Sensors

16 pages, 3276 KiB

Open AccessArticle

Methods for Simultaneous Robot-World-Hand–Eye Calibration: A Comparative Study

by Ihtisham Ali, Olli Suominen, Atanas Gotchev and Emilio Ruiz Morales

Sensors 2019, 19(12), 2837; https://doi.org/10.3390/s19122837 - 25 Jun 2019

Cited by 58 | Viewed by 10576

In this paper, we propose two novel methods for robot-world-hand–eye calibration and provide a comparative analysis against six state-of-the-art methods. We examine the calibration problem from two alternative geometrical interpretations, called ‘hand–eye’ and ‘robot-world-hand–eye’, respectively. The study analyses the effects of specifying the [...] Read more.

In this paper, we propose two novel methods for robot-world-hand–eye calibration and provide a comparative analysis against six state-of-the-art methods. We examine the calibration problem from two alternative geometrical interpretations, called ‘hand–eye’ and ‘robot-world-hand–eye’, respectively. The study analyses the effects of specifying the objective function as pose error or reprojection error minimization problem. We provide three real and three simulated datasets with rendered images as part of the study. In addition, we propose a robotic arm error modeling approach to be used along with the simulated datasets for generating a realistic response. The tests on simulated data are performed in both ideal cases and with pseudo-realistic robotic arm pose and visual noise. Our methods show significant improvement and robustness on many metrics in various scenarios compared to state-of-the-art methods. Full article

(This article belongs to the Special Issue Intelligent Systems and Sensors for Robotics)

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Formulations relating geometrical transformation for calibration; (a) hand–eye calibration; (b) robot-world-hand–eye Calibration. Full article ">Figure 2
An example of the setup for acquiring the datasets; (a) robotic arm moving in the workspace; (b) cameras and Lenses for data acquisition. Full article ">Figure 3
Example of captured images from the dataset 1 through 3; (a) checkerboard from dataset 1; (b) checkerboard from dataset 2; (c) ChArUco from dataset 3. Full article ">Figure 4
Example of rendered images for simulated datasets from the datasets 4 through 6; (a) excerpt from dataset 4; (b) excerpt from dataset 5; (c) excerpt from dataset 6. Full article ">Figure 5
Flowchart of the orientation noise modelling approach. Full article ">Figure 6
Probability distributions functions; (a) the measured position error from the robotic arm; (b) the modeled orientation error for the robotic arm. Full article ">Figure 7
Metric error results for Dataset 5 with constant robot pose noise; (a) mean rotation error; (b) mean translation error; (c) reprojection error; (d) absolute rotation error against ground truth; (e) absolute translation error against ground truth. Full article ">Figure 7 Cont.
Metric error results for Dataset 5 with constant robot pose noise; (a) mean rotation error; (b) mean translation error; (c) reprojection error; (d) absolute rotation error against ground truth; (e) absolute translation error against ground truth. Full article ">

22 pages, 2145 KiB

Open AccessArticle

AMiCUS—A Head Motion-Based Interface for Control of an Assistive Robot

by Nina Rudigkeit and Marion Gebhard

Sensors 2019, 19(12), 2836; https://doi.org/10.3390/s19122836 - 25 Jun 2019

Cited by 26 | Viewed by 4923

Abstract

Within this work we present AMiCUS, a Human-Robot Interface that enables tetraplegics to control a multi-degree of freedom robot arm in real-time using solely head motion, empowering them to perform simple manipulation tasks independently. The article describes the hardware, software and signal processing [...] Read more.

Within this work we present AMiCUS, a Human-Robot Interface that enables tetraplegics to control a multi-degree of freedom robot arm in real-time using solely head motion, empowering them to perform simple manipulation tasks independently. The article describes the hardware, software and signal processing of AMiCUS and presents the results of a volunteer study with 13 able-bodied subjects and 6 tetraplegics with severe head motion limitations. As part of the study, the subjects performed two different pick-and-place tasks. The usability was assessed with a questionnaire. The overall performance and the main control elements were evaluated with objective measures such as completion rate and interaction time. The results show that the mapping of head motion onto robot motion is intuitive and the given feedback is useful, enabling smooth, precise and efficient robot control and resulting in high user-acceptance. Furthermore, it could be demonstrated that the robot did not move unintendedly, giving a positive prognosis for safety requirements in the framework of a certification of a product prototype. On top of that, AMiCUS enabled every subject to control the robot arm, independent of prior experience and degree of head motion limitation, making the system available for a wide range of motion impaired users. Full article

(This article belongs to the Special Issue Assistance Robotics and Biosensors 2019)

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13 pages, 2256 KiB

Open AccessArticle

Real-time Precise Point Positioning with a Xiaomi MI 8 Android Smartphone

by Bo Chen, Chengfa Gao, Yongsheng Liu and Puyu Sun

Sensors 2019, 19(12), 2835; https://doi.org/10.3390/s19122835 - 25 Jun 2019

Cited by 97 | Viewed by 8791

Abstract

The Global Navigation Satellite System (GNSS) positioning technology using smartphones can be applied to many aspects of mass life, and the world’s first dual-frequency GNSS smartphone Xiaomi MI 8 represents a new trend in the development of GNSS positioning technology with mobile phones. [...] Read more.

The Global Navigation Satellite System (GNSS) positioning technology using smartphones can be applied to many aspects of mass life, and the world’s first dual-frequency GNSS smartphone Xiaomi MI 8 represents a new trend in the development of GNSS positioning technology with mobile phones. The main purpose of this work is to explore the best real-time positioning performance that can be achieved on a smartphone without reference stations. By analyzing the GNSS raw measurements, it is found that all the three mobile phones tested have the phenomenon that the differences between pseudorange observations and carrier phase observations are not fixed, thus a PPP (precise point positioning) method is modified accordingly. Using a Xiaomi MI 8 smartphone, the modified real-time PPP positioning strategy which estimates two clock biases of smartphone was applied. The results show that using multi-GNSS systems data can effectively improve positioning performance; the average horizontal and vertical RMS positioning error are 0.81 and 1.65 m respectively (using GPS, BDS, and Galileo data); and the time required for each time period positioning errors in N and E directions to be under 1 m is less than 30s. Full article

(This article belongs to the Section Remote Sensors)

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Mobile phones and geodetic receivers at the site of first and third dataset. There is a plastic board on the top of the middle tripod, and smartphones are placed on the board. Full article ">Figure 2
The control point named GE01 at Southeast University Jiulonghu Campus. The precise coordinates of this control point are obtained by a geodesic receiver through the network RTK positioning method. (a) Distant view of the control point; (b) Close-up of the control point; (c) A Xiaomi MI 8 smartphone placed on the control point. Full article ">Figure 3
The pseudorange and carrier phase observations (BDS 02 satellite) of a geodetic receiver and a Huawei P10 smartphone. (a) The observations of a geodetic receiver; (b) The observations of a Huawei P10 smartphone. The actual acquired carrier phase of smartphones is a set of data that is cumulatively incremented from 0 m at the beginning of observation, thus the values are small. In this figure, the mobile phone carrier phase values are added a constant. Full article ">Figure 4
The observations (Galileo 03 satellite) and its change rate of a Xiaomi MI 8 smartphone. (a) The raw observations; (b) The change rate of observations. Full article ">Figure 5
The differences between pseudorange change rate and carrier phase change rate of all GNSS satellites of a Huawei P10 smartphone and a Xiaomi MI 8 smartphone (L1/E1 frequency). (a) Huawei P10 smartphone; (b) Xiaomi MI 8 smartphone (L1/E1 frequency). Full article ">Figure 6
The North (N), East (E), and Up (U) direction errors of precise point positioning (PPP) positioning results of the five time periods. (a) 1st time period (G + C + E); (b) 2nd time period (G + C + E); (c) 3rd time period (G + C + E); (d) 4th time period (G + C + E); (e) 5th time period (G + C + E); (f) 1st time period (GPS); (g) 2nd time period (GPS); (h) 4th time period (GPS). The “G”, “C” and “E” denote GPS, BDS, and Galileo. Full article ">

11 pages, 3297 KiB

Open AccessArticle

Nano-Cracked Strain Sensor with High Sensitivity and Linearity by Controlling the Crack Arrangement

by Hyunsuk Jung, Chan Park, Hyunwoo Lee, Seonguk Hong, Hyonguk Kim and Seong J. Cho

Sensors 2019, 19(12), 2834; https://doi.org/10.3390/s19122834 - 25 Jun 2019

Cited by 30 | Viewed by 7697

Abstract

Studies on wearable sensors that monitor various movements by attaching them to a body have received considerable attention. Crack-based strain sensors are more sensitive than other sensors. Owing to their high sensitivity, these sensors have been investigated for measuring minute deformations occurring on [...] Read more.

