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Sensors, Volume 13, Issue 2 (February 2013) – 78 articles , Pages 1385-2699

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615 KiB  
Article
A Unified Framework for Activity Recognition-Based Behavior Analysis and Action Prediction in Smart Homes
by Iram Fatima, Muhammad Fahim, Young-Koo Lee and Sungyoung Lee
Sensors 2013, 13(2), 2682-2699; https://doi.org/10.3390/s130202682 - 22 Feb 2013
Cited by 77 | Viewed by 9903
Abstract
In recent years, activity recognition in smart homes is an active research area due to its applicability in many applications, such as assistive living and healthcare. Besides activity recognition, the information collected from smart homes has great potential for other application domains like [...] Read more.
In recent years, activity recognition in smart homes is an active research area due to its applicability in many applications, such as assistive living and healthcare. Besides activity recognition, the information collected from smart homes has great potential for other application domains like lifestyle analysis, security and surveillance, and interaction monitoring. Therefore, discovery of users common behaviors and prediction of future actions from past behaviors become an important step towards allowing an environment to provide personalized service. In this paper, we develop a unified framework for activity recognition-based behavior analysis and action prediction. For this purpose, first we propose kernel fusion method for accurate activity recognition and then identify the significant sequential behaviors of inhabitants from recognized activities of their daily routines. Moreover, behaviors patterns are further utilized to predict the future actions from past activities. To evaluate the proposed framework, we performed experiments on two real datasets. The results show a remarkable improvement of 13.82% in the accuracy on average of recognized activities along with the extraction of significant behavioral patterns and precise activity predictions with 6.76% increase in F-measure. All this collectively help in understanding the users” actions to gain knowledge about their habits and preferences. Full article
(This article belongs to the Section Physical Sensors)
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<p>The architecture of the proposed framework.</p> Full article ">
<p>Set of sequences with activity relationships.</p> Full article ">
<p>The design of CRF for activity sequences.</p> Full article ">
<p>Individual class accuracy of different kernel functions for <span class="html-italic">Milan2009.</span></p> Full article ">
<p>Individual class accuracy of different kernel functions for <span class="html-italic">Aruba.</span></p> Full article ">
<p>Sequential behavioral patterns for <span class="html-italic">Milan2009</span>.</p> Full article ">
<p>Sequential behavioral patterns for <span class="html-italic">Aruba.</span></p> Full article ">
<p>Behavioral predictions for <span class="html-italic">Milan2009.</span></p> Full article ">
<p>Behavioral predictions for <span class="html-italic">Aruba.</span></p> Full article ">
2169 KiB  
Article
An Incremental Target-Adapted Strategy for Active Geometric Calibration of Projector-Camera Systems
by Chia-Yen Chen and Hsiang-Jen Chien
Sensors 2013, 13(2), 2664-2681; https://doi.org/10.3390/s130202664 - 22 Feb 2013
Cited by 20 | Viewed by 8686
Abstract
The calibration of a projector-camera system is an essential step toward accurate 3-D measurement and environment-aware data projection applications, such as augmented reality. In this paper we present a two-stage easy-to-deploy strategy for robust calibration of both intrinsic and extrinsic parameters of a [...] Read more.
The calibration of a projector-camera system is an essential step toward accurate 3-D measurement and environment-aware data projection applications, such as augmented reality. In this paper we present a two-stage easy-to-deploy strategy for robust calibration of both intrinsic and extrinsic parameters of a projector. Two key components of the system are the automatic generation of projected light patterns and the incremental calibration process. Based on the incremental strategy, the calibration process first establishes a set of initial parameters, and then it upgrades these parameters incrementally using the projection and captured images of dynamically-generated calibration patterns. The scene-driven light patterns allow the system to adapt itself to the pose of the calibration target, such that the difficulty in feature detection is greatly lowered. The strategy forms a closed-loop system that performs self-correction as more and more observations become available. Compared to the conventional method, which requires a time-consuming process for the acquisition of dense pixel correspondences, the proposed method deploys a homography-based coordinate computation, allowing the calibration time to be dramatically reduced. The experimental results indicate that an improvement of 70% in reprojection errors is achievable and 95% of the calibration time can be saved. Full article
(This article belongs to the Section Physical Sensors)
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<p>(<b>a</b>) A chessboard commonly used to calibration an image sensor. (<b>b</b>) Dense reconstruction of the projector's view. (<b>c</b>) Visualization of camera-projector <span class="html-italic">x</span>-coordinate correspondences acquired using seven Gray-coded patterns and eight phase-shifting patterns.</p> Full article ">
<p>(<b>a</b>) Projection of calibration pattern onto a checkerboard. (<b>b</b>) The same pattern adaptively aligned to the checkerboard using the proposed method. By taking the geometric displacement into account, the feature points (inner corners) of the two patterns can now be identified distinguishingly.</p> Full article ">
<p>Core components of the proposed incremental calibration method.</p> Full article ">
<p>(<b>a</b>) Chessboard with the projection of line pattern. (<b>b</b>) Detection of the brightest pixels. (<b>c</b>) Result of applying the described RANSAC multi-modal line fitting algorithm.</p> Full article ">
<p>(<b>a</b>) A base image annotated with the <span class="html-italic">x</span>- and <span class="html-italic">y</span>-axis of the world coordinate system. Note the pattern is shifted by 10 mm in both directions, so that the corner features will hit square centers of the calibration target (<b>b</b>) A calibration pattern generated from the base image.</p> Full article ">
<p>(<b>a</b>) Image of the checkerboard with projection of the generated calibration pattern. (<b>b</b>) Rectified region of interest. (<b>c</b>) Histogram and the optimally determined thresholds. (<b>d</b>) Classified pixels, blue, red, and white pixels represent “dark”, “gray” and “bright” categories respectively.</p> Full article ">
<p>(<b>a</b>) Convolution kernel designed to respond corner feature. (<b>b</b>) Corner scores computed using convolution (<b>c</b>) Crosshairs showing the expected location (in red) and the actual location (in green) of a feature point. (<b>d</b>) The same algorithm without convolution can also be used to track spot features.</p> Full article ">
<p>History RMS of reprojection errors during the calibration process.</p> Full article ">
<p>Plane residuals of control points after triangulated using parameters calibrated from datasets (<b>a</b>) <b>A<span class="html-small-caps">da</span>C<span class="html-small-caps">heckers</span></b> (<b>b</b>) <b>A<span class="html-small-caps">da</span>S<span class="html-small-caps">pots</span></b><span class="html-small-caps">,</span> and (<b>c</b>) <b>C<span class="html-small-caps">onventional</span></b>.</p> Full article ">
1283 KiB  
Article
Autonomous Docking Based on Infrared System for Electric Vehicle Charging in Urban Areas
by Joshué Pérez, Fawzi Nashashibi, Benjamin Lefaudeux, Paulo Resende and Evangeline Pollard
Sensors 2013, 13(2), 2645-2663; https://doi.org/10.3390/s130202645 - 21 Feb 2013
Cited by 21 | Viewed by 11634
Abstract
Electric vehicles are progressively introduced in urban areas, because of their ability to reduce air pollution, fuel consumption and noise nuisance. Nowadays, some big cities are launching the first electric car-sharing projects to clear traffic jams and enhance urban mobility, as an alternative [...] Read more.
Electric vehicles are progressively introduced in urban areas, because of their ability to reduce air pollution, fuel consumption and noise nuisance. Nowadays, some big cities are launching the first electric car-sharing projects to clear traffic jams and enhance urban mobility, as an alternative to the classic public transportation systems. However, there are still some problems to be solved related to energy storage, electric charging and autonomy. In this paper, we present an autonomous docking system for electric vehicles recharging based on an embarked infrared camera performing infrared beacons detection installed in the infrastructure. A visual servoing system coupled with an automatic controller allows the vehicle to dock accurately to the recharging booth in a street parking area. The results show good behavior of the implemented system, which is currently deployed as a real prototype system in the city of Paris. Full article
(This article belongs to the Special Issue New Trends towards Automatic Vehicle Control and Perception Systems)
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<p>Elements of the system and docking maneuver of the AMARE project.</p> Full article ">
<p>Automated vehicle on the AMARE project.</p> Full article ">
<p>Recharging and docking station on the AMARE project.</p> Full article ">
<p>Control architecture for autonomous vehicles based on IR camera information.</p> Full article ">
<p>Detection algorithms using different models.</p> Full article ">
<p>Summary of the perception pipeline.</p> Full article ">
<p>Typical view from the system, on the side of a busy road.</p> Full article ">
<p>Variables used in the autonomous docking and experiments.</p> Full article ">
<p>Validation tests: positioning.</p> Full article ">
822 KiB  
Article
On the Effects of the Lateral Strains on the Fiber Bragg Grating Response
by Marco Lai, Dimitris Karalekas and John Botsis
Sensors 2013, 13(2), 2631-2644; https://doi.org/10.3390/s130202631 - 21 Feb 2013
Cited by 35 | Viewed by 8769
Abstract
In this paper, a combined experimental-numerical based work was undertaken to investigate the Bragg wavelength shift response of an embedded FBG sensor when subjected to different conditions of multi-axial loading (deformation). The following cases are examined: (a) when an isotropic host material with [...] Read more.
