Sensors

21 pages, 5796 KiB

Open AccessArticle

Predicting the Early-Age Time-Dependent Behaviors of a Prestressed Concrete Beam by Using Physics-Informed Neural Network

by Hyun-Woo Park and Jin-Ho Hwang

Sensors 2023, 23(14), 6649; https://doi.org/10.3390/s23146649 - 24 Jul 2023

Cited by 2 | Viewed by 2253

Abstract

This paper proposes a physics-informed neural network (PINN) for predicting the early-age time-dependent behaviors of prestressed concrete beams. The PINN utilizes deep neural networks to learn the time-dependent coupling among the effective prestress force and the several factors that affect the time-dependent behavior [...] Read more.

This paper proposes a physics-informed neural network (PINN) for predicting the early-age time-dependent behaviors of prestressed concrete beams. The PINN utilizes deep neural networks to learn the time-dependent coupling among the effective prestress force and the several factors that affect the time-dependent behavior of the beam, such as concrete creep and shrinkage, tendon relaxation, and changes in concrete elastic modulus. Unlike traditional numerical algorithms such as the finite difference method, the PINN directly solves the integro-differential equation without the need for discretization, offering an efficient and accurate solution. Considering the trade-off between solution accuracy and the computing cost, optimal hyperparameter combinations are determined for the PINN. The proposed PINN is verified through the comparison to the numerical results from the finite difference method for two representative cross sections of PSC beams. Full article

(This article belongs to the Section Physical Sensors)

► Show Figures

Figure 1

30 pages, 35272 KiB

Open AccessArticle

Graph Neural Network-Based Method of Spatiotemporal Land Cover Mapping Using Satellite Imagery

by Domen Kavran, Domen Mongus, Borut Žalik and Niko Lukač

Sensors 2023, 23(14), 6648; https://doi.org/10.3390/s23146648 - 24 Jul 2023

Cited by 11 | Viewed by 3297

Abstract

Multispectral satellite imagery offers a new perspective for spatial modelling, change detection and land cover classification. The increased demand for accurate classification of geographically diverse regions led to advances in object-based methods. A novel spatiotemporal method is presented for object-based land cover classification [...] Read more.

Multispectral satellite imagery offers a new perspective for spatial modelling, change detection and land cover classification. The increased demand for accurate classification of geographically diverse regions led to advances in object-based methods. A novel spatiotemporal method is presented for object-based land cover classification of satellite imagery using a Graph Neural Network. This paper introduces innovative representation of sequential satellite images as a directed graph by connecting segmented land region through time. The method’s novel modular node classification pipeline utilises the Convolutional Neural Network as a multispectral image feature extraction network, and the Graph Neural Network as a node classification model. To evaluate the performance of the proposed method, we utilised EfficientNetV2-S for feature extraction and the GraphSAGE algorithm with Long Short-Term Memory aggregation for node classification. This innovative application on Sentinel-2 L2A imagery produced complete 4-year intermonthly land cover classification maps for two regions: Graz in Austria, and the region of Portorož, Izola and Koper in Slovenia. The regions were classified with Corine Land Cover classes. In the level 2 classification of the Graz region, the method outperformed the state-of-the-art UNet model, achieving an average F1-score of 0.841 and an accuracy of 0.831, as opposed to UNet’s 0.824 and 0.818, respectively. Similarly, the method demonstrated superior performance over UNet in both regions under the level 1 classification, which contains fewer classes. Individual classes have been classified with accuracies up to 99.17%. Full article

(This article belongs to the Special Issue Deep Learning for Environmental Remote Sensing)

► Show Figures

Figure 1

18 pages, 3828 KiB

Open AccessArticle

Global Path Planning of Unmanned Surface Vehicle Based on Improved A-Star Algorithm

by Huixia Zhang, Yadong Tao and Wenliang Zhu

Sensors 2023, 23(14), 6647; https://doi.org/10.3390/s23146647 - 24 Jul 2023

Cited by 24 | Viewed by 2921

Abstract

To make unmanned surface vehicles that are better applied to the field of environmental monitoring in inland rivers, reservoirs, or coasts, we propose a global path-planning algorithm based on the improved A-star algorithm. The path search is carried out using the raster method [...] Read more.

To make unmanned surface vehicles that are better applied to the field of environmental monitoring in inland rivers, reservoirs, or coasts, we propose a global path-planning algorithm based on the improved A-star algorithm. The path search is carried out using the raster method for environment modeling and the 8-neighborhood search method: a bidirectional search strategy and an evaluation function improvement method are used to reduce the total number of traversing nodes; the planned path is smoothed to remove the inflection points and solve the path folding problem. The simulation results reveal that the improved A-star algorithm is more efficient in path planning, with fewer inflection points and traversing nodes, and the smoothed paths are more to meet the actual navigation demands of unmanned surface vehicles than the conventional A-star algorithm. Full article

(This article belongs to the Section Vehicular Sensing)

► Show Figures

Figure 1

15 pages, 10414 KiB

Open AccessArticle

Traction Machine State Recognition Method Based on DPCA Algorithm and Convolution Neural Network

by Dongyang Li, Jianyi Yang, Zaisheng Pan and Nanyang Li

Sensors 2023, 23(14), 6646; https://doi.org/10.3390/s23146646 - 24 Jul 2023

Viewed by 1246

Abstract

It is important to improve the identification accuracy of the operating status of elevator traction machines. The distribution difference of the time-frequency signals utilized to identify operating circumstances is modest, making it difficult to extract features from the vibration signals of traction machines [...] Read more.

It is important to improve the identification accuracy of the operating status of elevator traction machines. The distribution difference of the time-frequency signals utilized to identify operating circumstances is modest, making it difficult to extract features from the vibration signals of traction machines under various operating conditions, leading to low recognition accuracy. A novel method for identifying the operating status of traction machines based on signal demodulation method and convolutional neural network (CNN) is proposed. The original vibration time-frequency signals are demodulated by the demodulation method based on time-frequency analysis and principal component analysis (DPCA). Firstly, the signal demodulation method based on principal component analysis is used to extract the modulation features of the experimentally measured vibration signals. Then, The CNN is used for feature vector extraction, and the training model is obtained through multiple iterations to achieve automatic recognition of the running state. The experimental results show that the proposed method can effectively extract feature parameters under different states. The diagnostic accuracy is up to 96.94%, which is about 16.61% higher than conventional methods. It provides a feasible solution for identifying the operating status of elevator traction machines. Full article

(This article belongs to the Section Electronic Sensors)

► Show Figures

Figure 1

20 pages, 6100 KiB

Open AccessArticle

Rolling Bearing Fault Diagnosis Based on Support Vector Machine Optimized by Improved Grey Wolf Algorithm

by Weijie Shen, Maohua Xiao, Zhenyu Wang and Xinmin Song

Sensors 2023, 23(14), 6645; https://doi.org/10.3390/s23146645 - 24 Jul 2023

Cited by 10 | Viewed by 1739

Abstract

This study targets the low accuracy and efficiency of the support vector machine (SVM) algorithm in rolling bearing fault diagnosis. An improved grey wolf optimizer (IGWO) algorithm was proposed based on deep learning and a swarm intelligence optimization algorithm to optimize the structural [...] Read more.

