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Sensors, Volume 11, Issue 7 (July 2011) – 50 articles , Pages 6494-7301

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Open AccessArticle
Electromechanical Impedance Response of a Cracked Timoshenko Beam
Sensors 2011, 11(7), 7285-7301; https://doi.org/10.3390/s110707285 - 22 Jul 2011
Cited by 15 | Viewed by 4893
Abstract
Typically, the Electromechanical Impedance (EMI) technique does not use an analytical model for basic damage identification. However, an accurate model is necessary for getting more information about any damage. In this paper, an EMI model is presented for predicting the electromechanical impedance of [...] Read more.
Typically, the Electromechanical Impedance (EMI) technique does not use an analytical model for basic damage identification. However, an accurate model is necessary for getting more information about any damage. In this paper, an EMI model is presented for predicting the electromechanical impedance of a cracked beam structure quantitatively. A coupled system of a cracked Timoshenko beam with a pair of PZT patches bonded on the top and bottom surfaces has been considered, where the bonding layers are assumed as a Kelvin-Voigt material. The shear lag model is introduced to describe the load transfer between the PZT patches and the beam structure. The beam crack is simulated as a massless torsional spring; the dynamic equations of the coupled system are derived, which include the crack information and the inertial forces of both PZT patches and adhesive layers. According to the boundary conditions and continuity conditions, the analytical expression of the admittance of PZT patch is obtained. In the case study, the influences of crack and the inertial forces of PZT patches are analyzed. The results show that: (1) the inertial forces affects significantly in high frequency band; and (2) the use of appropriate frequency range can improve the accuracy of damage identification. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle
Visual Odometry Based on Structural Matching of Local Invariant Features Using Stereo Camera Sensor
Sensors 2011, 11(7), 7262-7284; https://doi.org/10.3390/s110707262 - 18 Jul 2011
Cited by 12 | Viewed by 6211
Abstract
This paper describes a novel sensor system to estimate the motion of a stereo camera. Local invariant image features are matched between pairs of frames and linked into image trajectories at video rate, providing the so-called visual odometry, i.e., motion estimates from visual [...] Read more.
This paper describes a novel sensor system to estimate the motion of a stereo camera. Local invariant image features are matched between pairs of frames and linked into image trajectories at video rate, providing the so-called visual odometry, i.e., motion estimates from visual input alone. Our proposal conducts two matching sessions: the first one between sets of features associated to the images of the stereo pairs and the second one between sets of features associated to consecutive frames. With respect to previously proposed approaches, the main novelty of this proposal is that both matching algorithms are conducted by means of a fast matching algorithm which combines absolute and relative feature constraints. Finding the largest-valued set of mutually consistent matches is equivalent to finding the maximum-weighted clique on a graph. The stereo matching allows to represent the scene view as a graph which emerge from the features of the accepted clique. On the other hand, the frame-to-frame matching defines a graph whose vertices are features in 3D space. The efficiency of the approach is increased by minimizing the geometric and algebraic errors to estimate the final displacement of the stereo camera between consecutive acquired frames. The proposed approach has been tested for mobile robotics navigation purposes in real environments and using different features. Experimental results demonstrate the performance of the proposal, which could be applied in both industrial and service robot fields. Full article
(This article belongs to the Section Physical Sensors)
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Open AccessArticle
Direct Sensor Orientation of a Land-Based Mobile Mapping System
Sensors 2011, 11(7), 7243-7261; https://doi.org/10.3390/s110707243 - 18 Jul 2011
Cited by 27 | Viewed by 5060
Abstract
A land-based mobile mapping system (MMS) is flexible and useful for the acquisition of road environment geospatial information. It integrates a set of imaging sensors and a position and orientation system (POS). The positioning quality of such systems is highly dependent on the [...] Read more.
A land-based mobile mapping system (MMS) is flexible and useful for the acquisition of road environment geospatial information. It integrates a set of imaging sensors and a position and orientation system (POS). The positioning quality of such systems is highly dependent on the accuracy of the utilized POS. This limitation is the major drawback due to the elevated cost associated with high-end GPS/INS units, particularly the inertial system. The potential accuracy of the direct sensor orientation depends on the architecture and quality of the GPS/INS integration process as well as the validity of the system calibration (i.e., calibration of the individual sensors as well as the system mounting parameters). In this paper, a novel single-step procedure using integrated sensor orientation with relative orientation constraint for the estimation of the mounting parameters is introduced. A comparative analysis between the proposed single-step and the traditional two-step procedure is carried out. Moreover, the estimated mounting parameters using the different methods are used in a direct geo-referencing procedure to evaluate their performance and the feasibility of the implemented system. Experimental results show that the proposed system using single-step system calibration method can achieve high 3D positioning accuracy. Full article
(This article belongs to the Special Issue State-of-the-Art Sensors in Canada)
Open AccessArticle
Automated Counting of Airborne Asbestos Fibers by a High-Throughput Microscopy (HTM) Method
Sensors 2011, 11(7), 7231-7242; https://doi.org/10.3390/s110707231 - 18 Jul 2011
Cited by 10 | Viewed by 4615
Abstract
Inhalation of airborne asbestos causes serious health problems such as lung cancer and malignant mesothelioma. The phase-contrast microscopy (PCM) method has been widely used for estimating airborne asbestos concentrations because it does not require complicated processes or high-priced equipment. However, the PCM method [...] Read more.