In this paper, a combined experimental-numerical based work was undertaken to investigate the Bragg wavelength shift response of an embedded FBG sensor when subjected to different conditions of multi-axial loading (deformation). The following cases are examined: (a) when an isotropic host material with no constrains on planes normal to the embedded sensor’s axis is biaxially loaded, (b) when the same isotropic host material is subjected to hydrostatic pressure and (c) when the hydrostatically loaded host material is an anisotropic one, as in the case of a composite material, where the optical fiber is embedded along the reinforcing fibers. The comparison of the experimental results and the finite element simulations shows that, when the axial strain on the FBG sensor is the dominant component, the standard wavelength-shift strain relation can be used even if large lateral strains apply on the sensor. However when this is not the case, large errors may be introduced in the conversion of the wavelength to axial strains on the fiber. This situation arises when the FBG is placed parallel to high modulus reinforcing fibers of a polymer composite. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
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<p>Schematic of an optical fiber with an FBG sensor subjected to strains.</p> Full article ">
<p>Evolution of normalized axial strains according to <a href="#FD9" class="html-disp-formula">Equation (7)</a>. See text for details.</p> Full article ">
<p>(<b>a</b>) FBG equipped specimen and loading actuators for biaxial testing, (<b>b</b>) Schematic of the pressure chamber setup (dimensions in mm).</p> Full article ">
<p>(<b>a</b>) Simulated axial and lateral deformations of the sensor in terms of <span class="html-italic">z</span>, (<b>b</b>) simulated axial strains at the specimen's center with different friction coefficients between epoxy block and grips compared to experimental data shown by the blue lines.</p> Full article ">
<p>Simulated strains in the fiber core in the case of, (<b>a</b>) bare fiber, (<b>b</b>) embedded in an epoxy cylinder, (<b>c</b>) embedded in a composite. The pressure is 1 MPa and the units are mm.</p> Full article ">
<p>Bare fiber subjected to hydrostatic pressure: comparison between strain calculated from the wavelength shift measurements and <a href="#FD4" class="html-disp-formula">Equation (4a)</a> with <span class="html-italic">p<sub>e</sub></span> = 0.2108 as well as <a href="#FD7" class="html-disp-formula">Equation (6a)</a> with <math display="inline"> <semantics id="sm31"> <mrow> <msubsup> <mi>p</mi> <mi>e</mi> <mrow> <mtext mathvariant="italic">eff</mtext></mrow></msubsup> <mo>=</mo> <mn>0.7122</mn></mrow></semantics></math>. The vertical dashed lines indicate the application time of each pressure step. The FE prediction for 10 MPa pressure is also shown.</p> Full article ">
<p>Epoxy cylinder subjected to hydrostatic pressure: comparison between strain calculated from the wavelength measurements and with <a href="#FD4" class="html-disp-formula">Equation (4a)</a> and <span class="html-italic">p<sub>e</sub></span> = 0.2108 as well as <a href="#FD7" class="html-disp-formula">Equation (6a)</a> and <math display="inline"> <semantics id="sm32"> <mrow> <msubsup> <mi>p</mi> <mi>e</mi> <mrow> <mtext mathvariant="italic">eff</mtext></mrow></msubsup> <mo>=</mo> <mn>0.2515</mn></mrow></semantics></math>. The vertical dashed lines indicate the application time of each pressure step. The FE prediction for 9.2 MPa pressure is also shown.</p> Full article ">
<p>Unidirectional composite subjected to hydrostatic pressure: comparison between strain calculated from the wavelength measurements and <a href="#FD4" class="html-disp-formula">Equation (4a)</a> with <span class="html-italic">p<sub>e</sub></span> = 0.2108 as well as <a href="#FD7" class="html-disp-formula">Equation (6a)</a> with <math display="inline"> <semantics id="sm33"> <mrow> <msubsup> <mi>p</mi> <mi>e</mi> <mrow> <mtext mathvariant="italic">eff</mtext></mrow></msubsup> <mo>=</mo> <mn>1.6040</mn></mrow></semantics></math>. The vertical dashed lines indicate the application time of each pressure step. The FE prediction for 10MPa pressure is also shown.</p> Full article ">
705 KiB  
Article
A Neuro-Fuzzy System for Characterization of Arm Movements
by Alexandre Balbinot and Gabriela Favieiro
Sensors 2013, 13(2), 2613-2630; https://doi.org/10.3390/s130202613 - 21 Feb 2013
Cited by 57 | Viewed by 8269
Abstract
The myoelectric signal reflects the electrical activity of skeletal muscles and contains information about the structure and function of the muscles which make different parts of the body move. Advances in engineering have extended electromyography beyond the traditional diagnostic applications to also include [...] Read more.
The myoelectric signal reflects the electrical activity of skeletal muscles and contains information about the structure and function of the muscles which make different parts of the body move. Advances in engineering have extended electromyography beyond the traditional diagnostic applications to also include applications in diverse areas such as rehabilitation, movement analysis and myoelectric control of prosthesis. This paper aims to study and develop a system that uses myoelectric signals, acquired by surface electrodes, to characterize certain movements of the human arm. To recognize certain hand-arm segment movements, was developed an algorithm for pattern recognition technique based on neuro-fuzzy, representing the core of this research. This algorithm has as input the preprocessed myoelectric signal, to disclosed specific characteristics of the signal, and as output the performed movement. The average accuracy obtained was 86% to 7 distinct movements in tests of long duration (about three hours). Full article
(This article belongs to the Section Physical Sensors)
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<p>A block-diagram representation of the system.</p> Full article ">
<p>(<b>a</b>) Example of a Sugeno Inference Model: three inputs and two rules and (<b>b</b>) The equivalent ANFIS architecture.</p> Full article ">
<p>Block diagram of the proposed system.</p> Full article ">
<p>Picture showing the electrodes positions in the same arm (right arm).</p> Full article ">
<p>Details virtual model: (<b>A</b>) zoom of the hand: (<b>a</b>) hand contraction, (<b>b</b>) wrist extension, (<b>c</b>) forearm rotation, (<b>d</b>) wrist flexion, (<b>e</b>) forearm flexion e; (<b>B</b>) whole body model.</p> Full article ">
<p>Static representation of a simple movement: wrist extension movement.</p> Full article ">
<p>System output for Subject 1–Section 3 (5 repetitions).</p> Full article ">
<p>System output for Subject 27–Section 2 (5 repetitions).</p> Full article ">
<p>Overall result of the system for each movement.</p> Full article ">
1289 KiB  
Article
Virtual and Remote Robotic Laboratory Using EJS, MATLAB and LabVIEW
by Dictino Chaos, Jesús Chacón, Jose Antonio Lopez-Orozco and Sebastián Dormido
Sensors 2013, 13(2), 2595-2612; https://doi.org/10.3390/s130202595 - 21 Feb 2013
Cited by 73 | Viewed by 13574
Abstract
This paper describes the design and implementation of a virtual and remote laboratory based on Easy Java Simulations (EJS) and LabVIEW. The main application of this laboratory is to improve the study of sensors in Mobile Robotics, dealing with the problems that arise [...] Read more.
This paper describes the design and implementation of a virtual and remote laboratory based on Easy Java Simulations (EJS) and LabVIEW. The main application of this laboratory is to improve the study of sensors in Mobile Robotics, dealing with the problems that arise on the real world experiments. This laboratory allows the user to work from their homes, tele-operating a real robot that takes measurements from its sensors in order to obtain a map of its environment. In addition, the application allows interacting with a robot simulation (virtual laboratory) or with a real robot (remote laboratory), with the same simple and intuitive graphical user interface in EJS. Thus, students can develop signal processing and control algorithms for the robot in simulation and then deploy them on the real robot for testing purposes. Practical examples of application of the laboratory on the inter-University Master of Systems Engineering and Automatic Control are presented. Full article
(This article belongs to the Section Physical Sensors)
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<p>Laboratory Architecture.</p> Full article ">
<p>Server side of the laboratory.</p> Full article ">
<p>Robot.vi.</p> Full article ">
<p>Camera.vi.</p> Full article ">
<p>RobotEJS.vi.</p> Full article ">
<p>Definition of the model in EJS. (<b>a</b>) Subpanel Evolution of EJS; (<b>b</b>) Subpanel Variables of EJS.</p> Full article ">
<p>The GUI of the remote and virtual laboratory in EJS.</p> Full article ">
<p>UNEDLabs Website and Autonomous Robots course.</p> Full article ">
<p>Example of a successful execution of a student code.</p> Full article ">
1559 KiB  
Article
Wedge-Filtering of Geomorphologic Terrestrial Laser Scan Data
by Helmut Panholzer and Alexander Prokop
Sensors 2013, 13(2), 2579-2594; https://doi.org/10.3390/s130202579 - 20 Feb 2013
Cited by 18 | Viewed by 8465
Abstract
Terrestrial laser scanning is of increasing importance for surveying and hazard assessments. Digital terrain models are generated using the resultant data to analyze surface processes. In order to determine the terrain surface as precisely as possible, it is often necessary to filter out [...] Read more.
Terrestrial laser scanning is of increasing importance for surveying and hazard assessments. Digital terrain models are generated using the resultant data to analyze surface processes. In order to determine the terrain surface as precisely as possible, it is often necessary to filter out points that do not represent the terrain surface. Examples are vegetation, vehicles, and animals. Filtering in mountainous terrain is more difficult than in other topography types. Here, existing automatic filtering solutions are not acceptable, because they are usually designed for airborne scan data. The present article describes a method specifically suitable for filtering terrestrial laser scanning data. This method is based on the direct line of sight between the scanner and the measured point and the assumption that no other surface point can be located in the area above this connection line. This assumption is only true for terrestrial laser data, but not for airborne data. We present a comparison of the wedge filtering to a modified inverse distance filtering method (IDWMO) filtered point cloud data. Both methods use manually filtered surfaces as reference. The comparison shows that the mean error and root–mean-square-error (RSME) between the results and the manually filtered surface of the two methods are similar. A significantly higher number of points of the terrain surface could be preserved, however, using the wedge-filtering approach. Therefore, we suggest that wedge-filtering should be integrated as a further parameter into already existing filtering processes, but is not suited as a standalone solution so far. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
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<p>Cross-section of a terrestrial laser scan showing connections between laser scanner and recorded points.</p> Full article ">
<p>Frontal view of a terrestrial laser scan recording. Marked is the V-shaped elimination area. The blue dots are further away from the laser scanner than the red dots. Part <b>A</b> shows a larger filter angle than part <b>B</b>.</p> Full article ">
<p>Oblique view of a terrestrial laser scan. The elimination areas are shown three-dimensionally and thus appear in the form of wedges.</p> Full article ">
<p>Laser scan of a wall with three different horizontal angles; seen from the side (<b>A</b>) and from above (<b>B</b>).</p> Full article ">
<p>Test are ((<b>A</b>): ÖK 50; (<b>B</b>) aerial photo); image source: © Land Tirol, <span class="html-italic">tiris</span>, <a href="http://www.tirol.gv.at/tiris" target="_blank">www.tirol.gv.at/tiris</a>.</p> Full article ">
<p>Inclination map of the test area, generated with the “slope” function of ArcGIS.</p> Full article ">
<p>Aerial photos Galierm, 2001 (<b>A</b>) und 2006 (<b>B</b>); image source: © Land Vorarlberg, <a href="http://vogis.cnv.at" target="_blank">http://vogis.cnv.at</a>.</p> Full article ">
<p>Location of the two test areas; image source: © Geoland, <a href="http://www.geoland.at" target="_blank">www.geoland.at</a>.</p> Full article ">
<p>Screenshot of the calculation using our own computer program.</p> Full article ">
2703 KiB  
Article
Photonic Crystal Biosensor Based on Optical Surface Waves
by Valery N. Konopsky, Tanya Karakouz, Elena V. Alieva, Chiara Vicario, Sergey K. Sekatskii and Giovanni Dietler
Sensors 2013, 13(2), 2566-2578; https://doi.org/10.3390/s130202566 - 19 Feb 2013
Cited by 82 | Viewed by 11465
Abstract
A label-free biosensor device based on registration of photonic crystal surface waves is described. Angular interrogation of the optical surface wave resonance is used to detect changes in the thickness of an adsorbed layer, while an additional simultaneous detection of the critical angle [...] Read more.
A label-free biosensor device based on registration of photonic crystal surface waves is described. Angular interrogation of the optical surface wave resonance is used to detect changes in the thickness of an adsorbed layer, while an additional simultaneous detection of the critical angle of total internal reflection provides independent data of the liquid refractive index. The abilities of the device are demonstrated by measuring of biotin molecule binding to a streptavidin monolayer, and by measuring association and dissociation kinetics of immunoglobulin G proteins. Additionally, deposition of PSS / PAH polyelectrolytes is recorded in situ resulting calculation of PSS and PAH monolayer thicknesses separately. Full article
(This article belongs to the Special Issue Photonic Crystal Sensors)
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<p>A sketch of the biosensor based on angle interrogation of a PC SW. The typical reflection profile is shown near the CMOS matrix in (<b>A</b>) and is illustrated in (<b>B</b>) at different distances from the ID PC. The angular resonance curves are shown in red for s -polarization, and in blue for <span class="html-italic">p</span> -polarization.</p> Full article ">
<p>Immobilization of streptavidin on a biotinylated surface.</p> Full article ">
<p>Free biotin binding to the streptavidin monolayer.</p> Full article ">
<p>A time slice of the thickness growth of the polyelectrolyte assembly (<b>A</b>) and the total layer thickness registered upon polyelectrolyte assembly for different RI of the adsorption layer (<b>B</b>).</p> Full article ">
<p>Schematic representation of PC SW surface bioactivation and further receptor recognition.</p> Full article ">
<p>Typical signal obtained by the PC SW optical sensor upon binding of the ligand (40 <span class="html-italic">μ</span>g/mL Rabbit IgG) and the analyte (15 <span class="html-italic">μ</span>g/mL anti-Rabbit IgG).</p> Full article ">
<p>Normalized sensograms of anti-rabbit IgG binding to immobilized rabbit IgG.</p> Full article ">
799 KiB  
Article
A Novel Two-Axis Load Sensor Designed for in Situ Scratch Testing inside Scanning Electron Microscopes
by Hu Huang, Hongwei Zhao, Boda Wu, Shunguang Wan and Chengli Shi
Sensors 2013, 13(2), 2552-2565; https://doi.org/10.3390/s130202552 - 18 Feb 2013
Cited by 8 | Viewed by 7061
Abstract
Because of a lack of available miniaturized multiaxial load sensors to measure the normal load and the lateral load simultaneously, quantitative in situ scratch devices inside scanning electron microscopes and the transmission electron microscopes have barely been developed up to now. A novel [...] Read more.
