support phases, with SI = −13.33% and −23.53%, respectively. The study outcomes supply information about intra-subject variability, which is very important in follow-up examinations and comparison with other target groups of children. Full article
(This article belongs to the Section Biomedical Sensors)
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20 pages, 3969 KiB  
Article
Periodic Tubular Structures and Phononic Crystals towards High-Q Liquid Ultrasonic Inline Sensors for Pipes
by Nikolay Mukhin and Ralf Lucklum
Sensors 2021, 21(17), 5982; https://doi.org/10.3390/s21175982 - 6 Sep 2021
Cited by 6 | Viewed by 2789
Abstract
The article focuses on a high-resolution ultrasound sensor for real-time monitoring of liquid analytes in cylindrical pipes, tubes, or capillaries. The development of such a sensor faces the challenges of acoustic energy losses, including dissipation at liquid/solid interface and acoustic wave radiation along [...] Read more.
The article focuses on a high-resolution ultrasound sensor for real-time monitoring of liquid analytes in cylindrical pipes, tubes, or capillaries. The development of such a sensor faces the challenges of acoustic energy losses, including dissipation at liquid/solid interface and acoustic wave radiation along the pipe. Furthermore, we consider acoustic resonant mode coupling and mode conversion. We show how the concept of phononic crystals can be applied to solve these problems and achieve the maximum theoretically possible Q-factor for resonant ultrasonic sensors. We propose an approach for excitation and measurement of an isolated radial resonant mode with minimal internal losses. The acoustic energy is effectively localized in a narrow probing area due to the introduction of periodically arranged sectioned rings around the tube. We present a sensor design concept, which optimizes the coupling between the tubular resonator and external piezoelectric transducers. We introduce a 2D-phononic crystal in the probing region for this purpose. The Q-factor of the proposed structures show the high prospects for phononic crystal pipe sensors. Full article
(This article belongs to the Special Issue Development, Investigation and Application of Acoustic Sensors)
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10 pages, 1247 KiB  
Article
Novel Application of Light-Emitting Diode Therapy in the Treatment of Eyebrow Loss in Frontal Fibrosing Alopecia
by Agnieszka Gerkowicz, Joanna Bartosińska, Dorota Raczkiewicz, Mirosław Kwaśny and Dorota Krasowska
Sensors 2021, 21(17), 5981; https://doi.org/10.3390/s21175981 - 6 Sep 2021
Cited by 3 | Viewed by 3070
Abstract
Background: Eyebrow loss in the course of frontal fibrosing alopecia (FFA) is becoming a growing issue among older females. It has a considerable negative impact on patients’ quality of life. Since there is no standardized treatment, photobiomodulation with light-emitting diodes (LEDs) could be [...] Read more.
Background: Eyebrow loss in the course of frontal fibrosing alopecia (FFA) is becoming a growing issue among older females. It has a considerable negative impact on patients’ quality of life. Since there is no standardized treatment, photobiomodulation with light-emitting diodes (LEDs) could be an option. Here we assess, for the first time, the efficacy of LED therapy in the treatment of eyebrow loss in females with FFA. Methods: 16 female patients with FFA aged 60–74 years were enrolled in the study. LED therapy was performed once a week for a 10-week session. The LEDs’ effectiveness was assessed at the baseline, after 10 irradiations, and 6 months after the end of treatment during a follow-up visit. Results: The therapy was well tolerated. After 10 irradiations, the total eyebrow hair count increased significantly, as did the number of thick hairs and mid-thick hairs (p = 0.002, p = 0.002, and p = 0.044, respectively). During the follow-up visit, the total number of eyebrow hairs remained significantly higher than before treatment (p = 0.002). Conclusion: The study revealed that LED therapy seems to be a novel and promising therapeutic option for eyebrow loss in patients with FFA. It is safe and well tolerated and leads to clinically and cosmetically acceptable improvement. Full article
(This article belongs to the Special Issue Advances in Light- and Sound-Based Techniques in Biomedicine)
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13 pages, 897 KiB  
Article
Kinematics Adaptation and Inter-Limb Symmetry during Gait in Obese Adults
by Massimiliano Pau, Paolo Capodaglio, Bruno Leban, Micaela Porta, Manuela Galli and Veronica Cimolin
Sensors 2021, 21(17), 5980; https://doi.org/10.3390/s21175980 - 6 Sep 2021
Cited by 13 | Viewed by 3318
Abstract
The main purpose of this study is to characterize lower limb joint kinematics during gait in obese individuals by analyzing inter-limb symmetry and angular trends of lower limb joints during walking. To this purpose, 26 obese individuals (mean age 28.5 years) and 26 [...] Read more.
The main purpose of this study is to characterize lower limb joint kinematics during gait in obese individuals by analyzing inter-limb symmetry and angular trends of lower limb joints during walking. To this purpose, 26 obese individuals (mean age 28.5 years) and 26 normal-weight age- and sex-matched were tested using 3D gait analysis. Raw kinematic data were processed to derive joint-specific angle trends and angle-angle diagrams (synchronized cyclograms) which were characterized in terms of area, orientation and trend symmetry parameters. The results show that obese individuals exhibit a kinematic pattern which significantly differs from those of normal weight especially in the stance phase. In terms of inter-limb symmetry, higher values were found in obese individuals for all the considered parameters, even though the statistical significance was detected only in the case of trend symmetry index at ankle joint. The described alterations of gait kinematics in the obese individuals and especially the results on gait asymmetry are important, because the cyclic uneven movement repeated for hours daily can involve asymmetrical spine loading and cause lumbar pain and could be dangerous for overweight individuals. Full article
(This article belongs to the Special Issue Wearables for Movement Analysis in Healthcare)
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9 pages, 2552 KiB  
Communication
Optical Angular Sensor for Space Applications
by Alexander Dabsch, Christoph Rosenberg, Majesa Trimmel and Franz Keplinger
Sensors 2021, 21(17), 5979; https://doi.org/10.3390/s21175979 - 6 Sep 2021
Cited by 1 | Viewed by 2058
Abstract
This paper describes a silicon/glass sensing structure for axial angle measurements. The presented optical angular sensor can statically measure the angle φ of any apparatus depending on the torsion of the optical component against the sensor housing. Core element of the sensor is [...] Read more.