Studies on wearable sensors that monitor various movements by attaching them to a body have received considerable attention. Crack-based strain sensors are more sensitive than other sensors. Owing to their high sensitivity, these sensors have been investigated for measuring minute deformations occurring on the skin, such as pulse. However, existing studies have limited sensitivity at low strain range and nonlinearity that renders any calibration process complex and difficult. In this study, we propose a pre-strain and sensor-extending process to improve the sensitivity and linearity of the sensor. By using these pre-strain and sensor-extending processes, we were able to control the morphology and alignment of cracks and regulate the sensitivity and linearity of the sensor. Even if the sensor was fabricated in the same manner, the sensor that involved the pre-strain and extending processes had a sensitivity 100 times greater than normal sensors. Thus, our crack-based strain sensor had high sensitivity (gauge factor > 5000, gauge factor (GF = (△R/R₀)/ε), linearity, and low hysteresis at low strain (<1% strain). Given its high sensing performance, the sensor can be used to measure micro-deformation, such as pulse wave and voice. Full article

(This article belongs to the Section Sensor Materials)

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(a) Fabrication process of the crack-based strain sensor. (b) Schematic of the four sensor types and their pre-processing prior to measurement. (c) Relative change in resistance of the four sensor types under 1% strain. Full article ">Figure 2
(a) Schematic of the sensor-evaluating system. (b) Schematic of the sensor. Full article ">Figure 3
(a) Schematic of the pre-strained sensor and its scanning electron microscope (SEM) images. (b) Previous strain’s resistance value affects the following strain’s resistance value, (c) Shortcoming of pre-strained sensor, (d) Schematic of the sensor-extending process, its concept and SEM images of the extended sensor, (e) Strain-relative change in resistance graph according to sensor-extending, (f) Shortcoming of sensor-extending, high initial resistance. Full article ">Figure 4
(a) Relative resistance change of the four sensor types under 1% strain. (b) Gauge factor at 0.6% and 1% strain according to the pre-strain percentage under 1% sensor extension. (c) Relative resistance change under 20% strain: red line box, pre-strain 20% and sensor-extending 2% under 1% strain; orange dotted line box, pre-strain 20% and sensor-extending 3% under 1% strain. (d) Relative resistance change under 10% strain: red line box, pre-strain 10% and sensor-extending 2% under 1% strain; orange dotted line box, pre-strain 10% and sensor-extending 3% under 1% strain. Full article ">Figure 5
(a) Relative resistance change during the cycling at the 0–1% strain. (b) Relative resistance change during 2000 cycles (inlet: resistance change at specific cycles). (c) High GF strain sensor after the pre-strain and sensor-extending processes. (d) Linear strain sensor after the pre-strain and sensor-extending processes. Full article ">Figure 6
(a) Schematic of the sensor attached on a speaker, generating 60 BPM metronome. (b–c) Difference in the relative resistance change between with and without the hybrid process. (d) Relative resistance change when PU bead loading and unloading. (e) Relative resistance change of the pulse signal (inlet: photograph of the attached spot). Full article ">

16 pages, 4898 KiB

Open AccessArticle

Improving Optical Measurements: Non-Linearity Compensation of Compact Charge-Coupled Device (CCD) Spectrometers

by Münevver Nehir, Carsten Frank, Steffen Aßmann and Eric P. Achterberg

Sensors 2019, 19(12), 2833; https://doi.org/10.3390/s19122833 - 25 Jun 2019

Cited by 20 | Viewed by 10813

Abstract

Charge-coupled device (CCD) spectrometers are widely used as detectors in analytical laboratory instruments and as sensors for in situ optical measurements. However, as the applications become more complex, the physical and electronic limits of the CCD spectrometers may restrict their applicability. The errors [...] Read more.

Charge-coupled device (CCD) spectrometers are widely used as detectors in analytical laboratory instruments and as sensors for in situ optical measurements. However, as the applications become more complex, the physical and electronic limits of the CCD spectrometers may restrict their applicability. The errors due to dark currents, temperature variations, and blooming can be readily corrected. However, a correction for uncertainty of integration time and wavelength calibration is typically lacking in most devices, and detector non-linearity may distort the signal by up to 5% for some measurements. Here, we propose a simple correction method to compensate for non-linearity errors in optical measurements where compact CCD spectrometers are used. The results indicate that the error due to the non-linearity of a spectrometer can be reduced from several hundred counts to about 40 counts if the proposed correction function is applied. Full article

(This article belongs to the Section Physical Sensors)

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26 pages, 1046 KiB

Open AccessArticle

PALOT: Profiling and Authenticating Users Leveraging Internet of Things

by Pantaleone Nespoli, Mattia Zago, Alberto Huertas Celdrán, Manuel Gil Pérez, Félix Gómez Mármol and Félix J. García Clemente

Sensors 2019, 19(12), 2832; https://doi.org/10.3390/s19122832 - 25 Jun 2019

Cited by 15 | Viewed by 5663

Abstract

Continuous authentication was introduced to propose novel mechanisms to validate users’ identity and address the problems and limitations exposed by traditional techniques. However, this methodology poses several challenges that remain unsolved. In this paper, we present a novel framework, PALOT, that leverages IoT [...] Read more.

Continuous authentication was introduced to propose novel mechanisms to validate users’ identity and address the problems and limitations exposed by traditional techniques. However, this methodology poses several challenges that remain unsolved. In this paper, we present a novel framework, PALOT, that leverages IoT to provide context-aware, continuous and non-intrusive authentication and authorization services. To this end, we propose a formal information system model based on ontologies, representing the main source of knowledge of our framework. Furthermore, to recognize users’ behavioral patterns within the IoT ecosystem, we introduced a new module called “confidence manager”. The module is then integrated into an extended version of our early framework architecture, IoTCAF, which is consequently adapted to include the above-mentioned component. Exhaustive experiments demonstrated the efficacy, feasibility and scalability of the proposed solution. Full article

(This article belongs to the Special Issue Sensor Systems for Internet of Things)

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16 pages, 8221 KiB

Open AccessArticle

3D Pose Detection of Closely Interactive Humans Using Multi-View Cameras

by Xiu Li, Zhen Fan, Yebin Liu, Yipeng Li and Qionghai Dai

Sensors 2019, 19(12), 2831; https://doi.org/10.3390/s19122831 - 25 Jun 2019

Cited by 18 | Viewed by 6350

Abstract

We propose a method to automatically detect 3D poses of closely interactive humans from sparse multi-view images at one time instance. It is a challenging problem due to the strong partial occlusion and truncation between humans and no tracking process to provide priori [...] Read more.

We propose a method to automatically detect 3D poses of closely interactive humans from sparse multi-view images at one time instance. It is a challenging problem due to the strong partial occlusion and truncation between humans and no tracking process to provide priori poses information. To solve this problem, we first obtain 2D joints in every image using OpenPose and human semantic segmentation results from Mask R-CNN. With the 3D joints triangulated from multi-view 2D joints, a two-stage assembling method is proposed to select the correct 3D pose from thousands of pose seeds combined by joint semantic meanings. We further present a novel approach to minimize the interpenetration between human shapes with close interactions. Finally, we test our method on multi-view human-human interaction (MHHI) datasets. Experimental results demonstrate that our method achieves high visualized correct rate and outperforms the existing method in accuracy and real-time capability. Full article

(This article belongs to the Special Issue Multi-Modal Sensors for Human Behavior Monitoring)

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18 pages, 5542 KiB

Open AccessArticle

Analyses of Time Series InSAR Signatures for Land Cover Classification: Case Studies over Dense Forestry Areas with L-Band SAR Images

by Hye-Won Yun, Jung-Rack Kim, Yun-Soo Choi and Shih-Yuan Lin

Sensors 2019, 19(12), 2830; https://doi.org/10.3390/s19122830 - 25 Jun 2019

Cited by 16 | Viewed by 3382

Abstract

As demonstrated in prior studies, InSAR holds great potential for land cover classification, especially considering its wide coverage and transparency to climatic conditions. In addition to features such as backscattering coefficient and phase coherence, the temporal migration in InSAR signatures provides information that [...] Read more.