Because of a lack of available miniaturized multiaxial load sensors to measure the normal load and the lateral load simultaneously, quantitative in situ scratch devices inside scanning electron microscopes and the transmission electron microscopes have barely been developed up to now. A novel two-axis load sensor was designed in this paper. With an I-shaped structure, the sensor has the function of measuring the lateral load and the normal load simultaneously, and at the same time it has compact dimensions. Finite element simulations were carried out to evaluate stiffness and modal characteristics. A decoupling algorithm was proposed to resolve the cross-coupling between the two-axis loads. Natural frequency of the sensor was tested. Linearity and decoupling parameters were obtained from the calibration experiments, which indicate that the sensor has good linearity and the cross-coupling between the two axes is not strong. Via the decoupling algorithm and the corresponding decoupling parameters, simultaneous measurement of the lateral load and the normal load can be realized via the developed two-axis load sensor. Preliminary applications of the load sensor for scratch testing indicate that the load sensor can work well during the scratch testing. Taking advantage of the compact structure, it has the potential ability for applications in quantitative in situ scratch testing inside SEMs. Full article
(This article belongs to the Section Physical Sensors)
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<p>The schematic diagram (<b>a</b>) and the corresponding prototype (<b>b</b>) of the sensor.</p> Full article ">
<p>The Wheatstone bridge.</p> Full article ">
<p>Deformation diagrams of the elastic body under (<b>a</b>) lateral load <span class="html-italic">F</span><sub>x</sub> and (<b>b</b>) normal load <span class="html-italic">F</span><sub>y</sub>.</p> Full article ">
<p>Deformation of the elastic body including the indenter (<b>a</b>) under the lateral load of 1 N and (<b>b</b>) under the normal load of 1 N.</p> Full article ">
<p>The first six order mode shapes of the elastic body including the indenter.</p> Full article ">
<p>The experimental system.</p> Full article ">
<p>Frequency response of the two-axis load sensor.</p> Full article ">
<p>Loading programs for (<b>a</b>) the normal load and (<b>b</b>) the lateral load.</p> Full article ">
<p>Calibration curves of the two-axis load sensor. (<b>a</b>) is the relationship between the normal load <span class="html-italic">F</span><sub>y</sub> and the output voltage <span class="html-italic">U</span><sub>y</sub> from the strain gauges on the middle of the elastic body; (<b>b</b>) is the relationship between the normal load <span class="html-italic">F</span><sub>y</sub> and the output voltage <span class="html-italic">U</span><sub>x</sub> from the strain gauges on the two sides of the elastic body; (<b>c</b>) is the relationship between the lateral load <span class="html-italic">F</span><sub>x</sub> and the output voltage <span class="html-italic">U</span><sub>x</sub> from the strain gauges on the two sides of the elastic body; (<b>d</b>) is the relationship between the lateral load <span class="html-italic">F</span><sub>x</sub> and the output voltage <span class="html-italic">U</span><sub>y</sub> from the strain gauges on the middle of the elastic body.</p> Full article ">
673 KiB  
Article
Heart Sound Biometric System Based on Marginal Spectrum Analysis
by Zhidong Zhao, Qinqin Shen and Fangqin Ren
Sensors 2013, 13(2), 2530-2551; https://doi.org/10.3390/s130202530 - 18 Feb 2013
Cited by 32 | Viewed by 9669
Abstract
This work presents a heart sound biometric system based on marginal spectrum analysis, which is a new feature extraction technique for identification purposes. This heart sound identification system is comprised of signal acquisition, pre-processing, feature extraction, training, and identification. Experiments on the selection [...] Read more.
This work presents a heart sound biometric system based on marginal spectrum analysis, which is a new feature extraction technique for identification purposes. This heart sound identification system is comprised of signal acquisition, pre-processing, feature extraction, training, and identification. Experiments on the selection of the optimal values for the system parameters are conducted. The results indicate that the new spectrum coefficients result in a significant increase in the recognition rate of 94.40% compared with that of the traditional Fourier spectrum (84.32%) based on a database of 280 heart sounds from 40 participants. Full article
(This article belongs to the Section Physical Sensors)
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<p>Various biometric features.</p> Full article ">
<p>Typical waveform of S1 and S2.</p> Full article ">
<p>(<b>a</b>) Simulation signal; (<b>b</b>) IMFs of the simulation signal obtained by using EMD; (<b>c</b>) IMFs of the simulation signal obtained by using EEMD.</p> Full article ">
<p>(<b>a</b>) Cardiac cycle of a heart sound signal; (<b>b</b>) First five IMF components of (<b>a</b>)'s signal; (<b>c</b>) Last four IMF components of (<b>a</b>)'s signal.</p> Full article ">
<p>(<b>a</b>) Hilbert spectrum of the cardiac cycle; (<b>b</b>) Marginal spectrum of the cardiac cycle; and (<b>c</b>) Fourier spectrum of the cardiac cycle.</p> Full article ">
<p>Block diagram of heart sound identification system.</p> Full article ">
<p>Equipment for signal acquisition.</p> Full article ">
<p>Raw heart sound signal and the corresponding de-noised signal.</p> Full article ">
<p>Block diagram of feature extraction process.</p> Full article ">
1532 KiB  
Article
Forgery Detection and Value Identification of Euro Banknotes
by Arcangelo Bruna, Giovanni Maria Farinella, Giuseppe Claudio Guarnera and Sebastiano Battiato
Sensors 2013, 13(2), 2515-2529; https://doi.org/10.3390/s130202515 - 18 Feb 2013
Cited by 41 | Viewed by 11022
Abstract
This paper describes both hardware and software components to detect counterfeits of Euro banknotes. The proposed system is also able to recognize the banknote values. Differently than other state-of-the-art methods, the proposed approach makes use of banknote images acquired with a near infrared [...] Read more.
This paper describes both hardware and software components to detect counterfeits of Euro banknotes. The proposed system is also able to recognize the banknote values. Differently than other state-of-the-art methods, the proposed approach makes use of banknote images acquired with a near infrared camera to perform recognition and authentication. This allows one to build a system that can effectively deal with real forgeries, which are usually not detectable with visible light. The hardware does not use any mechanical parts, so the overall system is low-cost. The proposed solution is reliable for ambient light and banknote positioning. Users should simply lean the banknote to be analyzed on a flat glass, and the system detects forgery, as well as recognizes the banknote value. The effectiveness of the proposed solution has been properly tested on a dataset composed by genuine and fake Euro banknotes provided by Italy's central bank. Full article
(This article belongs to the Section Physical Sensors)
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<p>Among the various security features, the one encoded into the infrared light spectra is incorporated into all euro banknotes to protect them against counterfeiting [<a href="#b6-sensors-13-02515" class="html-bibr">6</a>]. Here is reported an example of five Euro banknotes under infrared light, as it is shown on the official website of the European Bank [<a href="#b6-sensors-13-02515" class="html-bibr">6</a>]. Only the right side of the main image and the silvery stripe are visible.</p> Full article ">
<p>Examples of banknote values acquired by the infrared (IR) camera of the proposed system. A simple visual comparison between the above banknotes and the one in <a href="#f1-sensors-13-02515" class="html-fig">Figure 1</a> reveals the different problems (e.g., distortion, illumination variation, misalignment) that should be taken into account in building a low cost counterfeit detection system. (<b>a</b>) 5 Euro;(<b>b</b>) 10 Euro; (<b>c</b>) 20 Euro; (<b>d</b>) 50 Euro; (<b>e</b>) 100 Euro; (<b>f</b>) 200 Euro; (<b>g</b>) 500 Euro.</p> Full article ">
<p>Overall schema of the proposed approach.</p> Full article ">
<p>A banknote of 50 Euro as acquired by the IR camera of the proposed system, and the set of regions used to test its genuineness. White: overall considered region of interest. Blue: the threshold to binarize the image is calculated in this area. Green: this area must bedark under infrared light. Red: when acquired under infrared light, this area must be bright and without noticeable patterns. Magenta: additional area used to check the genuineness of some denominations.</p> Full article ">
<p>Learned patches related to the different banknote values, (<b>a</b>) 5 Euro; (<b>b</b>) 10 Euro;(<b>c</b>) 20 Euro; (<b>d</b>) 50 Euro; (<b>e</b>) 100 Euro; (<b>f</b>) 200 Euro; (<b>g</b>) 500 Euro.</p> Full article ">
<p>The schema of the hardware prototype.</p> Full article ">
<p>The main board containing the microprocessor in the center, the A/D converter on the right side, the external SRAM memory in the upper part and the power supply in the lower/right side.</p> Full article ">
<p>The display board containing eight-segment displays. Also, three IR LEDs are visible.</p> Full article ">
<p>The final prototype of our system.</p> Full article ">
906 KiB  
Article
High Throughput Molecular Confirmation of β-Thalassemia Mutations Using Novel TaqMan Probes
by Siew Leng Kho, Kek Heng Chua, Elizabeth George and Jin Ai Mary Anne Tan
Sensors 2013, 13(2), 2506-2514; https://doi.org/10.3390/s130202506 - 18 Feb 2013
Cited by 9 | Viewed by 8189
Abstract
β-Thalassemia is a public health problem where 4.5% of Malaysians are β-thalassemia carriers. The genetic disorder is caused by defects in the β-globin gene complex which lead to reduced or complete absence of β-globin chain synthesis. Five TaqMan genotyping assays were designed and [...] Read more.
