http://www.mdpi.com/section/physicalsensors http://www.mdpi.com/1424-8220/12/2/2005/ Studies on fault detection and diagnosis of planetary gearboxes are quite limited compared with those of fixed-axis gearboxes. Different from fixed-axis gearboxes, planetary gearboxes exhibit unique behaviors, which invalidate fault diagnosis methods that work well for fixed-axis gearboxes. It is a fact that for systems as complex as planetary gearboxes, multiple sensors mounted on different locations provide complementary information on the health condition of the systems. On this basis, a fault detection method based on multi-sensor data fusion is introduced in this paper. In this method, two features developed for planetary gearboxes are used to characterize the gear health conditions, and an adaptive neuro-fuzzy inference system (ANFIS) is utilized to fuse all features from different sensors. In order to demonstrate the effectiveness of the proposed method, experiments are carried out on a planetary gearbox test rig, on which multiple accelerometers are mounted for data collection. The comparisons between the proposed method and the methods based on individual sensors show that the former achieves much higher accuracies in detecting planetary gearbox faults. http://www.mdpi.com/1424-8220/12/2/2005/ Fri, 10 Feb 2012 00:00:00 CET Sensors 2012-02-10 12 2 Article 2005 2017 1424-8220 A Method Based on Multi-Sensor Data Fusion for Fault Detection of Planetary Gearboxes 2012-02-10 doi: 10.3390/s120202005 Yaguo Lei Jing Lin Zhengjia He Detong Kong http://www.mdpi.com/1424-8220/12/2/1990/ The mean shift algorithm has achieved considerable success in target tracking due to its simplicity and robustness. However, the lack of spatial information may result in its failure to get high tracking precision. This might be even worse when the target is scale variant and the sequences are gray-levels. This paper presents a novel multiple subtemplates based tracking algorithm for the terminal guidance application. By applying a separate tracker to each subtemplate, it can handle more complicated situations such as rotation, scaling, and partial coverage of the target. The innovations include: (1) an optimal subtemplates selection algorithm is designed, which ensures that the selected subtemplates maximally represent the information of the entire template while having the least mutual redundancy; (2) based on the serial tracking results and the spatial constraint prior to those subtemplates, a Gaussian weighted voting method is proposed to locate the target center; (3) the optimal scale factor is determined by maximizing the voting results among the scale searching layers, which avoids the complicated threshold setting problem. Experiments on some videos with static scenes show that the proposed method greatly improves the tracking accuracy compared to the original mean shift algorithm. http://www.mdpi.com/1424-8220/12/2/1990/ Fri, 10 Feb 2012 00:00:00 CET Sensors 2012-02-10 12 2 Article 1990 2004 1424-8220 Robust Kernel-Based Tracking with Multiple Subtemplates in Vision Guidance System 2012-02-10 doi: 10.3390/s120201990 Yuzhuang Yan Xinsheng Huang Wanying Xu Lurong Shen http://www.mdpi.com/1424-8220/12/2/1967/ Methodologies and algorithms are presented for the secure cooperation of a team of autonomous mobile underwater sensors, connected through an acoustic communication network, within surveillance and patrolling applications. In particular, the work proposes a cooperative algorithm in which the mobile underwater sensors (installed on Autonomous Underwater Vehicles—AUVs) respond to simple local rules based on the available information to perform the mission and maintain the communication link with the network (behavioral approach). The algorithm is intrinsically robust: with loss of communication among the vehicles the coverage performance (i.e., the mission goal) is degraded but not lost. The ensuing form of graceful degradation provides also a reactive measure against Denial of Service. The cooperative algorithm relies on the fact that the available information from the other sensors, though not necessarily complete, is trustworthy. To ensure trustworthiness, a security suite has been designed, specifically oriented to the underwater scenario, and in particular with the goal of reducing the communication overhead introduced by security in terms of number and size of messages. The paper gives implementation details on the integration between the security suite and the cooperative algorithm and provides statistics on the performance of the system as collected during the UAN project sea trial held in Trondheim, Norway, in May 2011. http://www.mdpi.com/1424-8220/12/2/1967/ Fri, 10 Feb 2012 00:00:00 CET Sensors 2012-02-10 12 2 Article 1967 1989 1424-8220 Secure Cooperation of Autonomous Mobile Sensors Using an Underwater Acoustic Network 2012-02-10 doi: 10.3390/s120201967 Andrea Caiti Vincenzo Calabrò Gianluca Dini Angelica Lo Duca Andrea Munafò http://www.mdpi.com/1424-8220/12/2/1950/ We present a study of an electrical model of electromechanically active carbon-polymer composite (CPC) with carbide-derived carbon (CDC) electrodes. The major focus is on investigation of surface electrode behavior upon external bending of the material. We show that electrical impedance measured from the surface of the CDC-based CPC can be used to determine the curvature of the material and, hence, the tip displacement of a CPC laminate in a cantilever configuration. It is also shown that by measuring surface signals in the process of an actuator’s work-cycle, we obtain a self-sensing collision-detecting CPC actuator that can be considered as a counterpart of biomimetic vibrissae. http://www.mdpi.com/1424-8220/12/2/1950/ Fri, 10 Feb 2012 00:00:00 CET Sensors 2012-02-10 12 2 Article 1950 1966 1424-8220 Electrical Model of a Carbon-Polymer Composite (CPC) Collision Detector 2012-02-10 doi: 10.3390/s120201950 Karl Kruusamäe Andres Punning Alvo Aabloo http://www.mdpi.com/1424-8220/12/2/1930/ Water monitoring is important in domains including documenting climate change, weather prediction and fishing. This paper presents a simple and energy efficient localization strategy for near surface buoy based sensors. Sensors can be dropped randomly in the ocean and thus self-calibrate in terms of geographic location such that geo-tagged observations of water quality can be made without the need for costly and energy consuming GPS-hardware. The strategy is based on nodes with an accurate clock and light sensors that can regularly sample the level of light intensity. The measurements are fitted into a celestial model of the earth motion around the sun. By identifying the trajectory of the sun across the skies one can accurately determine sunrise and sunset times, and thus extract the longitude and latitude of the sensor. Unlike previous localization techniques for underwater sensors, the current approach does not rely on stationary or mobile reference points. http://www.mdpi.com/1424-8220/12/2/1930/ Fri, 10 Feb 2012 00:00:00 CET Sensors 2012-02-10 12 2 Article 1930 1949 1424-8220 Sunlight Intensity Based Global Positioning System for Near-Surface Underwater Sensors 2012-02-10 doi: 10.3390/s120201930 Javier V. Gómez Frode E. Sandnes Borja Fernández http://www.mdpi.com/1424-8220/12/2/1919/ There have been only few studies to substantiate the kinematic characteristics of cursor movement. In this study, a quantitative experimental research method was used to explore the effect of moving direction on the kinematics of cursor movement in 24 typical young persons using our previously developed computerized measuring program. The results of multiple one way repeated measures ANOVAs and post hoc LSD tests demonstrated that the moving direction had effects on average velocity, movement time, movement unit and peak velocity. Moving leftward showed better efficiency than moving rightward, upward and downward from the kinematic evidences such as velocity, movement unit and time. Moreover, the unique pattern of the power spectral density (PSD) of velocity (strategy for power application) explained why the smoothness was still maintained while moving leftward even under an unstable situation with larger momentum. Moreover, the information from this cursor moving study can guide us to relocate the toolbars and icons in the window interface, especially for individuals with physical disabilities whose performances are easily interrupted while controlling the cursor in specific directions. http://www.mdpi.com/1424-8220/12/2/1919/ Fri, 10 Feb 2012 00:00:00 CET Sensors 2012-02-10 12 2 Article 1919 1929 1424-8220 The Effect of Direction on Cursor Moving Kinematics 2012-02-10 doi: 10.3390/s120201919 Ling-Fu Meng Hsin-Yung Chen Chiu-Ping Lu Ming-Chung Chen Chi-Nung Chu http://www.mdpi.com/1424-8220/12/2/1898/ Because of their small size, passive nature, immunity to electromagnetic interference, and capability to directly measure physical parameters such as temperature and strain, fiber Bragg grating sensors have developed beyond a laboratory curiosity and are becoming a mainstream sensing technology. Recently, high