Inhalation of airborne asbestos causes serious health problems such as lung cancer and malignant mesothelioma. The phase-contrast microscopy (PCM) method has been widely used for estimating airborne asbestos concentrations because it does not require complicated processes or high-priced equipment. However, the PCM method is time-consuming and laborious as it is manually performed off-site by an expert. We have developed a high-throughput microscopy (HTM) method that can detect fibers distinguishable from other spherical particles in a sample slide by image processing both automatically and quantitatively. A set of parameters for processing and analysis of asbestos fiber images was adjusted for standard asbestos samples with known concentrations. We analyzed sample slides containing airborne asbestos fibers collected at 11 different workplaces following PCM and HTM methods, and found a reasonably good agreement in the asbestos concentration. Image acquisition synchronized with the movement of the robotic sample stages followed by an automated batch processing of a stack of sample images enabled us to count asbestos fibers with greatly reduced time and labors. HTM should be a potential alternative to conventional PCM, moving a step closer to realization of on-site monitoring of asbestos fibers in air. Full article
(This article belongs to the Section Physical Sensors)
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Open AccessArticle
Development of Sensor Cells Using NF-κB Pathway Activation for Detection of Nanoparticle-Induced Inflammation
Sensors 2011, 11(7), 7219-7230; https://doi.org/10.3390/s110707219 - 18 Jul 2011
Cited by 20 | Viewed by 5326
Abstract
The increasing use of nanomaterials in consumer and industrial products has aroused concerns regarding their fate in biological systems. An effective detection method to evaluate the safety of bio-nanomaterials is therefore very important. Titanium dioxide (TiO2), which is manufactured worldwide in [...] Read more.
The increasing use of nanomaterials in consumer and industrial products has aroused concerns regarding their fate in biological systems. An effective detection method to evaluate the safety of bio-nanomaterials is therefore very important. Titanium dioxide (TiO2), which is manufactured worldwide in large quantities for use in a wide range of applications, including pigment and cosmetic manufacturing, was once thought to be an inert material, but recently, more and more studies have indicated that TiO2 nanoparticles (TiO2 NPs) can cause inflammation and be harmful to humans by causing lung and brain problems. In order to evaluate the safety of TiO2 NPs for the environment and for humans, sensor cells for inflammation detection were developed, and these were transfected with the Toll-like receptor 4 (TLR4) gene and Nuclear Factor Kappa B (NF-κB) reporter gene. NF-κB as a primary cause of inflammation has received a lot of attention, and it can be activated by a wide variety of external stimuli. Our data show that TiO2 NPs-induced inflammation can be detected by our sensor cells through NF-κB pathway activation. This may lead to our sensor cells being used for bio-nanomaterial safety evaluation. Full article
(This article belongs to the Special Issue Live Cell-Based Sensors)
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Open AccessArticle
Research on the Filtering Algorithm in Speed and Position Detection of Maglev Trains
Sensors 2011, 11(7), 7204-7218; https://doi.org/10.3390/s110707204 - 14 Jul 2011
Cited by 25 | Viewed by 3481
Abstract
This paper introduces in brief the traction system of a permanent magnet electrodynamic suspension (EDS) train. The synchronous traction mode based on long stators and track cable is described. A speed and position detection system is recommended. It is installed on board and [...] Read more.
This paper introduces in brief the traction system of a permanent magnet electrodynamic suspension (EDS) train. The synchronous traction mode based on long stators and track cable is described. A speed and position detection system is recommended. It is installed on board and is used as the feedback end. Restricted by the maglev train’s structure, the permanent magnet electrodynamic suspension (EDS) train uses the non-contact method to detect its position. Because of the shake and the track joints, the position signal sent by the position sensor is always aberrant and noisy. To solve this problem, a linear discrete track-differentiator filtering algorithm is proposed. The filtering characters of the track-differentiator (TD) and track-differentiator group are analyzed. The four series of TD are used in the signal processing unit. The result shows that the track-differentiator could have a good effect and make the traction system run normally. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle
Data Collection Method for Mobile Sensor Networks Based on the Theory of Thermal Fields
Sensors 2011, 11(7), 7188-7203; https://doi.org/10.3390/s110707188 - 14 Jul 2011
Cited by 7 | Viewed by 4564
Abstract
Many sensor applications are aimed for mobile objects, where conventional routing approaches of data delivery might fail. Such applications are habitat monitoring, human probes or vehicular sensing systems. This paper targets such applications and proposes lightweight proactive distributed data collection scheme for Mobile [...] Read more.
Many sensor applications are aimed for mobile objects, where conventional routing approaches of data delivery might fail. Such applications are habitat monitoring, human probes or vehicular sensing systems. This paper targets such applications and proposes lightweight proactive distributed data collection scheme for Mobile Sensor Networks (MSN) based on the theory of thermal fields. By proper mapping, we create distribution function which allows considering characteristics of a sensor node. We show the functionality of our proposed forwarding method when adapted to the energy of sensor node. We also propose enhancement in order to maximize lifetime of the sensor nodes. We thoroughly evaluate proposed solution and discuss the tradeoffs. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle
Numerical Modeling of Plasmonic Nanoantennas with Realistic 3D Roughness and Distortion
Sensors 2011, 11(7), 7178-7187; https://doi.org/10.3390/s110707178 - 13 Jul 2011
Cited by 15 | Viewed by 4396
Abstract
Nanostructured plasmonic metamaterials, including optical nanoantenna arrays, are important for advanced optical sensing and imaging applications including surface-enhanced fluorescence, chemiluminescence, and Raman scattering. Although designs typically use ideally smooth geometries, realistic nanoantennas have nonzero roughness, which typically results in a modified enhancement factor [...] Read more.