β-Thalassemia is a public health problem where 4.5% of Malaysians are β-thalassemia carriers. The genetic disorder is caused by defects in the β-globin gene complex which lead to reduced or complete absence of β-globin chain synthesis. Five TaqMan genotyping assays were designed and developed to detect the common β-thalassemia mutations in Malaysian Malays. The assays were evaluated with 219 "blinded" DNA samples and the results showed 100% sensitivity and specificity. The in-house designed TaqMan genotyping assays were found to be cost- and time-effective for characterization of β-thalassemia mutations in the Malaysian population. Full article
(This article belongs to the Section Biosensors)
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<p>Binding of primers and probes on the DNA template for detection of IVS1-1 (G-T). (<b>a</b>) Normal probe of IVS1-1 and primer hybridized to the DNA template. Fluorescence signal is released from VIC dye (green) when cleaved by <span class="html-italic">Taq</span> DNA polymerase. (<b>b</b>) Mutant probe of IVS1-1 and primer hybridized to the DNA template. Fluorescence signal is released from FAM dye (blue) when cleaved by <span class="html-italic">Taq</span> DNA polymerase.</p> Full article ">
<p>Allelic discrimination plots of TaqMan genotyping assays for the five β-thalassemia mutations; normal allele at x-axis and mutant allele at y-axis. Black dots indicate no amplification (non-template PCR control), red dots indicate individuals negative for the mutation, green dots indicate individuals heterozygous for the mutation and blue dots indicate individuals homozygous for the mutation. (<b>a</b>) IVS1-1. (<b>b</b>) IVS1-5. (<b>c</b>) CD41/42. (<b>d</b>) Poly A. (<b>e</b>) CD26 (HbE).</p> Full article ">
<p>Scatter plots of TaqMan genotyping assays for the 5 mutations with VIC dye fluorescence at x-axis and FAM dye fluorescence at y-axis. Squares indicated controls. (<b>a</b>) IVS1-1, (<b>b</b>) IVS1-5, (<b>c</b>) CD41/42 and (<b>d</b>) CD26 (HbE), red dots indicate individuals who do not possess the specific mutation, green dots indicate carriers and blue dots indicate individuals homozygous for the mutation; (<b>e</b>) Poly A, blue dots indicate individuals who do not possess the Poly A mutation and green dots indicate carriers.</p> Full article ">
508 KiB  
Article
Hardware Implementation of Lorenz Circuit Systems for Secure Chaotic Communication Applications
by Hsin-Chieh Chen, Ben-Yi Liau and Yi-You Hou
Sensors 2013, 13(2), 2494-2505; https://doi.org/10.3390/s130202494 - 18 Feb 2013
Cited by 21 | Viewed by 6966
Abstract
This paper presents the synchronization between the master and slave Lorenz chaotic systems by slide mode controller (SMC)-based technique. A proportional-integral (PI) switching surface is proposed to simplify the task of assigning the performance of the closed-loop error system in sliding mode. Then, [...] Read more.
This paper presents the synchronization between the master and slave Lorenz chaotic systems by slide mode controller (SMC)-based technique. A proportional-integral (PI) switching surface is proposed to simplify the task of assigning the performance of the closed-loop error system in sliding mode. Then, extending the concept of equivalent control and using some basic electronic components, a secure communication system is constructed. Experimental results show the feasibility of synchronizing two Lorenz circuits via the proposed SMC. Full article
(This article belongs to the Section Physical Sensors)
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<p>Block diagram of SMC-based scheme secure communication system.</p> Full article ">
<p>Electronic implementation of the master Lorenz circuit.</p> Full article ">
<p>Electronic implementation of the slave Lorenz circuit.</p> Full article ">
<p>Electronic implementation of the error dynamics <span class="html-italic">e</span>(t) and the switch surface <span class="html-italic">s</span>(t) circuit.</p> Full article ">
<p>Electronic implementation of <span class="html-italic">u<sub>eq</sub></span>(<span class="html-italic">t</span>) circuit.</p> Full article ">
<p>Electronic implementation of <math display="inline"> <semantics id="sm16"> <mrow> <mi>η</mi> <mi>ψ</mi> <mrow> <mo>[</mo> <mrow> <mfrac> <mrow> <mi>s</mi> <mo stretchy="false">(</mo> <mi>t</mi> <mo stretchy="false">)</mo></mrow> <mrow> <mo>|</mo> <mi>s</mi> <mo stretchy="false">(</mo> <mi>t</mi> <mo stretchy="false">)</mo> <mo>|</mo> <mo>+</mo> <mi>σ</mi></mrow></mfrac></mrow> <mo>]</mo></mrow></mrow></semantics></math>circuit.</p> Full article ">
<p>The trajectories of the Lorenz system.</p> Full article ">
<p>Experimental results of synchronization between state <span class="html-italic">x<sub>m</sub></span> and state <span class="html-italic">x<sub>s</sub></span>.</p> Full article ">
<p>Experimental results of errors between state <span class="html-italic">x<sub>m</sub></span> and state <span class="html-italic">x<sub>s</sub></span>.</p> Full article ">
653 KiB  
Article
Detection of Micrococcus Luteus Biofilm Formation in Microfluidic Environments by pH Measurement Using an Ion-Sensitive Field-Effect Transistor
by Koji Matsuura, Yuka Asano, Akira Yamada and Keiji Naruse
Sensors 2013, 13(2), 2484-2493; https://doi.org/10.3390/s130202484 - 18 Feb 2013
Cited by 25 | Viewed by 10345
Abstract
Biofilm formation in microfluidic channels is difficult to detect because sampling volumes are too small for conventional turbidity measurements. To detect biofilm formation, we used an ion-sensitive field-effect transistor (ISFET) measurement system to measure pH changes in small volumes of bacterial suspension. Cells [...] Read more.
Biofilm formation in microfluidic channels is difficult to detect because sampling volumes are too small for conventional turbidity measurements. To detect biofilm formation, we used an ion-sensitive field-effect transistor (ISFET) measurement system to measure pH changes in small volumes of bacterial suspension. Cells of Micrococcus luteus (M. luteus) were cultured in polystyrene (PS) microtubes and polymethylmethacrylate (PMMA)-based microfluidic channels laminated with polyvinylidene chloride. In microtubes, concentrations of bacteria and pH in the suspension were analyzed by measuring turbidity and using an ISFET sensor, respectively. In microfluidic channels containing 20 μL of bacterial suspension, we measured pH changes using the ISFET sensor and monitored biofilm formation using a microscope. We detected acidification and alkalinization phases of M. luteus from the ISFET sensor signals in both microtubes and microfluidic channels. In the alkalinization phase, after 2 day culture, dense biofilm formation was observed at the bottom of the microfluidic channels. In this study, we used an ISFET sensor to detect biofilm formation in clinical and industrial microfluidic environments by detecting alkalinization of the culture medium. Full article
(This article belongs to the Special Issue Microfluidic Devices)
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<p>Bacterial culture systems used in this study. (<b>a</b>) Schematic view of PS microtubes and (<b>b</b>) microfluidic channels. (<b>c</b>) A microfluidic channel array.</p> Full article ">
<p>Detection device of the ISFET measurement system. (<b>a</b>) Side and (<b>b</b>) Top view of schematic presentation. (<b>c</b>) Photograph of the measurement system. (<b>d</b>) Linear relationship between pH and gate-source voltage (V<sub>s</sub>) of optimized buffers at pH 4, 6, and 8.</p> Full article ">
<p>(<b>a</b>) Relationship between turbidity and pH measured by ISFET in medium containing <span class="html-italic">M. luteus</span>. Voltages in the vertical axis indicate the difference between the <span class="html-italic">M. luteus</span> suspension and the medium (ΔV<sub>s</sub>). Absorbance is shown in a log scale. (<b>b</b>) Biofilm formation in the PS microtube. A <span class="html-italic">M. luteus</span> biofilm was observed at the bottom of the microtube (red square).</p> Full article ">
<p>(<b>a</b>,<b>b</b>) Relationship between the percentage of stained biofilm coverage in the microfluidic channels and pH of the medium containing <span class="html-italic">M. luteus</span> measured using ISFET. Horizontal axes in (a) and (b) are percent coverage in channel regions and in circle and channel regions, respectively. Voltages in the vertical axes are the difference between those of <span class="html-italic">M. luteus</span> suspensions and medium (ΔV<sub>s</sub>). (<b>c</b>) Images of <span class="html-italic">M. luteus</span> biofilms formed in the microfluidic channels under alkalinized (left) and acidified (right) conditions. The biofilms were stained with crystal violet. The width of the microfluidic channel was 1 mm. (<b>d</b>) Grayscale microscopic images of the stained biofilms at the bottom of the microfluidic channels. The left and right images in (c) correspond to those in (d), respectively. Yellow rectangles and circles indicate ROIs in which the percent coverage of the biofilms was evaluated.</p> Full article ">
<p>Schematic presentation of the mechanism of <span class="html-italic">M. luteus</span> biofilm formation. Biofilm formation was facilitated in the alkalinization phase. Changes in turbidity and pH measured using the ISFET sensor are shown with black and red lines, respectively. The yellow shadow indicates the phase of biofilm formation.</p> Full article ">
432 KiB  
Article
Performance Enhancement of a GaAs Detector with a Vertical Field and an Embedded Thin Low-Temperature Grown Layer
by Marc Currie, Pouya Dianat, Anna Persano, Maria Concetta Martucci, Fabio Quaranta, Adriano Cola and Bahram Nabet
Sensors 2013, 13(2), 2475-2483; https://doi.org/10.3390/s130202475 - 18 Feb 2013
Cited by 8 | Viewed by 7573
Abstract
Low temperature growth of GaAs (LT-GaAs) near 200 °C results in a recombination lifetime of nearly 1 ps, compared with approximately 1 ns for regular temperature ~600 °C grown GaAs (RT-GaAs), making it suitable for ultra high speed detection applications. However, LT-GaAs detectors [...] Read more.
Low temperature growth of GaAs (LT-GaAs) near 200 °C results in a recombination lifetime of nearly 1 ps, compared with approximately 1 ns for regular temperature ~600 °C grown GaAs (RT-GaAs), making it suitable for ultra high speed detection applications. However, LT-GaAs detectors usually suffer from low responsivity due to low carrier mobility. Here we report electro-optic sampling time response measurements of a detector that employs an AlGaAs heterojunction, a thin layer of LT-GaAs, a channel of RT-GaAs, and a vertical electric field that together facilitate collection of optically generated electrons while suppressing collection of lower mobility holes. Consequently, these devices have detection efficiency near that of RT-GaAs yet provide pulse widths nearly an order of magnitude faster—~6 ps for a cathode-anode separation of 1.3 μm and ~12 ps for distances more than 3 μm. Full article
(This article belongs to the Special Issue Photodetectors)
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<p>Image (top) and sketch (bottom) of the electro-optic sampling test setup highlight the (a) RF probe contacting the transmission line, (b) MSM photodetector, (c) optical fiber and (d) electro-optic crystal. The RF probe (a) is at one end of a transmission line, in the middle of which the interdigitated MSM device (b) is located. An inset shows an image of the fabricated device (b). The pump beam is delivered by an optical fiber (c) and the probe beam samples the propagating transient through the electro optic crystal (d).</p> Full article ">
<p>Electric field distribution in devices with 1-<span class="html-italic">μ</span>m (<b>a</b>) and 3-<span class="html-italic">μ</span>m (<b>b</b>) electrode spacings under 9 V applied bias. The layer structure is also shown in the vertical axis, and has a different scale from horizontal axis. Vectors show the calculated direction of the electric field. The electrostatic potential diagrams for the 1-<span class="html-italic">μ</span>m (<b>c</b>) and 3-<span class="html-italic">μ</span>m (<b>d</b>) detail the effects of the Schottky contact, bias, and the δ-doping profile.</p> Full article ">
<p>(<b>a</b>) Current-voltage curves of the 1.3 <span class="html-italic">μ</span>m device illuminated with 11 <span class="html-italic">μ</span>W average optical power at wavelengths ranging from 770–920 nm, as well ambient room lights. (<b>b</b>) Photocurrent profiles of a 1 <span class="html-italic">μ</span>m diameter, 200 <span class="html-italic">μ</span>W laser as it is translated across a 7 <span class="html-italic">μ</span>m electrode spacing for three applied bias voltages +5, +2, and –5 V (red, black and green traces, respectively). The gray shaded regions show the position of each electrode.</p> Full article ">
<p>Time response measured by electro-optic sampling of devices with 1.3, 3.2, 5.1, and 8.1 <span class="html-italic">μ</span>m separations between cathode and anode (black, red, green and blue traces, respectively). A 6.3 ps FWHM pulse width and a 0.15 A/W responsivity is observed for the smallest device while all others separations have a ∼12 ps FWHM pulse width. Inset of the figure shows the peak response for each device (scaled to the device's active area).</p> Full article ">
2281 KiB  
Review
Progress in the Development of CdZnTe Unipolar Detectors for Different Anode Geometries and Data Corrections
by Qiushi Zhang, Congzhe Zhang, Yanye Lu, Kun Yang and Qiushi Ren
Sensors 2013, 13(2), 2447-2474; https://doi.org/10.3390/s130202447 - 18 Feb 2013
Cited by 44 | Viewed by 12424
Abstract
CdZnTe detectors have been under development for the past two decades, providing good stopping power for gamma rays, lightweight camera heads and improved energy resolution. However, the performance of this type of detector is limited primarily by incomplete charge collection problems resulting from [...] Read more.