As demonstrated in prior studies, InSAR holds great potential for land cover classification, especially considering its wide coverage and transparency to climatic conditions. In addition to features such as backscattering coefficient and phase coherence, the temporal migration in InSAR signatures provides information that is capable of discriminating types of land cover in target area. The exploitation of InSAR signatures was expected to provide merits to trace land cover change in extensive areas; however, the extraction of suitable features from InSAR signatures was a challenging task. Combining time series amplitudes and phase coherences through linear and nonlinear compressions, we showed that the InSAR signatures could be extracted and transformed into reliable classification features for interpreting land cover types. The prototype was tested in mountainous areas that were covered with a dense vegetation canopy. It was demonstrated that InSAR time series signature analyses reliably identified land cover types and also recognized tracing of temporal land cover change. Based on the robustness of the developed scheme against the temporal noise components and the availability of advanced spatial and temporal resolution SAR data, classification of finer land cover types and identification of stable scatterers for InSAR time series techniques can be expected. The advanced spatial and temporal resolution of future SAR assets combining the scheme in this study can be applicable for various important applications including global land cover changes monitoring. Full article

(This article belongs to the Section Remote Sensors)

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17 pages, 19875 KiB

Open AccessArticle

A Dark Target Detection Method Based on the Adjacency Effect: A Case Study on Crack Detection

by Li Yu, Yugang Tian and Wei Wu

Sensors 2019, 19(12), 2829; https://doi.org/10.3390/s19122829 - 25 Jun 2019

Cited by 7 | Viewed by 3893

Abstract

Dark target detection is important for engineering applications but the existing methods do not consider the imaging environment of dark targets, such as the adjacency effect. The adjacency effect will affect the quantitative applications of remote sensing, especially for high contrast images and [...] Read more.

Dark target detection is important for engineering applications but the existing methods do not consider the imaging environment of dark targets, such as the adjacency effect. The adjacency effect will affect the quantitative applications of remote sensing, especially for high contrast images and images with ever-increasing resolution. Further, most studies have focused on how to eliminate the adjacency effect and there is almost no research about the application of the adjacency effect. However, the adjacency effect leads to some unique characteristics for the dark target surrounded by a bright background. This paper utilizes these characteristics to assist in the detection of the dark object, and the low-high threshold detection strategy and the adaptive threshold selection method under the assumption of Gaussian distribution are designed. Meanwhile, preliminary case experiments are carried out on the crack detection of concrete slope protection. Finally, the experiment results show that it is feasible to utilize the adjacency effect for dark target detection. Full article

(This article belongs to the Special Issue Advance and Applications of RGB Sensors)

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15 pages, 952 KiB

Open AccessArticle

An Evaluation Method of Safe Driving for Senior Adults Using ECG Signals

by Dong-Woo Koh and Sang-Goog Lee

Sensors 2019, 19(12), 2828; https://doi.org/10.3390/s19122828 - 25 Jun 2019

Cited by 11 | Viewed by 4012

Abstract

The elderly are more susceptible to stress than younger people. In particular, heart palpitations are one of the causes of heart failure, which can lead to serious accidents. To prevent heart palpitations, we have devised the Safe Driving Intensity (SDI) and Cardiac Reaction [...] Read more.

The elderly are more susceptible to stress than younger people. In particular, heart palpitations are one of the causes of heart failure, which can lead to serious accidents. To prevent heart palpitations, we have devised the Safe Driving Intensity (SDI) and Cardiac Reaction Time (CRT) as new methods of estimating the correlations between effects on the driver’s heart and the movement of a vehicle. In SDI measurement, recommended acceleration value of vehicle for safe driving is inferred from the suggested correlation algorithm using machine learning. A higher SDI value than other people means less pressure on the heart. CRT is an estimated value of the occurring time of heart palpitations caused by stressful driving. In particular, it is proved by SDI that elderly subjects tend to overestimate their driving abilities in personal assessment questionnaires. Furthermore, we validated our SDI using other general statistical methods. When comparing the results using a t-test, we obtained reliable results for the equivalent variance. Our results can be used as a basis for evaluating elderly people’s driving ability, as well as allowing for the implementation of a personalized safe driving system for the elderly. Full article

(This article belongs to the Special Issue Sensors for Biopotential, Physiological and Biomedical Monitoring)

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Illustration of the SDI and CRT, which are correlated interactions between (A) and (B). It is an important measure to evaluate safe driving ability. The portable Shimmer3 EEG unit(Shimmer, Dublin, Ireland) was used to monitor the ECG signal while driving (C). Full article ">Figure 2
Experimental stages. Data were collected over the course of 11 minutes divided into three stages. During the main stage of the experiment (stressful driving; 500 seconds), the subjects were instructed to drive a vehicle on a difficult course with sharp turns. During the initial (before-driving) and final (after-driving) stages of the experiment, the subjects were instructed to relax. Full article ">Figure 3
Sample ECG original signals that exhibit big differences between young and elderly subjects. The QRS amplitude of elderly people tends to be weaker than that of young people. Full article ">Figure 4
#n points of maximum acceleration within MTW (30 s, Maximum Time Window). These moments were considered to be most stressful driving moment, which cause heart palpitations. Full article ">Figure 5
Main algorithm of SDI/CRT. Full article ">Figure 6
Procedure for obtaining the SDI and CRT. As shown here, the SDI is originated from the acceleration value and the CRT is the averaged distance between maximum the acceleration value within the MTW and each clustering heart palpitations RR interval value. Full article ">Figure 7
Histogram of the heart palpitation summation at every acceleration value per 0.1 m/s<math display="inline"><semantics> <msup> <mrow/> <mn>2</mn> </msup> </semantics></math>. As shown here, the safe driving intensity value is 3.1 according to the highest gap obtained using this method. Full article ">

18 pages, 6685 KiB

Open AccessArticle

Acoustic Impulsive Noise Based on Non-Gaussian Models: An Experimental Evaluation

by Danilo Pena, Carlos Lima, Matheus Dória, Luan Pena, Allan Martins and Vicente Sousa

Sensors 2019, 19(12), 2827; https://doi.org/10.3390/s19122827 - 25 Jun 2019

Cited by 13 | Viewed by 4253

Abstract

In general, acoustic channels are not Gaussian distributed neither are second-order stationary. Considering them for signal processing methods designed for Gaussian assumptions is inadequate, consequently yielding in poor performance of such methods. This paper presents an analysis for audio signal corrupted by impulsive [...] Read more.

In general, acoustic channels are not Gaussian distributed neither are second-order stationary. Considering them for signal processing methods designed for Gaussian assumptions is inadequate, consequently yielding in poor performance of such methods. This paper presents an analysis for audio signal corrupted by impulsive noise using non-Gaussian models. Audio samples are compared to the Gaussian,

α

-stable and Gaussian mixture models, evaluating the fitting by graphical and numerical methods. We discuss fitting properties as the window length and the overlap, finally concluding that the

α

-stable model has the best fit for all tested scenarios. Full article

(This article belongs to the Section Intelligent Sensors)

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22 pages, 5391 KiB

Open AccessArticle

Conservative Sensor Error Modeling Using a Modified Paired Overbound Method and its Application in Satellite-Based Augmentation Systems

by Yan Zhang, Zhibin Xiao, Pengpeng Li, Xiaomei Tang and Gang Ou

Sensors 2019, 19(12), 2826; https://doi.org/10.3390/s19122826 - 24 Jun 2019

Cited by 5 | Viewed by 3471

Abstract

Conservative sensor error modeling is of great significance in the field of safety-of-life. At present, the overbound method has been widely used in areas such as satellite-based augmentation systems (SBASs) and ground-based augmentation systems (GBASs) that provide integrity service. It can effectively solve [...] Read more.

Conservative sensor error modeling is of great significance in the field of safety-of-life. At present, the overbound method has been widely used in areas such as satellite-based augmentation systems (SBASs) and ground-based augmentation systems (GBASs) that provide integrity service. It can effectively solve the difficulties of non-Gaussian and non-zero mean error modeling and confidence interval estimation of user position error. However, there is still a problem in that the model is too conservative and leads to the lack of availability. In order to further improve the availability of SBASs, an improved paired overbound method is proposed in this paper. Compared with the traditional method, the improved algorithm no longer requires the overbound function to conform to the characteristics of the probability distribution function, so that under the premise of ensuring the integrity of the system, the real error characteristics can be more accurately modeled and measured. The experimental results show that the modified paired overbound method can improve the availability of the system with a probability of about 99%. In view of the fact that conservative error modeling is more sensitive to large deviations, this paper analyzes the robustness of the improved algorithm in the case of abnormal data loss. The maximum deviation under a certain integrity risk is used to illustrate the effectiveness of the improved paired overbound method compared with the original method. Full article

(This article belongs to the Special Issue Wireless Networks for Real Time Communication)

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17 pages, 24052 KiB

Open AccessArticle

Microwave Staring Correlated Imaging Based on Unsteady Aerostat Platform

by Zheng Jiang, Yuanyue Guo, Jie Deng, Weidong Chen and Dongjin Wang

Sensors 2019, 19(12), 2825; https://doi.org/10.3390/s19122825 - 24 Jun 2019

Cited by 4 | Viewed by 3543

Abstract

Microwave staring correlated imaging (MSCI), with the technical capability of high-resolution imaging on relatively stationary targets, is a promising approach for remote sensing. For the purpose of continuous observation of a fixed key area, a tethered floating aerostat is often used as the [...] Read more.

