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Sensors, Volume 16, Issue 6 (June 2016) – 190 articles

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20 pages, 1035 KiB  
Article
FuGeF: A Resource Bound Secure Forwarding Protocol for Wireless Sensor Networks
by Idris Abubakar Umar, Zurina Mohd Hanapi, A. Sali and Zuriati A. Zulkarnain
Sensors 2016, 16(6), 943; https://doi.org/10.3390/s16060943 - 22 Jun 2016
Cited by 12 | Viewed by 6322
Abstract
Resource bound security solutions have facilitated the mitigation of spatio-temporal attacks by altering protocol semantics to provide minimal security while maintaining an acceptable level of performance. The Dynamic Window Secured Implicit Geographic Forwarding (DWSIGF) routing protocol for Wireless Sensor Network (WSN) has been [...] Read more.
Resource bound security solutions have facilitated the mitigation of spatio-temporal attacks by altering protocol semantics to provide minimal security while maintaining an acceptable level of performance. The Dynamic Window Secured Implicit Geographic Forwarding (DWSIGF) routing protocol for Wireless Sensor Network (WSN) has been proposed to achieve a minimal selection of malicious nodes by introducing a dynamic collection window period to the protocol’s semantics. However, its selection scheme suffers substantial packet losses due to the utilization of a single distance based parameter for node selection. In this paper, we propose a Fuzzy-based Geographic Forwarding protocol (FuGeF) to minimize packet loss, while maintaining performance. The FuGeF utilizes a new form of dynamism and introduces three selection parameters: remaining energy, connectivity cost, and progressive distance, as well as a Fuzzy Logic System (FLS) for node selection. These introduced mechanisms ensure the appropriate selection of a non-malicious node. Extensive simulation experiments have been conducted to evaluate the performance of the proposed FuGeF protocol as compared to DWSIGF variants. The simulation results show that the proposed FuGeF outperforms the two DWSIGF variants (DWSIGF-P and DWSIGF-R) in terms of packet delivery. Full article
(This article belongs to the Special Issue Trusted and Secure Wireless Sensor Network Designs and Deployments)
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14 pages, 5173 KiB  
Article
A Low Cost/Low Power Open Source Sensor System for Automated Tuberculosis Drug Susceptibility Testing
by Kyukwang Kim, Hyeong Keun Kim, Hwijoon Lim and Hyun Myung
Sensors 2016, 16(6), 942; https://doi.org/10.3390/s16060942 - 22 Jun 2016
Cited by 4 | Viewed by 8852
Abstract
In this research an open source, low power sensor node was developed to check the growth of mycobacteria in a culture bottle with a nitrate reductase assay method for a drug susceptibility test. The sensor system reports the temperature and color sensor output [...] Read more.
In this research an open source, low power sensor node was developed to check the growth of mycobacteria in a culture bottle with a nitrate reductase assay method for a drug susceptibility test. The sensor system reports the temperature and color sensor output frequency change of the culture bottle when the device is triggered. After the culture process is finished, a nitrite ion detecting solution based on a commercial nitrite ion detection kit is injected into the culture bottle by a syringe pump to check bacterial growth by the formation of a pigment by the reaction between the solution and the color sensor. Sensor status and NRA results are broadcasted via a Bluetooth low energy beacon. An Android application was developed to collect the broadcasted data, classify the status of cultured samples from multiple devices, and visualize the data for the end users, circumventing the need to examine each culture bottle manually during a long culture period. The authors expect that usage of the developed sensor will decrease the cost and required labor for handling large amounts of patient samples in local health centers in developing countries. All 3D-printerable hardware parts, a circuit diagram, and software are available online. Full article
(This article belongs to the Special Issue Sensing Technology for Healthcare System)
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19 pages, 4830 KiB  
Article
An Ultrahigh Frequency Partial Discharge Signal De-Noising Method Based on a Generalized S-Transform and Module Time-Frequency Matrix
by Yushun Liu, Wenjun Zhou, Pengfei Li, Shuai Yang and Yan Tian
Sensors 2016, 16(6), 941; https://doi.org/10.3390/s16060941 - 22 Jun 2016
Cited by 36 | Viewed by 7438
Abstract
Due to electromagnetic interference in power substations, the partial discharge (PD) signals detected by ultrahigh frequency (UHF) antenna sensors often contain various background noises, which may hamper high voltage apparatus fault diagnosis and localization. This paper proposes a novel de-noising method based on [...] Read more.
Due to electromagnetic interference in power substations, the partial discharge (PD) signals detected by ultrahigh frequency (UHF) antenna sensors often contain various background noises, which may hamper high voltage apparatus fault diagnosis and localization. This paper proposes a novel de-noising method based on the generalized S-transform and module time-frequency matrix to suppress noise in UHF PD signals. The sub-matrix maximum module value method is employed to calculate the frequencies and amplitudes of periodic narrowband noise, and suppress noise through the reverse phase cancellation technique. In addition, a singular value decomposition de-noising method is employed to suppress Gaussian white noise in UHF PD signals. Effective singular values are selected by employing the fuzzy c-means clustering method to recover the PD signals. De-noising results of simulated and field detected UHF PD signals prove the feasibility of the proposed method. Compared with four conventional de-noising methods, the results show that the proposed method can suppress background noise in the UHF PD signal effectively, with higher signal-to-noise ratio and less waveform distortion. Full article
(This article belongs to the Special Issue Non-Contact Sensing)
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16 pages, 3413 KiB  
Article
Systematic Calibration for Ultra-High Accuracy Inertial Measurement Units
by Qingzhong Cai, Gongliu Yang, Ningfang Song and Yiliang Liu
Sensors 2016, 16(6), 940; https://doi.org/10.3390/s16060940 - 22 Jun 2016
Cited by 50 | Viewed by 7824
Abstract
An inertial navigation system (INS) has been widely used in challenging GPS environments. With the rapid development of modern physics, an atomic gyroscope will come into use in the near future with a predicted accuracy of 5 × 10−6°/h or better. [...] Read more.