This paper describes a silicon/glass sensing structure for axial angle measurements. The presented optical angular sensor can statically measure the angle φ of any apparatus depending on the torsion of the optical component against the sensor housing. Core element of the sensor is an optical medium with an etched structure, which diffracts light from an LED according to the Fresnel equation. Two photodiodes, one for angle determination and one as reference, conduct the measurement. Hence, the signal splits up into two parts: one part transmits trough the optical system and the second part (the reflected wave) is used as reference signal. For self-referencing purposes, the wavelength spectrum of the LED has its maximum in the infrared regime near to the wavelength where silicon gets transparent (l~1000 nm). More precisely, torsion angle and light intensity show a dependency given by Tstot if a straight etching structure (refraction profile) is used. To avoid multiple reflections of light, a coating layer restricts the illuminated area in the optical medium. With this setting a resolution of 0.05-degree rotation angle has been achieved and by stacking the construction, the sensor can measure an angular range from 30° up to 270°. Full article
(This article belongs to the Section Electronic Sensors)
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12 pages, 4720 KiB  
Article
Langasite as Piezoelectric Substrate for Sensors in Harsh Environments: Investigation of Surface Degradation under High-Temperature Air Atmosphere
by Thierry Aubert, Ninel Kokanyan and Omar Elmazria
Sensors 2021, 21(17), 5978; https://doi.org/10.3390/s21175978 - 6 Sep 2021
Cited by 2 | Viewed by 2470
Abstract
Langasite crystals (LGS) are known for their exceptional piezoelectric properties at high temperatures up to 1000 °C and more. In this respect, many studies have been conducted in order to achieve surface acoustic wave (SAW) sensors based on LGS crystals dedicated to high-temperature [...] Read more.
Langasite crystals (LGS) are known for their exceptional piezoelectric properties at high temperatures up to 1000 °C and more. In this respect, many studies have been conducted in order to achieve surface acoustic wave (SAW) sensors based on LGS crystals dedicated to high-temperature operations. Operating temperatures of more than 1000 °C and 600 °C for wired and wireless sensors, respectively, have been reached. These outstanding performances have been obtained under an air atmosphere since LGS crystals are not stable in high-temperature conditions under a low-oxygen atmosphere due to their oxide nature. However, if the stability of bulk LGS crystals under a high-temperature air atmosphere is well established, the surface deterioration under such conditions has been hardly investigated, as most of the papers dedicated to LGS-based SAW sensors are essentially focused on the development of thin film electrodes that are able to withstand very elevated temperatures to be combined with LGS crystals. Yet, any surface modification of the substrate can dramatically change the performance of SAW sensors. Consequently, the aim of this paper is to study the stability of the LGS surface under a high-temperature air environment. To do so, LGS substrates have been annealed in an air atmosphere at temperatures between 800 and 1200 °C and for durations between one week and one month. The morphology, microstructure, and chemical composition of the LGS surface was examined before and after annealing treatments by numerous and complementary methods, while the surface acoustic properties have been probed by SAW measurements. These investigations reveal that depending on both the temperature and the annealing duration, many defects with a corolla-like shape appear at the surface of LGS crystals in high-temperature prolonged exposure in an air atmosphere. These defects are related to the formation of a new phase, likely an oxiapatite ternary compound, the chemical formula of which is La14GaxSi9−xO39−x/2. These defects are located on the surface and penetrate into the depth of the sample by no more than 1–2 microns. However, SAW measurements show that the surface acoustic properties are modified by the high-temperature exposure at a larger deepness of at least several tens of microns. These perturbations of the LGS surface acoustic properties could induce, in the case of LGS-based SAW sensors operating in the 434 MHz ISM band, temperature measurement errors around 10 °C. Full article
(This article belongs to the Special Issue Development, Investigation and Application of Acoustic Sensors)
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22 pages, 7481 KiB  
Article
Small-Angle Particle Counting Coupled Photometry for Real-Time Detection of Respirable Particle Size Segmentation Mass Concentration
by Rongrui Zhang and Heng Zhao
Sensors 2021, 21(17), 5977; https://doi.org/10.3390/s21175977 - 6 Sep 2021
Cited by 6 | Viewed by 3003
Abstract
Respirable particulate matter air pollution is positively associated with SARS-CoV-2 mortality. Real-time and accurate monitoring of particle concentration changes is the first step to prevent and control air pollution from inhalable particles. In this research, a new light scattering instrument has been developed [...] Read more.
Respirable particulate matter air pollution is positively associated with SARS-CoV-2 mortality. Real-time and accurate monitoring of particle concentration changes is the first step to prevent and control air pollution from inhalable particles. In this research, a new light scattering instrument has been developed to detect the mass concentration of inhalable particles. This instrument couples the forward small-angle single particle counting method with the lateral group particle photometry method in a single device. The mass concentration of four sizes of inhalable particles in the environment can be detected simultaneously in a large area in real-time without using a particle impactor. Different from the traditional light scattering instrument, this new optical instrument can detect darker particles with strong light absorption, and the measurement results mainly depend on the particle size and ignore the properties of the particles. Comparative experiments have shown that the instrument can detect particles with different properties by simply calibrating the environmental density parameters, and the measurement results have good stability and accuracy. Full article
(This article belongs to the Section Optical Sensors)
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14 pages, 3563 KiB  
Article
Programming Robots by Demonstration Using Augmented Reality
by Inês Soares, Marcelo Petry and António Paulo Moreira
Sensors 2021, 21(17), 5976; https://doi.org/10.3390/s21175976 - 6 Sep 2021
Cited by 16 | Viewed by 3570
Abstract
The world is living the fourth industrial revolution, marked by the increasing intelligence and automation of manufacturing systems. Nevertheless, there are types of tasks that are too complex or too expensive to be fully automated, it would be more efficient if the machines [...] Read more.