Microwave staring correlated imaging (MSCI), with the technical capability of high-resolution imaging on relatively stationary targets, is a promising approach for remote sensing. For the purpose of continuous observation of a fixed key area, a tethered floating aerostat is often used as the carrying platform for MSCI radar system; however, its non-cooperative random motion of the platform caused by winds and its unbalance will result in blurred imaging, and even in imaging failure. This paper presents a method that takes into account the instabilities of the platform, combined with an adaptive variable suspension (AVS) and a position and orientation system (POS), which can automatically control the antenna beam orientation to the target area and measure dynamically the position and attitude of the stochastic radiation radar array, respectively. By analyzing the motion feature of aerostat platform, the motion model of the radar array is established, then its real-time position vector and attitude angles of each antenna can be represented; meanwhile the selection matrix of beam coverage is introduced to indicate the dynamic illumination of the radar antenna beam in the overall imaging area. Due to the low-speed discrete POS data, a curve-fitting algorithm can be used to estimate its accurate position vector and attitude of each antenna at each high-speed sampling time during the imaging period. Finally, the MSCI model based on the unsteady aerostat platform is set up. In the simulations, the proposed scheme is validated such that under the influence of different unstable platform movements, a better imaging performance can be achieved compared with the conventional MSCI method. Full article

(This article belongs to the Special Issue Recent Advancements in Radar Imaging and Sensing Technology)

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13 pages, 2602 KiB

Open AccessArticle

Facile Non-Enzymatic Electrochemical Sensing for Glucose Based on Cu₂O–BSA Nanoparticles Modified GCE

by Zhikuang Dai, Ailing Yang, Xichang Bao and Renqiang Yang

Sensors 2019, 19(12), 2824; https://doi.org/10.3390/s19122824 - 24 Jun 2019

Cited by 31 | Viewed by 5540

Abstract

Transition-metal nanomaterials are very important to non-enzymatic glucose sensing because of their excellent electrocatalytic ability, good selectivity, the fact that they are not easily interfered with by chloride ion (Cl⁻), and low cost. However, the linear detection range needs to be [...] Read more.

Transition-metal nanomaterials are very important to non-enzymatic glucose sensing because of their excellent electrocatalytic ability, good selectivity, the fact that they are not easily interfered with by chloride ion (Cl⁻), and low cost. However, the linear detection range needs to be expanded. In this paper, Cu₂O–bovine serum albumin (BSA) core-shell nanoparticles (NPs) were synthesized for the first time in air at room temperature by a facile and green route. The structure and morphology of Cu₂O–BSA NPs were characterized. The as-prepared Cu₂O–BSA NPs were used to modify the glassy carbon electrode (GCE) in a Nafion matrix. By using cyclic voltammetry (CV), the influence from scanning speed, concentration of NaOH, and load of Cu₂O–BSA NPs for the modified electrodes was probed. Cu₂O–BSA NPs showed direct electrocatalytic activity for the oxidation of glucose in 50 mM NaOH solution at 0.6 V. The chronoamperometry result showed this constructing sensor in the detection of glucose with a lowest detection limit of 0.4 μM, a linear detection range up to 10 mM, a high sensitivity of 1144.81 μAmM⁻¹cm⁻² and reliable anti-interference property to Cl⁻, uric acid (UA), ascorbic acid (AA), and acetaminophen (AP). Cu₂O–BSA NPs are promising nanostructures for the fabrication of non-enzymatic glucose electrochemical sensing devices. Full article

(This article belongs to the Special Issue Electrochemical Nanobiosensors)

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Graphical abstract

Graphical abstract
Full article ">Figure 1
TEM images (A–C) and XRD pattern (D) of Cu2O–BSA NPs. The red lines in D are the standard peaks (PDF No. 65-3288) of Cu2O. Full article ">Figure 2
(A) Redox peaks of the present Nafion/Cu2O–BSA/GCE in the 50 mM NaOH solution with 0 (a) and 2 mM (b) of glucose at the scan rate of 5 mV/s, (B) Nafion/Cu2O–BSA/GCE and Nafion/GCE (inset) in the absence (a and c) and presence (b and d) of 5.0 mM glucose at the same pH with scanning speed of 50 mV/s. Full article ">Figure 3
(A) CVs of the Nafion/Cu2O–BSA/GCE in 50 mM NaOH solution with 2 mM of glucose at different scan rates, (B) Linear dependence of oxidation and reduction peak current densities in (A) with the scan rates, (C) CVs at different concentrations of NaOH, (D) Current density changing with the loads of Cu2O–BSA NPs modified on the GCE. 2 mM of glucose and 50 mV/s scan rate in (C) and (D). Full article ">Figure 4
Chroamperometric response (A), calibration curve (B) and detection limit (C) of Nafion/Cu2O–BSA/GCE for successive addition of various concentrations of glucose to 50 mM NaOH solution at 0.6 V. Full article ">Figure 5
(A) Chroamperometric response of Nafion/Cu2O–BSA/GCE to glucose in 0 M (a) and 0.1 M (b) chloride ions; (B) Interference test of Nafion/Cu2O–BSA/GCE to 0.3 mM UA, 0.1 mM AA and 0.1 mM AP in 50 m NaOH at 0.6 V. Full article ">Figure 6
Amperometric response of Nafion/Cu2O–BSA/GCE to glucose over time. Full article ">

18 pages, 3766 KiB

Open AccessArticle

Trajectory Optimization in a Cooperative Aerial Reconnaissance Model

by Petr Stodola, Jan Drozd, Jan Nohel, Jan Hodický and Dalibor Procházka

Sensors 2019, 19(12), 2823; https://doi.org/10.3390/s19122823 - 24 Jun 2019

Cited by 13 | Viewed by 3559

Abstract

In recent years, the use of modern technology in military operations has become standard practice. Unmanned systems play an important role in operations such as reconnaissance and surveillance. This article examines a model for planning aerial reconnaissance using a fleet of mutually cooperating [...] Read more.

In recent years, the use of modern technology in military operations has become standard practice. Unmanned systems play an important role in operations such as reconnaissance and surveillance. This article examines a model for planning aerial reconnaissance using a fleet of mutually cooperating unmanned aerial vehicles to increase the effectiveness of the task. The model deploys a number of waypoints such that, when every waypoint is visited by any vehicle in the fleet, the area of interest is fully explored. The deployment of waypoints must meet the conditions arising from the technical parameters of the sensory systems used and tactical requirements of the task at hand. This paper proposes an improvement of the model by optimizing the number and position of waypoints deployed in the area of interest, the effect of which is to improve the trajectories of individual unmanned systems, and thus increase the efficiency of the operation. To achieve this optimization, a modified simulated annealing algorithm is proposed. The improvement of the model is verified by several experiments. Two sets of benchmark problems were designed: (a) benchmark problems for verifying the proposed algorithm for optimizing waypoints, and (b) benchmark problems based on typical reconnaissance scenarios in the real environment to prove the increased effectiveness of the reconnaissance operation. Moreover, an experiment in the SteelBeast simulation system was also conducted. Full article

(This article belongs to the Special Issue Deployment and Navigation of Aerial Drones for Surveillance and Monitoring)

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15 pages, 20848 KiB

Open AccessArticle

Characterization of Nile Red as a Tracer for Laser-Induced Fluorescence Spectroscopy of Gasoline and Kerosene and Their Mixture with Biofuels

by Matthias Koegl, Christopher Mull, Kevin Baderschneider, Jan Wislicenus, Stefan Will and Lars Zigan

Sensors 2019, 19(12), 2822; https://doi.org/10.3390/s19122822 - 24 Jun 2019

Cited by 18 | Viewed by 5121

Abstract

Suitable fluorescence tracers (“dyes”) are needed for the planar measurement of droplet sizes by using a combination of laser-induced fluorescence (LIF) and Mie scattering. Currently, no suitable tracers have been characterized for application in planar droplet sizing in gasoline and kerosene fuels, as [...] Read more.