temperature stable gratings based on regeneration techniques and femtosecond infrared laser processing have shown promise for use in extreme environments such as high temperature, pressure or ionizing radiation. Such gratings are ideally suited for energy production applications where there is a requirement for advanced energy system instrumentation and controls that are operable in harsh environments. This paper will present a review of some of the more recent developments. http://www.mdpi.com/1424-8220/12/2/1898/ Fri, 10 Feb 2012 00:00:00 CET Sensors 2012-02-10 12 2 Review 1898 1918 1424-8220 Fiber Bragg Grating Sensors for Harsh Environments 2012-02-10 doi: 10.3390/s120201898 Stephen J. Mihailov http://www.mdpi.com/1424-8220/12/2/1863/ This paper proposes a novel hardware implementation of a dense recovery of stereovision 3D measurements. Traditionally 3D stereo systems have imposed the maximum number of stereo correspondences, introducing a large restriction on artificial vision algorithms. The proposed system-on-chip (SoC) provides great performance and efficiency, with a scalable architecture available for many different situations, addressing real time processing of stereo image flow. Using double buffering techniques properly combined with pipelined processing, the use of reconfigurable hardware achieves a parametrisable SoC which gives the designer the opportunity to decide its right dimension and features. The proposed architecture does not need any external memory because the processing is done as image flow arrives. Our SoC provides 3D data directly without the storage of whole stereo images. Our goal is to obtain high processing speed while maintaining the accuracy of 3D data using minimum resources. Configurable parameters may be controlled by later/parallel stages of the vision algorithm executed on an embedded processor. Considering hardware FPGA clock of 100 MHz, image flows up to 50 frames per second (fps) of dense stereo maps of more than 30,000 depth points could be obtained considering 2 Mpix images, with a minimum initial latency. The implementation of computer vision algorithms on reconfigurable hardware, explicitly low level processing, opens up the prospect of its use in autonomous systems, and they can act as a coprocessor to reconstruct 3D images with high density information in real time. http://www.mdpi.com/1424-8220/12/2/1863/ Fri, 10 Feb 2012 00:00:00 CET Sensors 2012-02-10 12 2 Article 1863 1884 1424-8220 Parametric Dense Stereovision Implementation on a System-on Chip (SoC) 2012-02-10 doi: 10.3390/s120201863 Alfredo Gardel Pablo Montejo Jorge García Ignacio Bravo José L. Lázaro http://www.mdpi.com/1424-8220/12/2/1827/ Deploying a multi-hop underwater acoustic sensor network (UASN) in a large area brings about new challenges in reliable data transmissions and survivability of network due to the limited underwater communication range/bandwidth and the limited energy of underwater sensor nodes. In order to address those challenges and achieve the objectives of maximization of data delivery ratio and minimization of energy consumption of underwater sensor nodes, this paper proposes a new underwater routing scheme, namely AURP (AUV-aided underwater routing protocol), which uses not only heterogeneous acoustic communication channels but also controlled mobility of multiple autonomous underwater vehicles (AUVs). In AURP, the total data transmissions are minimized by using AUVs as relay nodes, which collect sensed data from gateway nodes and then forward to the sink. Moreover, controlled mobility of AUVs makes it possible to apply a short-range high data rate underwater channel for transmissions of a large amount of data. To the best to our knowledge, this work is the first attempt to employ multiple AUVs as relay nodes in a multi-hop UASN to improve the network performance in terms of data delivery ratio and energy consumption. Simulations, which are incorporated with a realistic underwater acoustic communication channel model, are carried out to evaluate the performance of the proposed scheme, and the results indicate that a high delivery ratio and low energy consumption can be achieved. http://www.mdpi.com/1424-8220/12/2/1827/ Thu, 09 Feb 2012 00:00:00 CET Sensors 2012-02-09 12 2 Article 1827 1845 1424-8220 AURP: An AUV-Aided Underwater Routing Protocol for Underwater Acoustic Sensor Networks 2012-02-09 doi: 10.3390/s120201827 Seokhoon Yoon Abul K. Azad Hoon Oh Sunghwan Kim http://www.mdpi.com/1424-8220/12/2/1771/ This paper presents an architecture for computing vector disparity for active vision systems as used on robotics applications. The control of the vergence angle of a binocular system allows us to efficiently explore dynamic environments, but requires a generalization of the disparity computation with respect to a static camera setup, where the disparity is strictly 1-D after the image rectification. The interaction between vision and motor control allows us to develop an active sensor that achieves high accuracy of the disparity computation around the fixation point, and fast reaction time for the vergence control. In this contribution, we address the development of a real-time architecture for vector disparity computation using an FPGA device. We implement the disparity unit and the control module for vergence, version, and tilt to determine the fixation point. In addition, two on-chip different alternatives for the vector disparity engines are discussed based on the luminance (gradient-based) and phase information of the binocular images. The multiscale versions of these engines are able to estimate the vector disparity up to 32 fps on VGA resolution images with very good accuracy as shown using benchmark sequences with known ground-truth. The performances in terms of frame-rate, resource utilization, and accuracy of the presented approaches are discussed. On the basis of these results, our study indicates that the gradient-based approach leads to the best trade-off choice for the integration with the active vision system. http://www.mdpi.com/1424-8220/12/2/1771/ Thu, 09 Feb 2012 00:00:00 CET Sensors 2012-02-09 12 2 Article 1771 1799 1424-8220 Vector Disparity Sensor with Vergence Control for Active Vision Systems 2012-02-09 doi: 10.3390/s120201771 Francisco Barranco Javier Diaz Agostino Gibaldi Silvio P. Sabatini Eduardo Ros http://www.mdpi.com/1424-8220/12/2/1702/ Social interactions are a very important component in people’s lives. Social network analysis has become a common technique used to model and quantify the properties of social interactions. In this paper, we propose an integrated framework to explore the characteristics of a social network extracted from multimodal dyadic interactions. For our study, we used a set of videos belonging to New York Times’ Blogging Heads opinion blog. The Social Network is represented as an oriented graph, whose directed links are determined by the Influence Model. The links’ weights are a measure of the “influence” a person has over the other. The states of the Influence Model encode automatically extracted audio/visual features from our videos using state-of-the art algorithms. Our results are reported in terms of accuracy of audio/visual data fusion for speaker segmentation and centrality measures used to characterize the extracted social network. http://www.mdpi.com/1424-8220/12/2/1702/ Tue, 07 Feb 2012 00:00:00 CET Sensors 2012-02-07 12 2 Article 1702 1719 1424-8220 Social Network Extraction and Analysis Based on Multimodal Dyadic Interaction 2012-02-07 doi: 10.3390/s120201702 Sergio Escalera Xavier Baró Jordi Vitrià Petia Radeva Bogdan Raducanu http://www.mdpi.com/1424-8220/12/2/1688/ As the Internet evolved, social networks (such as Facebook) have bloomed and brought together an astonishing number of users. Mashing up mobile phones and sensors with these social environments enables the creation of people-centric sensing systems which have great potential for expanding our current social networking usage. However, such systems also have many associated technical challenges, such as privacy concerns, activity detection mechanisms or intermittent connectivity, as well as limitations due to the heterogeneity of sensor nodes and networks. Considering the openness of the Web 2.0, good technical solutions for these cases consist of frameworks that expose sensing data and functionalities as common Web-Services. This paper presents our RESTful Web Service-based model for people-centric sensing frameworks, which uses sensors and mobile phones to detect users’ activities and locations, sharing this information amongst the user’s friends within a social networking site. We also present some screenshot results of our experimental prototype. http://www.mdpi.com/1424-8220/12/2/1688/ Tue, 07 Feb 2012 00:00:00 CET Sensors 2012-02-07 12 2 Article 1688 1701 1424-8220 A Web Service-Based Framework Model for People-Centric Sensing Applications Applied to Social Networking 2012-02-07 doi: 10.3390/s120201688 David Nunes Thanh-Dien Tran Duarte Raposo André Pinto André Gomes Jorge Sá Silva http://www.mdpi.com/1424-8220/12/2/1612/ When a mobile wireless sensor is