Sensors

18 pages, 28319 KiB

Open AccessArticle

FeinPhone: Low-cost Smartphone Camera-based 2D Particulate Matter Sensor

by Matthias Budde, Simon Leiner, Marcel Köpke, Johannes Riesterer, Till Riedel and Michael Beigl

Sensors 2019, 19(3), 749; https://doi.org/10.3390/s19030749 - 12 Feb 2019

Cited by 11 | Viewed by 9702

Abstract

Precise, location-specific fine dust measurement is central for the assessment of urban air quality. Classic measurement approaches require dedicated hardware, of which professional equipment is still prohibitively expensive (>10k$) for dense measurements, and inexpensive sensors do not meet accuracy demands. As a step [...] Read more.

Precise, location-specific fine dust measurement is central for the assessment of urban air quality. Classic measurement approaches require dedicated hardware, of which professional equipment is still prohibitively expensive (>10k$) for dense measurements, and inexpensive sensors do not meet accuracy demands. As a step towards filling this gap, we propose FeinPhone, a phone-based fine dust measurement system that uses camera and flashlight functions that are readily available on today’s off-the-shelf smart phones. We introduce a cost-effective passive hardware add-on together with a novel counting approach based on light-scattering particle sensors. Since our approach features a 2D sensor (the camera) instead of a single photodiode, we can employ it to capture the scatter traces from individual particles rather than just retaining a light intensity sum signal as in simple photometers. This is a more direct way of assessing the particle count, it is robust against side effects, e.g., from camera image compression, and enables gaining information on the size spectrum of the particles. Our proof-of-concept evaluation comparing several FeinPhone sensors with data from a high-quality APS/SMPS (Aerodynamic Particle Sizer/Scanning Mobility Particle Sizer) reference device at the World Calibration Center for Aerosol Physics shows that the collected data shows excellent correlation with the inhalable coarse fraction of fine dust particles (r > 0.9) and can successfully capture its levels under realistic conditions. Full article

(This article belongs to the Special Issue Sensors Signal Processing and Visual Computing)

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14 pages, 3395 KiB

Open AccessArticle

Enhanced Auditory Steady-State Response Using an Optimized Chirp Stimulus-Evoked Paradigm

by Xiaoya Liu, Shuang Liu, Dongyue Guo, Yue Sheng, Yufeng Ke, Xingwei An, Feng He and Dong Ming

Sensors 2019, 19(3), 748; https://doi.org/10.3390/s19030748 - 12 Feb 2019

Cited by 10 | Viewed by 5326

Abstract

Objectives: It has been reported recently that gamma measures of the electroencephalogram (EEG) might provide information about the candidate biomarker of mental diseases like schizophrenia, Alzheimer’s disease, affective disorder and so on, but as we know it is a difficult issue to [...] Read more.

Objectives: It has been reported recently that gamma measures of the electroencephalogram (EEG) might provide information about the candidate biomarker of mental diseases like schizophrenia, Alzheimer’s disease, affective disorder and so on, but as we know it is a difficult issue to induce visual and tactile evoked responses at high frequencies. Although a high-frequency response evoked by auditory senses is achievable, the quality of the recording response is not ideal, such as relatively low signal-to-noise ratio (SNR). Recently, auditory steady-state responses (ASSRs) play an essential role in the field of basic auditory studies and clinical uses. However, how to improve the quality of ASSRs is still a challenge which researchers have been working on. This study aims at designing a more comfortable and suitable evoked paradigm and then enhancing the quality of the ASSRs in healthy subjects so as to further apply it in clinical practice. Methods: Chirp and click stimuli with 40 Hz and 60 Hz were employed to evoke the gamma-ASSR respectively, and the sound adjusted to 45 dB sound pressure level (SPL). Twenty healthy subjects with normal-hearing participated, and 64-channel EEGs were simultaneously recorded during the experiment. Event-related spectral perturbation (ERSP) and SNR of the ASSRs were measured and analyzed to verify the feasibility and adaptability of the proposed evoked paradigm. Results: The results showed that the evoked paradigm proposed in this study could enhance ASSRs with strong feasibility and adaptability. (1) ASSR waves in time domain indicated that 40 Hz stimuli could significantly induce larger peak-to-peak values of ASSRs compared to 60 Hz stimuli (p < 0.01**); ERSP showed that obvious ASSRs were obtained at each lead for both 40 Hz and 60 Hz, as well as the click and chirp stimuli. (2) The SNR of the ASSRs were –3.23 ± 1.68, –2.44 ± 2.90, –4.66 ± 2.09, and –3.53 ± 3.49 respectively for 40 Hz click, 40 Hz chirp, 60 Hz click and 60 Hz chirp, indicating the chirp stimuli could induce significantly better ASSR than the click, and 40 Hz ASSRs had the higher SNR than 60 Hz (p < 0.01**). Limitation: In this study, sample size was small and the age span was not large enough. Conclusions: This study verified the feasibility and adaptability of the proposed evoked paradigm to improve the quality of the gamma-ASSR, which is significant in clinical application. The results suggested that 40 Hz ASSR evoked by chirp stimuli had the best performance and was expected to be used in clinical practice, especially in the field of mental diseases such as schizophrenia, Alzheimer’s disease, and affective disorder. Full article

(This article belongs to the Special Issue Neurophysiological Data Denoising and Enhancement)

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Figure 1
The schematic representation of the click and chirp stimuli: (a) the waveform of the chirp stimuli; (b) the waveform of the click stimuli. 40 Hz stimuli waveform at the top and 60 Hz stimuli waveform at the bottom in each subgraph. Full article ">Figure 2
The flow chart of auditory evoked paradigm in this study: each frequency is represented 28 times in each block. Full article ">Figure 3
The scoring criteria of the degree of tolerance for click stimuli and chirp stimuli in the evoked paradigm. Full article ">Figure 4
Mean time-domain waveforms of auditory steady-state responses (ASSRs) for 20 healthy subjects under selected leads: (a) Mean ASSR amplitude: the black line represents ASSR amplitude within 1s after stimulus, and the red line represents ASSR amplitude within 0.5 s after stimulus; (b) The boxplot of mean ASSR peak-peak value: the red line represents the median; ■ and ° represent outliers; ** represents p ≤ 0.01. Full article ">Figure 5
The event-related spectral perturbation (ERSP) averaged across all leads from 20 subjects: 40 Hz ERSP at the top and 60 Hz ERSP at the bottom. The left column represents the click stimuli and the right represents chirp stimuli. The dotted black lines represent the stimulus moment, namely the 0 time. The larger the number on the color bar, the stronger the evoked ASSRs response. Full article ">Figure 6
Mean signal-to-noise (SNR) electroencephalogram across 20 subjects: (a) 40 Hz electroencephalogram at the top and 60 Hz electroencephalogram at the bottom. The left column represents the click stimuli and the right represents chirp stimuli; (b) histogram of the mean SNR of ASSR under the whole leads. Full article ">Figure 7
Mean SNR histogram at each lead across 20 subjects: (a) the mean SNR histogram of 40 Hz chirp stimulus and 40 Hz click stimulus; (b) the mean SNR histogram of 40 Hz chirp stimulus and 60 Hz chirp stimulus; * represents P ≤ 0.05, ** represents P ≤ 0.01. Full article ">Figure 7 Cont.
Mean SNR histogram at each lead across 20 subjects: (a) the mean SNR histogram of 40 Hz chirp stimulus and 40 Hz click stimulus; (b) the mean SNR histogram of 40 Hz chirp stimulus and 60 Hz chirp stimulus; * represents P ≤ 0.05, ** represents P ≤ 0.01. Full article ">

19 pages, 5976 KiB

Open AccessArticle

Analysis and Evaluation of the Image Preprocessing Process of a Six-Band Multispectral Camera Mounted on an Unmanned Aerial Vehicle for Winter Wheat Monitoring

by Jiale Jiang, Hengbiao Zheng, Xusheng Ji, Tao Cheng, Yongchao Tian, Yan Zhu, Weixing Cao, Reza Ehsani and Xia Yao

Sensors 2019, 19(3), 747; https://doi.org/10.3390/s19030747 - 12 Feb 2019

Cited by 28 | Viewed by 5528

Abstract

Unmanned aerial vehicle (UAV)-based multispectral sensors have great potential in crop monitoring due to their high flexibility, high spatial resolution, and ease of operation. Image preprocessing, however, is a prerequisite to make full use of the acquired high-quality data in practical applications. Most [...] Read more.