Suitable fluorescence tracers (“dyes”) are needed for the planar measurement of droplet sizes by using a combination of laser-induced fluorescence (LIF) and Mie scattering. Currently, no suitable tracers have been characterized for application in planar droplet sizing in gasoline and kerosene fuels, as well as biofuel blends. One promising tracer is nile red, which belongs to the fluorophore group. For its utilization for droplet size measurements, preliminary characterization of the fluorescence of the respective fuel tracer mixtures are mandatory. For this purpose, the fluorescence and absorption behavior of nile red dissolved in the surrogate fuels Toliso and Jet A-1 as well as in biofuel blends was investigated. The fluorescence signal for nile red that was dissolved in the two base fuels Toliso and Jet A-1 showed a linear behavior as a function of dye concentration. The temperature effect on spectral absorption and emission of nile red was investigated in a specially designed test cell. An ethanol admixture to Toliso led to a spectral shift towards higher wavelengths. The absorption and emission bands were shifted towards lower wavelengths with increasing temperature for all fuels. Both absorption and fluorescence decreased with increasing temperature for all fuels, except for E20, which showed an increased fluorescence signal with increasing temperature. Jet A-1 and its blends with hydroprocessed esters and fatty acids (HEFA) and farnesane did not exhibit explicit variations in spectral absorption or emission, but these blends showed a more distinct temperature dependence compared to the Toliso-ethanol-blends. The effect of photo-dissociation of the LIF signal of the fuel tracer mixtures was studied, and all fuel mixtures besides Toliso showed a more or less distinct decay in the fluorescence signal with time. In summary, all investigated fuel-tracer mixtures are suitable for LIF/Mie ratio droplet sizing in combination with nile red at moderate temperatures and low evaporation cooling rates. Full article

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Figure 1
Optical arrangement of the laser-induced fluorescence (LIF)-setup (left); detail of the internal design of the microcell (right). Full article ">Figure 2
Emission spectra of nile red (left: normalized to maximum intensity at 9.38 mg/L; right: all spectra normalized to their respective maximum value; inserted diagram showing linearity of the integral LIF-signal) for various dye concentrations in Toliso and Jet A-1, 293 K, 0.1 MPa Full article ">Figure 3
Normalized absorption (left curves) and emission spectra (right) for nile red (9.38 mg/L) in Toliso at various temperatures, 0.1 MPa. (Please note that the absorption signal is divided by a factor of two for clarity). Full article ">Figure 4
Spectral absorption and emission spectra for nile red (9.38 mg/L) in various fuels at various temperatures, 0.1 MPa. (Please note that the absorption signal is divided by a factor of two for clarity). Full article ">Figure 5
Normalized integral fluorescence intensities of the dye nile red in the investigated fuels for various temperatures, 0.1 MPa. All standard deviations are <0.5% and are smaller than the symbols. The moderate temperature domain is marked grey. Full article ">Figure 6
Normalized absorption and emission spectra for nile red (9.375 mg/L) for various automotive (a) and aviation (b) fuel mixtures. (Please note that the absorption signal is divided by a factor of two for clarity). Normalized absorption spectra (c) of the investigated fuel-dye mixtures; all spectra are normalized to the maximum absorption of E40; normalized emission spectra (d) of the investigated fuel-dye mixtures; all spectra are normalized to the maximum signal of E20, 293 K, 0.1 MPa. Full article ">Figure 7
Photo-bleaching effect of the investigated fuel-dye mixtures at 293 K, 0.1 MPa. All standard deviations are <0.5% and are smaller than the symbols. Full article ">

11 pages, 4734 KiB

Open AccessArticle

Trimodal Waveguide Demonstration and Its Implementation as a High Order Mode Interferometer for Sensing Application

by Jhonattan C. Ramirez, Lucas H. Gabrielli, Laura M. Lechuga and Hugo E. Hernandez-Figueroa

Sensors 2019, 19(12), 2821; https://doi.org/10.3390/s19122821 - 24 Jun 2019

Cited by 15 | Viewed by 3274

Abstract

This work implements and demonstrates an interferometric transducer based on a trimodal optical waveguide concept. The readout signal is generated from the interference between the fundamental and second-order modes propagating on a straight polymer waveguide. Intuitively, the higher the mode order, the larger [...] Read more.

This work implements and demonstrates an interferometric transducer based on a trimodal optical waveguide concept. The readout signal is generated from the interference between the fundamental and second-order modes propagating on a straight polymer waveguide. Intuitively, the higher the mode order, the larger the fraction of power (evanescent field) propagating outside the waveguide core, hence the higher the sensitivity that can be achieved when interfering against the strongly confined fundamental mode. The device is fabricated using the polymer SU-8 over a SiO₂ substrate and shows a free spectral range of 20.2 nm and signal visibility of 5.7 dB, reaching a sensitivity to temperature variations of 0.0586 dB/°C. The results indicate that the proposed interferometer is a promising candidate for highly sensitive, compact and low-cost photonic transducer for implementation in different types of sensing applications, among these, point-of-care. Full article

(This article belongs to the Section Optical Sensors)

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16 pages, 1436 KiB

Open AccessArticle

Autonomic Nervous System Response during Light Physical Activity in Adolescents with Anorexia Nervosa Measured by Wearable Devices

by Lucia Billeci, Alessandro Tonacci, Elena Brunori, Rossella Raso, Sara Calderoni, Sandra Maestro and Maria Aurora Morales

Sensors 2019, 19(12), 2820; https://doi.org/10.3390/s19122820 - 24 Jun 2019

Cited by 15 | Viewed by 4948

Abstract

Anorexia nervosa (AN) is associated with a wide range of disturbances of the autonomic nervous system. The aim of the present study was to monitor the heart rate (HR) and the heart rate variability (HRV) during light physical activity in a group of [...] Read more.

Anorexia nervosa (AN) is associated with a wide range of disturbances of the autonomic nervous system. The aim of the present study was to monitor the heart rate (HR) and the heart rate variability (HRV) during light physical activity in a group of adolescent girls with AN and in age-matched controls using a wearable, minimally obtrusive device. For the study, we enrolled a sample of 23 adolescents with AN and 17 controls. After performing a 12-lead electrocardiogram and echocardiography, we used a wearable device to record a one-lead electrocardiogram for 5 min at baseline for 5 min during light physical exercise (Task) and for 5 min during recovery. From the recording, we extracted HR and HRV indices. Among subjects with AN, the HR increased at task and decreased at recovery, whereas among controls it did not change between the test phases. HRV features showed a different trend between the two groups, with an increased low-to-high frequency ratio (LF/HF) in the AN group due to increased LF and decreased HF, differently from controls that, otherwise, slightly increased their standard deviation of NN intervals (SDNN) and the root mean square of successive differences (RMSSD). The response in the AN group during the task as compared to that of healthy adolescents suggests a possible sympathetic activation or parasympathetic withdrawal, differently from controls. This result could be related to the low energy availability associated to the excessive loss of fat and lean mass in subjects with AN, that could drive to autonomic imbalance even during light physical activity. Full article

(This article belongs to the Special Issue Wearable Sensors and Devices for Healthcare Applications)

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22 pages, 12660 KiB

Open AccessArticle

An Investigation on a Quantitative Tomographic SHM Technique for a Containment Liner Plate in a Nuclear Power Plant with Guided Wave Mode Selection

by Yonghee Lee and Younho Cho

Sensors 2019, 19(12), 2819; https://doi.org/10.3390/s19122819 - 24 Jun 2019

Cited by 10 | Viewed by 4189

Abstract

The containment liner plate (CLP) in a nuclear power plant is the most critical part of the structure of a power plant, as it prevents the radioactive contamination of the surrounding area. This paper presents feasibility of structural health monitoring (SHM) and an [...] Read more.

The containment liner plate (CLP) in a nuclear power plant is the most critical part of the structure of a power plant, as it prevents the radioactive contamination of the surrounding area. This paper presents feasibility of structural health monitoring (SHM) and an elastic wave tomography method based on ultrasonic guided waves (GW), for evaluating the integrity of CLP. It aims to check the integrity for a dynamic response to a damaged isotropic structure. The proposed SHM technique relies on sensors and, therefore, it can be placed on the structure permanently and can monitor either passively or actively. For applying this method, a suitable guided wave mode tuning is required to verify wave propagation. A finite element analysis (FEA) is performed to figure out the suitable GW mode for a CLP by considering geometric and material condition. Furthermore, elastic wave tomography technique is modified to evaluate the CLP condition and its visualization. A modified reconstruction algorithm for the probabilistic inspection of damage tomography algorithm is used to quantify corrosion defects in the CLP. The location and shape of the wall-thinning defects are successfully obtained by using elastic GW based SHM. Making full use of verified GW mode to Omni-directional transducer, it can be expected to improve utilization of the SHM based evaluation technique for CLP. Full article

(This article belongs to the Special Issue Selected Papers from 7th Asia-Pacific Workshop on Structural Health Monitoring 2018 (APWSHM 2018))

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27 pages, 364 KiB

Open AccessReview

Exact Closed-Form Multitarget Bayes Filters

by Ronald Mahler

Sensors 2019, 19(12), 2818; https://doi.org/10.3390/s19122818 - 24 Jun 2019

Cited by 18 | Viewed by 3474

Abstract

The finite-set statistics (FISST) foundational approach to multitarget tracking and information fusion has inspired work by dozens of research groups in at least 20 nations; and FISST publications have been cited tens of thousands of times. This review paper addresses a recent and [...] Read more.