moving along heterogeneous wireless sensor networks, it can be under the coverage of more than one network many times. In these situations, the Vertical Handoff process can happen, where the mobile sensor decides to change its connection from a network to the best network among the available ones according to their quality of service characteristics. A fitness function is used for the handoff decision, being desirable to minimize it. This is an optimization problem which consists of the adjustment of a set of weights for the quality of service. Solving this problem efficiently is relevant to heterogeneous wireless sensor networks in many advanced applications. Numerous works can be found in the literature dealing with the vertical handoff decision, although they all suffer from the same shortfall: a non-comparable efficiency. Therefore, the aim of this work is twofold: first, to develop a fast decision algorithm that explores the entire space of possible combinations of weights, searching that one that minimizes the fitness function; and second, to design and implement a system on chip architecture based on reconfigurable hardware and embedded processors to achieve several goals necessary for competitive mobile terminals: good performance, low power consumption, low economic cost, and small area integration. http://www.mdpi.com/1424-8220/12/2/1612/ Tue, 07 Feb 2012 00:00:00 CET Sensors 2012-02-07 12 2 Article 1612 1624 1424-8220 Fast Decision Algorithms in Low-Power Embedded Processors for Quality-of-Service Based Connectivity of Mobile Sensors in Heterogeneous Wireless Sensor Networks 2012-02-07 doi: 10.3390/s120201612 María D. Jaraíz-Simón Juan A. Gómez-Pulido Miguel A. Vega-Rodríguez Juan M. Sánchez-Pérez http://www.mdpi.com/1424-8220/12/2/1594/ In this paper, a gait analysis system which estimates step length and foot angles is proposed. A measurement unit, which consists of a camera and inertial sensors, is installed on a shoe. When the foot touches the floor, markers are recognized by the camera to obtain the current position and attitude. A simple planar marker with 4,096 different codes is used. These markers printed on paper are placed on the floor. When the foot is moving off the floor, the position and attitude are estimated using an inertial navigation algorithm. For accurate estimation, a smoother is proposed, where vision information and inertial sensor data are combined. Through experiments, it is shown that the proposed system can both track foot motion and estimate step length. http://www.mdpi.com/1424-8220/12/2/1594/ Tue, 07 Feb 2012 00:00:00 CET Sensors 2012-02-07 12 2 Article 1594 1611 1424-8220 Gait Analysis Using Floor Markers and Inertial Sensors 2012-02-07 doi: 10.3390/s120201594 Tri Nhut Do Young Soo Suh http://www.mdpi.com/1424-8220/12/2/1529/ The pervasive use of wireless sensors in a growing spectrum of human activities reinforces the need for devices with low energy dissipation. In this work, coded communication between a couple of wireless sensor devices is considered as a method to reduce the dissipated energy per transmitted bit with respect to uncoded communication. Different Low Density Parity Check (LDPC) codes are considered to this purpose and post layout results are shown for a low-area low-energy decoder, which offers percentage energy savings with respect to the uncoded solution in the range of 40%–80%, depending on considered environment, distance and bit error rate. http://www.mdpi.com/1424-8220/12/2/1529/ Mon, 06 Feb 2012 00:00:00 CET Sensors 2012-02-06 12 2 Article 1529 1543 1424-8220 An LDPC Decoder Architecture for Wireless Sensor Network Applications 2012-02-06 doi: 10.3390/s120201529 Andrea Dario Giancarlo Biroli Maurizio Martina Guido Masera http://www.mdpi.com/1424-8220/12/2/1509/ This paper introduces a flexible hardware and software architecture for a smart video sensor. This sensor has been applied in a video surveillance application where some of these video sensors are deployed, constituting the sensory nodes of a distributed surveillance system. In this system, a video sensor node processes images locally in order to extract objects of interest, and classify them. The sensor node reports the processing results to other nodes in the cloud (a user or higher level software) in the form of an XML description. The hardware architecture of each sensor node has been developed using two DSP processors and an FPGA that controls, in a flexible way, the interconnection among processors and the image data flow. The developed node software is based on pluggable components and runs on a provided execution run-time. Some basic and application-specific software components have been developed, in particular: acquisition, segmentation, labeling, tracking, classification and feature extraction. Preliminary results demonstrate that the system can achieve up to 7.5 frames per second in the worst case, and the true positive rates in the classification of objects are better than 80%. http://www.mdpi.com/1424-8220/12/2/1509/ Fri, 03 Feb 2012 00:00:00 CET Sensors 2012-02-03 12 2 Article 1509 1528 1424-8220 Video Sensor Architecture for Surveillance Applications 2012-02-03 doi: 10.3390/s120201509 Jordi Sánchez Ginés Benet José E. Simó http://www.mdpi.com/1424-8220/12/2/1468/ This paper presents a proposal for an Artificial Neural Network (ANN)-based architecture for completion and prediction of data retrieved by underwater sensors. Due to the specific conditions under which these sensors operate, it is not uncommon for them to fail, and maintenance operations are difficult and costly. Therefore, completion and prediction of the missing data can greatly improve the quality of the underwater datasets. A performance study using real data is presented to validate the approach, concluding that the proposed architecture is able to provide very low errors. The numbers show as well that the solution is especially suitable for cases where large portions of data are missing, while in situations where the missing values are isolated the improvement over other simple interpolation methods is limited. http://www.mdpi.com/1424-8220/12/2/1468/ Thu, 02 Feb 2012 00:00:00 CET Sensors 2012-02-02 12 2 Article 1468 1481 1424-8220 Performance Study of the Application of Artificial Neural Networks to the Completion and Prediction of Data Retrieved by Underwater Sensors 2012-02-02 doi: 10.3390/s120201468 Carlos Baladrón Javier M. Aguiar Lorena Calavia Belén Carro Antonio Sánchez-Esguevillas Luis Hernández http://www.mdpi.com/1424-8220/12/2/1437/ Consumer-grade range cameras such as the Kinect sensor have the potential to be used in mapping applications where accuracy requirements are less strict. To realize this potential insight into the geometric quality of the data acquired by the sensor is essential. In this paper we discuss the calibration of the Kinect sensor, and provide an analysis of the accuracy and resolution of its depth data. Based on a mathematical model of depth measurement from disparity a theoretical error analysis is presented, which provides an insight into the factors influencing the accuracy of the data. Experimental results show that the random error of depth measurement increases with increasing distance to the sensor, and ranges from a few millimeters up to about 4 cm at the maximum range of the sensor. The quality of the data is also found to be influenced by the low resolution of the depth measurements. http://www.mdpi.com/1424-8220/12/2/1437/ Wed, 01 Feb 2012 00:00:00 CET Sensors 2012-02-01 12 2 Article 1437 1454 1424-8220 Accuracy and Resolution of Kinect Depth Data for Indoor Mapping Applications 2012-02-01 doi: 10.3390/s120201437 Kourosh Khoshelham Sander Oude Elberink http://www.mdpi.com/1424-8220/12/2/1398/ The temporal variability of hydrological variables in the Guadalquivir estuary was examined during three years through a real-time remote monitoring network (RTRM). The network was developed with the aim of studying the influence of hydrodynamical and hydrological features within the estuary on the functioning of the pelagic ecosystem. Completing this data-gathering network, monthly cruises were performed in order to measure biogeochemical variables that are indicative of the trophic status of the aquatic environment. The results showed that several sources of physical forcing, such as wind, tide-associated currents and river discharge were responsible for the spatio-temporal patterns of dissolved oxygen, salinity and turbidity in the estuary. The analysis was conducted under tidal and flood regime, which allowed us to identify river discharge as the main forcing agent of the hydrology inside the estuary. In particular, episodes of elevated turbidity detected by the network, together with episodes of low salinity and dissolved oxygen were closely related to the increase in water supply from a dam located upstream. The network installed provided accurate data that can be rapidly used for research or educational applications and by policy-makers or agencies in charge of the management of the coastal area. http://www.mdpi.com/1424-8220/12/2/1398/ Wed, 01 Feb 2012 00:00:00 CET Sensors 2012-02-01 