Unmanned aerial vehicle (UAV)-based multispectral sensors have great potential in crop monitoring due to their high flexibility, high spatial resolution, and ease of operation. Image preprocessing, however, is a prerequisite to make full use of the acquired high-quality data in practical applications. Most crop monitoring studies have focused on specific procedures or applications, and there has been little attempt to examine the accuracy of the data preprocessing steps. This study focuses on the preprocessing process of a six-band multispectral camera (Mini-MCA6) mounted on UAVs. First, we have quantified and analyzed the components of sensor error, including noise, vignetting, and lens distortion. Next, different methods of spectral band registration and radiometric correction were evaluated. Then, an appropriate image preprocessing process was proposed. Finally, the applicability and potential for crop monitoring were assessed in terms of accuracy by measurement of the leaf area index (LAI) and the leaf biomass inversion under variable growth conditions during five critical growth stages of winter wheat. The results show that noise and vignetting could be effectively removed via use of correction coefficients in image processing. The widely used Brown model was suitable for lens distortion correction of a Mini-MCA6. Band registration based on ground control points (GCPs) (Root-Mean-Square Error, RMSE = 1.02 pixels) was superior to that using PixelWrench2 (PW2) software (RMSE = 1.82 pixels). For radiometric correction, the accuracy of the empirical linear correction (ELC) method was significantly higher than that of light intensity sensor correction (ILSC) method. The multispectral images that were processed using optimal correction methods were demonstrated to be reliable for estimating LAI and leaf biomass. This study provides a feasible and semi-automatic image preprocessing process for a UAV-based Mini-MCA6, which also serves as a reference for other array-type multispectral sensors. Moreover, the high-quality data generated in this study may stimulate increased interest in remote high-efficiency monitoring of crop growth status. Full article

(This article belongs to the Section Remote Sensors)

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14 pages, 19797 KiB

Open AccessArticle

Three-Dimensional Visualization System with Spatial Information for Navigation of Tele-Operated Robots

by Seung-Hun Kim, Chansung Jung and Jaeheung Park

Sensors 2019, 19(3), 746; https://doi.org/10.3390/s19030746 - 12 Feb 2019

Cited by 3 | Viewed by 4482

Abstract

This study describes a three-dimensional visualization system with spatial information for the effective control of a tele-operated robot. The environmental visualization system for operating the robot is very important. The tele-operated robot performs tasks in a disaster area that is not accessible to [...] Read more.

This study describes a three-dimensional visualization system with spatial information for the effective control of a tele-operated robot. The environmental visualization system for operating the robot is very important. The tele-operated robot performs tasks in a disaster area that is not accessible to humans. The visualization system should perform in real-time to cope with rapidly changing situations. The visualization system should also provide accurate and high-level information so that the tele-operator can make the right decisions. The proposed system consists of four fisheye cameras and a 360° laser scanner. When the robot moves to the unknown space, a spatial model is created using the spatial information data of the laser scanner, and a single-stitched image is created using four images from cameras and mapped in real-time. The visualized image contains the surrounding spatial information; hence, the tele-operator can not only grasp the surrounding space easily, but also knows the relative position of the robot in space. In addition, it provides various angles of view without moving the robot or sensor, thereby coping with various situations. The experimental results show that the proposed method has a more natural appearance than the conventional methods. Full article

(This article belongs to the Special Issue Sensors Signal Processing and Visual Computing)

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17 pages, 5915 KiB

Open AccessArticle

Research on Damage Detection of a 3D Steel Frame Model Using Smartphones

by Botao Xie, Jinke Li and Xuefeng Zhao

Sensors 2019, 19(3), 745; https://doi.org/10.3390/s19030745 - 12 Feb 2019

Cited by 20 | Viewed by 4500

Abstract

Smartphones which are built into the suite of sensors, network transmission, data storage, and embedded processing capabilities provide a wide range of response measurement opportunities for structural health monitoring (SHM). The objective of this work was to evaluate and validate the use of [...] Read more.

Smartphones which are built into the suite of sensors, network transmission, data storage, and embedded processing capabilities provide a wide range of response measurement opportunities for structural health monitoring (SHM). The objective of this work was to evaluate and validate the use of smartphones for monitoring damage states in a three-dimensional (3D) steel frame structure subjected to shaking table earthquake excitation. The steel frame is a single-layer structure with four viscous dampers mounted at the beam-column joints to simulate different damage states at their respective locations. The structural acceleration and displacement responses of undamaged and damaged frames were obtained simultaneously by using smartphones and conventional sensors, while the collected response data were compared. Since smartphones can be used to monitor 3D acceleration in a given space and biaxial displacement in a given plane, the acceleration and displacement responses of the Y-axis of the model structure were obtained. Wavelet packet decomposition and relative wavelet entropy (RWE) were employed to analyze the acceleration data to detect damage. The results show that the acceleration responses that were monitored by the smartphones are well matched with the traditional sensors and the errors are generally within 5%. The comparison of the displacement acquired by smartphones and laser displacement sensors is basically good, and error analysis shows that smartphones with a displacement response sampling rate of 30 Hz are more suitable for monitoring structures with low natural frequencies. The damage detection using two kinds of sensors are relatively good. However, the asymmetry of the structure’s spatial stiffness will lead to greater RWE value errors being obtained from the smartphones monitoring data. Full article

(This article belongs to the Special Issue Smart Sensors for Structural Health Monitoring)

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Schematic illustration of the test frame model. Full article ">Figure 2
The various sensors instrumented in different locations in the steel frame testbed are shown. Full article ">Figure 3
Schematic illustration of an earthquake wave. Full article ">Figure 4
The acceleration time-history responses, as collected by the piezoelectric accelerometers (PAs) and smartphones (SPs) for four damage cases subjected to Nr-1 cm excitation, are compared. Representative results from (a) frame 1 and (b) frame 2 in the undamaged and damaged 1 cases, as well as (c) frame 1 and (d) frame 2 in the damaged 2 and damaged 3 cases are overlaid. Full article ">Figure 5
Using the acceleration time-history measurements from <a href="#sensors-19-00745-f004" class="html-fig">Figure 4</a>, the power spectral density functions of (a) frame 1 and (b) frame 2 in the undamaged and damaged 1 cases, as well as (c) frame 1 and (d) frame 2 in the damaged 2 and damaged 3 cases are compared. Full article ">Figure 5 Cont.
Using the acceleration time-history measurements from <a href="#sensors-19-00745-f004" class="html-fig">Figure 4</a>, the power spectral density functions of (a) frame 1 and (b) frame 2 in the undamaged and damaged 1 cases, as well as (c) frame 1 and (d) frame 2 in the damaged 2 and damaged 3 cases are compared. Full article ">Figure 6
The Y-axis acceleration time-history responses as collected by smartphones subjected to Nr-1 cm are shown (a) in the undamaged and damaged 1 cases and (b) in the damaged 2 and 3 cases. Full article ">Figure 7
The displacement time-history responses as collected by the LDSs (laser displacement sensors) and SPs with Nr-1 cm excitation for four damage cases are compared and found to show good agreement. Representative results are shown from (a) frame 1 and (b) frame 2 in the undamaged case and damaged 1 case, as well as from (c) frame 1 and (d) frame 2 in the damaged 2 and 3 cases. Full article ">Figure 8
Displacement of the frame in the Y direction for (a) the Northridge-1 cm case and (b) the Northridge-2 cm case. Full article ">Figure 9
The displacement time-history responses as collected by SPs compared with LDSs using different sampling rates of (a) 100 Hz, (b) 50 Hz, and (c) 25 Hz. (d) A comparison of all sampling rates. Full article ">Figure 10
pj calculated for (a) frame 1 and (b) frame 2 in the damaged 1 case, (c) frame 1 and (d) frame 2 in the damaged 2 case, and (e) frame 1 and (f) frame 2 in the damaged 3 case when structure is subjected to Nr-1 cm excitation. Full article ">Figure 10 Cont.
pj calculated for (a) frame 1 and (b) frame 2 in the damaged 1 case, (c) frame 1 and (d) frame 2 in the damaged 2 case, and (e) frame 1 and (f) frame 2 in the damaged 3 case when structure is subjected to Nr-1 cm excitation. Full article ">