The world is living the fourth industrial revolution, marked by the increasing intelligence and automation of manufacturing systems. Nevertheless, there are types of tasks that are too complex or too expensive to be fully automated, it would be more efficient if the machines were able to work with the human, not only by sharing the same workspace but also as useful collaborators. A possible solution to that problem is on human–robot interaction systems, understanding the applications where they can be helpful to implement and what are the challenges they face. This work proposes the development of an industrial prototype of a human–machine interaction system through Augmented Reality, in which the objective is to enable an industrial operator without any programming experience to program a robot. The system itself is divided into two different parts: the tracking system, which records the operator’s hand movement, and the translator system, which writes the program to be sent to the robot that will execute the task. To demonstrate the concept, the user drew geometric figures, and the robot was able to replicate the operator’s path recorded. Full article
(This article belongs to the Topic Augmented and Mixed Reality)
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12 pages, 6447 KiB  
Communication
Wavelength-Tunable L-Band High Repetition Rate Erbium-Doped Fiber Laser Based on Dissipative Four-Wave Mixing
by Kai Li, Qianqian Huang, Junjie Jiang, Zinan Huang and Chengbo Mou
Sensors 2021, 21(17), 5975; https://doi.org/10.3390/s21175975 - 6 Sep 2021
Cited by 6 | Viewed by 2411
Abstract
A wavelength-tunable high repetition rate (HRR) erbium-doped fiber laser in L-band based on dissipative four-wave mixing (DFWM) mechanism is demonstrated. The cavity can generate a single-soliton train and bound-soliton train with a fixed repetition rate of ~126 GHz, which is determined by the [...] Read more.
A wavelength-tunable high repetition rate (HRR) erbium-doped fiber laser in L-band based on dissipative four-wave mixing (DFWM) mechanism is demonstrated. The cavity can generate a single-soliton train and bound-soliton train with a fixed repetition rate of ~126 GHz, which is determined by the free spectral range of the intra-cavity Lyot filter. A wide wavelength-tuning operation can also be obtained by rotating the polarization controllers. The wavelength-tuning ranges of the HRR single-soliton state and HRR bound-soliton state are ~38.3 nm and ~22.6 nm, respectively. This laser provides useful references for the area of a wavelength-tunable fiber laser with high repetition rate. The laser may also find useful applications in high-speed communication, sensing, etc. Full article
(This article belongs to the Special Issue Advanced Fiber Photonic Devices and Sensors)
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32 pages, 33785 KiB  
Article
The Effect of Synergistic Approaches of Features and Ensemble Learning Algorithms on Aboveground Biomass Estimation of Natural Secondary Forests Based on ALS and Landsat 8
by Chunyu Du, Wenyi Fan, Ye Ma, Hung-Il Jin and Zhen Zhen
Sensors 2021, 21(17), 5974; https://doi.org/10.3390/s21175974 - 6 Sep 2021
Cited by 12 | Viewed by 2805
Abstract
Although the combination of Airborne Laser Scanning (ALS) data and optical imagery and machine learning algorithms were proved to improve the estimation of aboveground biomass (AGB), the synergistic approaches of different data and ensemble learning algorithms have not been fully investigated, especially for [...] Read more.
Although the combination of Airborne Laser Scanning (ALS) data and optical imagery and machine learning algorithms were proved to improve the estimation of aboveground biomass (AGB), the synergistic approaches of different data and ensemble learning algorithms have not been fully investigated, especially for natural secondary forests (NSFs) with complex structures. This study aimed to explore the effects of the two factors on AGB estimation of NSFs based on ALS data and Landsat 8 imagery. The synergistic method of extracting novel features (i.e., COLI1 and COLI2) using optimal Landsat 8 features and the best-performing ALS feature (i.e., elevation mean) yielded higher accuracy of AGB estimation than either optical-only or ALS-only features. However, both of them failed to improve the accuracy compared to the simple combination of the untransformed features that generated them. The convolutional neural networks (CNN) model was much superior to other classic machine learning algorithms no matter of features. The stacked generalization (SG) algorithms, a kind of ensemble learning algorithms, greatly improved the accuracies compared to the corresponding base model, and the SG with the CNN meta-model performed best. This study provides technical support for a wall-to-wall AGB mapping of NSFs of northeastern China using efficient features and algorithms. Full article
(This article belongs to the Special Issue Deep Learning Methods for Remote Sensing)
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20 pages, 8334 KiB  
Article
Mask Attention-SRGAN for Mobile Sensing Networks
by Chi-En Huang, Ching-Chun Chang and Yung-Hui Li
Sensors 2021, 21(17), 5973; https://doi.org/10.3390/s21175973 - 6 Sep 2021
Cited by 2 | Viewed by 2817
Abstract
Biometrics has been shown to be an effective solution for the identity recognition problem, and iris recognition, as well as face recognition, are accurate biometric modalities, among others. The higher resolution inside the crucial region reveals details of the physiological characteristics which provides [...] Read more.