12 2 Article 1398 1421 1424-8220 Use of a Real-Time Remote Monitoring Network (RTRM) to Characterize the Guadalquivir Estuary (Spain) 2012-02-01 doi: 10.3390/s120201398 Gabriel Navarro Isabel Emma Huertas Eduardo Costas Susana Flecha Manuel Díez-Minguito Isabel Caballero Victoria López-Rodas Laura Prieto Javier Ruiz http://www.mdpi.com/1424-8220/12/2/1336/ The feasibility of using Commercial Off-The-Shelf (COTS) sensor nodes is studied in a distributed network, aiming at dynamic surveillance and tracking of ground targets. Data acquisition by low-cost ( http://www.mdpi.com/1424-8220/12/2/1336/ Tue, 31 Jan 2012 00:00:00 CET Sensors 2012-01-31 12 2 Article 1336 1351 1424-8220 A Radar-Enabled Collaborative Sensor Network Integrating COTS Technology for Surveillance and Tracking 2012-01-31 doi: 10.3390/s120201336 Robert Kozma Lan Wang Khan Iftekharuddin Ernest McCracken Muhammad Khan Khandakar Islam Sushil R. Bhurtel R. Murat Demirer http://www.mdpi.com/1424-8220/12/2/1312/ Several Medium Access Control (MAC) and routing protocols have been developed in the last years for Underwater Wireless Sensor Networks (UWSNs). One of the main difficulties to compare and validate the performance of different proposals is the lack of a common standard to model the acoustic propagation in the underwater environment. In this paper we analyze the evolution of underwater acoustic prediction models from a simple approach to more detailed and accurate models. Then, different high layer network protocols are tested with different acoustic propagation models in order to determine the influence of environmental parameters on the obtained results. After several experiments, we can conclude that higher-level protocols are sensitive to both: (a) physical layer parameters related to the network scenario and (b) the acoustic propagation model. Conditions like ocean surface activity, scenario location, bathymetry or floor sediment composition, may change the signal propagation behavior. So, when designing network architectures for UWSNs, the role of the physical layer should be seriously taken into account in order to assert that the obtained simulation results will be close to the ones obtained in real network scenarios. http://www.mdpi.com/1424-8220/12/2/1312/ Tue, 31 Jan 2012 00:00:00 CET Sensors 2012-01-31 12 2 Article 1312 1335 1424-8220 Underwater Wireless Sensor Networks: How Do Acoustic Propagation Models Impact the Performance of Higher-Level Protocols? 2012-01-31 doi: 10.3390/s120201312 Jesús Llor Manuel P. Malumbres http://www.mdpi.com/1424-8220/12/2/1299/ Non-destructive methods are of great interest for the analysis of cultural heritage. Among the different possible techniques, this paper presents a low cost prototype based on the emission and reception of airborne ultrasound without direct contact with the test specimen. We successfully performed a method test for the detection of brick joints under a XVth century Renaissance fresco of the Metropolitan Cathedral of the city of Valencia (Spain). Both laboratory and in situ results are in agreement. Using this prototype system, an early moisture detection system has been installed in the dome that supports the fresco. The result is encouraging and opens interesting prospects for future research. http://www.mdpi.com/1424-8220/12/2/1299/ Tue, 31 Jan 2012 00:00:00 CET Sensors 2012-01-31 12 2 Article 1299 1311 1424-8220 Development of a Low-Cost Airborne Ultrasound Sensor for the Detection of Brick Joints behind a Wall Painting 2012-01-31 doi: 10.3390/s120201299 Fernando-Juan García-Diego José María Bravo Juan Pérez-Miralles Héctor Estrada Angel Fernández-Navajas http://www.mdpi.com/1424-8220/12/2/1288/ This paper describes the design, simulation and fabrication of an inductive angular position sensor on a flexible substrate. The sensor is composed of meandering silver coils printed on a flexible substrate (Kapton film) using inkjet technology. The flexibility enables that after printing in the plane, the coils could be rolled and put inside each other. By changing the angular position of the internal coil (rotor) related to the external one (stator), the mutual inductance is changed and consequently the impedance. It is possible to determine the angular position from the measured real and imaginary part of the impedance, in our case in the frequency range from 1 MHz to 10 MHz. Experimental results were compared with simulation results obtained by in-house developed software tool, and very good agreement has been achieved. Thanks to the simple design and fabrication, smaller package space requirements and weight, the presented sensor represents a cost-effective alternative to the other sensors currently used in series production applications. http://www.mdpi.com/1424-8220/12/2/1288/ Tue, 31 Jan 2012 00:00:00 CET Sensors 2012-01-31 12 2 Article 1288 1298 1424-8220 A Compact Inductive Position Sensor Made by Inkjet Printing Technology on a Flexible Substrate 2012-01-31 doi: 10.3390/s120201288 Nikola Jeranče Dragana Vasiljević Nataša Samardžić Goran Stojanović http://www.mdpi.com/1424-8220/12/2/1280/ To increase the responsivity is one of the vital issues for a photodetector. By employing ZnO as a representative material of ultraviolet photodetectors and Si as a representative material of visible photodetectors, an impact ionization process, in which additional carriers can be generated in an insulating layer at a relatively large electric field, has been employed to increase the responsivity of a semiconductor photodetector. It is found that the responsivity of the photodetectors can be enhanced by tens of times via this impact ionization process. The results reported in this paper provide a general route to enhance the responsivity of a photodetector, thus may represent a step towards high-performance photodetectors. http://www.mdpi.com/1424-8220/12/2/1280/ Tue, 31 Jan 2012 00:00:00 CET Sensors 2012-01-31 12 2 Article 1280 1287 1424-8220 Enhanced Responsivity of Photodetectors Realized via Impact Ionization 2012-01-31 doi: 10.3390/s120201280 Ji Yu Chong-Xin Shan Qian Qiao Xiu-Hua Xie Shuang-Peng Wang Zhen-Zhong Zhang De-Zhen Shen http://www.mdpi.com/1424-8220/12/2/1211/ A brain-computer interface (BCI) is a hardware and software communications system that permits cerebral activity alone to control computers or external devices. The immediate goal of BCI research is to provide communications capabilities to severely disabled people who are totally paralyzed or ‘locked in’ by neurological neuromuscular disorders, such as amyotrophic lateral sclerosis, brain stem stroke, or spinal cord injury. Here, we review the state-of-the-art of BCIs, looking at the different steps that form a standard BCI: signal acquisition, preprocessing or signal enhancement, feature extraction, classification and the control interface. We discuss their advantages, drawbacks, and latest advances, and we survey the numerous technologies reported in the scientific literature to design each step of a BCI. First, the review examines the neuroimaging modalities used in the signal acquisition step, each of which monitors a different functional brain activity such as electrical, magnetic or metabolic activity. Second, the review discusses different electrophysiological control signals that determine user intentions, which can be detected in brain activity. Third, the review includes some techniques used in the signal enhancement step to deal with the artifacts in the control signals and improve the performance. Fourth, the review studies some mathematic algorithms used in the feature extraction and classification steps which translate the information in the control signals into commands that operate a computer or other device. Finally, the review provides an overview of various BCI applications that control a range of devices. http://www.mdpi.com/1424-8220/12/2/1211/ Tue, 31 Jan 2012 00:00:00 CET Sensors 2012-01-31 12 2 Review 1211 1279 1424-8220 Brain Computer Interfaces, a Review 2012-01-31 doi: 10.3390/s120201211 Luis Fernando Nicolas-Alonso Jaime Gomez-Gil http://www.mdpi.com/1424-8220/12/2/1194/ Underwater environments are quite different from terrestrial environments in terms of the communication media and operating conditions associated with those environments. In underwater sensor networks, the probability of node failure is high because sensor nodes are deployed in harsher environments than ground-based networks. The sensor nodes are surrounded by salt water and moved around by waves and currents. Many studies have focused on underwater communication environments in an effort to improve the data transmission throughput. In this paper, we present a checkpointing scheme for the head nodes to quickly recover from a head node failure. Experimental results show that the proposed scheme enhances the reliability of the networks and makes them more efficient in terms of energy consumption and the recovery latency compared to the previous scheme without checkpointing. http://www.mdpi.com/1424-8220/12/2/1194/ Tue, 31 Jan 2012 00:00:00 CET Sensors 2012-01-31 12 2 Article 1194 1210 1424-8220 Enhancing the Reliability of Head Nodes in