CdZnTe detectors have been under development for the past two decades, providing good stopping power for gamma rays, lightweight camera heads and improved energy resolution. However, the performance of this type of detector is limited primarily by incomplete charge collection problems resulting from charge carriers trapping. This paper is a review of the progress in the development of CdZnTe unipolar detectors with some data correction techniques for improving performance of the detectors. We will first briefly review the relevant theories. Thereafter, two aspects of the techniques for overcoming the hole trapping issue are summarized, including irradiation direction configuration and pulse shape correction methods. CdZnTe detectors of different geometries are discussed in detail, covering the principal of the electrode geometry design, the design and performance characteristics, some detector prototypes development and special correction techniques to improve the energy resolution. Finally, the state of art development of 3-D position sensing and Compton imaging technique are also discussed. Spectroscopic performance of CdZnTe semiconductor detector will be greatly improved even to approach the statistical limit on energy resolution with the combination of some of these techniques. Full article
(This article belongs to the Section Physical Sensors)
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<p>Planar configuration of a semiconductor detector. The cathode is applied with a negative voltage and anode grounded. Electron-hole pairs excited by gamma rays are swept by the bias voltage.</p> Full article ">
<p>A typical <sup>241</sup>Am spectrum obtained with 4 × 4 × 2 mm<sup>3</sup> CZT detector, which is irradiated from the cathode side (dashed line) and anode side (solid line). The photopeak can be resolved if gamma rays are irradiated from the cathode side but not from the anode side [<a href="#b7-sensors-13-02447" class="html-bibr">7</a>] (©IEEE, 2001).</p> Full article ">
<p>Typical amplification circuit of a semiconductor planar detector. The total charge on the feedback capacitor consists of two parts: free electrons that drift to the anode and the charges induced by trapped electrons and holes within the detector. Positive charges induced on the anode will add electrons and negative charges will reduce electrons on the feedback capacitor. The amplitude of output signal is proportional to the charges that are generated on the feedback capacitor.</p> Full article ">
<p>Schematic of the basic configuration for the Frisch grid detector. Three regions that are separated by the grid can be seen. Charge carrier e.g., <span class="html-italic">q<sub>e</sub></span> which drifts into the measurement region will induce charges on the anode, while <span class="html-italic">q<sub>h</sub></span> in the will not.</p> Full article ">
<p>Weighting potential distribution of the Frisch grid detector. X- and Y-coordinate are indicated in <a href="#f4-sensors-13-02447" class="html-fig">Figure 4</a>. <b>left:</b> caculated weighting potential projected on the X-coordinate. D (<span class="html-italic">p</span>) are the distance between the cathode (anode) and the grid. <span class="html-italic">d</span> is the distance between the grid elements and <span class="html-italic">r</span> is the half length of the element. As expected, weighting potential value for x &lt; 0 is nearly zero and abruptly changes for x &gt; 0. A slight y-dependence of weighting potential is shown in the inset map that zooms into the origin of X-coordinate. <b>Right:</b> 2-D map of weighting potential around the Frisch grid (X: −1 to +1, Y: 0 to 1.0) [<a href="#b25-sensors-13-02447" class="html-bibr">25</a>] (Image courtesy of Elsevier).</p> Full article ">
<p><b>Left:</b> 3-D geometric diagram of trapezoid prism detector. The anode has a smaller area with two parallel strips at along sides as the Frisch grids. The trapezoid height is often several times longer than the distance between the Frisch grid and the anode so that a much smaller volume of measurement region is generated. A cross-section cut through the width in the device center is shown; <b>Right:</b> weighting potential distribution of the cross-section as shown in the left diagram [<a href="#b28-sensors-13-02447" class="html-bibr">28</a>] (Image courtesy of Elsevier).</p> Full article ">
<p>The capacitive Frisch grid device and its components: a bar-shaped detector, an insulating coating and a conductive Frisch ring. (<b>a</b>) The detector bar with Teflon coated outside is non-contacted with the Frisch ring. (<b>b</b>) When the detector is inserted into the Frisch ring, the special weighting potential near the anode is generated and thus effectively eliminating the induction from charge motion in the region extending from the ring edge to the cathode [<a href="#b29-sensors-13-02447" class="html-bibr">29</a>] (Image courtesy of American Institute of Physics).</p> Full article ">
<p>Geometry design of pixelate, coplanar grid and orthogonal strip detector [<a href="#b37-sensors-13-02447" class="html-bibr">37</a>] (©IEEE, 2007).</p> Full article ">
<p>The shape of weighting potential in a pixelate CZT detector with pixel size of 1mm. <b>Left:</b> 2-D distribution of the weighting potential. The small pixel effect can be seen clearly in the vicinity of the pixel's anode. <b>Right:</b> the correlation between weighting potential and interaction distance from the anode [<a href="#b41-sensors-13-02447" class="html-bibr">41</a>] (Image courtesy of American Association of Physicists in Medicine).</p> Full article ">
1241 KiB  
Article
Fusion of Building Information and Range Imaging for Autonomous Location Estimation in Indoor Environments
by Tobias K. Kohoutek, Rainer Mautz and Jan D. Wegner
Sensors 2013, 13(2), 2430-2446; https://doi.org/10.3390/s130202430 - 14 Feb 2013
Cited by 7 | Viewed by 8203
Abstract
We present a novel approach for autonomous location estimation and navigation in indoor environments using range images and prior scene knowledge from a GIS database (CityGML). What makes this task challenging is the arbitrary relative spatial relation between GIS and Time-of-Flight (ToF) range [...] Read more.
We present a novel approach for autonomous location estimation and navigation in indoor environments using range images and prior scene knowledge from a GIS database (CityGML). What makes this task challenging is the arbitrary relative spatial relation between GIS and Time-of-Flight (ToF) range camera further complicated by a markerless configuration. We propose to estimate the camera’s pose solely based on matching of GIS objects and their detected location in image sequences. We develop a coarse-to-fine matching strategy that is able to match point clouds without any initial parameters. Experiments with a state-of-the-art ToF point cloud show that our proposed method delivers an absolute camera position with decimeter accuracy, which is sufficient for many real-world applications (e.g., collision avoidance). Full article
(This article belongs to the Section Physical Sensors)
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<p>Overall concept of the presented approach.</p> Full article ">
<p>Acquired point cloud from ToF range camera.</p> Full article ">
<p>Origin (x,y,z) as delivered by the camera. Reproduced with permission from MESA Imaging AG, SR4000 User Manual; published by MESA Imaging AG, 2011 [<a href="#b28-sensors-13-02430" class="html-bibr">28</a>].</p> Full article ">
<p>VRML model of the test object with seven surfaces and ten object points (<b>left</b>), as wire frame model (<b>middle</b>) and with added random points (<b>right</b>).</p> Full article ">
<p>Time-of-flight principle. Reproduced with permission from T. Kahlmann and H. Ingensand, Proc. SPIE 6758; published by SPIE, 2007 [<a href="#b33-sensors-13-02430" class="html-bibr">33</a>].</p> Full article ">
<p>Final test results after calibration by manufacturer. All deviations are within the 20 mm tolerance. The absolute error represents the deviation between a reference distance and the distance measurements. Reproduced with permission from MESA Imaging AG, SR4000 Final Test Report; published by MESA Imaging AG, 2011 [<a href="#b34-sensors-13-02430" class="html-bibr">34</a>].</p> Full article ">
<p>Acquired and model point cloud after <math display="inline"> <semantics id="sm20"> <mrow> <msubsup> <mtext>T</mtext> <mtext>i</mtext> <mtext>G</mtext></msubsup></mrow></semantics></math> translation (SR4000 point cloud without floor in white and model point cloud in red).</p> Full article ">
<p>Solution of NDT algorithm (input data: object model point cloud in green and SR4000 point cloud in white).</p> Full article ">
<p>Solution of CG algorithm from different viewing angles; filtered SR4000 point cloud (white) and GIS object model point cloud (green).</p> Full article ">
840 KiB  
Article
Light-Intensity-Induced Characterization of Elastic Constants and d33 Piezoelectric Coefficient of PLZT Single Fiber Based Transducers
by Lucjan Kozielski, Jiri Erhart and Frank Jörg Clemens
Sensors 2013, 13(2), 2419-2429; https://doi.org/10.3390/s130202419 - 12 Feb 2013
Cited by 6 | Viewed by 8422
Abstract
Enhanced functionality of electro-optic devices by implementing piezoelectric micro fibers into their construction is proposed. Lanthanum-modified lead zirconate titanate (PLZT) ceramics are known to exhibit high light transparency, desirable electro-optic properties and fast response. In this study PLZT fibers with a diameter of [...] Read more.
Enhanced functionality of electro-optic devices by implementing piezoelectric micro fibers into their construction is proposed. Lanthanum-modified lead zirconate titanate (PLZT) ceramics are known to exhibit high light transparency, desirable electro-optic properties and fast response. In this study PLZT fibers with a diameter of around 300 microns were produced by a thermoplastic processing method and their light-induced impedance and piezoelectric coefficient were investigated at relatively low light intensity (below 50 mW/cm2). The authors experimentally proved higher performance of light controlled microfiber transducers in comparison to their bulk form. The advantage of the high surface area to volume ratio is shown to be an excellent technique to design high quality light sensors by using fibrous materials. The UV absorption induced change in elastic constants of 3% and 4% for the piezoelectric coefficient d33. Full article
(This article belongs to the Special Issue Piezoelectric Sensors and Actuators)
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<p>Measurement setup and electrical equivalent circuit of piezoelectric fiber resonator.</p> Full article ">
<p>SEM images of the fracture surface of PLZT fiber (<b>a</b>) and polished cross section of the investigated fiber (<b>b</b>).</p> Full article ">
<p>XRD diffraction pattern with the Rietveld approximation of PLZT fibers.</p> Full article ">
<p>Light conditions influence on PLZT fiber impedance modulus |Z| (<b>a</b>) and phase P (<b>b</b>) at the antiresonance peak of frequency characteristics.</p> Full article ">
<p>Light intensity influence on PLZT fiber impedance |Z| (<b>a</b>) and phase P (<b>b</b>) at the peak of frequency detailed presented in (<b>c</b>) and electrical equivalent circuit values for light induced variations (<b>d</b>).</p> Full article ">
1238 KiB  
Article
An Infrastructureless Approach to Estimate Vehicular Density in Urban Environments
by Julio A. Sanguesa, Manuel Fogue, Piedad Garrido, Francisco J. Martinez, Juan-Carlos Cano, Carlos T. Calafate and Pietro Manzoni
Sensors 2013, 13(2), 2399-2418; https://doi.org/10.3390/s130202399 - 11 Feb 2013
Cited by 37 | Viewed by 7913
Abstract
In Vehicular Networks, communication success usually depends on the density of vehicles, since a higher density allows having shorter and more reliable wireless links. Thus, knowing the density of vehicles in a vehicular communications environment is important, as better opportunities for wireless communication [...] Read more.
