Sensors

31 pages, 3339 KiB

Open AccessArticle

5G SLAM Using the Clustering and Assignment Approach with Diffuse Multipath

by Yu Ge, Fuxi Wen, Hyowon Kim, Meifang Zhu, Fan Jiang, Sunwoo Kim, Lennart Svensson and Henk Wymeersch

Sensors 2020, 20(16), 4656; https://doi.org/10.3390/s20164656 - 18 Aug 2020

Cited by 41 | Viewed by 5190

Abstract

5G communication systems operating above 24 GHz have promising properties for user localization and environment mapping. Existing studies have either relied on simplified abstract models of the signal propagation and the measurements, or are based on direct positioning approaches, which directly map the [...] Read more.

5G communication systems operating above 24 GHz have promising properties for user localization and environment mapping. Existing studies have either relied on simplified abstract models of the signal propagation and the measurements, or are based on direct positioning approaches, which directly map the received waveform to a position. In this study, we consider an intermediate approach, which consists of four phases—downlink data transmission, multi-dimensional channel estimation, channel parameter clustering, and simultaneous localization and mapping (SLAM) based on a novel likelihood function. This approach can decompose the problem into simpler steps, thus leading to lower complexity. At the same time, by considering an end-to-end processing chain, we are accounting for a wide variety of practical impairments. Simulation results demonstrate the efficacy of the proposed approach. Full article

(This article belongs to the Special Issue Sensor Network Signal Processing)

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18 pages, 5287 KiB

Open AccessArticle

Extraction and Analysis of Blue Steel Roofs Information Based on CNN Using Gaofen-2 Imageries

by Meiwei Sun, Yingbin Deng, Miao Li, Hao Jiang, Haoling Huang, Wenyue Liao, Yangxiaoyue Liu, Ji Yang and Yong Li

Sensors 2020, 20(16), 4655; https://doi.org/10.3390/s20164655 - 18 Aug 2020

Cited by 10 | Viewed by 2698

Abstract

Blue steel roof is advantageous for its low cost, durability, and ease of installation. It is generally used by industrial areas. The accurate and rapid mapping of blue steel roof is important for the preliminary assessment of inefficient industrial areas and is one [...] Read more.

Blue steel roof is advantageous for its low cost, durability, and ease of installation. It is generally used by industrial areas. The accurate and rapid mapping of blue steel roof is important for the preliminary assessment of inefficient industrial areas and is one of the key elements for quantifying environmental issues like urban heat islands. Here, the DeeplabV3+ semantic segmentation neural network based on GaoFen-2 images was used to analyze the quantity and spatial distribution of blue steel roofs in the Nanhai district, Foshan (including the towns of Shishan, Guicheng, Dali, and Lishui), which is the important manufacturing industry base of China. We found that: (1) the DeeplabV3+ performs well with an overall accuracy of 92%, higher than the maximum likelihood classification; (2) the distribution of blue steel roofs was not even across the whole study area, but they were evenly distributed within the town scale; and (3) strong positive correlation was observed between blue steel roofs area and industrial gross output. These results not only can be used to detect the inefficient industrial areas for regional planning but also provide fundamental data for studies of urban environmental issues. Full article

(This article belongs to the Special Issue Recent Advances in Multi- and Hyperspectral Image Analysis)

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16 pages, 5686 KiB

Open AccessArticle

Integrity Monitoring of Multimodal Perception System for Vehicle Localization

by Arjun Balakrishnan, Sergio Rodriguez Florez and Roger Reynaud

Sensors 2020, 20(16), 4654; https://doi.org/10.3390/s20164654 - 18 Aug 2020

Cited by 4 | Viewed by 2867

Abstract

Autonomous driving systems tightly rely on the quality of the data from sensors for tasks such as localization and navigation. In this work, we present an integrity monitoring framework that can assess the quality of multimodal data from exteroceptive sensors. The proposed multisource [...] Read more.

Autonomous driving systems tightly rely on the quality of the data from sensors for tasks such as localization and navigation. In this work, we present an integrity monitoring framework that can assess the quality of multimodal data from exteroceptive sensors. The proposed multisource coherence-based integrity assessment framework is capable of handling highway as well as complex semi-urban and urban scenarios. To achieve such generalization and scalability, we employ a semantic-grid data representation, which can efficiently represent the surroundings of the vehicle. The proposed method is used to evaluate the integrity of sources in several scenarios, and the integrity markers generated are used for identifying and quantifying unreliable data. A particular focus is given to real-world complex scenarios obtained from publicly available datasets where integrity localization requirements are of high importance. Those scenarios are examined to evaluate the performance of the framework and to provide proof-of-concept. We also establish the importance of the proposed integrity assessment framework in context-based localization applications for autonomous vehicles. The proposed method applies the integrity assessment concepts in the field of aviation to ground vehicles and provides the Protection Level markers (Horizontal, Lateral, Longitudinal) for perception systems used for vehicle localization. Full article

(This article belongs to the Section Intelligent Sensors)

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23 pages, 6334 KiB

Open AccessArticle

The CMOS Highly Linear Current Amplifier with Current Controlled Gain for Sensor Measurement Applications

by Roman Prokop, Roman Sotner and Vilem Kledrowetz

Sensors 2020, 20(16), 4653; https://doi.org/10.3390/s20164653 - 18 Aug 2020

Cited by 1 | Viewed by 3699

Abstract

This paper introduces a new current-controlled current-amplifier suitable for precise measurement applications. This amplifier was developed with strong emphasis on linearity leading to low total harmonic distortion (THD) of the output signal, and on linearity of the gain control. The presented circuit is [...] Read more.

This paper introduces a new current-controlled current-amplifier suitable for precise measurement applications. This amplifier was developed with strong emphasis on linearity leading to low total harmonic distortion (THD) of the output signal, and on linearity of the gain control. The presented circuit is characterized by low input and high output impedances. Current consumption is significantly smaller than with conventional quadratic current multipliers and is comparable in order to the maximum processed input current, which is ±200 µA. This circuit is supposed to be used in many sensor applications, as well as a precise current multiplier for general analog current signal processing. The presented amplifier (current multiplier) was designed by an uncommon topology based on linear sub-blocks using MOS transistors working in their linear region. The described circuit was designed and fabricated in a C035 I3T25 0.35-µm ON Semiconductor process because of the demand of the intended application for higher supply voltage. Nevertheless, the topology is suitable also for modern smaller CMOS technologies and lower supply voltages. The performance of the circuit was verified by laboratory measurement with parameters comparable to the Cadence simulation results and presented here. Full article

(This article belongs to the Special Issue Integrated Analog Circuits, Systems, and Sensors, and Their Applications)

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14 pages, 2312 KiB

Open AccessArticle

A New Optical Sensor Based on Laser Speckle and Chemometrics for Precision Agriculture: Application to Sunflower Plant-Breeding

by Maxime Ryckewaert, Daphné Héran, Emma Faur, Pierre George, Bruno Grèzes-Besset, Frédéric Chazallet, Yannick Abautret, Myriam Zerrad, Claude Amra and Ryad Bendoula

Sensors 2020, 20(16), 4652; https://doi.org/10.3390/s20164652 - 18 Aug 2020

Cited by 5 | Viewed by 3708

Abstract

New instruments to characterize vegetation must meet cost constraints while providing accurate information. In this paper, we study the potential of a laser speckle system as a low-cost solution for non-destructive phenotyping. The objective is to assess an original approach combining laser speckle [...] Read more.