Underwater Sensor Networks 2012-01-31 doi: 10.3390/s120201194 Hong Min Yookun Cho Junyoung Heo http://www.mdpi.com/1424-8220/12/2/1170/ There is no literature mentioning the electromechanical behavior of micro structures driven by traveling electrostatic forces. This article is thus the first to present the dynamics and stabilities of a micro-ring subjected to a traveling electrostatic force. The traveling electrostatic force may be induced by sequentially actuated electrodes which are arranged around the flexible micro-ring. The analysis is based on a linearized distributed model considering the electromechanical coupling effects between electrostatic force and structure. The micro-ring will resonate when the traveling speeds of the electrostatic force approach some critical speeds. The critical speeds are equal to the ratio of the natural frequencies to the wave number of the correlative natural mode of the ring. Apart from resonance, the ring may be unstable at some unstable traveling speeds. The unstable regions appear not only near the critical speeds, but also near some fractions of some critical speeds differences. Furthermore the unstable regions expand with increasing driving voltage. This article may lead to a new research branch on electrostatic-driven micro devices. http://www.mdpi.com/1424-8220/12/2/1170/ Mon, 30 Jan 2012 00:00:00 CET Sensors 2012-01-30 12 2 Article 1170 1180 1424-8220 The Electromechanical Behavior of a Micro-Ring Driven by Traveling Electrostatic Force 2012-01-30 doi: 10.3390/s120201170 Xiuqian Ye Yibao Chen Da-Chih Chen Kuo-Yi Huang Yuh-Chung Hu http://www.mdpi.com/1424-8220/12/2/1148/ This paper presents a complete traffic sign recognition system based on vision sensor onboard a moving vehicle which detects and recognizes up to one hundred of the most important road signs, including circular and triangular signs. A restricted Hough transform is used as detection method from the information extracted in contour images, while the proposed recognition system is based on Support Vector Machines (SVM). A novel solution to the problem of discarding detected signs that do not pertain to the host road is proposed. For that purpose infrastructure-to-vehicle (I2V) communication and a stereo vision sensor are used. Furthermore, the outputs provided by the vision sensor and the data supplied by the CAN Bus and a GPS sensor are combined to obtain the global position of the detected traffic signs, which is used to identify a traffic sign in the I2V communication. This paper presents plenty of tests in real driving conditions, both day and night, in which an average detection rate over 95% and an average recognition rate around 93% were obtained with an average runtime of 35 ms that allows real-time performance. http://www.mdpi.com/1424-8220/12/2/1148/ Mon, 30 Jan 2012 00:00:00 CET Sensors 2012-01-30 12 2 Article 1148 1169 1424-8220 Complete Vision-Based Traffic Sign Recognition Supported by an I2V Communication System 2012-01-30 doi: 10.3390/s120201148 Miguel A. García-Garrido Manuel Ocaña David F. Llorca Estefanía Arroyo Jorge Pozuelo Miguel Gavilán http://www.mdpi.com/1424-8220/12/1/1100/ Contemporary 3D digitization systems employed by reverse engineering (RE) feature ever-growing scanning speeds with the ability to generate large quantity of points in a unit of time. Although advantageous for the quality and efficiency of RE modelling, the huge number of point datas can turn into a serious practical problem, later on, when the CAD model is generated. In addition, 3D digitization processes are very often plagued by measuring errors, which can be attributed to the very nature of measuring systems, various characteristics of the digitized objects and subjective errors by the operator, which also contribute to problems in the CAD model generation process. This paper presents an integral system for the pre-processing of point data, i.e., filtering, smoothing and reduction, based on a cross-sectional RE approach. In the course of the proposed system development, major emphasis was placed on the module for point data reduction, which was designed according to a novel approach with integrated deviation analysis and fuzzy logic reasoning. The developed system was verified through its application on three case studies, on point data from objects of versatile geometries obtained by contact and laser 3D digitization systems. The obtained results demonstrate the effectiveness of the system. http://www.mdpi.com/1424-8220/12/1/1100/ Fri, 20 Jan 2012 00:00:00 CET Sensors 2012-01-20 12 1 Article 1100 1126 1424-8220 Pre-Processing of Point-Data from Contact and Optical 3D Digitization Sensors 2012-01-20 doi: 10.3390/s120101100 Igor Budak Djordje Vukelić Drago Bračun Janko Hodolič Mirko Soković http://www.mdpi.com/1424-8220/12/1/1042/ A method for testing electronic instrument transformers is described, including electronic voltage and current transformers (EVTs, ECTs) with both analog and digital outputs. A testing device prototype is developed. It is based on digital signal processing of the signals that are measured at the secondary outputs of the tested transformer and the reference transformer when the same excitation signal is fed to their primaries. The test that estimates the performance of the prototype has been carried out at the National Centre for High Voltage Measurement and the prototype is approved for testing transformers with precision class up to 0.2 at the industrial frequency (50 Hz or 60 Hz). The device is suitable for on-site testing due to its high accuracy, simple structure and low-cost hardware. http://www.mdpi.com/1424-8220/12/1/1042/ Wed, 18 Jan 2012 00:00:00 CET Sensors 2012-01-18 12 1 Article 1042 1051 1424-8220 Electronic Voltage and Current Transformers Testing Device 2012-01-18 doi: 10.3390/s120101042 Feng Pan Ruimin Chen Yong Xiao Weiming Sun http://www.mdpi.com/1424-8220/12/1/1014/ The accurate measurement of diverse displacements of structures is an important index for the evaluation of a structure’s safety. In this study, a comparative analysis was conducted to determine the integrated RTK-GPS/accelerometer method that can provide the most precise structure displacement measurements. For this purpose, three methods of calculating the dynamic displacements from the acceleration data were comparatively analyzed. In addition, two methods of determining dynamic, static, and quasi-static displacements by integrating the displacements measured from the RTK-GPS system and the accelerometer were also comparatively analyzed. To ensure precise comparison results, a cantilever beam was manufactured onto which diverse types of displacements were generated to evaluate the measurement accuracy by method. Linear variable differential transformer (LVDT) measurements were used as references for the evaluation to ensure accuracy. The study results showed that the most suitable method of measuring the dynamic displacement with the accelerometer was to calculate the displacement by filtering and double-integrating the acceleration data using the FIR band-pass filter. The integration method that uses frequency-based displacement extraction was most appropriate for the integrated RTK-GPS/accelerometer method of comprehensively measuring the dynamic, static, and quasi-static displacements. http://www.mdpi.com/1424-8220/12/1/1014/ Tue, 17 Jan 2012 00:00:00 CET Sensors 2012-01-17 12 1 Article 1014 1034 1424-8220 Optimal Methods of RTK-GPS/Accelerometer Integration to Monitor the Displacement of Structures 2012-01-17 doi: 10.3390/s120101014 Jinsang Hwang Hongsik Yun Sun-Kyu Park Dongha Lee Sungnam Hong http://www.mdpi.com/1424-8220/12/1/1002/ Atrial fibrillation (AF) is the most common type of arrhythmia, and is characterized by a disordered contractile activity of the atria (top chambers of the heart). A popular treatment for AF is radiofrequency (RF) ablation. In about 2.4% of cardiac RF ablation procedures, the catheter is accidently pushed through the heart wall due to the application of excessive force. Despite the various capabilities of currently available technology, there has yet to be any data establishing how cardiac perforation can be reliably predicted. Thus, two new FBG based sensor prototypes were developed to monitor contact levels and predict perforation. Two live sheep were utilized during the study. It was observed during operation that peaks appeared in rhythm with the heart rate whenever firm contact was made between the sensor and the endocardial wall. The magnitude of these peaks varied with pressure applied by the operator. Lastly, transmural perforation of the left atrial wall was characterized by a visible loading phase and a rapid signal drop-off correlating to perforation. A possible pre-perforation signal was observed for the epoxy-based sensor in the form of a slight signal reversal (12–26% of loading phase magnitude) prior to perforation (occurring over 8 s). http://www.mdpi.com/1424-8220/12/1/1002/ Tue, 17 Jan 2012 00:00:00 CET Sensors 2012-01-17 12 1 Article 1002 1013 1424-8220 FBG Sensor for Contact Level Monitoring and Prediction of Perforation in Cardiac Ablation 2012-01-17 doi: 