In Vehicular Networks, communication success usually depends on the density of vehicles, since a higher density allows having shorter and more reliable wireless links. Thus, knowing the density of vehicles in a vehicular communications environment is important, as better opportunities for wireless communication can show up. However, vehicle density is highly variable in time and space. This paper deals with the importance of predicting the density of vehicles in vehicular environments to take decisions for enhancing the dissemination of warning messages between vehicles. We propose a novel mechanism to estimate the vehicular density in urban environments. Our mechanism uses as input parameters the number of beacons received per vehicle, and the topological characteristics of the environment where the vehicles are located. Simulation results indicate that, unlike previous proposals solely based on the number of beacons received, our approach is able to accurately estimate the vehicular density, and therefore it could support more efficient dissemination protocols for vehicular environments, as well as improve previously proposed schemes. Full article
(This article belongs to the Section Physical Sensors)
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<p>Scenarios used in our simulations. Fragments of the cities of: (<b>a</b>) Rome (Italy), (<b>b</b>) Rio de Janeiro (Brazil), (<b>c</b>) Valencia (Spain), (<b>d</b>) Sydney (Australia), (<b>e</b>) Amsterdam (Netherlands), (<b>f</b>) Madrid (Spain), (<b>g</b>) San Francisco (USA), and (<b>h</b>) Los Angeles (USA).</p> Full article ">
<p>Number of beacons received when varying the vehicular density.</p> Full article ">
<p>3D representation of our density estimation function.</p> Full article ">
<p>Number of beacons received per vehicle when varying the time period and the city roadmap when simulating: (<b>a</b>) 100 vehicles·km<sup>−2</sup>, and (<b>b</b>) 200 vehicles·km<sup>−2</sup>.</p> Full article ">
<p>Different criteria when counting the number of streets.</p> Full article ">
<p>Comparison between simulated and estimated average results.</p> Full article ">
<p>Absolute error histogram.</p> Full article ">
<p>Graphical comparison between simulated and estimated results for each function.</p> Full article ">
6753 KiB  
Article
Rapid Characterization of Vegetation Structure with a Microsoft Kinect Sensor
by George Azzari, Michael L. Goulden and Radu B. Rusu
Sensors 2013, 13(2), 2384-2398; https://doi.org/10.3390/s130202384 - 11 Feb 2013
Cited by 106 | Viewed by 11201
Abstract
The importance of vegetation structure and biomass in controlling land-atmosphere exchange is widely recognized, but measurements of canopy structure are challenging, time consuming, and often rely on destructive methods. The Microsoft Kinect is an infrared sensor designed for video gaming that outputs synchronized [...] Read more.
The importance of vegetation structure and biomass in controlling land-atmosphere exchange is widely recognized, but measurements of canopy structure are challenging, time consuming, and often rely on destructive methods. The Microsoft Kinect is an infrared sensor designed for video gaming that outputs synchronized color and depth images and that has the potential to allow rapid characterization of vegetation structure. We compared depth images from a Kinect sensor with manual measurements of plant structure and size for two species growing in a California grassland. The depth images agreed well with the horizontal and vertical measurements of plant size made manually. Similarly, the plant volumes calculated with a three-dimensional convex hulls approach was well related to plant biomass. The Kinect showed some limitations for ecological observation associated with a short measurement range and daytime light contamination. Nonetheless, the Kinect’s light weight, fast acquisition time, low power requirement, and cost make it a promising tool for rapid field surveys of canopy structure, especially in small-statured vegetation. Full article
(This article belongs to the Section Physical Sensors)
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<p>(<b>a</b>) The “tower mode” experimental setup used for nadir measurements with Kinect (see Sections 2.3 and 2.4). (<b>b</b>) Side view and (<b>c</b>) nadir view of a wild artichoke plant recorded during the field test (see Section 2.4). Blue and red lines represent plant's basal diameter and height as measured manually with a ruler.</p> Full article ">
<p>Comparison between nadir-only (a and c; collected using the “Tower Mode”) and co-registered multi-angular (b and d; collected using the “Multi-angular Mode”) point clouds. The upper panels show the point clouds viewed from an arbitrary horizontal perspective. The lower panels show convex (<b>c</b>) and concave (<b>d</b>) hulls superimposed as white lines. Panel (<b>c</b>) shows the shade (grey) and border (white) points used to define the convex hulls. Point cloud color scale is distance (meters) from the sensor at nadir.</p> Full article ">
<p>Comparison between raw infrared output from Kinect (<b>a, c, e</b>) and corresponding point clouds (<b>b, d, f</b>) in different light conditions. All images are for a potted rubber tree plant that was about 1.10 m tall (<span class="html-italic">i.e</span>., <a href="#f1-sensors-13-02384" class="html-fig">Figure 1(a)</a>). Point cloud color scale is distance (meters) from the sensor at nadir.</p> Full article ">
<p>Direct comparison of manual and Kinect measurements of plant basal diameter (“Base”; the average of x and y measurements) and plant height (“Height”). Solid lines represent least squares linear fits.</p> Full article ">
<p>Direct comparison of volumes obtained from convex hulls and those derived from manual measurements with various solid shape approximations. Solid lines represent least squares linear fits.</p> Full article ">
<p>Allometric relations between Kinect-derived dimensions (base and height) and dry biomass measurements. Solid lines represent least squares logarithmic fits of the form <span class="html-italic">y</span> = <span class="html-italic">A</span> + <span class="html-italic">B</span> · log(<span class="html-italic">x</span> + <span class="html-italic">C</span>)/(<span class="html-italic">log</span>(<span class="html-italic">D</span>) + 1).</p> Full article ">
875 KiB  
Article
Development of a Compact Wireless Laplacian Electrode Module for Electromyograms and Its Human Interface Applications
by Yutaka Fukuoka, Kenji Miyazawa, Hiroki Mori, Manabi Miyagi, Masafumi Nishida, Yasuo Horiuchi, Akira Ichikawa, Hiroshi Hoshino, Makoto Noshiro and Akinori Ueno
Sensors 2013, 13(2), 2368-2383; https://doi.org/10.3390/s130202368 - 8 Feb 2013
Cited by 12 | Viewed by 8844
Abstract
In this study, we developed a compact wireless Laplacian electrode module for electromyograms (EMGs). One of the advantages of the Laplacian electrode configuration is that EMGs obtained with it are expected to be sensitive to the firing of the muscle directly beneath the [...] Read more.
In this study, we developed a compact wireless Laplacian electrode module for electromyograms (EMGs). One of the advantages of the Laplacian electrode configuration is that EMGs obtained with it are expected to be sensitive to the firing of the muscle directly beneath the measurement site. The performance of the developed electrode module was investigated in two human interface applications: character-input interface and detection of finger movement during finger Braille typing. In the former application, the electrode module was combined with an EMG-mouse click converter circuit. In the latter, four electrode modules were used for detection of finger movements during finger Braille typing. Investigation on the character-input interface indicated that characters could be input stably by contraction of (a) the masseter, (b) trapezius, (c) anterior tibialis and (d) flexor carpi ulnaris muscles. This wide applicability is desirable when the interface is applied to persons with physical disabilities because the disability differs one to another. The investigation also demonstrated that the electrode module can work properly without any skin preparation. Finger movement detection experiments showed that each finger movement was more clearly detectable when comparing to EMGs recorded with conventional electrodes, suggesting that the Laplacian electrode module is more suitable for detecting the timing of finger movement during typing. This could be because the Laplacian configuration enables us to record EMGs just beneath the electrode. These results demonstrate the advantages of the Laplacian electrode module. Full article
(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Japan 2012)
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<p>Schematic diagrams of measuring electrodes for deriving a surface Laplacian potential. (<b>a</b>) The unipolar electrode configuration. The potential data are collected at <span class="html-italic">n</span> points over small circles surrounding the observation point 0. (<b>b</b>) The bipolar concentric electrode configuration composed of a conductive disk at the center and a conductive ring surrounding the central disk.</p> Full article ">
<p>MacKay's configuration of electrodes and a circuit connected to them for deriving an approximate surface Laplacian potential.</p> Full article ">
<p>Configuration and appearance of the developed wireless electrode module. (<b>a</b>) Configuration and (<b>b</b>) Top and bottom views.</p> Full article ">
<p>Block diagram of the assembled EMG-click converter circuit.</p> Full article ">
<p>Execution screens of the character-input software with a scanning cursor. (<b>a</b>) Horizontal and (<b>b</b>) Vertical scanning modes. For those who are not familiar with Japanese characters, the main idea presented in this figure was reproduced in alphabets in <a href="#f11-sensors-13-02368" class="html-fig">Figure A1</a>.</p> Full article ">
<p>Arrangement of the wireless electrodes and the disposable electrodes for detection of finger movements during finger Braille typing. Four Laplacian modules, two on each flexor carpi ulnaris muscle, were attached to the finger Braille interpreter.</p> Full article ">
<p>Recordings of the Laplacian EMG signals obtained from various sites with muscle contractions and corresponding pulse signals generated by the EMG-click converter circuit. (<b>a</b>) Masseter, (<b>b</b>) trapezius, (<b>c</b>) <span class="html-italic">anterior tibialis</span>, and (<b>d</b>) <span class="html-italic">flexor carpi ulnaris</span> muscles.</p> Full article ">
<p>Comparison between the mean IEMGs obtained with the conventional and Laplacian electrodes.</p> Full article ">
<p>Typical recordings of the Laplacian (<b>top</b>) and conventional (<b>bottom</b>) EMGs during real time interpretation of broadcast news to finger Braille.</p> Full article ">
527 KiB  
Article
Energy Harvesting Thermoelectric Generators Manufactured Using the Complementary Metal Oxide Semiconductor Process
by Ming-Zhi Yang, Chyan-Chyi Wu, Ching-Liang Dai and Wen-Jung Tsai
Sensors 2013, 13(2), 2359-2367; https://doi.org/10.3390/s130202359 - 8 Feb 2013
Cited by 52 | Viewed by 8967
Abstract
This paper presents the fabrication and characterization of energy harvesting thermoelectric micro generators using the commercial complementary metal oxide semiconductor (CMOS) process. The micro generator consists of 33 thermocouples in series. Thermocouple materials are p-type and n-type polysilicon since they have a large [...] Read more.