Biometrics has been shown to be an effective solution for the identity recognition problem, and iris recognition, as well as face recognition, are accurate biometric modalities, among others. The higher resolution inside the crucial region reveals details of the physiological characteristics which provides discriminative information to achieve extremely high recognition rate. Due to the growing needs for the IoT device in various applications, the image sensor is gradually integrated in the IoT device to decrease the cost, and low-cost image sensors may be preferable than high-cost ones. However, low-cost image sensors may not satisfy the minimum requirement of the resolution, which definitely leads to the decrease of the recognition accuracy. Therefore, how to maintain high accuracy for biometric systems without using expensive high-cost image sensors in mobile sensing networks becomes an interesting and important issue. In this paper, we proposed MA-SRGAN, a single image super-resolution (SISR) algorithm, based on the mask-attention mechanism used in Generative Adversarial Network (GAN). We modified the latest state-of-the-art (nESRGAN+) in the GAN-based SR model by adding an extra part of a discriminator with an additional loss term to force the GAN to pay more attention within the region of interest (ROI). The experiments were performed on the CASIA-Thousand-v4 dataset and the Celeb Attribute dataset. The experimental results show that the proposed method successfully learns the details of features inside the crucial region by enhancing the recognition accuracies after image super-resolution (SR). Full article
(This article belongs to the Special Issue Security for Mobile Sensing Networks)
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12 pages, 1704 KiB  
Article
A Novel Tool for Gait Analysis: Validation Study of the Smart Insole PODOSmart®
by Efthymios Ziagkas, Andreas Loukovitis, Dimitrios Xypolias Zekakos, Thomas Duc-Phu Chau, Alexandros Petrelis and George Grouios
Sensors 2021, 21(17), 5972; https://doi.org/10.3390/s21175972 - 6 Sep 2021
Cited by 21 | Viewed by 6108
Abstract
The new smart insole PODOSmart®, is introduced as a new tool for gait analysis against high cost laboratory based equipment. PODOSmart® system measures walking profile and gait variables in real life conditions. PODOSmart® insoles consists of wireless sensors, can [...] Read more.
The new smart insole PODOSmart®, is introduced as a new tool for gait analysis against high cost laboratory based equipment. PODOSmart® system measures walking profile and gait variables in real life conditions. PODOSmart® insoles consists of wireless sensors, can be fitted into any shoe and offer the ability to measure spatial, temporal, and kinematic gait parameters. The intelligent insoles feature several sensors that detect and capture foot movements and a microprocessor that calculates gait related biomechanical data. Gait analysis results are presented in PODOSmart® platform. This study aims to present the characteristics of this tool and to validate it comparing with a stereophotogrammetry-based system. Validation was performed by gait analysis for eleven healthy individuals on a six-meters walkway using both PODOSmart® and Vicon system. Intraclass correlation coefficients (ICC) were calculated for gait parameters. ICC for the validation ranged from 0.313 to 0.990 in gait parameters. The highest ICC was observed in cadence, circumduction, walking speed, stride length and stride duration. PODOSmart® is a valid tool for gait analysis compared to the gold standard Vicon. As PODOSmart®, is a portable gait analysis tool with an affordable cost it can be a useful novel tool for gait analysis in healthy and pathological population. Full article
(This article belongs to the Collection Sensors for Gait, Human Movement Analysis, and Health Monitoring)
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19 pages, 2204 KiB  
Article
Feasibility of Novel Rear-Side Mirage Deflection Method for Thermal Conductivity Measurements
by Gwantaek Kim, Moojoong Kim and Hyunjung Kim
Sensors 2021, 21(17), 5971; https://doi.org/10.3390/s21175971 - 6 Sep 2021
Viewed by 1887
Abstract
Among the noncontact measurement technologies used to acquire thermal property information, those that use the photothermal effect are attracting attention. However, it is difficult to perform measurements for new materials with different optical and thermal properties, owing to limitations of existing thermal conductivity [...] Read more.
Among the noncontact measurement technologies used to acquire thermal property information, those that use the photothermal effect are attracting attention. However, it is difficult to perform measurements for new materials with different optical and thermal properties, owing to limitations of existing thermal conductivity measurement methods using the photothermal effect. To address this problem, this study aimed to develop a rear-side mirage deflection method capable of measuring thermal conductivity regardless of the material characteristics based on the photothermal effect. A thin copper film (of 20 µm thickness) was formed on the surfaces of the target materials so that measurements could not be affected by the characteristics of the target materials. In addition, phase delay signals were acquired from the rear sides of the target materials to exclude the influence of the pump beam, which is a problem in existing thermal conductivity measurement methods that use the photothermal effect. To verify the feasibility of the proposed measurement technique, thermal conductivity was measured for copper, aluminum, and stainless steel samples with a 250 µm thickness. The results were compared with literature values and showed good agreement with relative errors equal to or less than 0.2%. Full article
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11 pages, 2365 KiB  
Communication
Wavelength-Tunable, Ultra-Broadband, Biconical, Long-Period Fiber Grating Mode Converter Based on the Dual-Resonance Effect
by Yu Zheng, Huiyi Guo, Mao Feng, Zhi Wang and Yange Liu
Sensors 2021, 21(17), 5970; https://doi.org/10.3390/s21175970 - 6 Sep 2021
Cited by 6 | Viewed by 2224
Abstract
We demonstrated a wavelength-tunable, ultra-wideband, biconical, long-period fiber grating (BLPFG) mode converter in a two-mode fiber based on fusion taper technology and CO2 laser writing technology. Theoretical and experimental results show that after changing the diameter of the two-mode fiber by fusing [...] Read more.