10.3390/s120101002 Siu Chun Michael Ho Mehdi Razavi Alireza Nazeri Gangbing Song http://www.mdpi.com/1424-8220/12/1/954/ This work provides a design for two types of sensors, based on the thermal dissipation and heat ratio methods of sap flow calculation, for moderate to large scale deployments for the purpose of monitoring tree transpiration. These designs include a procedure for making these sensors, a quality control method for the final products, and a complete list of components with vendors and pricing information. Both sensor designs were field tested alongside a commercial sap flow sensor to assess their performance and show the importance for quality controlling the sensor outputs. Results show that for roughly 2% of the cost of commercial sensors, self-made sap flow sensors can provide acceptable estimates of the sap flow measurements compared to the commercial sensors. http://www.mdpi.com/1424-8220/12/1/954/ Mon, 16 Jan 2012 00:00:00 CET Sensors 2012-01-16 12 1 Article 954 971 1424-8220 Sap Flow Sensors: Construction, Quality Control and Comparison 2012-01-16 doi: 10.3390/s120100954 Tyler W. Davis Chen-Min Kuo Xu Liang Pao-Shan Yu http://www.mdpi.com/1424-8220/12/1/905/ Particle separation is of great interest in many biological and biomedical applications. Flow-based methods have been used to sort particles and cells. However, the main challenge with flow based particle separation systems is the need for a sheath flow for successful operation. Existence of the sheath liquid dilutes the analyte, necessitates precise flow control between sample and sheath flow, requires a complicated design to create sheath flow and separation efficiency depends on the sheath liquid composition. In this paper, we present a microfluidic platform for sheathless particle separation using standing surface acoustic waves. In this platform, particles are first lined up at the center of the channel without introducing any external sheath flow. The particles are then entered into the second stage where particles are driven towards the off-center pressure nodes for size based separation. The larger particles are exposed to more lateral displacement in the channel due to the acoustic force differences. Consequently, different-size particles are separated into multiple collection outlets. The prominent feature of the present microfluidic platform is that the device does not require the use of the sheath flow for positioning and aligning of particles. Instead, the sheathless flow focusing and separation are integrated within a single microfluidic device and accomplished simultaneously. In this paper, we demonstrated two different particle size-resolution separations; (1) 3 µm and 10 µm and (2) 3 µm and 5 µm. Also, the effects of the input power, the flow rate, and particle concentration on the separation efficiency were investigated. These technologies have potential to impact broadly various areas including the essential microfluidic components for lab-on-a-chip system and integrated biological and biomedical applications. http://www.mdpi.com/1424-8220/12/1/905/ Mon, 16 Jan 2012 00:00:00 CET Sensors 2012-01-16 12 1 Article 905 922 1424-8220 Sheathless Size-Based Acoustic Particle Separation 2012-01-16 doi: 10.3390/s120100905 Rasim Guldiken Myeong Chan Jo Nathan D. Gallant Utkan Demirci Jiang Zhe http://www.mdpi.com/1424-8220/12/1/839/ This research presents a distributed and formula-based bilateration algorithm that can be used to provide initial set of locations. In this scheme each node uses distance estimates to anchors to solve a set of circle-circle intersection (CCI) problems, solved through a purely geometric formulation. The resulting CCIs are processed to pick those that cluster together and then take the average to produce an initial node location. The algorithm is compared in terms of accuracy and computational complexity with a Least-Squares localization algorithm, based on the Levenberg–Marquardt methodology. Results in accuracy vs. computational performance show that the bilateration algorithm is competitive compared with well known optimized localization algorithms. http://www.mdpi.com/1424-8220/12/1/839/ Thu, 12 Jan 2012 00:00:00 CET Sensors 2012-01-12 12 1 Article 839 862 1424-8220 A Low-Complexity Geometric Bilateration Method for Localization in Wireless Sensor Networks and Its Comparison with Least-Squares Methods 2012-01-12 doi: 10.3390/s120100839 Juan Cota-Ruiz Jose-Gerardo Rosiles Ernesto Sifuentes Pablo Rivas-Perea http://www.mdpi.com/1424-8220/12/1/753/ There is a need for low-cost, high-accuracy measurement of water content in various materials. This study assesses the performance of a new microwave swept frequency domain instrument (SFI) that has promise to provide a low-cost, high-accuracy alternative to the traditional and more expensive time domain reflectometry (TDR). The technique obtains permittivity measurements of soils in the frequency domain utilizing a through transmission configuration, transmissometry, which provides a frequency domain transmissometry measurement (FDT). The measurement is comparable to time domain transmissometry (TDT) with the added advantage of also being able to separately quantify the real and imaginary portions of the complex permittivity so that the measured bulk permittivity is more accurate that the measurement TDR provides where the apparent permittivity is impacted by the signal loss, which can be significant in heavier soils. The experimental SFI was compared with a high-end 12 GHz TDR/TDT system across a range of soils at varying soil water contents and densities. As propagation delay is the fundamental measurement of interest to the well-established TDR or TDT technique; the first set of tests utilized precision propagation delay lines to test the accuracy of the SFI instrument’s ability to resolve propagation delays across the expected range of delays that a soil probe would present when subjected to the expected range of soil types and soil moisture typical to an agronomic cropping system. The results of the precision-delay line testing suggests the instrument is capable of predicting propagation delays with a RMSE of +/−105 ps across the range of delays ranging from 0 to 12,000 ps with a coefficient of determination of r2 = 0.998. The second phase of tests noted the rich history of TDR for prediction of soil moisture and leveraged this history by utilizing TDT measured with a high-end Hewlett Packard TDR/TDT instrument to directly benchmark the SFI instrument over a range of soil types, at varying levels of moisture. This testing protocol was developed to provide the best possible comparison between SFI to TDT than would otherwise be possible by using soil moisture as the bench mark, due to variations in soil density between soil water content levels which are known to impact the calibration between TDR’s estimate of soil water content from the measured propagation delay which is converted to an apparent permittivity measurement. This experimental decision, to compare propagation delay of TDT to FDT, effectively removes the errors due to variations in packing density from the evaluation and provides a direct comparison between the SFI instrument and the time domain technique of TDT. The tests utilized three soils (a sand, an Acuff loam and an Olton clay-loam) that were packed to varying bulk densities and prepared to provide a range of water contents and electrical conductivities by which to compare the performance of the SFI technology to TDT measurements of propagation delay. For each sample tested, the SFI instrument and the TDT both performed the measurements on the exact same probe, thereby both instruments were measuring the exact same soil/soil-probe response to ensure the most accurate means to compare the SFI instrument to a high-end TDT instrument. Test results provided an estimated instrumental accuracy for the SFI of +/−0.98% of full scale, RMSE basis, for the precision delay lines and +/−1.32% when the SFI was evaluated on loam and clay loam soils, in comparison to TDT as the bench-mark. Results from both experiments provide evidence that the low-cost SFI approach is a viable alternative to conventional TDR/TDT for high accuracy applications. http://www.mdpi.com/1424-8220/12/1/753/ Wed, 11 Jan 2012 00:00:00 CET Sensors 2012-01-11 12 1 Article 753 767 1424-8220 Soil Moisture Sensing via Swept Frequency Based Microwave Sensors 2012-01-11 doi: 10.3390/s120100753 Mathew G. Pelletier Sundar Karthikeyan Timothy R. Green Robert C. Schwartz John D. Wanjura Greg A. Holt http://www.mdpi.com/1424-8220/12/1/704/ The specific characteristics of underwater environments introduce new challenges for networking protocols. In this paper, a specialized architecture for underwater sensor networks (UWSNs) is proposed and evaluated. Experiments are conducted in order to analyze the suitability of this protocol for the subaquatic transmission medium. Moreover, different scheduling techniques are applied to the architecture in order to study their performance. In addition, given the harsh conditions of the underwater medium, different retransmission methods are combined with the