This paper presents the fabrication and characterization of energy harvesting thermoelectric micro generators using the commercial complementary metal oxide semiconductor (CMOS) process. The micro generator consists of 33 thermocouples in series. Thermocouple materials are p-type and n-type polysilicon since they have a large Seebeck coefficient difference. The output power of the micro generator depends on the temperature difference in the hot and cold parts of the thermocouples. In order to increase this temperature difference, the hot part of the thermocouples is suspended to reduce heat-sinking. The micro generator needs a post-CMOS process to release the suspended structures of hot part, which the post-process includes an anisotropic dry etching to etch the sacrificial oxide layer and an isotropic dry etching to remove the silicon substrate. Experiments show that the output power of the micro generator is 9.4 mW at a temperature difference of 15 K. Full article
(This article belongs to the Special Issue Modeling, Testing and Reliability Issues in MEMS Engineering 2013)
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<p>Schematic structure of the energy harvesting thermoelectric generator.</p> Full article ">
<p>Simulated results of the output voltage for the thermoelectric generator.</p> Full article ">
<p>Simulated results of the output power for the thermoelectric generator.</p> Full article ">
<p>Fabrication flow of the thermoelectric generator, (<b>a</b>) after completion of the CMOS process; (<b>b</b>) etching the oxide sacrificial layer; (<b>c</b>) etching the silicon substrate.</p> Full article ">
<p>SEM image of the thermoelectric generator.</p> Full article ">
<p>SEM image of cross-sectional view for the thermoelectric generator.</p> Full article ">
<p>Measurement setup of the thermoelectric generator.</p> Full article ">
<p>Measured results of the output voltage for the thermoelectric generator.</p> Full article ">
<p>Measured results of the output power for the thermoelectric generator.</p> Full article ">
762 KiB  
Article
High-Visibility Photonic Crystal Fiber Interferometer as Multifunctional Sensor
by G. A. Cárdenas-Sevilla, Fernando C. Fávero and Joel Villatoro
Sensors 2013, 13(2), 2349-2358; https://doi.org/10.3390/s130202349 - 8 Feb 2013
Cited by 29 | Viewed by 7907
Abstract
A photonic crystal fiber (PCF) interferometer that exhibits record fringe contrast (~40 dB) is demonstrated along with its sensing applications. The device operates in reflection mode and consists of a centimeter-long segment of properly selected PCF fusion spliced to single mode optical fibers. [...] Read more.
A photonic crystal fiber (PCF) interferometer that exhibits record fringe contrast (~40 dB) is demonstrated along with its sensing applications. The device operates in reflection mode and consists of a centimeter-long segment of properly selected PCF fusion spliced to single mode optical fibers. Two identical collapsed zones in the PCF combined with its modal properties allow high-visibility interference patterns. The interferometer is suitable for refractometric and liquid level sensing. The measuring refractive index range goes from 1.33 to 1.43 and the maximum resolution is ~1.6 × 10−5. Full article
(This article belongs to the Special Issue Photonic Crystal Sensors)
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<p>Drawings of our interferometer showing two possible terminations and schematic representation of the interrogation set up. FOC stands fiber optic circulator; SMF for single mode fiber, L for PCF length, and <span class="html-italic">l</span> is the length of SMF at the distal end. The micrographs show the PCF cross section and details of the PCF-SMF junction. The broadening of the beam when it enters the collapsed region is illustrated.</p> Full article ">
<p>Fringe contrast in a mode interferometer as a function of <span class="html-italic">k</span> or the intensity of the cladding mode to that of the core mode ratio. The inset shows the theoretical reflection spectrum in the case of <span class="html-italic">k</span> = 0.4 (dotted line) and <span class="html-italic">k</span> = 0.96 (solid line).</p> Full article ">
<p>(<b>a</b>) Normalized reflection of a 12 mm-long interferometer for different lengths of SMF at the distal end. (<b>b</b>) Normalized transmission and reflection spectra of a 16 mm-long interferometer when a highly reflecting mirror was used. In all cases the external medium was air and the PCF was LMA-10.</p> Full article ">
<p>(<b>a</b>) Interference pattern of a 12 mm-long interferometer immersed in different indices. (<b>b</b>) Corresponding interference pattern shift <span class="html-italic">versus</span> RI. The measurements were carried out at room temperature with fluctuations on the order of 2 °C.</p> Full article ">
<p>(<b>a</b>) Reflection spectra for three RI values that are closed to each other. (<b>b</b>) Reflection changes observed at λ = 1,554.8 nm as a function of the external RI. The interferometer was 12 mm long.</p> Full article ">
<p>Reflection spectra of an interferometer at different percentages of the length of the PCF immersed in water and the corresponding calibration curve. The PCF length, L, was 11 mm.</p> Full article ">
561 KiB  
Review
Diverse Applications of Electronic-Nose Technologies in Agriculture and Forestry
by Alphus D. Wilson
Sensors 2013, 13(2), 2295-2348; https://doi.org/10.3390/s130202295 - 8 Feb 2013
Cited by 275 | Viewed by 23654
Abstract
Electronic-nose (e-nose) instruments, derived from numerous types of aroma-sensor technologies, have been developed for a diversity of applications in the broad fields of agriculture and forestry. Recent advances in e-nose technologies within the plant sciences, including improvements in gas-sensor designs, innovations in data [...] Read more.
Electronic-nose (e-nose) instruments, derived from numerous types of aroma-sensor technologies, have been developed for a diversity of applications in the broad fields of agriculture and forestry. Recent advances in e-nose technologies within the plant sciences, including improvements in gas-sensor designs, innovations in data analysis and pattern-recognition algorithms, and progress in material science and systems integration methods, have led to significant benefits to both industries. Electronic noses have been used in a variety of commercial agricultural-related industries, including the agricultural sectors of agronomy, biochemical processing, botany, cell culture, plant cultivar selections, environmental monitoring, horticulture, pesticide detection, plant physiology and pathology. Applications in forestry include uses in chemotaxonomy, log tracking, wood and paper processing, forest management, forest health protection, and waste management. These aroma-detection applications have improved plant-based product attributes, quality, uniformity, and consistency in ways that have increased the efficiency and effectiveness of production and manufacturing processes. This paper provides a comprehensive review and summary of a broad range of electronic-nose technologies and applications, developed specifically for the agriculture and forestry industries over the past thirty years, which have offered solutions that have greatly improved worldwide agricultural and agroforestry production systems. Full article
(This article belongs to the Special Issue Sensor-Based Technologies and Processes in Agriculture and Forestry)
761 KiB  
Article
Statistical Modeling of Large-Scale Signal Path Loss in Underwater Acoustic Networks
by Jesús Llor and Manuel Perez Malumbres
Sensors 2013, 13(2), 2279-2294; https://doi.org/10.3390/s130202279 - 8 Feb 2013
Cited by 17 | Viewed by 8578
Abstract
In an underwater acoustic channel, the propagation conditions are known to vary in time, causing the deviation of the received signal strength from the nominal value predicted by a deterministic propagation model. To facilitate a large-scale system design in such conditions (e.g., power [...] Read more.
In an underwater acoustic channel, the propagation conditions are known to vary in time, causing the deviation of the received signal strength from the nominal value predicted by a deterministic propagation model. To facilitate a large-scale system design in such conditions (e.g., power allocation), we have developed a statistical propagation model in which the transmission loss is treated as a random variable. By applying repetitive computation to the acoustic field, using ray tracing for a set of varying environmental conditions (surface height, wave activity, small node displacements around nominal locations, etc.), an ensemble of transmission losses is compiled and later used to infer the statistical model parameters. A reasonable agreement is found with log-normal distribution, whose mean obeys a log-distance increases, and whose variance appears to be constant for a certain range of inter-node distances in a given deployment location. The statistical model is deemed useful for higher-level system planning, where simulation is needed to assess the performance of candidate network protocols under various resource allocation policies, i.e., to determine the transmit power and bandwidth allocation necessary to achieve a desired level of performance (connectivity, throughput, reliability, etc.). Full article
(This article belongs to the Special Issue Last Trends in Acoustic Sensing)
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<p>An ensemble of transmission losses calculated by the Bellhop model. Solid line indicates the average calculated over the total run time. Dashed lines indicate the values of one standard deviation σ.</p> Full article ">
<p>Tradeoff between model propagation accuracy and computational complexity.</p> Full article ">
<p>Network deployment in Valencia, Spain.</p> Full article ">
<p>Network node movement model.</p> Full article ">
<p>Average transmission loss <span class="html-italic">vs.</span> frequency; (<b>a</b>) Bellhop, and (<b>b</b>) SPM mean.</p> Full article ">
<p>Attenuation of bandwidth signals with DPM and SPM single frequency proposal.</p> Full article ">
<p>Bandwidth signals loss with DPM and SPM single frequency proposal after applying the bandwidth correction factor.</p> Full article ">
<p>Attenuation <span class="html-italic">vs.</span> distance with different node movement at 5-15 kHz bandwidth signals.</p> Full article ">
<p>Gateway reachability (central node) from Node #1 (bottom leftmost node).</p> Full article ">
479 KiB  
Article
Label-Free Potentiometry for Detecting DNA Hybridization Using Peptide Nucleic Acid and DNA Probes
by Tatsuro Goda, Ankit Balram Singi, Yasuhiro Maeda, Akira Matsumoto, Masaki Torimura, Hiroshi Aoki and Yuji Miyahara
Sensors 2013, 13(2), 2267-2278; https://doi.org/10.3390/s130202267 - 7 Feb 2013
Cited by 39 | Viewed by 11641
Abstract
Peptide nucleic acid (PNA) has outstanding affinity over DNA for complementary nucleic acid sequences by forming a PNA-DNA heterodimer upon hybridization via Watson-Crick base-pairing. To verify whether PNA probes on an electrode surface enhance sensitivity for potentiometric DNA detection or not, we conducted [...] Read more.
Peptide nucleic acid (PNA) has outstanding affinity over DNA for complementary nucleic acid sequences by forming a PNA-DNA heterodimer upon hybridization via Watson-Crick base-pairing. To verify whether PNA probes on an electrode surface enhance sensitivity for potentiometric DNA detection or not, we conducted a comparative study on the hybridization of PNA and DNA probes on the surface of a 10-channel gold electrodes microarray. Changes in the charge density as a result of hybridization at the solution/electrode interface on the self-assembled monolayer (SAM)-formed microelectrodes were directly transformed into potentiometric signals using a high input impedance electrometer. The charge readout allows label-free, reagent-less, and multi-parallel detection of target oligonucleotides without any optical assistance. The differences in the probe lengths between 15- to 22-mer dramatically influenced on the sensitivity of the PNA and DNA sensors. Molecular type of the capturing probe did not affect the degree of potential shift. Theoretical model for charged rod-like duplex using the Gouy-Chapman equation indicates the dominant effect of electrostatic attractive forces between anionic DNA and underlying electrode at the electrolyte/electrode interface in the potentiometry. Full article
(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Japan 2012)
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<p>Schematic representation of label-free electrical detection of DNA hybridization using PNA or DNA probes. (<b>a</b>) Electrometer-based potentiometric setup for monitoring changes in charge density upon capturing DNA target at the solution/microelectrodes interface. The images indicate the gold microelectrodes array. (<b>b</b>) Differences in the backbone structure and electrostatic nature of PNA and DNA.</p> Full article ">
<p>(<b>a</b>) Time-course of potential changes at the solution/electrode interface by applying DNA target with increasing concentration in 5× SSC buffer and by rinsing with 0.1× DPBS in stepwise manner to the gold electrode modified with MCH SAM containing the 20-mer PNA probes. (<b>b</b>) Stability of measured potential with repeated cycles of blank-rinse solutions. DNA target concentration: <b>a</b>. blank; <b>b</b>. 100 aM; <b>c</b>. 1 fM; <b>d</b>. 10 fM; <b>e</b>. 100 fM; <b>f</b>. 1 pM; <b>g</b>. 10 pM; <b>h</b>. 100 pM. R: rinsing.</p> Full article ">
<p>Potential shifts as a function of DNA target concentrations for the electrodes modified by PNA probes (22-mer, 20-mer, and 15-mer) and MCH SAM in bulk and after rinse conditions. Colors in red and blue represent the signals from DNA target and non-target, respectively. (* <span class="html-italic">p</span> &lt; 0.01).</p> Full article ">
<p>Potential shifts as a function of DNA target concentrations for the electrode modified by DNA probes (20-mer and 15-mer) and MCH SAM in bulk and after rinse conditions. Colors in red and blue represent the signals from DNA target and non-target, respectively. (* <span class="html-italic">p</span> &lt; 0.01).</p> Full article ">
<p>Electrostatic energy for 20-mer PNA-DNA or DNA-DNA duplexes using the charged rod-like model under the attractive Gouy-Chapman potential above the positive surface potential (Φ0 = 50 mV). Concentrations of monovalent salt in solution are 15 mM (rinse buffer: 0.1× DPBS) and 750 mM (hybridization buffer: 5× SSC).</p> Full article ">
783 KiB  
Article
Investigations on a Novel Inductive Concept Frequency Technique for the Grading of Oil Palm Fresh Fruit Bunches
by Noor Hasmiza Harun, Norhisam Misron, Roslina Mohd Sidek, Ishak Aris, Desa Ahmad, Hiroyuki Wakiwaka and Kunihisa Tashiro
Sensors 2013, 13(2), 2254-2266; https://doi.org/10.3390/s130202254 - 7 Feb 2013
Cited by 26 | Viewed by 12196
Abstract
From the Malaysian harvester’s perspective, the determination of the ripeness of the oil palm (FFB) is a critical factor to maximize palm oil production. A preliminary study of a novel oil palm fruit sensor to detect the maturity of oil palm fruit bunches [...] Read more.