Nanostructured plasmonic metamaterials, including optical nanoantenna arrays, are important for advanced optical sensing and imaging applications including surface-enhanced fluorescence, chemiluminescence, and Raman scattering. Although designs typically use ideally smooth geometries, realistic nanoantennas have nonzero roughness, which typically results in a modified enhancement factor that should be involved in their design. Herein we aim to treat roughness by introducing a realistic roughened geometry into the finite element (FE) model. Even if the roughness does not result in significant loss, it does result in a spectral shift and inhomogeneous broadening of the resonance, which could be critical when fitting the FE simulations of plasmonic nanoantennas to experiments. Moreover, the proposed approach could be applied to any model, whether mechanical, acoustic, electromagnetic, thermal, etc, in order to simulate a given roughness-generated physical phenomenon. Full article
(This article belongs to the Special Issue Metamaterials for Sensing)
Open AccessArticle
Phase-Modulated Waveform Design for Extended Target Detection in the Presence of Clutter
Sensors 2011, 11(7), 7162-7177; https://doi.org/10.3390/s110707162 - 12 Jul 2011
Cited by 19 | Viewed by 4376
Abstract
The problem to be addressed in this paper is a phase-modulated waveform design for the detection of extended targets contaminated by signal-dependent noise (clutter) and additive noise in practical radar systems. An optimal waveform design method that leads to the energy spectral density [...] Read more.
The problem to be addressed in this paper is a phase-modulated waveform design for the detection of extended targets contaminated by signal-dependent noise (clutter) and additive noise in practical radar systems. An optimal waveform design method that leads to the energy spectral density (ESD) of signal under the maximum signal-to-clutter-and-noise ratio (SCNR) criterion is introduced first. In order to make full use of the transmission power, a novel phase-iterative algorithm is then proposed for designing the phase-modulated waveform with a constant envelope, whose ESD matches the optimal one. This method is proven to be able to achieve a small SCNR loss by minimizing the mean-square spectral distance between the optimal waveform and the designed waveform. The results of extensive simulations demonstrate that our approach provides less than 1 dB SCNR loss when the signal duration is greater than 1 μs, and outperforms the stationary phase method and other phase-modulated waveform design methods. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle
Long-Range Wireless Mesh Network for Weather Monitoring in Unfriendly Geographic Conditions
Sensors 2011, 11(7), 7141-7161; https://doi.org/10.3390/s110707141 - 12 Jul 2011
Cited by 5 | Viewed by 5263
Abstract
In this paper a long-range wireless mesh network system is presented. It consists of three main parts: Remote Terminal Units (RTUs), Base Terminal Units (BTUs) and a Central Server (CS). The RTUs share a wireless network transmitting in the industrial, scientific and medical [...] Read more.
In this paper a long-range wireless mesh network system is presented. It consists of three main parts: Remote Terminal Units (RTUs), Base Terminal Units (BTUs) and a Central Server (CS). The RTUs share a wireless network transmitting in the industrial, scientific and medical applications ISM band, which reaches up to 64 Km in a single point-to-point communication. A BTU controls the traffic within the network and has as its main task interconnecting it to a Ku-band satellite link using an embedded microcontroller-based gateway. Collected data is stored in a CS and presented to the final user in a numerical and a graphical form in a web portal. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle
Nanocrystalline SnO2:F Thin Films for Liquid Petroleum Gas Sensors
Sensors 2011, 11(7), 7127-7140; https://doi.org/10.3390/s110707127 - 11 Jul 2011
Cited by 63 | Viewed by 5516
Abstract
This paper reports the improvement in the sensing performance of nanocrystalline SnO2-based liquid petroleum gas (LPG) sensors by doping with fluorine (F). Un-doped and F-doped tin oxide films were prepared on glass substrates by the dip-coating technique using a layer-by-layer deposition [...] Read more.
This paper reports the improvement in the sensing performance of nanocrystalline SnO2-based liquid petroleum gas (LPG) sensors by doping with fluorine (F). Un-doped and F-doped tin oxide films were prepared on glass substrates by the dip-coating technique using a layer-by-layer deposition cycle (alternating between dip-coating a thin layer followed by a drying in air after each new layer). The results showed that this technique is superior to the conventional technique for both improving the film thickness uniformity and film transparency. The effect of F concentration on the structural, surface morphological and LPG sensing properties of the SnO2 films was investigated. Atomic Force Microscopy (AFM) and X-ray diffraction pattern measurements showed that the obtained thin films are nanocrystalline SnO2 with nanoscale-textured surfaces. Gas sensing characteristics (sensor response and response/recovery time) of the SnO2:F sensors based on a planar interdigital structure were investigated at different operating temperatures and at different LPG concentrations. The addition of fluorine to SnO2 was found to be advantageous for efficient detection of LPG gases, e.g., F-doped sensors are more stable at a low operating temperature (300 °C) with higher sensor response and faster response/recovery time, compared to un-doped sensor materials. The sensors based on SnO2:F films could detect LPG even at a low level of 25% LEL, showing the possibility of using this transparent material for LPG leak detection. Full article
(This article belongs to the Section Chemical Sensors)
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Open AccessArticle
Steering a Tractor by Means of an EMG-Based Human-Machine Interface
Sensors 2011, 11(7), 7110-7126; https://doi.org/10.3390/s110707110 - 11 Jul 2011
Cited by 49 | Viewed by 10208
Abstract
An electromiographic (EMG)-based human-machine interface (HMI) is a communication pathway between a human and a machine that operates by means of the acquisition and processing of EMG signals. This article explores the use of EMG-based HMIs in the steering of farm tractors. An [...] Read more.