An inertial navigation system (INS) has been widely used in challenging GPS environments. With the rapid development of modern physics, an atomic gyroscope will come into use in the near future with a predicted accuracy of 5 × 10−6°/h or better. However, existing calibration methods and devices can not satisfy the accuracy requirements of future ultra-high accuracy inertial sensors. In this paper, an improved calibration model is established by introducing gyro g-sensitivity errors, accelerometer cross-coupling errors and lever arm errors. A systematic calibration method is proposed based on a 51-state Kalman filter and smoother. Simulation results show that the proposed calibration method can realize the estimation of all the parameters using a common dual-axis turntable. Laboratory and sailing tests prove that the position accuracy in a five-day inertial navigation can be improved about 8% by the proposed calibration method. The accuracy can be improved at least 20% when the position accuracy of the atomic gyro INS can reach a level of 0.1 nautical miles/5 d. Compared with the existing calibration methods, the proposed method, with more error sources and high order small error parameters calibrated for ultra-high accuracy inertial measurement units (IMUs) using common turntables, has a great application potential in future atomic gyro INSs. Full article
(This article belongs to the Special Issue Inertial Sensors and Systems 2016)
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21 pages, 3577 KiB  
Article
Integration of GMR Sensors with Different Technologies
by María-Dolores Cubells-Beltrán, Càndid Reig, Jordi Madrenas, Andrea De Marcellis, Joana Santos, Susana Cardoso and Paulo P. Freitas
Sensors 2016, 16(6), 939; https://doi.org/10.3390/s16060939 - 22 Jun 2016
Cited by 87 | Viewed by 13751
Abstract
Less than thirty years after the giant magnetoresistance (GMR) effect was described, GMR sensors are the preferred choice in many applications demanding the measurement of low magnetic fields in small volumes. This rapid deployment from theoretical basis to market and state-of-the-art applications can [...] Read more.
Less than thirty years after the giant magnetoresistance (GMR) effect was described, GMR sensors are the preferred choice in many applications demanding the measurement of low magnetic fields in small volumes. This rapid deployment from theoretical basis to market and state-of-the-art applications can be explained by the combination of excellent inherent properties with the feasibility of fabrication, allowing the real integration with many other standard technologies. In this paper, we present a review focusing on how this capability of integration has allowed the improvement of the inherent capabilities and, therefore, the range of application of GMR sensors. After briefly describing the phenomenological basis, we deal on the benefits of low temperature deposition techniques regarding the integration of GMR sensors with flexible (plastic) substrates and pre-processed CMOS chips. In this way, the limit of detection can be improved by means of bettering the sensitivity or reducing the noise. We also report on novel fields of application of GMR sensors by the recapitulation of a number of cases of success of their integration with different heterogeneous complementary elements. We finally describe three fully functional systems, two of them in the bio-technology world, as the proof of how the integrability has been instrumental in the meteoric development of GMR sensors and their applications. Full article
(This article belongs to the Special Issue Giant Magnetoresistive Sensors)
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13 pages, 12497 KiB  
Article
Smart Coat with a Fully-Embedded Textile Antenna for IoT Applications
by Caroline Loss, Ricardo Gonçalves, Catarina Lopes, Pedro Pinho and Rita Salvado
Sensors 2016, 16(6), 938; https://doi.org/10.3390/s16060938 - 22 Jun 2016
Cited by 71 | Viewed by 12695
Abstract
The Internet of Things (IoT) scenario is strongly related with the advance of the development of wireless sensor networks (WSN) and radio frequency identification (RFID) systems. Additionally, in the WSN context, for a continuous feed, the integration of textile antennas for energy harvesting [...] Read more.
The Internet of Things (IoT) scenario is strongly related with the advance of the development of wireless sensor networks (WSN) and radio frequency identification (RFID) systems. Additionally, in the WSN context, for a continuous feed, the integration of textile antennas for energy harvesting into smart clothing is a particularly interesting solution when the replacement of batteries is not easy to practice, such as in wearable devices. This paper presents the E-Caption: Smart and Sustainable Coat. It has an embedded dual-band textile antenna for electromagnetic energy harvesting, operating at global system for mobile communication (GSM) 900 and digital cellular system (DCS) 1800 bands. This printed antenna is fully integrated, as its dielectric is the textile material composing the coat itself. The E-Caption illustrates the innovative concept of textile antennas that can be manipulated as simple emblems. Seven prototypes of these “emblem” antennas, manufactured by lamination and embroidering techniques are also presented. It is shown that the orientation of the conductive fabric does not influence the performance of the antenna. It is also shown that the direction and number of the stitches in the embroidery may influence the performance of the antenna. Moreover, the comparison of results obtained before and after the integration of the antenna into cloth shows the integration does not affect the behavior of the antenna. Full article
(This article belongs to the Special Issue Selected Papers from the 2nd International Electronic Conference on Sensors and Applications)
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24 pages, 3003 KiB  
Article
Distributed Information Compression for Target Tracking in Cluster-Based Wireless Sensor Networks
by Shi-Kuan Liao, Kai-Jay Lai, Hsiao-Ping Tsai and Chih-Yu Wen
Sensors 2016, 16(6), 937; https://doi.org/10.3390/s16060937 - 22 Jun 2016
Cited by 4 | Viewed by 6012
Abstract
Target tracking is a critical wireless sensor application, which involves signal and information processing technologies. In conventional target position estimation methods, an estimate is usually demonstrated by an average target position. In contrast, this work proposes a distributed information compression method to describe [...] Read more.
Target tracking is a critical wireless sensor application, which involves signal and information processing technologies. In conventional target position estimation methods, an estimate is usually demonstrated by an average target position. In contrast, this work proposes a distributed information compression method to describe the measurement uncertainty of tracking problems in cluster-based wireless sensor networks. The leader-based information processing scheme is applied to perform target positioning and energy conservation. A two-level hierarchical network topology is adopted for energy-efficient target tracking with information compression. A Level 1 network architecture is a cluster-based network topology for managing network operations. A Level 2 network architecture is an event-based and leader-based topology, utilizing the concept of information compression to process the estimates of sensor nodes. The simulation results show that compared to conventional schemes, the proposed data processing scheme has a balanced system performance in terms of tracking accuracy, data size for transmission and energy consumption. Full article
(This article belongs to the Special Issue Scalable Localization in Wireless Sensor Networks)
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18 pages, 12635 KiB  
Article
Contrast Enhancement Algorithm Based on Gap Adjustment for Histogram Equalization
by Chung-Cheng Chiu and Chih-Chung Ting
Sensors 2016, 16(6), 936; https://doi.org/10.3390/s16060936 - 22 Jun 2016
Cited by 27 | Viewed by 9311
Abstract
Image enhancement methods have been widely used to improve the visual effects of images. Owing to its simplicity and effectiveness histogram equalization (HE) is one of the methods used for enhancing image contrast. However, HE may result in over-enhancement and feature loss problems [...] Read more.