We demonstrated a wavelength-tunable, ultra-wideband, biconical, long-period fiber grating (BLPFG) mode converter in a two-mode fiber based on fusion taper technology and CO2 laser writing technology. Theoretical and experimental results show that after changing the diameter of the two-mode fiber by fusing and tapering, the dispersion turning point of the fiber is adjusted and wavelength-tunable broadband mode conversion is achieved efficiently. Theoretical simulation shows that the mode conversion bandwidth can cover the O + E + S + C band. In the experiment, we fabricated adiabatic tapers with cladding diameters of 113 μm and 121 μm and wrote gratings on these tapers to achieve dual-resonance coupling, thus realizing mode conversion from LP01 to LP11, with a 15 dB bandwidth of 148.8 nm from 1229.0 nm to 1377.8 nm and of 168.5 nm from 1319.7 nm to 1488.2 nm, respectively. As far as we know, this is the first time that fusion taper technology has been used to adjust the window of the dual-resonant coupling of an optical fiber. This work broadens the scope of application of the dual-resonance effect and proposes a general method for widening the bandwidth of a fiber grating with tunable wavelength. Full article
(This article belongs to the Special Issue 25 Years of Long-Period Fiber Gratings)
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10 pages, 1912 KiB  
Communication
Temperature-Dependent Broadening of the Ultraviolet Photoelectron Spectrum of Au(110)
by Tomonari Nishida, Ikuo Kinoshita and Juntaro Ishii
Sensors 2021, 21(17), 5969; https://doi.org/10.3390/s21175969 - 6 Sep 2021
Cited by 2 | Viewed by 1956
Abstract
To determine the thermodynamic temperature of a solid surface from the electron energy distribution measured by photoelectron spectroscopy, it is necessary to accurately evaluate the energy broadening of the photoelectron spectrum and investigate its temperature dependence. Broadening functions in the photoelectron spectrum of [...] Read more.
To determine the thermodynamic temperature of a solid surface from the electron energy distribution measured by photoelectron spectroscopy, it is necessary to accurately evaluate the energy broadening of the photoelectron spectrum and investigate its temperature dependence. Broadening functions in the photoelectron spectrum of Au(110)’s surface near the Fermi level were estimated successfully using the relationship between the Fourier transform and the convolution integral. The Fourier transform could simultaneously reduce the noise of the spectrum when the broadening function was derived. The derived function was in the form of a Gaussian, whose width depended on the thermodynamic temperature of the sample and became broader at higher temperatures. The results contribute to improve accuracy of the determination of thermodynamic temperature from the photoelectron spectrum and provide useful information on the temperature dependence of electron scattering in photoelectron emission processes. Full article
(This article belongs to the Special Issue Opto-Thermal Sensor Technologies)
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30 pages, 5076 KiB  
Article
ROBINA: Rotational Orbit-Based Inter-Node Adjustment for Acoustic Routing Path in the Internet of Underwater Things (IoUTs)
by Umar Draz, Sana Yasin, Tariq Ali, Amjad Ali, Zaid Bin Faheem, Ning Zhang, Muhammad Hasan Jamal and Dong-Young Suh
Sensors 2021, 21(17), 5968; https://doi.org/10.3390/s21175968 - 6 Sep 2021
Cited by 2 | Viewed by 2377
Abstract
The Internet of Underwater Things (IoUTs) enables various underwater objects be connected to accommodate a wide range of applications, such as oil and mineral exportations, disaster detection, and tracing tracking systems. As about 71% of our earth is covered by water and one-fourth [...] Read more.
The Internet of Underwater Things (IoUTs) enables various underwater objects be connected to accommodate a wide range of applications, such as oil and mineral exportations, disaster detection, and tracing tracking systems. As about 71% of our earth is covered by water and one-fourth of the population lives around this, the IoUT expects to play a vital role. It is imperative to pursue reliable communication in this vast domain, as human beings’ future depends on water activities and resources. Therefore, there is a urgent need for underwater communication to be reliable, end-to-end secure, and collision/void node-free, especially when the routing path is established between sender and sonobuoys. The foremost issue discussed in this area is its routing path, which has high security and bandwidth without simultaneous multiple reflections. Short communication range is also a problem (because of an absence of inter-node adjustment); the acoustic signals have short ranges and maximum-scaling factors that cause a delay in communication. Therefore, we proposed Rotational Orbit-Based Inter Node Adjustment (ROBINA) with variant Path-Adjustment (PA-ROBINA) and Path Loss (PL-ROBINA) for IoUTs to achive reliable communication between the sender and sonobuoys. Additionally, the mathematical-based path loss model was discussed to cover the PL-ROBINA strategy. Extensive simulations were conducted with various realistic parameters and the results were compared with state-of-the-art routing protocols. Extensive simulations proved that the proposed routing scheme outperformed different realistic parameters; for example, packet transmission 45% increased with an average end-to-end delay of only 0.3% respectively. Furthermore, the transmission loss and path loss (measured in dB) were 25 and 46 dB, respectively, compared with other algorithms, for example, EBER2 54%, WDFAD-BDR 54%, AEDG 49%, ASEGD 55%, AVH-AHH-VBF 54.5%, and TANVEER 39%, respectively. In addition, the individual parameters with ROBINA and TANVEER were also compared, in which ROBINA achieved a 98% packet transmission ratio compared with TANVEER, which was only 82%. Full article
(This article belongs to the Special Issue Wireless Sensor Networks for Water and Environmental Monitoring)
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27 pages, 469 KiB  
Review
Security, Privacy, and Usability in Continuous Authentication: A Survey
by Ahmed Fraz Baig and Sigurd Eskeland
Sensors 2021, 21(17), 5967; https://doi.org/10.3390/s21175967 - 6 Sep 2021
Cited by 38 | Viewed by 7403
Abstract
Continuous authentication has been proposed as a possible approach for passive and seamless user authentication, using sensor data comprising biometric, behavioral, and context-oriented characteristics. Since these are personal data being transmitted and are outside the control of the user, this approach causes privacy [...] Read more.