New instruments to characterize vegetation must meet cost constraints while providing accurate information. In this paper, we study the potential of a laser speckle system as a low-cost solution for non-destructive phenotyping. The objective is to assess an original approach combining laser speckle with chemometrics to describe scattering and absorption properties of sunflower leaves, related to their chemical composition or internal structure. A laser diode system at two wavelengths 660 nm and 785 nm combined with polarization has been set up to differentiate four sunflower genotypes. REP-ASCA was used as a method to analyze parameters extracted from speckle patterns by reducing sources of measurement error. First findings have shown that measurement errors are mostly due to unwilling residual specular reflections. Moreover, results outlined that the genotype significantly impacts measurements. The variables involved in genotype dissociation are mainly related to scattering properties within the leaf. Moreover, an example of genotype classification using REP-ASCA outcomes is given and classify genotypes with an average error of about 20%. These encouraging results indicate that a laser speckle system is a promising tool to compare sunflower genotypes. Furthermore, an autonomous low-cost sensor based on this approach could be used directly in the field. Full article

(This article belongs to the Special Issue Sensors in Agriculture 2020)

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Experimental setup of speckle measurements: (a) image and (b) scheme. Full article ">Figure 2
Speckle patterns at <math display="inline"><semantics> <mrow> <mn>660</mn> <mspace width="0.277778em"/> <mi mathvariant="normal">n</mi> <mi mathvariant="normal">m</mi> </mrow> </semantics></math> for (a) pp-polarization (b) ps-polarization with a color scale defined by the minimum and maximum values of pixels. Full article ">Figure 3
Speckle patterns at <math display="inline"><semantics> <mrow> <mn>785</mn> <mspace width="0.277778em"/> <mi mathvariant="normal">n</mi> <mi mathvariant="normal">m</mi> </mrow> </semantics></math> for (a) pp-polarization (b) ps-polarization with a color scale defined by the minimum and maximum values of pixels. Full article ">Figure 4
Influence of the number k of components taken into account for the orthogonal projection on (a) total variance SSQ of <math display="inline"><semantics> <msub> <mi mathvariant="bold">X</mi> <mo>⊥</mo> </msub> </semantics></math> and (b) percentages of variance explained for each factor. Full article ">Figure 5
Correlation circle of the first three components of <math display="inline"><semantics> <mi mathvariant="bold">W</mi> </semantics></math>. Full article ">Figure 6
Permutation tests: comparison of the factor variance (red dot) with variances obtained by random permutations of level assignments. Full article ">Figure 7
Correlation circle of the first three principal components of the term <math display="inline"><semantics> <msub> <mi mathvariant="bold">X</mi> <mi>G</mi> </msub> </semantics></math>. Full article ">Figure 8
Average scores and confidence ellipses of the calibration set for each genotype on the principal components of the genotype factor. Full article ">

17 pages, 820 KiB

Open AccessArticle

Cache-Based Privacy Preserving Solution for Location and Content Protection in Location-Based Services

by Yuanbo Cui, Fei Gao, Wenmin Li, Yijie Shi, Hua Zhang, Qiaoyan Wen and Emmanouil Panaousis

Sensors 2020, 20(16), 4651; https://doi.org/10.3390/s20164651 - 18 Aug 2020

Cited by 14 | Viewed by 2957

Abstract

Location-Based Services (LBSs) are playing an increasingly important role in people’s daily activities nowadays. While enjoying the convenience provided by LBSs, users may lose privacy since they report their personal information to the untrusted LBS server. Although many approaches have been proposed to [...] Read more.

Location-Based Services (LBSs) are playing an increasingly important role in people’s daily activities nowadays. While enjoying the convenience provided by LBSs, users may lose privacy since they report their personal information to the untrusted LBS server. Although many approaches have been proposed to preserve users’ privacy, most of them just focus on the user’s location privacy, but do not consider the query privacy. Moreover, many existing approaches rely heavily on a trusted third-party (TTP) server, which may suffer from a single point of failure. To solve the problems above, in this paper we propose a Cache-Based Privacy-Preserving (CBPP) solution for users in LBSs. Different from the previous approaches, the proposed CBPP solution protects location privacy and query privacy simultaneously, while avoiding the problem of TTP server by having users collaborating with each other in a mobile peer-to-peer (P2P) environment. In the CBPP solution, each user keeps a buffer in his mobile device (e.g., smartphone) to record service data and acts as a micro TTP server. When a user needs LBSs, he sends a query to his neighbors first to seek for an answer. The user only contacts the LBS server when he cannot obtain the required service data from his neighbors. In this way, the user reduces the number of queries sent to the LBS server. We argue that the fewer queries are submitted to the LBS server, the less the user’s privacy is exposed. To users who have to send live queries to the LBS server, we employ the l-diversity, a powerful privacy protection definition that can guarantee the user’s privacy against attackers using background knowledge, to further protect their privacy. Evaluation results show that the proposed CBPP solution can effectively protect users’ location and query privacy with a lower communication cost and better quality of service. Full article

(This article belongs to the Section Sensor Networks)

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6 pages, 182 KiB

Open AccessCorrection

Correction: Garcia-Gonzalez, D.; Rivero, D.; Fernandez-Blanco, E.; Luaces, M.R. A Public Domain Dataset for Real-Life Human Activity Recognition Using Smartphone Sensors. Sensors 2020, 20, 2200

by Daniel Garcia-Gonzalez, Daniel Rivero, Enrique Fernandez-Blanco and Miguel R. Luaces

Sensors 2020, 20(16), 4650; https://doi.org/10.3390/s20164650 - 18 Aug 2020

Cited by 6 | Viewed by 2232

Abstract

The authors wish to make the following corrections to this paper [...] Full article

(This article belongs to the Special Issue Artificial Intelligence and Sensors)

19 pages, 6586 KiB

Open AccessArticle

Weber Texture Local Descriptor for Identification of Group-Housed Pigs

by Weijia Huang, Weixing Zhu, Changhua Ma and Yizheng Guo

Sensors 2020, 20(16), 4649; https://doi.org/10.3390/s20164649 - 18 Aug 2020

Cited by 5 | Viewed by 2680

Abstract

The individual identification of group-housed pigs plays an important role in breeding process management and individual behavior analysis. Recently, livestock identification methods based on the side view or face image have strict requirements on the position and posture of livestock, which poses a [...] Read more.

The individual identification of group-housed pigs plays an important role in breeding process management and individual behavior analysis. Recently, livestock identification methods based on the side view or face image have strict requirements on the position and posture of livestock, which poses a challenge for the application of the monitoring scene of group-housed pigs. To address the issue above, a Weber texture local descriptor (WTLD) is proposed for the identification of group-housed pigs by extracting the local features of back hair, skin texture, spots, and so on. By calculating the differential excitation and multi-directional information of pixels, the local structure features of the main direction are fused to enhance the description ability of features. The experimental results show that the proposed WTLD achieves higher recognition rates with a lower feature dimension. This method can identify pig individuals with different positions and postures in the pig house. Without limitations on pig movement, this method can facilitate the identification of individual pigs with greater convenience and universality. Full article

(This article belongs to the Section Sensing and Imaging)

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15 pages, 5504 KiB

Open AccessReview

DNA/RNA Electrochemical Biosensing Devices a Future Replacement of PCR Methods for a Fast Epidemic Containment

by Manikandan Santhanam, Itay Algov and Lital Alfonta

Sensors 2020, 20(16), 4648; https://doi.org/10.3390/s20164648 - 18 Aug 2020

Cited by 39 | Viewed by 11252

Abstract

Pandemics require a fast and immediate response to contain potential infectious carriers. In the recent 2020 Covid-19 worldwide pandemic, authorities all around the world have failed to identify potential carriers and contain it on time. Hence, a rapid and very sensitive testing method [...] Read more.