scheduling techniques. Finally, simulation results illustrate the performance achievements of the proposed protocol in end-to-end delay, packet delivery ratio and energy consumption, showing that this protocol can be very suitable for the underwater medium. http://www.mdpi.com/1424-8220/12/1/704/ Tue, 10 Jan 2012 00:00:00 CET Sensors 2012-01-10 12 1 Article 704 731 1424-8220 Underwater Sensor Networks: A New Energy Efficient and Robust Architecture 2012-01-10 doi: 10.3390/s120100704 Salvador Climent Juan Vicente Capella Nirvana Meratnia Juan José Serrano http://www.mdpi.com/1424-8220/12/1/585/ Background subtraction is considered the first processing stage in video surveillance systems, and consists of determining objects in movement in a scene captured by a static camera. It is an intensive task with a high computational cost. This work proposes an embedded novel architecture on FPGA which is able to extract the background on resource-limited environments and offers low degradation (produced because of the hardware-friendly model modification). In addition, the original model is extended in order to detect shadows and improve the quality of the segmentation of the moving objects. We have analyzed the resource consumption and performance in Spartan3 Xilinx FPGAs and compared to others works available on the literature, showing that the current architecture is a good trade-off in terms of accuracy, performance and resources utilization. With less than a 65% of the resources utilization of a XC3SD3400 Spartan-3A low-cost family FPGA, the system achieves a frequency of 66.5 MHz reaching 32.8 fps with resolution 1,024 x 1,024 pixels, and an estimated power consumption of 5.76 W. http://www.mdpi.com/1424-8220/12/1/585/ Thu, 05 Jan 2012 00:00:00 CET Sensors 2012-01-05 12 1 Article 585 611 1424-8220 FPGA Implementation for Real-Time Background Subtraction Based on Horprasert Model 2012-01-05 doi: 10.3390/s120100585 Rafael Rodriguez-Gomez Enrique J. Fernandez-Sanchez Javier Diaz Eduardo Ros http://www.mdpi.com/1424-8220/12/1/573/ Vision-based abnormal event detection for home healthcare systems can be greatly improved using visual sensor-based techniques able to detect, track and recognize objects in the scene. However, in moving object detection and tracking processes, moving cast shadows can be misclassified as part of objects or moving objects. Shadow removal is an essential step for developing video surveillance systems. The goal of the primary is to design novel computer vision techniques that can extract objects more accurately and discriminate between abnormal and normal activities. To improve the accuracy of object detection and tracking, our proposed shadow removal algorithm is employed. Abnormal event detection based on visual sensor by using shape features variation and 3-D trajectory is presented to overcome the low fall detection rate. The experimental results showed that the success rate of detecting abnormal events was 97% with a false positive rate of 2%. Our proposed algorithm can allow distinguishing diverse fall activities such as forward falls, backward falls, and falling asides from normal activities. http://www.mdpi.com/1424-8220/12/1/573/ Thu, 05 Jan 2012 00:00:00 CET Sensors 2012-01-05 12 1 Article 573 584 1424-8220 Visual Sensor Based Abnormal Event Detection with Moving Shadow Removal in Home Healthcare Applications 2012-01-05 doi: 10.3390/s120100573 Young-Sook Lee Wan-Young Chung http://www.mdpi.com/1424-8220/12/1/534/ This study proposes trenching piezoelectric (PZT) material in a thicker PZT pyroelectric cell to improve the temperature variation rate to enhance the efficiency of thermal energy-harvesting conversion by pyroelectricity. A thicker pyroelectric cell is beneficial in generating electricity pyroelectrically, but it hinders rapid temperature variations. Therefore, the PZT sheet was fabricated to produce deeper trenches to cause lateral temperature gradients induced by the trenched electrode, enhancing the temperature variation rate under homogeneous heat irradiation. When the trenched electrode type with an electrode width of 200 μm and a cutting depth of 150 μm was used to fabricate a PZT pyroelectric cell with a 200 μm thick PZT sheet, the temperature variation rate was improved by about 55%. Therefore, the trenched electrode design did indeed enhance the temperature variation rate and the efficiency of pyroelectric energy converters. http://www.mdpi.com/1424-8220/12/1/534/ Thu, 05 Jan 2012 00:00:00 CET Sensors 2012-01-05 12 1 Article 534 548 1424-8220 Improvement of Pyroelectric Cells for Thermal Energy Harvesting 2012-01-05 doi: 10.3390/s120100534 Chun-Ching Hsiao An-Shen Siao Jing-Chih Ciou http://www.mdpi.com/1424-8220/12/1/518/ Condition assessment of cables has gained considerable attention for the bridge safety. A magnetic flux leakage and magnetostrictive guided wave hybrid transducer is provided to inspect bridge cables. The similarities and differences between the two methods are investigated. The hybrid transducer for bridge cables consists of an aluminum framework, climbing modules, embedded magnetizers and a ribbon coil. The static axial magnetic field provided by the magnetizers meets the needs of the magnetic flux leakage testing and the magnetostrictive guided wave testing. The magnetizers also provide the attraction for the climbing modules. In the magnetic flux leakage testing for the free length of cable, the coil induces the axial leakage magnetic field. In the magnetostrictive guided wave testing for the anchorage zone, the coil provides a pulse high power variational magnetic field for generating guided waves; the coil induces the magnetic field variation for receiving guided waves. The experimental results show that the transducer with the corresponding inspection system could be applied to detect the broken wires in the free length and in the anchorage zone of bridge cables. http://www.mdpi.com/1424-8220/12/1/518/ Thu, 05 Jan 2012 00:00:00 CET Sensors 2012-01-05 12 1 Article 518 533 1424-8220 A Magnetic Flux Leakage and Magnetostrictive Guided Wave Hybrid Transducer for Detecting Bridge Cables 2012-01-05 doi: 10.3390/s120100518 Jiang Xu Xinjun Wu Cheng Cheng Anran Ben http://www.mdpi.com/1424-8220/12/1/489/ Surface electromyography (sEMG) is an important measurement for monitoring exercise and fitness. Because if its high sampling frequency requirement, wireless transmission of sEMG data is a challenge. In this article a wireless sEMG measurement system with a sampling frequency of 2 KHz is developed based upon a MSP 430 microcontroller and Bluetooth transmission. Standard isotonic and isometric muscle contraction are clearly represented in the receiving user interface. Muscle fatigue detection is an important application of sEMG. Traditional muscle fatigue is detected from the median frequency of the sEMG power spectrum. The regression slope of the linear regression of median frequency is an important muscle fatigue index. A more negative slope value represents a higher muscle fatigue condition. To test the system performance, muscle fatigue detection was examined by having subjects run on a pedaled-multifunctional elliptical trainer for approximately 30 minutes at three loading levels. Ten subjects underwent a total of 60 exercise sessions to provide the experimental data. Results showed that the regression slope gradually decreases as expected, and there is a significant gender difference. http://www.mdpi.com/1424-8220/12/1/489/ Thu, 05 Jan 2012 00:00:00 CET Sensors 2012-01-05 12 1 Article 489 499 1424-8220 A Wireless sEMG Recording System and Its Application to Muscle Fatigue Detection 2012-01-05 doi: 10.3390/s120100489 Kang-Ming Chang Shin-Hong Liu Xuan-Han Wu http://www.mdpi.com/1424-8220/12/1/429/ This paper presents a sensor fusion strategy applied for Simultaneous Localization and Mapping (SLAM) in dynamic environments. The designed approach consists of two features: (i) the first one is a fusion module which synthesizes line segments obtained from laser rangefinder and line features extracted from monocular camera. This policy eliminates any pseudo segments that appear from any momentary pause of dynamic objects in laser data. (ii) The second characteristic is a modified multi-sensor point estimation fusion SLAM (MPEF-SLAM) that incorporates two individual Extended Kalman Filter (EKF) based SLAM algorithms: monocular and laser SLAM. The error of the localization in fused SLAM is reduced compared with those of individual SLAM. Additionally, a new data association technique based on the homography transformation matrix is developed for monocular SLAM. This data association method relaxes the pleonastic computation. The experimental results validate the performance of the proposed sensor fusion and data association method. http://www.mdpi.com/1424-8220/12/1/429/ Wed, 04 Jan 2012 00:00:00 CET Sensors 2012-01-04 12 1 Article 429 452 1424-8220 Sensor Fusion of Monocular Cameras and Laser Rangefinders for Line-Based Simultaneous Localization and Mapping (SLAM) Tasks in Autonomous Mobile Robots 2012-01-04 doi: 10.3390/s120100429 Xinzheng Zhang Ahmad B. Rad Yiu-Kwong Wong