This study targets the low accuracy and efficiency of the support vector machine (SVM) algorithm in rolling bearing fault diagnosis. An improved grey wolf optimizer (IGWO) algorithm was proposed based on deep learning and a swarm intelligence optimization algorithm to optimize the structural parameters of SVM and improve the rolling bearing fault diagnosis. A nonlinear contraction factor update strategy was also proposed. The variable coefficient changes with the shrinkage factor α. Thus, the search ability was balanced at different early and late stages by controlling the dynamic changes of the variable coefficient. In the early stages of optimization, its speed is low to avoid falling into local optimization. In the later stages of optimization, the speed is higher, and finding the optimal solution is easier, balancing the two different global and local optimization capabilities to complete efficient convergence. The dynamic weight update strategy was adopted to perform position updates based on adaptive dynamic weights. First, the dataset of Case Western Reserve University was used for simulation, and the results showed that the diagnosis accuracy of IGWO-SVM was 98.75%. Then, the IGWO-SVM model was trained and tested using data obtained from the full-life-cycle test platform of mechanical transmission bearings independently researched and developed by Nanjing Agricultural University. The fault diagnosis accuracy and convergence value of the adaptation curve were compared with those of PSO-SVM (particle swarm optimization) and GWO-SVM diagnosis models. Results showed that the IGWO-SVM model had the highest rolling bearing fault diagnosis accuracy and the best diagnosis convergence. Full article

(This article belongs to the Section Fault Diagnosis & Sensors)

► Show Figures

Figure 1

19 pages, 2200 KiB

Open AccessArticle

Automatic Recognition Reading Method of Pointer Meter Based on YOLOv5-MR Model

by Le Zou, Kai Wang, Xiaofeng Wang, Jie Zhang, Rui Li and Zhize Wu

Sensors 2023, 23(14), 6644; https://doi.org/10.3390/s23146644 - 24 Jul 2023

Cited by 10 | Viewed by 2679

Abstract

Meter reading is an important part of intelligent inspection, and the current meter reading method based on target detection has problems of low accuracy and large error. In order to improve the accuracy of automatic meter reading, this paper proposes an automatic reading [...] Read more.

Meter reading is an important part of intelligent inspection, and the current meter reading method based on target detection has problems of low accuracy and large error. In order to improve the accuracy of automatic meter reading, this paper proposes an automatic reading method for pointer-type meters based on the YOLOv5-Meter Reading (YOLOv5-MR) model. Firstly, in order to improve the detection performance of small targets in YOLOv5 framework, a multi-scale target detection layer is added to the YOLOv5 framework, and a set of Anchors is designed based on the lightning rod dial data set; secondly, the loss function and up-sampling method are improved to enhance the model training convergence speed and obtain the optimal up-sampling parameters; Finally, a new external circle fitting method of the dial is proposed, and the dial reading is calculated by the center angle algorithm. The experimental results on the self-built dataset show that the Mean Average Precision (mAP) of the YOLOv5-MR target detection model reaches 79%, which is 3% better than the YOLOv5 model, and outperforms other advanced pointer-type meter reading models. Full article

(This article belongs to the Special Issue Image/Video Restoration Based on Deep Learning and Its Application in Sensing)

► Show Figures

Figure 1

16 pages, 5648 KiB

Open AccessArticle

Automated Laser-Fiber Coupling Module for Optical-Resolution Photoacoustic Microscopy

by Seongyi Han, Hyunjun Kye, Chang-Seok Kim, Tae-Kyoung Kim, Jinwoo Yoo and Jeesu Kim

Sensors 2023, 23(14), 6643; https://doi.org/10.3390/s23146643 - 24 Jul 2023

Viewed by 2064

Abstract

Photoacoustic imaging has emerged as a promising biomedical imaging technique that enables visualization of the optical absorption characteristics of biological tissues in vivo. Among the different photoacoustic imaging system configurations, optical-resolution photoacoustic microscopy stands out by providing high spatial resolution using a tightly [...] Read more.

Photoacoustic imaging has emerged as a promising biomedical imaging technique that enables visualization of the optical absorption characteristics of biological tissues in vivo. Among the different photoacoustic imaging system configurations, optical-resolution photoacoustic microscopy stands out by providing high spatial resolution using a tightly focused laser beam, which is typically transmitted through optical fibers. Achieving high-quality images depends significantly on optical fluence, which is directly proportional to the signal-to-noise ratio. Hence, optimizing the laser-fiber coupling is critical. Conventional coupling systems require manual adjustment of the optical path to direct the laser beam into the fiber, which is a repetitive and time-consuming process. In this study, we propose an automated laser-fiber coupling module that optimizes laser delivery and minimizes the need for manual intervention. By incorporating a motor-mounted mirror holder and proportional derivative control, we successfully achieved efficient and robust laser delivery. The performance of the proposed system was evaluated using a leaf-skeleton phantom in vitro and a human finger in vivo, resulting in high-quality photoacoustic images. This innovation has the potential to significantly enhance the quality and efficiency of optical-resolution photoacoustic microscopy. Full article

(This article belongs to the Special Issue Photoacoustic Imaging and Sensing)

► Show Figures

Figure 1

Figure 1
Schematic illustration of the system. (a) The automated laser-fiber coupling module, which selectively connected to the power measurement unit or the OR-PAM module. Ch1 and Ch2, respectively control the horizontal and vertical angle of MM1, while Ch3 and Ch4, respectively control the horizontal and vertical angle of MM2. (b) The OR-PAM module for scanning the imaging targets. PA, photoacoustic; OR-PAM, optical-resolution PA microscopy; AT, attenuator; MM, motorized mirror; Ch, control channel; CL, collimator; OF, optical fiber; PD, photodiode; OL, objective lens; BC, opto-acoustic beam combiner; AL, acoustic lens; TR, ultrasound transducer; AMP, amplifier; DAQ, data acquisition module; MEMS, microelectromechanical system. Full article ">Figure 2
Schematic illustration of the control algorithm for optimizing the laser-fiber coupling efficiency. Full article ">Figure 3
The evaluation for the automated laser-fiber coupling module. (a) The measured laser power during the optimization processing. Dashed lines indicate the boundary of each iteration. Laser power variations are depicted as different colors for each channel. (b) The measured laser power during the 15 optimizations. The yellow area is a 5% deviation of the mean laser power. (c) Beam profiles of the delivered laser at the disturbed and optimized states. Full article ">Figure 4
The feasibility test of the automated laser-fiber coupling module through in vitro phantom imaging. (a) The measured laser power during the multiple image acquisition. Red and green points represent disturbed (D1–D4) and optimized (O1–O4) points, respectively. (b) PA images of a leaf-skeleton phantom at each disturbed or optimized point. White and blue area denote the signal and background regions, respectively. Laser power was measured before each image acquisition. (c) The average and standard deviation of PA amplitude in the signal region (white dashed area in (b)) at each measured point. Red and green represent disturbed and optimized points, respectively. (d) Correlated SNR and laser power. The dashed line is the first-order polynomial regression of the measured SNR. PA, photoacoustic; SNR, signal-to-noise ratio. Full article ">Figure 5
The in vivo validation of the automated laser-fiber coupling module. (a) The measured laser power during the multiple PA image acquisition. (b) A photograph of the imaging area in the little finger of a healthy volunteer. (c) Digital microscope image of the microvasculature in the imaging area. (d) PA images in the imaging area at the disturbed (D) and optimized (O1–O4) states. White and blue area denote the signal and background regions, respectively. Black arrows in (c,d) denote corresponding blood vessels. PA, photoacoustic. Full article ">

15 pages, 3833 KiB

Open AccessArticle

Multi-Temporal Hyperspectral Classification of Grassland Using Transformer Network

by Xuanhe Zhao, Shengwei Zhang, Ruifeng Shi, Weihong Yan and Xin Pan

Sensors 2023, 23(14), 6642; https://doi.org/10.3390/s23146642 - 24 Jul 2023

Cited by 7 | Viewed by 1781

Abstract

In recent years, grassland monitoring has shifted from traditional field surveys to remote-sensing-based methods, but the desired level of accuracy has not yet been obtained. Multi-temporal hyperspectral data contain valuable information about species and growth season differences, making it a promising tool for [...] Read more.