Image enhancement methods have been widely used to improve the visual effects of images. Owing to its simplicity and effectiveness histogram equalization (HE) is one of the methods used for enhancing image contrast. However, HE may result in over-enhancement and feature loss problems that lead to unnatural look and loss of details in the processed images. Researchers have proposed various HE-based methods to solve the over-enhancement problem; however, they have largely ignored the feature loss problem. Therefore, a contrast enhancement algorithm based on gap adjustment for histogram equalization (CegaHE) is proposed. It refers to a visual contrast enhancement algorithm based on histogram equalization (VCEA), which generates visually pleasing enhanced images, and improves the enhancement effects of VCEA. CegaHE adjusts the gaps between two gray values based on the adjustment equation, which takes the properties of human visual perception into consideration, to solve the over-enhancement problem. Besides, it also alleviates the feature loss problem and further enhances the textures in the dark regions of the images to improve the quality of the processed images for human visual perception. Experimental results demonstrate that CegaHE is a reliable method for contrast enhancement and that it significantly outperforms VCEA and other methods. Full article
(This article belongs to the Section Physical Sensors)
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13 pages, 2073 KiB  
Article
Electrochemical Sensing toward Trace As(III) Based on Mesoporous MnFe2O4/Au Hybrid Nanospheres Modified Glass Carbon Electrode
by Shaofeng Zhou, Xiaojuan Han, Honglei Fan and Yaqing Liu
Sensors 2016, 16(6), 935; https://doi.org/10.3390/s16060935 - 22 Jun 2016
Cited by 42 | Viewed by 6899
Abstract
Au nanoparticles decorated mesoporous MnFe2O4 nanocrystal clusters (MnFe2O4/Au hybrid nanospheres) were used for the electrochemical sensing of As(III) by square wave anodic stripping voltammetry (SWASV). Modified on a cheap glass carbon electrode, these MnFe2O [...] Read more.
Au nanoparticles decorated mesoporous MnFe2O4 nanocrystal clusters (MnFe2O4/Au hybrid nanospheres) were used for the electrochemical sensing of As(III) by square wave anodic stripping voltammetry (SWASV). Modified on a cheap glass carbon electrode, these MnFe2O4/Au hybrid nanospheres show favorable sensitivity (0.315 μA/ppb) and limit of detection (LOD) (3.37 ppb) toward As(III) under the optimized conditions in 0.1 M NaAc-HAc (pH 5.0) by depositing for 150 s at the deposition potential of −0.9 V. No obvious interference from Cd(II) and Hg(II) was recognized during the detection of As(III). Additionally, the developed electrode displayed good reproducibility, stability, and repeatability, and offered potential practical applicability for electrochemical detection of As(III) in real water samples. The present work provides a potential method for the design of new and cheap sensors in the application of electrochemical determination toward trace As(III) and other toxic metal ions. Full article
(This article belongs to the Special Issue The Use of New and/or Improved Materials for Sensing Applications)
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18 pages, 821 KiB  
Article
Optimization of the Coverage and Accuracy of an Indoor Positioning System with a Variable Number of Sensors
by Francisco Domingo-Perez, Jose Luis Lazaro-Galilea, Ignacio Bravo, Alfredo Gardel and David Rodriguez
Sensors 2016, 16(6), 934; https://doi.org/10.3390/s16060934 - 22 Jun 2016
Cited by 35 | Viewed by 6737
Abstract
This paper focuses on optimal sensor deployment for indoor localization with a multi-objective evolutionary algorithm. Our goal is to obtain an algorithm to deploy sensors taking the number of sensors, accuracy and coverage into account. Contrary to most works in the literature, we [...] Read more.
This paper focuses on optimal sensor deployment for indoor localization with a multi-objective evolutionary algorithm. Our goal is to obtain an algorithm to deploy sensors taking the number of sensors, accuracy and coverage into account. Contrary to most works in the literature, we consider the presence of obstacles in the region of interest (ROI) that can cause occlusions between the target and some sensors. In addition, we aim to obtain all of the Pareto optimal solutions regarding the number of sensors, coverage and accuracy. To deal with a variable number of sensors, we add speciation and structural mutations to the well-known non-dominated sorting genetic algorithm (NSGA-II). Speciation allows one to keep the evolution of sensor sets under control and to apply genetic operators to them so that they compete with other sets of the same size. We show some case studies of the sensor placement of an infrared range-difference indoor positioning system with a fairly complex model of the error of the measurements. The results obtained by our algorithm are compared to sensor placement patterns obtained with random deployment to highlight the relevance of using such a deployment algorithm. Full article
(This article belongs to the Special Issue Trusted and Secure Wireless Sensor Network Designs and Deployments)
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19 pages, 2115 KiB  
Article
Indirect Correspondence-Based Robust Extrinsic Calibration of LiDAR and Camera
by Sungdae Sim, Juil Sock and Kiho Kwak
Sensors 2016, 16(6), 933; https://doi.org/10.3390/s16060933 - 22 Jun 2016
Cited by 42 | Viewed by 12015
Abstract
LiDAR and cameras have been broadly utilized in computer vision and autonomous vehicle applications. However, in order to convert data between the local coordinate systems, we must estimate the rigid body transformation between the sensors. In this paper, we propose a robust extrinsic [...] Read more.
LiDAR and cameras have been broadly utilized in computer vision and autonomous vehicle applications. However, in order to convert data between the local coordinate systems, we must estimate the rigid body transformation between the sensors. In this paper, we propose a robust extrinsic calibration algorithm that can be implemented easily and has small calibration error. The extrinsic calibration parameters are estimated by minimizing the distance between corresponding features projected onto the image plane. The features are edge and centerline features on a v-shaped calibration target. The proposed algorithm contributes two ways to improve the calibration accuracy. First, we use different weights to distance between a point and a line feature according to the correspondence accuracy of the features. Second, we apply a penalizing function to exclude the influence of outliers in the calibration datasets. Additionally, based on our robust calibration approach for a single LiDAR-camera pair, we introduce a joint calibration that estimates the extrinsic parameters of multiple sensors at once by minimizing one objective function with loop closing constraints. We conduct several experiments to evaluate the performance of our extrinsic calibration algorithm. The experimental results show that our calibration method has better performance than the other approaches. Full article
(This article belongs to the Section Physical Sensors)
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20 pages, 7801 KiB  
Article
Matching Aerial Images to 3D Building Models Using Context-Based Geometric Hashing
by Jaewook Jung, Gunho Sohn, Kiin Bang, Andreas Wichmann, Costas Armenakis and Martin Kada
Sensors 2016, 16(6), 932; https://doi.org/10.3390/s16060932 - 22 Jun 2016
Cited by 16 | Viewed by 6371
Abstract
A city is a dynamic entity, which environment is continuously changing over time. Accordingly, its virtual city models also need to be regularly updated to support accurate model-based decisions for various applications, including urban planning, emergency response and autonomous navigation. A concept of [...] Read more.