Continuous authentication has been proposed as a possible approach for passive and seamless user authentication, using sensor data comprising biometric, behavioral, and context-oriented characteristics. Since these are personal data being transmitted and are outside the control of the user, this approach causes privacy issues. Continuous authentication has security challenges concerning poor matching rates and susceptibility of replay attacks. The security issues are mainly poor matching rates and the problems of replay attacks. In this survey, we present an overview of continuous authentication and comprehensively discusses its different modes, and issues that these modes have related to security, privacy, and usability. A comparison of privacy-preserving approaches dealing with the privacy issues is provided, and lastly recommendations for secure, privacy-preserving, and user-friendly continuous authentication. Full article
(This article belongs to the Section Internet of Things)
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13 pages, 42352 KiB  
Communication
A Simple Printed Cross-Dipole Antenna with Modified Feeding Structure and Dual-Layer Printed Reflector for Direction Finding Systems
by Kyei Anim, Bonghyuk Park, Hui Dong Lee, Seunghyun Jang, Sunwoo Kong and Young-Bae Jung
Sensors 2021, 21(17), 5966; https://doi.org/10.3390/s21175966 - 6 Sep 2021
Cited by 3 | Viewed by 6218
Abstract
In this paper, a simple printed cross-dipole (PCD) antenna to achieve a right-hand circular polarization (RHCP) at the L/S-band for direction finding (DF) systems is presented. The radiating part of the antenna consists of two printed dipoles that interlock with each other and [...] Read more.
In this paper, a simple printed cross-dipole (PCD) antenna to achieve a right-hand circular polarization (RHCP) at the L/S-band for direction finding (DF) systems is presented. The radiating part of the antenna consists of two printed dipoles that interlock with each other and are mounted orthogonally on a dual-layer printed reflector. To connect the feedlines of the dipole elements to the antenna’s feed network, which is located on the backside of the reflector, a through-hole signal via (THSV) is employed as the signal interconnection instead of the mainstream approach of using coaxial bead conductor. This feeding technique provides a degree of freedom to control the impedance of the signal path between the feedlines and the feed network in the numerical simulation for improved matching conditions. The proposed THSV extending through the dual-layer printed reflector is more reliable, durable, and mechanically robust to stabilize the matching conditions of the fabricated antenna in contrast to the coaxial-based approach that is more susceptible to impedance mismatch due to solder fatigue. Thus, the proposed PCD antenna offers advantages of broadband, flexible impedance matching, and fabrication ease. The antenna exhibits an impedance bandwidth (IBW) of 59% (1.59–2.93 GHz), a 3-dB axial ratio bandwidth (ARBW) of 57% (1.5–2.7 GHz), and a peak of 7.5 dB within the operating frequency band. Full article
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15 pages, 910 KiB  
Communication
Highly Reliable Fuzzy-Logic-Assisted AODV Routing Algorithm for Mobile Ad Hoc Networks
by Jiamin Li, Mengling Wang, Pengcheng Zhu, Dongming Wang and Xiaohu You
Sensors 2021, 21(17), 5965; https://doi.org/10.3390/s21175965 - 6 Sep 2021
Cited by 9 | Viewed by 3289
Abstract
Due to the noncentered, self-organizing, and self-healing characteristics, mobile ad hoc networks (MANET) have been more and more widely used as an alternative access technology for regions having no fixed infrastructure. On-demand routing protocols (e.g., ad hoc on-demand distance vector (AODV)) are used [...] Read more.
Due to the noncentered, self-organizing, and self-healing characteristics, mobile ad hoc networks (MANET) have been more and more widely used as an alternative access technology for regions having no fixed infrastructure. On-demand routing protocols (e.g., ad hoc on-demand distance vector (AODV)) are used to cope with the rapidly changing topology of MANET and reduce the network overhead. Taking delay, stability, and remaining energy of nodes into consideration, a fuzzy-logic-assisted AODV (FL-AODV) routing algorithm is proposed in this paper to further improve the reliability of the route in MANET. In the route discovery phase, the node with the highest reliability is selected as the relay node, and the route with the highest accumulated reliability is reserved for data transmission. Simulation results show that, compared with the traditional AODV protocol and the fuzzy logic routing algorithm (FLRA), the proposed routing protocol has higher reliability without increasing delay, i.e., better link connectivity and longer route life. The average routing reliability is about 18% higher than AODV while the average delay is the same low when the number of node greater than 70. Full article
(This article belongs to the Special Issue Dependability of Wireless Sensor Networks)
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13 pages, 3123 KiB  
Communication
Plantar Pressure Detection System Based on Flexible Hydrogel Sensor Array and WT-RF
by Wei Liu, Yineng Xiao, Xiaoming Wang and Fangming Deng
Sensors 2021, 21(17), 5964; https://doi.org/10.3390/s21175964 - 6 Sep 2021
Cited by 3 | Viewed by 2307
Abstract
This paper presents a hydrogel-based flexible sensor array to detect plantar pressure distribution and recognize the gait patterns to assist those who suffer from gait disorders to rehabilitate better. The traditional pressure detection array is composed of rigid metal sensors, which have poor [...] Read more.
This paper presents a hydrogel-based flexible sensor array to detect plantar pressure distribution and recognize the gait patterns to assist those who suffer from gait disorders to rehabilitate better. The traditional pressure detection array is composed of rigid metal sensors, which have poor biocompatibility and expensive manufacturing costs. To solve the above problems, we have designed and fabricated a novel flexible sensor array based on AAM/NaCl (Acrylamide/Sodium chloride) hydrogel and PI (Polyimide) membrane. The proposed array exhibits excellent structural flexibility (209 KPa) and high sensitivity (12.3 mV·N−1), which allows it to be in full contact with the sole of the foot to collect pressure signals accurately. The Wavelet Transform-Random Forest (WT-RF) algorithm is introduced to recognize the gaits based on the plantar pressure signals. Wavelet transform realizes the signal filtering and normalization, and random forest is responsible for the classification of the processed signals. The classification accuracy of the WT-RF algorithm reaches 91.9%, which ensures the precise recognition of gaits. Full article
(This article belongs to the Section Biosensors)
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22 pages, 699 KiB  
Article
Keystroke Dynamics Patterns While Writing Positive and Negative Opinions
by Agata Kołakowska and Agnieszka Landowska
Sensors 2021, 21(17), 5963; https://doi.org/10.3390/s21175963 - 6 Sep 2021
Cited by 3 | Viewed by 2814
Abstract
This paper deals with analysis of behavioural patterns in human–computer interaction. In the study, keystroke dynamics were analysed while participants were writing positive and negative opinions. A semi-experiment with 50 participants was performed. The participants were asked to recall the most negative and [...] Read more.