In recent years, grassland monitoring has shifted from traditional field surveys to remote-sensing-based methods, but the desired level of accuracy has not yet been obtained. Multi-temporal hyperspectral data contain valuable information about species and growth season differences, making it a promising tool for grassland classification. Transformer networks can directly extract long-sequence features, which is superior to other commonly used analysis methods. This study aims to explore the transformer network’s potential in the field of multi-temporal hyperspectral data by fine-tuning it and introducing it into high-powered grassland detection tasks. Subsequently, the multi-temporal hyperspectral classification of grassland samples using the transformer network (MHCgT) is proposed. To begin, a total of 16,800 multi-temporal hyperspectral data were collected from grassland samples at different growth stages over several years using a hyperspectral imager in the wavelength range of 400–1000 nm. Second, the MHCgT network was established, with a hierarchical architecture, which generates a multi-resolution representation that is beneficial for grass hyperspectral time series’ classification. The MHCgT employs a multi-head self-attention mechanism to extract features, avoiding information loss. Finally, an ablation study of MHCgT and comparative experiments with state-of-the-art methods were conducted. The results showed that the proposed framework achieved a high accuracy rate of 98.51% in identifying grassland multi-temporal hyperspectral which outperformed CNN, LSTM-RNN, SVM, RF, and DT by 6.42–26.23%. Moreover, the average classification accuracy of each species was above 95%, and the August mature period was easier to identify than the June growth stage. Overall, the proposed MHCgT framework shows great potential for precisely identifying multi-temporal hyperspectral species and has significant applications in sustainable grassland management and species diversity assessment. Full article

(This article belongs to the Section Sensing and Imaging)

► Show Figures

Figure 1

Figure 1
Location of the study area within China (Inner Mongolia Autonomous Region, China) and the grass species located in the study site over a topographic map (<a href="https://ditu.amap.com" target="_blank">https://ditu.amap.com</a>, accessed on 23 January 2023). Full article ">Figure 2
The overall architecture of the proposed MHCgT framework. Full article ">Figure 3
Structure of the encoder block. Full article ">Figure 4
Multi-temporal hyperspectral data of seven grass species, namely, (a) Medicago sativa, (b) Medicago ruthenica, (c) Elymus canadensis, (d) Hordeum brevisubulatum, (e) Medicago varia, (f) Onobrychis viciaefolia, (g) Bromus ciliatus. Full article ">Figure 5
Relationship between epoch, accuracy, and loss in MHCgT network. (a) 202006, (b) 202008, (c) 202106, (d) 202108, acc: train accuracy, val_acc: validation accuracy, loss: train loss, val_loss: validation loss. Full article ">Figure 6
The confusion matrix is used for seven classifications. Rows represent actual classes, and columns represent prediction classes (test set 10%). Full article ">Figure 7
Confusion matrices of grassland multi-temporal hyperspectral data using MHCgT network (test set 10%). Rows indicate correct labels, and columns indicate predicted labels. Full article ">

26 pages, 712 KiB

Open AccessArticle

Enabling Trust and Security in Digital Twin Management: A Blockchain-Based Approach with Ethereum and IPFS

by Austine Onwubiko, Raman Singh , Shahid Awan , Zeeshan Pervez and Naeem Ramzan

Sensors 2023, 23(14), 6641; https://doi.org/10.3390/s23146641 - 24 Jul 2023

Cited by 11 | Viewed by 2717

Abstract

The emergence of Industry 5.0 has highlighted the significance of information usage, processing, and data analysis when maintaining physical assets. This has enabled the creation of the Digital Twin (DT). Information about an asset is generated and consumed during its entire life cycle. [...] Read more.

The emergence of Industry 5.0 has highlighted the significance of information usage, processing, and data analysis when maintaining physical assets. This has enabled the creation of the Digital Twin (DT). Information about an asset is generated and consumed during its entire life cycle. The main goal of DT is to connect and represent physical assets as close to reality as possible virtually. Unfortunately, the lack of security and trust among DT participants remains a problem as a result of data sharing. This issue cannot be resolved with a central authority when dealing with large organisations. Blockchain technology has been proposed as a solution for DT information sharing and security challenges. This paper proposes a Blockchain-based solution for digital twin using Ethereum blockchain with performance and cost analysis. This solution employs a smart contract for information management and access control for stakeholders of the digital twin, which is secure and tamper-proof. This implementation is based on Ethereum and IPFS. We use IPFS storage servers to store stakeholders’ details and manage information. A real-world use-case of a production line of a smartphone, where a conveyor belt is used to carry different parts, is presented to demonstrate the proposed system. The performance evaluation of our proposed system shows that it is secure and achieves performance improvement when compared with other methods. The comparison of results with state-of-the-art methods showed that the proposed system consumed fewer resources in a transaction cost, with an 8% decrease. The execution cost increased by 10%, but the cost of ether was 93% less than the existing methods. Full article

(This article belongs to the Special Issue Human Digital Twins for Industry 5.0: Current Perspectives and Future Directions)

► Show Figures

Figure 1

19 pages, 3659 KiB

Open AccessArticle

Enhancing Speech Emotion Recognition Using Dual Feature Extraction Encoders

by Ilkhomjon Pulatov, Rashid Oteniyazov, Fazliddin Makhmudov and Young-Im Cho

Sensors 2023, 23(14), 6640; https://doi.org/10.3390/s23146640 - 24 Jul 2023

Cited by 6 | Viewed by 3151

Abstract

Understanding and identifying emotional cues in human speech is a crucial aspect of human–computer communication. The application of computer technology in dissecting and deciphering emotions, along with the extraction of relevant emotional characteristics from speech, forms a significant part of this process. The [...] Read more.

Understanding and identifying emotional cues in human speech is a crucial aspect of human–computer communication. The application of computer technology in dissecting and deciphering emotions, along with the extraction of relevant emotional characteristics from speech, forms a significant part of this process. The objective of this study was to architect an innovative framework for speech emotion recognition predicated on spectrograms and semantic feature transcribers, aiming to bolster performance precision by acknowledging the conspicuous inadequacies in extant methodologies and rectifying them. To procure invaluable attributes for speech detection, this investigation leveraged two divergent strategies. Primarily, a wholly convolutional neural network model was engaged to transcribe speech spectrograms. Subsequently, a cutting-edge Mel-frequency cepstral coefficient feature abstraction approach was adopted and integrated with Speech2Vec for semantic feature encoding. These dual forms of attributes underwent individual processing before they were channeled into a long short-term memory network and a comprehensive connected layer for supplementary representation. By doing so, we aimed to bolster the sophistication and efficacy of our speech emotion detection model, thereby enhancing its potential to accurately recognize and interpret emotion from human speech. The proposed mechanism underwent a rigorous evaluation process employing two distinct databases: RAVDESS and EMO-DB. The outcome displayed a predominant performance when juxtaposed with established models, registering an impressive accuracy of 94.8% on the RAVDESS dataset and a commendable 94.0% on the EMO-DB dataset. This superior performance underscores the efficacy of our innovative system in the realm of speech emotion recognition, as it outperforms current frameworks in accuracy metrics. Full article

(This article belongs to the Special Issue Application of Semantic Technologies in Sensors and Sensing Systems)

► Show Figures

Figure 1

26 pages, 7913 KiB

Open AccessArticle

Contextual Cluster-Based Glow-Worm Swarm Optimization (GSO) Coupled Wireless Sensor Networks for Smart Cities

by P. S. Ramesh, P. Srivani, Miroslav Mahdal, Lingala Sivaranjani, Shafiqul Abidin, Shivakumar Kagi and Muniyandy Elangovan

Sensors 2023, 23(14), 6639; https://doi.org/10.3390/s23146639 - 24 Jul 2023

Cited by 3 | Viewed by 1657

Abstract

The cluster technique involves the creation of clusters and the selection of a cluster head (CH), which connects sensor nodes, known as cluster members (CM), to the CH. The CH receives data from the CM and collects data from sensor nodes, removing unnecessary [...] Read more.