A city is a dynamic entity, which environment is continuously changing over time. Accordingly, its virtual city models also need to be regularly updated to support accurate model-based decisions for various applications, including urban planning, emergency response and autonomous navigation. A concept of continuous city modeling is to progressively reconstruct city models by accommodating their changes recognized in spatio-temporal domain, while preserving unchanged structures. A first critical step for continuous city modeling is to coherently register remotely sensed data taken at different epochs with existing building models. This paper presents a new model-to-image registration method using a context-based geometric hashing (CGH) method to align a single image with existing 3D building models. This model-to-image registration process consists of three steps: (1) feature extraction; (2) similarity measure; and matching, and (3) estimating exterior orientation parameters (EOPs) of a single image. For feature extraction, we propose two types of matching cues: edged corner features representing the saliency of building corner points with associated edges, and contextual relations among the edged corner features within an individual roof. A set of matched corners are found with given proximity measure through geometric hashing, and optimal matches are then finally determined by maximizing the matching cost encoding contextual similarity between matching candidates. Final matched corners are used for adjusting EOPs of the single airborne image by the least square method based on collinearity equations. The result shows that acceptable accuracy of EOPs of a single image can be achievable using the proposed registration approach as an alternative to a labor-intensive manual registration process. Full article
(This article belongs to the Section Remote Sensors)
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14 pages, 2655 KiB  
Article
A Fiber-Coupled Self-Mixing Laser Diode for the Measurement of Young’s Modulus
by Ke Lin, Yanguang Yu, Jiangtao Xi, Huijun Li, Qinghua Guo, Jun Tong and Lihong Su
Sensors 2016, 16(6), 928; https://doi.org/10.3390/s16060928 - 22 Jun 2016
Cited by 19 | Viewed by 7409
Abstract
This paper presents the design of a fiber-coupled self-mixing laser diode (SMLD) for non-contact and non-destructive measurement of Young’s modulus. By the presented measuring system, the Young’s modulus of aluminum 6061 and brass are measured as 70.0 GPa and 116.7 GPa, respectively, showing [...] Read more.
This paper presents the design of a fiber-coupled self-mixing laser diode (SMLD) for non-contact and non-destructive measurement of Young’s modulus. By the presented measuring system, the Young’s modulus of aluminum 6061 and brass are measured as 70.0 GPa and 116.7 GPa, respectively, showing a good agreement within the standards in the literature and yielding a much smaller deviation and a higher repeatability compared with traditional tensile testing. Its fiber-coupled characteristics make the system quite easy to be installed in many application cases. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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13 pages, 1461 KiB  
Article
Evaluating Soil Moisture Status Using an e-Nose
by Andrzej Bieganowski, Katarzyna Jaromin-Glen, Łukasz Guz, Grzegorz Łagód, Grzegorz Jozefaciuk, Wojciech Franus, Zbigniew Suchorab and Henryk Sobczuk
Sensors 2016, 16(6), 886; https://doi.org/10.3390/s16060886 - 22 Jun 2016
Cited by 42 | Viewed by 7000
Abstract
The possibility of distinguishing different soil moisture levels by electronic nose (e-nose) was studied. Ten arable soils of various types were investigated. The measurements were performed for air-dry (AD) soils stored for one year, then moistened to field water capacity and finally dried [...] Read more.
The possibility of distinguishing different soil moisture levels by electronic nose (e-nose) was studied. Ten arable soils of various types were investigated. The measurements were performed for air-dry (AD) soils stored for one year, then moistened to field water capacity and finally dried within a period of 180 days. The volatile fingerprints changed during the course of drying. At the end of the drying cycle, the fingerprints were similar to those of the initial AD soils. Principal component analysis (PCA) and artificial neural network (ANN) analysis showed that e-nose results can be used to distinguish soil moisture. It was also shown that different soils can give different e-nose signals at the same moistures. Full article
(This article belongs to the Special Issue E-noses: Sensors and Applications)
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16 pages, 4585 KiB  
Article
An Intelligent Parking Management System for Urban Areas
by Juan A. Vera-Gómez, Alexis Quesada-Arencibia, Carmelo R. García, Raúl Suárez Moreno and Fernando Guerra Hernández
Sensors 2016, 16(6), 931; https://doi.org/10.3390/s16060931 - 21 Jun 2016
Cited by 40 | Viewed by 16897
Abstract
In this article we describe a low-cost, minimally-intrusive system for the efficient management of parking spaces on both public roads and controlled zones. This system is based on wireless networks of photoelectric sensors that are deployed on the access roads into and out [...] Read more.
In this article we describe a low-cost, minimally-intrusive system for the efficient management of parking spaces on both public roads and controlled zones. This system is based on wireless networks of photoelectric sensors that are deployed on the access roads into and out of these areas. The sensors detect the passage of vehicles on these roads and communicate this information to a data centre, thus making it possible to know the number of vehicles in the controlled zone and the occupancy levels in real-time. This information may be communicated to drivers to facilitate their search for a parking space and to authorities so that they may take steps to control traffic when congestion is detected. Full article
(This article belongs to the Special Issue Selected Papers from UCAmI, IWAAL and AmIHEALTH 2015)
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15 pages, 3346 KiB  
Article
Analysis and Visualization of 3D Motion Data for UPDRS Rating of Patients with Parkinson’s Disease
by Neltje E. Piro, Lennart K. Piro, Jan Kassubek and Ronald A. Blechschmidt-Trapp
Sensors 2016, 16(6), 930; https://doi.org/10.3390/s16060930 - 21 Jun 2016
Cited by 24 | Viewed by 10488
Abstract
Remote monitoring of Parkinson’s Disease (PD) patients with inertia sensors is a relevant method for a better assessment of symptoms. We present a new approach for symptom quantification based on motion data: the automatic Unified Parkinson Disease Rating Scale (UPDRS) classification in combination [...] Read more.