Pandemics require a fast and immediate response to contain potential infectious carriers. In the recent 2020 Covid-19 worldwide pandemic, authorities all around the world have failed to identify potential carriers and contain it on time. Hence, a rapid and very sensitive testing method is required. Current diagnostic tools, reverse transcription PCR (RT-PCR) and real-time PCR (qPCR), have its pitfalls for quick pandemic containment such as the requirement for specialized professionals and instrumentation. Versatile electrochemical DNA/RNA sensors are a promising technological alternative for PCR based diagnosis. In an electrochemical DNA sensor, a nucleic acid hybridization event is converted into a quantifiable electrochemical signal. A critical challenge of electrochemical DNA sensors is sensitive detection of a low copy number of DNA/RNA in samples such as is the case for early onset of a disease. Signal amplification approaches are an important tool to overcome this sensitivity issue. In this review, the authors discuss the most recent signal amplification strategies employed in the electrochemical DNA/RNA diagnosis of pathogens. Full article

(This article belongs to the Special Issue Biosensors – Recent Advances and Future Challenges)

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Nucleic acids electrochemical biosensor general principles. (A) A sandwich type genosensor model: A capture probe is employed to capture the target (DNA/RNA) from the solution phase to the electrode surface. The electrode bound target DNA is quantified indirectly by binding the reporter probes conjugated with a redox signal amplifier. The redox signal amplifier could be an enzyme or a nanomaterial, which produces the redox-active molecules. The redox-active molecules undergo an oxidation/reduction reaction, which is then quantified as an electrical response (current–voltage response) using electrochemical analytical methods. The whole strategy depends solely on hybridization efficiency between the nucleic acid probes and the target molecules (RNA/DNA/PNA). In this approach, target DNA does not need any modification. (B) The double-helical structure of DNA and Watson and Crick base pairing in DNA. DNA consists of two strands. The two strands are held together by complementary base pairing between the bases, i.e., hydrogen bonds (A with T and G with C). Two hydrogen bonds attach A to T; three hydrogen bonds attach G to C. High temperature can denature the double-stranded DNA into single-strands. These complementary single-stranded DNAs can specifically rehybridized to form a double-stranded helix by reducing the reaction temperature. Full article ">Figure 2
Schematic presentation of an HRP amplified electrochemical signal for DNA detection yth of enzyme molecules for the electrochemical signal. (A) DNA tetrahedral nanostructure for enhanced signal detection on gold surfaces [<a href="#B71-sensors-20-04648" class="html-bibr">71</a>]. (B) PolyA–gold surface interaction for immobilization of capture DNA, which was combined with multiple reporter probes and was attached to multiple HRP enzyme copies for signal amplification [<a href="#B50-sensors-20-04648" class="html-bibr">50</a>]. Adapted with permission from cited sources. Full article ">Figure 3
Schematic presentation of an electrochemical signal amplification for DNA detection. (A) DNA sandwich with a lipase labeled reporter probe for detection of Lactobacillus brevis DNA. Lipase was designed to bind with capture and target molecular recognition elements. During electrochemical analysis, lipase cleaves off the ferrocene from 9-mercaptononyl, 4-ferrocene aminobutanoate monolayer over the electrode surface. This results in the reduction of the observed current using cyclic voltammetry [<a href="#B74-sensors-20-04648" class="html-bibr">74</a>]. (B) Multiple invertase copies coated magnetic bead was conjugated with each capture and target molecular recognition element. The invertase was used to convert sucrose to glucose. Glucose was detected by a glucose meter. This system was reported for detection of HIV DNA [<a href="#B11-sensors-20-04648" class="html-bibr">11</a>]. (C) Similar to invertase, CdS coated polystyrene bead was used as a signal amplifier for the detection of urinary tract pathogens [<a href="#B61-sensors-20-04648" class="html-bibr">61</a>]. The Cds nanoparticle bound to the molecular recognition element was dissolved in the acid solution and resulting cadmium ions were quantified electrochemically. Adapted with permission from cited sources. Full article ">Figure 4
Enhancement of nucleic acid detection by employing polymerase and other isothermal amplification approaches on the electrode surface. (A) Strand displacement reaction and rolling circle amplification coupled system [<a href="#B78-sensors-20-04648" class="html-bibr">78</a>]. (B) Ligation and rolling circle amplification coupled system [<a href="#B68-sensors-20-04648" class="html-bibr">68</a>]. Adapted with permission from cited sources. Full article ">

38 pages, 3457 KiB

Open AccessReview

A Comprehensive Survey about Thermal Comfort under the IoT Paradigm: Is Crowdsensing the New Horizon?

by Valentina Tomat, Alfonso P. Ramallo-González and Antonio F. Skarmeta Gómez

Sensors 2020, 20(16), 4647; https://doi.org/10.3390/s20164647 - 18 Aug 2020

Cited by 21 | Viewed by 4320

Abstract

This paper presents a review of technologies under the paradigm 4.0 applied to the study of the thermal comfort and, implicitly, energy efficiency. The research is based on the analysis of the Internet of Things (IoT) literature, presenting a comparison among several approaches [...] Read more.

This paper presents a review of technologies under the paradigm 4.0 applied to the study of the thermal comfort and, implicitly, energy efficiency. The research is based on the analysis of the Internet of Things (IoT) literature, presenting a comparison among several approaches adopted. The central objective of the research is to outline the path that has been taken throughout the last decade towards a people-centric approach, discussing how users switched from being passive receivers of IoT services to being an active part of it. Basing on existing studies, authors performed what was a necessary and unprecedented grouping of the IoT applications to the thermal comfort into three categories: the thermal comfort studies with IoT hardware, in which the approach focuses on physical devices, the mimicking of IoT sensors and comfort using Building Simulation Models, based on the dynamic modelling of the thermal comfort through IoT systems, and Crowdsensing, a new concept in which people can express their sensation proactively using IoT devices. Analysing the trends of the three categories, the results showed that Crowdsensing has a promising future in the investigation through the IoT, although some technical steps forward are needed to achieve a satisfactory application to the thermal comfort matter. Full article

(This article belongs to the Section Internet of Things)

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21 pages, 19304 KiB

Open AccessArticle

Front Vehicle Detection Algorithm for Smart Car Based on Improved SSD Model

by Jingwei Cao, Chuanxue Song, Shixin Song, Silun Peng, Da Wang, Yulong Shao and Feng Xiao

Sensors 2020, 20(16), 4646; https://doi.org/10.3390/s20164646 - 18 Aug 2020

Cited by 50 | Viewed by 6555

Abstract

Vehicle detection is an indispensable part of environmental perception technology for smart cars. Aiming at the issues that conventional vehicle detection can be easily restricted by environmental conditions and cannot have accuracy and real-time performance, this article proposes a front vehicle detection algorithm [...] Read more.

Vehicle detection is an indispensable part of environmental perception technology for smart cars. Aiming at the issues that conventional vehicle detection can be easily restricted by environmental conditions and cannot have accuracy and real-time performance, this article proposes a front vehicle detection algorithm for smart car based on improved SSD model. Single shot multibox detector (SSD) is one of the current mainstream object detection frameworks based on deep learning. This work first briefly introduces the SSD network model and analyzes and summarizes its problems and shortcomings in vehicle detection. Then, targeted improvements are performed to the SSD network model, including major advancements to the basic structure of the SSD model, the use of weighted mask in network training, and enhancement to the loss function. Finally, vehicle detection experiments are carried out on the basis of the KITTI vision benchmark suite and self-made vehicle dataset to observe the algorithm performance in different complicated environments and weather conditions. The test results based on the KITTI dataset show that the mAP value reaches 92.18%, and the average processing time per frame is 15 ms. Compared with the existing deep learning-based detection methods, the proposed algorithm can obtain accuracy and real-time performance simultaneously. Meanwhile, the algorithm has excellent robustness and environmental adaptability for complicated traffic environments and anti-jamming capabilities for bad weather conditions. These factors are of great significance to ensure the accurate and efficient operation of smart cars in real traffic scenarios and are beneficial to vastly reduce the incidence of traffic accidents and fully protect people’s lives and property. Full article

(This article belongs to the Section Intelligent Sensors)

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14 pages, 2333 KiB

Open AccessLetter

Wavelength Selection FOR Rapid Identification of Different Particle Size Fractions of Milk Powder Using Hyperspectral Imaging

by Asma Khan, Muhammad Tajammal Munir, Wei Yu and Brent Young

Sensors 2020, 20(16), 4645; https://doi.org/10.3390/s20164645 - 18 Aug 2020

Cited by 16 | Viewed by 3087

Abstract

Hyperspectral imaging (HSI) in the spectral range of 400–1000 nm was tested to differentiate three different particle size fractions of milk powder. Partial least squares discriminant analysis (PLS-DA) was performed to observe the relationship of spectral data and particle size information for various [...] Read more.