The cluster technique involves the creation of clusters and the selection of a cluster head (CH), which connects sensor nodes, known as cluster members (CM), to the CH. The CH receives data from the CM and collects data from sensor nodes, removing unnecessary data to conserve energy. It compresses the data and transmits them to base stations through multi-hop to reduce network load. Since CMs only communicate with their CH and have a limited range, they avoid redundant information. However, the CH’s routing, compression, and aggregation functions consume power quickly compared to other protocols, like TPGF, LQEAR, MPRM, and P-LQCLR. To address energy usage in wireless sensor networks (WSNs), heterogeneous high-power nodes (HPN) are used to balance energy consumption. CHs close to the base station require effective algorithms for improvement. The cluster-based glow-worm optimization technique utilizes random clustering, distributed cluster leader selection, and link-based routing. The cluster head routes data to the next group leader, balancing energy utilization in the WSN. This algorithm reduces energy consumption through multi-hop communication, cluster construction, and cluster head election. The glow-worm optimization technique allows for faster convergence and improved multi-parameter selection. By combining these methods, a new routing scheme is proposed to extend the network’s lifetime and balance energy in various environments. However, the proposed model consumes more energy than TPGF, and other protocols for packets with 0 or 1 retransmission count in a 260-node network. This is mainly due to the short INFO packets during the neighbor discovery period and the increased hop count of the proposed derived pathways. Herein, simulations are conducted to evaluate the technique’s throughput and energy efficiency. Full article

(This article belongs to the Section Sensor Networks)

► Show Figures

Figure 1

18 pages, 4552 KiB

Open AccessArticle

Adaptive Control Method for Gait Detection and Classification Devices with Inertial Measurement Unit

by Hyeonjong Kim, Ji-Won Kim and Junghyuk Ko

Sensors 2023, 23(14), 6638; https://doi.org/10.3390/s23146638 - 24 Jul 2023

Viewed by 1430

Abstract

Cueing and feedback training can be effective in maintaining or improving gait in individuals with Parkinson’s disease. We previously designed a rehabilitation assist device that can detect and classify a user’s gait at only the swing phase of the gait cycle, for the [...] Read more.

Cueing and feedback training can be effective in maintaining or improving gait in individuals with Parkinson’s disease. We previously designed a rehabilitation assist device that can detect and classify a user’s gait at only the swing phase of the gait cycle, for the ease of data processing. In this study, we analyzed the impact of various factors in a gait detection algorithm on the gait detection and classification rate (GDCR). We collected acceleration and angular velocity data from 25 participants (1 male and 24 females with an average age of 62 ± 6 years) using our device and analyzed the data using statistical methods. Based on these results, we developed an adaptive GDCR control algorithm using several equations and functions. We tested the algorithm under various virtual exercise scenarios using two control methods, based on acceleration and angular velocity, and found that the acceleration threshold was more effective in controlling the GDCR (average Spearman correlation −0.9996, p < 0.001) than the gyroscopic threshold. Our adaptive control algorithm was more effective in maintaining the target GDCR than the other algorithms (p < 0.001) with an average error of 0.10, while other tested methods showed average errors of 0.16 and 0.28. This algorithm has good scalability and can be adapted for future gait detection and classification applications. Full article

(This article belongs to the Special Issue Biomechanical Analysis of Motion and Postural Control: Sensors Methods and Data Analytics—2nd Edition)

► Show Figures

Figure 1

24 pages, 3742 KiB

Open AccessArticle

Gaussian-Filtered High-Frequency-Feature Trained Optimized BiLSTM Network for Spoofed-Speech Classification

by Hiren Mewada, Jawad F. Al-Asad, Faris A. Almalki, Adil H. Khan, Nouf Abdullah Almujally, Samir El-Nakla and Qamar Naith

Sensors 2023, 23(14), 6637; https://doi.org/10.3390/s23146637 - 24 Jul 2023

Cited by 4 | Viewed by 1744

Abstract

Voice-controlled devices are in demand due to their hands-free controls. However, using voice-controlled devices in sensitive scenarios like smartphone applications and financial transactions requires protection against fraudulent attacks referred to as “speech spoofing”. The algorithms used in spoof attacks are practically unknown; hence, [...] Read more.

Voice-controlled devices are in demand due to their hands-free controls. However, using voice-controlled devices in sensitive scenarios like smartphone applications and financial transactions requires protection against fraudulent attacks referred to as “speech spoofing”. The algorithms used in spoof attacks are practically unknown; hence, further analysis and development of spoof-detection models for improving spoof classification are required. A study of the spoofed-speech spectrum suggests that high-frequency features are able to discriminate genuine speech from spoofed speech well. Typically, linear or triangular filter banks are used to obtain high-frequency features. However, a Gaussian filter can extract more global information than a triangular filter. In addition, MFCC features are preferable among other speech features because of their lower covariance. Therefore, in this study, the use of a Gaussian filter is proposed for the extraction of inverted MFCC (iMFCC) features, providing high-frequency features. Complementary features are integrated with iMFCC to strengthen the features that aid in the discrimination of spoof speech. Deep learning has been proven to be efficient in classification applications, but the selection of its hyper-parameters and architecture is crucial and directly affects performance. Therefore, a Bayesian algorithm is used to optimize the BiLSTM network. Thus, in this study, we build a high-frequency-based optimized BiLSTM network to classify the spoofed-speech signal, and we present an extensive investigation using the ASVSpoof 2017 dataset. The optimized BiLSTM model is successfully trained with the least epoch and achieved a 99.58% validation accuracy. The proposed algorithm achieved a 6.58% EER on the evaluation dataset, with a relative improvement of 78% on a baseline spoof-identification system. Full article

(This article belongs to the Section Sensor Networks)

► Show Figures

Figure 1

14 pages, 4759 KiB

Open AccessArticle

Estimation Method of an Electrical Equivalent Circuit for Sonar Transducer Impedance Characteristic of Multiple Resonance

by Jejin Jang, Jaehyuk Choi, Donghun Lee and Hyungsoo Mok

Sensors 2023, 23(14), 6636; https://doi.org/10.3390/s23146636 - 24 Jul 2023

Cited by 3 | Viewed by 1623

Abstract

Improving the operational efficiency and optimizing the design of sound navigation and ranging (sonar) systems require accurate electrical equivalent models within the operating frequency range. The power conversion system within the sonar system increases power efficiency through impedance-matching circuits. Impedance matching is used [...] Read more.

Improving the operational efficiency and optimizing the design of sound navigation and ranging (sonar) systems require accurate electrical equivalent models within the operating frequency range. The power conversion system within the sonar system increases power efficiency through impedance-matching circuits. Impedance matching is used to enhance the power transmission efficiency of the sonar system. Therefore, to increase the efficiency of the sonar system, an electrical-matching circuit is employed, and this necessitates an accurate equivalent circuit for the sonar transducer within the operating frequency range. In conventional equivalent circuit derivation methods, errors occur because they utilize the same number of RLC branches as the resonant frequency of the sonar transducer, based on its physical properties. Hence, this paper proposes an algorithm for deriving an equivalent circuit independent of resonance by employing multiple electrical components and particle swarm optimization (PSO). A comparative verification was also performed between the proposed and existing approaches using the Butterworth–van Dyke (BVD) model, which is a method for deriving electrical equivalent circuits. Full article

(This article belongs to the Special Issue Acoustic Sensors and Their Applications)

► Show Figures

Figure 1

26 pages, 1198 KiB

Open AccessReview

Advancements in Forest Fire Prevention: A Comprehensive Survey

by Francesco Carta, Chiara Zidda, Martina Putzu, Daniele Loru, Matteo Anedda and Daniele Giusto

Sensors 2023, 23(14), 6635; https://doi.org/10.3390/s23146635 - 24 Jul 2023

Cited by 24 | Viewed by 15403

Abstract

Nowadays, the challenges related to technological and environmental development are becoming increasingly complex. Among the environmentally significant issues, wildfires pose a serious threat to the global ecosystem. The damages inflicted upon forests are manifold, leading not only to the destruction of terrestrial ecosystems [...] Read more.