34 pages, 22213 KiB

Open AccessArticle

A Knowledge-Driven Approach for 3D High Temporal-Spatial Measurement of an Arbitrary Contouring Error of CNC Machine Tools Using Monocular Vision

by Xiao Li, Wei Liu, Yi Pan, Jianwei Ma and Fuji Wang

Sensors 2019, 19(3), 744; https://doi.org/10.3390/s19030744 - 12 Feb 2019

Cited by 15 | Viewed by 5520

Abstract

Periodic health checks of contouring errors under unloaded conditions are critical for machine performance evaluation and value-added manufacturing. Aiming at breaking the dimension, range and speed measurement limitations of the existing devices, a cost-effective knowledge-driven approach for detecting error motions of arbitrary paths [...] Read more.

Periodic health checks of contouring errors under unloaded conditions are critical for machine performance evaluation and value-added manufacturing. Aiming at breaking the dimension, range and speed measurement limitations of the existing devices, a cost-effective knowledge-driven approach for detecting error motions of arbitrary paths using a single camera is proposed. In combination with the PNP algorithm, the three-dimensional (3D) evaluation of large-scale contouring error in relatively high feed rate conditions can be deduced from a priori geometrical knowledge. The innovations of this paper focus on improving the accuracy, efficiency and ability of the vision measurement. Firstly, a camera calibration method considering distortion partition of the depth-of-field (DOF) is presented to give an accurate description of the distortion behavior in the entire photography domain. Then, to maximize the utilization of the decimal involved in the feature encoding, new high-efficient encoding markers are designed on a cooperative target to characterize motion information of the machine. Accordingly, in the image processing, markers are automatically identified and located by the proposed decoding method based on finding the optimal start bit. Finally, with the selected imaging parameters and the precalibrated position of each marker, the 3D measurement of large-scale contouring error under relatively high dynamic conditions can be realized by comparing the curve that is measured by PNP algorithm with the nominal one. Both detection and verification experiments are conducted for two types of paths (i.e., planar and spatial trajectory), and experimental results validate the measurement accuracy and advantages of the proposed method. Full article

(This article belongs to the Special Issue Optical Sensors, Biosensors and Sensing Methodologies: Novel Materials, Approaches, Configurations and Applications)

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16 pages, 7412 KiB

Open AccessArticle

Monitoring Land Subsidence in Wuhan City (China) using the SBAS-InSAR Method with Radarsat-2 Imagery Data

by Yang Zhang, Yaolin Liu, Manqi Jin, Ying Jing, Yi Liu, Yanfang Liu, Wei Sun, Junqing Wei and Yiyun Chen

Sensors 2019, 19(3), 743; https://doi.org/10.3390/s19030743 - 12 Feb 2019

Cited by 80 | Viewed by 8324

Abstract

Wuhan city is the biggest city in central China and has suffered subsidence problems in recent years because of its rapid urban construction. However, longtime and wide range monitoring of land subsidence is lacking. The causes of subsidence also require further study, such [...] Read more.

Wuhan city is the biggest city in central China and has suffered subsidence problems in recent years because of its rapid urban construction. However, longtime and wide range monitoring of land subsidence is lacking. The causes of subsidence also require further study, such as natural conditions and human activities. We use small baseline subset (SBAS) interferometric synthetic aperture radar (InSAR) method and high-resolution RADARSAT-2 images acquired between 2015 and 2018 to derive subsidence. The SBAS-InSAR results are validated by 56 leveling benchmarks where two readings of elevation were recorded. Two natural factors (carbonate rock and soft soils) and three human factors (groundwater exploitation, subway excavation and urban construction) are investigated for their relationships with land subsidence. Results show that four major areas of subsidence are detected and the subsidence rate varies from −51.56 to 27.80 millimeters per year (mm/yr) with an average of −0.03 mm/yr. More than 83.81% of persistent scattered (PS) points obtain a standard deviation of less than −6 mm/yr, and the difference between SBAS-InSAR method and leveling data is less than 5 mm/yr. Thus, we conclude that SBAS-InSAR method with Radarsat-2 data is reliable for longtime monitoring of land subsidence covering a large area in Wuhan city. In addition, land subsidence is caused by a combination of natural conditions and human activities. Natural conditions provide a basis for subsidence and make subsidence possible. Human activities are driving factors and make subsidence happen. Moreover, subsidence information could be used in disaster prevention, urban planning, and hydrological modeling. Full article

(This article belongs to the Special Issue Synthetic Aperture Radar (SAR) Techniques and Applications)

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13 pages, 4350 KiB

Open AccessArticle

Finer SHM-Coverage of Inter-Plies and Bondings in Smart Composite by Dual Sinusoidal Placed Distributed Optical Fiber Sensors

by Venkadesh Raman, Monssef Drissi-Habti, Preshit Limje and Aghiad Khadour

Sensors 2019, 19(3), 742; https://doi.org/10.3390/s19030742 - 12 Feb 2019

Cited by 20 | Viewed by 4380

Abstract

Designing of new generation offshore wind turbine blades is a great challenge as size of blades are getting larger (typically larger than 100 m). Structural Health Monitoring (SHM), which uses embedded Fiber Optics Sensors (FOSs), is incorporated in critical stressed zones such as [...] Read more.

Designing of new generation offshore wind turbine blades is a great challenge as size of blades are getting larger (typically larger than 100 m). Structural Health Monitoring (SHM), which uses embedded Fiber Optics Sensors (FOSs), is incorporated in critical stressed zones such as trailing edges and spar webs. When FOS are embedded within composites, a ‘penny shape’ region of resin concentration is formed around the section of FOS. The size of so-formed defects are depending on diameter of the FOS. Penny shape defects depend of FOS diameter. Consequently, care must be given to embed in composites reliable sensors that are as small as possible. The way of FOS placement within composite plies is the second critical issue. Previous research work done in this field (1) investigated multiple linear FOS and sinusoidal FOS placement, as well. The authors pointed out that better structural coverage of the critical zones needs some new concepts. Therefore, further advancement is proposed in the current article with novel FOS placement (anti-phasic sinusoidal FOS placement), so as to cover more critical area and sense multi-directional strains, when the wind blade is in-use. The efficiency of the new positioning is proven by numerical and experimental study. Full article

(This article belongs to the Section Physical Sensors)

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17 pages, 2723 KiB

Open AccessArticle

Tracking and Estimation of Multiple Cross-Over Targets in Clutter

by Sufyan Ali Memon, Myungun Kim and Hungsun Son

Sensors 2019, 19(3), 741; https://doi.org/10.3390/s19030741 - 12 Feb 2019

Cited by 11 | Viewed by 3806

Abstract

Tracking problems, including unknown number of targets, target trajectories behaviour and uncertain motion of targets in the surveillance region, are challenging issues. It is also difficult to estimate cross-over targets in heavy clutter density environment. In addition, tracking algorithms including smoothers which use [...] Read more.