http://www.mdpi.com/1424-8220/12/1/415/ A micro-displacement sensor consisting of a fiber-loop made with a tapered fiber is reported. The sensor operation is based on the interaction between the fundamental cladding mode propagating through the taper waist and higher order cladding modes excited when the taper is deformed to form a loop. As a result, a transmission spectrum with several notches is observed, where the notch wavelength resonances shift as a function of the loop diameter. The loop diameter is varied by the spatial displacement of one end of the fiber-loop attached to a linear translation stage. In a displacement range of 3.125 mm the maximum wavelength shift is 360.93 nm, with 0.116 nm/μm sensitivity. By using a 1,280 nm broadband low-power LED source and a single Ge-photodetector in a power transmission sensor setup, a sensitivity in the order of 2.7 nW/μm is obtained in ~1 mm range. The proposed sensor is easy to implement and has a plenty of room to improve its performance. http://www.mdpi.com/1424-8220/12/1/415/ Wed, 04 Jan 2012 00:00:00 CET Sensors 2012-01-04 12 1 Article 415 428 1424-8220 An Intrinsic Fiber-Optic Single Loop Micro-Displacement Sensor 2012-01-04 doi: 10.3390/s120100415 Alejandro Martinez-Rios David Monzon-Hernandez Ismael Torres-Gomez Guillermo Salceda-Delgado http://www.mdpi.com/1424-8220/12/1/373/ The micro-scale and meso-scale ocean dynamic processes which are nonlinear and have large variability, have a significant impact on the fisheries, natural resources, and marine climatology. A rapid, refined and sophisticated observation system is therefore needed in marine scientific research. The maneuverability and controllability of mobile sensor platforms make them a preferred choice to establish ocean observing networks, compared to the static sensor observing platform. In this study, marine vehicles are utilized as the nodes of mobile sensor networks for coverage sampling of a regional ocean area and ocean feature tracking. A synoptic analysis about marine vehicle dynamic control, multi vehicles mission assignment and path planning methods, and ocean feature tracking and observing techniques is given. Combined with the observation plan in the South China Sea, we provide an overview of the mobile sensor networks established with marine vehicles, and the corresponding simulation results. http://www.mdpi.com/1424-8220/12/1/373/ Mon, 02 Jan 2012 00:00:00 CET Sensors 2012-01-02 12 1 Article 373 390 1424-8220 Marine Vehicle Sensor Network Architecture and Protocol Designs for Ocean Observation 2012-01-02 doi: 10.3390/s120100373 Shaowei Zhang Jiancheng Yu Aiqun Zhang Lei Yang Yeqiang Shu http://www.mdpi.com/1424-8220/12/1/334/ Train wheel sets must be periodically inspected for possible or actual premature failures and it is very significant to record the wear history for the full life of utilization of wheel sets. This means that an online measuring system could be of great benefit to overall process control. An online non-contact method for measuring a wheel set’s geometric parameters based on the opto-electronic measuring technique is presented in this paper. A charge coupled device (CCD) camera with a selected optical lens and a frame grabber was used to capture the image of the light profile of the wheel set illuminated by a linear laser. The analogue signals of the image were transformed into corresponding digital grey level values. The ‘mapping function method’ is used to transform an image pixel coordinate to a space coordinate. The images of wheel sets were captured when the train passed through the measuring system. The rim inside thickness and flange thickness were measured and analyzed. The spatial resolution of the whole image capturing system is about 0.33 mm. Theoretic and experimental results show that the online measurement system based on computer vision can meet wheel set measurement requirements. http://www.mdpi.com/1424-8220/12/1/334/ Fri, 30 Dec 2011 00:00:00 CET Sensors 2011-12-30 12 1 Article 334 346 1424-8220 Computer Vision Based Method and System for Online Measurement of Geometric Parameters of Train Wheel Sets 2011-12-30 doi: 10.3390/s120100334 Zhi-Feng Zhang Zhan Gao Yuan-Yuan Liu Feng-Chun Jiang Yan-Li Yang Yu-Fen Ren Hong-Jun Yang Kun Yang Xiao-Dong Zhang http://www.mdpi.com/1424-8220/12/1/320/ This paper presents the design of a wireless pressure-monitoring system for harsh-environment applications. Two types of ceramic pressure sensors made with a low-temperature cofired ceramic (LTCC) were considered. The first type is a piezoresistive strain gauge pressure sensor. The second type is a capacitive pressure sensor, which is based on changes of the capacitance values between two electrodes: one electrode is fixed and the other is movable under an applied pressure. The design was primarily focused on low power consumption. Reliable operation in the presence of disturbances, like electromagnetic interference, parasitic capacitances, etc., proved to be contradictory constraints. A piezoresistive ceramic pressure sensor with a high bridge impedance was chosen for use in a wireless pressure-monitoring system and an acceptable solution using energy-harvesting techniques has been achieved. The described solution allows for the integration of a sensor element with an energy harvester that has a printed thick-film battery and complete electronics in a single substrate packaged inside a compact housing. http://www.mdpi.com/1424-8220/12/1/320/ Thu, 29 Dec 2011 00:00:00 CET Sensors 2011-12-29 12 1 Article 320 333 1424-8220 Ceramic MEMS Designed for Wireless Pressure Monitoring in the Industrial Environment 2011-12-29 doi: 10.3390/s120100320 Marko Pavlin Darko Belavic Franc Novak http://www.mdpi.com/1424-8220/12/1/278/ One of the greatest difficulties in stereo vision is the appearance of ambiguities when matching similar points from different images. In this article we analyze the effectiveness of using a fusion of multiple baselines and a range finder from a theoretical point of view, focusing on the results of using both prismatic and rotational articulations for baseline generation, and offer a practical case to prove its efficiency on an autonomous vehicle. http://www.mdpi.com/1424-8220/12/1/278/ Wed, 28 Dec 2011 00:00:00 CET Sensors 2011-12-28 12 1 Article 278 296 1424-8220 Fusion of a Variable Baseline System and a Range Finder 2011-12-28 doi: 10.3390/s120100278 Javier Hernández-Aceituno Leopoldo Acosta Rafael Arnay http://www.mdpi.com/1424-8220/12/1/233/ Deep displacement observation is one basic means of landslide dynamic study and early warning monitoring and a key part of engineering geological investigation. In our previous work, we proposed a novel electromagnetic induction-based deep displacement sensor (I-type) to predict deep horizontal displacement and a theoretical model called equation-based equivalent loop approach (EELA) to describe its sensing characters. However in many landslide and related geological engineering cases, both horizontal displacement and vertical displacement vary apparently and dynamically so both may require monitoring. In this study, a II-type deep displacement sensor is designed by revising our I-type sensor to simultaneously monitor the deep horizontal displacement and vertical displacement variations at different depths within a sliding mass. Meanwhile, a new theoretical modeling called the numerical integration-based equivalent loop approach (NIELA) has been proposed to quantitatively depict II-type sensors’ mutual inductance properties with respect to predicted horizontal displacements and vertical displacements. After detailed examinations and comparative studies between measured mutual inductance voltage, NIELA-based mutual inductance and EELA-based mutual inductance, NIELA has verified to be an effective and quite accurate analytic model for characterization of II-type sensors. The NIELA model is widely applicable for II-type sensors’ monitoring on all kinds of landslides and other related geohazards with satisfactory estimation accuracy and calculation efficiency. http://www.mdpi.com/1424-8220/12/1/233/ Wed, 28 Dec 2011 00:00:00 CET Sensors 2011-12-28 12 1 Article 233 259 1424-8220 A Theoretical Model to Predict Both Horizontal Displacement and Vertical Displacement for Electromagnetic Induction-Based Deep Displacement Sensors 2011-12-28 doi: 10.3390/s120100233 Nanying Shentu Hongjian Zhang Qing Li Hongliang Zhou Renyuan Tong Xiong Li http://www.mdpi.com/1424-8220/12/1/226/ A 1.1 µW power dissipation, voltage-output humidity sensor with 10% relative humidity accuracy was developed in the LFoundry 0.15 µm CMOS technology without post-processing. The sensor consists of a woven lateral array of electrodes implemented in CMOS top metal, a humidity-sensitive layer of Intervia Photodielectric 8023D-10, a CMOS capacitance to voltage converter, and the self-calibration circuitry. http://www.mdpi.com/1424-8220/12/1/226/ Tue, 27 Dec 2011 00:00:00 CET Sensors 2011-12-27 12 1 Article 226 232 1424-8220 Self-Calibrated Humidity Sensor in CMOS without Post-Processing 2011-12-27 doi: 10.3390/s120100226 Oleg Nizhnik Kohei Higuchi Kazusuke Maenaka