An electromiographic (EMG)-based human-machine interface (HMI) is a communication pathway between a human and a machine that operates by means of the acquisition and processing of EMG signals. This article explores the use of EMG-based HMIs in the steering of farm tractors. An EPOC, a low-cost human-computer interface (HCI) from the Emotiv Company, was employed. This device, by means of 14 saline sensors, measures and processes EMG and electroencephalographic (EEG) signals from the scalp of the driver. In our tests, the HMI took into account only the detection of four trained muscular events on the driver’s scalp: eyes looking to the right and jaw opened, eyes looking to the right and jaw closed, eyes looking to the left and jaw opened, and eyes looking to the left and jaw closed. The EMG-based HMI guidance was compared with manual guidance and with autonomous GPS guidance. A driver tested these three guidance systems along three different trajectories: a straight line, a step, and a circumference. The accuracy of the EMG-based HMI guidance was lower than the accuracy obtained by manual guidance, which was lower in turn than the accuracy obtained by the autonomous GPS guidance; the computed standard deviations of error to the desired trajectory in the straight line were 16 cm, 9 cm, and 4 cm, respectively. Since the standard deviation between the manual guidance and the EMG-based HMI guidance differed only 7 cm, and this difference is not relevant in agricultural steering, it can be concluded that it is possible to steer a tractor by an EMG-based HMI with almost the same accuracy as with manual steering. Full article
(This article belongs to the Special Issue Sensors in Agriculture and Forestry)
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Open AccessArticle
Mapping Wide Row Crops with Video Sequences Acquired from a Tractor Moving at Treatment Speed
Sensors 2011, 11(7), 7095-7109; https://doi.org/10.3390/s110707095 - 11 Jul 2011
Cited by 28 | Viewed by 6729
Abstract
This paper presents a mapping method for wide row crop fields. The resulting map shows the crop rows and weeds present in the inter-row spacing. Because field videos are acquired with a camera mounted on top of an agricultural vehicle, a method for [...] Read more.
This paper presents a mapping method for wide row crop fields. The resulting map shows the crop rows and weeds present in the inter-row spacing. Because field videos are acquired with a camera mounted on top of an agricultural vehicle, a method for image sequence stabilization was needed and consequently designed and developed. The proposed stabilization method uses the centers of some crop rows in the image sequence as features to be tracked, which compensates for the lateral movement (sway) of the camera and leaves the pitch unchanged. A region of interest is selected using the tracked features, and an inverse perspective technique transforms the selected region into a bird’s-eye view that is centered on the image and that enables map generation. The algorithm developed has been tested on several video sequences of different fields recorded at different times and under different lighting conditions, with good initial results. Indeed, lateral displacements of up to 66% of the inter-row spacing were suppressed through the stabilization process, and crop rows in the resulting maps appear straight. Full article
(This article belongs to the Special Issue Sensors in Agriculture and Forestry)
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Open AccessArticle
Novel Wireless Sensor System for Dynamic Characterization of Borehole Heat Exchangers
Sensors 2011, 11(7), 7082-7094; https://doi.org/10.3390/s110707082 - 08 Jul 2011
Cited by 21 | Viewed by 5438
Abstract
The design and field test of a novel sensor system based in autonomous wireless sensors to measure the temperature of the heat transfer fluid along a borehole heat exchanger (BHE) is presented. The system, by means of two specials valves, inserts and extracts [...] Read more.
The design and field test of a novel sensor system based in autonomous wireless sensors to measure the temperature of the heat transfer fluid along a borehole heat exchanger (BHE) is presented. The system, by means of two specials valves, inserts and extracts miniaturized wireless sensors inside the pipes of the borehole, which are carried by the thermal fluid. Each sensor is embedded in a small sphere of just 25 mm diameter and 8 gr weight, containing a transceiver, a microcontroller, a temperature sensor and a power supply. A wireless data processing unit transmits to the sensors the acquisition configuration before the measurements, and also downloads the temperature data measured by the sensor along its way through the BHE U-tube. This sensor system is intended to improve the conventional thermal response test (TRT) and it allows the collection of information about the thermal characteristics of the geological structure of subsurface and its influence in borehole thermal behaviour, which in turn, facilitates the implementation of TRTs in a more cost-effective and reliable way. Full article
(This article belongs to the Section Remote Sensors)
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Open AccessArticle
Evaluation of Sentinel-2 Red-Edge Bands for Empirical Estimation of Green LAI and Chlorophyll Content
Sensors 2011, 11(7), 7063-7081; https://doi.org/10.3390/s110707063 - 08 Jul 2011
Cited by 203 | Viewed by 7852
Abstract
ESA’s upcoming satellite Sentinel-2 will provide Earth images of high spatial, spectral and temporal resolution and aims to ensure continuity for Landsat and SPOT observations. In comparison to the latter sensors, Sentinel-2 incorporates three new spectral bands in the red-edge region, which are [...] Read more.