Tracking problems, including unknown number of targets, target trajectories behaviour and uncertain motion of targets in the surveillance region, are challenging issues. It is also difficult to estimate cross-over targets in heavy clutter density environment. In addition, tracking algorithms including smoothers which use measurements from upcoming scans to estimate the targets are often unsuccessful in tracking due to low detection probabilities. For efficient and better tracking performance, the smoother must rely on backward tracking to fetch measurement from future scans to estimate forward track in the current time. This novel idea is utilized in the joint integrated track splitting (JITS) filter to develop a new fixed-interval smoothing JITS (FIsJITS) algorithm for tracking multiple cross-over targets. The FIsJITS initializes tracks employing JITS in two-way directions: Forward-time moving JITS (fJITS) and backward-time moving JITS (bJITS). The fJITS acquires the bJITS predictions when they arrive from future scans to the current scan for smoothing. As a result, the smoothing multi-target data association probabilities are obtained for computing the fJITS and smoothing output estimates. This significantly improves estimation accuracy for multiple cross-over targets in heavy clutter. To verify this, numerical assessments of the FIsJITS are tested and compared with existing algorithms using simulations. Full article

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23 pages, 4320 KiB

Open AccessArticle

Joint Optimization for Task Offloading in Edge Computing: An Evolutionary Game Approach

by Chongwu Dong and Wushao Wen

Sensors 2019, 19(3), 740; https://doi.org/10.3390/s19030740 - 12 Feb 2019

Cited by 43 | Viewed by 7910

Abstract

The mobile edge computing (MEC) paradigm provides a promising solution to solve the resource-insufficiency problem in mobile terminals by offloading computation-intensive and delay-sensitive tasks to nearby edge nodes. However, limited computation resources in edge nodes may not be sufficient to serve excessive offloading [...] Read more.

The mobile edge computing (MEC) paradigm provides a promising solution to solve the resource-insufficiency problem in mobile terminals by offloading computation-intensive and delay-sensitive tasks to nearby edge nodes. However, limited computation resources in edge nodes may not be sufficient to serve excessive offloading tasks exceeding the computation capacities of edge nodes. Therefore, multiple edge clouds with a complementary central cloud coordinated to serve users is the efficient architecture to satisfy users’ Quality-of-Service (QoS) requirements while trying to minimize some network service providers’ cost. We study a dynamic, decentralized resource-allocation strategy based on evolutionary game theory to deal with task offloading to multiple heterogeneous edge nodes and central clouds among multi-users. In our strategy, the resource competition among multi-users is modeled by the process of replicator dynamics. During the process, our strategy can achieve one evolutionary equilibrium, meeting users’ QoS requirements under resource constraints of edge nodes. The stability and fairness of this strategy is also proved by mathematical analysis. Illustrative studies show the effectiveness of our proposed strategy, outperforming other alternative methods. Full article

(This article belongs to the Special Issue Recent Advances in Fog/Edge Computing in Internet of Things)

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17 pages, 13689 KiB

Open AccessArticle

Accurate and Cost-Effective Micro Sun Sensor based on CMOS Black Sun Effect

by Rashid Saleem and Sukhan Lee

Sensors 2019, 19(3), 739; https://doi.org/10.3390/s19030739 - 12 Feb 2019

Cited by 9 | Viewed by 7031

Abstract

An accurate and cost-effective micro sun sensor based on the extraction of the sun vector using a phenomenon called the “black sun” is presented. Unlike conventional image-based sun sensors where there is difficulty in accurately detecting the sun center, the black sun effect [...] Read more.

An accurate and cost-effective micro sun sensor based on the extraction of the sun vector using a phenomenon called the “black sun” is presented. Unlike conventional image-based sun sensors where there is difficulty in accurately detecting the sun center, the black sun effect allows the sun center to be accurately extracted even with the sun image appearing irregular and noisy due to glare. This allows the proposed micro sun sensor to achieve high accuracy even when a 1 mm × 1 mm CMOS image sensor with a resolution of 250 × 250 pixels is used. The proposed micro sun sensor is implemented in two application modes: (1) a stationary mode targeted at tracking the sun for heliostats or solar panels with a fixed pose of single image sensor of 1 mm × 1 mm × 1.74 mm in size and (2) a non-stationary mode targeted at determining the orientation of moving platforms with six sensors on the platform, which is configured in an icosahedron geometry of 23 mm × 23 mm × 12 mm in size. For the stationary mode, we obtained an accuracy of 0.013° by applying Kalman filter to the sun sensor measurement for a particular sensor orientation. For the non-stationary mode, we obtained an improved accuracy of 0.05° by fusing the measurements from three sun sensors available at any instant of time. Furthermore, experiments indicate that the black sun effect makes the precision of sun vector extraction independent of the sun location captured on the image plane. Full article

(This article belongs to the Section Physical Sensors)

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14 pages, 8465 KiB

Open AccessArticle

Natural Fibre-Reinforced Polymer Composites (NFRP) Fabricated from Lignocellulosic Fibres for Future Sustainable Architectural Applications, Case Studies: Segmented-Shell Construction, Acoustic Panels, and Furniture

by Hanaa Dahy

Sensors 2019, 19(3), 738; https://doi.org/10.3390/s19030738 - 12 Feb 2019

Cited by 67 | Viewed by 12958

Abstract

Due to the high amounts of waste generated from the building industry field, it has become essential to search for renewable building materials to be applied in wider and more innovative methods in architecture. One of the materials with the highest potential in [...] Read more.

Due to the high amounts of waste generated from the building industry field, it has become essential to search for renewable building materials to be applied in wider and more innovative methods in architecture. One of the materials with the highest potential in this area is natural fibre-reinforced polymers (NFRP), which are also called biocomposites, and are filled or reinforced with annually renewable lignocellulosic fibres. This would permit variable closed material cycles’ scenarios and should decrease the amounts of waste generated in the building industry. Throughout this paper, this discussion will be illustrated through a number of developments and 1:1 mockups fabricated from newly developed lignocellulosic-based biocomposites from both bio-based and non-bio-based thermoplastic and thermoset polymers. Recyclability, closed materials cycles, and design variations with diverse digital fabrication technologies will be discussed in each case. The mock-ups’ concepts, materials’ compositions, and fabrication methods are illustrated. In the first case study, a structural segmented shell construction is developed and constructed. In the second case study, acoustic panels were developed. The final case studies are two types of furniture, where each is developed from a different lignocellulosic-based biocomposite. All of the presented case studies show diverse architectural design possibilities, structural abilities, and physical building characteristics. Full article

(This article belongs to the Special Issue Advances in FRP Composites: Applications, Sensing, and Monitoring)

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20 pages, 5070 KiB

Open AccessArticle

A Non-Invasive Medical Device for Parkinson’s Patients with Episodes of Freezing of Gait

by Catalina Punin, Boris Barzallo, Roger Clotet, Alexander Bermeo, Marco Bravo, Juan Pablo Bermeo and Carlos Llumiguano

Sensors 2019, 19(3), 737; https://doi.org/10.3390/s19030737 - 12 Feb 2019

Cited by 31 | Viewed by 7724

Abstract

A critical symptom of Parkinson’s disease (PD) is the occurrence of Freezing of Gait (FOG), an episodic disorder that causes frequent falls and consequential injuries in PD patients. There are various auditory, visual, tactile, and other types of stimulation interventions that can be [...] Read more.