Remote monitoring of Parkinson’s Disease (PD) patients with inertia sensors is a relevant method for a better assessment of symptoms. We present a new approach for symptom quantification based on motion data: the automatic Unified Parkinson Disease Rating Scale (UPDRS) classification in combination with an animated 3D avatar giving the neurologist the impression of having the patient live in front of him. In this study we compared the UPDRS ratings of the pronation-supination task derived from: (a) an examination based on video recordings as a clinical reference; (b) an automatically classified UPDRS; and (c) a UPDRS rating from the assessment of the animated 3D avatar. Data were recorded using Magnetic, Angular Rate, Gravity (MARG) sensors with 15 subjects performing a pronation-supination movement of the hand. After preprocessing, the data were classified with a J48 classifier and animated as a 3D avatar. Video recording of the movements, as well as the 3D avatar, were examined by movement disorder specialists and rated by UPDRS. The mean agreement between the ratings based on video and (b) the automatically classified UPDRS is 0.48 and with (c) the 3D avatar it is 0.47. The 3D avatar is similarly suitable for assessing the UPDRS as video recordings for the examined task and will be further developed by the research team. Full article
(This article belongs to the Collection Sensors for Globalized Healthy Living and Wellbeing)
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17 pages, 4008 KiB  
Article
Flexible Bond Wire Capacitive Strain Sensor for Vehicle Tyres
by Siyang Cao, Simon Pyatt, Carl J. Anthony, Ammar I. Kubba, Ali E. Kubba and Oluremi Olatunbosun
Sensors 2016, 16(6), 929; https://doi.org/10.3390/s16060929 - 21 Jun 2016
Cited by 9 | Viewed by 8487
Abstract
The safety of the driving experience and manoeuvrability of a vehicle can be improved by detecting the strain in tyres. To measure strain accurately in rubber, the strain sensor needs to be flexible so that it does not deform the medium that it [...] Read more.
The safety of the driving experience and manoeuvrability of a vehicle can be improved by detecting the strain in tyres. To measure strain accurately in rubber, the strain sensor needs to be flexible so that it does not deform the medium that it is measuring. In this work, a novel flexible bond wire capacitive strain sensor for measuring the strain in tyres is developed, fabricated and calibrated. An array of 25 micron diameter wire bonds in an approximately 8 mm × 8 mm area is built to create an interdigitated structure, which consists of 50 wire loops resulting in 49 capacitor pairs in parallel. Laser machining was used to pattern copper on a flexible printed circuit board PCB to make the bond pads for the wire attachment. The wire array was finally packaged and embedded in polydimethylsiloxane (PDMS), which acts as the structural material that is strained. The capacitance of the device is in a linear like relationship with respect to the strain, which can measure the strain up to at least ±60,000 micro-strain (±6%) with a resolution of ~132 micro-strain (0.013%). In-tyre testing under static loading has shown the ability of the sensor to measure large tyre strains. The technology used for sensor fabrication lends itself to mass production and so the design is considered to be consistent with low cost commercialisable strain sensing technology. Full article
(This article belongs to the Collection Modeling, Testing and Reliability Issues in MEMS Engineering)
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21 pages, 7061 KiB  
Review
Single Photon Counting UV Solar-Blind Detectors Using Silicon and III-Nitride Materials
by Shouleh Nikzad, Michael Hoenk, April D. Jewell, John J. Hennessy, Alexander G. Carver, Todd J. Jones, Timothy M. Goodsall, Erika T. Hamden, Puneet Suvarna, J. Bulmer, F. Shahedipour-Sandvik, Edoardo Charbon, Preethi Padmanabhan, Bruce Hancock and L. Douglas Bell
Sensors 2016, 16(6), 927; https://doi.org/10.3390/s16060927 - 21 Jun 2016
Cited by 45 | Viewed by 12568
Abstract
Ultraviolet (UV) studies in astronomy, cosmology, planetary studies, biological and medical applications often require precision detection of faint objects and in many cases require photon-counting detection. We present an overview of two approaches for achieving photon counting in the UV. The first approach [...] Read more.
Ultraviolet (UV) studies in astronomy, cosmology, planetary studies, biological and medical applications often require precision detection of faint objects and in many cases require photon-counting detection. We present an overview of two approaches for achieving photon counting in the UV. The first approach involves UV enhancement of photon-counting silicon detectors, including electron multiplying charge-coupled devices and avalanche photodiodes. The approach used here employs molecular beam epitaxy for delta doping and superlattice doping for surface passivation and high UV quantum efficiency. Additional UV enhancements include antireflection (AR) and solar-blind UV bandpass coatings prepared by atomic layer deposition. Quantum efficiency (QE) measurements show QE > 50% in the 100–300 nm range for detectors with simple AR coatings, and QE ≅ 80% at ~206 nm has been shown when more complex AR coatings are used. The second approach is based on avalanche photodiodes in III-nitride materials with high QE and intrinsic solar blindness. Full article
(This article belongs to the Special Issue Photon-Counting Image Sensors)
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11 pages, 3452 KiB  
Article
Spatially Multiplexed Micro-Spectrophotometry in Bright Field Mode for Thin Film Characterization
by Valerio Pini, Priscila M. Kosaka, Jose J. Ruz, Oscar Malvar, Mario Encinar, Javier Tamayo and Montserrat Calleja
Sensors 2016, 16(6), 926; https://doi.org/10.3390/s16060926 - 21 Jun 2016
Cited by 1 | Viewed by 6284
Abstract
Thickness characterization of thin films is of primary importance in a variety of nanotechnology applications, either in the semiconductor industry, quality control in nanofabrication processes or engineering of nanoelectromechanical systems (NEMS) because small thickness variability can strongly compromise the device performance. Here, we [...] Read more.