ESA’s upcoming satellite Sentinel-2 will provide Earth images of high spatial, spectral and temporal resolution and aims to ensure continuity for Landsat and SPOT observations. In comparison to the latter sensors, Sentinel-2 incorporates three new spectral bands in the red-edge region, which are centered at 705, 740 and 783 nm. This study addresses the importance of these new bands for the retrieval and monitoring of two important biophysical parameters: green leaf area index (LAI) and chlorophyll content (Ch). With data from several ESA field campaigns over agricultural sites (SPARC, AgriSAR, CEFLES2) we have evaluated the efficacy of two empirical methods that specifically make use of the new Sentinel-2 bands. First, it was shown that LAI can be derived from a generic normalized difference index (NDI) using hyperspectral data, with 674 nm with 712 nm as best performing bands. These bands are positioned closely to the Sentinel-2 B4 (665 nm) and the new red-edge B5 (705 nm) band. The method has been applied to simulated Sentinel-2 data. The resulting green LAI map was validated against field data of various crop types, thereby spanning a LAI between 0 and 6, and yielded a RMSE of 0.6. Second, the recently developed “Normalized Area Over reflectance Curve” (NAOC), an index that derives Ch from hyperspectral data, was studied on its compatibility with simulated Sentinel-2 data. This index integrates the reflectance curve between 643 and 795 nm, thereby including the new Sentinel-2 bands in the red-edge region. We found that these new bands significantly improve the accuracy of Ch estimation. Both methods emphasize the importance of red-edge bands for operational estimation of biophysical parameters from Sentinel-2. Full article
(This article belongs to the Section Remote Sensors)
Open AccessArticle
Measurement of Fluorescence in a Rhodamine-123 Doped Self-Assembled “Giant” Mesostructured Silica Sphere Using a Smartphone as Optical Hardware
Sensors 2011, 11(7), 7055-7062; https://doi.org/10.3390/s110707055 - 06 Jul 2011
Cited by 21 | Viewed by 5159
Abstract
The blue OLED emission from a mobile phone was characterised, revealing a sharp emission band centred at λ = 445 nm with a 3dB bandwidth Δλ ~ 20 nm. It was used to excite Rhodamine 123 doped within a “giant” mesostructured silica [...] Read more.
The blue OLED emission from a mobile phone was characterised, revealing a sharp emission band centred at λ = 445 nm with a 3dB bandwidth Δλ ~ 20 nm. It was used to excite Rhodamine 123 doped within a “giant” mesostructured silica sphere during fabrication through evaporative self-assembly of silica nanoparticles. Fluorescence was able to be detected using a standard optical microscope fitted with a green transmission pass filter and cooled CCD and with 1 ms exposure time demonstrating the potential of mobile platforms as the basis for portable diagnostics in the field. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle
Real-Time Fault Classification for Plasma Processes
Sensors 2011, 11(7), 7037-7054; https://doi.org/10.3390/s110707037 - 06 Jul 2011
Viewed by 3920
Abstract
Plasma process tools, which usually cost several millions of US dollars, are often used in the semiconductor fabrication etching process. If the plasma process is halted due to some process fault, the productivity will be reduced and the cost will increase. In order [...] Read more.
Plasma process tools, which usually cost several millions of US dollars, are often used in the semiconductor fabrication etching process. If the plasma process is halted due to some process fault, the productivity will be reduced and the cost will increase. In order to maximize the product/wafer yield and tool productivity, a timely and effective fault process detection is required in a plasma reactor. The classification of fault events can help the users to quickly identify fault processes, and thus can save downtime of the plasma tool. In this work, optical emission spectroscopy (OES) is employed as the metrology sensor for in-situ process monitoring. Splitting into twelve different match rates by spectrum bands, the matching rate indicator in our previous work (Yang, R.; Chen, R.S. Sensors 2010, 10, 5703-5723) is used to detect the fault process. Based on the match data, a real-time classification of plasma faults is achieved by a novel method, developed in this study. Experiments were conducted to validate the novel fault classification. From the experimental results, we may conclude that the proposed method is feasible inasmuch that the overall accuracy rate of the classification for fault event shifts is 27 out of 28 or about 96.4% in success. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle
An Asynchronous Multi-Sensor Micro Control Unit for Wireless Body Sensor Networks (WBSNs)
Sensors 2011, 11(7), 7022-7036; https://doi.org/10.3390/s110707022 - 06 Jul 2011
Cited by 19 | Viewed by 5594
Abstract
In this work, an asynchronous multi-sensor micro control unit (MCU) core is proposed for wireless body sensor networks (WBSNs). It consists of asynchronous interfaces, a power management unit, a multi-sensor controller, a data encoder (DE), and an error correct coder (ECC). To improve [...] Read more.
In this work, an asynchronous multi-sensor micro control unit (MCU) core is proposed for wireless body sensor networks (WBSNs). It consists of asynchronous interfaces, a power management unit, a multi-sensor controller, a data encoder (DE), and an error correct coder (ECC). To improve the system performance and expansion abilities, the asynchronous interface is created for handshaking different clock domains between ADC and RF with MCU. To increase the use time of the WBSN system, a power management technique is developed for reducing power consumption. In addition, the multi-sensor controller is designed for detecting various biomedical signals. To prevent loss error from wireless transmission, use of an error correct coding technique is important in biomedical applications. The data encoder is added for lossless compression of various biomedical signals with a compression ratio of almost three. This design is successfully tested on a FPGA board. The VLSI architecture of this work contains 2.68-K gate counts and consumes power 496-μW at 133-MHz processing rate by using TSMC 0.13-μm CMOS process. Compared with the previous techniques, this work offers higher performance, more functions, and lower hardware cost than other micro controller designs. Full article
(This article belongs to the Special Issue Bioinspired Sensor Systems)
Open AccessArticle
Energy Efficient In-network RFID Data Filtering Scheme in Wireless Sensor Networks
Sensors 2011, 11(7), 7004-7021; https://doi.org/10.3390/s110707004 - 06 Jul 2011
Cited by 37 | Viewed by 5028
Abstract
RFID (Radio frequency identification) and wireless sensor networks are backbone technologies for pervasive environments. In integration of RFID and WSN, RFID data uses WSN protocols for multi-hop communications. Energy is a critical issue in WSNs; however, RFID data contains a lot of duplication. [...] Read more.