A critical symptom of Parkinson’s disease (PD) is the occurrence of Freezing of Gait (FOG), an episodic disorder that causes frequent falls and consequential injuries in PD patients. There are various auditory, visual, tactile, and other types of stimulation interventions that can be used to induce PD patients to escape FOG episodes. In this article, we describe a low cost wearable system for non-invasive gait monitoring and external delivery of superficial vibratory stimulation to the lower extremities triggered by FOG episodes. The intended purpose is to reduce the duration of the FOG episode, thus allowing prompt resumption of gait to prevent major injuries. The system, based on an Android mobile application, uses a tri-axial accelerometer device for gait data acquisition. Gathered data is processed via a discrete wavelet transform-based algorithm that precisely detects FOG episodes in real time. Detection activates external vibratory stimulation of the legs to reduce FOG time. The integration of detection and stimulation in one low cost device is the chief novel contribution of this work. We present analyses of sensitivity, specificity and effectiveness of the proposed system to validate its usefulness. Full article

(This article belongs to the Special Issue Sensors Applied in Multimodal Systems—Selected Papers from the Second Ecuador Technical Chapters Meeting (IEEE-ETCM))

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23 pages, 1174 KiB

Open AccessArticle

NOMA-Assisted Multiple Access Scheme for IoT Deployment: Relay Selection Model and Secrecy Performance Improvement

by Dinh-Thuan Do, Minh-Sang Van Nguyen, Thi-Anh Hoang and Miroslav Voznak

Sensors 2019, 19(3), 736; https://doi.org/10.3390/s19030736 - 12 Feb 2019

Cited by 62 | Viewed by 6640

Abstract

In this paper, an Internet-of-Things (IoT) system containing a relay selection is studied as employing an emerging multiple access scheme, namely non-orthogonal multiple access (NOMA). This paper proposes a new scheme to consider secure performance, to be called relay selection NOMA (RS-NOMA). In [...] Read more.

In this paper, an Internet-of-Things (IoT) system containing a relay selection is studied as employing an emerging multiple access scheme, namely non-orthogonal multiple access (NOMA). This paper proposes a new scheme to consider secure performance, to be called relay selection NOMA (RS-NOMA). In particular, we consider metrics to evaluate secure performance in such an RS-NOMA system where a base station (master node in IoT) sends confidential messages to two main sensors (so-called NOMA users) under the influence of an external eavesdropper. In the proposed IoT scheme, both two NOMA sensors and an illegal sensor are served with different levels of allocated power at the base station. It is noticed that such RS-NOMA operates in two hop transmission of the relaying system. We formulate the closed-form expressions of secure outage probability (SOP) and the strictly positive secure capacity (SPSC) to examine the secrecy performance under controlling setting parameters such as transmit signal-to-noise ratio (SNR), the number of selected relays, channel gains, and threshold rates. The different performance is illustrated as performing comparisons between NOMA and orthogonal multiple access (OMA). Finally, the advantage of NOMA in secure performance over orthogonal multiple access (OMA) is confirmed both analytically and numerically. Full article

(This article belongs to the Special Issue Internet of Things and Machine-to-Machine Communication)

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13 pages, 2011 KiB

Open AccessArticle

3D SSY Estimate of EPFM Constraint Parameter under Biaxial Loading for Sensor Structure Design

by Ping Ding and Xin Wang

Sensors 2019, 19(3), 735; https://doi.org/10.3390/s19030735 - 12 Feb 2019

Cited by 3 | Viewed by 3370

Abstract

Conventional sensor structure design and related fracture mechanics analysis are based on the single J-integral parameter approach of elastic-plastic fracture mechanics (EPFM). Under low crack constraint cases, the EPFM one-parameter approach generally gives a stress overestimate, which results in a great cost [...] Read more.

Conventional sensor structure design and related fracture mechanics analysis are based on the single J-integral parameter approach of elastic-plastic fracture mechanics (EPFM). Under low crack constraint cases, the EPFM one-parameter approach generally gives a stress overestimate, which results in a great cost waste of labor and sensor components. The J-A two-parameter approach overcomes this limitation. To enable the extensive application of the J-A approach on theoretical research and sensor engineering problem, under small scale yielding (SSY) conditions, the authors developed an estimate method to conveniently and quickly obtain the constraint (second) parameter A values directly from T-stress. Practical engineering application of sensor structure analysis and design focuses on three-dimensional (3D) structures with biaxial external loading, while the estimate method was developed based on two-dimensional (2D) plain strain condition with uniaxial loading. In the current work, the estimate method was successfully extended to a 3D structure with biaxial loading cases, which is appropriate for practical sensor design. The estimate method extension and validation process was implemented through a thin 3D single edge cracked plate (SECP) specimen. The process implementation was completed in two specified planes of 3D SECP along model thickness. A wide range of material and geometrical properties were applied for the extension and validation process, with material hardening exponent value 3, 5 and 10, and crack length ratio 0.1, 0.3 and 0.7. Full article

(This article belongs to the Special Issue Sensors for Prognostics and Health Management)

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Three-dimensional (3D) modified boundary layer model. Full article ">Figure 2
Finite element mesh for 3D modified boundary layer (MBL) model (crack front). Full article ">Figure 3
3D single edge cracked plate (SECP) specimen model. Full article ">Figure 4
Finite element mesh for 3D SECP specimen (crack front). Full article ">Figure 5
A-T relationship curves from 3D MBL formulation, for plane I (a) and II (b), λ = 1.0. Full article ">Figure 6
Comparisons of predicted 3D SECP A values with finite element analysis (FEA) data, biaxial ratio λ = 1.0, a/W = 0.1, in plane I. Full article ">Figure 7
Comparisons of predicted 3D SECP A values with FEA data, biaxial ratio λ = 1.0, a/W = 0.7, in plane I. Full article ">

20 pages, 4487 KiB

Open AccessArticle

Multi-UAV Reconnaissance Task Assignment for Heterogeneous Targets Based on Modified Symbiotic Organisms Search Algorithm

by Hao-Xiang Chen, Ying Nan and Yi Yang

Sensors 2019, 19(3), 734; https://doi.org/10.3390/s19030734 - 12 Feb 2019

Cited by 55 | Viewed by 5347

Abstract

This paper considers a reconnaissance task assignment problem for multiple unmanned aerial vehicles (UAVs) with different sensor capacities. A modified Multi-Objective Symbiotic Organisms Search algorithm (MOSOS) is adopted to optimize UAVs’ task sequence. A time-window based task model is built for heterogeneous targets. [...] Read more.

This paper considers a reconnaissance task assignment problem for multiple unmanned aerial vehicles (UAVs) with different sensor capacities. A modified Multi-Objective Symbiotic Organisms Search algorithm (MOSOS) is adopted to optimize UAVs’ task sequence. A time-window based task model is built for heterogeneous targets. Then, the basic task assignment problem is formulated as a Multiple Time-Window based Dubins Travelling Salesmen Problem (MTWDTSP). Double-chain encoding rules and several criteria are established for the task assignment problem under logical and physical constraints. Pareto dominance determination and global adaptive scaling factors is introduced to improve the performance of original MOSOS. Numerical simulation and Monte-Carlo simulation results for the task assignment problem are also presented in this paper, whereas comparisons with non-dominated sorting genetic algorithm (NSGA-II) and original MOSOS are made to verify the superiority of the proposed method. The simulation results demonstrate that modified SOS outperforms the original MOSOS and NSGA-II in terms of optimality and efficiency of the assignment results in MTWDTSP. Full article

(This article belongs to the Section Physical Sensors)

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12 pages, 2760 KiB

Open AccessArticle

A Piezoelectric Sensor Signal Analysis Method for Identifying Persons Groups

by Hitoshi Ueno

Sensors 2019, 19(3), 733; https://doi.org/10.3390/s19030733 - 12 Feb 2019

Cited by 3 | Viewed by 4848

Abstract

The is an increasing number of elderly single-person households causing lonely deaths and it is a social problem. We study a watching system for elderly families by laying the piezoelectric sensors inside the house. There are few privacy issues of this system because [...] Read more.