The finite-set statistics (FISST) foundational approach to multitarget tracking and information fusion has inspired work by dozens of research groups in at least 20 nations; and FISST publications have been cited tens of thousands of times. This review paper addresses a recent and cutting-edge aspect of this research: exact closed-form—and, therefore, provably Bayes-optimal—approximations of the multitarget Bayes filter. The five proposed such filters—generalized labeled multi-Bernoulli (GLMB), labeled multi-Bernoulli mixture (LMBM), and three Poisson multi-Bernoulli mixture (PMBM) filter variants—are assessed in depth. This assessment includes a theoretically rigorous, but intuitive, statistical theory of “undetected targets”, and concrete formulas for the posterior undetected-target densities for the “standard” multitarget measurement model. Full article

(This article belongs to the Section Physical Sensors)

23 pages, 1522 KiB

Open AccessArticle

A Secure and Efficient Digital-Data-Sharing System for Cloud Environments

by Zhen-Yu Wu

Sensors 2019, 19(12), 2817; https://doi.org/10.3390/s19122817 - 24 Jun 2019

Cited by 3 | Viewed by 4234

Abstract

“Education Cloud” is a cloud-computing application used in educational contexts to facilitate the use of comprehensive digital technologies and establish data-based learning environments. The immense amount of digital resources, data, and teaching materials involved in these environments must be stored in robust data-access [...] Read more.

“Education Cloud” is a cloud-computing application used in educational contexts to facilitate the use of comprehensive digital technologies and establish data-based learning environments. The immense amount of digital resources, data, and teaching materials involved in these environments must be stored in robust data-access systems. These systems must be equipped with effective security mechanisms to guarantee confidentiality and ensure the integrity of the cloud-computing environment. To minimize the potential risk of privacy exposure, digital sharing service providers must encrypt their digital resources, data, and teaching materials, and digital-resource owners must have complete control over what data or materials they share. In addition, the data in these systems must be accessible to e-learners. In other words, data-access systems should not only encrypt data, but also provide access control mechanisms by which users may access the data. In cloud environments, digital sharing systems no longer target single users, and the access control by numerous users may overload a system and increase management burden and complexity. This study addressed these challenges to create a system that preserves the benefits of combining digital sharing systems and cloud computing. A cloud-based and learner-centered access control mechanism suitable for multi-user digital sharing was developed. The proposed mechanism resolves the problems concerning multi-user access requests in cloud environments and dynamic updating in digital-sharing systems, thereby reducing the complexity of security management. Full article

(This article belongs to the Special Issue Selected Papers from TIKI IEEE ICASI 2019)

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11 pages, 3695 KiB

Open AccessArticle

An Approach to Measure Tilt Motion, Straightness and Position of Precision Linear Stage with a 3D Sinusoidal-Groove Linear Reflective Grating and Triangular Wave-Based Subdivision Method

by Hsiu-An Tsai and Yu-Lung Lo

Sensors 2019, 19(12), 2816; https://doi.org/10.3390/s19122816 - 24 Jun 2019

Cited by 3 | Viewed by 4293

Abstract

This work presents a novel and compact method for simultaneously measuring errors in linear displacement and vertical straightness of a moving linear air-bearing stage using 3D sinusoidal-groove linear reflective grating and a novel triangular wave-based sequence signal analysis method. The new scheme is [...] Read more.

This work presents a novel and compact method for simultaneously measuring errors in linear displacement and vertical straightness of a moving linear air-bearing stage using 3D sinusoidal-groove linear reflective grating and a novel triangular wave-based sequence signal analysis method. The new scheme is distinct from the previous studies as it considers two signals to analyze linear displacement and vertical straightness. In addition, the tilt motion of the precision linear stage could also be measured using the 3D sinusoidal-groove linear reflective grating. The proposed system is similar to a linear encoder and can make online measurements of stage errors to analyze automatic processes and also be used for real-time monitoring. The performance of the proposed method and its reliability have been verified by experiments. The experiments show that the maximum error of measured tilt angle, linear displacement, and vertical straightness error is less than 0.058°, 0.239 μm, and 0.188 μm, respectively. The maximum repeatability error on measurement of tilt angle, linear displacement, and vertical straightness error is less than ±0.189^o, ±0.093 μm, and ±0.016 μm, respectively. The proposed system is suitable for error compensation in the multi-axis system and finds application in most industries. Full article

(This article belongs to the Special Issue Selected Papers from IEEE ICKII 2019)

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Configuration of the proposed measurement system. Full article ">Figure 2
Clock Waveform: (a) Positive Clock Pulse; (b) Negative Clock Pulse. Full article ">Figure 3
Photograph of the circuit board of the proposed triangular wave-based pulse-triggering method, and scheme illustration of the corresponding signal output in measurement system. I0: quadrant photo diode (QPD) output signal, IS: the corresponding signal output from the QPD, IT: the triangular signal output of the IS signal, and IP: the pulse signal output of the IS signal. The OP is the number of the pulse wave edge triggering counting. Full article ">Figure 4
(a) Schematic of experimental setup with the proposed system. (b) Photograph of the experimental system. Full article ">Figure 5
The measured profiles and photograph of the two-dimensional sinusoidal grating. Full article ">Figure 6
The measured experimental results of tilt angle (θZ) tests by the proposed system. Full article ">Figure 7
The measured average results and error bars of linear positioning by the developed system and an interferometer measurement system (Renishaw XL-80). Full article ">Figure 8
The measured results and error bars of vertical straightness by the developed system and an interferometer measurement system (Renishaw XL-80). Full article ">

14 pages, 3524 KiB

Open AccessArticle

Photoacoustic/Ultrasound/Optical Coherence Tomography Evaluation of Melanoma Lesion and Healthy Skin in a Swine Model

by Karl Kratkiewicz, Rayyan Manwar, Ali Rajabi-Estarabadi, Joseph Fakhoury, Jurgita Meiliute, Steven Daveluy, Darius Mehregan and Kamran (Mohammad) Avanaki

Sensors 2019, 19(12), 2815; https://doi.org/10.3390/s19122815 - 24 Jun 2019

Cited by 61 | Viewed by 7865

Abstract

The marked increase in the incidence of melanoma coupled with the rapid drop in the survival rate after metastasis has promoted the investigation into improved diagnostic methods for melanoma. High-frequency ultrasound (US), optical coherence tomography (OCT), and photoacoustic imaging (PAI) are three potential [...] Read more.

The marked increase in the incidence of melanoma coupled with the rapid drop in the survival rate after metastasis has promoted the investigation into improved diagnostic methods for melanoma. High-frequency ultrasound (US), optical coherence tomography (OCT), and photoacoustic imaging (PAI) are three potential modalities that can assist a dermatologist by providing extra information beyond dermoscopic features. In this study, we imaged a swine model with spontaneous melanoma using these modalities and compared the images with images of nearby healthy skin. Histology images were used for validation. Full article

(This article belongs to the Special Issue Skin Sensors)

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Principle of photoacoustic imaging. (a) Schematic of photoacoustic imaging setup for the acquisition of images from swine skin. (b) Optical absorption spectrum for most abundant photoacoustic absorbers in the skin with dashed lines showing wavelengths used in this study. Left: 532 nm; right: 1064 nm. Full article ">Figure 2
Ultrasound (US)/photoacoustic (PA) system components. (a) Optical coherence tomography (OCT) system. (b) US/PA DAQ, processing, and storage units, (i) Vantage 128 DAQ system, and (ii) processing unit. (c) US/PA probe specifications. (d) US/PA probe in use on swine melanoma lesion. DAQ: Data acquisition unit, HSL: High-speed swept-source laser. Full article ">Figure 3
Imaged suspect lesions. (a) (i) Abdominal, dark-brown pigmented plaque with irregular border confirmed as melanoma (black-circle), (ii) histology of nearby healthy skin (red-circle), and (iii) histology of the suspect lesion. (b) (i) Flank, large dark-brown plaque confirmed as melanoma (circled), (ii) histology of nearby healthy skin, and (iii) histology of the suspect lesion. Full article ">Figure 4
Ultrasound images of melanoma lesion and nearby healthy skin. (a) Abdominal: (i) Lesion, (ii) nearby healthy. (b) Flank: (i) Lesion, (ii) healthy. (c) Bar chart of average pixel intensity from epidermal region of US images. E: Epidermis, d: Dermis, sc: Subcutaneous tissue. Fibrotic septa (arrows), epidermal layer pixels (yellow dashes). Full article ">Figure 5
OCT images of melanoma lesion and nearby healthy skin. (a) Abdominal: (i) Lesion and (ii) healthy. (b) Flank: (i) Lesion and (ii) healthy. Melanomas demonstrate disorganization and thickening of the epidermis, larger rete ridges, an obscured dermal–epidermal junction (DEJ), and dermal tumor nests. Yellow circles: Dermal nests of melanocytes. Red lines: Dermal–epidermal junction. Green brackets: Epidermis. Light blue brackets: Dermis. Full article ">Figure 6
Photoacoustic images of melanoma lesion and nearby healthy skin at 532 nm illumination wavelength. (a) Abdominal: (i) Lesion and (ii) healthy. (b) Flank: (i) Lesion and (ii) healthy. (c) Bar chart of average pixel intensity from epidermal region in the PA images of 532 nm. E: Epidermis. Epidermal pixels (white dashes). The PA signal was increased in the melanoma, highlighting the increase in melanin. Full article ">Figure 7
Photoacoustic images of melanoma lesion and nearby healthy skin at 1064 nm illumination wavelength. (a) Abdominal: (i) Lesion and (ii) healthy. (b) Flank: (i) Lesion and (ii) healthy. (c) Bar chart of average pixel intensity from epidermal region at 1064 nm images. E: Epidermis. Fibrotic septa (arrows); averaged epidermal pixels (white dashes). Full article ">