Thickness characterization of thin films is of primary importance in a variety of nanotechnology applications, either in the semiconductor industry, quality control in nanofabrication processes or engineering of nanoelectromechanical systems (NEMS) because small thickness variability can strongly compromise the device performance. Here, we present an alternative optical method in bright field mode called Spatially Multiplexed Micro-Spectrophotometry that allows rapid and non-destructive characterization of thin films over areas of mm2 and with 1 μm of lateral resolution. We demonstrate an accuracy of 0.1% in the thickness characterization through measurements performed on four microcantilevers that expand an area of 1.8 mm2 in one minute of analysis time. The measured thickness variation in the range of few tens of nm translates into a mechanical variability that produces an error of up to 2% in the response of the studied devices when they are used to measure surface stress variations. Full article
(This article belongs to the Special Issue Nanomechanics for Sensing and Spectrometry)
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15 pages, 1843 KiB  
Article
A Compact Forearm Crutch Based on Force Sensors for Aided Gait: Reliability and Validity
by Gema Chamorro-Moriana, José Luis Sevillano and Carmen Ridao-Fernández
Sensors 2016, 16(6), 925; https://doi.org/10.3390/s16060925 - 21 Jun 2016
Cited by 21 | Viewed by 11267
Abstract
Frequently, patients who suffer injuries in some lower member require forearm crutches in order to partially unload weight-bearing. These lesions cause pain in lower limb unloading and their progression should be controlled objectively to avoid significant errors in accuracy and, consequently, complications and [...] Read more.
Frequently, patients who suffer injuries in some lower member require forearm crutches in order to partially unload weight-bearing. These lesions cause pain in lower limb unloading and their progression should be controlled objectively to avoid significant errors in accuracy and, consequently, complications and after effects in lesions. The design of a new and feasible tool that allows us to control and improve the accuracy of loads exerted on crutches during aided gait is necessary, so as to unburden the lower limbs. In this paper, we describe such a system based on a force sensor, which we have named the GCH System 2.0. Furthermore, we determine the validity and reliability of measurements obtained using this tool via a comparison with the validated AMTI (Advanced Mechanical Technology, Inc., Watertown, MA, USA) OR6-7-2000 Platform. An intra-class correlation coefficient demonstrated excellent agreement between the AMTI Platform and the GCH System. A regression line to determine the predictive ability of the GCH system towards the AMTI Platform was found, which obtained a precision of 99.3%. A detailed statistical analysis is presented for all the measurements and also segregated for several requested loads on the crutches (10%, 25% and 50% of body weight). Our results show that our system, designed for assessing loads exerted by patients on forearm crutches during assisted gait, provides valid and reliable measurements of loads. Full article
(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Spain 2015)
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29 pages, 7278 KiB  
Article
A Type of Low-Latency Data Gathering Method with Multi-Sink for Sensor Networks
by Chao Sha, Jian-mei Qiu, Shu-yan Li, Meng-ye Qiang and Ru-chuan Wang
Sensors 2016, 16(6), 923; https://doi.org/10.3390/s16060923 - 21 Jun 2016
Cited by 12 | Viewed by 7104
Abstract
To balance energy consumption and reduce latency on data transmission in Wireless Sensor Networks (WSNs), a type of low-latency data gathering method with multi-Sink (LDGM for short) is proposed in this paper. The network is divided into several virtual regions consisting of three [...] Read more.
To balance energy consumption and reduce latency on data transmission in Wireless Sensor Networks (WSNs), a type of low-latency data gathering method with multi-Sink (LDGM for short) is proposed in this paper. The network is divided into several virtual regions consisting of three or less data gathering units and the leader of each region is selected according to its residual energy as well as distance to all of the other nodes. Only the leaders in each region need to communicate with the mobile Sinks which have effectively reduced energy consumption and the end-to-end delay. Moreover, with the help of the sleep scheduling and the sensing radius adjustment strategies, redundancy in network coverage could also be effectively reduced. Simulation results show that LDGM is energy efficient in comparison with MST as well as MWST and its time efficiency on data collection is higher than one Sink based data gathering methods. Full article
(This article belongs to the Special Issue Data in the IoT: from Sensing to Meaning)
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13 pages, 4959 KiB  
Article
The Reusable Load Cell with Protection Applied for Online Monitoring of Overhead Transmission Lines Based on Fiber Bragg Grating
by Guoming Ma, Naiqiang Mao, Yabo Li, Jun Jiang, Hongyang Zhou and Chengrong Li
Sensors 2016, 16(6), 922; https://doi.org/10.3390/s16060922 - 21 Jun 2016
Cited by 29 | Viewed by 7419
Abstract
Heavy ice coating of high–voltage overhead transmission lines may lead to conductor breakage and tower collapse causing the unexpected interrupt of power supply. The optical load cell applied in ice monitoring systems is immune to electromagnetic interference and has no need of a [...] Read more.
Heavy ice coating of high–voltage overhead transmission lines may lead to conductor breakage and tower collapse causing the unexpected interrupt of power supply. The optical load cell applied in ice monitoring systems is immune to electromagnetic interference and has no need of a power supply on site. Therefore, it has become a hot research topic in China and other countries. In this paper, to solve the problem of eccentric load in measurement, we adopt the shearing structure with additional grooves to improve the strain distribution and acquire good repeatability. Then, the fiber Bragg grating (FBG) with a permanent weldable package are mounted onto the front/rear groove of the elastic element by spot welding, the direction deviation of FBGs is 90° from each other to achieve temperature compensation without an extra FBG. After that, protection parts are designed to guarantee high sensitivity for a light load condition and industrial safety under a heavy load up to 65 kN. The results of tension experiments indicate that the sensitivity and resolution of the load cell is 0.1285 pm/N and 7.782 N in the conventional measuring range (0–10 kN). Heavy load tension experiments prove that the protection structure works and the sensitivity and resolution are not changed after several high load (65 kN) cycles. In addition, the experiment shows that the resolution of the sensor is 87.79 N in the large load range, allowing the parameter to be used in heavy icing monitoring. Full article
(This article belongs to the Special Issue Recent Advances in Fiber Bragg Grating Sensing)
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9 pages, 5395 KiB  
Article
A 3D Model of the Thermoelectric Microwave Power Sensor by MEMS Technology
by Zhenxiang Yi and Xiaoping Liao
Sensors 2016, 16(6), 921; https://doi.org/10.3390/s16060921 - 21 Jun 2016
Cited by 7 | Viewed by 6171
Abstract
In this paper, a novel 3D model is proposed to describe the temperature distribution of the thermoelectric microwave power sensor. In this 3D model, the heat flux density decreases from the upper surface to the lower surface of the GaAs substrate while it [...] Read more.