The is an increasing number of elderly single-person households causing lonely deaths and it is a social problem. We study a watching system for elderly families by laying the piezoelectric sensors inside the house. There are few privacy issues of this system because piezoelectric sensor detects only a person’s vibration signal. Furthermore, it has a benefit of sensing the ability for a bio-signal including the respiration cycle and cardiac cycle. We propose a method of identifying the person who is on the sensor by analyzing the frequency spectrum of the bio-signal. Multiple peaks of harmonics originating from the heartbeat appear in the graph of the frequency spectrum. We propose a method to identify people by using the peak shape as a discrimination criterion. Full article

(This article belongs to the Special Issue Sensors Signal Processing and Visual Computing)

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14 pages, 1947 KiB

Open AccessReview

Single-Pixel Imaging and Its Application in Three-Dimensional Reconstruction: A Brief Review

by Ming-Jie Sun and Jia-Min Zhang

Sensors 2019, 19(3), 732; https://doi.org/10.3390/s19030732 - 11 Feb 2019

Cited by 171 | Viewed by 14929

Abstract

Whereas modern digital cameras use a pixelated detector array to capture images, single-pixel imaging reconstructs images by sampling a scene with a series of masks and associating the knowledge of these masks with the corresponding intensity measured with a single-pixel detector. Though not [...] Read more.

Whereas modern digital cameras use a pixelated detector array to capture images, single-pixel imaging reconstructs images by sampling a scene with a series of masks and associating the knowledge of these masks with the corresponding intensity measured with a single-pixel detector. Though not performing as well as digital cameras in conventional visible imaging, single-pixel imaging has been demonstrated to be advantageous in unconventional applications, such as multi-wavelength imaging, terahertz imaging, X-ray imaging, and three-dimensional imaging. The developments and working principles of single-pixel imaging are reviewed, a mathematical interpretation is given, and the key elements are analyzed. The research works of three-dimensional single-pixel imaging and their potential applications are further reviewed and discussed. Full article

(This article belongs to the Special Issue Depth Sensors and 3D Vision)

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Full article ">Figure 1
Schematics of two imaging architectures: (a) In single-pixel imaging, the object is first illuminated by the light source, then imaged by a camera lens onto the focal plane, where a spatial light modulator (SLM) is placed. The SLM modulates the image with different masks, and the reflected or transmitted light intensities are measured by a single-pixel detector. A computational algorithm uses knowledge of the masks. along with their corresponding measurements, to reconstruct an image of the object; (b) in ghost imaging, the object is illuminated by the structured light distribution generated from different masks on an SLM, and the reflected or transmitted light intensities are then measured by a single-pixel detector. A computational algorithm uses knowledge of the masks along, with their corresponding measurements, to reconstruct an image of the object. Full article ">Figure 2
Single-pixel imaging reconstructions (64 × 64 pixel resolution) using experimental data with different numbers of measurements. Full article ">Figure 3
Space–time trade-off relationship for performing N measurements: (a) Single-pixel imaging and digital cameras are at the two ends of the curve, while the idea of using T pixels and N/T measurements is a compromise between the two extremes; (b) by using a quadrant detector, the imaging system is 4 times faster in data acquisition [<a href="#B79-sensors-19-00732" class="html-bibr">79</a>]. Full article ">Figure 4
Overview of the image cube method: (a) The illuminating laser pulses back-scattered from a scene are measured as (b) broadened signals; (c) an image cube, containing images at different depths, is obtained using the measured signals; (d) each transverse location has an intensity distribution along the longitudinal axis, indicating depth information; (e) reflectivity and (f) a depth map can be estimated from the image cube, and then be used to reconstruct (g), a 3D image of the scene. Experimental data used in this figure is from the work of [<a href="#B45-sensors-19-00732" class="html-bibr">45</a>]. Full article ">Figure 5
Schematic of a stereo vision based 3D single-pixel imaging. Full article ">

21 pages, 15553 KiB

Open AccessArticle

High-Sensitivity Real-Time Tracking System for High-Speed Pipeline Inspection Gauge

by Guanyu Piao, Jingbo Guo, Tiehua Hu and Yiming Deng

Sensors 2019, 19(3), 731; https://doi.org/10.3390/s19030731 - 11 Feb 2019

Cited by 13 | Viewed by 7190

Abstract

Real-time tracking of pipeline inspection gauges (PIGs) is an important aspect of ensuring the safety of oil and gas pipeline inline inspections (ILIs). Transmitting and receiving extremely low frequency (ELF) magnetic signals is one of the preferred methods of tracking. Due to the [...] Read more.

Real-time tracking of pipeline inspection gauges (PIGs) is an important aspect of ensuring the safety of oil and gas pipeline inline inspections (ILIs). Transmitting and receiving extremely low frequency (ELF) magnetic signals is one of the preferred methods of tracking. Due to the increase in physical parameters of the pipeline including transportation speed, wall thickness and burial depth, the ELF magnetic signals received are short transient (1-second duration) and very weak (10 pT), making the existing above-ground-marker (AGM) systems difficult to operate correctly. Based on the short transient very weak characteristics of ELF signals studied with a 2-D finite-element method (FEM) simulation, a data fusion model was derived to fuse the envelope decay rates of ELF signals by a least square (LS) criterion. Then, a fast-decision-tree (FDT) method is proposed to estimate the fused envelope decay rate to output the maximized orthogonal signal power for the signal detection through a determined topology and a fast calculation process, which was demonstrated to have excellent real-time detection performance. We show that simulation and experimental results validated the effectiveness of the proposed FDT method, and describe the high-sensitivity detection and real-time implementation of a high-speed PIG tracking system, including a transmitter, a receiver, and a pair of orthogonal search coil sensors. Full article

(This article belongs to the Special Issue Sensing in Oil and Gas Applications)

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20 pages, 4069 KiB

Open AccessArticle

Design of a 1-bit MEMS Gyroscope using the Model Predictive Control Approach

by Xiaofeng Wu, Zhicheng Xie, Xueliang Bai and Trevor Kwan

Sensors 2019, 19(3), 730; https://doi.org/10.3390/s19030730 - 11 Feb 2019

Cited by 6 | Viewed by 4640

Abstract

In this paper, a bi-level Delta-Sigma modulator-based MEMS gyroscope design is presented based on a Model Predictive Control (MPC) approach. The MPC is popular because of its capability of handling hard constraints. In this work, we propose to combine the 1-bit nature of [...] Read more.

In this paper, a bi-level Delta-Sigma modulator-based MEMS gyroscope design is presented based on a Model Predictive Control (MPC) approach. The MPC is popular because of its capability of handling hard constraints. In this work, we propose to combine the 1-bit nature of the bi-level Delta-Sigma modulator output with the MPC to develop a 1-bit processing-based MPC (OBMPC). This paper will focus on the affine relationship between the 1-bit feedback and the in-loop MPC controller, as this can potentially remove the multipliers from the controller. In doing so, the computational requirement of the MPC control is significantly alleviated, which makes the 1-bit MEMS Gyroscope feasible for implementation. In addition, a stable constrained MPC is designed, so that the input will not overload the quantizer while maintaining a higher Signal-to-Noise Ratio (SNR). Full article

(This article belongs to the Special Issue MEMS Technology Based Sensors for Human Centered Applications)

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18 pages, 7621 KiB

Open AccessArticle

A High-Computational Efficiency Human Detection and Flow Estimation Method Based on TOF Measurements

by Weihang Wang, Peilin Liu, Rendong Ying, Jun Wang, Jiuchao Qian, Jialu Jia and Jiefeng Gao

Sensors 2019, 19(3), 729; https://doi.org/10.3390/s19030729 - 11 Feb 2019

Cited by 13 | Viewed by 4643

Abstract

State-of-the-art human detection methods focus on deep network architectures to achieve higher recognition performance, at the expense of huge computation. However, computational efficiency and real-time performance are also important evaluation indicators. This paper presents a fast real-time human detection and flow estimation method [...] Read more.