This paper deals with analysis of behavioural patterns in human–computer interaction. In the study, keystroke dynamics were analysed while participants were writing positive and negative opinions. A semi-experiment with 50 participants was performed. The participants were asked to recall the most negative and positive learning experiences (subject and teacher) and write an opinion about it. Keystroke dynamics were captured and over 50 diverse features were calculated and checked against the ability to differentiate positive and negative opinions. Moreover, classification of opinions was performed providing accuracy slightly above the random guess level. The second classification approach used self-report labels of pleasure and arousal and showed more accurate results. The study confirmed that it was possible to recognize positive and negative opinions from the keystroke patterns with accuracy above the random guess; however, combination with other modalities might produce more accurate results. Full article
(This article belongs to the Special Issue Emotion Recognition Based on Sensors)
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14 pages, 10910 KiB  
Article
The Effects of the Structural and Acoustic Parameters of the Skull Model on Transcranial Focused Ultrasound
by Hao Zhang, Yanqiu Zhang, Minpeng Xu, Xizi Song, Shanguang Chen, Xiqi Jian and Dong Ming
Sensors 2021, 21(17), 5962; https://doi.org/10.3390/s21175962 - 5 Sep 2021
Cited by 11 | Viewed by 4601
Abstract
Transcranial focused ultrasound (tFUS) has great potential in brain imaging and therapy. However, the structural and acoustic differences of the skull will cause a large number of technical problems in the application of tFUS, such as low focus energy, focal shift, and defocusing. [...] Read more.
Transcranial focused ultrasound (tFUS) has great potential in brain imaging and therapy. However, the structural and acoustic differences of the skull will cause a large number of technical problems in the application of tFUS, such as low focus energy, focal shift, and defocusing. To have a comprehensive understanding of the skull effect on tFUS, this study investigated the effects of the structural parameters (thickness, radius of curvature, and distance from the transducer) and acoustic parameters (density, acoustic speed, and absorption coefficient) of the skull model on tFUS based on acrylic plates and two simulation methods (self-programming and COMSOL). For structural parameters, our research shows that as the three factors increase the unit distance, the attenuation caused from large to small is the thickness (0.357 dB/mm), the distance to transducer (0.048 dB/mm), and the radius of curvature (0.027 dB/mm). For acoustic parameters, the attenuation caused by density (0.024 dB/30 kg/m3) and acoustic speed (0.021 dB/30 m/s) are basically the same. Additionally, as the absorption coefficient increases, the focus acoustic pressure decays exponentially. The thickness of the structural parameters and the absorption coefficient of the acoustic parameters are the most important factors leading to the attenuation of tFUS. The experimental and simulation trends are highly consistent. This work contributes to the comprehensive and quantitative understanding of how the skull influences tFUS, which further enhances the application of tFUS in neuromodulation research and treatment. Full article
(This article belongs to the Special Issue Development, Investigation and Application of Acoustic Sensors)
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20 pages, 8123 KiB  
Article
Multi-Excitation Infrared Fusion for Impact Evaluation of Aluminium-BFRP/GFRP Hybrid Composites
by Jue Hu, Hai Zhang, Stefano Sfarra, Stefano Perilli, Claudia Sergi, Fabrizio Sarasini and Xavier Maldague
Sensors 2021, 21(17), 5961; https://doi.org/10.3390/s21175961 - 5 Sep 2021
Cited by 5 | Viewed by 2231
Abstract
Fibre metal laminates are widely implemented in the aerospace industry owing to the merits of fatigue resistance and plastic properties. An effective defect assessment technique needs to be investigated for this type of composite materials. In order to achieve accurate impact-induced damage evaluation, [...] Read more.
Fibre metal laminates are widely implemented in the aerospace industry owing to the merits of fatigue resistance and plastic properties. An effective defect assessment technique needs to be investigated for this type of composite materials. In order to achieve accurate impact-induced damage evaluation, a multi-excitation infrared fusion method is introduced in this study. Optical excitation thermography with high performance on revealing surface and subsurface defects is combined with vibro-thermography to improve the capability of detection on defects. Quantitative analysis is carried out on the temperature curve to assess the impact-induced deformation. A new image fusion framework including feature extraction, feature selection and fusion steps is proposed to fully utilize the information from two excitation modalities. Six fibre metal laminates which contain aluminium-basalt fibre reinforced plastic and aluminium-glass fibre reinforced plastic are investigated. Features from different perspectives are compared and selected via intensity contrast on deformation area for fusion imaging. Both types of defects (i.e., surface and sub-surface) and the internal deformation situation of these six samples are characterized clearly and intuitively. Full article
(This article belongs to the Special Issue Computational Methods in Imagery (CMI))
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13 pages, 3142 KiB  
Article
Peculiarities and Applications of Stochastic Processes with Fractal Properties
by Oleg Semenovich Amosov and Svetlana Gennadievna Amosova
Sensors 2021, 21(17), 5960; https://doi.org/10.3390/s21175960 - 5 Sep 2021
Cited by 5 | Viewed by 1900
Abstract
In this paper, the fractal properties of stochastic processes and objects in different areas were specified and investigated. These included: measuring systems and sensors, navigation and motion controls, telecommunication systems and networks, and flaw detection technologies. Additional options that occur through the use [...] Read more.