In this paper, a novel 3D model is proposed to describe the temperature distribution of the thermoelectric microwave power sensor. In this 3D model, the heat flux density decreases from the upper surface to the lower surface of the GaAs substrate while it was supposed to be a constant in the 2D model. The power sensor is fabricated by a GaAs monolithic microwave integrated circuit (MMIC) process and micro-electro-mechanical system (MEMS) technology. The microwave performance experiment shows that the S11 is less than −26 dB over the frequency band of 1–10 GHz. The power response experiment demonstrates that the output voltage increases from 0 mV to 27 mV, while the incident power varies from 1 mW to 100 mW. The measured sensitivity is about 0.27 mV/mW, and the calculated result from the 3D model is 0.28 mV/mW. The relative error has been reduced from 7.5% of the 2D model to 3.7% of the 3D model. Full article
(This article belongs to the Special Issue Advanced Technologies and Techniques for Microwave and Wireless Sensors)
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26 pages, 8146 KiB  
Article
The Traffic Adaptive Data Dissemination (TrAD) Protocol for both Urban and Highway Scenarios
by Bin Tian, Kun Mean Hou and Haiying Zhou
Sensors 2016, 16(6), 920; https://doi.org/10.3390/s16060920 - 21 Jun 2016
Cited by 14 | Viewed by 6312
Abstract
The worldwide economic cost of road crashes and injuries is estimated to be US$518 billion per year and the annual congestion cost in France is estimated to be €5.9 billion. Vehicular Ad hoc Networks (VANETs) are one solution to improve transport features such [...] Read more.
The worldwide economic cost of road crashes and injuries is estimated to be US$518 billion per year and the annual congestion cost in France is estimated to be €5.9 billion. Vehicular Ad hoc Networks (VANETs) are one solution to improve transport features such as traffic safety, traffic jam and infotainment on wheels, where a great number of event-driven messages need to be disseminated in a timely way in a region of interest. In comparison with traditional wireless networks, VANETs have to consider the highly dynamic network topology and lossy links due to node mobility. Inter-Vehicle Communication (IVC) protocols are the keystone of VANETs. According to our survey, most of the proposed IVC protocols focus on either highway or urban scenarios, but not on both. Furthermore, too few protocols, considering both scenarios, can achieve high performance. In this paper, an infrastructure-less Traffic Adaptive data Dissemination (TrAD) protocol which takes into account road traffic and network traffic status for both highway and urban scenarios will be presented. TrAD has double broadcast suppression techniques and is designed to adapt efficiently to the irregular road topology. The performance of the TrAD protocol was evaluated quantitatively by means of realistic simulations taking into account different real road maps, traffic routes and vehicular densities. The obtained simulation results show that TrAD is more efficient in terms of packet delivery ratio, number of transmissions and delay in comparison with the performance of three well-known reference protocols. Moreover, TrAD can also tolerate a reasonable degree of GPS drift and still achieve efficient data dissemination. Full article
(This article belongs to the Special Issue Smart City: Vision and Reality)
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6 pages, 2312 KiB  
Technical Note
Development and Performance Characteristics of Personal Gamma Spectrometer for Radiation Monitoring Applications
by Hye Min Park and Koan Sik Joo
Sensors 2016, 16(6), 919; https://doi.org/10.3390/s16060919 - 21 Jun 2016
Cited by 11 | Viewed by 7494
Abstract
In this study, a personal gamma (γ) spectrometer was developed for use in applications in various fields, such as homeland security and environmental radiation monitoring systems. The prototype consisted of a 3 × 3 × 20 mm3 Ce-doped Gd–Al–Ga–garnet (Ce:GAGG) crystal that [...] Read more.
In this study, a personal gamma (γ) spectrometer was developed for use in applications in various fields, such as homeland security and environmental radiation monitoring systems. The prototype consisted of a 3 × 3 × 20 mm3 Ce-doped Gd–Al–Ga–garnet (Ce:GAGG) crystal that was coupled to a Si photomultiplier (SiPM) to measure γ radiation. The γ spectrometer could be accessed remotely via a mobile device. At room temperature, the implemented Ce:GAGG-SiPM spectrometer achieved energy resolutions of 13.5%, 6.9%, 5.8%, and 2.3% for 133Ba at 0.356 MeV, 22Na at 0.511 MeV, 137Cs at 0.662 MeV, and 60Co at 1.33 MeV, respectively. It consumed only about 2.7 W of power, had a mass of just 340 g (including the battery), and measured only 5.0 × 7.0 cm2. Full article
(This article belongs to the Section Physical Sensors)
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11 pages, 2674 KiB  
Article
A Single Nanobelt Transistor for Gas Identification: Using a Gas-Dielectric Strategy
by Bin Cai, Zhiqi Song, Yanhong Tong, Qingxin Tang, Talgar Shaymurat and Yichun Liu
Sensors 2016, 16(6), 917; https://doi.org/10.3390/s16060917 - 21 Jun 2016
Cited by 4 | Viewed by 5904
Abstract
Despite tremendous potential and urgent demand in high-response low-cost gas identification, the development of gas identification based on a metal oxide semiconductor nanowire/nanobelt remains limited by fabrication complexity and redundant signals. Researchers have shown a multisensor-array strategy with “one key to one lock” [...] Read more.
Despite tremendous potential and urgent demand in high-response low-cost gas identification, the development of gas identification based on a metal oxide semiconductor nanowire/nanobelt remains limited by fabrication complexity and redundant signals. Researchers have shown a multisensor-array strategy with “one key to one lock” configuration. Here, we describe a new strategy to create high-response room-temperature gas identification by employing gas as dielectric. This enables gas discrimination down to the part per billion (ppb) level only based on one pristine single nanobelt transistor, with the excellent average Mahalanobis distance (MD) as high as 35 at the linear discriminant analysis (LDA) space. The single device realizes the selective recognition function of electronic nose. The effect of the gas dielectric on the response of the multiple field-effect parameters is discussed by the comparative investigation of gas and solid-dielectric devices and the studies on trap density changes in the conductive channel. The current work opens up exciting opportunities for room-temperature gas recognition based on the pristine single device. Full article
(This article belongs to the Special Issue Gas Nanosensors)
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26 pages, 5421 KiB  
Article
Angle-of-Arrival Assisted GNSS Collaborative Positioning
by Bin Huang, Zheng Yao, Xiaowei Cui and Mingquan Lu
Sensors 2016, 16(6), 918; https://doi.org/10.3390/s16060918 - 20 Jun 2016
Cited by 9 | Viewed by 8575
Abstract
For outdoor and global navigation satellite system (GNSS) challenged scenarios, collaborative positioning algorithms are proposed to fuse information from GNSS satellites and terrestrial wireless systems. This paper derives the Cramer-Rao lower bound (CRLB) and algorithms for the angle-of-arrival (AOA)-assisted GNSS collaborative positioning. Based [...] Read more.