State-of-the-art human detection methods focus on deep network architectures to achieve higher recognition performance, at the expense of huge computation. However, computational efficiency and real-time performance are also important evaluation indicators. This paper presents a fast real-time human detection and flow estimation method using depth images captured by a top-view TOF camera. The proposed algorithm mainly consists of head detection based on local pooling and searching, classification refinement based on human morphological features, and tracking assignment filter based on dynamic multi-dimensional feature. A depth image dataset record with more than 10k entries and departure events with detailed human location annotations is established. Taking full advantage of the distance information implied in the depth image, we achieve high-accuracy human detection and people counting with accuracy of 97.73% and significantly reduce the running time. Experiments demonstrate that our algorithm can run at 23.10 ms per frame on a CPU platform. In addition, the proposed robust approach is effective in complex situations such as fast walking, occlusion, crowded scenes, etc. Full article

(This article belongs to the Special Issue Depth Sensors and 3D Vision)

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9 pages, 3137 KiB

Open AccessArticle

Hybrid Printed Energy Harvesting Technology for Self-Sustainable Autonomous Sensor Application

by Sangkil Kim, Manos M. Tentzeris and Apostolos Georgiadis

Sensors 2019, 19(3), 728; https://doi.org/10.3390/s19030728 - 11 Feb 2019

Cited by 21 | Viewed by 5579

Abstract

In this paper, the far-field energy harvesting system for self-sustainable wireless autonomous sensor application is presented. The proposed autonomous sensor system consists of a wireless power supplier (active antenna) and far-field energy harvesting technology-enabled autonomous battery-less sensors. The wireless power supplier converts solar [...] Read more.

In this paper, the far-field energy harvesting system for self-sustainable wireless autonomous sensor application is presented. The proposed autonomous sensor system consists of a wireless power supplier (active antenna) and far-field energy harvesting technology-enabled autonomous battery-less sensors. The wireless power supplier converts solar power to electromagnetic power in order to transfer power to multiple autonomous sensors wirelessly. The autonomous sensors have far-field energy harvesters which convert transmitted RF power to voltage regulated DC power to power-on the sensor system. The hybrid printing technology was chosen to build the autonomous sensors and the wireless power suppliers. Two popular hybrid electronics technologies (direct nano-particle printing and indirect copper thin film printing techniques) are discussed in detail. Full article

(This article belongs to the Special Issue Passive Electromagnetic Sensors for Autonomous Wireless Networks)

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16 pages, 685 KiB

Open AccessArticle

Improving IoT Botnet Investigation Using an Adaptive Network Layer

by João Marcelo Ceron, Klaus Steding-Jessen, Cristine Hoepers, Lisandro Zambenedetti Granville and Cíntia Borges Margi

Sensors 2019, 19(3), 727; https://doi.org/10.3390/s19030727 - 11 Feb 2019

Cited by 56 | Viewed by 8249

Abstract

IoT botnets have been used to launch Distributed Denial-of-Service (DDoS) attacks affecting the Internet infrastructure. To protect the Internet from such threats and improve security mechanisms, it is critical to understand the botnets’ intents and characterize their behavior. Current malware analysis solutions, when [...] Read more.

IoT botnets have been used to launch Distributed Denial-of-Service (DDoS) attacks affecting the Internet infrastructure. To protect the Internet from such threats and improve security mechanisms, it is critical to understand the botnets’ intents and characterize their behavior. Current malware analysis solutions, when faced with IoT, present limitations in regard to the network access containment and network traffic manipulation. In this paper, we present an approach for handling the network traffic generated by the IoT malware in an analysis environment. The proposed solution can modify the traffic at the network layer based on the actions performed by the malware. In our study case, we investigated the Mirai and Bashlite botnet families, where it was possible to block attacks to other systems, identify attacks targets, and rewrite botnets commands sent by the botnet controller to the infected devices. Full article

(This article belongs to the Special Issue Threat Identification and Defence for Internet-of-Things)

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14 pages, 2699 KiB

Open AccessEditor’s ChoiceArticle

Enhanced Hydrogen Detection in ppb-Level by Electrospun SnO₂-Loaded ZnO Nanofibers

by Jae-Hyoung Lee, Jin-Young Kim, Jae-Hun Kim and Sang Sub Kim

Sensors 2019, 19(3), 726; https://doi.org/10.3390/s19030726 - 11 Feb 2019

Cited by 47 | Viewed by 5774

Abstract

High-performance hydrogen sensors are important in many industries to effectively address safety concerns related to the production, delivering, storage and use of H₂ gas. Herein, we present a highly sensitive hydrogen gas sensor based on SnO₂-loaded ZnO nanofibers (NFs). The [...] Read more.

High-performance hydrogen sensors are important in many industries to effectively address safety concerns related to the production, delivering, storage and use of H₂ gas. Herein, we present a highly sensitive hydrogen gas sensor based on SnO₂-loaded ZnO nanofibers (NFs). The xSnO₂-loaded (x = 0.05, 0.1 and 0.15) ZnO NFs were fabricated using an electrospinning technique followed by calcination at high temperature. Microscopic analyses demonstrated the formation of NFs with expected morphology and chemical composition. Hydrogen sensing studies were performed at various temperatures and the optimal working temperature was selected as 300 °C. The optimal gas sensor (0.1 SnO₂ loaded ZnO NFs) not only showed a high response to 50 ppb hydrogen gas, but also showed an excellent selectivity to hydrogen gas. The excellent performance of the gas sensor to hydrogen gas was mainly related to the formation of SnO₂-ZnO heterojunctions and the metallization effect of ZnO. Full article

(This article belongs to the Section Chemical Sensors)

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14 pages, 3896 KiB

Open AccessArticle

Establishment and Verification of the Cutting Grinding Force Model for the Disc Wheel Based on Piezoelectric Sensors

by Jing Ni, Kai Feng, M.S.H. Al-Furjan, Xiaojiao Xu and Jing Xu

Sensors 2019, 19(3), 725; https://doi.org/10.3390/s19030725 - 11 Feb 2019

Cited by 10 | Viewed by 4025

Abstract

In this paper, a new model of cutting grinding force for disc wheels is presented. Initially, it was proposed that the grinding cutting force was formed by the grinding force and cutting force in combination. Considering the single-grit morphology, the single-grit average grinding [...] Read more.

In this paper, a new model of cutting grinding force for disc wheels is presented. Initially, it was proposed that the grinding cutting force was formed by the grinding force and cutting force in combination. Considering the single-grit morphology, the single-grit average grinding depth, the effective number of grits, and the contact arc length between the grit and the workpiece comprehensively, the grinding force model and the cutting force model were established, respectively. Then, a universal grinding cutting force model was optimized by introducing the effective grit coefficient model, dependent on the probability statistical method and the grit height coefficient model with Rayleigh’s distribution theory. Finally, according to the different proportions of the grinding force and cutting force, the grinding cutting force model, with multi-particles, was established. Simulation and experimental results based on piezoelectric sensors showed that the proposed model could predict the intermittent grinding cutting force well. Moreover, the inclusion of the grit height coefficient and the effective grits number coefficient improved the modeling accuracy. The error between the simulation and experimental findings in grinding cutting force was reduced to 7.8% in comparison with the traditional model. In addition, the grinding cutting force can be divided into three segments; increasing, steadiness, and decreasing, respectively found through modeling. Full article

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10 pages, 8637 KiB

Open AccessArticle

Resonant Photoacoustic Spectroscopy of NO₂ with a UV-LED Based Sensor

by Johannes Kapp, Christian Weber, Katrin Schmitt, Hans-Fridtjof Pernau and Jürgen Wöllenstein

Sensors 2019, 19(3), 724; https://doi.org/10.3390/s19030724 - 11 Feb 2019

Cited by 22 | Viewed by 7695

Abstract

Nitrogen dioxide (NO₂) is a poisonous trace gas that requires monitoring in urban areas. Accurate measurement in sub-ppm concentrations represents a wide application field for suitable economical sensors. We present a novel approach to measure NO₂ with a photoacoustic sensor [...] Read more.