Hyperspectral imaging (HSI) in the spectral range of 400–1000 nm was tested to differentiate three different particle size fractions of milk powder. Partial least squares discriminant analysis (PLS-DA) was performed to observe the relationship of spectral data and particle size information for various samples of instant milk powder. The PLS-DA model on full wavelengths successfully classified the three fractions of milk powder with a coefficient of prediction 0.943. Principal component analysis (PCA) identified each of the milk powder fractions as separate clusters across the first two principal components (PC₁ and PC₂) and five characteristic wavelengths were recognised by the loading plot of the first three principal components. Weighted regression coefficient (WRC) analysis of the partial least squares model identified 11 important wavelengths. Simplified PLS-DA models were developed from two sets of reduced wavelengths selected by PCA and WRC and showed better performance with predictive correlation coefficients (R_p²) of 0.962 and 0.979, respectively, while PLS-DA with complete spectrum had R_p² of 0.943. Similarly, classification accuracy of PLS-DA was improved to 92.2% for WRC based predictive model. Calculation time was also reduced to 2.1 and 2.8 s for PCA and WRC based simplified PLS-DA models in comparison to the complete spectrum model that was taking 32.2 s on average to predict the classification of milk powder samples. These results demonstrated that HSI with appropriate data analysis methods could become a potential analyser for non-invasive testing of milk powder in the future. Full article

(This article belongs to the Special Issue Non-destructive Sensors and Machine Learning for Food Safety & Quality Inspection)

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Flowchart of the key steps involved in hyperspectral imaging analysis. Full article ">Figure 2
Average spectra of three different milk powder size fractions after pre-processing. Full article ">Figure 3
Latent variable selection using the root mean square error of cross-validation. Full article ">Figure 4
Prediction of milk powder samples into coarse, medium, and fine fractions. Full article ">Figure 5
Principal component analysis of coarse, medium, and fine fraction of milk powder samples. (a) score plots; (b) loading plots. Full article ">Figure 6
Selection of eleven wavelengths from the weighted regression coefficient method. Full article ">Figure 7
Example of prediction map of discrete particle fractions of milk powder (a) fine particle fraction sample; (b) medium particle fraction sample; (c) coarse particle fraction sample; and (d) recombined fractions sample. Full article ">

14 pages, 4283 KiB

Open AccessArticle

A Novel Sensor Prototype with Enhanced and Adaptive Sensitivity Based on Negative Stiffness Mechanism

by Lijun Liu, Yongzhong Nie and Ying Lei

Sensors 2020, 20(16), 4644; https://doi.org/10.3390/s20164644 - 18 Aug 2020

Cited by 2 | Viewed by 2667

Abstract

Loess–mudstone/soil-rock interfacial landslide is one of the prominent landslide hazards that occurs in soil rock contacting zones. It is necessary to develop sensors with high sensitivity to weak and low frequency vibrations for the early warning of such interfacial landslides. In this paper, [...] Read more.

Loess–mudstone/soil-rock interfacial landslide is one of the prominent landslide hazards that occurs in soil rock contacting zones. It is necessary to develop sensors with high sensitivity to weak and low frequency vibrations for the early warning of such interfacial landslides. In this paper, a novel monitoring sensor prototype with enhanced and adaptive sensitivity is developed for this purpose. The novelty of the sensitive sensor is based on the variable capacitances and negative stiffness mechanism due to the electric filed forces on the vibrating plate. Owing to the feedback control of adjustable electrostatic field by an embedded micro controller, the sensor has adaptive amplification characteristics with high sensitivity to weak and low frequency input and low sensitivity to high input. The design and manufacture of the proposed sensor prototype by Micro-Electro-Mechanical Systems (MEMS) with proper packaging are introduced. Post-signal processing is also presented. Some preliminary testing of the prototype and experimental monitoring of sand interfacial slide which mimics soil–rock interfacial landslide were performed to demonstrate the performance of the developed sensor prototype with adaptive amplification and enhanced sensitivity. Full article

(This article belongs to the Special Issue Innovative Sensors for Civil Infrastructure Condition Assessment)

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13 pages, 4875 KiB

Open AccessLetter

Characterization of Second-Order Reflection Bands from a Cholesteric Liquid Crystal Cell Based on a Wavelength-Swept Laser

by Soyeon Ahn, Myeong Ock Ko, Jong-Hyun Kim, Zhongping Chen and Min Yong Jeon

Sensors 2020, 20(16), 4643; https://doi.org/10.3390/s20164643 - 18 Aug 2020

Cited by 9 | Viewed by 2714

Abstract

We report the results of an experimental study of the characterization of second-order reflection bands from a cholesteric liquid crystal (CLC) cell that depends on the applied electric field, using a wide bandwidth wavelength-swept laser. The second-order reflection bands around 1300 nm and [...] Read more.

We report the results of an experimental study of the characterization of second-order reflection bands from a cholesteric liquid crystal (CLC) cell that depends on the applied electric field, using a wide bandwidth wavelength-swept laser. The second-order reflection bands around 1300 nm and 1500 nm were observed using an optical spectrum analyzer when an electric field was applied to a horizontally oriented electrode cell with a pitch of 1.77 μm. A second-order reflection spectrum began to appear when the intensity of the electric field was 1.03 V_rms/μm with the angle of incidence to the CLC cell fixed at 36°. The reflectance increased as the intensity of the electric field increased at an angle of incidence of 20°, whereas at an incident angle of 36°, when an electric field of a predetermined value or more was applied to the CLC cell, it was confirmed that deformation was completely formed in the liquid crystal and the reflectance was saturated to a constant level. As the intensity of the electric field increased further, the reflection band shifted to a longer wavelength and discontinuous wavelength shift due to the pitch jump was observed rather than a continuous wavelength increase. In addition, the reflection band changed when the angle of incidence on the CLC cell was changed. As the angle of incidence gradually increased, the center wavelength of the reflection band moved towards shorter wavelengths. In the future, we intend to develop a device for optical wavelength filters based on side-polished optical fibers. This is expected to have a potential application as a wavelength notch filter or a bandpass filter. Full article

(This article belongs to the Special Issue Fiber Optic Sensors and Fiber Lasers)

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11 pages, 3497 KiB

Open AccessLetter

Experimental Investigation of Actively Q-Switched Er³⁺:ZBLAN Fiber Laser Operating at around 2.8 µm

by Lukasz Sojka, Lukasz Pajewski, Samir Lamrini, Mark Farries, Trevor M. Benson, Angela B. Seddon and Slawomir Sujecki

Sensors 2020, 20(16), 4642; https://doi.org/10.3390/s20164642 - 18 Aug 2020

Cited by 16 | Viewed by 3931

Abstract

A diode-pumped Q-switched Er³⁺:ZBLAN double-clad, single-transverse mode fiber laser is practically realized. The Q-switched laser characteristics as a function of pump power, repetition rate, and fiber length are experimentally investigated. The results obtained show that the Q-switched operation with 46 µJ [...] Read more.

A diode-pumped Q-switched Er³⁺:ZBLAN double-clad, single-transverse mode fiber laser is practically realized. The Q-switched laser characteristics as a function of pump power, repetition rate, and fiber length are experimentally investigated. The results obtained show that the Q-switched operation with 46 µJ pulse energy, 56 ns long pulses, and 0.821 kW peak power is achieved at a pulse repetition rate of 10 kHz. To the best of our knowledge, this is the highest-ever demonstrated peak power emitted from an actively Q-switched, single-transverse mode Er³⁺:ZBLAN fiber laser operating near 2.8 µm. Full article

(This article belongs to the Special Issue Selected Papers from the 19th Conference on Optical Fibers and Their Applications (OFTA 2020))

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19 pages, 4386 KiB

Open AccessArticle

Efficient Caoshu Character Recognition Scheme and Service Using CNN-Based Recognition Model Optimization

by Boseon Hong and Bongjae Kim

Sensors 2020, 20(16), 4641; https://doi.org/10.3390/s20164641 - 18 Aug 2020

Cited by 2 | Viewed by 2912

Abstract

Deep learning-based artificial intelligence models are widely used in various computing fields. Especially, Convolutional Neural Network (CNN) models perform very well for image recognition and classification. In this paper, we propose an optimized CNN-based recognition model to recognize Caoshu characters. In the proposed [...] Read more.