In this paper, the fractal properties of stochastic processes and objects in different areas were specified and investigated. These included: measuring systems and sensors, navigation and motion controls, telecommunication systems and networks, and flaw detection technologies. Additional options that occur through the use of fractality were also indicated and exemplified for each application. Regarding the problems associated with navigation information processing, the following fractal nature processes were identified: errors of inertial sensors based on the microelectromechanical systems called MEMS, in particular gyroscopic drift and accelerometer bias, and; the trajectory movement of mobile objects. With regard to navigation problems specifically, the estimation problem statement and its solution are given by way of the Bayesian approach for processing fractal processes. The modified index of self-similarity for telecommunication series was proposed, and the self-similarity of network traffic based on the R/S method and wavelet analysis was identified. In failure detection, fractality manifested as porosity, wrinkles, surface fractures, and ultrasonic echo signals measured using non-destructive sensors used for rivet compound testing. Full article
(This article belongs to the Special Issue State-of-the-Art Optical Sensors Technology in Russia 2021-2022)
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10 pages, 1967 KiB  
Communication
Stopping the Mobile Robotic Vehicle at a Defined Distance from the Obstacle by Means of an Infrared Distance Sensor
by Frantisek Klimenda, Roman Cizek, Matej Pisarik and Jan Sterba
Sensors 2021, 21(17), 5959; https://doi.org/10.3390/s21175959 - 5 Sep 2021
Cited by 4 | Viewed by 3022
Abstract
The article deals with the creation of a program for stopping an autonomous robotic vehicle Robotino® 4. generation at a defined distance from an obstacle. One of the nine infrared distance sensors located on the frame of the robotic vehicle in the [...] Read more.
The article deals with the creation of a program for stopping an autonomous robotic vehicle Robotino® 4. generation at a defined distance from an obstacle. One of the nine infrared distance sensors located on the frame of the robotic vehicle in the front part of the frame is used for this application task. The infrared distance sensor characteristic is created from the measured experimental data, which is then linearized in the given section. The main aim of the experiment is to find such an equation of a line that corresponds to the stopping of a robotic vehicle with a given accuracy from an obstacle. The determined equation of the line is applied to the resulting program for autonomous control of the robotic vehicle. This issue is one of the many tasks performed by AGV in the industry. The introduction of AGVs into the industry is one of the many possibilities within Industry 4.0. Full article
(This article belongs to the Section Vehicular Sensing)
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9 pages, 1567 KiB  
Communication
Silicon Based Coplanar Capacitive Device for Liquid Sensor Applications
by Andrea G. Martinez-Lopez, David E. Guzmán-Caballero, Israel Mejia and Julio C. Tinoco
Sensors 2021, 21(17), 5958; https://doi.org/10.3390/s21175958 - 5 Sep 2021
Cited by 2 | Viewed by 2533
Abstract
The development of silicon-based sensor devices has enabled the possibility to pursue novel integrated smart sensor technologies. Under this scenario, capacitive sensor devices are one viable option for implementing different kinds of applications. In this paper, an interdigitated coplanar capacitive device fabricated over [...] Read more.
The development of silicon-based sensor devices has enabled the possibility to pursue novel integrated smart sensor technologies. Under this scenario, capacitive sensor devices are one viable option for implementing different kinds of applications. In this paper, an interdigitated coplanar capacitive device fabricated over a silicon substrate is presented and its potential use as liquid sensor is demonstrated. Additionally, a detailed capacitance model, which includes the parasitic capacitances introduced by the silicon substrate, was developed. The capacitance model has been theoretically validated through finite-element simulations as well as experimentally by comparison with fabricated devices. A polydimethylsiloxane mold has been fabricated and bonded to the sensor device with the aim of defining a cavity to collect the liquid sample into the device’s active region. The active capacitance component correlates to the electric field coupling between adjacent metal lines. Therefore, any change to the dielectric constant of the medium above the coplanar metal lines will produce a change to the device capacitance. Finally, the main guidelines for device performance improvement are depicted. Full article
(This article belongs to the Section Electronic Sensors)
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14 pages, 1619 KiB  
Article
A Tutorial on Hardware-Implemented Fault Injection and Online Fault Diagnosis for High-Speed Trains
by Xiaoyue Yang, Xinyu Qiao, Chao Cheng, Kai Zhong and Hongtian Chen
Sensors 2021, 21(17), 5957; https://doi.org/10.3390/s21175957 - 5 Sep 2021
Cited by 3 | Viewed by 2353
Abstract
Electrical drive systems are the core of high-speed trains, providing energy transmission from electric power to traction force. Therefore, their safety and reliability topics are always active in practice. Among the current research, fault injection (FI) and fault diagnosis (FD) are representative techniques, [...] Read more.
Electrical drive systems are the core of high-speed trains, providing energy transmission from electric power to traction force. Therefore, their safety and reliability topics are always active in practice. Among the current research, fault injection (FI) and fault diagnosis (FD) are representative techniques, where FI is an important way to recur faults, and FD ensures the recurring faults can be successfully detected as soon as possible. In this paper, a tutorial on a hardware-implemented (HIL) platform that blends FI and FD techniques is given for electrical drive systems of high-speed trains. The main contributions of this work are fourfold: (1) An HIL platform is elaborated for realistic simulation of faults, which provides the test and verification environment for FD tasks. (2) Basics of both the static and dynamic FD methods are reviewed, whose purpose is to guide the engineers and researchers. (3) Multiple performance indexes are defined for comprehensively evaluating the FD approaches from the application viewpoints. (4) It is an integrated platform making the FI and FD work together. Finally, a summary of FD research based on the HIL platform is made. Full article
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