Nitrogen dioxide (NO₂) is a poisonous trace gas that requires monitoring in urban areas. Accurate measurement in sub-ppm concentrations represents a wide application field for suitable economical sensors. We present a novel approach to measure NO₂ with a photoacoustic sensor using a T-shaped resonance cell. An inexpensive UV-LED with a peak wavelength of 405 nm as radiation source as well as a commercial MEMS microphone for acoustic detection were used. In this work, a cell has been developed that enables a “non-contact” feedthrough of the divergent LED beam. Thus, unwanted background noise due to absorption on the inside walls is minimized. As part of the development, an acoustic simulation has been carried out to find the resonance frequencies and to visualize the resulting standing wave patterns in various geometries. The pressure amplitude was calculated for different shapes and sizes. A model iteratively optimized in this way forms the basis of a construction that was built for gas measurement by rapid prototyping methods. The real resonance frequencies were compared to the ones found in simulation. The limit of detection was determined in a nitrogen dioxide measurement to be 200 ppb (6 σ) for a cell made of aluminum. Full article

(This article belongs to the Collection Gas Sensors)

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12 pages, 3866 KiB

Open AccessArticle

A Wear Debris Segmentation Method for Direct Reflection Online Visual Ferrography

by Song Feng, Guang Qiu, Jiufei Luo, Leng Han, Junhong Mao and Yi Zhang

Sensors 2019, 19(3), 723; https://doi.org/10.3390/s19030723 - 11 Feb 2019

Cited by 12 | Viewed by 4554

Abstract

Wear debris in lube oil was observed using a direct reflection online visual ferrograph (OLVF) to monitor the machine running condition and judge wear failure online. The existing research has mainly concentrated on extraction of wear debris concentration and size according to ferrograms [...] Read more.

Wear debris in lube oil was observed using a direct reflection online visual ferrograph (OLVF) to monitor the machine running condition and judge wear failure online. The existing research has mainly concentrated on extraction of wear debris concentration and size according to ferrograms under transmitted light. Reports on the segmentation algorithm of the wear debris ferrograms under reflected light are lacking. In this paper, a wear debris segmentation algorithm based on edge detection and contour classification is proposed. The optimal segmentation threshold is obtained by an adaptive canny algorithm, and the contour classification filling method is applied to overcome the problems of excessive brightness or darkness of some wear debris that is often neglected by traditional segmentation algorithms such as the Otsu and Kittler algorithms. Full article

(This article belongs to the Special Issue Sensors for Prognostics and Health Management)

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22 pages, 5190 KiB

Open AccessArticle

Collective Anomalies Detection for Sensing Series of Spacecraft Telemetry with the Fusion of Probability Prediction and Markov Chain Model

by Jingyue Pang, Datong Liu, Yu Peng and Xiyuan Peng

Sensors 2019, 19(3), 722; https://doi.org/10.3390/s19030722 - 11 Feb 2019

Cited by 22 | Viewed by 4788

Abstract

Telemetry series, generally acquired from sensors, are the only basis for the ground management system to judge the working performance and health status of orbiting spacecraft. In particular, anomalies within telemetry can reflect sensor failure, transmission errors, and the major faults of the [...] Read more.

Telemetry series, generally acquired from sensors, are the only basis for the ground management system to judge the working performance and health status of orbiting spacecraft. In particular, anomalies within telemetry can reflect sensor failure, transmission errors, and the major faults of the related subsystem. Therefore, anomaly detection for telemetry series has drawn great attention from the aerospace area, where probability prediction methods, e.g., Gaussian process regression and relevance vector machine, have an inherent advantage for anomaly detection in time series with uncertainty presentation. However, labelling a single point with probability prediction faces many isolated false alarms, as well as a lower detection rate for collective anomalies that significantly limits its practical application. Simple sliding window fusion can decrease the false positives, but the support number of anomalies within the sliding window is difficult to set effectively for different series. Therefore, in this work, fused with the probability prediction-based method, the Markov chain is designed to compute the support probability of each testing series to realize the improvement on collective anomaly mode. The experiments on simulated data sets and the actual telemetry series validated the effectiveness and applicability of our proposed method. Full article

(This article belongs to the Special Issue Sensors for Prognostics and Health Management)

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19 pages, 2275 KiB

Open AccessArticle

Household Power Demand Prediction Using Evolutionary Ensemble Neural Network Pool with Multiple Network Structures

by Songpu Ai, Antorweep Chakravorty and Chunming Rong

Sensors 2019, 19(3), 721; https://doi.org/10.3390/s19030721 - 10 Feb 2019

Cited by 42 | Viewed by 5386

Abstract

The progress of technology on energy and IoT fields has led to an increasingly complicated electric environment in low-voltage local microgrid, along with the extensions of electric vehicle, micro-generation, and local storage. It is required to establish a home energy management system (HEMS) [...] Read more.

The progress of technology on energy and IoT fields has led to an increasingly complicated electric environment in low-voltage local microgrid, along with the extensions of electric vehicle, micro-generation, and local storage. It is required to establish a home energy management system (HEMS) to efficiently integrate and manage household energy micro-generation, consumption and storage, in order to realize decentralized local energy systems at the community level. Domestic power demand prediction is of great importance for establishing HEMS on realizing load balancing as well as other smart energy solutions with the support of IoT techniques. Artificial neural networks with various network types (e.g., DNN, LSTM/GRU based RNN) and other configurations are widely utilized on energy predictions. However, the selection of network configuration for each research is generally a case by case study achieved through empirical or enumerative approaches. Moreover, the commonly utilized network initialization methods assign parameter values based on random numbers, which cause diversity on model performance, including learning efficiency, forecast accuracy, etc. In this paper, an evolutionary ensemble neural network pool (EENNP) method is proposed to achieve a population of well-performing networks with proper combinations of configuration and initialization automatically. In the experimental study, power demand predictions of multiple households are explored in three application scenarios: optimizing potential network configuration set, forecasting single household power demand, and refilling missing data. The impacts of evolutionary parameters on model performance are investigated. The experimental results illustrate that the proposed method achieves better solutions on the considered scenarios. The optimized potential network configuration set using EENNP achieves a similar result to manual optimization. The results of household demand prediction and missing data refilling perform better than the naïve and simple predictors. Full article

(This article belongs to the Special Issue Intelligent Computing, Networking, Security and Robustness in Internet of Things)

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35 pages, 1306 KiB

Open AccessArticle

Energy/Area-Efficient Scalar Multiplication with Binary Edwards Curves for the IoT

by Carlos Andres Lara-Nino, Arturo Diaz-Perez and Miguel Morales-Sandoval

Sensors 2019, 19(3), 720; https://doi.org/10.3390/s19030720 - 10 Feb 2019

Cited by 9 | Viewed by 4900

Abstract

Making Elliptic Curve Cryptography (ECC) available for the Internet of Things (IoT) and related technologies is a recent topic of interest. Modern IoT applications transfer sensitive information which needs to be protected. This is a difficult task due to the processing power and [...] Read more.

Making Elliptic Curve Cryptography (ECC) available for the Internet of Things (IoT) and related technologies is a recent topic of interest. Modern IoT applications transfer sensitive information which needs to be protected. This is a difficult task due to the processing power and memory availability constraints of the physical devices. ECC mainly relies on scalar multiplication (kP)—which is an operation-intensive procedure. The broad majority of kP proposals in the literature focus on performance improvements and often overlook the energy footprint of the solution. Some IoT technologies—Wireless Sensor Networks (WSN) in particular—are critically sensitive in that regard. In this paper we explore energy-oriented improvements applied to a low-area scalar multiplication architecture for Binary Edwards Curves (BEC)—selected given their efficiency. The design and implementation costs for each of these energy-oriented techniques—in hardware—are reported. We propose an evaluation method for measuring the effectiveness of these optimizations. Under this novel approach, the energy-reducing techniques explored in this work contribute to achieving the scalar multiplication architecture with the most efficient area/energy trade-offs in the literature, to the best of our knowledge. Full article

(This article belongs to the Special Issue Privacy and Security for Resource Constrained IoT Devices and Networks)

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