From the Malaysian harvester’s perspective, the determination of the ripeness of the oil palm (FFB) is a critical factor to maximize palm oil production. A preliminary study of a novel oil palm fruit sensor to detect the maturity of oil palm fruit bunches is presented. To optimize the functionality of the sensor, the frequency characteristics of air coils of various diameters are investigated to determine their inductance and resonant characteristics. Sixteen samples from two categories, namely ripe oil palm fruitlets and unripe oil palm fruitlets, are tested from 100 Hz up to 100 MHz frequency. The results showed the inductance and resonant characteristics of the air coil sensors display significant changes among the samples of each category. The investigations on the frequency characteristics of the sensor air coils are studied to observe the effect of variations in the coil diameter. The effect of coil diameter yields a significant 0.02643 MHz difference between unripe samples to air and 0.01084 MHz for ripe samples to air. The designed sensor exhibits significant potential in determining the maturity of oil palm fruits. Full article
(This article belongs to the Special Issue Sensor-Based Technologies and Processes in Agriculture and Forestry)
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<p>Samples of oil palm fruitlet (<b>a</b>) Oil palm fruit tree (<b>b</b>) Two category of samples.</p> Full article ">
<p>Ladder stages of the Oil Palm Fresh Fruit Bunch (FFB).</p> Full article ">
<p>Chemical contents of the oil palm fresh fruit bunch (FFB) (<b>a</b>) Ripe (<b>b</b>) Unripe.</p> Full article ">
<p>Structure of the air coil.</p> Full article ">
<p>Frequency characteristics experimental setup.</p> Full article ">
<p>Inductance characteristics for the air coil.</p> Full article ">
<p>Frequency characteristics for the air coil.</p> Full article ">
<p>Inductance characteristics for different coil diameter (<b>a</b>) 24 mm (<b>b</b>) 26 mm (<b>c</b>) 28 mm.</p> Full article ">
<p>Effects of coil diameter (<b>a</b>) 24mm (<b>b</b>) 26mm (<b>c</b>) 28mm.</p> Full article ">
1306 KiB  
Article
Architecture for Multi-Technology Real-Time Location Systems
by Javier Rodas, Valentín Barral and Carlos J. Escudero
Sensors 2013, 13(2), 2220-2253; https://doi.org/10.3390/s130202220 - 7 Feb 2013
Cited by 12 | Viewed by 8922
Abstract
The rising popularity of location-based services has prompted considerable research in the field of indoor location systems. Since there is no single technology to support these systems, it is necessary to consider the fusion of the information coming from heterogeneous sensors. This paper [...] Read more.
The rising popularity of location-based services has prompted considerable research in the field of indoor location systems. Since there is no single technology to support these systems, it is necessary to consider the fusion of the information coming from heterogeneous sensors. This paper presents a software architecture designed for a hybrid location system where we can merge information from multiple sensor technologies. The architecture was designed to be used by different kinds of actors independently and with mutual transparency: hardware administrators, algorithm developers and user applications. The paper presents the architecture design, work-flow, case study examples and some results to show how different technologies can be exploited to obtain a good estimation of a target position. Full article
(This article belongs to the Section Sensor Networks)
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<p>UML class diagram of the system nodes, sensors, networks, <span class="html-italic">etc.</span></p> Full article ">
<p>Proposed architecture for Hybrid Real-Time Location Systems.</p> Full article ">
<p>Workflow of the proposed system divided into six groups of messages: (<b>A</b>) Infrastructure (maps, anchor and network), mobile node and sensor registration process; (<b>B</b>) New measurements from mobiles or sensors; (<b>C</b>) Target administration with association to mobiles and/or sensors; (<b>D</b>) Location algorithm initialization steps to know the elements available; (<b>E</b>) Position estimation process where, a location algorithm estimates new positions after reading measurements; (<b>F</b>) The localization clients continuously get position estimations, optionally filtering and merging positioning data.</p> Full article ">
<p>Once the network infrastructure is registered, and the location algorithms and clients configured, these actors continuously use the same type of messages to save and retrieve data with the system.</p> Full article ">
<p>The zb_uwb_accel_target identifier represents a virtual target device, and it is associated to the zb_Ml and uwb_Ml mobile devices and to the accel_l generic sensor.</p> Full article ">
<p>Groups of messages A, B and C.</p> Full article ">
<p>Groups of messages D, E and F.</p> Full article ">
<p>The wifi_target represents a target device associated to the wifi_sensor1 or wifi_sensor2 implemented with the same physical smartphone device, in the example.</p> Full article ">
<p>UML class diagram representing how to implement any Fingerprinting algorithm in any language (e.g., a KNN programmed in Java).</p> Full article ">
886 KiB  
Article
Frequency Noise Properties of Lasers for Interferometry in Nanometrology
by Jan Hrabina, Josef Lazar, Miroslava Holá and Ondřej Číp
Sensors 2013, 13(2), 2206-2219; https://doi.org/10.3390/s130202206 - 7 Feb 2013
Cited by 31 | Viewed by 8327
Abstract
In this contribution we focus on laser frequency noise properties and their influence on the interferometric displacement measurements. A setup for measurement of laser frequency noise is proposed and tested together with simultaneous measurement of fluctuations in displacement in the Michelson interferometer. Several [...] Read more.
In this contribution we focus on laser frequency noise properties and their influence on the interferometric displacement measurements. A setup for measurement of laser frequency noise is proposed and tested together with simultaneous measurement of fluctuations in displacement in the Michelson interferometer. Several laser sources, including traditional He-Ne and solid-state lasers, and their noise properties are evaluated and compared. The contribution of the laser frequency noise to the displacement measurement is discussed in the context of other sources of uncertainty associated with the interferometric setup, such as, mechanics, resolution of analog-to-digital conversion, frequency bandwidth of the detection chain, and variations of the refractive index of air. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
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<p>Principal schematic of a Michelson interferometer; BS—beamsplitter, M—mirrors, DET—photodetector, L<sub>REF</sub>—optical length of reference arm, L<sub>DIFF</sub>—difference distance between optical lenghts of reference and measuring arm of the interferometer.</p> Full article ">
<p>Length difference between the measuring and reference arms of the interferometer and corresponding limiting level of frequency fluctuations for 532 nm wavelength. (resolutions of the A/D conversion from top: 8, 12, 16, 20, 24 bits).</p> Full article ">
<p>Schematic of the experimental setup for amplitude and frequency noise measurements. PBS-polarizing beam splitters, M-full reflective mirrors, Det-photodetectors (Det1 measuring amplitude noise, Det2 frequency noise throught the Fabry-Perot cavity, Det3 frequency noise throught the interferometer). PZT tuning option is included only in L1 laser and it was used only for evaluation of correct function of the frequency discriminators before the experiment itself.</p> Full article ">
<p>Optical power (amplitude) noise measurements of tested laser heads.</p> Full article ">
<p>Frequency noise measurements of tested laser heads (Fabry-Perot cavity).</p> Full article ">
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Article
Monolithically Integrated Mid-Infrared Quantum Cascade Laser and Detector
by Benedikt Schwarz, Peter Reininger, Hermann Detz, Tobias Zederbauer, Aaron Maxwell Andrews, Werner Schrenk and Gottfried Strasser
Sensors 2013, 13(2), 2196-2205; https://doi.org/10.3390/s130202196 - 6 Feb 2013
Cited by 34 | Viewed by 10571
Abstract
We demonstrate the monolithic integration of a mid-infrared laser and detector utilizing a bi-functional quantum cascade active region. When biased, this active region provides optical gain, while it can be used as a detector at zero bias. With our novel approach we can [...] Read more.
We demonstrate the monolithic integration of a mid-infrared laser and detector utilizing a bi-functional quantum cascade active region. When biased, this active region provides optical gain, while it can be used as a detector at zero bias. With our novel approach we can measure the light intensity of the laser on the same chip without the need of external lenses or detectors. Based on a bound-to-continuum design, the bi-functional active region has an inherent broad electro-luminescence spectrum of 200 cm-1, which indicates its use for single mode laser arrays. We have measured a peak signal of 191.5 mV at the on-chip detector, without any amplification. The room-temperature pulsed emission with an averaged power consumption of 4 mW and the high-speed detection makes these devices ideal for low-power sensors. The combination of the on-chip detection functionality, the broad emission spectrum and the low average power consumption indicates the potential of our bi-functional quantum cascade structures to build a mid-infrared lab-on-a-chip based on quantum cascade laser technology. Full article
(This article belongs to the Special Issue Laser Sensing and Imaging)
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<p>Schematic conduction band structure of a QCL and a QCD. The functionality of these devices is combined into our QCLD, a bi-functional active region for same-frequency lasing and detecting.</p> Full article ">
<p>Sketch of the monolithic integrated QCL and QCD. The inset shows a SEM image of the etched laser facet of the 15 μm wide ridge. The gap between the laser and the detector is 10 μm.</p> Full article ">
<p>Schematic DC circuit diagram of the device with a shared bottom-side contact <b>(left)</b> and separated bottom contacts <b>(right).</b> The laser bias voltage is indicated by a red arrow. Separated bottom contacts allow to minimize electrical crosstalk to the detector, as both detector contacts are affected in the same manner. Thus a potential fluctuation at node“A” cancel out.</p> Full article ">
<p>Optical power versus current density of the laser measured with a calibrated external triglycine sulfate pyroelectric detector (DTGS) at the front-facet and the on-chipQCD at the back-facet. All components were operating at room temperature in atmosphere. The laser was operated in pulsed mode with 40 ns pulses at 5 kHz.</p> Full article ">
<p>Atmospheric absorption and emission spectra of the QCL at different current densities.</p> Full article ">
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