Deep learning-based artificial intelligence models are widely used in various computing fields. Especially, Convolutional Neural Network (CNN) models perform very well for image recognition and classification. In this paper, we propose an optimized CNN-based recognition model to recognize Caoshu characters. In the proposed scheme, an image pre-processing and data augmentation techniques for our Caoshu dataset were applied to optimize and enhance the CNN-based Caoshu character recognition model’s recognition performance. In the performance evaluation, Caoshu character recognition performance was compared and analyzed according to the proposed performance optimization. Based on the model validation results, the recognition accuracy was up to about 98.0% in the case of TOP-1. Based on the testing results of the optimized model, the accuracy, precision, recall, and F1 score are 88.12%, 81.84%, 84.20%, and 83.0%, respectively. Finally, we have designed and implemented a Caoshu recognition service as an Android application based on the optimized CNN based Cahosu recognition model. We have verified that the Caoshu recognition service could be performed in real-time. Full article

(This article belongs to the Special Issue Computational Intelligence and Intelligent Contents (CIIC))

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18 pages, 2726 KiB

Open AccessArticle

Application of Artificial Neural Networks for Accurate Determination of the Complex Permittivity of Biological Tissue

by Julian Bonello, Andrea Demarco, Iman Farhat, Lourdes Farrugia and Charles V. Sammut

Sensors 2020, 20(16), 4640; https://doi.org/10.3390/s20164640 - 18 Aug 2020

Cited by 11 | Viewed by 3437

Abstract

Medical devices making use of radio frequency (RF) and microwave (MW) fields have been studied as alternatives to existing diagnostic and therapeutic modalities since they offer several advantages. However, the lack of accurate knowledge of the complex permittivity of different biological tissues continues [...] Read more.

Medical devices making use of radio frequency (RF) and microwave (MW) fields have been studied as alternatives to existing diagnostic and therapeutic modalities since they offer several advantages. However, the lack of accurate knowledge of the complex permittivity of different biological tissues continues to hinder progress in of these technologies. The most convenient and popular measurement method used to determine the complex permittivity of biological tissues is the open-ended coaxial line, in combination with a vector network analyser (VNA) to measure the reflection coefficient (S11) which is then converted to the corresponding tissue permittivity using either full-wave analysis or through the use of equivalent circuit models. This paper proposes an innovative method of using artificial neural networks (ANN) to convert measured S11 to tissue permittivity, circumventing the requirement of extending the VNA measurement plane to the coaxial line open end. The conventional three-step calibration technique used with coaxial open-ended probes lacks repeatability, unless applied with extreme care by experienced persons, and is not adaptable to alternative sensor antenna configurations necessitated by many potential diagnostic and monitoring applications. The method being proposed does not require calibration at the tip of the probe, thus simplifying the measurement procedure while allowing arbitrary sensor design, and was experimentally validated using S11 measurements and the corresponding complex permittivity of 60 standard liquid and 42 porcine tissue samples. Following ANN training, validation and testing, we obtained a prediction accuracy of 5% for the complex permittivity. Full article

(This article belongs to the Special Issue Measurements Techniques of Biological Tissues Dielectric Properties, Updated Data and Current Applications)

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23 pages, 4386 KiB

Open AccessArticle

Graph Eigen Decomposition-Based Feature-Selection Method for Epileptic Seizure Detection Using Electroencephalography

by Md. Khademul Islam Molla, Kazi Mahmudul Hassan, Md. Rabiul Islam and Toshihisa Tanaka

Sensors 2020, 20(16), 4639; https://doi.org/10.3390/s20164639 - 18 Aug 2020

Cited by 24 | Viewed by 3378

Abstract

Epileptic seizure is a sudden alteration of behavior owing to a temporary change in the electrical functioning of the brain. There is an urgent demand for an automatic epilepsy detection system using electroencephalography (EEG) for clinical application. In this paper, the EEG signal [...] Read more.

Epileptic seizure is a sudden alteration of behavior owing to a temporary change in the electrical functioning of the brain. There is an urgent demand for an automatic epilepsy detection system using electroencephalography (EEG) for clinical application. In this paper, the EEG signal is divided into short time frames. Discrete wavelet transform is used to decompose each frame into a number of subbands. Different entropies as well as a group of features with which to characterize the spike events are extracted from each subband signal of an EEG frame. The features extracted from individual subbands are concatenated, yielding a high-dimensional feature vector. A discriminative subset of features is selected from the feature vector using a graph eigen decomposition (GED)-based approach. Thus, the reduced number of features obtained is effective for differentiating the underlying characteristics of EEG signals that indicate seizure events and those that indicate nonseizure events. The GED method ranks the features according to their contribution to correct classification. The selected features are used to classify seizure and nonseizure EEG signals using a feedforward neural network (FfNN). The performance of the proposed method is evaluated by conducting various experiments with a standard dataset obtained from the University of Bonn. The experimental results show that the proposed seizure-detection scheme achieves a classification accuracy of 99.55%, which is higher than that of state-of-the-art methods. The efficiency of FfNN is compared with linear discriminant analysis and support vector machine classifiers, which have classification accuracies of 98.72% and 99.39%, respectively. Hence, the proposed method is confirmed as a potential marker for EEG-based seizure detection. Full article

(This article belongs to the Section Biomedical Sensors)

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23 pages, 11147 KiB

Open AccessArticle

Multilabel Image Classification Based Fresh Concrete Mix Proportion Monitoring Using Improved Convolutional Neural Network

by Han Yang, Shuang-Jian Jiao and Feng-De Yin

Sensors 2020, 20(16), 4638; https://doi.org/10.3390/s20164638 - 18 Aug 2020

Cited by 8 | Viewed by 2927

Abstract

Proper and accurate mix proportion is deemed to be crucial for the concrete in service to implement its structural functions in a specific environment and structure. Neither existing testing methods nor previous studies have, to date, addressed the problem of real-time and full-scale [...] Read more.

Proper and accurate mix proportion is deemed to be crucial for the concrete in service to implement its structural functions in a specific environment and structure. Neither existing testing methods nor previous studies have, to date, addressed the problem of real-time and full-scale monitoring of fresh concrete mix proportion during manufacturing. Green manufacturing and safety construction are hindered by such defects. In this study, a state-of-the-art method based on improved convolutional neural network multilabel image classification is presented for mix proportion monitoring. Elaborately planned, uniformly distributed, widely covered and high-quality images of concrete mixtures were collected as dataset during experiments. Four convolutional neural networks were improved or fine-tuned based on two solutions for multilabel image classification problems, since original networks are tailored for single-label multiclassification tasks, but mix proportions are determined by multiple parameters. Various metrices for effectiveness evaluation of training and testing all indicated that four improved network models showed outstanding learning and generalization ability during training and testing. The best-performing one was embedded into executable application and equipped with hardware facilities to establish fresh concrete mix proportion monitoring system. Such system was deployed to terminals and united with mechanical and weighing sensors to establish integrated intelligent sensing system. Fresh concrete mix proportion real-time and full-scale monitoring and inaccurate mix proportion sensing and warning could be achieved simply by taking pictures and feeding pictures into such sensing system instead of conducting experiments in laboratory after specimen retention. Full article

(This article belongs to the Special Issue Artificial Intelligence for Smart Manufacturing: Methods and Applications)

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20 pages, 7300 KiB

Open AccessArticle

Applying a 6 DoF Robotic Arm and Digital Twin to Automate Fan-Blade Reconditioning for Aerospace Maintenance, Repair, and Overhaul

by John Oyekan, Michael Farnsworth, Windo Hutabarat, David Miller and Ashutosh Tiwari

Sensors 2020, 20(16), 4637; https://doi.org/10.3390/s20164637 - 18 Aug 2020

Cited by 40 | Viewed by 7330

Abstract

The UK is home to several major air commercial and transport hubs. As a result, there is a high demand for Maintenance, Repair, and Overhaul (MRO) services to ensure that fleets of aircraft are in airworthy conditions. MRO services currently involve heavy manual [...] Read more.