Nowadays, the challenges related to technological and environmental development are becoming increasingly complex. Among the environmentally significant issues, wildfires pose a serious threat to the global ecosystem. The damages inflicted upon forests are manifold, leading not only to the destruction of terrestrial ecosystems but also to climate changes. Consequently, reducing their impact on both people and nature requires the adoption of effective approaches for prevention, early warning, and well-coordinated interventions. This document presents an analysis of the evolution of various technologies used in the detection, monitoring, and prevention of forest fires from past years to the present. It highlights the strengths, limitations, and future developments in this field. Forest fires have emerged as a critical environmental concern due to their devastating effects on ecosystems and the potential repercussions on the climate. Understanding the evolution of technology in addressing this issue is essential to formulate more effective strategies for mitigating and preventing wildfires. Full article

(This article belongs to the Special Issue Feature Papers in the 'Sensor Networks' Section 2023)

► Show Figures

Figure 1

24 pages, 9446 KiB

Open AccessReview

Advancements in Triboelectric Nanogenerators (TENGs) for Intelligent Transportation Infrastructure: Enhancing Bridges, Highways, and Tunnels

by Arash Rayegani, Ali Matin Nazar and Maria Rashidi

Sensors 2023, 23(14), 6634; https://doi.org/10.3390/s23146634 - 24 Jul 2023

Cited by 5 | Viewed by 3297

Abstract

The development of triboelectric nanogenerators (TENGs) over time has resulted in considerable improvements to the efficiency, effectiveness, and sensitivity of self-powered sensing. Triboelectric nanogenerators have low restriction and high sensitivity while also having high efficiency. The vast majority of previous research has found [...] Read more.

The development of triboelectric nanogenerators (TENGs) over time has resulted in considerable improvements to the efficiency, effectiveness, and sensitivity of self-powered sensing. Triboelectric nanogenerators have low restriction and high sensitivity while also having high efficiency. The vast majority of previous research has found that accidents on the road can be attributed to road conditions. For instance, extreme weather conditions, such as heavy winds or rain, can reduce the safety of the roads, while excessive temperatures might make it unpleasant to be behind the wheel. Air pollution also has a negative impact on visibility while driving. As a result, sensing road surroundings is the most important technical system that is used to evaluate a vehicle and make decisions. This paper discusses both monitoring driving behavior and self-powered sensors influenced by triboelectric nanogenerators (TENGs). It also considers energy harvesting and sustainability in smart road environments such as bridges, tunnels, and highways. Furthermore, the information gathered in this study can help readers enhance their knowledge concerning the advantages of employing these technologies for innovative uses of their powers. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Intelligent Transportation Systems)

► Show Figures

Figure 1

16 pages, 8356 KiB

Open AccessArticle

Detection of Sensor Faults with or without Disturbance Using Analytical Redundancy Methods: An Application to Orifice Flowmeter

by Vemulapalli Sravani and Santhosh Krishnan Venkata

Sensors 2023, 23(14), 6633; https://doi.org/10.3390/s23146633 - 24 Jul 2023

Viewed by 1752

Abstract

Sensors and transducers play a vital role in the productivity of any industry. A sensor that is frequently used in industries to monitor flow is an orifice flowmeter. In certain instances, faults can occur in the flowmeter, hindering the operation of other dependent [...] Read more.

Sensors and transducers play a vital role in the productivity of any industry. A sensor that is frequently used in industries to monitor flow is an orifice flowmeter. In certain instances, faults can occur in the flowmeter, hindering the operation of other dependent systems. Hence, the present study determines the occurrence of faults in the flowmeter with a model-based approach. To do this, the model of the system is developed from the transient data obtained from computational fluid dynamics. This second-order transfer function is further used for the development of linear-parameter-varying observers, which generates the residue for fault detection. With or without disturbance, the suggested method is capable of effectively isolating drift, open-circuit, and short-circuit defects in the orifice flowmeter. The outcomes of the LPV observer are compared with those of a neural network. The open- and short-circuit faults are traced within 1 s, whereas the minimum time duration for the detection of a drift fault is 5.2 s and the maximum time is 20 s for different combinations of threshold and slope. Full article

(This article belongs to the Section Fault Diagnosis & Sensors)

► Show Figures

Figure 1

16 pages, 12947 KiB

Open AccessCommunication

Integrated Fiber Ring Laser Temperature Sensor Based on Vernier Effect with Lyot–Sagnac Interferometer

by Yuhui Liu, Weihao Lin, Jie Hu, Fang Zhao, Feihong Yu, Shuaiqi Liu, Jinna Chen, Huanhuan Liu, Perry Ping Shum and Xuming Zhang

Sensors 2023, 23(14), 6632; https://doi.org/10.3390/s23146632 - 24 Jul 2023

Cited by 3 | Viewed by 1538

Abstract

The Vernier effect created using an incorporated Lyot–Sagnac loop is used to create an ultra-high sensitivity temperature sensor based on a ring laser cavity. Unlike standard double Sagnac loop systems, the proposed sensor is fused into a single Sagnac loop by adjusting the [...] Read more.

The Vernier effect created using an incorporated Lyot–Sagnac loop is used to create an ultra-high sensitivity temperature sensor based on a ring laser cavity. Unlike standard double Sagnac loop systems, the proposed sensor is fused into a single Sagnac loop by adjusting the welding angle between two polarization-maintaining fibers (PMFs) to achieve effective temperature sensitivity amplification. The PMFs are separated into two arms of 0.8 m and 1 m in length, with a 45° angle difference between the fast axes. The sensor’s performance is examined both theoretically and experimentally. The experimental results reveal that the Vernier amplification effect can be achieved via PMF rotating shaft welding. The temperature sensitivity in the laser cavity can reach 2.391 nm/°C, which is increased by a factor of more than eight times compared with a single Sagnac loop structure (0.298 nm/°C) with a length of 0.8 m without the Vernier effect at temperatures ranging from 20 °C to 30 °C. Furthermore, unlike traditional optical fiber sensing that uses a broadband light source (BBS) for detection, which causes issues such as low signal-to-noise ratio and broad bandwidth, the Sagnac loop can be employed as a filter by inserting itself into the fiber ring laser (FRL) cavity. When the external parameters change, the laser is offset by the interference general modulation, allowing the external temperature to be monitored. The superior performance of signal-to-noise ratios of up to 50 dB and bandwidths of less than 0.2 nm is achieved. The proposed sensor has a simple structure and high sensitivity and is expected to play a role in biological cell activity monitoring. Full article

(This article belongs to the Special Issue Developments and Applications of Optical Fiber Sensors)

► Show Figures

Figure 1

15 pages, 1187 KiB

Open AccessArticle

Packets-to-Prediction: An Unobtrusive Mechanism for Identifying Coarse-Grained Sleep Patterns with WiFi MAC Layer Traffic

by Dheryta Jaisinghani and Nishtha Phutela

Sensors 2023, 23(14), 6631; https://doi.org/10.3390/s23146631 - 24 Jul 2023

Cited by 2 | Viewed by 1536

Abstract

A good night’s sleep is of the utmost importance for the seamless execution of our cognitive capabilities. Unfortunately, the research shows that one-third of the US adult population is severely sleep deprived. With college students as our focused group, we devised a contactless, [...] Read more.

A good night’s sleep is of the utmost importance for the seamless execution of our cognitive capabilities. Unfortunately, the research shows that one-third of the US adult population is severely sleep deprived. With college students as our focused group, we devised a contactless, unobtrusive mechanism to detect sleep patterns, which, contrary to existing sensor-based solutions, does not require the subject to put on any sensors on the body or buy expensive sleep sensing equipment. We named this mechanism Packets-to-Predictions(P2P) because we leverage the WiFi MAC layer traffic collected in the home and university environments to predict “sleep” and “awake” periods. We first manually established that extracting such patterns is feasible, and then, we trained various machine learning models to identify these patterns automatically. We trained six machine learning models—K nearest neighbors, logistic regression, random forest classifier, support vector classifier, gradient boosting classifier, and multilayer perceptron. K nearest neighbors gave the best performance with 87% train accuracy and 83% test accuracy. Full article

(This article belongs to the Section Sensor Networks)

► Show Figures

Figure 1

25 pages, 8646 KiB

Open AccessArticle

Construction, Spectral Modeling, Parameter Inversion-Based Calibration, and Application of an Echelle Spectrometer

by Yuming Wang, Youshan Qu, Hui Zhao and Xuewu Fan

Sensors 2023, 23(14), 6630; https://doi.org/10.3390/s23146630 - 24 Jul 2023

Cited by 1 | Viewed by 1653

Abstract

We have developed a compact, asymmetric three-channel echelle spectrometer with remarkable high-spectral resolution capabilities. In order to achieve the desired spectral resolution, we initially establish a theoretical spectral model based on the two-dimensional coordinates of spot positions corresponding to each wavelength. Next, we [...] Read more.