For outdoor and global navigation satellite system (GNSS) challenged scenarios, collaborative positioning algorithms are proposed to fuse information from GNSS satellites and terrestrial wireless systems. This paper derives the Cramer-Rao lower bound (CRLB) and algorithms for the angle-of-arrival (AOA)-assisted GNSS collaborative positioning. Based on the CRLB model and collaborative positioning algorithms, theoretical analysis are performed to specify the effects of various factors on the accuracy of collaborative positioning, including the number of users, their distribution and AOA measurements accuracy. Besides, the influences of the relative location of the collaborative users are also discussed in order to choose appropriate neighboring users, which is in favor of reducing computational complexity. Simulations and actual experiment are carried out with several GNSS receivers in different scenarios, and the results are consistent with theoretical analysis. Full article
(This article belongs to the Section Physical Sensors)
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11 pages, 1259 KiB  
Article
An Assessment of the Influence of the Industry Distribution Chain on the Oxygen Levels in Commercial Modified Atmosphere Packaged Cheddar Cheese Using Non-Destructive Oxygen Sensor Technology
by Karen A.M. O’ Callaghan, Dmitri B. Papkovsky and Joseph P. Kerry
Sensors 2016, 16(6), 916; https://doi.org/10.3390/s16060916 - 20 Jun 2016
Cited by 18 | Viewed by 5533
Abstract
The establishment and control of oxygen levels in packs of oxygen-sensitive food products such as cheese is imperative in order to maintain product quality over a determined shelf life. Oxygen sensors quantify oxygen concentrations within packaging using a reversible optical measurement process, and [...] Read more.
The establishment and control of oxygen levels in packs of oxygen-sensitive food products such as cheese is imperative in order to maintain product quality over a determined shelf life. Oxygen sensors quantify oxygen concentrations within packaging using a reversible optical measurement process, and this non-destructive nature ensures the entire supply chain can be monitored and can assist in pinpointing negative issues pertaining to product packaging. This study was carried out in a commercial cheese packaging plant and involved the insertion of 768 sensors into 384 flow-wrapped cheese packs (two sensors per pack) that were flushed with 100% carbon dioxide prior to sealing. The cheese blocks were randomly assigned to two different storage groups to assess the effects of package quality, packaging process efficiency, and handling and distribution on package containment. Results demonstrated that oxygen levels increased in both experimental groups examined over the 30-day assessment period. The group subjected to a simulated industrial distribution route and handling procedures of commercial retailed cheese exhibited the highest level of oxygen detected on every day examined and experienced the highest rate of package failure. The study concluded that fluctuating storage conditions, product movement associated with distribution activities, and the possible presence of cheese-derived contaminants such as calcium lactate crystals were chief contributors to package failure. Full article
(This article belongs to the Section Chemical Sensors)
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16 pages, 3102 KiB  
Article
Love Acoustic Wave-Based Devices and Molecularly-Imprinted Polymers as Versatile Sensors for Electronic Nose or Tongue for Cancer Monitoring
by Corinne Dejous, Hamida Hallil, Vincent Raimbault, Jean-Luc Lachaud, Bernard Plano, Raphaël Delépée, Patrick Favetta, Luigi Agrofoglio and Dominique Rebière
Sensors 2016, 16(6), 915; https://doi.org/10.3390/s16060915 - 20 Jun 2016
Cited by 30 | Viewed by 8560
Abstract
Cancer is a leading cause of death worldwide and actual analytical techniques are restrictive in detecting it. Thus, there is still a challenge, as well as a need, for the development of quantitative non-invasive tools for the diagnosis of cancers and the follow-up [...] Read more.
Cancer is a leading cause of death worldwide and actual analytical techniques are restrictive in detecting it. Thus, there is still a challenge, as well as a need, for the development of quantitative non-invasive tools for the diagnosis of cancers and the follow-up care of patients. We introduce first the overall interest of electronic nose or tongue for such application of microsensors arrays with data processing in complex media, either gas (e.g., Volatile Organic Compounds or VOCs as biomarkers in breath) or liquid (e.g., modified nucleosides as urinary biomarkers). Then this is illustrated with a versatile acoustic wave transducer, functionalized with molecularly-imprinted polymers (MIP) synthesized for adenosine-5′-monophosphate (AMP) as a model for nucleosides. The device including the thin film coating is described, then static measurements with scanning electron microscopy (SEM) and electrical characterization after each step of the sensitive MIP process (deposit, removal of AMP template, capture of AMP target) demonstrate the thin film functionality. Dynamic measurements with a microfluidic setup and four targets are presented afterwards. They show a sensitivity of 5 Hz·ppm−1 of the non-optimized microsensor for AMP detection, with a specificity of three times compared to PMPA, and almost nil sensitivity to 3′AMP and CMP, in accordance with previously published results on bulk MIP. Full article
(This article belongs to the Special Issue E-noses: Sensors and Applications)
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9 pages, 3788 KiB  
Article
Characterization of a Functional Hydrogel Layer on a Silicon-Based Grating Waveguide for a Biochemical Sensor
by Yoo-Seung Hong, Jongseong Kim and Hyuk-Kee Sung
Sensors 2016, 16(6), 914; https://doi.org/10.3390/s16060914 - 18 Jun 2016
Cited by 8 | Viewed by 5408
Abstract
We numerically demonstrated the characteristics of a functional hydrogel layer on a silicon-based grating waveguide for a simple, cost-effective refractive index (RI) biochemical sensor. The RI of the functional hydrogel layer changes when a specific biochemical interaction occurs between the hydrogel-linked receptors and [...] Read more.
We numerically demonstrated the characteristics of a functional hydrogel layer on a silicon-based grating waveguide for a simple, cost-effective refractive index (RI) biochemical sensor. The RI of the functional hydrogel layer changes when a specific biochemical interaction occurs between the hydrogel-linked receptors and injected ligand molecules. The transmission spectral profile of the grating waveguide shifts depends on the amount of RI change caused by the functional layer. Our characterization includes the effective RI change caused by the thickness, functional volume ratio, and functional strength of the hydrogel layer. The results confirm the feasibility of, and set design rules for, hydrogel-assisted silicon-based grating waveguides. Full article
(This article belongs to the Special Issue Label-Free Optical Biosensors)
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