The UK is home to several major air commercial and transport hubs. As a result, there is a high demand for Maintenance, Repair, and Overhaul (MRO) services to ensure that fleets of aircraft are in airworthy conditions. MRO services currently involve heavy manual labor. This creates bottlenecks, low repeatability, and low productivity. Presented in this paper is an investigation to create an automation cell for the fan-blade reconditioning component of MRO. The design and prototype of the automation cell is presented. Furthermore, a digital twin of the grinding process is developed and used as a tool to explore the required grinding force parameters needed to effectively remove surface material. An integration of a 6-DoF industrial robot with an end-effector grinder and a computer vision system was undertaken. The computer vision system was used for the digitization of the fan-blade surface as well as tracking and guidance of material removal. Our findings reveal that our proposed system can perform material removal, track the state of the fan blade during the reconditioning process and do so within a closed-loop automated robotic work cell. Full article

(This article belongs to the Special Issue Sensing Applications in Robotics)

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22 pages, 9390 KiB

Open AccessArticle

BlockSIEM: Protecting Smart City Services through a Blockchain-based and Distributed SIEM

by Juan Velandia Botello, Andrés Pardo Mesa, Fabián Ardila Rodríguez, Daniel Díaz-López, Pantaleone Nespoli and Félix Gómez Mármol

Sensors 2020, 20(16), 4636; https://doi.org/10.3390/s20164636 - 18 Aug 2020

Cited by 22 | Viewed by 4775

Abstract

The Internet of Things (IoT) paradigm has revolutionized several industries (e.g., manufacturing, health, transport, education, among others) by allowing objects to connect to the Internet and, thus, enabling a variety of novel applications. In this sense, IoT devices have become an essential component [...] Read more.

The Internet of Things (IoT) paradigm has revolutionized several industries (e.g., manufacturing, health, transport, education, among others) by allowing objects to connect to the Internet and, thus, enabling a variety of novel applications. In this sense, IoT devices have become an essential component of smart cities, allowing many novel and useful services, but, at the same time, bringing numerous cybersecurity threats. The paper at hand proposes BlockSIEM, a blockchain-based and distributed Security Information and Event Management (SIEM) solution framework for the protection of the aforementioned smart city services. The proposed SIEM relies on blockchain technology to securely store and access security events. Such security events are generated by IoT sentinels that are in charge of shielding groups of IoT devices. The IoT sentinels may be deployed in smart city scenarios, such as smart hospitals, smart transport systems, smart airports, among others, ensuring a satisfactory level of protection. The blockchain guarantees the non-repudiation and traceability of the registry of security events due to its features. To demonstrate the feasibility of the proposed approach, our proposal is implemented using Ethereum and validated through different use cases and experiments. Full article

(This article belongs to the Special Issue Blockchain Security and Privacy for the Internet of Things)

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17 pages, 2744 KiB

Open AccessArticle

A Polynomial-Exponent Model for Calibrating the Frequency Response of Photoluminescence-Based Sensors

by Angel de la Torre, Santiago Medina-Rodríguez, Jose C. Segura and Jorge F. Fernández-Sánchez

Sensors 2020, 20(16), 4635; https://doi.org/10.3390/s20164635 - 18 Aug 2020

Cited by 4 | Viewed by 2069

Abstract

In this work, we propose a new model describing the relationship between the analyte concentration and the instrument response in photoluminescence sensors excited with modulated light sources. The concentration is modeled as a polynomial function of the analytical signal corrected with an exponent, [...] Read more.

In this work, we propose a new model describing the relationship between the analyte concentration and the instrument response in photoluminescence sensors excited with modulated light sources. The concentration is modeled as a polynomial function of the analytical signal corrected with an exponent, and therefore the model is referred to as a polynomial-exponent (PE) model. The proposed approach is motivated by the limitations of the classical models for describing the frequency response of the luminescence sensors excited with a modulated light source, and can be considered as an extension of the Stern–Volmer model. We compare the calibration provided by the proposed PE-model with that provided by the classical Stern–Volmer, Lehrer, and Demas models. Compared with the classical models, for a similar complexity (i.e., with the same number of parameters to be fitted), the PE-model improves the trade-off between the accuracy and the complexity. The utility of the proposed model is supported with experiments involving two oxygen-sensitive photoluminescence sensors in instruments based on sinusoidally modulated light sources, using four different analytical signals (phase-shift, amplitude, and the corresponding lifetimes estimated from them). Full article

(This article belongs to the Special Issue Calibration of Chemical Sensors Based on Photoluminescence)

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19 pages, 4973 KiB

Open AccessArticle

Modeling of Stochastic Wind Based on Operational Flight Data Using Karhunen–Loève Expansion Method

by Xiaolong Wang, Lukas Beller, Claudia Czado and Florian Holzapfel

Sensors 2020, 20(16), 4634; https://doi.org/10.3390/s20164634 - 18 Aug 2020

Cited by 1 | Viewed by 2660

Abstract

Wind has a significant influence on the operational flight safety. To quantify the influence of the wind characteristics, a wind series generator is required in simulations. This paper presents a method to model the stochastic wind based on operational flight data using the [...] Read more.

Wind has a significant influence on the operational flight safety. To quantify the influence of the wind characteristics, a wind series generator is required in simulations. This paper presents a method to model the stochastic wind based on operational flight data using the Karhunen–Loève expansion. The proposed wind model allows us to generate new realizations of wind series, which follow the original statistical characteristics. To improve the accuracy of this wind model, a vine copula is used in this paper to capture the high dimensional dependence among the random variables in the expansions. Besides, the proposed stochastic model based on the Karhunen–Loève expansion is compared with the well-known von Karman turbulence model based on the spectral representation in this paper. Modeling results of turbulence data validate that the Karhunen–Loève expansion and the spectral representation coincide in the stationary process. Furthermore, construction results of the non-stationary wind process from operational flights show that the generated wind series have a good match in the statistical characteristics with the raw data. The proposed stochastic wind model allows us to integrate the new wind series into the Monte Carlo Simulation for quantitative assessments. Full article

(This article belongs to the Special Issue Sensor Data Fusion and Analysis for Automation Systems)

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12 pages, 806 KiB

Open AccessLetter

Energy Efficiency in RF Energy Harvesting-Powered Distributed Antenna Systems for the Internet of Things

by Jiaxin Li, Ke Xiong, Jie Cao, Xi Yang and Tong Liu

Sensors 2020, 20(16), 4631; https://doi.org/10.3390/s20164631 - 18 Aug 2020

Cited by 6 | Viewed by 2741

Abstract

This paper studies a distributed antenna system (DAS) network with radio frequency (RF) energy harvesting (EH) technology where the distributed antenna ports (DAPs) transmit energy and information to multiple users simultaneously. The time division multiple access (TDMA) protocol is adopted, so for each [...] Read more.

This paper studies a distributed antenna system (DAS) network with radio frequency (RF) energy harvesting (EH) technology where the distributed antenna ports (DAPs) transmit energy and information to multiple users simultaneously. The time division multiple access (TDMA) protocol is adopted, so for each time slot is allowed to receive information, while the rest of the users harvest energy. In order to maximize the system energy efficiency (EE), subject to the EH requirements and data rate requirements of the users, the transmission time and power assignment are jointly optimized. In order to deal with this non-convex problem, based on Dinkelbach theory and the block-coordinate descent (BCD) scheme, an efficient algorithm is designed to obtain the global optimal solution. Then, simulation results are presented to show that the proposed method achieves much higher system EE compared with benchmark methods. With the increase of the user’s minimum information rate, the system EE decreases rapidly. Full article

(This article belongs to the Special Issue Energy-Efficient Communications for beyond 5G Green Networks)

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24 pages, 7035 KiB

Open AccessReview

Wind Tunnel Measurement Systems for Unsteady Aerodynamic Forces on Bluff Bodies: Review and New Perspective

by Zengshun Chen, Yemeng Xu, Hailin Huang and Kam Tim Tse

Sensors 2020, 20(16), 4633; https://doi.org/10.3390/s20164633 - 17 Aug 2020

Cited by 14 | Viewed by 6466

Abstract

Wind tunnel tests have become one of the most effective ways to evaluate aerodynamics and aeroelasticity in bluff bodies. This paper has firstly overviewed the development of conventional wind tunnel test techniques, including high frequency base balance technique, static synchronous multi-pressure sensing system [...] Read more.

Wind tunnel tests have become one of the most effective ways to evaluate aerodynamics and aeroelasticity in bluff bodies. This paper has firstly overviewed the development of conventional wind tunnel test techniques, including high frequency base balance technique, static synchronous multi-pressure sensing system test technique and aeroelastic test, and summarized their advantages and shortcomings. Subsequently, two advanced test approaches, a forced vibration test technique and hybrid aeroelastic- force balance wind tunnel test technique have been comprehensively reviewed. Then the characteristics and calculation procedure of the conventional and advanced wind tunnel test techniques were discussed and summarized. The results indicated that the conventional wind tunnel test techniques ignored the effect of structural oscillation on the measured aerodynamics as the test model is rigid. A forced vibration test can include that effect. Unfortunately, a test model in a forced vibration test cannot respond like a structure in the real world; it only includes the effect of structural oscillation on the surrounding flow and cannot consider the feedback from the surrounding flow to the oscillation test model. A hybrid aeroelastic-pressure/force balance test technique that can observe unsteady aerodynamics of a test model during its aeroelastic oscillation completely takes the effect of structural oscillation into consideration and is, therefore, effective in evaluation of aerodynamics and aeroelasticity in bluff bodies. This paper has not only advanced our understanding for aerodynamics and aeroelasticity in bluff bodies, but also provided a new perspective for advanced wind tunnel test techniques that can be used for fundamental studies and engineering applications. Full article

(This article belongs to the Section Physical Sensors)

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25 pages, 440 KiB

Open AccessArticle

NTRU-Like Random Congruential Public-Key Cryptosystem for Wireless Sensor Networks

by Anas Ibrahim, Alexander Chefranov, Nagham Hamad, Yousef-Awwad Daraghmi, Ahmad Al-Khasawneh and Joel J. P. C. Rodrigues

Sensors 2020, 20(16), 4632; https://doi.org/10.3390/s20164632 - 17 Aug 2020

Viewed by 3210

Abstract

Wireless sensor networks (WSNs) are the core of the Internet of Things and require cryptographic protection. Cryptographic methods for WSN should be fast and consume low power as these networks rely on battery-powered devices and microcontrollers. NTRU, the fastest and secure public key [...] Read more.

Wireless sensor networks (WSNs) are the core of the Internet of Things and require cryptographic protection. Cryptographic methods for WSN should be fast and consume low power as these networks rely on battery-powered devices and microcontrollers. NTRU, the fastest and secure public key cryptosystem, uses high degree, N, polynomials and is susceptible to the lattice basis reduction attack (LBRA). Congruential public key cryptosystem (CPKC), proposed by the NTRU authors, works on integers modulo q and is easily attackable by LBRA since it uses small numbers for the sake of the correct decryption. Herein, RCPKC, a random congruential public key cryptosystem working on degree

N = 0

polynomials modulo q, is proposed, such that the norm of a two-dimensional vector formed by its private key is greater than

\sqrt{q}

. RCPKC works as NTRU, and it is a secure version of insecure CPKC. RCPKC specifies a range from which the random numbers shall be selected, and it provides correct decryption for valid users and incorrect decryption for an attacker using LBRA by Gaussian lattice reduction. RCPKC asymmetric encryption padding (RAEP), similar to its NTRU analog, NAEP, is IND-CCA2 secure. Due to the use of big numbers instead of high degree polynomials, RCPKC is about 27 times faster in encryption and decryption than NTRU. Furthermore, RCPKC is more than three times faster than the most effective known NTRU variant, BQTRU. Compared to NTRU, RCPKC reduces energy consumption at least thirty times, which allows increasing the life-time of unattended WSNs more than thirty times. Full article

(This article belongs to the Section Sensor Networks)

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15 pages, 6694 KiB

Open AccessArticle

Epitaxial Growth of Sc_0.09Al_0.91N and Sc_0.18Al_0.82N Thin Films on Sapphire Substrates by Magnetron Sputtering for Surface Acoustic Waves Applications

by Florian Bartoli, Jérémy Streque, Jaafar Ghanbaja, Philippe Pigeat, Pascal Boulet, Sami Hage-Ali, Natalya Naumenko, A. Redjaïmia, Thierry Aubert and Omar Elmazria

Sensors 2020, 20(16), 4630; https://doi.org/10.3390/s20164630 - 17 Aug 2020

Cited by 6 | Viewed by 3074

Abstract

Scandium aluminum nitride (Sc_xAl_1-xN) films are currently intensively studied for surface acoustic waves (SAW) filters and sensors applications, because of the excellent tradeoff they present between high SAW velocity, large piezoelectric properties and wide bandgap for the intermediate compositions [...] Read more.

Scandium aluminum nitride (Sc_xAl_1-xN) films are currently intensively studied for surface acoustic waves (SAW) filters and sensors applications, because of the excellent tradeoff they present between high SAW velocity, large piezoelectric properties and wide bandgap for the intermediate compositions with an Sc content between 10 and 20%. In this paper, the growth of Sc_0.09Al_0.91N and Sc_0.18Al_0.82N films on sapphire substrates by sputtering method is investigated. The plasma parameters were optimized, according to the film composition, in order to obtain highly-oriented films. X-ray diffraction rocking-curve measurements show a full width at half maximum below 1.5°. Moreover, high-resolution transmission electron microscopy investigations reveal the epitaxial nature of the growth. Electrical characterizations of the Sc_0.09Al_0.91N/sapphire-based SAW devices show three identified modes. Numerical investigations demonstrate that the intermediate compositions between 10 and 20% of scandium allow for the achievement of SAW devices with an electromechanical coupling coefficient up to 2%, provided the film is combined with electrodes constituted by a metal with a high density. Full article

(This article belongs to the Special Issue Advances in Surface Acoustic Wave Sensors)

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22 pages, 2354 KiB

Open AccessArticle

Evaluation of Hyperparameter Optimization in Machine and Deep Learning Methods for Decoding Imagined Speech EEG

by Ciaran Cooney, Attila Korik, Raffaella Folli and Damien Coyle

Sensors 2020, 20(16), 4629; https://doi.org/10.3390/s20164629 - 17 Aug 2020

Cited by 57 | Viewed by 6734

Abstract

Classification of electroencephalography (EEG) signals corresponding to imagined speech production is important for the development of a direct-speech brain–computer interface (DS-BCI). Deep learning (DL) has been utilized with great success across several domains. However, it remains an open question whether DL methods provide [...] Read more.