We have developed a compact, asymmetric three-channel echelle spectrometer with remarkable high-spectral resolution capabilities. In order to achieve the desired spectral resolution, we initially establish a theoretical spectral model based on the two-dimensional coordinates of spot positions corresponding to each wavelength. Next, we present an innovative and refined method for precisely calibrating echelle spectrometers through parameter inversion. Our analysis delves into the complexities of the nonlinear two-dimensional echelle spectrogram. We employ a variety of optimization techniques, such as grid exploration, simulated annealing, genetic algorithms, and genetic simulated annealing (GSA) algorithms, to accurately invert spectrogram parameters. Our proposed GSA algorithm synergistically integrates the strengths of global and local searches, thereby enhancing calibration accuracy. Compared to the conventional grid exploration method, GSA reduces the error function by 22.8%, convergence time by 2.16 times, and calibration accuracy by 7.05 times. Experimental validation involves calibrating a low-pressure mercury lamp, resulting in an average spectral accuracy error of 0.0257 nm after performing crucial parameter inversion. Furthermore, the echelle spectrometer undergoes a laser-induced breakdown spectroscopy experiment, demonstrating exceptional spectral resolution and sub-10 ns time-resolved capability. Overall, our research offers a comprehensive and efficient solution for constructing, modeling, calibrating, and applying echelle spectrometers, significantly enhancing calibration accuracy and efficiency. This work contributes to the advancement of spectrometry and opens up new possibilities for high-resolution spectral analysis across various research and industry domains. Full article

(This article belongs to the Special Issue Optical Sensing and Technologies)

► Show Figures

Figure 1

17 pages, 6106 KiB

Open AccessArticle

Quantitative Visualization of Buried Defects in GFRP via Microwave Reflectometry

by Ruonan Wang, Yang Fang, Qianxiang Gao, Yong Li, Xihan Yang and Zhenmao Chen

Sensors 2023, 23(14), 6629; https://doi.org/10.3390/s23146629 - 24 Jul 2023

Viewed by 1320

Abstract

Glass fiber-reinforced polymer (GFRP) is widely used in engineering fields involving aerospace, energy, transportation, etc. If internal buried defects occur due to hostile environments during fabrication and practical service, the structural integrity and safety of GFRP structures would be severely undermined. Therefore, it [...] Read more.

Glass fiber-reinforced polymer (GFRP) is widely used in engineering fields involving aerospace, energy, transportation, etc. If internal buried defects occur due to hostile environments during fabrication and practical service, the structural integrity and safety of GFRP structures would be severely undermined. Therefore, it is indispensable to carry out effective quantitative nondestructive testing (NDT) of internal defects buried within GFRP structures. Along with the development of composite materials, microwave NDT is promising in non-intrusive inspection of defects in GFRPs. In this paper, quantitative screening of the subsurface impact damage and air void in a unidirectional GFRP via microwave reflectometry was intensively investigated. The influence of the microwave polarization direction with respect to the GFRP fiber direction on the reflection coefficient was investigated by using the equivalent relative permittivity calculated with theoretical analysis. Following this, a microwave NDT system was built up for further investigation regarding the imaging and quantitative evaluation of buried defects in GFRPs. A direct-wave suppression method based on singular-value decomposition was proposed to obtain high-quality defect images. The defect in-plane area was subsequently assessed via a proposed defect-edge identification method. The simulation and experimental results revealed that (1) the testing sensitivity to buried defects was the highest when the electric-field polarization direction is parallel to the GFRP fiber direction; and (2) the averaged evaluation accuracy regarding the in-plane area of the buried defect reached approximately 90% by applying the microwave reflectometry together with the proposed processing methods. Full article

(This article belongs to the Special Issue Electromagnetic Non-destructive Testing and Evaluation)

► Show Figures

Figure 1

17 pages, 3190 KiB

Open AccessArticle

Novel Multi-Parametric Sensor System for Comprehensive Multi-Wavelength Photoplethysmography Characterization

by Joan Lambert Cause, Ángel Solé Morillo, Bruno da Silva, Juan C. García-Naranjo and Johan Stiens

Sensors 2023, 23(14), 6628; https://doi.org/10.3390/s23146628 - 24 Jul 2023

Cited by 5 | Viewed by 1893

Abstract

Photoplethysmography (PPG) is widely used to assess cardiovascular health. However, its usage and standardization are limited by the impact of variable contact force and temperature, which influence the accuracy and reliability of the measurements. Although some studies have evaluated the impact of these [...] Read more.

Photoplethysmography (PPG) is widely used to assess cardiovascular health. However, its usage and standardization are limited by the impact of variable contact force and temperature, which influence the accuracy and reliability of the measurements. Although some studies have evaluated the impact of these phenomena on signal amplitude, there is still a lack of knowledge about how these perturbations can distort the signal morphology, especially for multi-wavelength PPG (MW-PPG) measurements. This work presents a modular multi-parametric sensor system that integrates continuous and real-time acquisition of MW-PPG, contact force, and temperature signals. The implemented design solution allows for a comprehensive characterization of the effects of the variations in these phenomena on the contour of the MW-PPG signal. Furthermore, a dynamic DC cancellation circuitry was implemented to improve measurement resolution and obtain high-quality raw multi-parametric data. The accuracy of the MW-PPG signal acquisition was assessed using a synthesized reference PPG optical signal. The performance of the contact force and temperature sensors was evaluated as well. To determine the overall quality of the multi-parametric measurement, an in vivo measurement on the index finger of a volunteer was performed. The results indicate a high precision and accuracy in the measurements, wherein the capacity of the system to obtain high-resolution and low-distortion MW-PPG signals is highlighted. These findings will contribute to developing new signal-processing approaches, advancing the accuracy and robustness of PPG-based systems, and bridging existing gaps in the literature. Full article

(This article belongs to the Section Biomedical Sensors)

► Show Figures

Figure 1

12 pages, 3413 KiB

Open AccessArticle

Can Wearable Sensors Provide Accurate and Reliable 3D Tibiofemoral Angle Estimates during Dynamic Actions?

by Mirel Ajdaroski and Amanda Esquivel

Sensors 2023, 23(14), 6627; https://doi.org/10.3390/s23146627 - 24 Jul 2023

Viewed by 1475

Abstract

The ability to accurately measure tibiofemoral angles during various dynamic activities is of clinical interest. The purpose of this study was to determine if inertial measurement units (IMUs) can provide accurate and reliable angle estimates during dynamic actions. A tuned quaternion conversion (TQC) [...] Read more.

The ability to accurately measure tibiofemoral angles during various dynamic activities is of clinical interest. The purpose of this study was to determine if inertial measurement units (IMUs) can provide accurate and reliable angle estimates during dynamic actions. A tuned quaternion conversion (TQC) method tuned to dynamics actions was used to calculate Euler angles based on IMU data, and these calculated angles were compared to a motion capture system (our “gold” standard) and a commercially available sensor fusion algorithm. Nine healthy athletes were instrumented with APDM Opal IMUs and asked to perform nine dynamic actions; five participants were used in training the parameters of the TQC method, with the remaining four being used to test validity. Accuracy was based on the root mean square error (RMSE) and reliability was based on the Bland–Altman limits of agreement (LoA). Improvement across all three orthogonal angles was observed as the TQC method was able to more accurately (lower RMSE) and more reliably (smaller LoA) estimate an angle than the commercially available algorithm. No significant difference was observed between the TQC method and the motion capture system in any of the three angles (p < 0.05). It may be feasible to use this method to track tibiofemoral angles with higher accuracy and reliability than the commercially available sensor fusion algorithm. Full article

(This article belongs to the Special Issue Recent Advance and Application of Wearable Inertial Sensors in Motion Analysis)

► Show Figures

Figure 1

10 pages, 2359 KiB

Open AccessCommunication

Two-Photon Excited Fluorescence Lifetime Imaging of Tetracycline-Labeled Retinal Calcification

by Kavita R. Hegde, Krishanu Ray, Henryk Szmacinski, Sharon Sorto, Adam C. Puche, Imre Lengyel and Richard B. Thompson

Sensors 2023, 23(14), 6626; https://doi.org/10.3390/s23146626 - 24 Jul 2023

Cited by 2 | Viewed by 1324

Abstract

Deposition of calcium-containing minerals such as hydroxyapatite and whitlockite in the subretinal pigment epithelial (sub-RPE) space of the retina is linked to the development of and progression to the end-stage of age-related macular degeneration (AMD). AMD is the most common eye disease causing [...] Read more.