RFID (Radio frequency identification) and wireless sensor networks are backbone technologies for pervasive environments. In integration of RFID and WSN, RFID data uses WSN protocols for multi-hop communications. Energy is a critical issue in WSNs; however, RFID data contains a lot of duplication. These duplications can be eliminated at the base station, but unnecessary transmissions of duplicate data within the network still occurs, which consumes nodes’ energy and affects network lifetime. In this paper, we propose an in-network RFID data filtering scheme that efficiently eliminates the duplicate data. For this we use a clustering mechanism where cluster heads eliminate duplicate data and forward filtered data towards the base station. Simulation results prove that our approach saves considerable amounts of energy in terms of communication and computational cost, compared to existing filtering schemes. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle
A Celestial Assisted INS Initialization Method for Lunar Explorers
Sensors 2011, 11(7), 6991-7003; https://doi.org/10.3390/s110706991 - 04 Jul 2011
Cited by 21 | Viewed by 3934
Abstract
The second and third phases of the Chinese Lunar Exploration Program (CLEP) are planning to achieve Moon landing, surface exploration and automated sample return. In these missions, the inertial navigation system (INS) and celestial navigation system (CNS) are two indispensable autonomous navigation systems [...] Read more.
The second and third phases of the Chinese Lunar Exploration Program (CLEP) are planning to achieve Moon landing, surface exploration and automated sample return. In these missions, the inertial navigation system (INS) and celestial navigation system (CNS) are two indispensable autonomous navigation systems which can compensate for limitations in the ground based navigation system. The accurate initialization of the INS and the precise calibration of the CNS are needed in order to achieve high navigation accuracy. Neither the INS nor the CNS can solve the above problems using the ground controllers or by themselves on the lunar surface. However, since they are complementary to each other, these problems can be solved by combining them together. A new celestial assisted INS initialization method is presented, in which the initial position and attitude of the explorer as well as the inertial sensors’ biases are estimated by aiding the INS with celestial measurements. Furthermore, the systematic error of the CNS is also corrected by the help of INS measurements. Simulations show that the maximum error in position is 300 m and in attitude 40″, which demonstrates this method is a promising and attractive scheme for explorers on the lunar surface. Full article
(This article belongs to the Special Issue Modeling, Testing and Reliability Issues in MEMS Engineering 2011)
Open AccessArticle
Fabrication of a Micro-Fluid Gathering Tool for the Gastrointestinal Juice Sampling Function of a Versatile Capsular Endoscope
Sensors 2011, 11(7), 6978-6990; https://doi.org/10.3390/s110706978 - 04 Jul 2011
Cited by 1 | Viewed by 5023
Abstract
This paper presents a micro-fluid gathering tool for a versatile capsular endoscope that employs a solid chemical propellant, azobisisobutyronitrile (AIBN). The proposed tool consists of a micro-heater, an AIBN matrix, a Venturi tube, a reservoir, an inlet, and an outlet. The micro-heater heats [...] Read more.
This paper presents a micro-fluid gathering tool for a versatile capsular endoscope that employs a solid chemical propellant, azobisisobutyronitrile (AIBN). The proposed tool consists of a micro-heater, an AIBN matrix, a Venturi tube, a reservoir, an inlet, and an outlet. The micro-heater heats the AIBN matrix to be decomposed into by-products and nitrogen gas. This nitrogen gas generates negative pressure passing through the Venturi tube. The generated negative pressure inhales a target fluid from around the inlet into the reservoir. All the parts are designed to be embedded inside a cylindrical shape with a diameter of 17 mm and a height of 2.3 mm in order to integrate it into a versatile developmental capsular endoscope without any scaledown. Two sets of the proposed tools are fabricated and tested: one is made of polydimethylsiloxane (PDMS) and the other is made of polymethylmethacrylate (PMMA). In performance comparisons, the PDMS gathering tool can withstand a stronger pulling force, and the PMMA gathering tool requires a less negative pressure for inhaling the same target fluid. Due to the instant and full activation of the thin AIBN matrix, both types of gathering tool show analogous performance in the sample gathering evaluation. The gathered volume is approximately 1.57 μL using approximately 25.4 μL of AIBN compound. Full article
(This article belongs to the Section Biosensors)
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Open AccessArticle
Characterization and Optimization of Polymer-Ceramic Pressure-Sensitive Paint by Controlling Polymer Content
Sensors 2011, 11(7), 6967-6977; https://doi.org/10.3390/s110706967 - 04 Jul 2011
Cited by 33 | Viewed by 3278
Abstract
A pressure-sensitive paint (PSP) with fast response characteristics that can be sprayed on a test article is studied. This PSP consists of a polymer for spraying and a porous particle for providing the fast response. We controlled the polymer content (%) from 10 [...] Read more.
A pressure-sensitive paint (PSP) with fast response characteristics that can be sprayed on a test article is studied. This PSP consists of a polymer for spraying and a porous particle for providing the fast response. We controlled the polymer content (%) from 10 to 90% to study its effects on PSP characteristics: the signal level, pressure sensitivity, temperature dependency, and time response. The signal level and temperature dependency shows a peak in the polymer content around 50 to 70%. The pressure sensitivity was fairly constant in the range between 0.8 and 0.9 %/kPa. The time response is improved by lowering the polymer content. The variation of the time response is shown to be on the order of milliseconds to ten seconds. A weight coefficient is introduced to optimize the resultant PSPs. By setting the weight coefficient, we can optimize the PSP for sensing purposes. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle
A Bragg Wavelength-Insensitive Fiber Bragg Grating Ultrasound Sensing System that Uses a Broadband Light and No Optical Filter
Sensors 2011, 11(7), 6954-6966; https://doi.org/10.3390/s110706954 - 04 Jul 2011
Cited by 5 | Viewed by 3979
Abstract
An optical filter is incorporated in a conventional ultrasound detection system that uses a fiber Bragg grating (FBG) and broadband light source, to demodulate the FBG sensor signal. A novel ultrasound sensing system that does not require an optical filter is presented herein. [...] Read more.
An optical filter is incorporated in a conventional ultrasound detection system that uses a fiber Bragg grating (FBG) and broadband light source, to demodulate the FBG sensor signal. A novel ultrasound sensing system that does not require an optical filter is presented herein. Ultrasound could be detected via the application of signal processing techniques, such as signal averaging and frequency filters, to the photodetector output that corresponds to the intensity of the reflected light from a broadband light-illuminated FBG. Ultrasonic sensitivity was observed to be enhanced when an FBG was installed as a resonant sensor. This FBG ultrasound detection system is small and cheap to fabricate because it does not use a demodulating optical filter. The experimental results demonstrate that this system could be applied to ultrasonic damage inspection and acoustic emission measurements. Furthermore, this system was able to detect ultrasound despite the amount of strain or temperature that was applied to the FBG sensor because the ultrasound detection was not sensitive to the Bragg wavelength of the FBG sensor. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle
Highly Mass-Sensitive Thin Film Plate Acoustic Resonators (FPAR)
Sensors 2011, 11(7), 6942-6953; https://doi.org/10.3390/s110706942 - 04 Jul 2011
Cited by 12 | Viewed by 4104
Abstract
The mass sensitivity of thin aluminum nitride (AlN) film S0 Lamb wave resonators is theoretically and experimentally studied. Theoretical predictions based on modal and finite elements method analysis are experimentally verified. Here, two-port 888 MHz synchronous FPARs are micromachined and subsequently coated with [...] Read more.
The mass sensitivity of thin aluminum nitride (AlN) film S0 Lamb wave resonators is theoretically and experimentally studied. Theoretical predictions based on modal and finite elements method analysis are experimentally verified. Here, two-port 888 MHz synchronous FPARs are micromachined and subsequently coated with hexamethyl-disiloxane(HMDSO)-plasma-polymerized thin films of various thicknesses. Systematic data on frequency shift and insertion loss versus film thickness are presented. FPARs demonstrate high mass-loading sensitivity as well as good tolerance towards the HMDSO viscous losses. Initial measurements in gas phase environment are further presented. Full article
(This article belongs to the Special Issue Emerging Acoustic Wave-Based Sensors)
Open AccessArticle
Effect of Coating on the Strain Transfer of Optical Fiber Sensors
Sensors 2011, 11(7), 6926-6941; https://doi.org/10.3390/s110706926 - 01 Jul 2011
Cited by 76 | Viewed by 5491
Abstract
Optical fiber strain sensors with light weight, small dimensions and immunity to electromagnetic interference are widely used in structural health monitoring devices. As a sensor, it is expected that the strains between the optical fiber and host structure are the same. However, due [...] Read more.
Optical fiber strain sensors with light weight, small dimensions and immunity to electromagnetic interference are widely used in structural health monitoring devices. As a sensor, it is expected that the strains between the optical fiber and host structure are the same. However, due to the shear deformation of the protective coating, the optical fiber strain is different from that of host structure. To improve the measurement accuracy, the strain measured by the optical fiber needs to be modified to reflect the influence of the coating. In this investigation, a theoretical model of the strain transferred from the host material to the optical fiber is developed to evaluate the interaction between the host material and coating. The theoretical predictions are validated with a numerical analysis using the finite element method. Experimental tests are performed to reveal the differential strains between the optical fiber strain sensor and test specimen. The Mach-Zehnder interferometric type fiber-optic sensor is adopted to measure the strain. Experimental results show that the strain measured at the optical fiber is lower than the true strain in the test specimen. The percentage of strain in the test specimen actually transferred to the optical fiber is dependent on the bonded length of the optical fiber and the protective coating. The general trend of the strain transformation obtained from both experimental tests and theoretical predictions shows that the longer the bonded length and the stiffer the coating the more strain is transferred to the optical fiber. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2012)
Open AccessArticle
Localization Algorithm with On-line Path Loss Estimation and Node Selection
Sensors 2011, 11(7), 6905-6925; https://doi.org/10.3390/s110706905 - 01 Jul 2011
Cited by 19 | Viewed by 5219
Abstract
RSS-based localization is considered a low-complexity algorithm with respect to other range techniques such as TOA or AOA. The accuracy of RSS methods depends on the suitability of the propagation models used for the actual propagation conditions. In indoor environments, in particular, it [...] Read more.
RSS-based localization is considered a low-complexity algorithm with respect to other range techniques such as TOA or AOA. The accuracy of RSS methods depends on the suitability of the propagation models used for the actual propagation conditions. In indoor environments, in particular, it is very difficult to obtain a good propagation model. For that reason, we present a cooperative localization algorithm that dynamically estimates the path loss exponent by using RSS measurements. Since the energy consumption is a key point in sensor networks, we propose a node selection mechanism to limit the number of neighbours of a given node that are used for positioning purposes. Moreover, the selection mechanism is also useful to discard bad links that could negatively affect the performance accuracy. As a result, we derive a practical solution tailored to the strict requirements of sensor networks interms of complexity, size and cost. We present results based on both computer simulations and real experiments with the Crossbow MICA2 motes showing that the proposed scheme offers a good trade-off in terms of position accuracy and energy efficiency. Full article
(This article belongs to the Section Physical Sensors)
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Open AccessArticle
Effects of Textural Properties on the Response of a SnO2-Based Gas Sensor for the Detection of Chemical Warfare Agents
Sensors 2011, 11(7), 6893-6904; https://doi.org/10.3390/s110706893 - 01 Jul 2011
Cited by 27 | Viewed by 5796
Abstract
The sensing behavior of SnO2-based thick film gas sensors in a flow system in the presence of a very low concentration (ppb level) of chemical agent simulants such as acetonitrile, dipropylene glycol methyl ether (DPGME), dimethyl methylphosphonate (DMMP), and dichloromethane (DCM) [...] Read more.