Classification of electroencephalography (EEG) signals corresponding to imagined speech production is important for the development of a direct-speech brain–computer interface (DS-BCI). Deep learning (DL) has been utilized with great success across several domains. However, it remains an open question whether DL methods provide significant advances over traditional machine learning (ML) approaches for classification of imagined speech. Furthermore, hyperparameter (HP) optimization has been neglected in DL-EEG studies, resulting in the significance of its effects remaining uncertain. In this study, we aim to improve classification of imagined speech EEG by employing DL methods while also statistically evaluating the impact of HP optimization on classifier performance. We trained three distinct convolutional neural networks (CNN) on imagined speech EEG using a nested cross-validation approach to HP optimization. Each of the CNNs evaluated was designed specifically for EEG decoding. An imagined speech EEG dataset consisting of both words and vowels facilitated training on both sets independently. CNN results were compared with three benchmark ML methods: Support Vector Machine, Random Forest and regularized Linear Discriminant Analysis. Intra- and inter-subject methods of HP optimization were tested and the effects of HPs statistically analyzed. Accuracies obtained by the CNNs were significantly greater than the benchmark methods when trained on both datasets (words: 24.97%, p < 1 × 10^–7, chance: 16.67%; vowels: 30.00%, p < 1 × 10^–7, chance: 20%). The effects of varying HP values, and interactions between HPs and the CNNs were both statistically significant. The results of HP optimization demonstrate how critical it is for training CNNs to decode imagined speech. Full article

(This article belongs to the Special Issue Brain–Computer Interfaces: Advances and Challenges)

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Experimental paradigm and montage used for data acquisition. (a) During vowel production, subjects performed imagined speech for the duration of the task period. During the words task, subjects received 3 audible cues instructing them to begin. (b) The 10–20 system of electrode placement was used, with the 6 electrodes (F3, F4, C3, C4, P3 and P4) highlighted. Full article ">Figure 2
Network architectures of the shallow and deep CNNs, and the EEGNet. (a) is the shallow CNN: EEG signals are fed into the temporal convolution layer before proceeding through the spatial convolution layer. (b) is the deep CNN: it has the same initial structure as the shallow CNN, but with the addition of three identical convolution blocks. (c) is the EEGNet: EEG signals are fed into a 2D convolution layer. Depthwise and separable convolutions are also contained within its architecture. Full article ">Figure 3
Mean inner-fold validation accuracy by activation function. (a) Imagined words (chance accuracy: 16.67%). (b) Imagined vowels (chance accuracy: 20%). *** p < 1 × 10–6. Full article ">Figure 4
Inner-fold validation accuracy as a function of (a,b) loss (c) learning rate and (d) epochs. *** p < 1 × 10–8. Full article ">Figure 5
Distribution of hyperparameters selected for different CNN architectures. (a) Number of instances each activation function was selected. (b) Number of instances each learning rate was selected. (c) Number of instances each number of training epochs was selected. (d) Number of instances each loss function was selected. Full article ">Figure 6
Classification accuracies for (a) imagined words and (b) imagined vowels using intra- and inter-subject modes. *** p < 1 × 10–7. Full article ">

17 pages, 1508 KiB

Open AccessArticle

Collaborative Filtering to Predict Sensor Array Values in Large IoT Networks

by Fernando Ortega, Ángel González-Prieto, Jesús Bobadilla and Abraham Gutiérrez

Sensors 2020, 20(16), 4628; https://doi.org/10.3390/s20164628 - 17 Aug 2020

Cited by 4 | Viewed by 2498

Abstract

Internet of Things (IoT) projects are increasing in size over time, and some of them are growing to reach the whole world. Sensor arrays are deployed world-wide and their data is sent to the cloud, making use of the Internet. These huge networks [...] Read more.

Internet of Things (IoT) projects are increasing in size over time, and some of them are growing to reach the whole world. Sensor arrays are deployed world-wide and their data is sent to the cloud, making use of the Internet. These huge networks can be used to improve the quality of life of the humanity by continuously monitoring many useful indicators, like the health of the users, the air quality or the population movements. Nevertheless, in this scalable context, a percentage of the sensor data readings can fail due to several reasons like sensor reliabilities, network quality of service or extreme weather conditions, among others. Moreover, sensors are not homogeneously replaced and readings from some areas can be more precise than others. In order to address this problem, in this paper we propose to use collaborative filtering techniques to predict missing readings, by making use of the whole set of collected data from the IoT network. State of the art recommender systems methods have been chosen to accomplish this task, and two real sensor array datasets and a synthetic dataset have been used to test this idea. Experiments have been carried out varying the percentage of failed sensors. Results show a good level of prediction accuracy which, as expected, decreases as the failure rate increases. Results also point out a failure rate threshold below which is better to make use of memory-based approaches, and above which is better to choose model-based methods. Full article

(This article belongs to the Special Issue Information Fusion and Machine Learning for Sensors)

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Collaborative filtering approach to predict sensors failed values. Full article ">Figure 2
Collaborative filtering operation in the IoT sensor arrays context. Full article ">Figure 3
Distribution of the first 8 features in the [<a href="#B39-sensors-20-04628" class="html-bibr">39</a>] dataset. Each subplot shows the distribution of a reading of the sensor array. In grey, the histogram of the feature, and in orange a Gaussian kernel estimator of its density. Full article ">Figure 4
Boxplot of the normalized range of values for the 16 sensors in the [<a href="#B39-sensors-20-04628" class="html-bibr">39</a>] dataset. x-axis: sensor id, y-axis: range of results. Full article ">Figure 5
Correlation matrix for the 16 sensors in the [<a href="#B39-sensors-20-04628" class="html-bibr">39</a>] dataset. Warm colors (with maximum light orange) stand for strong positive correlation and cool colors (with maximum light blue) mean strong negative correlation. Black indicates no linear correlation. Full article ">Figure 6
Correlation matrix for the 128 sensors in the [<a href="#B40-sensors-20-04628" class="html-bibr">40</a>] dataset. Warm colors (with maximum light orange) stand for strong positive correlation and cool colors (with maximum light blue) mean strong negative correlation. Black indicates no linear correlation. Full article ">Figure 7
Prediction quality results. Left side: [<a href="#B39-sensors-20-04628" class="html-bibr">39</a>] dataset, right side: [<a href="#B40-sensors-20-04628" class="html-bibr">40</a>] dataset; x-axis: sparsity levels; y-axis: prediction error. Best results are the closest to zero (low errors). Full article ">Figure 8
Prediction quality results obtained from the synthetic dataset. Full article ">

16 pages, 22818 KiB

Open AccessArticle

An Online Classification Method for Fault Diagnosis of Railway Turnouts

by Dongxiu Ou, Yuqing Ji, Lei Zhang and Hu Liu

Sensors 2020, 20(16), 4627; https://doi.org/10.3390/s20164627 - 17 Aug 2020

Cited by 21 | Viewed by 3531

Abstract

Railway turnout system is a key infrastructure to railway safety and efficiency. However, it is prone to failure in the field. Therefore, many railway departments have adopted a monitoring system to monitor the operation status of turnouts. With monitoring data collected, many researchers [...] Read more.

Railway turnout system is a key infrastructure to railway safety and efficiency. However, it is prone to failure in the field. Therefore, many railway departments have adopted a monitoring system to monitor the operation status of turnouts. With monitoring data collected, many researchers have proposed different fault-diagnosis methods. However, many of the existing methods cannot realize real-time updating or deal with new fault types. This paper—based on imbalanced data—proposes a Bayes-based online turnout fault-diagnosis method, which realizes incremental learning and scalable fault recognition. First, the basic conceptions of the turnout system are introduced. Next, the feature extraction and processing of the imbalanced monitoring data are introduced. Then, an online diagnosis method based on Bayesian incremental learning and scalable fault recognition is proposed, followed by the experiment with filed data from Guangzhou Railway. The results show that the scalable fault-recognition method can reach an accuracy of 99.11%, and the training time of the Bayesian incremental learning model reduces 29.97% without decreasing the accuracy, which demonstrates the high accuracy, adaptability and efficiency of the proposed model, of great significance for labor-saving, timely maintenance and further, safety and efficiency of railway transportation. Full article

(This article belongs to the Special Issue Deep Learning, Artificial Neural Networks and Sensors for Fault Diagnosis)

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