Deposition of calcium-containing minerals such as hydroxyapatite and whitlockite in the subretinal pigment epithelial (sub-RPE) space of the retina is linked to the development of and progression to the end-stage of age-related macular degeneration (AMD). AMD is the most common eye disease causing blindness amongst the elderly in developed countries; early diagnosis is desirable, particularly to begin treatment where available. Calcification in the sub-RPE space is also directly linked to other diseases such as Pseudoxanthoma elasticum (PXE). We found that these mineral deposits could be imaged by fluorescence using tetracycline antibiotics as specific stains. Binding of tetracyclines to the minerals was accompanied by increases in fluorescence intensity and fluorescence lifetime. The lifetimes for tetracyclines differed substantially from the known background lifetime of the existing natural retinal fluorophores, suggesting that calcification could be visualized by lifetime imaging. However, the excitation wavelengths used to excite these lifetime changes were generally shorter than those approved for retinal imaging. Here, we show that tetracycline-stained drusen in post mortem human retinas may be imaged by fluorescence lifetime contrast using multiphoton (infrared) excitation. For this pilot study, ten eyes from six anonymous deceased donors (3 female, 3 male, mean age 83.7 years, range 79–97 years) were obtained with informed consent from the Maryland State Anatomy Board with ethical oversight and approval by the Institutional Review Board. Full article

(This article belongs to the Special Issue Modern Sensor Technology in Ophthalmology and Optometry for Diagnostics and Surgery)

► Show Figures

Figure 1

Figure 1
Two-photon-excited fluorescence intensity micrograph (left panel) with color-coded intensities (arbitrary units) on the right side of the panel, and fluorescence lifetime micrograph of the same field (right panel) fit to a single component with time indicated by false colors with scale in nanoseconds on the right. Experiments were carried out on an infusion-stained, flat-mounted retina, following the removal of the RPE and neurosensory retina (97-year-old female donor; cause of death: cardiovascular disease). Sample was labelled with Cl-Tet. Approximate size of the field: 250 × 250 μm2; further details can be found in the Methods. Full article ">Figure 2
Fluorescence intensity micrograph (left panel) of doxycycline-stained drusen in the retina of a 79-year-old white male donor (cause of death: chronic myelocytic anemia); the intensities are false colored according to the scale (arbitrary units) on the right of the image. The (right panel) shows the time-resolved fluorescence decay of the aggregated pixels in the indicated region of interest (pink); The purple dots indicate the individual time-resolved fluorescence intensity data points, the red line through the dots indicates the best fit to the data, the orange curve before two nanoseconds indicates the instrument response function, and the vertical lines at 1.3 and 10 nanoseconds indicate the beginning and end, respectively, of the data included in the fit. The solid purple line in the lower part of the right panel depicts the “residuals”: the differences between the actual measured data points and the values calculated for that time point by the best fit parameters. Full article ">Figure 3
Close-ups of the druse in <a href="#sensors-23-06626-f002" class="html-fig">Figure 2</a> at higher (60×) magnification ((upper left panel): fluorescence intensity in false color with scale on right side in arbitrary units; (lower left panel): single component fluorescence lifetime in false color with scale on the right in nanoseconds) and best two component fits to the pink region of interest at X = −33 μm, Y = −17 μm in the upper left panel, with both lifetimes floating (upper right panel), and with one lifetime fixed to 3.7 ns (lower right panel). The upper and lower right panels depict the decays using the same conventions as described in the <a href="#sensors-23-06626-f002" class="html-fig">Figure 2</a> legend. Full article ">

16 pages, 2569 KiB

Open AccessArticle

An L-Shaped Three-Level and Single Common Element Sparse Sensor Array for 2-D DOA Estimation

by Bo Du, Weijia Cui, Bin Ba, Haiyun Xu and Wubin Gao

Sensors 2023, 23(14), 6625; https://doi.org/10.3390/s23146625 - 23 Jul 2023

Cited by 3 | Viewed by 1141

Abstract

The degree of freedom (DOF) is an important performance metric for evaluating the design of a sparse array structure. Designing novel sparse arrays with higher degrees of freedom, while ensuring that the array structure can be mathematically represented, is a crucial research direction [...] Read more.

The degree of freedom (DOF) is an important performance metric for evaluating the design of a sparse array structure. Designing novel sparse arrays with higher degrees of freedom, while ensuring that the array structure can be mathematically represented, is a crucial research direction in the field of direction of arrival (DOA) estimation. In this paper, we propose a novel L-shaped sparse sensor array by adjusting the physical placement of the sensors in the sparse array. The proposed L-shaped sparse array consists of two sets of three-level and single-element sparse arrays (TSESAs), which estimate the azimuth and elevation angles, respectively, through one-dimensional (1-D) spatial spectrum search. Each TSESA is composed of a uniform linear subarray and two sparse subarrays, with one single common element in the two sparse subarrays. Compared to existing L-shaped sparse arrays, the proposed array achieves higher degrees of freedom, up to

4 Q_{1} Q_{2} + 8 Q_{1} - 5

, when estimating DOA using the received signal covariance. To facilitate the correct matching of azimuth and elevation angles, the cross-covariance between the two TSESA arrays is utilized for estimation. By comparing and analyzing performance parameters with commonly used L-shaped and other sparse arrays, it is found that the proposed L-shaped TSESA has higher degrees of freedom and array aperture, leading to improved two-dimensional (2-D) DOA estimation results. Finally, simulation experiments validate the excellent performance of the L-shaped TSESA in 2-D DOA estimation. Full article

(This article belongs to the Section Intelligent Sensors)

► Show Figures

Figure 1

15 pages, 287 KiB

Open AccessArticle

Identifying Current Feelings of Mild and Moderate to High Depression in Young, Healthy Individuals Using Gait and Balance: An Exploratory Study

by Ali Boolani, Allison H. Gruber, Ahmed Ali Torad and Andreas Stamatis

Sensors 2023, 23(14), 6624; https://doi.org/10.3390/s23146624 - 23 Jul 2023

Cited by 3 | Viewed by 2125

Abstract

Depressive mood states in healthy populations are prevalent but often under-reported. Biases exist in self-reporting of depression in otherwise healthy individuals. Gait and balance control can serve as objective markers for identifying those individuals, particularly in real-world settings. We utilized inertial measurement units [...] Read more.