The sensing behavior of SnO2-based thick film gas sensors in a flow system in the presence of a very low concentration (ppb level) of chemical agent simulants such as acetonitrile, dipropylene glycol methyl ether (DPGME), dimethyl methylphosphonate (DMMP), and dichloromethane (DCM) was investigated. Commercial SnO2 [SnO2(C)] and nano-SnO2 prepared by the precipitation method [SnO2(P)] were used to prepare the SnO2 sensor in this study. In the case of DCM and acetonitrile, the SnO2(P) sensor showed higher sensor response as compared with the SnO2(C) sensors. In the case of DMMP and DPGME, however, the SnO2(C) sensor showed higher responses than those of the SnO2(P) sensors. In particular, the response of the SnO2(P) sensor increased as the calcination temperature increased from 400 °C to 800 °C. These results can be explained by the fact that the response of the SnO2-based gas sensor depends on the textural properties of tin oxide and the molecular size of the chemical agent simulant in the detection of the simulant gases (0.1–0.5 ppm). Full article
(This article belongs to the Section Chemical Sensors)
Open AccessArticle
Vision-Based Finger Detection, Tracking, and Event Identification Techniques for Multi-Touch Sensing and Display Systems
Sensors 2011, 11(7), 6868-6892; https://doi.org/10.3390/s110706868 - 01 Jul 2011
Cited by 14 | Viewed by 7257
Abstract
This study presents efficient vision-based finger detection, tracking, and event identification techniques and a low-cost hardware framework for multi-touch sensing and display applications. The proposed approach uses a fast bright-blob segmentation process based on automatic multilevel histogram thresholding to extract the pixels of [...] Read more.
This study presents efficient vision-based finger detection, tracking, and event identification techniques and a low-cost hardware framework for multi-touch sensing and display applications. The proposed approach uses a fast bright-blob segmentation process based on automatic multilevel histogram thresholding to extract the pixels of touch blobs obtained from scattered infrared lights captured by a video camera. The advantage of this automatic multilevel thresholding approach is its robustness and adaptability when dealing with various ambient lighting conditions and spurious infrared noises. To extract the connected components of these touch blobs, a connected-component analysis procedure is applied to the bright pixels acquired by the previous stage. After extracting the touch blobs from each of the captured image frames, a blob tracking and event recognition process analyzes the spatial and temporal information of these touch blobs from consecutive frames to determine the possible touch events and actions performed by users. This process also refines the detection results and corrects for errors and occlusions caused by noise and errors during the blob extraction process. The proposed blob tracking and touch event recognition process includes two phases. First, the phase of blob tracking associates the motion correspondence of blobs in succeeding frames by analyzing their spatial and temporal features. The touch event recognition process can identify meaningful touch events based on the motion information of touch blobs, such as finger moving, rotating, pressing, hovering, and clicking actions. Experimental results demonstrate that the proposed vision-based finger detection, tracking, and event identification system is feasible and effective for multi-touch sensing applications in various operational environments and conditions. Full article
(This article belongs to the Section Physical Sensors)
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Open AccessArticle
Miniature Microring Resonator Sensor Based on a Hybrid Plasmonic Waveguide
Sensors 2011, 11(7), 6856-6867; https://doi.org/10.3390/s110706856 - 01 Jul 2011
Cited by 52 | Viewed by 6098
Abstract
We propose a compact 1-mm-radius microring resonator sensor based on a hybrid plasmonic waveguide on a silicon-on-insulator substrate. The hybrid waveguide is composed of a metal-gap-silicon structure, where the optical energy is greatly enhanced in the narrow gap. We use the finite element [...] Read more.
We propose a compact 1-mm-radius microring resonator sensor based on a hybrid plasmonic waveguide on a silicon-on-insulator substrate. The hybrid waveguide is composed of a metal-gap-silicon structure, where the optical energy is greatly enhanced in the narrow gap. We use the finite element method to numerically analyze the device optical characteristics as a biochemical sensor. As the optical field in the hybrid micoring resonator has a large overlap with the upper-cladding sensing medium, the sensitivity is very high compared to other dielectric microring resonator sensors. The compactness of the hybrid microring resonator is resulted from the balance between bending radiation loss and metal absorption loss. The proposed hybrid microring resonator sensors have the main advantages of small footprint and high sensitivity and can be potentially integrated in an array form on a chip for highly-efficient lab-on-chip biochemical sensing applications. Full article
(This article belongs to the Section Physical Sensors)
Open AccessArticle
Lessons from the Field—Two Years of Deploying Operational Wireless Sensor Networks on the Great Barrier Reef
Sensors 2011, 11(7), 6842-6855; https://doi.org/10.3390/s110706842 - 30 Jun 2011
Cited by 6 | Viewed by 4087
Abstract
Wireless Sensor Networks promised to do for observation systems what consumer electronics have done for areas like photography—drive down the price per observation (photograph), introduce new functionality and capabilities, and make, what had been a relatively exclusive set of technologies and capabilities, ubiquitous. [...] Read more.
Wireless Sensor Networks promised to do for observation systems what consumer electronics have done for areas like photography—drive down the price per observation (photograph), introduce new functionality and capabilities, and make, what had been a relatively exclusive set of technologies and capabilities, ubiquitous. While this may have been true for some terrestrial sensor networks there are issues in the marine environment that have limited the realization of ubiquitous cheap sensing. This paper reports on the lessons learned from two years of operation of wireless sensor networks deployed at seven coral reefs along the Great Barrier Reef in north-eastern Australia. Full article
(This article belongs to the Section Physical Sensors)
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