16 pages, 6228 KiB

Open AccessArticle

A New Approach to Fall Detection Based on Improved Dual Parallel Channels Convolutional Neural Network

by Xiaoguang Liu, Huanliang Li, Cunguang Lou, Tie Liang, Xiuling Liu and Hongrui Wang

Sensors 2019, 19(12), 2814; https://doi.org/10.3390/s19122814 - 24 Jun 2019

Cited by 12 | Viewed by 3164

Abstract

Falls are the major cause of fatal and non-fatal injury among people aged more than 65 years. Due to the grave consequences of the occurrence of falls, it is necessary to conduct thorough research on falls. This paper presents a method for the [...] Read more.

Falls are the major cause of fatal and non-fatal injury among people aged more than 65 years. Due to the grave consequences of the occurrence of falls, it is necessary to conduct thorough research on falls. This paper presents a method for the study of fall detection using surface electromyography (sEMG) based on an improved dual parallel channels convolutional neural network (IDPC-CNN). The proposed IDPC-CNN model is designed to identify falls from daily activities using the spectral features of sEMG. Firstly, the classification accuracy of time domain features and spectrograms are compared using linear discriminant analysis (LDA), k-nearest neighbor (KNN) and support vector machine (SVM). Results show that spectrograms provide a richer way to extract pattern information and better classification performance. Therefore, the spectrogram features of sEMG are selected as the input of IDPC-CNN to distinguish between daily activities and falls. Finally, The IDPC-CNN is compared with SVM and three different structure CNNs under the same conditions. Experimental results show that the proposed IDPC-CNN achieves 92.55% accuracy, 95.71% sensitivity and 91.7% specificity. Overall, The IDPC-CNN is more effective than the comparison in accuracy, efficiency, training and generalization. Full article

(This article belongs to the Section Biosensors)

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16 pages, 812 KiB

Open AccessArticle

Traffic Estimation for Large Urban Road Network with High Missing Data Ratio

by Kennedy John Offor, Lubos Vaci and Lyudmila S. Mihaylova

Sensors 2019, 19(12), 2813; https://doi.org/10.3390/s19122813 - 24 Jun 2019

Cited by 7 | Viewed by 3870

Abstract

Intelligent transportation systems require the knowledge of current and forecasted traffic states for effective control of road networks. The actual traffic state has to be estimated as the existing sensors does not capture the needed state. Sensor measurements often contain missing or incomplete [...] Read more.

Intelligent transportation systems require the knowledge of current and forecasted traffic states for effective control of road networks. The actual traffic state has to be estimated as the existing sensors does not capture the needed state. Sensor measurements often contain missing or incomplete data as a result of communication issues, faulty sensors or cost leading to incomplete monitoring of the entire road network. This missing data poses challenges to traffic estimation approaches. In this work, a robust spatio-temporal traffic imputation approach capable of withstanding high missing data rate is presented. A particle based approach with Kriging interpolation is proposed. The performance of the particle based Kriging interpolation for different missing data ratios was investigated for a large road network comprising 1000 segments. Results indicate that the effect of missing data in a large road network can be mitigated by the Kriging interpolation within the particle filter framework. Full article

(This article belongs to the Section Intelligent Sensors)

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19 pages, 12454 KiB

Open AccessArticle

Understanding Collective Human Mobility Spatiotemporal Patterns on Weekdays from Taxi Origin-Destination Point Data

by Jing Yang, Yizhong Sun, Bowen Shang, Lei Wang and Jie Zhu

Sensors 2019, 19(12), 2812; https://doi.org/10.3390/s19122812 - 24 Jun 2019

Cited by 19 | Viewed by 4002

Abstract

With the availability of large geospatial datasets, the study of collective human mobility spatiotemporal patterns provides a new way to explore urban spatial environments from the perspective of residents. In this paper, we constructed a classification model for mobility patterns that is suitable [...] Read more.

With the availability of large geospatial datasets, the study of collective human mobility spatiotemporal patterns provides a new way to explore urban spatial environments from the perspective of residents. In this paper, we constructed a classification model for mobility patterns that is suitable for taxi OD (Origin-Destination) point data, and it is comprised of three parts. First, a new aggregate unit, which uses a road intersection as the constraint condition, is designed for the analysis of the taxi OD point data. Second, the time series similarity measurement is improved by adding a normalization procedure and time windows to address the particular characteristics of the taxi time series data. Finally, the DBSCAN algorithm is used to classify the time series into different mobility patterns based on a proximity index that is calculated using the improved similarity measurement. In addition, we used the random forest algorithm to establish a correlation model between the mobility patterns and the regional functional characteristics. Based on the taxi OD point data from Nanjing, we delimited seven mobility patterns and illustrated that the regional functions have obvious driving effects on these mobility patterns. These findings are applicable to urban planning, traffic management and planning, and land use analyses in the future. Full article

(This article belongs to the Special Issue Mobile Sensing: Platforms, Technologies and Challenges)

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24 pages, 13117 KiB

Open AccessArticle

A Low-Cost, Wireless, 3-D-Printed Custom Armband for sEMG Hand Gesture Recognition

by Ulysse Côté-Allard, Gabriel Gagnon-Turcotte, François Laviolette and Benoit Gosselin

Sensors 2019, 19(12), 2811; https://doi.org/10.3390/s19122811 - 24 Jun 2019

Cited by 55 | Viewed by 12580

Abstract

Wearable technology can be employed to elevate the abilities of humans to perform demanding and complex tasks more efficiently. Armbands capable of surface electromyography (sEMG) are attractive and noninvasive devices from which human intent can be derived by leveraging machine learning. However, the [...] Read more.

Wearable technology can be employed to elevate the abilities of humans to perform demanding and complex tasks more efficiently. Armbands capable of surface electromyography (sEMG) are attractive and noninvasive devices from which human intent can be derived by leveraging machine learning. However, the sEMG acquisition systems currently available tend to be prohibitively costly for personal use or sacrifice wearability or signal quality to be more affordable. This work introduces the 3DC Armband designed by the Biomedical Microsystems Laboratory in Laval University; a wireless, 10-channel, 1000 sps, dry-electrode, low-cost (∼150 USD) myoelectric armband that also includes a 9-axis inertial measurement unit. The proposed system is compared with the Myo Armband by Thalmic Labs, one of the most popular sEMG acquisition systems. The comparison is made by employing a new offline dataset featuring 22 able-bodied participants performing eleven hand/wrist gestures while wearing the two armbands simultaneously. The 3DC Armband systematically and significantly (

p < 0.05

) outperforms the Myo Armband, with three different classifiers employing three different input modalities when using ten seconds or more of training data per gesture. This new dataset, alongside the source code, Altium project and 3-D models are made readily available for download within a Github repository. Full article

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

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16 pages, 4459 KiB

Open AccessArticle

An Implantable Inductive Near-Field Communication System with 64 Channels for Acquisition of Gastrointestinal Bioelectrical Activity

by Amir Javan-Khoshkholgh and Aydin Farajidavar

Sensors 2019, 19(12), 2810; https://doi.org/10.3390/s19122810 - 24 Jun 2019

Cited by 18 | Viewed by 5240

Abstract

High-resolution (HR) mapping of the gastrointestinal (GI) bioelectrical activity is an emerging method to define the GI dysrhythmias such as gastroparesis and functional dyspepsia. Currently, there is no solution available to conduct HR mapping in long-term studies. We have developed an implantable 64-channel [...] Read more.

High-resolution (HR) mapping of the gastrointestinal (GI) bioelectrical activity is an emerging method to define the GI dysrhythmias such as gastroparesis and functional dyspepsia. Currently, there is no solution available to conduct HR mapping in long-term studies. We have developed an implantable 64-channel closed-loop near-field communication system for real-time monitoring of gastric electrical activity. The system is composed of an implantable unit (IU), a wearable unit (WU), and a stationary unit (SU) connected to a computer. Simultaneous data telemetry and power transfer between the IU and WU is carried out through a radio-frequency identification (RFID) link operating at 13.56 MHz. Data at the IU are encoded according to a self-clocking differential pulse position algorithm, and load shift keying modulated with only 6.25% duty cycle to be back scattered to the WU over the inductive path. The retrieved data at the WU are then either transmitted to the SU for real-time monitoring through an ISM-band RF transceiver or stored locally on a micro SD memory card. The measurement results demonstrated successful data communication at the rate of 125 kb/s when the distance between the IU and WU is less than 5 cm. The signals recorded in vitro at IU and received by SU were verified by a graphical user interface. Full article

(This article belongs to the Special Issue Near-Field Communication (NFC) Sensors)

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47 pages, 3820 KiB

Open AccessReview

A Literature Review: Geometric Methods and Their Applications in Human-Related Analysis

by Wenjuan Gong, Bin Zhang, Chaoqi Wang, Hanbing Yue, Chuantao Li, Linjie Xing, Yu Qiao, Weishan Zhang and Faming Gong

Sensors 2019, 19(12), 2809; https://doi.org/10.3390/s19122809 - 23 Jun 2019

Cited by 1 | Viewed by 5019

Abstract

Geometric features, such as the topological and manifold properties, are utilized to extract geometric properties. Geometric methods that exploit the applications of geometrics, e.g., geometric features, are widely used in computer graphics and computer vision problems. This review presents a literature review on [...] Read more.

Geometric features, such as the topological and manifold properties, are utilized to extract geometric properties. Geometric methods that exploit the applications of geometrics, e.g., geometric features, are widely used in computer graphics and computer vision problems. This review presents a literature review on geometric concepts, geometric methods, and their applications in human-related analysis, e.g., human shape analysis, human pose analysis, and human action analysis. This review proposes to categorize geometric methods based on the scope of the geometric properties that are extracted: object-oriented geometric methods, feature-oriented geometric methods, and routine-based geometric methods. Considering the broad applications of deep learning methods, this review also studies geometric deep learning, which has recently become a popular topic of research. Validation datasets are collected, and method performances are collected and compared. Finally, research trends and possible research topics are discussed. Full article

(This article belongs to the Section Intelligent Sensors)

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18 pages, 4480 KiB

Open AccessArticle

Validation of Electroencephalographic Recordings Obtained with a Consumer-Grade, Single Dry Electrode, Low-Cost Device: A Comparative Study

by Héctor Rieiro, Carolina Diaz-Piedra, José Miguel Morales, Andrés Catena, Samuel Romero, Joaquin Roca-Gonzalez, Luis J. Fuentes and Leandro L. Di Stasi

Sensors 2019, 19(12), 2808; https://doi.org/10.3390/s19122808 - 23 Jun 2019

Cited by 41 | Viewed by 8854

Abstract

The functional validity of the signal obtained with low-cost electroencephalography (EEG) devices is still under debate. Here, we have conducted an in-depth comparison of the EEG-recordings obtained with a medical-grade golden-cup electrodes ambulatory device, the SOMNOwatch + EEG-6, vs those obtained with a [...] Read more.

The functional validity of the signal obtained with low-cost electroencephalography (EEG) devices is still under debate. Here, we have conducted an in-depth comparison of the EEG-recordings obtained with a medical-grade golden-cup electrodes ambulatory device, the SOMNOwatch + EEG-6, vs those obtained with a consumer-grade, single dry electrode low-cost device, the NeuroSky MindWave, one of the most affordable devices currently available. We recorded EEG signals at Fp1 using the two different devices simultaneously on 21 participants who underwent two experimental phases: a 12-minute resting state task (alternating two cycles of closed/open eyes periods), followed by 60-minute virtual-driving task. We evaluated the EEG recording quality by comparing the similarity between the temporal data series, their spectra, their signal-to-noise ratio, the reliability of EEG measurements (comparing the closed eyes periods), as well as their blink detection rate. We found substantial agreement between signals: whereas, qualitatively, the NeuroSky MindWave presented higher levels of noise and a biphasic shape of blinks, the similarity metric indicated that signals from both recording devices were significantly correlated. While the NeuroSky MindWave was less reliable, both devices had a similar blink detection rate. Overall, the NeuroSky MindWave is noise-limited, but provides stable recordings even through long periods of time. Furthermore, its data would be of adequate quality compared to that of conventional wet electrode EEG devices, except for a potential calibration error and spectral differences at low frequencies. Full article

(This article belongs to the Collection Wearable and Unobtrusive Biomedical Monitoring)

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Figure 1
Experiment structure. (a) EEG recording configuration. Red elements and arrows indicate the electrodes used by the SOMNOwatch device. Blue elements and arrows indicate electrodes used by the MindWave device. (b) UML (Unified Modeling Language) activity diagram for the implementation and data acquisition of the experiment. The session started with the placement of the electrodes. After checking the signal quality, EEG data collection started. The experiment started with the resting state task (~15 min) structured as two cycles of task 1 (closed eyes, 3 min each) and task 2 (open eyes, 3 min each). The experiment started with either task 1 or task 2, as the order was random for each participant. Afterwards, the driving task (task 3) started (a 60-minute driving session without breaks). MindWave data was visualized in real time (RTD visualization) for all tasks. Once the three tasks finished, the session ended. Full article ">Figure 2
Data processing. UML (Unified Modeling Language) activity diagram for the experimental data processing. The process started by checking the device type. For the MindWave, we read the data file and downsampled it to 256 Hz; for the SOMNOwatch, we just read the data file (already at 256 Hz). Next, we applied an Order 10 Chebychev type II filter, followed by a signal alignment. We segmented the data into the three tasks (closed eyes, open eyes, and driving tasks). For each task, we detected blink artifacts, calculated the similarity measure, and removed high-amplitude artifacts, to finally compute the signal-to-noise ratio (SNR) and to perform the spectral estimation. Note that rectangles indicate processes, diamonds indicate decisions, and parallelograms indicate output data. Full article ">Figure 3
Differences between recording sites (Fp1 and AF3) and reference sites (mastoid and lobe) when recorded with the SOMNOwatch. (a) EEG recording configuration. Red arrows indicate the four electrodes’ placements of the SOMNOwatch used to compare the data. (b) Linear regression model for Fp1 and AF3 when recorded with the SOMNOwatch for five participants. The cloud of points shows the data for each subject first centered (by subtracting the average) and divided by its standard deviation, while the solid line represents the result of a linear regression of the form AF3 = b + g × Fp1. The numerical results for the regression and the correspondent determination coefficient are shown in the graph inset. (c) Linear regression model for Mastoid and Lobe references when recorded with the SOMNOwatch for five participants. In this case, the solid line represents the result of a linear regression of the form Lobe = b + g × Mastoid. Full article ">Figure 4
Comparison of temporal data series. (a) Left panel shows example traces of a simultaneous recording in one participant. The different noise levels and different shape of blinks are easy to observe. (b) The right panel shows the similarity measures (open circles) between the recordings for each participant and each of the three separate tasks (closed eyes, open eyes, driving task), as compared to a baseline value (dotted lines at the bottom). The values for each subject are displaced on the horizontal axis for representation purposes. Full article ">Figure 5
Spectral comparison between recording devices. (a) Spectrograms of the simultaneous recordings, in a single participant, with the two acquisition devices. The different tasks (open eyes, closed eyes, and the driving task) are delineated in the temporal axis. While the recordings are qualitatively similar, a higher level of noise can be appreciated in the MindWave data. (b) Power spectral densities obtained from the closed eyes (left), open eyes (center), and driving (right) tasks. Thin lines show individual participants, thick lines the average result. The devices differed in their response at lower frequencies, as evidenced by the MindWave peak around 3Hz. Full article ">Figure 6
Waveform and rate of detected blinks. Average waveforms and blink detection rate for each individual participant (N = 21, thin lines) and the population mean (thick lines). (a) Average waveform, with the timepoint of crossing the amplitude threshold (see Methods section) aligned to zero. Amplitudes of individual artifacts are normalized to a maximum value of 1. The different shape of blinks is apparent. (b) Blink detection rate obtained from the closed eyes (left), open eyes (center), and driving (right) tasks. Thin lines show individual participants and thick lines are the average result. Full article ">Figure 7
Signal-to-noise ratio (SNR) estimation. (a) Additive white noise model employed for the estimation of the SNR. The physiological signal x is filtered by the impulse response, resulting in filtered signal y, of both recording devices, at which point white noise (w) is added, resulting in the recorded signals. The SNR is defined as the ratio between the power of the filtered signal and the power of noise. (b) Results for each participant (thin lines) and average (thick line) the closed eyes (left), open eyes (center), and driving (right) tasks. SNR for the SOMNOwatch is on average 2 dB above that of the MindWave. Full article ">Figure 8
Normalized alpha waves as simultaneously captured by both devices during periods of closed eyes and open eyes. Alpha waves were separated from the rest of the signal using a 10th-order Chebychev filter. The alpha amplitude is clearly increased in closed eyes periods. Full article ">

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