Depressive mood states in healthy populations are prevalent but often under-reported. Biases exist in self-reporting of depression in otherwise healthy individuals. Gait and balance control can serve as objective markers for identifying those individuals, particularly in real-world settings. We utilized inertial measurement units (IMU) to measure gait and balance control. An exploratory, cross-sectional design was used to compare individuals who reported feeling depressed at the moment (n = 49) with those who did not (n = 84). The Quality Assessment Tool for Observational Cohort and Cross-sectional Studies was employed to ensure internal validity. We recruited 133 participants aged between 18–36 years from the university community. Various instruments were used to evaluate participants’ present depressive symptoms, sleep, gait, and balance. Gait and balance variables were used to detect depression, and participants were categorized into three groups: not depressed, mild depression, and moderate–high depression. Participant characteristics were analyzed using ANOVA and Kruskal–Wallis tests, and no significant differences were found in age, height, weight, BMI, and prior night’s sleep between the three groups. Classification models were utilized for depression detection. The most accurate model incorporated both gait and balance variables, yielding an accuracy rate of 84.91% for identifying individuals with moderate–high depression compared to non-depressed individuals. Full article

(This article belongs to the Section Wearables)

24 pages, 9476 KiB

Open AccessReview

Research Progress of Vertical Channel Thin Film Transistor Device

by Benxiao Sun, Huixue Huang, Pan Wen, Meng Xu, Cong Peng, Longlong Chen, Xifeng Li and Jianhua Zhang

Sensors 2023, 23(14), 6623; https://doi.org/10.3390/s23146623 - 23 Jul 2023

Cited by 2 | Viewed by 4801

Abstract

Thin film transistors (TFTs) as the core devices for displays, are widely used in various fields including ultra-high-resolution displays, flexible displays, wearable electronic skins and memory devices, especially in terms of sensors. TFTs have now started to move towards miniaturization. Similarly to MOSFETs [...] Read more.

Thin film transistors (TFTs) as the core devices for displays, are widely used in various fields including ultra-high-resolution displays, flexible displays, wearable electronic skins and memory devices, especially in terms of sensors. TFTs have now started to move towards miniaturization. Similarly to MOSFETs problem, traditional planar structure TFTs have difficulty in reducing the channel’s length sub-1μm under the existing photolithography technology. Vertical channel thin film transistors (V-TFTs) are proposed. It is an effective solution to overcome the miniaturization limit of traditional planar TFTs. So, we summarize the different aspects of VTFTs. Firstly, this paper introduces the structure types, key parameters, and the impact of different preparation methods in devices of V-TFTs. Secondly, an overview of the research progress of V-TFTs’ active layer materials in recent years, the characteristics of V-TFTs and their application in examples has proved the enormous application potential of V-TFT in sensing. Finally, in addition to the advantages of V-TFTs, the current technical challenge and their potential solutions are put forward, and the future development trend of this new structure of V-TFTs is proposed. Full article

(This article belongs to the Special Issue Polyimide Based Flexible and Bio-Inspired Sensors: From Fundamental to Application)

► Show Figures

Figure 1

15 pages, 15368 KiB

Open AccessArticle

Frequency-Domain Reverse-Time Migration with Analytic Green’s Function for the Seismic Imaging of Shallow Water Column Structures in the Arctic Ocean

by Seung-Goo Kang and U Geun Jang

Sensors 2023, 23(14), 6622; https://doi.org/10.3390/s23146622 - 23 Jul 2023

Viewed by 1270

Abstract

Seismic oceanography can provide a two- or three-dimensional view of the water column thermocline structure at a vertical and horizontal resolution from the multi-channel seismic dataset. Several seismic imaging methods and techniques for seismic oceanography have been presented in previous research. In this [...] Read more.

Seismic oceanography can provide a two- or three-dimensional view of the water column thermocline structure at a vertical and horizontal resolution from the multi-channel seismic dataset. Several seismic imaging methods and techniques for seismic oceanography have been presented in previous research. In this study, we suggest a new formulation of the frequency-domain reverse-time migration method for seismic oceanography based on the analytic Green’s function. For imaging thermocline structures in the water column from the seismic data, our proposed seismic reverse-time migration method uses the analytic Green’s function for numerically calculating the forward- and backward-modeled wavefield rather than the wave propagation modeling in the conventional algorithm. The frequency-domain reverse-time migration with analytic Green’s function does not require significant computational memory, resources, or a multifrontal direct solver to calculate the migration seismic images as like conventional reverse-time migration. The analytic Green’s function in our reverse-time method makes it possible to provide a high-resolution seismic water column image with a meter-scale grid size, consisting of full-band frequency components for a modest cost and in a low-memory environment for computation. Our method was applied to multi-channel seismic data acquired in the Arctic Ocean and successfully constructed water column seismic images containing the oceanographic reflections caused by thermocline structures of the water mass. From the numerical test, we note that the oceanographic reflections of the migrated seismic images reflected the distribution of Arctic waters in a shallow depth and showed good correspondence with the anomalies of measured temperatures and calculated reflection coefficients from each XCDT profile. Our proposed method has been verified for field data application and accuracy of imaging performance. Full article

(This article belongs to the Special Issue Advanced Sensor Applications in Marine Objects Recognition)

► Show Figures

Figure 1

16 pages, 1707 KiB

Open AccessArticle

A Size, Weight, Power, and Cost-Efficient 32-Channel Time to Digital Converter Using a Novel Wave Union Method

by Saleh M. Alshahry, Awwad H. Alshehry, Abdullah K. Alhazmi and Vamsy P. Chodavarapu

Sensors 2023, 23(14), 6621; https://doi.org/10.3390/s23146621 - 23 Jul 2023

Cited by 3 | Viewed by 1943

Abstract

We present a Tapped Delay Line (TDL)-based Time to Digital Converter (TDC) using Wave Union type A (WU-A) architecture for applications that require high-precision time interval measurements with low size, weight, power, and cost (SWaP-C) requirements. The proposed TDC is implemented on a [...] Read more.

We present a Tapped Delay Line (TDL)-based Time to Digital Converter (TDC) using Wave Union type A (WU-A) architecture for applications that require high-precision time interval measurements with low size, weight, power, and cost (SWaP-C) requirements. The proposed TDC is implemented on a low-cost Field-Programmable Gate Array (FPGA), Artix-7, from Xilinx. Compared to prior works, our high-precision multi-channel TDC has the lowest SWaP-C requirements. We demonstrate an average time precision of less than 3 ps and a Root Mean Square resolution of about 1.81 ps. We propose a novel Wave Union type A architecture where only the first multiplexer is used to generate the wave union pulse train at the arrival of the start signal to minimize the required computational processing. In addition, an auto-calibration algorithm is proposed to help improve the TDC performance by improving the TDC Differential Non-Linearity and Integral Non-Linearity. Full article

(This article belongs to the Special Issue Algorithms, Systems and Applications of Smart Sensor Networks)

► Show Figures

Figure 1

12 pages, 1804 KiB

Open AccessArticle

Changes in Heart Rate, Heart Rate Variability, Breathing Rate, and Skin Temperature throughout Pregnancy and the Impact of Emotions—A Longitudinal Evaluation Using a Sensor Bracelet

by Verena Bossung, Adrian Singer, Tiara Ratz, Martina Rothenbühler, Brigitte Leeners and Nina Kimmich

Sensors 2023, 23(14), 6620; https://doi.org/10.3390/s23146620 - 23 Jul 2023

Cited by 3 | Viewed by 3872

Abstract

(1) Background: Basic vital signs change during normal pregnancy as they reflect the adaptation of maternal physiology. Electronic wearables like fitness bracelets have the potential to provide vital signs continuously in the home environment of pregnant women. (2) Methods: We performed a prospective [...] Read more.

(1) Background: Basic vital signs change during normal pregnancy as they reflect the adaptation of maternal physiology. Electronic wearables like fitness bracelets have the potential to provide vital signs continuously in the home environment of pregnant women. (2) Methods: We performed a prospective observational study from November 2019 to November 2020 including healthy pregnant women, who recorded their wrist skin temperature, heart rate, heart rate variability, and breathing rate using an electronic wearable. In addition, eight emotions were assessed weekly using five-point Likert scales. Descriptive statistics and a multivariate model were applied to correlate the physiological parameters with maternal emotions. (3) Results: We analyzed data from 23 women using the electronic wearable during pregnancy. We calculated standard curves for each physiological parameter, which partially differed from the literature. We showed a significant association of several emotions like feeling stressed, tired, or happy with the course of physiological parameters. (4) Conclusions: Our data indicate that electronic wearables are helpful for closely observing vital signs in pregnancy and to establish modern curves for the physiological course of these parameters. In addition to physiological adaptation mechanisms and pregnancy disorders, emotions have the potential to influence the course of physiological parameters in pregnancy. Full article

(This article belongs to the Section Wearables)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Sensors, Volume 23, Issue 14 (July-2 2023) – 405 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI